Abnormality detection device

The present invention relates to an abnormality detection device configured to detect abnormalities of a brake system.

A configuration disclosed in PTL 1 is known as one mode of a brake system. The brake system illustrated in FIG. 1 in PTL 1 is capable of detecting abnormalities of the brake system from a relationship between a control target hydraulic pressure determined by a pedal stroke of a brake pedal and an actually detected hydraulic pressure. For example, the abnormality detection device for detecting abnormalities of the brake system may be configured to set a determination area from the control target hydraulic pressure and detects an occurrence of abnormality when an actually detected hydraulic pressure is out of the determination area.

Patent Literature

PTL 1: JP-A-2005-231462

Technical Problem

When the control target hydraulic pressure is in a maintaining state in an abnormality detection device for detecting abnormalities of a brake system disclosed in PTL 1 described above, further adequate setting of a determination area and hence further accurate detection of abnormalities are required.

Accordingly, in order to solve the above-described problem, it is an object of the present invention to provide an abnormality detection device configured to detect abnormalities of a brake system further accurately.

Solution to Problem

In order to solve the above-described problem, an aspect of the invention of an abnormality detection device is an abnormality detection device configured to detect an abnormality of a brake system, including: a control target braking force related physical amount calculating portion configured to calculate a control target braking force related physical amount in accordance with an operation state of a brake operating member or a requirement from other system; a braking force related physical amount obtaining portion configured to obtain a braking force related physical amount of an operating fluid controlled to be a control target braking force related physical amount calculated by the control target braking force related physical amount calculating portion from a braking force related physical amount sensor; a state determining portion configured to perform a state determination for determining whether the control target braking force related physical amount is in a maintaining state of being maintained at a constant value, in an increasing state of being increased, or in a decreasing state of being decreased; a threshold value setting portion configured to set a threshold value that defines a permissible divergence range between the braking force related physical amount obtained by the braking force related physical amount obtaining portion and the control target braking force related physical amount calculated by the control target braking force related physical amount calculating portion; a threshold value changing portion configured to change the threshold value so as to be closer to the control target braking force related physical amount calculated by the control target braking force related physical amount calculating portion in a stepwise manner when the state determining portion determines that the control target braking force related physical amount is in the maintaining state; and an abnormality determining portion configured to determine the abnormality of the brake system when the braking force related physical amount obtained by the braking force related physical amount obtaining portion is deviated from the permissible divergence range.

Advantageous Effects of Invention

In this configuration, when the control target braking force related physical amount is determined to be in the maintaining state, the threshold value that defines the permissible divergence range for determining abnormalities of the brake system is changed to be closer to the control target braking force related physical amount in a stepwise manner. Consequently, the permissible divergence range can be set to an adequate value. Therefore, a reduction of time required for determination and improved adequacy of determination are achieved.

FIG. 1 is a schematic drawing illustrating an embodiment of an abnormality detection device according to the present invention.

FIG. 2 is a block diagram of a brake ECU illustrated in FIG. 1 .

FIG. 3 is a flowchart of a control program (a control target hydraulic pressure is transferred from an increasing state to a maintaining state) to be executed by the brake ECU illustrated in FIG. 1 .

FIG. 4 is a time chart illustrating an operation (the control target hydraulic pressure is transferred from the increasing state to the maintaining state) of the abnormality detection device according to the embodiment.

FIG. 5 is a flowchart of a control program (the control target hydraulic pressure is transferred from a decreasing state to the maintaining state) to be executed by the brake ECU illustrated in FIG. 1 .

FIG. 6 is a time chart illustrating an operation of the abnormality detection device according to an embodiment of the present invention (the control target hydraulic pressure is transferred from the decreasing state to the maintaining state).

Referring now to drawings, an embodiment of an abnormality detection device according to the present invention applied to a vehicle will be described. The vehicle is provided with a hydraulic pressure braking force generating device A configured to brake the vehicle by applying a hydraulic braking force directly to wheels Wfl, Wfr, Wrl, and Wrr. As illustrated in FIG. 1 , the hydraulic pressure braking force generating device A includes a brake pedal 11 which is a braking operation member, a master cylinder 12 , a stroke simulator portion 13 , a reservoir 14 , a booster mechanism 15 , an actuator (brake hydraulic pressure adjusting device) 16 , a brake ECU 17 (abnormality detection device), and a wheel cylinder WC. The hydraulic pressure braking force generating device A is a brake system.

The wheel cylinder WC restricts the rotation of a vehicle wheel W and is provided at a caliper CL. The wheel cylinder WC functions as a braking force applying mechanism which applies braking force to the vehicle wheel W based on the pressure of brake fluid (braking hydraulic pressure) from the actuator 16 . When the braking hydraulic pressure is applied to the wheel cylinder WC, each piston (not shown) of the wheel cylinder WC pushes a pair of brake pads (not shown) which is the friction member to sandwich and squeeze a disc rotor DR which is a rotational member rotating unitary with the vehicle wheel W at both sides of the rotor DR to thereby restrict the rotation of the rotor. In this embodiment, a disc type brake system is adopted, but a drum type brake system can be adopted. The vehicle wheel W means any of the front left wheel Wfl, front right wheel Wfr, rear left wheel Wrl and rear right wheel Wrr.

The brake pedal 11 is a brake operation member, and is connected to the stroke simulator portion 13 and the master cylinder 12 via an operating rod 11 a.

Provided in the vicinity of the brake pedal 11 is a pedal stroke sensor (may be referred to as a stroke sensor, hereinafter) 11 c configured to detect a brake pedal stroke (operating amount: may be referred to as a stroke, hereinafter) which is a brake operation state based on the depression of the brake pedal 11 . The stroke sensor 11 c is connected to the brake ECU 17 , and is configured to output a detection signal (detection result) to the brake ECU 17 .

The master cylinder 12 supplies the brake fluid with the actuator 16 in response to the operating amount of the brake pedal 11 (brake operating member) and is formed by a cylinder body 12 a , an input piston 12 b , a first master piston 12 c , and a second master piston 12 d , etc.

The cylinder body 12 a is formed into a bottomed substantially cylindrical shape. The cylinder body 12 a includes in the interior thereof a partition wall portion 12 a 2 having an inwardly projecting flange shape. The partition wall portion 12 a 2 includes a through hole 12 a 3 penetrating at a center thereof in a fore-and-aft direction. The cylinder body 12 a houses the first master piston 12 c and the second master piston 12 d so as to be movable along an axial direction in a liquid-tight manner in a portion forward of the partitioning wall portion 12 a 2 .

The cylinder body 12 a houses the input piston 12 b so as to be movable along the axial direction in a liquid-tight manner in a portion rearward of the partitioning wall portion 12 a 2 . The input piston 12 b is a piston sliding in the cylinder body 12 a in response to an operation of the brake pedal 11 .

The input piston 12 b is connected to the operating rod 11 a which moves in association with the movement of the brake pedal 11 . The input piston 12 b is biased by a compression spring 11 b in a direction where the volume of a first hydraulic pressure chamber R 3 is extended, i.e., in a rearward direction (right direction as vied in the drawing). When the brake pedal 11 is depressed, the operating rod 11 a moves forward against the biasing force of the compression spring 11 b . Along with the advancement of the operating rod 11 a , the input piston 12 b also advances interlockingly. Also, when the depression of the brake pedal 11 is released, the input piston 12 b retreats by the biasing force of the compression spring 11 b until it contacts with a restriction projecting portion 12 a 4 and is positioned thereby.

The first master piston 12 c integrally includes a pressurizing cylindrical portion 12 c 1 , a flange portion 12 c 2 , and a projecting portion 12 c 3 arranged in this order from the front. The pressurizing cylindrical portion 12 c 1 is formed into a bottomed substantially cylindrical shape opening toward the front, and is disposed in the cylinder body 12 a so as to be slidable with respect to an inner peripheral surface thereof in a liquid tight manner. The pressurizing cylindrical portion 12 c 1 includes a coil spring 12 c 4 , which is a biasing member, disposed in an internal space thereof against the second master piston 12 d . The first master piston 12 c is biased rearward by the coil spring 12 c 4 . In other words, the first master piston 12 c is biased rearward by the coil spring 12 c 4 , and finally is positioned by coming into abutment with a restriction projecting portion 12 a 5 . This position corresponds to an original position (predetermined position) when a depressing operation of the brake pedal 11 is released.

