Control device and control method for automatic transmission

1. A control device for an automatic transmission having a torque converter, in which a target gear position is set on a basis of a vehicle speed and an engine load, comprising:

a determining unit that determines whether to set a friction element that locks up the torque converter through oil pressure control in an engaged condition or a disengaged condition on a basis of at least a vehicle speed;

a control unit that outputs an engagement command or a disengagement command on a basis of a determination result of the determining unit; and

an oil pressure control unit that controls to engage the friction element upon reception of the engagement command by performing a precharge control that controls oil pressure to set the friction element before the engaged condition and then controlling supplied oil pressure to a predetermined oil pressure and to disengage the friction element upon reception of the disengagement command by draining the oil pressure supplied to the friction element,

wherein the control unit comprises a prohibiting unit that prohibits output of the disengagement command in relation to the friction element following control of the friction element from the disengaged condition to the engaged condition until the precharge control is completed.

2. The control device as defined in claim 1 , wherein the control unit determines that the precharge control is completed when a predetermined time elapses following control of the friction element from the disengaged condition to the engaged condition.

3. The control device as defined in claim 1 , wherein the control unit determines that the precharge control is completed when the oil pressure supplied for the friction element is sufficient to set the friction element in the engaged condition following control of the friction element from the disengaged condition to the engaged condition.

4. The control device as defined in claim 1 , further comprising:

a vehicle speed detecting unit that detects a vehicle speed of the vehicle; and

a storage unit that stores a determination reference used to determine whether to set the friction element in the engaged condition or the disengaged condition,

wherein the determining unit determines that the friction element is to be set in the engaged condition when the vehicle speed is equal to or higher than the determination reference and determines that the friction element is to be set in the disengaged condition when the vehicle speed is lower than the determination reference.

5. A control method for an automatic transmission having a torque converter, in which a target gear position is set on a basis of a vehicle speed and an engine load, comprising:

a determining step, for determining whether to set a friction element that locks up a torque converter through oil pressure control in an engaged condition or a disengaged condition on a basis of at least a vehicle speed, using an automatic transmission controller;

a control step, for outputting an engagement command or a disengagement command on a basis of a determination result of the determining step, using the automatic transmission controller; and

an oil pressure control step, for performing control to engage the friction element upon reception of the engagement command by performing a precharge control that controls oil pressure to set the friction element before the engaged condition and then controlling supplied oil pressure to a predetermined oil pressure and to disengage the friction element upon reception of the disengagement command by draining the oil pressure supplied to the friction element,

wherein the control step comprises a prohibiting step for prohibiting output of the disengagement command in relation to the friction element following control of the friction element from the disengaged condition to the engaged condition until the precharge is completed.

6. The control method as defined in claim 5 , wherein the control step determines that the precharge control is completed when a predetermined time elapses following control of the friction element from the disengaged condition to the engaged condition.

7. The control method as defined in claim 5 , wherein the control step determines that the precharge control is completed when the oil pressure supplied for the friction element is sufficient to set the friction element in the engaged condition following control of the friction element from the disengaged condition to the engaged condition.

8. The control method as defined in claim 5 , further comprising:

a vehicle speed detecting step for detecting a vehicle speed of the vehicle; and

a storage step for storing a determination reference used to determine whether to set the friction element in the engaged condition or the disengaged condition,

wherein the determining step determines that the friction element is to be set in the engaged condition when the vehicle speed is equal to or higher than the determination reference and determines that the friction element is to be set in the disengaged condition in when the vehicle speed is lower than the determination reference.

9. A control device for an automatic transmission having a torque converter, in which a target gear position is set on a basis of a vehicle speed and an engine load, comprising:

determining means for determining whether to set a friction element that locks up a torque converter through oil pressure control in an engaged condition or a disengaged condition on a basis of at least a vehicle speed;

a control means for outputting an engagement command or a disengagement command on a basis of a determination result of the determining means; and

an oil pressure control means for performing control to engage the friction element upon reception of the engagement command by performing a precharge control that controls oil pressure to set the friction element before the engaged condition and then controlling supplied oil pressure to a predetermined oil pressure and to disengage the friction element upon reception of the disengagement command by draining the oil pressure supplied to the friction element,

wherein the control means comprises prohibiting means for prohibiting output of the disengagement command in relation to the friction element following control of the friction element from the disengaged condition to the engaged condition until the precharge control is completed.

10. The control device for an automatic transmission as defined in claim 9 , wherein the control means determines that the precharge control is completed when a predetermined time elapses following control of the friction element from the disengaged condition to the engaged condition.

11. The control device as defined in claim 9 , wherein the control means determines that the precharge control is completed when the oil pressure supplied for the friction element is sufficient to set the friction element in the engaged condition following control of the friction element from the disengaged condition to the engaged condition.

12. The control device as defined in claim 9 , further comprising:

a vehicle speed detecting means for detecting a vehicle speed of the vehicle; and

a storage means for storing a determination reference used to determine whether to set the friction element in the engaged condition or the disengaged condition,

wherein the determining means determines that the friction element is to be set in the engaged condition when the vehicle speed is equal to or higher than the determination reference and determines that the friction element is to be set in the disengaged condition when the vehicle speed is lower than the determination reference.