Automatic transmission and control method thereof

This invention relates to failed element specification control employed when a failure occurs in a friction element of a stepped automatic transmission.

A stepped automatic transmission comprises a planetary gear mechanism and a plurality of friction elements, and switches a gear position by switching an engagement state of each friction element such that a desired gear position is obtained.

It is known that when a release failure or an engagement failure occurs in a friction element in this type of automatic transmission, control is performed to specify the failed friction element in order to secure drivability.

For example, in a technique disclosed in JP11-280886A, characteristic data generated when a failure occurs in a friction element are stored in advance for each gear position, and on the basis of these stored data and an actual speed ratio, the failed friction element and the manner of the failure, i.e. whether the failure is a release failure or an engagement failure, are specified.

In the conventional technique described above, a normal/abnormal determination is executed only once on each friction element immediate after an ignition has been switched on, and when a normal determination is made, the normal/abnormal determination is not executed until the ignition is turned on again, or in other words until the current driving cycle is complete. Hence, when a failure occurs in a friction element during travel, an abnormal determination is not made until the ignition is turned on again, and therefore a large period of time is required to specify the friction element, leading to deterioration of the drivability. When a failure occurs in a vehicle, the driver often leaves the ignition on out of concern that it may be impossible to restart the engine, and in this case, the problem described above is aggravated.

It is an object of this invention to specify a failed element by detecting the occurrence of a failure early, thereby suppressing deterioration of the drivability to a minimum.

In order to achieve this object, this invention provides an automatic transmission which has a planetary gear and a plurality of friction elements, and in which a directed gear position is achieved by switching an engagement/release state of the plurality of friction elements, and the directed gear position is one of a plurality of gear positions. The automatic transmission comprises: failure detecting means for detecting repeatedly whether or not a release failure or an engagement failure has occurred in the friction elements while a vehicle is traveling, a release failure occurring when the friction element cannot be engaged even when an engagement command is output thereto and an engagement failure occurring when the friction element cannot be released even when a release command is output thereto; failed element specification control means for beginning control to specify the failed friction element when a vehicle speed falls to or below a predetermined value for the first time after a failure has been detected by the failure detecting means; and limp home control means for determining usable gear positions on the basis of the specified friction element when the failed friction element has been specified by the failed element specification control means, and performing shift control using only the usable gear positions.

According to this invention, a determination as to whether or not a failure has occurred in a friction element is made repeatedly while the vehicle is traveling, and control to specify the failed friction element is begun when the vehicle speed falls to or below the predetermined value for the first time following detection of the failure in the friction element. Hence, the time required to detect the failure in the friction element after the failure occurs and specify the failed friction element can be shortened. Accordingly, limp home control can be started more quickly, and therefore deterioration of the drivability can be suppressed to a minimum.

Embodiments and advantages of this invention will be described in detail below with reference to the attached drawings.

FIG. 1 is a skeleton diagram showing the constitution of an automatic transmission according to an embodiment.

FIG. 2 is a circuit diagram illustrating a hydraulic circuit of a CVU.

FIG. 3 is an engagement table showing an engagement state of each friction element at each gear position.

FIG. 4 is an alignment chart showing a rotational state of each rotary element at each gear position.

FIGS. 5A-5C are flowcharts showing control of the automatic transmission according to this embodiment.

FIG. 6 is an alignment chart showing the rotational state of each rotary element at a first speed and a 1.5 speed.

FIG. 7 is an alignment chart showing the rotational state of each rotary element at a second speed.

FIG. 8 is an alignment chart showing the rotational state of each rotary element at a third speed.

An embodiment of this invention will be described in detail below with reference to the drawings.

FIG. 1 is a skeleton diagram showing the constitution of an automatic transmission according to this embodiment. The automatic transmission of this embodiment is a stepped automatic transmission having seven forward speeds and one reverse speed, in which a drive force of an engine EG is input from an input shaft IS via a torque converter TC, varied in rotation speed by four planetary gears and seven friction elements, and output from an output shaft OS. An oil pump OP is provided coaxially with a pump impeller of the torque converter TC and driven to rotate by the drive force of the engine EG such that oil is pressurized.

An engine controller (ECU) 10 that controls a driving state of the engine EG, an automatic transmission controller (ATCU) 20 that controls a gear position and so on of the automatic transmission and a control valve unit (CVU) 30 that controls an oil pressure of each friction element on the basis of an output signal from the ATCU 20 are also provided. The ECU 10 and ATCU 20 are connected via a CAN communication line or the like, and share sensor information and control information with each other through communication.

An APO sensor 1 that detects an accelerator pedal operation amount generated by a driver, an engine rotation speed sensor 2 that detects an engine rotation speed and a throttle sensor 7 that detects a throttle opening are connected to the ECU 10 . The ECU 10 controls a fuel injection amount and the throttle opening on the basis of the engine rotation speed and accelerator pedal operation amount, and thereby controls the engine rotation speed and the torque.

A first turbine rotation speed sensor 3 that detects a rotation speed of a first carrier PC 1 , a second turbine rotation speed sensor 4 that detects a rotation speed of a first ring gear R 1 and an inhibitor switch 6 that detects a shift lever operation state generated by the driver are connected to the ATCU 20 . In a D range, the ATCU 20 selects an optimum directed gear position based on a vehicle speed Vsp and an accelerator pedal operation amount APO, and outputs a control command for achieving the directed gear position to the control valve unit CVU.

