Control apparatus for automatic transmission having fail-safe function during vehicle stop

1. A control apparatus for an automatic transmission of a vehicle, the automatic transmission including a plurality of frictional elements each arranged to be engaged by receiving supply of an engagement pressure regulated by a solenoid, the automatic transmission being arranged to attain a plurality of gear stages by combination of engagements of the frictional elements, the control apparatus comprising:

a failure occurrence sensing section configured to sense an occurrence of a failure-induced disengagement in one of the frictional elements based on a failure of one of the solenoids, based on an engine racing by a depression of an accelerator pedal in a state in which it is determined whether one of a forward range and a reverse range is selected during a stop of the vehicle; and

a command output section configured to output a limp home mode command to attain one of the gear stages to enable the vehicle to start at the time of the occurrence of the failure-induced disengagement.

2. The control apparatus as claimed in claim 1 , wherein the failure occurrence sensing section is configured to sense the occurrence of the failure-induced disengagement of the one of the frictional elements based on the failure of the one of the solenoids, based on the engine racing by the depression of the accelerator pedal in a state in which the reverse range is selected during the stop of the vehicle; and the control apparatus further comprises a switching valve arranged to switch from the engagement pressure regulated by the solenoid to a predetermined pressure which is not regulated by the solenoid, and to supply the predetermined pressure to the one of the frictional elements of the failure-induced disengagement based on the failure of the one of the solenoids; and the command output section is configured to output the limp home mode command to switch the switching valve to supply the predetermined pressure which is not regulated by the one of the solenoids to the one of the frictional elements of the failure-induced disengagement at the time of the occurrence of the failure-induced disengagement, so as to attain the reverse range.

3. The control apparatus as claimed in claim 1 , wherein the control apparatus further comprises a running sensing section configured to sense whether or not the vehicle can run after the command output section outputs the limp home mode command, and a limp home mode releasing section configured to release the limp home mode when the vehicle can not run.

4. The control apparatus as claimed in claim 1 , wherein the failure occurrence sensing section is configured to set a failure flag during the stop when the failure occurrence sensing section senses the failure-induced disengagement of the one of the frictional elements; the command output section is configured to output the limp home mode command based on the failure flag during the stop; and the failure occurrence sensing section is configured to clear the failure flag during the stop at a next stop of the vehicle.

5. A control apparatus for an automatic transmission of a vehicle, the automatic transmission including solenoids each arranged to generate a shift control pressure, pressure regulating valves each arranged to regulate an engagement pressure by using the shift control pressure from one of the solenoids as an operation signal pressure, and a plurality of frictional elements each arranged to be engaged by receiving supply of the engagement pressure from the one of the pressure regulating valves, the automatic transmission being arranged to attain a plurality of gear stages by combination of engagements of the frictional elements, the control apparatus comprising:

a failure occurrence sensing section configured to sense an occurrence of a failure-induced disengagement in one of the frictional elements based on a failure of one of the solenoids, based on an engine racing by a depression of an accelerator pedal in a state in which it is determined whether one of a forward range and a reverse range is selected during a stop of the vehicle; and

a command output section configured to output a limp home mode command to attain one of the gear stages to enable the vehicle to start at the time of the occurrence of the failure-induced disengagement.

6. The control apparatus as claimed in claim 5 , wherein the failure occurrence sensing section is configured to sense the occurrence of the failure-induced disengagement in the one of the frictional elements based on the failure of the one of the solenoids, based on the engine racing by the depression of the accelerator pedal in a state in which the forward range is selected during the stop of the vehicle; and the command output section is configured to output the limp home mode command to attain the one of the gear stages by engagements of the frictional elements other than the one of the frictional elements of the failure-induced disengagement at the time of the occurrence of the failure-induced disengagement.

7. The control apparatus as claimed in claim 5 , wherein the failure occurrence sensing section is configured to sense the occurrence of the failure-induced disengagement in the one of the frictional elements based on the failure of the one of the solenoids, based on the engine racing by the depression of the accelerator pedal in a state in which the reverse range is selected during the stop of the vehicle; the control apparatus further includes a switching valve arranged to switch from the engagement pressure of the one of the pressure regulating valves to a predetermined pressure which is not regulated by the one of the pressure regulating valves, and to supply the predetermined pressure to the one of the frictional element of the failure-induced disengagement based on the failure of the one of the solenoids; and the command output section is configured to output the limp home mode command to switch the switching valve to supply the predetermined pressure which is not regulated by the one of the solenoids to the frictional element of the failure-induced disengagement at the time of the occurrence of the failure-induced disengagement, so as to attain the reverse range.

8. The control apparatus as claimed in claim 7 , wherein the command output section is configured to output the limp home mode command after an engine speed becomes smaller than a predetermined threshold value in the state in which the reverse range is selected.

9. The control apparatus as claimed in claim 5 , wherein the control apparatus further comprises a running sensing section configured to sense whether or not the vehicle can run after the command output section outputs the limp home mode command, and a limp home mode releasing section configured to release the limp home mode when the vehicle can not run.

10. The control apparatus as claimed in claim 5 , wherein the failure occurrence sensing section is configured to set a failure flag during the stop when the failure occurrence sensing section senses the failure-induced disengagement of the one of the frictional elements; the command output section is configured to output the limp home mode command based on the failure flag during the stop; and the failure occurrence sensing section is configured to clear the failure flag during the stop at a next stop of the vehicle.

11. A control method for an automatic transmission of a vehicle, the automatic transmission including solenoids each arranged to generate a shift control pressure, pressure regulating valves each arranged to regulate an engagement pressure by using the shift control pressure from one of the solenoids as an operation signal pressure, and a plurality of frictional elements each arranged to be engaged by receiving supply of the engagement pressure from the one of the pressure regulating valves, the automatic transmission being arranged to attain a plurality of gear stages by combination of engagements of the frictional elements, the control method comprising:

sensing an occurrence of a failure-induced disengagement in one of the frictional elements based on a failure of one of the solenoids, based on an engine racing by a depression of an accelerator pedal in a state in which it is determined whether one of a forward range and a reverse range is selected during a stop of the vehicle; and

outputting a limp home mode command to attain one of the gear stages to enable to the vehicle to start at the time of the occurrence of the failure-induced disengagement.