The flange portion 12 c 2 is formed to have a diameter larger than that of the pressurizing cylindrical portion 12 c 1 , and is disposed so as to be slidable with respect to an inner peripheral surface of a large diameter portion 12 a 6 in the cylinder body 12 a in a liquid tight manner. The projecting portion 12 c 3 is formed to have a diameter smaller than that of the pressurizing cylindrical portion 12 c 1 , and is disposed in the through hole 12 a 3 of the partition wall portion 12 a 2 so as to be slidable in a liquid tight manner. A rear end portion of the projecting portion 12 c 3 penetrates through the through hole 12 a 3 , projects into an internal space of the cylinder body 12 a , and is apart from the inner peripheral surface of the cylinder body 12 a . A rear end surface of the projecting portion 12 c 3 is apart from a bottom surface of the input piston 12 b , and the distance therebetween may vary.

The second master piston 12 d is disposed forward of the first master piston 12 c in the cylinder body 12 a . The second master piston 12 d is formed into a bottomed substantially cylindrical shape opening forward. The second master piston 12 d includes a coil spring 12 d 1 , which is a biasing member, in an internal space of the second master piston 12 d against an inner bottom surface of the cylinder body 12 a . The second master piston 12 d is biased rearward by the coil spring 12 d 1 . In other words, the second master piston 12 d is biased by the coil spring 12 d 1 toward a preset original position.

The master cylinder 12 includes a first master chamber R 1 , a second master chamber R 2 , the first hydraulic pressure chamber R 3 , a second hydraulic pressure chamber R 4 , and a servo chamber (driving hydraulic pressure chamber) R 5 .

The first master chamber R 1 is partitioned and defined by the inner peripheral surface of the cylinder body 12 a , the first master piston 12 c (the front side of the pressurizing cylindrical portion 12 c 1 ), and the second master piston 12 d . The first master chamber R 1 is connected to the reservoir 14 via a hydraulic conduit 21 connected to a port PT 4 . The first master chamber R 1 is connected to a hydraulic passage 40 a (actuator 16 ) via a hydraulic conduit 22 connected to a port PT 5 .

The second master chamber R 2 is partitioned and defined by the inner peripheral surface of the cylinder body 12 a and a front side of the second master piston 12 d . The second master chamber R 2 is connected to the reservoir 14 via a hydraulic conduit 23 connected to a port PT 6 . The second master chamber R 2 is also connected to a hydraulic passage 50 a (actuator 16 ) via a hydraulic conduit 24 connected to a port PT 7 .

The first hydraulic pressure chamber R 3 is formed between the partition wall portion 12 a 2 and the input piston 12 b , and is partitioned and defined by the inner peripheral surface of the cylinder body 12 a , the partition wall portion 12 a 2 , the projecting portion 12 c 3 of the first master piston 12 c , and the input piston 12 b . The second hydraulic pressure chamber R 4 is formed laterally of the pressurizing cylindrical portion 12 c 1 of the first master piston 12 c , and is partitioned and defined by the large diameter portion 12 a 6 of the inner peripheral surface of the cylinder body 12 a , the pressurizing cylindrical portion 12 c 1 , and the flange portion 12 c 2 . The first hydraulic pressure chamber R 3 is connected to the second hydraulic pressure chamber R 4 via a hydraulic conduit 25 connected to the port PT 1 and the port PT 3 .

The servo chamber R 5 is formed between the partition wall portion 12 a 2 and the pressurizing cylindrical portion 12 c 1 of the first master piston 12 c , and is partitioned and defined by the inner peripheral surface and the partition wall portion 12 a 2 of the cylinder body 12 a , and the projecting portion 12 c 3 and the pressurizing cylindrical portion 12 c 1 of the first master piston 12 c . The servo chamber R 5 is connected to an output chamber R 12 via a hydraulic conduit 26 connected to the port PT 2 .

A pressure sensor (braking force related physical amount sensor) 26 a is a sensor configured to detect a servo pressure (driving hydraulic pressure) supplied to the servo chamber R 5 , that is, a hydraulic pressure (pressure), which is a physical amount relating to the braking force, and is connected to the hydraulic conduit 26 . The pressure sensor 26 a sends a detection signal (detection result) to the brake ECU 17 .

The stroke simulator portion 13 is formed by the cylinder body 12 a , the input piston 12 b , the first hydraulic pressure chamber R 3 and the stroke simulator 13 a which is connected to the first hydraulic pressure chamber R 3 .

The first hydraulic pressure chamber R 3 is connected to the stroke simulator 13 a via the conduits 25 and 27 which are connected to the port PT 1 . It is noted that the first hydraulic pressure chamber R 3 is connected to the reservoir 14 via a hydraulic conduit (not shown).

The stroke simulator 13 a generates a magnitude of stroke (reaction force) at the brake pedal 11 corresponding to the operation state of the brake pedal 11 . The stroke simulator 13 a is formed by a cylindrical portion 13 a 1 , a piston portion 13 a 2 , a reaction force hydraulic pressure chamber 13 a 3 and a spring 13 a 4 . The piston portion 13 a 2 liquid-tightly slidably moves in the cylindrical portion 13 a 1 in response to the brake operation by the brake pedal 11 . The reaction force hydraulic pressure chamber 13 a 3 is partitioned and formed between the cylindrical portion 13 a 1 and the piston portion 13 a 2 . The reaction force hydraulic pressure chamber 13 a 3 is connected to the first and the second hydraulic pressure chambers R 3 and R 4 via the hydraulic conduits 27 and 25 . The spring 13 a 4 biases the piston portion 13 a 2 in a direction where the volume of the reaction force hydraulic pressure chamber 13 a 3 decreases.

It is noted that the hydraulic conduit 25 is provided with a first control valve 25 a which is a normally closed type electromagnetic valve. A second control valve 28 a which is a normally open type electromagnetic valve is provided in a hydraulic conduit 28 which connects the hydraulic conduit 25 and the reservoir 14 . When the first control valve 25 a is in a closed state, the communication between the first hydraulic pressure chamber R 3 and the second hydraulic pressure chamber R 4 are interrupted. Under such state, the input piston 12 b and the first master piston 12 c are moved with a predetermined distance maintained therebetween. Further, when the first control valve 25 a is in an open state, the communication between the first hydraulic pressure chamber R 3 and the second hydraulic pressure chamber R 4 is established. Under this state, the volume change of the first hydraulic pressure chamber R 3 and the second hydraulic pressure chamber R 4 caused by the advance/retreat movement of the first master piston 12 c can be absorbed by the transfer of the brake fluid.

The pressure sensor 25 b is a sensor configured to detect a reaction force hydraulic pressure of the second hydraulic pressure chamber R 4 and the first hydraulic pressure chamber R 3 , and is connected to the hydraulic conduit 25 . The pressure sensor 25 b is also an operating force sensor configured to detect an operating force with respect to the brake pedal 11 , and has a relative relationship with respect to the amount of operation of the brake pedal 11 . The pressure sensor 25 b detects a pressure in the second hydraulic pressure chamber R 4 when the first control valve 25 a is in the closed state, and detects also a pressure (the reaction force hydraulic pressure) of the first hydraulic pressure chamber R 3 communicating therewith when the first control valve 25 a is in the opened state. The pressure sensor 25 b sends a detection signal (detection result) to the brake ECU 17 .

The booster mechanism 15 generates a servo pressure in accordance with the operating amount of the brake pedal 11 . The booster mechanism 15 is provided with a regulator 15 a and a pressure supplying device 15 b.

The regulator 15 a includes a cylinder body 15 a 1 and a spool 15 a 2 sliding in the cylinder body 15 a 1 . The regulator 15 a includes a pilot chamber R 11 , an output chamber R 12 , and a hydraulic pressure chamber R 13 .