Next, a gear mechanism that transmits the rotation of the input shaft IS to the output shaft OS while changing the speed thereof will be described. A first planetary gear set GS 1 and a second planetary gear set GS 2 are disposed in the gear mechanism in order from the input shaft IS side to the output shaft OS side in an axial direction. The gear mechanism is also provided with a plurality of clutches C 1 , C 2 , C 3 and brakes B 1 , B 2 , B 3 , B 4 serving as friction elements, and a plurality of one-way clutches F 1 , F 2 .

A first planetary gear G 1 is a single pinion planetary gear having a first sun gear S 1 , the first ring gear R 1 , and the first carrier PC 1 , which supports a first pinion P 1 that meshes with the two gears S 1 , R 1 . A second planetary gear G 2 is a single pinion planetary gear having a second sun gear S 2 , a second ring gear R 2 , and a second carrier PC 2 supporting a second pinion P 2 that meshes with the two gears S 2 , R 2 . A third planetary gear G 3 is a single pinion planetary gear having a third sun gear S 3 , a third ring gear R 3 , and a third carrier PC 3 supporting a third pinion P 3 that meshes with the two gears S 3 , R 3 . A fourth planetary gear G 4 is a single pinion planetary gear having a fourth sun gear S 4 , a fourth ring gear R 4 , and a fourth carrier PC 4 supporting a fourth pinion P 4 that meshes with the two gears S 4 , R 4 .

The input shaft IS is connected to the second ring gear R 2 and inputs a rotational drive force of the engine EG via the torque converter TC and so on. The output shaft OS is connected to the third carrier PC 3 and transmits an output rotational drive force to a drive wheel via a final gear and so on.

A first linking member M 1 links the first ring gear R 1 , second carrier PC 2 and fourth ring gear R 4 integrally. A second linking member M 2 links the third ring gear R 3 and fourth carrier PC 4 integrally. A third linking member M 3 links the first sun gear S 1 and second sun gear S 2 integrally.

The first planetary gear set GS 1 links the first planetary gear G 1 and second planetary gear G 2 using the first linking member M 1 and third linking member M 3 , and is constituted by four rotary elements. The second planetary gear set GS 2 links the third planetary gear G 3 and fourth planetary gear G 4 using the second linking member M 2 , and is constituted by five rotary elements.

In the first planetary gear set GS 1 , torque is input into the second ring gear R 2 from the input shaft IS, and the input torque is output to the second planetary gear set GS 2 via the first linking member M 1 . In the second planetary gear set GS 2 , torque is input directly into the second linking member M 2 from the input shaft IS and also input into the fourth ring gear R 4 via the first linking member M 1 , and the input torque is output to the output shaft OS from the third carrier PC 3 .

An input clutch C 1 selectively connects and disconnects the input shaft IS and the second linking member M 2 . A direct clutch C 2 selectively connects and disconnects the fourth sun gear S 4 and the fourth carrier PC 4 .

An H&LR clutch C 3 selectively connects and disconnects the third sun gear S 3 and the fourth sun gear S 4 . Further, a second one-way clutch F 2 is disposed between the third sun gear S 3 and fourth sun gear S 4 . Therefore, when the H&LR clutch C 3 is released and the rotation speed of the fourth sun gear S 4 is higher than that of the third sun gear S 3 , the third sun gear S 3 and fourth sun gear S 4 generate independent rotation speeds. As a result, the third planetary gear G 3 and fourth planetary gear G 4 are connected via the second linking member M 2 , and the respective planetary gears achieve independent speed ratios.

A front brake B 1 selectively stops the first carrier PC 1 from rotating. Further, the first one-way clutch F 1 is disposed in parallel with the front brake B 1 . A low brake B 2 selectively stops the third sun gear S 3 from rotating. A 2346 brake B 3 selectively stops the third linking member M 3 linking the first sun gear S 1 and second sun gear S 2 from rotating. A reverse brake B 4 selectively stops the fourth carrier PC 4 from rotating.

Next, referring to FIG. 2 , a hydraulic circuit of the CVU 30 will be described. FIG. 2 is a circuit diagram illustrating a hydraulic circuit of the CVU.

The hydraulic circuit is provided with the oil pump OP, which serves as an oil pressure source driven by the engine, a manual valve MV that operates in conjunction with a shift lever operation by the driver to switch an oil passage for supplying a line pressure PL, and a pilot valve PV that reduces the line pressure to a predetermined fixed pressure.

The hydraulic circuit is also provided with a first pressure regulating valve CV 1 that regulates an engagement pressure of the low brake B 2 , a second pressure regulating valve CV 2 that regulates an engagement pressure of the input clutch C 1 , a third pressure regulating valve CV 3 that regulates an engagement pressure of the front brake B 1 , a fourth pressure regulating valve CV 4 that regulates an engagement pressure of the H&LR clutch C 3 , a fifth pressure regulating valve CV 5 that regulates an engagement pressure of the 2346 brake B 3 , and a sixth pressure regulating valve CV 6 that regulates an engagement pressure of the direct clutch C 2 .

The hydraulic circuit is also provided with a first switching valve SV 1 that switches only one of a supply oil passage leading to the low brake B 2 and a supply oil passage leading to the input clutch C 1 to a communicating state, a second switching valve SV 2 that switches only one of a supply oil passage for supplying a D range pressure to the direct clutch C 2 and a supply oil passage for supplying an R range pressure to the direct clutch C 2 to a communicating state, a third switching valve SV 3 that switches an oil pressure supplied to the reverse brake B 4 between a supply oil pressure from the sixth pressure regulating valve CV 6 and a supply oil pressure from the R range pressure, and a fourth switching valve SV 4 for switching an oil pressure output by the sixth pressure regulating valve CV 6 between an oil passage 123 and an oil passage 122 .

