Hydraulic control device and method for automatic transmission

1. A hydraulic control device for an automatic transmission, the automatic transmission having a vehicle start-up engagement element hydraulically engaged for vehicle start-up when a shift lever is moved from a non-drive range position to a drive range position, the hydraulic control device comprising:

a target pressure setting section configured to, when the shift lever is moved from the non-drive range position to the drive range position, calculate a target value of hydraulic pressure to be supplied to the vehicle start-up engagement element at a completion of an engagement of the vehicle start-up engagement element based on a transmission input torque of the automatic transmission and to correct the target value periodically based on the transmission input torque until the completion of the engagement of the vehicle start-up engagement element; and

a hydraulic pressure control section configured to control the hydraulic pressure in such a manner that the hydraulic pressure supplied to the vehicle start-up engagement element reaches the corrected target value at the completion of the engagement of the vehicle start-up engagement element.

2. The hydraulic control device according to claim 1 , further comprising:

a change rate setting section configured to set a change rate for changing the hydraulic pressure to the target value during a time period from an initiation of the engagement of the vehicle start-up engagement element to the completion of the engagement of the vehicle start-up engagement element; and

a command pressure setting section configured to specify an elapsed time period from the initiation of the engagement of the vehicle start-up engagement element until a current time and to set a command value of the hydraulic pressure supplied to the vehicle start-up engagement element based on the change rate and the elapsed time period,

wherein, when the target pressure setting section corrects the target value, the change rate setting section is configured to correct the change rate based on the corrected target value; the command pressure setting section is configured to set the command value based on the corrected change rate and the elapsed time period; and the hydraulic pressure control section is configured to control the hydraulic pressure according to the command value.

3. The hydraulic control device according to claim 2 , wherein the change rate setting section is configured to set a first change rate for changing the hydraulic pressure from a value of the hydraulic pressure supplied to the vehicle start-up engagement element at the initiation of the engagement of the vehicle start-up engagement element to the target value during the time period from the initiation to the completion of engagement of the vehicle start-up engagement element and configured to set a second change rate for changing the hydraulic pressure from a minimum value of the hydraulic pressure required to move the vehicle start-up engagement element in an engagement direction thereof to the target value during the time period from the initiation to the completion of the engagement of the vehicle start-up engagement element; and

wherein the command pressure setting section is configured to set a first command value of the hydraulic pressure supplied to the vehicle start-up engagement element based on the first change rate and the elapsed time period, to set a second command value of the hydraulic pressure supplied to the vehicle start-up engagement element based on the second change rate and the elapsed time period, and to select a higher value of the first command value and the second command value as a current command value.

4. The hydraulic control device according to claim 3 , wherein the command pressure setting section is configured to set the first command value by applying thereto a gain that depends on a degree of engagement of the vehicle start-up engagement element and to set the second command value by applying thereto a value of the gain at the completion of the engagement of the vehicle start-up engagement element.

5. The hydraulic control device according to claim 1 , wherein the automatic transmission has an input shaft connected to an engine via a torque converter; and

wherein the target pressure setting section is configured to determine the transmission input torque based on a periodically detected engine speed, a capacity coefficient, and a torque ratio of the torque converter that depends on a speed ratio of the torque converter given by the engine speed, and a turbine speed of the automatic transmission at the completion of the engagement of the vehicle start-up engagement element.

6. A hydraulic control method for an automatic transmission, the automatic transmission having a vehicle start-up engagement element hydraulically engaged for vehicle start-up when a shift lever is moved from a non-drive range position to a drive range position, the hydraulic control method comprising:

when the shift lever is moved from the non-drive range position to the drive range position, setting a target value of hydraulic pressure to be supplied to the vehicle start-up engagement element at a completion of an engagement of the vehicle start-up engagement element based on a transmission input torque of the automatic transmission and correcting the target value periodically based on the transmission input torque until the completion of the engagement of the vehicle start-up engagement element; and

controlling the hydraulic pressure in such a manner that the hydraulic pressure supplied to the vehicle start-up engagement element reaches the corrected target value at the completion of the engagement of the vehicle start-up engagement element.