The pilot chamber R 11 is partitioned and defined by the cylinder body 15 a 1 and a front end surface of a second large diameter portion 15 a 2 b of the spool 15 a 2 . The pilot chamber R 11 is connected to a pressure decreasing valve 15 b 6 and a pressure increasing valve 15 b 7 (to a hydraulic conduit 31 ) connected to a port PT 11 . An inner peripheral surface of the cylinder body 15 a 1 is provided with a restriction projecting portion 15 a 4 which is positioned by abutment with a front end surface of the second large diameter portion 15 a 2 b of the spool 15 a 2 .

The output chamber R 12 is partitioned and defined by the cylinder body 15 a 1 , a small diameter portion 15 a 2 c of the spool 15 a 2 , and a rear end surface of the second large diameter portion 15 a 2 b , and a front end surface of a first large diameter portion 15 a 2 a . The output chamber R 12 is connected to the servo chamber R 5 of the master cylinder 12 via the hydraulic conduit 26 connected to a port PT 12 and the port PT 2 . The output chamber R 12 is connectable to an accumulator 15 b 2 via a hydraulic conduit 32 connected to a port PT 13 .

The hydraulic pressure chamber R 13 is partitioned and defined by the cylinder body 15 a 1 and a rear end surface of the first large diameter portion 15 a 2 a of the spool 15 a 2 . The hydraulic pressure chamber R 13 is connectable to a reservoir 15 b 1 via a hydraulic conduit 33 connected to a port PT 14 . The hydraulic pressure chamber R 13 houses a spring 15 a 3 configured to bias the hydraulic pressure chamber R 13 in a direction of extension.

The spool 15 a 2 is formed by the first large diameter portion 15 a 2 a , the second large diameter portion 15 a 2 b and the small diameter portion 15 a 2 c . The first large diameter portions 15 a 2 a and the second large diameter portion 15 a 2 b are formed such that they liquid-tightly slide within the cylinder body 15 a 1 . The small diameter portion 15 a 2 c is disposed between the first large diameter portion 15 a 2 a and the second large diameter portion 15 a 2 b and formed integrally therewith. The diameter of the small diameter portion 15 a 2 c is formed to be smaller than the diameters of the first large diameter portion 15 a 2 a and the second large diameter portion 15 a 2 b.

A communication passage 15 a 5 is provided at the spool 15 a 2 to connect the output chamber R 12 and the hydraulic pressure chamber R 13 .

The pressure supplying device 15 b is also a drive unit configured to drive the spool 15 a 2 . The pressure supplying device 15 b includes the reservoir 15 b 1 , which is a low-pressure source, the accumulator 15 b 2 , which is a high-pressure source, and configured to accumulate a braking fluid, a pump 15 b 3 configured to suck the braking fluid of the reservoir 15 b 1 and pump the same toward the accumulator 15 b 2 , and an electric motor 15 b 4 configured to drive the pump 15 b 3 . The reservoir 15 b 1 is opened to the atmosphere, and the hydraulic pressure in the reservoir 15 b 1 is the same as the atmospheric pressure. The low-pressure source provides a lower pressure than that from the high-pressure source. The pressure supplying device 15 b includes a pressure sensor 15 b 5 configured to detect the pressure of a brake fluid supplied from the accumulator 15 b 2 and outputs the detected pressure to the brake ECU 17 .

The pressure supplying device 15 b is further provided with a pressure decreasing valve 15 b 6 and a pressure increasing valve 15 b 7 . The pressure decreasing valve 15 b 6 is an electromagnetic valve of a structure (normally-open type) opening in a non-energized state, a flow rate of which is controlled by a command from the brake ECU 17 . One side of the pressure decreasing valve 15 b 6 is connected to the pilot chamber R 11 via the hydraulic conduit 31 , and the other side of the pressure decreasing valve 15 b 6 is connected to the reservoir 15 b 1 via a hydraulic conduit 34 . The pressure increasing valve 15 b 7 is an electromagnetic valve of a structure (normally-close type) closing in the non-energized state, a flow rate of which is controlled by a command from the brake ECU 17 . One side of the pressure increasing valve 15 b 7 is connected to the pilot chamber R 11 via the hydraulic conduit 31 , and the other side of the pressure increasing valve 15 b 7 is connected to the accumulator 15 b 2 via a hydraulic conduit 35 and the hydraulic conduit 32 connected to the hydraulic conduit 35 .

The operation of the regulator 15 a will be briefly described hereinafter. When no pilot pressure is supplied from the pressure decreasing valve 15 b 6 and the pressure increasing valve 15 b 7 to the pilot chamber R 11 , the spool 15 a 2 is biased by the spring 15 a 3 and is located at the original position (see FIG. 1 ). The original position of the spool 15 a 2 is a position where a front end surface of the spool 15 a 2 is positioned by coming into abutment with the restriction projecting portion 15 a 4 and a position immediately before a position where a rear end surface of the spool 15 a 2 closes the port PT 14 .

Thus, when the spool 15 a 2 is at the original position, the port PT 14 and the port PT 12 are in communication with each other via the communication passage 15 a 5 , and the port PT 13 is closed by the spool 15 a 2 .

When the pilot pressure established by the pressure decreasing valve 15 b 6 and the pressure increasing valve 15 b 7 in accordance with the operating amount of the brake pedal 11 increases, the spool 15 a 2 moves rearward (rightward in FIG. 1 ) against a biasing force of the spring 15 a 3 . Accordingly, the spool 15 a 2 is then moved to a position where the port PT 13 , which has been closed, opens. The port PT 14 , which has been opened, is closed by the spool 15 a 2 (Pressure increasing operation).

The spool 15 a 2 is positioned by a pressing force of the front end surface of the second large diameter portion 15 a 2 b of the spool 15 a 2 and a force corresponding to the servo pressure well balanced to each other. The position of the spool 15 a 2 at this time is referred to as a maintaining position. The port PT 13 and the port PT 14 are closed by the spool 15 a 2 (Pressure maintaining operation).

When the pilot pressure established by the pressure decreasing valve 15 b 6 and the pressure increasing valve 15 b 7 in accordance with the operating amount of the brake pedal 11 decreases, the spool 15 a 2 at the maintaining position is moved forward by the biasing force of the spring 15 a 3 . Then, the port PT 13 closed by the spool 15 a 2 is maintained in the closed state. The port PT 14 which has been closed are opened. At this time, the port PT 14 and the port PT 12 communicate with each other via the communication passage 15 a 5 (Pressure decreasing operation).

The booster mechanism 15 described above establishes the pilot pressure by the pressure decreasing valve 15 b 6 and the pressure increasing valve 15 b 7 in accordance with the stoke of the brake pedal 11 , and generates a servo pressure in accordance with the stroke of the brake pedal 11 by the pilot pressure. The generated servo pressure is supplied to the servo chamber R 5 of the master cylinder 12 , and the master cylinder 12 supplies a master cylinder pressure generated in accordance with the stroke of the brake pedal 11 to the wheel cylinder WC.

The actuator 16 is a device for adjusting a braking hydraulic pressure to be applied to each wheel cylinder WC, and is provided with first and second conduit systems 40 and 50 . The first conduit system 40 controls the braking hydraulic pressure applied to the rear-left wheel Wrl and the rear-right wheel Wrr, and the second conduit system 50 controls a braking hydraulic pressure applied to the front-right wheel Wfr and the front-left wheel Wfl. In other words, the configuration of conduit is fore-and-aft conduit.

The hydraulic pressure supplied from the master cylinder 12 is transmitted to each wheel cylinders WCrl, WCrr, WCfr, and WCfl through the first conduit system 40 and the second conduit system 50 . The first conduit system 40 is provided with the hydraulic passage 40 a which connects the wheel cylinders WCrl and WCrr and the hydraulic conduit 22 . The second conduit system 50 is provided with the hydraulic passage 50 a which connects the wheel cylinders WCfr, and WCfl and the hydraulic conduit 24 . The hydraulic pressure from the master cylinder 12 is transmitted to each wheel cylinders WCrl, WCrr, WCfr, and WCfl through these hydraulic passages 40 a and 50 a , respectively.