The hydraulic circuit is also provided with a first solenoid valve SOL 1 that outputs a pressure regulating signal to the first pressure regulating valve CV 1 , a second solenoid valve SOL 2 that outputs a pressure regulating signal to the second pressure regulating valve CV 2 , a third solenoid valve SOL 3 that outputs a pressure regulating signal to the third pressure regulating valve CV 3 , a fourth solenoid valve SOL 4 that outputs a pressure regulating signal to the fourth pressure regulating valve CV 4 , a fifth solenoid valve SOL 5 that outputs a pressure regulating signal to the fifth pressure regulating valve CV 5 , a sixth solenoid valve SOL 6 that outputs a pressure regulating signal to the sixth pressure regulating valve CV 6 , and a seventh solenoid valve SOL 7 that outputs a switching signal to the first switching valve SV 1 and the third switching valve SV 3 , these signals being output on the basis of a control signal from the ATCU 20 .

A discharge pressure of the oil pump OP driven by the engine is regulated to the line pressure and then supplied to an oil passage 101 and an oil passage 102 . An oil passage 101 a connected to the manual valve MV, which operates in conjunction with a shift lever operation by the driver, an oil passage 101 b that supplies a source pressure of the engagement pressure of the front brake B 1 , and an oil passage 101 c that supplies a source pressure of the engagement pressure of the H&LR clutch C 3 are connected to the oil passage 101 .

An oil passage 105 and an oil passage 106 that supplies the R range pressure selected during reverse traveling are connected to the manual valve MV. The manual valve MV switches between the oil passage 105 and the oil passage 106 in accordance with the shift lever operation.

An oil passage 105 a that supplies a source pressure of the engagement pressure of the low brake B 2 , an oil passage 105 b that supplies a source pressure of the engagement pressure of the input clutch C 1 , an oil passage 105 c that supplies a source pressure of the engagement pressure of the 2346 brake B 3 , an oil passage 105 d that supplies a source pressure of the engagement pressure of the direct clutch C 2 , and an oil passage 105 e that supplies a switching pressure of the second switching valve SV 2 , to be described below, are connected to the oil passage 105 .

An oil passage 106 a that supplies the switching pressure of the second switching valve SV 2 , an oil passage 106 b that supplies the source pressure of the engagement pressure of the direct clutch C 2 , and an oil passage 106 c that supplies an engagement pressure of the reverse brake B 4 are connected to the oil passage 106 .

An oil passage 103 that supplies a pilot pressure via the pilot valve PV is connected to the oil passage 102 . An oil passage 103 a that supplies the pilot pressure to the first solenoid valve SOL 1 , an oil passage 103 b that supplies the pilot pressure to the second solenoid valve SOL 2 , an oil passage 103 c that supplies the pilot pressure to the third solenoid valve SOL 3 , an oil passage 103 d that supplies the pilot pressure to the fourth solenoid valve SOL 4 , an oil passage 103 e that supplies the pilot pressure to the fifth solenoid valve SOL 5 , an oil passage 103 f that supplies the pilot pressure to the sixth solenoid valve SOL 5 , and an oil passage 103 g that supplies the pilot pressure to the seventh solenoid valve SOL 7 are provided on the oil passage 103 .

Next, an operation of the gear mechanism will be described with reference to FIGS. 3 and 4 . FIG. 3 is an engagement table showing the engagement state of each friction element at each gear position, a circle indicating that the corresponding friction element is engaged, and a circle in parentheses indicating that the corresponding friction element is engaged when a range position in which an engine brake operates has been selected. FIG. 4 is an alignment chart showing the rotational state of each rotary member at each gear position.

In a first speed, only the low brake B 2 is engaged, and the first one-way clutch F 1 and second one-way clutch F 2 are engaged. During an engine brake operation, the front brake B 1 and the H&LR clutch C 3 are also engaged.

When the first one-way clutch F 1 is engaged, the first carrier PC 1 stops rotating, and therefore the rotation that is input into the second ring gear R 2 from the input shaft IS is reduced in speed by the first planetary gear set GS 1 and then output to the fourth ring gear R 4 from the first linking member M 1 . Further, when the low brake B 2 is engaged and the second one-way clutch F 2 is engaged, the third sun gear S 3 and fourth sun gear S 4 stop rotating, and therefore the rotation that is input into the fourth ring gear R 4 is reduced in speed by the second planetary gear set GS 2 and then output from the third carrier PC 3 .

In other words, as shown by the alignment chart in FIG. 4 , the rotation of the input shaft IS is reduced in speed by the first planetary gear set GS 1 , further reduced in speed by the second planetary gear set GS 2 , and then output from the output shaft OS.

In a second speed, the low brake B 2 and the 2346 brake B 3 are engaged, and the second one-way clutch F 2 is engaged. During an engine brake operation, the H&LR clutch C 3 is also engaged.

When the 2346 brake B 3 is engaged, the first sun gear S 1 and second sun gear S 2 stop rotating, and therefore the rotation that is input into the second ring gear R 2 from the input shaft IS is reduced in speed by the second planetary gear G 2 alone and then output to the fourth ring gear R 4 from the first linking member M 1 . Further, when the low brake B 2 is engaged and the second one-way clutch F 2 is engaged, the third sun gear S 3 and fourth sun gear S 4 stop rotating, and therefore the rotation that is input into the fourth ring gear R 4 is reduced in speed by the second planetary gear set GS 2 and then output from the third carrier PC 3 .

