Automatic transmission

(1) Background of the Invention

The present invention relates to a technique on a fail-safe control when a failure of any one or more of frictional engaging elements in a multiple-speed (or planetary gear type stepped) automatic transmission.

(2) Description of Related Art

A Japanese Patent Application Publication (tokkai) 2005-155719 published on Jun. 16, 2005 (which corresponds to a U.S. Pat. No. 7,128,683 issued on Oct. 31, 2006) exemplifies a previously proposed multiple-speed (or planetary gear type stepped) automatic transmission which is equipped with four couples of planetary gears and seven couples of frictional engaging elements and which is capable of switching gear shift stages of forward seven speeds (forward seven gear ratios) and one reverse speed (one reverse gear ratio).

If any one of the frictional engaging elements which is in a clutched state at a second speed, a third speed, a fourth speed, and a sixth speed has failed to be disabled to be clutched (or has failed to be clutched), such a control at a time of such an abnormality as described above can be thought that a gear shift stage only of a first speed, a fifth speed, and a seventh speed at which it is not necessary for the failed frictional engaging element is used to make a vehicle in which this automatic transmission is equipped run. However, since a difference in the gear shift stages between the first speed and the fifth speed is large, a traveling performance (or called, a driveability) can remarkably be worsened.

Then, since a special gear shift stage not used in a normal operation state is set between the first speed and the fifth speed and is used during an abnormal state. In this case, it can be considered that the traveling performance can be improved if the special gear shift stage is used when the abnormality described above occurs.

However, since control data for the special gear shift is accordingly increased, the data capacity is needed to be accordingly increased. Especially, in the automatic transmission whose number of gear shaft stages are increased, a control date on the gear shift stages used in the normal operation state is large. Thus, an increase in the data capacity due to the addition of the control data in the case where the abnormality occurs becomes a major problem.

It is an object of the present invention to provide a multiple-speed (or planetary gear type stepped) automatic transmission in which an increase in the date capacity is suppressed while an intermediate gear shift stage which is not used in the normal operation state is usable during the failure in one of the frictional elements.

According to one aspect of the present invention, there is provided an automatic transmission, comprising: a plurality of planetary gears; a plurality of frictional engaging elements connected to rotational elements of the respective planetary gears, the automatic transmission achieving a plurality of gear shift stages based on a traveling state of a vehicle by changing clutched and released states of the respective frictional engaging elements and the plurality of gear shift stages including a third gear shift stage achieved by releasing a first frictional engaging element, the first frictional engaging element being clutched at a first gear shift stage and at a second gear shift stage, and excluding a fourth gear shift stage achieved by releasing the first frictional engaging element clutched at the second gear shift stage; a first shift control section configured to perform a gear shift control to shift the gear shift stage between the first gear shift stage and the second gear shift stage by referring to a first gear shift control data used when the gear shift stage is switched between the first gear shift stage and the second gear shift stage; an abnormality state detecting section configured to detect an abnormality state in which both of the first gear shift stage and the second gear shift stage are unachieved due to a failure of at least one of the first frictional engaging element and a second frictional engaging element which is released at both of the first gear shift stage and the second gear shift stage; and an abnormality state gear shift control section configured to perform the gear shift control to shift the gear shift stage between the third gear shift stage and the fourth gear shift stage through the first gear shift control section, while forcefully releasing the first frictional engaging element, when the abnormality state detecting section detects the abnormality state.

According to another aspect of the present invention, there is provided a control method applicable to an automatic transmission, the automatic transmission comprising: a plurality of planetary gears; and a plurality of frictional engaging elements connected to rotational elements of the respective planetary gears, the automatic transmission achieving a plurality of gear shift stages based on a traveling state of a vehicle by changing clutched and released states of the respective frictional engaging elements and the plurality of gear shift stages including a third gear shift stage achieved by releasing a first frictional engaging element, the first frictional engaging element being clutched at a first gear shift stage and at a second gear shift stage, and excluding a fourth gear shift stage achieved by releasing the first frictional engaging element clutched at the second gear shift stage, the control method comprising: performing a gear shift control to shift the gear shift stage between the first gear shift stage and the second gear shift stage by referring to a first gear shift control data used when the gear shift stage is switched between the first gear shift stage and the second gear shift stage; detecting an abnormality state in which both of the first gear shift stage and the second gear shift stage are unachieved due to a failure of at least one of the first frictional engaging element and a second frictional engaging element which is released at both of the first gear shift stage and the second gear shift stage; and performing the gear shift control to shift the gear shift stage between the third gear shift stage and the fourth gear shift stage by performing the gear shift control to shift the gear shift stage between the first gear shift stage and the second gear shift stage, while forcefully releasing the first frictional engaging element, when detecting the abnormality state.