The hydraulic passages 40 a and 50 a are branched off to respective two hydraulic passages 40 a 1 , 40 a 2 , 50 a 1 , and 50 a 2 , respectively. The hydraulic passages 40 a 1 and 50 a 1 are provided with first pressure increasing valves 41 and 51 which control the pressure increase of the brake hydraulic pressure to each wheel cylinders WCrl and WCfr, respectively. Another each hydraulic passage 40 a 2 and 50 a 2 is provided with second pressure increasing valves 42 and 52 which controls the pressure increase of the brake hydraulic pressure to each wheel cylinder WCrr and WCfl.

These first and second pressure increasing valves 41 , 42 , 51 , and 52 are formed by a two positional electromagnetic valve which can control connection/disconnection state of the valve. The first and the second pressure increasing valves 41 , 42 , 51 , and 52 are formed as a normally open type valve which becomes connected state when the control current to the solenoid coil provided in the respective valves 41 , 42 , 51 and 52 becomes zero (non-energized state) and becomes disconnected state when the control current flows through the solenoid coil (energized state).

The hydraulic passages 40 a and 50 a between the first and the second pressure increasing valves 41 , 42 , 51 and 52 and the wheel cylinders WCrl, WCrr, WCfr, and WCfl are connected to reservoirs 43 and 53 , respectively through the portions of hydraulic passages 40 b and 50 b functioning as the pressure decreasing hydraulic passage. In the hydraulic passages 40 b and 50 b , first and second pressure decreasing valves 44 , 45 , 54 , and 55 are respectively provided which are formed by a two positional electromagnetic valve which can control connection/disconnection state of the valve. The first and the second pressure decreasing valves 44 , 45 , 54 , and 55 are formed as a normally closed type valve which becomes disconnected state when the control current to the solenoid coil provided in the respective valves 44 , 45 , 54 , and 55 becomes zero (non-energized state) and becomes connected state when the control current flows through the solenoid coil (energized state).

The hydraulic passages 40 c and 50 c which serve as the return hydraulic passages are provided between the reservoirs 43 and 53 and the hydraulic passages 40 a and 50 a which are the main hydraulic passages. The hydraulic passages 40 c and 50 c are provided with pumps 46 and 56 configured to be driven by a motor 47 , which sucks and discharges the braking fluid from the reservoirs 43 and 53 toward the master cylinder 12 or toward the wheel cylinders WCrl, WCrr, WCfr, and WCfl.

The pumps 46 and 56 suck the brake fluid from the reservoirs 43 and 53 and discharge to the hydraulic passages 40 a and 50 a to supply the wheel cylinders WCrl, WCrr, WCfr, and WCfl with the brake fluid.

Further, the detected signals from wheel speed sensors Sfl, Srr, Sfr, and Srl provided in each wheel Wfl, Wrr, Wfr and Wrl of the vehicle are inputted to the brake ECU 17 . The brake ECU 17 calculates the wheel speed of each wheel, presumed vehicle body speed and slip ratio and so on, based on the detected signals from the wheel speed sensors Sfl, Srr, Sfr, and Srl. The brake ECU 17 executes the anti-skid control and so on, based on the calculation results.

Each control using the actuator 16 is executed at the brake ECU 17 . For example, by outputting the control current which controls each type of control valves 41 , 42 , 44 , 45 , 51 , 52 , 54 , and 55 provided in the actuator 16 and the motor 47 which drives the pumps, the brake ECU 17 controls the hydraulic pressure circuit provided in the actuator 16 to individually control the wheel cylinder pressures transmitted to the respective wheel cylinders WCrl, WCrr, WCfr, and WCfl. For example, the brake ECU 17 executes the anti-skid control which prevents wheels from locking by executing pressure decreasing, pressure maintaining and pressure increasing of the wheel cylinder pressure when a wheel slips upon braking operation or executes a stability control which allows to perform an ideal turning operation of the vehicle by suppressing the skidding tendency (under-steer or over steer tendency) by automatically increasing the wheel cylinder pressure of the control subject wheel.

The brake ECU 17 includes an operating amount obtaining portion 17 a , a control target hydraulic pressure calculating portion (control target braking force related physical amount calculating portion) 17 b , a state determining portion 17 c , a first determination threshold value setting portion 17 d , a second determination threshold value setting portion 17 e , a second determination threshold value changing portion 17 f , a hydraulic pressure obtaining portion (control target braking force related physical amount obtaining portion) 17 g , an abnormality determining portion 17 h , and an alert control portion 17 i.

The operating amount obtaining portion 17 a obtains the operating amount of the brake pedal 11 (the operating amount relating to the braking operation: hereinafter, may be referred to as stroke) from the stroke sensor 11 c . The operating amount obtaining portion 17 a may obtain an operating force detected by a sensor configured to detect an operating force (depressing force) applied directly to the brake pedal 11 instead of the operating amount of the brake pedal 11 .

The control target hydraulic pressure calculating portion 17 b obtains a stroke from the operating amount obtaining portion 17 a , and calculates a control target hydraulic pressure in accordance with an operation state (for example, the stroke) of brake operating members or requirements from other systems (other systems). The hydraulic pressure is a physical amount relating to a braking force (braking force related physical amount), and the control target hydraulic pressure is, for example, a control target of the servo pressure. The control target hydraulic pressure may be a control target of a master cylinder pressure (in this case, it is preferable to provide a pressure sensor configured to detect the master cylinder pressure). The control target hydraulic pressure calculating portion 17 b includes, for example, a map indicating a relating relationship between the stroke and the control target hydraulic pressure, and calculates the control target hydraulic pressure from the map.

Other systems are, for example, a pre-crash prevention system which generates a braking force automatically to prevent a crash when the vehicle detects probability of a crash. The control target hydraulic pressure calculating portion 17 b may be configured to obtain a required braking force (or required deceleration) from other systems.

The state determining portion 17 c performs a state determination for determining whether the control target hydraulic pressure is in a maintaining state of being maintained at a constant value, an increasing state of being increased, or a decreasing state of being decreased. More specifically, the state determining portion 17 c includes a control target hydraulic pressure gradient calculating portion (control target braking force related physical amount gradient calculating portion) 17 c 1 and a control target hydraulic pressure divergence amount calculating portion (control target braking force related physical amount divergence amount calculating portion) 17 c 2 . The control target hydraulic pressure gradient calculating portion 17 c 1 calculates a control target hydraulic pressure gradient (control target braking force related physical amount gradient), which is a gradient of the control target hydraulic pressure, from the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b . The control target hydraulic pressure divergence amount calculating portion 17 c 2 calculates a control target hydraulic pressure divergence amount (control target braking force related physical amount divergence amount) which is a divergence amount of the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g after a started time when the determination that the control target hydraulic pressure is in the maintaining state is started with respect to the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b at the started time.

The state determining portion 17 c performs the state determination from at least one of the control target hydraulic pressure gradient calculated by the control target hydraulic pressure gradient calculating portion 17 c 1 and the control target hydraulic pressure divergence amount calculated by the control target hydraulic pressure divergence amount calculating portion 17 c 2 .

When the control target hydraulic pressure gradient (an absolute value of the control target hydraulic pressure gradient) is larger than the determined gradient, the state determining portion 17 c may perform the state determination only by the control target hydraulic pressure gradient. When the control target hydraulic pressure gradient is steep, the state determination may be performed only by the control target hydraulic pressure gradient, and thus determination in the early stage is achieved.

When the control target hydraulic pressure divergence amount is larger than the determined divergence amount, the state determining portion 17 c may perform the state determination only by the control target hydraulic pressure divergence amount. When the control target hydraulic pressure gradient is gradual, reliable and adequate determination of the state is achieved by performing the state determination only by the control target hydraulic pressure divergence amount.