In other words, as shown by the alignment chart in FIG. 4 , the rotation of the input shaft IS is reduced in speed by the first planetary gear set GS 1 , further reduced in speed by the second planetary gear set GS 2 , and then output from the output shaft OS.

In a third speed, the low brake B 2 , 2346 brake B 3 and direct clutch C 2 are engaged.

When the 2346 brake B 3 is engaged, the first sun gear S 1 and second sun gear S 2 stop rotating, and therefore the rotation that is input into the second ring gear R 2 from the input shaft IS is reduced in speed by the second planetary gear G 2 and then output to the fourth ring gear R 4 from the first linking member M 1 . Further, when the direct clutch C 2 is engaged, the fourth planetary gear G 4 rotates integrally. The fourth planetary gear G 4 therefore contributes to torque transmission but does not contribute to the speed reduction action. Further, when the low brake B 2 is engaged, the third sun gear S 3 stops rotating, and therefore the rotation that is input into the third ring gear R 3 from the fourth carrier PC 4 , which rotates integrally with the fourth ring gear R 4 , via the second linking member M 2 is reduced in speed by the third planetary gear G 3 and then output from the third carrier PC 3 .

In other words, as shown by the alignment chart in FIG. 4 , the rotation of the input shaft IS is reduced in speed by the first planetary gear set GS 1 , further reduced in speed by the third planetary gear G 3 of the second planetary gear set GS 2 , and then output from the output shaft OS.

In a fourth speed, the 2346 brake B 3 , direct clutch C 2 and H&LR clutch C 3 are engaged.

When the 2346 brake B 3 is engaged, the first sun gear S 1 and second sun gear S 2 stop rotating, and therefore the rotation that is input into the second ring gear R 2 from the input shaft IS is reduced in speed by the second planetary gear G 2 alone and then output to the fourth ring gear R 4 from the first linking member M 1 . Further, when the direct clutch C 2 and the H&LR clutch C 3 are engaged, the second planetary gear set GS 2 rotates integrally, and therefore the rotation that is input into the fourth ring gear R 4 is output from the third carrier PC 3 as is.

In other words, as shown by the alignment chart in FIG. 4 , the rotation of the input shaft IS is reduced in speed by the first planetary gear set GS 1 and then output from the output shaft OS without being reduced in speed by the second planetary gear set GS 2 .

In a fifth speed, the input clutch C 1 , direct clutch C 2 and H&LR clutch C 3 are engaged.

When the input clutch C 1 is engaged, the rotation of the input shaft IS is input directly into the second linking member M 2 . Further, when the direct clutch C 2 and the H&LR clutch C 3 are engaged, the second planetary gear set GS 2 rotates integrally, and therefore the rotation of the input shaft IS is output from the third carrier PC 3 as is.

In other words, as shown by the alignment chart in FIG. 4 , the rotation of the input shaft IS is output from the output shaft OS as is, without being reduced in speed by either the first planetary gear set GS 1 or the second planetary gear set GS 2 .

In a sixth speed, the input clutch C 1 , H&LR clutch C 3 and 2346 brake B 3 are engaged.

When the input clutch C 1 is engaged, the rotation of the input shaft IS is input into the second ring gear and also input directly into the second linking member M 2 . Further, when the 2346 brake B 3 is engaged, the first sun gear S 1 and second sun gear S 2 stop rotating, and therefore the rotation of the input shaft IS is reduced in speed by the second planetary gear G 2 and then output to the fourth ring gear R 4 from the first linking member M 1 .

Further, when the H&LR clutch C 3 is engaged, the third sun gear S 3 and fourth sun gear S 4 rotate integrally, and therefore the second planetary gear set GS 2 outputs rotation that has been decided by the rotation of the fourth ring gear R 4 and the rotation of the second linking member M 2 from the third carrier PC 3 .

In other words, as shown by the alignment chart in FIG. 4 , a part of the rotation of the input shaft IS is reduced in speed by the first planetary gear set GS 1 , increased in speed by the second planetary gear set GS 2 , and then output from the output shaft OS.

In a seventh speed, the input clutch C 1 , H&LR clutch C 3 and front brake B 1 are engaged, and the first one-way clutch F 1 is engaged.

When the input clutch C 1 is engaged, the rotation of the input shaft IS is input into the second ring gear R 2 and also input directly into the second linking member M 2 . Further, when the front brake B 1 is engaged, the first carrier PC 1 stops rotating, and therefore the rotation of the input shaft IS is reduced in speed by the first planetary gear set GS 1 and then output to the fourth ring gear R 4 from the first linking member M 1 .

Further, when the H&LR clutch C 3 is engaged, the third sun gear S 3 and fourth sun gear S 4 rotate integrally, and therefore the second planetary gear set GS 2 outputs rotation that has been decided by the rotation of the fourth ring gear R 4 and the rotation of the second linking member M 2 from the third carrier PC 3 .

In other words, as shown by the alignment chart in FIG. 4 , a part of the rotation of the input shaft IS is reduced in speed by the first planetary gear set GS 1 , increased in speed by the second planetary gear set GS 2 , and then output from the output shaft OS.