Since, according to the present invention, the gear shift stage can be switched to the fourth gear shift stage excluded from the gear shift stages based on the traveling state of the vehicle during the failure in the first frictional engaging element or in the second frictional engaging element, a worsening of a traveling (driving) performance can be prevented. In addition, since the first gear shift control data can be used during the change in the gear shift stage between the first gear shift stage and the second gear shift stage when the gear shift from the third gear shift stage to the fourth gear shift stage is performed, no new gear shift control data used for the occurrence of failure is needed to be prepared and the increase in data capacity can accordingly be suppressed. This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features. The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

FIG. 1 is a skeleton view representing a structure of a multiple-speed (or planetary gear type stepped) automatic transmission to which an automatic transmission in a first preferred embodiment according to the present invention is applicable.

FIG. 2 is a clutch table representing clutched states of respective frictional engaging elements for respective gear shift stages in the automatic transmission shown in FIG. 1 .

FIG. 3 is a lever diagram representing a rotational state of respective rotational members of planetary gears at the respective gear shift stages of the automatic transmission shown in FIG. 1 .

FIG. 4 is a shift diagram representing a relationship between a vehicle speed, an accelerator pedal operating variable (quantity of driver operation on accelerator pedal), and shift line in the automatic transmission shown in FIG. 1 .

FIG. 5 shows a flowchart representing a fail safe control of the automatic transmission in the first preferred embodiment shown in FIG. 1 .

FIG. 6 is an engagement table representing the clutched state of the respective engaging elements at a forward first speed, at a forward second speed, at a forward 2.5 speed, and at a forward fourth speed.

FIG. 7 is a lever diagram representing rotation states of the respective rotational members of the planetary gears at the forward first speed through forward fourth speed.

FIG. 8 is a flowchart representing a fail safe control of the automatic transmission in a second preferred embodiment according to the present invention.

Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention.

First Embodiment

FIG. 1 shows a skeleton diagram representing a construction of a multiple-speed (or planetary gear type stepped) automatic transmission to which an automatic transmission in a first preferred embodiment according to the present invention is applicable. The automatic transmission in this embodiment is a multiple-speed (multiple gear ratios) planetary gear type stepped) automatic transmission configured to establish forward seven speeds (gear ratios) and one reverse speed (gear ratio). A driving force of an engine Eg is inputted to an input shaft Input via a torque converter TC having a lock-up clutch LUC and a revolution speed of engine Eg is subjected to a gear shift (or a gear ratio shift) by means of four planetary gears and seven frictional engaging elements (as will be described later) and is outputted via an output shaft Output. In addition, an oil pump OP is provided coaxially on a pump impeller of torque converter TC and is drivingly rotated according to the driving force of engine Eg to pressurize oil. That is to say, the revolution outputted from engine Eg rotatively drives the pump impeller and an oil pump OP of torque converter TC. Oil stirred due to the rotation of the oil impeller is transmitted to a turbine runner via a stator of torque converter TC to drive input shaft Input.

An engine controller (ECU (Engine Control Unit)) 10 configured to control a driving state of engine Eg, an automatic transmission controller (ATCU) 20 configured to control a state of transmission of the automatic transmission, and a control valve unit (CVU) 30 configured to control a hydraulic pressure for each of the frictional engaging elements on the basis of an output signal from ATCU 20 . It should be noted that ECU 10 and ATCU 20 are connected to each other via a CAN (Computer Area Network) communication line, sharing sensor information and control information by signal communication lines.

APO sensor 1 configured to detect a quantity of a driver's operation (also called, an operating variable) on an accelerator pedal and engine speed sensor 2 configured to detect a rotation speed of engine Eg (engine speed) are connected to ECU 10 . ECU 10 controls a fuel injection quantity and a throttle opening angle of an engine throttle valve on the basis of the engine speed and the quantity of the driver's operation on the accelerator pedal and controls the revolution speed and torque of the engine.

A first turbine revolution speed sensor 3 configured to detect a revolution speed of a first carrier PC 1 (as will be described later), a second turbine revolution speed sensor 4 configured to detect a revolution speed of a first ring carrier R 1 (as will be described later), and an inhibitor switch 6 configured to detect an operation state of a shift lever by the driver are connected to ATCU 20 . The shift lever has an engine braking position acting an engine braking and an ordinary forward running range position not acting the engine braking in addition to P, R, N, and D range. ATCU 20 selects an optimal command gear shift stage from a gear shift map on the basis of a vehicle speed Vsp (which corresponds to a signal outputted from an output shaft revolution speed sensor 5 ) and the quantity of the driver's operation on the accelerator pedal, viz., and outputs a control command to achieve the commanded gear shift stage to control valve unit (CVU) 30 . That is to say, ATCU 20 has a gear shift control section which outputs a control command to achieve the commanded gear shift stage to control valve unit (CVU).

Next, a gear shift mechanism configure to transmit the revolution of input shaft Input to output shaft Output while the revolution of input shaft being subjected to the gear ratio shift will be described below. The gear shift mechanism includes: a first planetary gear set GS 1 and a second planetary gear set GS 2 in an order from input shaft Input toward axial output shaft Output. A plurality of clutches C 1 , C 2 , C 3 , and a plurality of brakes B 1 , B 2 , B 3 , and B 4 are disposed in the gear shift mechanism as frictional engaging elements. Furthermore, a plurality of one-way clutches F 1 and F 2 are disposed in the gear shift mechanism.