When the control target hydraulic pressure gradient (the absolute value of the control target hydraulic pressure gradient) is smaller than the determined gradient, the state determining portion 17 c can perform the state determination by the control target hydraulic pressure gradient and together the control target hydraulic pressure divergence amount. Accordingly, reliable and accurate determination is achieved.

The first determination threshold value setting portion 17 d is a threshold value setting portion configured to set a threshold value that specifies a permissible divergence range between the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g and the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b . A first determination threshold value is a threshold value that specifies a permissible divergence range between the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g and the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b.

When the control target hydraulic pressure is in the increasing state or the decreasing state, the first determination threshold value setting portion 17 d sets the first determination threshold value by adding or subtracting a first predetermined value to or from the control target hydraulic pressure. When it is in the increasing state, the first determination threshold value is calculated by subtracting the first predetermined value from the control target hydraulic pressure. When it is in the decreasing state, the first determination threshold value is calculated by adding the first predetermined value to the control target hydraulic pressure.

When the control target hydraulic pressure is in the maintaining state, the first determination threshold value setting portion 17 d set the control target hydraulic pressure as the first determination threshold value.

The second determination threshold value setting portion 17 e is a threshold value setting portion configured to set a threshold value that specifies a permissible divergence range between the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g and the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b . A second determination threshold value is a threshold value that specifies a permissible divergence range between the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g and the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b.

The second determination threshold value setting portion 17 e sets the second determination threshold value (preset second determination threshold value) by adding or subtracting the second predetermined value to or from the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b irrespective of the state being determined by the state determining portion 17 c . The second predetermined value is set to a value smaller than the first predetermined value. In other words, the second determination threshold value (the preset second determination threshold value) is smaller than the first determination threshold value. It is because variations in hydraulic pressure in the increasing state or the decreasing state are larger than variations in hydraulic pressure in the maintaining state.

When the state determining portion 17 c determines that the control target hydraulic pressure is in the maintaining state, the second determination threshold value changing portion 17 f increases the second determination threshold value (threshold value) at the beginning of the maintaining state, and then changes the second determination threshold value in a stepwise manner to be closer to the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b (threshold value changing portion).

The second determination threshold value changing portion 17 f includes a changed second determination threshold value calculating portion 17 f 1 and a change permitting portion 17 f 2 .

The changed second determination threshold value calculating portion 17 f 1 calculates a changed second determination threshold value with respect to the preset second determination threshold value as a reference. At the beginning, the changed second determination threshold value calculating portion 17 f 1 calculates an initial value of the changed second determination threshold value, which is the changed second determination threshold value at a time when the maintaining state is started (at a time when the determination that the control target hydraulic pressure is in the maintaining state is started). The initial value of the changed second determination threshold value is set by adding or subtracting a third predetermined value, which is larger than the second predetermined value and smaller than the first predetermined value to or from the control target hydraulic pressure. In other words, the changed second determination threshold value is a value diverged from the control target hydraulic pressure compared with the preset second determination threshold value. The initial value of the changed second determination threshold value is a value diverged from the control target hydraulic pressure by the third predetermined value. When the state transfers from the increasing state to the maintaining state, the initial value of the changed second determination threshold value is smaller than the control target hydraulic pressure by the third predetermined value. In contrast, when the state transfers from the decreasing state to the maintaining state, the initial value of the changed second determination threshold value is a value larger than the control target hydraulic pressure by the third predetermined value.

The changed second determination threshold value calculating portion 17 f 1 (the second determination threshold value changing portion 17 f ) may set a value obtained by adding a predetermined value to the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g at the time point when the determination of the control target hydraulic pressure to be in the maintaining state is started as the initial value of the changed second determination threshold value (the threshold value).

Subsequently, the changed second determination threshold value calculating portion 17 f 1 calculates a value of the changed second determination threshold value in the present time by subtracting or adding a predetermined change amount to or from a previous value of the changed second determination threshold value. Accordingly, the changed second determination threshold value is changed to be closer to the control target hydraulic pressure in a stepwise manner by the change amount at every control cycle. When the state is transferred from the increasing state to the maintaining state, the changed second determination threshold value in the present time is calculated by adding the predetermined change amount to the previous changed second determination threshold value. In contrast, when the state is transferred from the decreasing state to the maintaining state, the changed second determination threshold value in the present time is calculated by subtracting the predetermined change amount from the previous changed second determination threshold value.

The change amount of the second determination threshold value to be changed by the second determination threshold value changing portion 17 f is determined by considering the viscosity of an operating fluid (may be estimated based on an actually measured temperature or an estimated temperature of the operating fluid) and the variations in a hydraulic pressure control system which constitutes the hydraulic pressure braking force generating device A.

This change continues until the changed second determination threshold value becomes equal to the preset second determination threshold value set by the second determination threshold value setting portion 17 e or until the state is switched from the maintaining state to the decreasing state or to the increasing state.

When the divergence amount of the second determination threshold value (threshold value) from the control target hydraulic pressure at the time when the determination that the control target hydraulic pressure is the maintaining state is started is larger than the divergence amount of the first determination threshold value (threshold value) from the control target hydraulic pressure before the time when the determination that the control target hydraulic pressure is the maintaining state is started, the change permitting portion 17 f 2 permits a change of the second determination threshold value by the second determination threshold value changing portion 17 f . In other words, the change permitting portion 17 f 2 prohibits the change of the second determination threshold value by the second determination threshold value changing portion 17 f when the initial value of the changed second determination threshold value immediate after the switching is smaller than the first determination threshold value immediately before being switched (when the divergence amount with respect to the control target hydraulic pressure is large). Accordingly, an unnecessary broadening of the determination threshold value when the state is switched from the increasing state or the decreasing state to the maintaining state can be avoided and hence an erroneous determination such as determining a state as abnormal that should be determined as normal can be avoided.

When the change of the second determination threshold value by the second determination threshold value changing portion 17 f is not permitted (prohibited), the preset second determination threshold value is used as the second determination threshold value.

The hydraulic pressure obtaining portion 17 g obtains a servo pressure having a relative relationship with the operating amount of the brake pedal 11 (the braking operation member) from the pressure sensor 26 a . The hydraulic pressure obtaining portion 17 g obtains a hydraulic pressure of the operating fluid controlled to become the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b from the pressure sensor 26 a.

The hydraulic pressure obtaining portion 17 g may obtain a master cylinder pressure detected by a sensor configured to detect a master cylinder pressure generated in the master cylinder 12 instead of the servo pressure.

The abnormality determining portion 17 h determines the hydraulic pressure braking force generating device A to be abnormal when the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g is deviated from the permissible divergence range.

The abnormality determining portion 17 h determines abnormalities of the hydraulic pressure braking force generating device A by determining whether the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g is deviated from the permissible divergence range specified by the changed second determination threshold value changed by the second determination threshold value changing portion 17 f or not, when the control target hydraulic pressure is determined to be in the maintaining state by the state determining portion 17 c.

Abnormalities of the hydraulic pressure braking force generating device A include leakage of an operating fluid from any portion, abnormal opening and closing of an electromagnetic control valve (abnormal energization, abnormalities of the electromagnetic valve itself), abnormalities of the pressure sensor 26 a.

Specifically, when the state is transferred from the increasing state to the maintaining state, the abnormality determining portion 17 h adopts a smaller one of the first determination threshold value and the preset second determination threshold value or the changed second determination threshold value (the one diverged more than the control target hydraulic pressure) as a determination threshold value. When the state is transferred from the decreasing state to the maintaining state, the larger one of the first determination threshold value and the second determination threshold value is adopted as the determination threshold value. It is because the controlled hydraulic pressure (for example, the servo pressure) has a response delay with respect to the target control hydraulic pressure (stroke).

When the hydraulic pressure measured value is larger than the determination threshold value, the abnormality determining portion 17 h determines that the hydraulic pressure system of the hydraulic pressure braking force generating device A is normal. In contrast, when the state in which the hydraulic pressure measured value is smaller than the determination threshold value continues for a predetermined period, the abnormality determining portion 17 h determines that the hydraulic pressure system of the hydraulic pressure braking force generating device A is abnormal.