In a reverse speed, the H&LR clutch C 3 , front brake B 1 and reverse brake B 4 are engaged.

When the front brake B 1 is engaged, the first carrier PC 1 stops rotating, and therefore the rotation of the input shaft IS is reduced in speed by the first planetary gear set GS 1 and then output to the fourth ring gear R 4 from the first inking member M 1 .

Further, when the H&LR clutch C 3 is engaged, the third sun gear S 3 and fourth sun gear S 4 rotate integrally, and when the reverse brake B 4 is engaged, the second linking member M 2 stops rotating. Therefore, in the second planetary gear set GS 2 , the rotation of the fourth ring gear R 4 is transmitted in reverse to the fourth sun gear S 4 , third sun gear S 3 and third carrier PC 3 , and then output from the third carrier PC 3 .

In other words, as shown by the alignment chart in FIG. 4 , the rotation of the input shaft IS is reduced in speed by the first planetary gear set GS 1 , reversed in the second planetary gear set GS 2 , and then output from the output shaft OS.

The automatic transmission is constituted as described above, and switching is performed between the first and seventh speeds to a desired gear position in accordance with a shift line set on the basis of the vehicle speed and throttle opening. When a failure occurs in one of the friction elements at this time, it becomes impossible to achieve the desired gear position, and as a result, the drivability deteriorates. Control performed in the ATCU 20 when a failure occurs in a friction element will now be described with reference to the flowchart in FIGS. 5A-5C .

FIGS. 5A-5C are flowcharts showing control of the automatic transmission according to this embodiment. This control is performed when a failure occurs in one of the friction elements of the automatic transmission to specify the failed friction element, determine whether the failure is a release failure or an engagement failure, and perform limp home control in accordance with the element of the failure and the manner of the failure. It should be noted that a release failure is a failure occurring when a friction element to which an engagement command has been output does not engage completely and remains released, while an engagement failure is a failure occurring when a friction element to which a release command has been output is not released and remains engaged.

In a step SS 1 , a determination is made as to whether or not any of an interlock failure, a speed ratio abnormality, a neutral abnormality, and over speed has been detected. When one of these abnormalities is detected, the routine advances to a step SS 2 , and when none of the abnormalities is detected, the step SS 1 is executed again.

An interlock failure denotes a state relating to a friction element engagement command, in which a friction element to which an engagement command has not been issued engages such that the rotation of the input shaft IS or output shaft OS of the transmission is locked. An interlock failure is detected when a deceleration rate of the vehicle reaches or exceeds a predetermined value despite the brake being inoperative, for example.

A neutral abnormality denotes a state relating to a friction element engagement command, in which a part of the friction elements to which engagement commands have been issued do not engage such that the power of the input shaft is not transmitted to the output shaft. A neutral abnormality is detected when an actual speed ratio becomes larger than the speed ratio of the directed gear position by a predetermined value or more, for example.

A speed ratio abnormality denotes a state relating to a friction element engagement command, in which the engagement capacity of a friction element is insufficient or a friction element to which an engagement command has not been issued has surplus engagement capacity. A speed ratio abnormality is detected when the actual speed ratio deviates from the speed ratio of the directed gear position by a predetermined value or more and a neutral abnormality is not detected, for example.

Over speed denotes a state in which the rotation speed of a rotary member other than the input shaft IS and output shaft OS increases to a rotation speed that cannot be obtained when the directed gear position is achieved normally. Over speed is detected when the rotation speed of a predetermined rotary member is detected directly or indirectly to have reached or exceeded a predetermined value, for example.

In the step SS 2 , provisional limp home is performed in accordance with the failure or abnormality detected in the step SS 1 . Provisional limp home is performed by fixing the gear position at a gear position other than the gear position at which the failure or abnormality was detected, for example.

In a step SS 3 , a determination is made as to whether or not the vehicle is stationary. When the vehicle is stationary, the routine advances to a step SS 4 , and when the vehicle is not stationary, the step SS 3 is executed again. It should be noted that the vehicle is determined to be stationary by determining whether or not the vehicle speed has reached or fallen below a predetermined vehicle speed (5 km/h, for example).

In the step SS 4 , determinations are made as to whether or not the failure detected in the step SS 1 is a neutral abnormality and whether or not the directed gear position at the time of detection is between the first and third speeds. When these conditions are satisfied, the routine advances to a step SS 5 , where shift control is performed using the fourth, fifth and sixth speeds as main limp home. When the failure is not a neutral abnormality or the directed gear position is not between the first and third speeds, the routine advances to a step SS 6 .

When the detected failure is a neutral abnormality and the directed gear position at the time of detection is between the first and third speeds, it can be assumed that a release failure has occurred in the low brake B 2 , which is always in an engaged state in the first through third speeds, and therefore shift control is performed using the fourth, fifth and sixth speeds and avoiding the first through third speeds that use the low brake B 2 .

In the control to be described below, probe control is performed to specify the element of the failure by setting the directed gear position from the first speed to the third speed and determining whether or not the actual gear position indicates a normal value relative to the directed gear position.

In the step SS 6 , the directed gear position is set at the first speed. Here, the directed gear position is set at the first speed regardless of the vehicle speed and throttle opening. In steps SS 17 and SS 28 to be described below, the directed gear position is similarly fixed at the second and third speeds, respectively. In other words, upshifts or downshifts based on the vehicle speed and throttle opening are prohibited during execution of the steps from this step onward.