First planetary gear G 1 is a single pinion planetary gear having a first sun gear S 1 , a first ring gear R 1 , and a first (planetary-pinion) carrier PC 1 supporting a first pinion P 1 meshed with both gears S 1 and R 1 . Second planetary gear G 2 is a single pinion planetary gear having a second ring gear R 2 , a second ring gear R 2 , and a second (planetary-pinion) carrier PC 2 supporting a second pinion P 2 in mesh with both gears S 2 and R 2 . Third planetary gear G 3 is a single pinion type planetary gear having a third gear S 3 , a third ring gear R 3 , and a third carrier PC 3 supporting a third pinion P 3 in mesh with both gears S 3 and R 3 . Fourth planetary gear G 4 is a single pinion type planetary gear having a fourth sun gear S 4 , a fourth ring gear R 4 , and a fourth pinion carrier PC 4 supporting a fourth pinion P 4 in mesh with both gears S 4 and R 4 .

An input shaft Input is coupled with second ring gear R 2 and receives the rotation driving force from engine Eg via torque converter TC and so forth. An output shaft Output is coupled with third carrier PC 3 in order for an input rotation driving force to be transmitted to driving wheels via final gears or so forth.

A first connection member M 1 is a member configured to integrally link with first ring gear R 1 , second carrier PC 2 , and fourth ring gear R 4 . A second connection member M 2 is a member configured to integrally link third ring gear R 3 and fourth carrier PC 4 . A third connection member M 3 is a member configured to integrally link first sun gear S 1 and second sun gear S 2 .

First planetary gear set GS 1 is constituted by four rotational elements and configured to link first planetary gear G 1 to second planetary gear G 2 through first connection member M 1 and third connection member M 3 . In addition, second planetary gear set GS 2 is constituted by five rotational elements and configured to link third planetary gear G 3 and fourth planetary gear G 4 via second connection member M 2 .

An input clutch (I/C) C 1 is a clutch which selectively connects and disconnects input shaft Input to and from second connection member M 2 . A direct clutch (D/C) C 2 is a clutch which selectively connect and disconnects fourth sun gear S 4 to and from fourth carrier PC 4 .

An H&LR clutch (H&LR/C) C 1 is a clutch which selectively connects and disconnects third sun gear S 3 to and from fourth sun gear S 4 . In addition, a second one-way clutch F 2 is interposed between third sun gear S 3 and fourth sun gear S 4 . This one-way clutch F 2 releases H&LR clutch C 3 . When a rotation speed of fourth sun gear S 4 is larger (faster) than that of third sun gear S 3 , third sun gear G 3 develops the rotation speed independently of fourth sun gear S 4 . Thus, third planetary gear G 3 is connected to fourth planetary gear G 4 via second connection member M 2 and their respective planetary gears achieve an independent gear ratio.

A front brake B 1 (Fr/B, second frictional engaging element) is a brake which selectively stops the revolution of first carrier PC 1 . First one-way clutch F 1 is disposed in parallel to front brake B 1 . A low brake (LOW/B) B 2 is a brake which selectively stops the rotation of third sun gear S 3 . A 2346-brake b 3 (2346/B, a first frictional engaging element) is a brake which selectively stops the rotation of third connection member M 3 linking first sun gear S 1 and second sun gear S 2 . A reverse brake (R/B) B 4 is a brake which selectively stops the rotation of fourth carrier PC 4 . ATCU 20 calculates a revolution speed of input shaft using the output signals of the first and second turbine sensors 3 and 4 since input shaft Input is linked to second ring gear R 2 . That is to say, N(R 2 )=(1+β)N(PC 2 )−(1/β)·N(PC 1 ), wherein a gear ratio between second ring gear R 2 and second carrier PC 2 is 1 and β denotes a gear ratio between first ring gear R 2 and first carrier PC 1 , N(R 2 ) denotes the rotation speed of the second ring gear R 2 , viz., input shaft Input, N(PC 2 ) denotes the rotation speed of second carrier PC 2 , and N(PC 1 ) denotes the rotation speed of first carrier PC 1 .

Next, referring to FIGS. 2 and 3 , the operation of the gear shift mechanism will be described below. FIG. 2 shows an engagement table representing an engagement state of each engaging element for each of gear ratio speed ranges. In FIG. 2 , a circle mark of O represents that the corresponding engaging element is in the clutched state and another circle mark of (O) represents that the corresponding engaging element is in the engaged state when a range position at which an engine braking is acted is selected. FIG. 3 shows a lever diagram representing a revolution state of each rotational member at the respective gear shift stages.

At a first speed (a third gear shift stage), only low brake B 2 is clutched. First, one-way clutch F 1 and second one-way clutch F 2 are engaged. In addition, when the engine braking is acted, front brake B 1 and H&LR clutch C 3 are furthermore clutched.