When the abnormality is determined by the abnormality determining portion 17 h , the alert control portion 17 i gives an information portion 18 an instruction to inform the abnormality of the brake system. The information portion 18 includes a display, a speaker, and the like, and displays and announces an abnormality of brake system in accordance with the information instruction.

In addition, the above-described operation performed by the brake system (when the state is transferred from the increasing state to the maintaining state) will be described in accordance with a flowchart illustrated in FIG. 3 . The brake ECU 17 executes a program in accordance with the flowchart at every predetermined short period.

The brake ECU 17 obtains the operating amount of the brake pedal 11 from the stroke sensor 11 c in Step S 102 . Step S 102 is a step corresponding to the operating amount obtaining portion 17 a as above-described.

The brake ECU 17 calculates the control target hydraulic pressure in accordance with the operating amount (stroke) in Step S 104 . Step S 104 is a step corresponding to the control target hydraulic pressure calculating portion 17 b as above-described.

The brake ECU 17 performs the state determination for determining whether the control target hydraulic pressure is in the maintaining state of being maintained at a constant value, an increasing state of being increased, or a decreasing state of being decreased in Step S 106 . Step S 106 is a step corresponding to the state determining portion 17 c as above-described.

When the control target hydraulic pressure is not in the maintaining state (When the control target hydraulic pressure is in the increasing state or in the decreasing state), the brake ECU 17 sets a first determination threshold value (n) in the present time to a value obtained by subtracting a first predetermined value “a” from a control target hydraulic pressure (n) calculated in the present time in Step S 110 . Step S 110 is a step corresponding to the first determination threshold value setting portion 17 d as above-described. The brake ECU 17 sets a second determination threshold value (n) in the present time to a value obtained by subtracting a second predetermined value “b 1 ” from the control target hydraulic pressure (n) calculated in the present time in Step S 112 . Step S 112 is a step corresponding to the second determination threshold value setting portion 17 e as above-described.

The brake ECU 17 sets a change end flag “F” OFF in Step S 108 .

The brake ECU 17 adopts a smaller one of the first determination threshold value (n) and the second determination threshold value (n) which are set previously as the determination threshold value in Step S 114 . Step S 114 is a step corresponding to the abnormality determining portion 17 h as above-described. As the controlled hydraulic pressure (for example, the servo pressure) has a response delay with respect to the target control hydraulic pressure (stroke), when the state is transferred from the maintaining state to the decreasing state, a larger one of the first determination threshold value (n) and the second determination threshold value (n) which are set previously is adopted as the determination threshold value.

The brake ECU 17 obtains the servo pressure (measured value) as the hydraulic pressure (measured value) in Step S 116 . Step S 116 is a step corresponding to the hydraulic pressure obtaining portion 17 g as above-described.

The brake ECU 17 determines abnormalities of the hydraulic pressure braking force generating device A in the process from Step S 118 to Step S 124 . This process is a process corresponding to the abnormality determining portion 17 h as above-described. When the hydraulic pressure measured value is larger than the determination threshold value, the brake ECU 17 determines that the hydraulic pressure system of the hydraulic pressure braking force generating device A is normal (Step S 122 ). In contrast, when the state in which the hydraulic pressure measured value is smaller than the determination threshold value continues for a predetermined period, the brake ECU 17 determines that the hydraulic pressure system of the hydraulic pressure braking force generating device A is abnormal (Step S 124 ).

When it is determined that the hydraulic pressure system is abnormal, the brake ECU 17 makes the information portion 18 inform that the brake system is abnormal in Step S 126 . Step S 126 is a step corresponding to the alert control portion 17 i as above-described.

When the change end flag F is “ON”, that is, when if the control target hydraulic pressure is in the maintaining state but the change of the second determination threshold value is finished or not necessary, the brake ECU 17 does not change the second determination threshold value in Step S 128 . At this time, the brake ECU 17 proceeds the program to Step S 110 and thereafter, sets the first determination threshold value and the second determination threshold value in the same manner as described above, sets the determination threshold value, and determines whether the hydraulic pressure system is normal or abnormal.

It is note that the change end flag “F” is a flag indicating whether the changing process on the second determination threshold value is terminated or not (necessary or not). The change end flag “F” indicates that the changing process is terminated (the changing process is not necessary) when the change end flag “F” is “ON”, and that the changing process is being performed (the changing process is necessary) when the change end flag “F” is “OFF”.

When the control target hydraulic pressure is in the maintaining state, the brake ECU 17 sets the first determination threshold value (n) in the present time to the control target hydraulic pressure (n) calculated in the present time in Step S 130 . Step S 130 is a step corresponding to the first determination threshold value setting portion 17 d as above-described. The brake ECU 17 sets the second determination threshold value (n) in the present time to a value obtained by subtracting a third predetermined value “b 2 ” from the control target hydraulic pressure (n) calculated in the present time in Step S 132 . Step S 132 is a step corresponding to the changed second determination threshold value calculating portion 17 f 1 as above-described. The third predetermined value “b 2 ” is preferably set to a value larger than the second predetermined value “b 1 ” and smaller than the first predetermined value “a”.

In addition, in the process from Step S 134 to Step S 142 , when the control target hydraulic pressure is switched from the increasing state or the decreasing state to the maintaining state and the initial value of the second determination threshold value (the changed second determination threshold value) immediately after switching is larger than the first determination threshold value immediately before switching (when the divergence amount from the control target hydraulic pressure is small, it is determined that “YES” in Step S 136 ), the brake ECU 17 permits changing of the second determination threshold value after the beginning of the maintaining state (Step S 142 ). This process is a process corresponding to the change permitting portion 17 f 2 as above-described. The brake ECU 17 then proceeds the program to Step S 144 .

In contrast, when the initial value of the changed second determination threshold value immediately after switching is smaller than the first determination threshold value immediately before switching (when the divergence amount from the control target hydraulic pressure is large, it is determined that “NO” in Step S 136 ), the brake ECU 17 prohibits changing of the second determination threshold value after the beginning of the maintaining state (Step S 138 ). The brake ECU 17 sets the change end flag F “ON” in Step S 140 and proceeds the program to Step S 110 and thereafter.

The brake ECU 17 calculates the present second determination threshold value (changed second determination threshold value) (n) by adding a predetermined change amount to the last second determination threshold value (changed second determination threshold value) (n−1) in Step S 144 . Step S 144 is a step corresponding to the changed second determination threshold value calculating portion 17 f 1 as above-described. Accordingly, the second determination threshold value (changed second determination threshold value) can be changed to be closer to the control target hydraulic pressure in a stepwise manner at every control cycle.

The brake ECU 17 continues the changing process of the second determination threshold value until the changed second determination threshold value (n) in the present time becomes equal to the preset second determination threshold value the control target hydraulic pressure (n) in the present time−the second predetermined value “b 1 ”) or until the state is switched from the maintaining state to the decreasing state (it is determined that “NO” in Step S 146 ). This process is a process corresponding to the second determination threshold value changing portion 17 f as above-described. The brake ECU 17 then proceeds the program to Step S 114 and thereafter.

In contrast, the brake ECU 17 terminates the changing process of the second determination threshold value (Step S 148 ) when the changed second determination threshold value (n) in the present time becomes equal to the preset second determination threshold value (the control target hydraulic pressure (n) in the present time−the second predetermined value “b 1 ”) or when the state is switched from the maintaining state to the decreasing state (it is determined that “YES” in Step S 146 ). This process is a process corresponding to the second determination threshold value changing portion 17 f as above-described. The brake ECU 17 sets the change end flag F “ON” in Step S 150 . The brake ECU 17 then proceeds the program to Step S 114 and thereafter.

In addition, the above-described operation performed by the brake system (when the state is transferred from the increasing state to the maintaining state) will be described in accordance with a time chart illustrated in FIG. 4 .

A case where the control target hydraulic pressure is in the increasing state (that is, when the stroke is in the increasing state) (a period from time t 1 to time t 2 ) will be described. The time t 1 is a time when the increasing state is started, and the time t 2 is a time when the maintaining state is started (that is, a time point when the state is switched from the increasing state to the maintaining state).