In a step SS 7 , a determination is made as to whether or not the respective signals of an output shaft rotation speed sensor 5 , the first turbine rotation speed sensor 3 , the second turbine rotation speed sensor 4 , the throttle sensor 7 , the engine rotation speed sensor 2 and the inhibitor switch 6 are normal. When the signals are normal, the routine advances to a step SS 9 , and when a signal is abnormal, the routine advances to a step SS 8 , where the directed gear position is fixed at the first speed, after which travel is continued at the first speed.

When the directed gear position is set at the first speed, an engagement command is issued to the low brake B 2 . In this state, even when an engagement failure occurs in another friction element, the actual speed ratio simply shifts to a speed ratio other than the speed ratio corresponding to the first speed, and a further failure such as interlocking does not occur. Hence, by fixing the directed gear position at the first speed when a signal abnormality occurs such that the failed element cannot be specified accurately, a situation in which limp home is performed erroneously, leading to deterioration of the drivability and excessive wear on the friction elements, does not arise.

In the step SS 9 , respective determinations are made as to whether or not the vehicle speed Vsp is higher than a predetermined speed, whether or not a rotation speed TbnREV of a turbine runner is higher than a predetermined rotation speed, whether or not an opening Tvo of a throttle valve is greater than a predetermined opening, and whether or not a value Ne−Nt obtained by subtracting the rotation speed of the turbine runner from the engine rotation speed is greater than a predetermined value. When all of these conditions are satisfied, the routine advances to a step SS 10 , and when any one of the conditions is not satisfied, the routine returns to the step SS 7 .

When the output shaft OS of the transmission does not rotate, the speed ratio cannot be detected accurately, and therefore the predetermined speed is set at a value that makes it possible to determine that the vehicle speed is sufficient to enable accurate detection of the speed ratio. Similarly, when the input shaft IS of the transmission does not rotate, the speed ratio cannot be detected accurately, and therefore the predetermined rotation speed is set at a value that makes it possible to determine that the turbine runner is rotating at a rotation speed enabling accurate detection of the speed ratio. Further, the predetermined opening and the predetermined value are set such that it is possible to determine that the drive force of the engine EG is being transmitted from the input shaft IS of the transmission to the output shaft OS, or in other words such that it is possible to determine that the vehicle is in a driving state rather than a coasting state.

In the step SS 10 , a determination is made as to whether or not a range signal indicates a range other than P, R and N. When the range signal indicates a range other than P, R and N, i.e. a forward traveling range, the routine advances to a step SS 11 , and when the range signal indicates one of P, R and N, the routine returns to the step SS 7 .

Engagement failures due to valve sticking often occur in a friction element when contamination or the like becomes trapped between a spool and a valve body bore of a pressure regulating valve that regulates the oil pressure of the friction element. When this type of failure occurs and the range is shifted from the forward traveling range to the P, R and N ranges, the oil pressure is discharged through a manual port, leading to large variation in the oil pressure acting on the pressure regulating valve, and as a result, the spool may separate from the valve body, thereby eliminating the engagement failure. Hence, when the range shifts from the forward traveling range to the P, R and N ranges during execution of this control, data obtained up to this point are reset and the control is performed anew.

In the step SS 11 , the actual speed ratio is detected. The actual speed ratio is calculated by dividing the rotation speed of the input shaft IS by the rotation speed of the output shaft OS of the transmission.

In a step SS 12 , a determination is made as to whether or not a predetermined time period has elapsed after setting the directed gear position at the first speed. The predetermined time period is set at a sufficient amount of time to exclude a case in which the conditions of the step SS 9 are satisfied temporarily, for example two seconds.

In a step SS 13 , a determination is made as to whether or not the actual speed ratio corresponds to a 1.5 speed. When the actual speed ratio corresponds to the 1.5 speed, the routine advances to a step SS 14 , where shift control is performed using the third, fourth and fifth speeds as the main limp home, and when the actual speed ratio does not correspond to the 1.5 speed, the routine advances to a step SS 15 . Here, the actual speed ratio comes to correspond to the 1.5 speed when the low brake B 2 , first one-way clutch F 1 and direct clutch C 2 are engaged, as shown in the alignment chart in FIG. 6 . Since the current directed gear position is the first speed and an engagement command has only been output to the low brake B 2 , it may be determined that an engagement failure has occurred in the direct clutch C 2 . Therefore, shift control is performed using only the third, fourth and fifth speeds, i.e. the gear positions in which the direct clutch C 2 is engaged.

In the step SS 15 , a determination is made as to whether or not the actual speed ratio corresponds to the second speed. When the actual speed ratio corresponds to the second speed, the routine advances to a step SS 16 , where shift control is performed using the second, third and fourth speeds as the main limp home, and when the actual speed ratio does not correspond to the second speed, the routine advances to a step SS 17 . Here, the actual speed ratio comes to correspond to the second speed, even though the directed gear position is the first speed, when an engagement failure occurs in the 2346 brake, as can be seen by comparing the first and second speeds in the engagement table of FIG. 3 , and therefore shift control is performed using only the second, third and fourth speeds from among the gear positions in which the 2346 brake is engaged.

In the step SS 17 , the directed gear position is set at the second speed.

In a step SS 18 , a determination is made as to whether or not the respective signals of the output shaft rotation speed sensor 5 , first turbine rotation speed sensor 3 , second turbine rotation speed sensor 4 , throttle sensor 7 , engine rotation speed sensor 2 and inhibitor switch 6 are normal. When the signals are normal, the routine advances to a step SS 20 , and when a signal is abnormal, the routine advances to a step SS 19 , where the directed gear position is fixed at the first speed.