If first one-way clutch F 1 is engaged, the rotation of first carrier PC 1 is stopped. Hence, the rotation inputted from Input shaft Input to second ring gear R 2 is speed-reduced by first planetary gear set GS 1 , this rotation is outputted from first connection member M 1 to fourth ring gear R 4 . In addition, low brake B 2 is engaged and second one-way clutch F 2 is engaged and second one-way clutch F 2 is engaged so that the rotations of third sun gear S 3 and fourth sun gear S 4 are stopped. Hence, the revolution inputted to fourth ring gear R 4 is speed-reduced by second planetary gear set GS 2 and is outputted from third carrier PC 3 .

That is to say, as shown in the lever diagram of FIG. 3 , the rotation of input shaft is speed-reduced by means of first planetary gear set GS 1 , is speed-reduced by second planetary gear set GS 2 , and is outputted from third carrier PC 3 . In details, the first speed, as shown in the lever diagram of FIG. 3 , is prescribed by a line connecting a clutching point of front brake B 1 which speed-reduces the output revolution of engine Eg to a clutching point of low brake B 2 which speed-reduces the speed-reduced rotation of first planetary gear set GS 1 and the rotation inputted from input shaft Input is speed-reduced and is outputted from output shaft Output.

At a second speed (a first gear shift stage), low brake B 2 and 2346-brake B 3 are engaged and second one-way clutch F 2 is engaged. In addition, during the operation of the engine brake, H&LR clutch C 3 is furthermore engaged.

If 2346-brake B 3 is engaged, the rotations of first sun gear S 1 and second sun gear S 2 are stopped. Hence, the rotation inputted from input shaft Input to second ring gear R 2 is speed-reduced only by means of second planetary gear G 2 . This rotation is outputted from first connection member M 1 to fourth ring gear R 4 . In addition, low brake B 2 is engaged and second one-way clutch F 2 is engaged. Thus, the rotations of third sun gear S 3 and fourth sun gear S 4 are stopped. Hence, the rotation inputted to fourth sun gear R 4 is speed-reduced through second planetary gear set GS 2 and is outputted from third carrier PC 3 .

That is to say, as shown in the lever diagram of FIG. 3 , the rotation of input shaft Input is speed-reduced by first planetary gear set GS 1 , is speed-reduced by second planetary gear set GS 2 and, thereafter, is outputted from output shaft Output. The second speed is prescribed by a line connecting a clutching point of 2346-brake B 3 which speed reduces the output revolution of engine Eg and a clutching point of low brake B 2 which speed reduces the speed-reduced rotation from second planetary gear G 2 , as shown in the lever diagram in FIG. 3 and the rotation inputted from input shaft Input is speed-reduced and is outputted form output shaft Output.

At a third speed, low brake B 2 , 2346-brake B 3 , and direct clutch C 2 are clutched.

Since 2346-brake B 3 is engaged, the rotations of first sun gear S 1 and second sun gear S 2 are stopped. Hence, the rotation inputted from input shaft Input to second ring gear R 2 is speed-reduced through second planetary gear G 2 and this rotation is outputted from first connection member M 1 to fourth ring gear R 4 . In addition, the engagement of direct clutch C 2 causes the rotation thereof together with fourth planetary gear G 4 . Hence, fourth planetary gear G 4 participates in the torque transmission but does not participate in a speed reduction action. Furthermore, the engagement of low brake B 2 causes the rotation of third sun gear S 3 to be stopped. Hence, the rotation inputted to third ring gear R 3 via second connection member M 2 from fourth carrier PC 4 which integrally rotates with fourth ring gear R 4 is speed-reduced through third planetary gear G 3 and is outputted from third carrier PC 3 .

That is to say, as shown in the lever diagram of FIG. 3 , the rotation of input shaft Input is speed-reduced through first planetary gear set GS 1 , is speed-reduced through first planetary gear G 3 of second planetary gear set GS 2 , and is outputted from output shaft Output. The fourth speed is prescribed by a line connecting the clutching point of 2346-brake B 3 and the clutching point of low brake B 2 which speed reduces of the speed reduced rotation of second planetary gear G 2 , as shown in the lever diagram of FIG. 3 .

At a fourth speed (a second gear shift stage), 2346-brake B 3 , direct clutch C 2 , and H&LR clutch C 3 are clutched.

The clutching of 2346-brake B 3 causes rotations of first sun gear S 1 and second sun gear S 2 to be stopped. The rotation inputted from input shaft Input to second ring gear R 2 is speed-reduced only through second planetary gear G 2 . This speed-reduced gear ratio is outputted from first connection member M 1 to fourth ring gear R 4 . In addition, direct clutch C 2 and H&LR clutch C 3 are clutched (engaged) to be rotated in a unit with second planetary gear set GS 2 . Hence, the rotation inputted to fourth ring gear R 4 is directly outputted from third carrier PC 3 .

That is to say, as shown in the lever diagram of FIG. 3 , the rotation of input shaft Input is speed-reduced through first planetary gear set GS 1 and is outputted from output shaft Output without speed reduction at second planetary gear set GS 2 . The fourth speed is prescribed by a line connecting the clutching point of 2346-brake B 3 which speed reduces the output rotation of engine Eg to the clutching points of direct clutch C 2 and H&LR clutch C 3 which directly output the speed-reduced rotation from second planetary gear G 2 .