During the period from the time t 1 to the time t 2 , the first determination threshold value is set to a value smaller than the control target hydraulic pressure (indicated by a thick solid line) by the first predetermined value “a” as indicated by a thick dot-and-dash line. The second determination threshold value is set to a value smaller than the control target hydraulic pressure (indicated by the thick solid line) by a second predetermined value “b 1 ” as indicated by the thin solid line. Therefore, the determination threshold value is set to the first determination threshold value.

During the period from the time t 2 to time t 3 , the first determination threshold value is set to the control target hydraulic pressure as indicated by the thick dot-and-dash line. In FIG. 4 , the first determination threshold value is indicated slightly apart from the control target hydraulic pressure for easy discrimination from the control target hydraulic pressure. The second determination threshold value (preset second determination threshold value) can be basically set to a value smaller than the control target hydraulic pressure (indicated by the thick solid line) by the second predetermined value b 1 as indicated by the thin solid line.

When the change of the second determination threshold value is permitted, the second determination threshold value (the changed second determination threshold value) is set such that the preset second determination threshold value is set as an initial value at the time point when the maintaining state is started as indicated by a thin dashed-two dotted line. The initial value is set to a value smaller than the control target hydraulic pressure (indicated by the thick solid line) by the second predetermined value “b 1 ”. After the time point when the maintaining state is started, the changed second determination threshold value is set to increase from the initial value by a predetermined change amount. In this manner, when the control target hydraulic pressure is determined to be in the maintaining state, the changed second determination threshold value (threshold value) that defines the permissible divergence range for determining the abnormality of the brake system is changed to be closer to the control target hydraulic pressure in a stepwise manner. Consequently, the permissible divergence range may be set to an adequate value. Therefore, a reduction of time required for determination and improved adequacy of determination are achieved.

In addition, as another example, when the change of the second determination threshold value is permitted, the second determination threshold value (the changed second determination threshold value) is set such that the changed second determination threshold value is set as an initial value at the time point when the maintaining state is started as indicated by a thin dot-and-dash line. The initial value is set to be a value smaller than the control target hydraulic pressure by the third predetermined value “b 2 ”. During a period from the time point when the maintaining state is started until the time point when the change terminates (time t 3 ), the changed second determination threshold value is set to increase from the initial value by a predetermined change amount. Therefore, the determination threshold value is set to the changed second determination threshold value. In other word, the determination threshold value can be extended with respect to the control target hydraulic pressure as compared with the case of the preset second determination threshold value.

When the change of the second determination threshold value is permitted, it is preferable to further delay the time point when the change terminates (time t 3 ) to set the changed second determination threshold value to be closer to the control target hydraulic pressure in a stepwise manner.

In this manner, at the beginning of the timing when the control target hydraulic pressure is switched to the maintaining state, a normal detection range of the brake system can be widened by broadening the determination threshold value with respect to the control target hydraulic pressure by the changed second determination threshold value. As a result, for example, when the temperature of the operating fluid is low, the responsiveness of the operating fluid is delayed, and accordingly, the hydraulic pressure of the operating fluid (controlled hydraulic pressure; indicated by a long dash line) is without the normal detection range specified by the preset second determination threshold value, and even when the brake system is erroneously determined to be abnormal, the hydraulic pressure of the operating fluid can be kept within the widened normal detection range. Therefore, even though the brake system itself is normal, an erroneous determination that the brake system is abnormal can be suppressed, for example, when the temperature of the operating fluid is low.

It is note that when the temperature of the operating fluid is high, since the responsiveness of the operating fluid is not delayed, the hydraulic pressure of the operating fluid (controlled hydraulic pressure; indicated by a short dot broken line) is within the normal detection range specified by the preset second determination threshold value, and the brake system is determined to be normal. Therefore, the brake system is not erroneously determined to be abnormal.

In the maintaining state after the time t 3 , the first determination threshold value is set to the control target hydraulic pressure as indicated by a thick dot-and-dash line. The second determination threshold value (preset second determination threshold value) is set to a value smaller than the control target hydraulic pressure (indicated by the thick solid line) by the second predetermined value “b 1 ” as indicated by the thin solid line.

In addition, the above-described operation performed by the brake system (when the state is transferred from the decreasing state to the maintaining state) will be described in accordance with a flowchart in FIG. 5 and a time chart in FIG. 6 . The flowchart will be described only on different points and the same points are denoted by the same reference signs to omit the description.

In Step S 210 , the brake ECU 17 sets the first determination threshold value (n) in the present time to a value obtained by adding the first predetermined value a to the control target hydraulic pressure (n) calculated in the present time. In Step S 212 , the brake ECU 17 sets the second determination threshold value (n) in the present time to a value obtained by adding the second predetermined value b 1 to the control target hydraulic pressure (n) calculated in the present time. In Step S 232 , the brake ECU 17 sets the second determination threshold value (n) in the present time to a value obtained by adding the third predetermined value b 2 to the control target hydraulic pressure (n) calculated in the present time.

When the initial value of the second determination threshold value (changed second determination threshold value) immediately after switching is smaller than the first determination threshold value immediately before switching (when the divergence amount from the control target hydraulic pressure is small, it is determined to be “YES” in Step S 236 ), the brake ECU 17 permits changing of the second determination threshold value after the beginning of the maintaining state (Step S 142 ). In contrast, when the initial value of the changed second determination threshold value immediately after switching is larger than the first determination threshold value immediately before switching (when the divergence amount from the control target hydraulic pressure is large, it is determined to be “NO” in Step S 236 ), the brake ECU 17 prohibits changing of the second determination threshold value after the beginning of the maintaining state (Step S 138 ).

In Step S 244 , the brake ECU 17 calculates the second determination threshold value in the present time (changed second determination threshold value) (n) by subtracting a predetermined change amount from the second determination threshold value in the last time (changed second determination threshold value) (n−1).

The brake ECU 17 continues the changing process of the second determination threshold value until the changed second determination threshold value (n) in the present time becomes equal to the preset second determination threshold value the control target hydraulic pressure in the present time (n)+the second predetermined value “b 1 ”) or until the state is switched from the maintaining state to the increasing state (it is determined to be “NO” in Step S 246 ). In contrast, the brake ECU 17 terminates the changing process of the second determination threshold value when the changed second determination threshold value in the present time (n) becomes equal to the preset second determination threshold value or when the state is switched from the maintaining state to the increasing state (it is determined to be “YES” in Step S 246 ).

The brake ECU 17 adopts a larger one of the first determination threshold value (n) and the second determination threshold value (n) which are set previously as the determination threshold value in Step S 214 .

When the hydraulic pressure measured value is smaller than the determination threshold value (it is determined to be “NO” in Step S 218 ), the brake ECU 17 determines that the hydraulic pressure system of the hydraulic pressure braking force generating device A is normal (Step S 122 ). In contrast, when the state in which the hydraulic pressure measured value is larger than the determination threshold value continues for a predetermined period (it is determined to be “Yes” in Step S 218 , 120 , respectively), the brake ECU 17 determines that the hydraulic pressure system of the hydraulic pressure braking force generating device A is abnormal (Step S 124 ).

A case where the control target hydraulic pressure is in the decreasing state (that is, when the stroke is in the decreasing state) (during a period from time t 11 to time t 12 ) will be described with reference to the time chart in FIG. 6 . The time t 11 indicates the time when the decreasing state starts, and the time t 12 indicates the time when the maintaining state starts (that is, a time point when the state is switched from the decreasing state to the maintaining state).

During the period from the time t 11 to the time t 12 , the first determination threshold value is set to a value larger than the control target hydraulic pressure (indicated by a thick solid line) by the first predetermined value “a” as indicated by a thick dot-and-dash line. The second determination threshold value is set to a value larger than the control target hydraulic pressure (indicated by the thick solid line) by the second predetermined value “b 1 ” as indicated by a thin solid line. Therefore, the determination threshold value is set to the first determination threshold value.