In the step SS 20 , respective determinations are made as to whether or not the vehicle speed Vsp is higher than the predetermined speed, whether or not the rotation speed TbnREV of the turbine runner is higher than the predetermined rotation speed, whether or not the opening Tvo of the throttle valve is greater than the predetermined opening, and whether or not the value Ne−Nt obtained by subtracting the rotation speed of the turbine runner from the engine rotation speed is greater than the predetermined value. When all of these conditions are satisfied, the routine advances to a step SS 21 , and when any one of the conditions is not satisfied, the routine returns to the step SS 18 .

In the step SS 21 , a determination is made as to whether or not the range signal indicates a range other than P, R and N. When the range signal indicates a range other than P, R and N, i.e. the forward traveling range, the routine advances to a step SS 22 , and when the range signal indicates one of P, R and N, the routine returns to the step SS 6 .

As described above in the step SS 10 , an engagement failure in a friction element may be eliminated when the range shifts from the forward traveling range to the P, R and N ranges, and in this case, if the control routine is continued while holding a result obtained in the failed element specification control of the steps SS 6 to SS 16 , which is performed with the directed gear position set at the first speed, excessive control may be executed, leading to deterioration of the drivability. Hence, when the range shifts from the forward traveling range to the P, R and N ranges, the directed gear position is reset at the first speed and the failed element specification control is performed again from the beginning.

In the step SS 22 , the actual speed ratio is detected.

In a step SS 23 , a determination is made as to whether or not a predetermined time period has elapsed after setting the directed gear position at the second speed. If the predetermined time period has elapsed, the routine advances to a step SS 24 , and if not, the routine returns to the step SS 18 .

In the step SS 24 , a determination is made as to whether or not the actual speed ratio corresponds to the first speed. When the actual speed ratio corresponds to the first speed, the routine advances to a step SS 25 , where shift control is performed using the first, fifth and seventh speeds as the main limp home, and when the actual speed ratio does not correspond to the first speed, the routine advances to a step SS 26 . Here, the actual speed ratio comes to correspond to the first speed, even though the directed gear position is the second speed, when a release failure occurs in the 2346 brake, as can be seen by comparing the first and second speeds in the engagement table of FIG. 3 , and therefore shift control is performed using only the first, fifth and seventh speeds, i.e. the gear positions in which the 2346 brake is released.

In the step SS 26 , a determination is made as to whether or not the actual speed ratio is a speed ratio (ILK) corresponding to interlocking. When the actual speed ratio is the speed ratio corresponding to interlocking, the routine advances to a step SS 27 , where shift control is performed using the first, second, fifth and seventh speeds as the main limp home, and when the actual speed ratio is not the speed ratio corresponding to interlocking, the routine advances to a step SS 28 . In an interlock failure, the speed ratio decreases when the input shaft is locked and increases when the output shaft is locked, and therefore the actual speed ratio is determined to correspond to interlocking when it is larger than the speed ratio corresponding to the first speed or smaller than the speed ratio corresponding to the second speed.

As shown in the alignment chart of FIG. 7 , when the directed gear position is set at the second speed, engagement commands are output to the low brake B 2 and the 2346 brake B 3 , and when an engagement failure occurs in the front brake B 1 in this state, the first carrier PC 1 stops rotating, causing the input shaft IS to lock such that an interlock failure occurs. Hence, shift control is performed using only the first, second, fifth and seventh speeds, i.e. the gear positions in which the front brake B 1 is engaged.

In the step SS 28 , the directed gear position is set at the third speed.

In a step SS 29 , a determination is made as to whether or not the respective signals of the output shaft rotation speed sensor 5 , first turbine rotation speed sensor 3 , second turbine rotation speed sensor 4 , throttle sensor 7 , engine rotation speed sensor 2 and inhibitor switch 6 are normal. When the signals are normal, the routine advances to a step SS 31 , and when a signal is abnormal, the routine advances to a step SS 30 , where the directed gear position is fixed at the first speed.

In the step SS 31 , respective determinations are made as to whether or not the vehicle speed Vsp is higher than the predetermined speed, whether or not the rotation speed TbnREV of the turbine runner is higher than the predetermined rotation speed, whether or not the opening Tvo of the throttle valve is greater than the predetermined opening, and whether or not the value Ne−Nt obtained by subtracting the rotation speed of the turbine runner from the engine rotation speed is greater than the predetermined value. When all of these conditions are satisfied, the routine advances to a step SS 32 , and when any one of the conditions is not satisfied, the routine returns to the step SS 29 .

In the step SS 32 , a determination is made as to whether or not the range signal indicates a range other than P, R and N. When the range signal indicates a range other than P, R and N, i.e. the forward traveling range, the routine advances to a step SS 33 , and when the range signal indicates one of P, R and N, the routine returns to the step SS 6 .

In the step SS 33 , the actual speed ratio is detected.

In a step SS 34 , a determination is made as to whether or not a predetermined time period has elapsed after setting the directed gear position at the third speed. If the predetermined time period has elapsed, the routine advances to a step SS 35 , and if not, the routine returns to the step SS 29 .