At a fifth speed (5th), input clutch C 1 , direct clutch C 2 , and H&LR clutch C 3 are clutched.

The clutching of input clutch C 1 causes the rotation of input shaft Input to be directly inputted to second connection member M 2 . In addition, the clutching of direct clutch C 2 and H&LR clutch C 3 causes second planetary gear set GS 2 to be integrally rotated. Hence, the rotation of input shaft Input is directly outputted from third carrier PC 3 .

That is to say, as shown in the lever diagram of FIG. 3 , the rotation of input shaft Input is speed-reduced through first planetary gear set GS 1 and is directly outputted from output shaft Output without the speed reduction at secondary planetary gear set GS 2 . The fifth speed is prescribed by a line connecting the clutching points of input clutch C 1 , direct clutch C 2 , and H&LR clutch C 3 and the rotation input from input shaft Input is directly outputted from output shaft Out.

At a sixth speed (6th), input clutch C 1 , H&LR clutch C 3 , and 2346-brake B 3 are clutched.

Since input clutch C 1 is clutched, the rotation of input shaft Input is inputted to second ring gear and is directly inputted to second ring gear R 2 and is directly inputted to second connection member M 2 . In addition, since 2346-brake B 3 is clutched, rotations of first sun gear S 1 and second sun gear S 2 are stopped. Hence, the rotation of input shaft Input is speed-reduced through second planetary gear G 2 and is outputted from first connection member M 1 to fourth ring gear R 4 .

Furthermore, since H&LR clutch C 3 is clutched, third sun gear S 3 and fourth sun gear S 4 are integrally rotated. Thus, second planetary gear set GR 2 outputs the rotation prescribed according to the rotation of fourth ring gear R 4 and the rotation of second connection member M 2 from third carrier PC 3 .

That is to say, as shown in the lever diagram of FIG. 3 , part of the rotation of input shaft input is speed-reduced at first planetary gear set GS 1 but is speed-increased at second planetary gear set GS 2 , and is outputted from output shaft output. The sixth speed is prescribed by a line connecting the clutching point of 2346-brake B 3 which speed reduces the output rotation of engine Eg, the clutching point of input clutch C 1 which transmits the output rotation of engine Eg directly to second connection member M 2 , and H&LR clutch C 3 which constitutes second planetary gear set GS 2 and the rotation inputted from input shaft Input is speed-increased and is outputted from output shaft Output.

At a seventh (7-th) speed, input clutch C 1 , H&L R clutch C 3 , and front brake B 1 are clutched and first one-way clutch F 1 is engaged.

Since input clutch C 1 is clutched, the rotation of input shaft Input is inputted to second ring gear R 2 and is directly inputted to second connection member M 2 . Since front brake B 1 is clutched, the rotation of first carrier PC 1 is stopped. Hence, the rotation of input shaft Input is speed-reduced at first planetary gear set GS 1 and this rotation is outputted from first connection member M 1 to fourth ring gear R 4 .

In addition, since H&LR clutch C 3 is clutched, third sun gear S 3 is rotated in a unit with (integrally rotated together with) fourth sun gear S 4 . Thus, second planetary gear set GS 2 outputs the rotation prescribed according to the rotation of fourth ring gear R 4 and according to the rotation of second connection member M 2 through third carrier PC 3 .

That is to say, as shown in the lever diagram of FIG. 3 , part of rotation of input shaft Input is speed-reduced at first planetary gear set GS 1 , is speed-increased at second planetary gear set GS 2 , and is outputted from output shaft output. The seventh speed is prescribed by a line connecting the clutching point of front brake B 1 which speed reduces the output rotation of engine Eg through first planetary gear set GS 1 , the clutching point of input clutch C 1 which transmits the output rotation of engine Eg directly to second connection member M 2 , and the clutching point of H&LR clutch C 3 constituting second planetary gear set GS 2 and the rotation inputted from input shaft Input is speed-increased and is outputted from output shaft Output.

At a reverse speed (reverse gear shift stage), H&LR clutch C 3 , front brake B 1 , and reverse brake B 4 are clutched.

Since front brake B 1 is clutched, rotation of first carrier PC 1 is stopped. Hence, the rotation of input shaft Input is speed-reduced through first planetary gear set GS 1 and this speed-reduced rotation is outputted from first connection member M 1 to fourth ring gear R 4 .

In addition, since H&LR clutch C 3 is clutched, third sun gear S 3 and fourth sun gear S 4 are integrally rotated. When reverse brake B 4 is clutched, the rotation of second connection member M 2 is stopped. Hence, in second planetary gear set GS 2 , the rotation of fourth ring gear R 4 is transmitted to fourth sun gear S 4 , third carrier PC 3 , while a reverse rotation is carried out, and is outputted from third carrier PC 3 .