During the period from the time t 12 to time t 13 , the first determination threshold value is set to the control target hydraulic pressure as indicated by a thick dot-and-dash line. In FIG. 6 , the first determination threshold value is indicated slightly apart from the control target hydraulic pressure for easy discrimination from the control target hydraulic pressure. The second determination threshold value (preset second determination threshold value) can be basically set to a value larger than the control target hydraulic pressure (indicated by the thick solid line) by the second predetermined value “b 1 ” as indicated by the thin solid line.

When the change of the second determination threshold value is permitted, the second determination threshold value (the changed second determination threshold value) is set such that the preset second determination threshold value at the time point when the maintaining state is started is set as an initial value as indicated by a thin dashed-two dotted line. The initial value is set to a value larger than the control target hydraulic pressure (indicated by the thick solid line) by the second predetermined value “b 1 ”. After the time point when the maintaining state is started, the changed second determination threshold value is set to decrease from the initial value by a predetermined change amount. In this manner, when the control target hydraulic pressure is determined to be in the maintaining state, the changed second determination threshold value (threshold value) that defines the permissible divergence range for determining the abnormality of the brake system is changed to be closer to the control target hydraulic pressure in a stepwise manner. Consequently, the permissible divergence range may be set to an adequate value. Therefore, a reduction of time required for determination and improved adequacy of determination are achieved.

In addition, as another example, when the change of the second determination threshold value is permitted, the second determination threshold value (the changed second determination threshold value) is set such that the changed second determination threshold value at the time point when the maintaining state is started is set as an initial value as indicated by a thin dot-and-dash line. The initial value is set to be a value larger than the control target hydraulic pressure by the third predetermined value “b 2 ”. During a period from the time point when the maintaining state is started until the time point when the change terminates (time t 13 ), the changed second determination threshold value is set to decrease from the initial value by a predetermined change amount. Therefore, the determination threshold value is set to the changed second determination threshold value. In other word, the determination threshold value can be extended with respect to the control target hydraulic pressure as compared with the case of the preset second determination threshold value.

When the change of the second determination threshold value is permitted, it is preferable to further delay the time point when the change terminates (time t 13 ) to set the changed second determination threshold value to be closer to the control target hydraulic pressure in a stepwise manner.

In this manner, at the beginning of the timing when the control target hydraulic pressure is switched to the maintaining state, a normal detection range of the brake system can be widened by broadening the determination threshold value with respect to the control target hydraulic pressure by the changed second determination threshold value. As a result, for example, when the temperature of the operating fluid is low, the responsiveness of the operating fluid is delayed, and accordingly, the hydraulic pressure of the operating fluid (controlled hydraulic pressure; indicated by a long dash line) falls outside the normal detection range specified by the preset second determination threshold value, and even when the brake system is erroneously determined to be abnormal, the hydraulic pressure of the operating fluid can be kept within the widened normal detection range. Therefore, even though the brake system itself is normal, an erroneous determination that the brake system is abnormal can be suppressed, for example, when the temperature of the operating fluid is low.

It is note that when the temperature of the operating fluid is high, the responsiveness of the operating fluid is not delayed, the hydraulic pressure of the operating fluid (controlled hydraulic pressure; indicated by a short dot broken line) is within the normal detection range specified by the preset second determination threshold value, and the brake system is determined to be normal. Therefore, the brake system is not erroneously determined to be abnormal.

In the maintaining state after the time t 13 , the first determination threshold value is set to the control target hydraulic pressure as indicated by a thick dot-and-dash line. The second determination threshold value (preset second determination threshold value) is set to a value larger than the control target hydraulic pressure (indicated by the thick solid line) by the second predetermined value “b 1 ” as indicated by the thin solid line.

As is apparent from the description descried above, the brake ECU 17 (abnormality detection device) of the embodiment is the abnormality detection device configured to detect an abnormality of the hydraulic pressure braking force generating device A (brake system), including: the control target hydraulic pressure calculating portion 17 b configured to calculate the control target hydraulic pressure in accordance with the operation state of the brake pedal 11 (brake operating member) or the requirement from other system; the hydraulic pressure obtaining portion 17 g configured to obtain the hydraulic pressure of the operating fluid controlled to become the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b from the pressure sensor 26 a ; the state determining portion 17 c configured to perform a state determination for determining whether the control target hydraulic pressure is in a maintaining state that the control target hydraulic pressure is maintained at a constant value, in an increasing state that the control target hydraulic pressure is increasing, or in a decreasing state that the control target hydraulic pressure is decreasing; the first and second determination threshold value setting portions 17 d , 17 e (threshold value setting portion) configured to set the threshold value that specifies the permissible divergence range between the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g and the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b ; the second determination threshold value changing portion 17 f (threshold value changing portion) configured to change the threshold value so as to be closer to the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b in a stepwise manner when the state determining portion 17 c determines that the control target hydraulic pressure is in the maintaining state; and the abnormality determining portion 17 h configured to determine the abnormality of the hydraulic pressure braking force generating device A when the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g is deviated from the permissible divergence range.

In this configuration, when the control target hydraulic pressure is determined to be in the maintaining state, the threshold value that defines the permissible divergence range for determining abnormalities of the hydraulic pressure braking force generating device A is changed to be closer to the control target hydraulic pressure in a stepwise manner. Consequently, the permissible divergence range can be set to an adequate value. Therefore, a reduction of time required for determination and improved adequacy of determination are achieved.

The state determining portion 17 c includes the control target hydraulic pressure gradient calculating portion 17 c 1 configured to calculate the control target hydraulic pressure gradient, which is a gradient of the control target hydraulic pressure, from the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b ; and the control target hydraulic pressure divergence amount calculating portion 17 c 2 configured to calculate the control target hydraulic pressure divergence amount which is a divergence amount of the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g at a time after the determination that the control target hydraulic pressure is in the maintaining state started from the control target hydraulic pressure calculated by the control target hydraulic pressure calculating portion 17 b at a time when the determination that the control target hydraulic pressure is in the maintaining state started, and the state determining portion 17 c performs the state determination from at least one of the control target hydraulic pressure gradient calculated by the control target hydraulic pressure gradient calculating portion 17 c 1 and the control target hydraulic pressure divergence amount calculated by the control target hydraulic pressure divergence amount calculating portion 17 c 2 .

In this configuration, both of the control target hydraulic pressure gradient and the control target hydraulic pressure divergence amount can be used, and thus adequate and accurate state determination is achieved.

In addition, the second determination threshold value changing portion 17 f sets a value obtained by adding a predetermined value to the hydraulic pressure obtained by the hydraulic pressure obtaining portion 17 g at the time when the determination that the control target hydraulic pressure is in the maintaining state is started as an initial value of the threshold value.

In this configuration, since the initial value of the threshold value is set based on the actually detected hydraulic pressure, it is possible to improve the failure detection accuracy when the control target hydraulic pressure is in the maintaining state.

In addition, the brake ECU 17 (abnormality detection device) further includes the change permitting portion 17 f 2 configured to permit the change of the threshold value by the second determination threshold value changing portion 17 f when the divergence amount of the threshold value from the control target hydraulic pressure at the time when the determination that the control target hydraulic pressure is in the maintaining state started is larger than a divergence amount of the threshold value from the control target hydraulic pressure at the time before the determination that the control target hydraulic pressure is in the maintaining state started.

In this configuration, it is possible to more accurately detect the abnormality of the hydraulic braking force generating device A.

In addition, the change amount of the threshold value to be changed by the second determination threshold value changing portion 17 f is determined by considering viscosity of the operating fluid and the variations in the hydraulic pressure control system which constitutes the hydraulic pressure braking force generating device A.

In this configuration, it is possible to more accurately detect the abnormality of the hydraulic braking force generating device A.

Although the hydraulic pressure is exemplified as the braking force related physical amount in the description of the embodiment described above, any physical amounts (for example, braking force, stroke of the master cylinder, stroke of the caliper piston, etc.) other than the hydraulic pressure may be adopted as long as those physical amounts relate to the braking force.