In the step SS 35 , a determination is made as to whether or not the actual speed ratio corresponds to the second speed. When the actual speed ratio corresponds to the second speed, the routine advances to a step SS 36 , where shift control is performed using the first and second speeds as the main limp home, and when the actual speed ratio does not correspond to the second speed, the routine advances to a step SS 37 . Here, the actual speed ratio comes to correspond to the second speed, even though the directed gear position is the third speed, when a release failure occurs in the direct clutch C 2 , as can be seen by comparing the second and third speeds in the engagement table of FIG. 3 , and therefore shift control is performed using only the first and second speeds from among the gear positions in which the direct clutch C 2 is released.

In the step SS 37 , a determination is made as to whether or not the actual speed ratio is the speed ratio corresponding to interlocking. When the actual speed ratio is the speed ratio corresponding to interlocking, the routine advances to a step SS 38 , where shift control is performed using the fourth, fifth, sixth and seventh speeds as the main limp home, and when the actual speed ratio is not the speed ratio corresponding to interlocking, the routine advances to a step SS 39 .

As shown in the alignment chart of FIG. 8 , when the directed gear position is set at the third speed, engagement commands are output to the direct clutch C 2 , the low brake B 2 and the 2346 brake B 3 , and when an engagement failure occurs in the H&LR clutch C 3 in this state, the fourth carrier PC 4 stops rotating, causing the output shaft OS to lock such that an interlock failure occurs. Hence, shift control is performed using only the fourth, fifth, sixth and seventh speeds, i.e. the gear positions at which the H&LR clutch C 3 is engaged.

In the step SS 39 , shift control is performed using only the first, second and third speeds as the main limp home. Failures are deduced from the actual speed ratio, which is detected at each directed gear position from the first speed to the third speed, but when a failure is not detected in any of these cases, this step is executed, and as a result, the failure is assumed to be an engagement failure or a release failure in the input clutch C 1 or a release failure in the H&LR clutch C 3 . Accordingly, shift control is performed using the first, second and third speeds, none of which are affected by these failures.

In the embodiment described above, determinations as to whether or not a failure has occurred in a friction element are performed repeatedly while the vehicle is running, and when a failure is detected in a friction element, control to specify the failed friction element is begun after the vehicle speed falls to or below a predetermined vehicle speed for the first time following the detection. Hence, the time required to detect a failure in a friction element after the failure occurs and specify the failed friction element can be shortened. Accordingly, limp home control can be started more quickly, and therefore deterioration of the drivability can be suppressed to a minimum.

Furthermore, when a failure is detected in a friction element, control is performed to specify the failed friction element while shifting the directed gear position sequentially from the first speed to the third speed, and when the failed friction element cannot be specified after shifting the gear position from the first speed to the third speed, shift control is performed using the first through third gear positions as limp home control. In other words, the directed gear position is not set at all seven gear positions in order to specify the failed friction element, and limp home control is begun after confining that a sufficient degree of drivability can be secured. Therefore, limp home control can be started quickly, and deterioration of the drivability can be suppressed to a minimum.

Furthermore, the failed friction element is specified while shifting the directed gear position sequentially to one or more gear positions selected from a plurality of gear positions, and when the failed friction element is specified, limp home control is performed without moving to the following selected gear position. Therefore, pointless control to shift the directed gear position sequentially after the failed friction element has been specified can be eliminated, and as a result, deterioration of the drivability can be suppressed even further.

Also, the failed friction element is specified on the basis of the directed gear position and the actual gear position, which is deducted from the actual speed ratio, and therefore the failed friction element can be specified early, without having to determine that the speed ratio has deviated from the directed gear position in all of the gear positions.

Moreover, when specifying the failed element, the directed gear position is shifted sequentially at predetermined time intervals, and therefore the gear position can be shifted reliably irrespective of the traveling conditions, in contrast to a case in which a shift instruction is issued on the basis of the vehicle speed and throttle opening. As a result, the friction element can be specified even earlier. When a failure occurs, the driver rarely presses the accelerator pedal, and therefore, if the directed gear position is shifted in accordance with the vehicle speed and throttle opening, a large period of time is required for the directed gear position to switch. According to this embodiment, however, the friction element can be specified early.

Furthermore, the directed gear position is shifted sequentially at predetermined time intervals and downshifts are prohibited. Therefore, the directed gear position can be shifted to the selected gear position reliably, and the failed friction element can be specified early.

Moreover, friction element specification is terminated when any one of conditions as to whether or not the vehicle speed Vsp is higher than the predetermined speed, whether or not the rotation speed TbnREV of the turbine runner is higher than the predetermined rotation speed, whether or not the opening Tvo of the throttle valve is greater than the predetermined opening, and whether or not the value Ne−Nt obtained by subtracting the rotation speed of the turbine runner from the engine rotation speed is greater than the predetermined value is not satisfied, and when these conditions are satisfied, friction element specification is resumed from the directed gear position at which specification of the friction element was terminated. Hence, when the conditions cease to be satisfied temporarily and are then satisfied again, specification is not resumed from a directed gear position that has already been set, and as a result, the failed friction element can be specified even earlier.

When the range signal is detected to indicate P, R and N, specification of the failed friction element is terminated, and when the range signal no longer indicates P, R and N, the directed gear position is returned to the first speed and control to specify the failed friction element is performed again from the beginning. Hence, when a temporary failure occurs in a friction element and the failure is eliminated by shifting the range position from the forward traveling range to the P, R and N ranges, the results of previous friction element specification control can be reset such that excessive control is not performed, and as a result, deterioration of the drivability can be suppressed.

This invention is not limited to the embodiment described above, and may be subjected to various alterations and modifications with the scope of the technical spirit thereof.