That is to say, as shown in the lever diagram of FIG. 3 , the rotation of input shaft Input is speed-reduced at first planetary gear set GS 1 , reversed at second planetary gear set GS 2 , and is outputted from Output shaft output. The reverse speed is prescribed by a line connecting the clutching point of front brake B 1 which speed reduces the output rotation of engine Eg through first planetary gear GS 1 , the clutching point of reverse brake B 4 which fixes the rotation of second connection member M 2 , and the clutching point of H&LR clutch C 3 constituting second planetary gear set GS 2 and the rotation inputted from input shaft Input is speed-reduced in the reverse direction and is outputted from output shaft Output.

The automatic transmission is constructed as described above and performs a change in the gear shift stages among first through seventh speeds on the basis of vehicle speed and quantity of driver's operation on the accelerator (pedal) in accordance with a shift schedule (shift lines) shown in FIG. 4 . At this time, if any one or more of frictional engaging elements has failed, a desired gear shift stage cannot be achieved and, therefore, the running performance becomes worsened. Therefore, in a case where a failure in the frictional engaging element occurs, a control executed in ATCU 20 will be explained with reference to a flowchart of FIG. 5 .

At a step S 11 (abnormality state detecting means (section)), ATCU 20 determines whether front brake B 1 fails to be released (a front brake clutch failure occurs). If ATCU 20 determines that front brake B 1 has failed to be released (or is stuck in the clutched state for the released state to be unachievable, viz., the front brake clutch failure occurs), the routine shown in FIG. 5 goes to a step S 12 . If no front brake clutch failure occurs (No) at step S 11 , the processing is ended. The engagement failure (or fails to be released) in front brake B 1 is such a failure that front break B 1 cannot be released with front brake B 1 retained in a clutched state and is developed with an open-and-closure valve which opens or closes a hydraulic pressure supply passage for front brake B 1 is stuck in an open state.

The determination of whether front brake B 1 fails to be released (the occurrence of the clutch failure in the engagement of front brake B 1 ) is made using a method, for example, disclosed in a Japanese Patent Application Publication No. 2007-120757 published on May 17, 2007. That is to say, if a vehicular deceleration in a non-operation state of a foot brake is larger (or faster) than a predetermined deceleration, ATCU 20 determines an occurrence of an interlock or determines a gear ratio abnormality from a relationship between a command gear ratio (gear shift stage) and an actual gear ratio. When these determinations are made, as a probing control, ATCU 20 detects the actual gear ratio in a state where the commanded gear shift stage is the second (2nd) speed and determines that front brake B 1 fails to be clutched in a case where the actual gear ratio is equal to or lower than a gear ratio corresponding to third speed (higher gear ratio side). When front brake B 1 has failed to be clutched, front brake B 1 is always in the clutched state irrespective of the commanded gear shift stage. Hence, any one or more of the gear shift stages that can normally be gear shifted without occurrence of the interlock are only the first speed, the seventh speed, and the reverse speed as appreciated from FIG. 2 . At this time, if the gear ratio (gear shift stage) is shifted from the first (1st) speed to the seventh (7th) speed, a difference in the gear ratio is too large to worsen a driveability remarkably. In addition, it is necessary to prepare gear shift hydraulic pressure data on the gear shift of first speed→seventh speed and a data capacity is accordingly increased.

Therefore, in the following steps in FIG. 5 , a method for achieving the shift to an intermediate gear shift stage (as will be described later) to be used only in a case where such an abnormality state as described above occurs using an ordinary used gear shift hydraulic pressure data will be described.

At step S 12 , ATCU 20 executes a forceful release of 2346-brake B 3 . Ordinarily, at the second speed, 2346-brake B 3 is clutched (refer to FIG. 2 ). However, in a case where front brake B 1 fails to be clutched, front brake B 1 is left clutched even at the second speed so that the interlock or so forth is developed. Hence, the forceful release of 2346-brake B 3 causes the gear shift stage to the first speed. At the next step S 13 , ATCU 20 determines whether it is necessary to perform the gear shift of the first speed to the second speed.

At the next step S 13 , ATCU 20 determines whether it is necessary to perform the gear shift of the first speed to the second speed on the basis of shift lines of shift diagram in FIG. 4 . If ATCU 20 determines that the gear shift of the first speed to the second speed is needed to be performed (Yes), the routine goes to a step S 14 . If ATCU 20 determines that no gear shift from the first speed to the second speed is needed to be performed (No), the routine goes to step S 12 .

At step S 14 (second gear shift control means(section)), ATCU 20 performs the gear shift control by referring to the gear shift hydraulic pressure data on the gear shift stage of first speed→second speed. At this time, automatic transmission recognizes that the gear shift control is executed on the basis of the above-described hydraulic pressure data in response to a gear shift command of the first speed→the second speed. However, actually, since 2346-brake B 3 is held at the forceful release thereof and front brake B 1 is maintained in the clutched state. Hence, the actual gear shift stage is maintained at the first speed.

At a step S 15 , ATCU 20 determines whether it is necessary to perform the gear shift of the second speed→the third speed on the basis of the gear shift lines of the shift diagram shown in FIG. 4 . If ATCU 20 determines that the gear shift from the second speed→the third speed is needed to be performed, the routine goes to a step S 16 . If ATCU 20 determines that it is not necessary to perform the gear shift from the second speed→the third speed, the routine returns to step S 14 .

At step S 16 , ATCU 20 modifies a target gear shift stage Gp from the third speed to the fourth speed and determines that it is necessary to perform the gear shift from the second speed to (→) the fourth speed.

At step S 17 (first gear shift control means(section)), ATCU 20 executes a gear shift control by referring to the hydraulic pressure data of the second speed to (→) the fourth speed. At this time, the automatic transmission recognizes that the gear shift control is executed on the basis of the gear shift hydraulic pressure data on the gear shift from the second speed to the fourth speed in response to the gear shift command of the second speed to (→) the fourth speed. However, the actual gear shift stage is transferred from the first speed to a 2.5 speed (this exemplifies the intermediate gear shift stage, viz., a fourth gear shift stage). It should be noted that, in the present specification, the shift stage which takes between the gear ratio corresponding to the second speed and that corresponding to the third speed is described as 2.5 speed for convenience.

The gear shift control executed at step S 17 will be explained with reference to the clutching table of FIG. 6 and the lever diagram of FIG. 7 . FIG. 6 shows the clutching table representing the clutched state of the respective clutching elements at the first speed, at the second speed, at 2.5 speed, and at the fourth speed. In FIG. 7 , each black circle denotes the clutched state and each black circle mark with brackets denotes the clutch state with the action of the engine braking. FIG. 7 shows the lever diagram representing rotation states of respective rotating members at the first speed through the fourth speed.

First, the gear shift control from the second speed to the fourth speed during the ordinary state (normal state) will be explained. At the second speed, both of low brake B 2 and 2346-brake B 3 are clutched. In addition, since second one-way clutch F 2 is engaged, approximately the same state in which H&LR clutch C 3 is engaged occurs. In addition, at the fourth speed, direct clutch C 2 , H&LR clutch C 3 , and 2346-brake B 3 are engaged. Hence, the gear shift hydraulic pressure data of the second speed to (→) the fourth speed stores data required with low brake B 2 released and direct clutch C 2 clutched.

Next, the gear shift control for the second speed→the fourth speed during the occurrence of the clutch failure of front brake B 1 will be explained. As described above, since the actual gear ratio provides the first speed when the command gear shift stage is the second speed, low brake B 2 is clutched and first one-way clutch F 1 and second one-way clutch F 2 are, furthermore, engaged so that the same states as the clutched states of front brake B 1 and H&LR clutch C 3 occur.

When low brake B 2 is released and direct clutch C 2 is clutched on the basis of the gear shift hydraulic pressure data on the second speed to (→) fourth speed, front brake B 1 , direct clutch C 2 , and H&LR clutch C 3 are in the clutched states. Finally, 2.5 speed is obtained which is not in the clutch table shown in FIG. 2 .

At 2.5 speed, front brake B 1 is clutched and the rotation of first carrier PC 1 is stopped. Therefore, the rotation from input shaft Input to second ring R 2 is speed-reduced through first planetary gear GS 1 . This rotation is outputted from first connection member M 1 to fourth ring gear R 4 . In addition, at 2.5 speed, direct clutch C 2 and H&LR clutch C 3 are clutched. Thus, second planetary gear G 2 is integrally rotated. Consequently, the rotation inputted to fourth ring gear R 4 is directly outputted from third carrier C 3 .

That is to say, as shown in the lever diagram of FIG. 7 , the rotation of input shaft Input is speed reduced through first planetary gear set GS 1 and is outputted from output shaft Output without speed reduction through second planetary gear set GS 2 . the rotation speed of output shaft Output is higher than the second speed but is lower than the third speed. Hence, it will be appreciated that the 2.5 speed is the intermediate gear shift stage between the second speed and the third speed.

As described hereinabove, since, during the occurrence in the clutch failure of front brake B 1 , the gear shift range can be switched to 2.5 speed which is the gear shift stage excluded from the ordinary gear shift stages at the normal operation based on the traveling (running) state of the vehicle, the worsening of the running (driving) performance (or driveablity) can be prevented even during the failure. In addition, when the gear shift stage is switched from first speed to 2.5 speed, the gear shift range hydraulic pressure data used in the gear shift stage from the second speed to the fourth speed can be used. Thus, new gear shift hydraulic pressure data is not needed to be prepared so that the data capacity can be suppressed.

In addition, when the gear shift from the first speed to the second speed is determined on the basis of the shift lines of the shift diagram, the gear shift stage is maintained at the first speed with the execution of the gear shift control using the gear shift hydraulic pressure data of the gear shift used for shifting the gear shift stage from the first speed to the second speed while 2346-brake B 3 is forcefully released. Thus, while the gear shift stage that the automatic transmission recognizes is apparently (or deceptively) shifted to the second speed, the actual gear shift stage can be the first speed. Thus, since the gear shift from the first speed to the 2.5 speed can be performed without setting shift line(s) exclusively used during the abnormality state. Consequently, the increase in the data capacity can be suppressed.

Second Embodiment

In this embodiment, the structure of the automatic transmission and clutched and released states of the respective frictional engaging elements for the respective gear shift stages are the same. However, only the control executed in ATCU 20 is different from the first embodiment. Hereinafter, the control executed in the ATCU 20 will be described below with reference to the flowchart of FIG. 8 .

That is to say, at a step S 21 (failure or abnormality state detecting means (section)), ATCU 20 determines whether 2346-brake B 3 fails to be clutched (a release failure occurs). If ATCU 20 determines that 2346-brake B 3 fails to be clutched, the routine goes to a step S 22 . If ATCU 20 determines that 2346-brake B 3 does not fail to be clutched (No), the processing of FIG. 8 is ended. It should be noted that the release failure of 2346-brake B 3 is a failure such that 2346-brake B 3 cannot be clutched with 2346-brake B 3 left released (is stuck in the released state for the clutched state to be unachievable). For example, an open-and-closure valve which opens or closes a hydraulic pressure supply passage to 2346-brake B 3 is stuck in a valve closure state.

If the determination of whether 2346-brake B 3 is stuck in the released state for the clutched state to be unachievable) fails to be released (release failure) is made by the method disclosed in, for example, the Japanese Patent Application Publication No. 2007-120757 described above. That is to say, the interlock has been determined to be developed when the vehicle deceleration in the non-operated state of the foot brake (a brake pedal) is larger than the predetermined deceleration or the gear ratio abnormality is detected from the relationship between the commanded gear shift stage and the actual gear shift stage. If these determinations are made, the actual gear ratio is detected with the commanded gear shift stage at the second speed. If the gear ratio corresponding to the first speed (first gear ratio) is resulted, 2346-brake B 3 is determined to fail to be stuck in the released state for the clutched state to be unachievable (left released).

When 2346-brake B 3 is determined to fail to be clutched (namely, to be stuck in the released state for the clutched state to be unachievable), 2346-brake B 3 is always in the release state irrespective of the commanded gear shift stage. Hence, any one or more of the gear shift stages that can normally gear shifted are only the first (1st) speed, the fifth (5th) speed, the seventh (7th) speed, and the reverse speed (gear ratio) as appreciated from FIG. 2 . At this time, the driveability is remarkably worsened since the difference between the gear ratios of the first speed and the fifth speed is too large to execute the gear shift and it is necessary to prepare the gear shift hydraulic pressure date from the first speed to the fifth speed. Consequently, the data capacity is augmented.

The gear shift method achievable to the intermediate gear shift stage used only in case of emergency (in the case of the abnormality state) using the ordinary gear shift hydraulic pressure data will be explained below.

At a step S 22 , ATCU 20 forcefully releases 2346-brake B 3 . In a case where 2346-brake B 3 fails to be released, 2346-brake B 3 is in the released state even if not forcefully released. However, in this control, 2346-brake B 3 is presumed to be forcefully in the released state.

The series of controls carried out at steps S 23 through S 27 are the same as those described in the first embodiment. Thus, even during the release failure of 2346-brake B 3 , the gear shift control is executed using the gear shift hydraulic pressure data from the second speed to (→) the fourth speed in the same way as the first embodiment in order for the actual gear shift stage from the first speed to the 2.5 speed which is intermediate between the third speed and the second speed.

As described hereinabove, during the release failure of 2346-brake B 3 , the gear shift stage can be switched to the 2.5 speed which is not included in the ordinary shift stages based on the traveling state of the vehicle. Hence, even if the failure occurs in 2346-brake B 3 , the worsening of the driving performance (driveability) can be prevented. In addition, when the gear shift from the first speed to the 2.5 speed is carried out, the gear shift hydraulic pressure data is used using the gear shift from the second speed to the fourth speed. Hence, it is not necessary to prepare new gear shift hydraulic pressure data during the occurrence in the release failure in 2346-brake B 3 . The augmentation of the data capacity can be suppressed.

The present invention is not limited to the preferred embodiments and various changes and modifications can be made without departing from the scope of the present invention. For example, in each of the first and second embodiments, an up-shift of the gear ratio (gear shift stage) from the first speed to the 2.5 speed in accordance with the shift command of the gear shift stage from the second speed to (→) the fourth speed has been explained. A down-shift from the 2.5 speed to the first speed in accordance with the gear shift command from the fourth speed to the second speed may be carried out.

It should be noted that the above-described embodiment is described in order to facilitate a better understanding of the present invention and do not limit the scope of the present invention. Hence, each essential element disclosed in the above-described embodiment includes all design modifications and equivalents belonging to the scope of the present invention. This application is based on a prior Japanese Patent Application No. 2006-342597. The entire contents of a Japanese Patent Application No. 2006-342597 with a filing date of Dec. 20, 2006 are hereby incorporated by reference. Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims.