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 the basis of a vehicle speed and an engine load comprising:

a vehicle speed detecting unit that detects the vehicle speed;

a storing unit that stores a determination reference used to determine whether to set a friction element for locking up the torque converter in an engaged condition or a disengaged condition;

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

an engagement control unit performs control to engage or disengage the friction element on the basis of a determination result of the determining unit,

wherein the engagement control unit comprise a prohibiting unit that prohibits setting of the friction element in the engaged condition until a predetermined condition is established, regardless of the determination result, after the friction element is controlled from the engaged condition to the disengaged condition.

2. The control device for an automatic transmission as defined in claim 1 , wherein the engagement control unit determines that the predetermined condition is established in case a predetermined time elapses after the friction element is controlled to the disengaged condition from the engaged condition.

3. The control device for an automatic transmission as defined in claim 1 , wherein the engagement control unit determines that the predetermined condition is established in case an accelerator pedal opening switches from a non-fully closed condition to a fully closed condition or from a fully closed condition to a non-fully closed condition after the friction element is controlled to the disengaged condition from the engaged condition.

4. The control device for an automatic transmission as defined in claim 1 , wherein the engagement control unit determines that the predetermined condition is established in case the accelerator pedal opening varies by at least a predetermined opening after the friction element is controlled to the disengaged condition from the engaged condition.

5. The control device for an automatic transmission as defined in claim 1 , wherein the engagement control unit determines that the predetermined condition is established in case the vehicle speed varies by at least a predetermined vehicle speed after the friction element is controlled to the disengaged condition from the engaged condition.

6. The control device for an automatic transmission as defined in claim 1 , further comprising a acceleration detecting unit that detects an acceleration of the vehicle,

wherein, in case the detected acceleration is equal to or greater than a predetermined acceleration, the engagement control unit allows the friction element to be set in the engaged condition on the basis of the determination result without having the prohibiting unit determines whether or not the predetermined condition is established.

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

a detecting step for detecting the vehicle speed;

a storing step for storing a determination reference used to determine whether to set a friction element for locking up the torque converter in an engaged condition or a disengaged condition;

a determining step for determining that the friction element is to be set in the engaged condition in case the vehicle speed is equal to or higher than the determination reference and determining that the friction element is to be set in the disengaged condition in case the vehicle speed is lower than the determination reference; and

an engagement control step for performing control to engage or disengage the friction element on the basis of a determination result of the determining step,

wherein the engagement control step comprise a prohibiting step for prohibiting setting of the friction element in the engaged condition until a predetermined condition is established, regardless of the determination result, after the friction element is controlled from the engaged condition to the disengaged condition.

8. The control method for an automatic transmission as defined in claim 7 , wherein the engagement control step determine that the predetermined condition is established in case a predetermined time elapses after the friction element is controlled to the disengaged condition from the engaged condition.

9. The control method for an automatic transmission as defined in claim 7 , wherein the engagement control step determine that the predetermined condition is established in case an accelerator pedal opening switches from a non-fully closed condition to a fully closed condition or from a fully closed condition to a non-fully closed condition after the friction element is controlled to the disengaged condition from the engaged condition.

10. The control method for an automatic transmission as defined in claim 7 , wherein the engagement control step determine that the predetermined condition is established in case the accelerator pedal opening varies by at least a predetermined opening after the friction element is controlled to the disengaged condition from the engaged condition.

11. The control method for an automatic transmission as defined in claim 7 , wherein the engagement control step determine that the predetermined condition is established in case the vehicle speed varies by at least a predetermined vehicle speed after the friction element is controlled to the disengaged condition from the engaged condition.

12. The control method for an automatic transmission as defined in claim 7 , further comprising an acceleration detecting step for detecting an acceleration of the vehicle,

wherein, in case the detected acceleration is equal to or greater than a predetermined acceleration, the engagement control step allow the friction element to be set in the engaged condition on the basis of the determination result without having the prohibiting step determine whether or not the predetermined condition is established.

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

vehicle speed detecting means for detecting the vehicle speed;

storing means for storing a determination reference used to determine whether to set a friction element for locking up the torque converter in an engaged condition or a disengaged condition;

determining means for determining that the friction element is to be set in the engaged condition in case the vehicle speed is equal to or higher than the determination reference and determining that the friction element is to be set in the disengaged condition in case the vehicle speed is lower than the determination reference; and

engagement control means for performing control to engage or disengage the friction element on the basis of a determination result of the determining means,

wherein the engagement control means comprise prohibiting means for prohibiting setting of the friction element in the engaged condition until a predetermined condition is established, regardless of the determination result, after the friction element is controlled from the engaged condition to the disengaged condition.

14. The control device for an automatic transmission as defined in claim 13 , wherein the engagement control means determine that the predetermined condition is established in case a predetermined time elapses after the friction element is controlled to the disengaged condition from the engaged condition.

15. The control device for an automatic transmission as defined in claim 13 , wherein the engagement control means determine that the predetermined condition is established in case an accelerator pedal opening switches from a non-fully closed condition to a fully closed condition or from a fully closed condition to a non-fully closed condition after the friction element is controlled to the disengaged condition from the engaged condition.

16. The control device for an automatic transmission as defined in claim 13 , wherein the engagement control means determine that the predetermined condition is established in case the accelerator pedal opening varies by at least a predetermined opening after the friction element is controlled to the disengaged condition from the engaged condition.

17. The control device for an automatic transmission as defined in claim 13 , wherein the engagement control means determine that the predetermined condition is established in case the vehicle speed varies by at least a predetermined vehicle speed after the friction element is controlled to the disengaged condition from the engaged condition.

18. The control device for an automatic transmission as defined in claim 13 , further comprising acceleration detecting means for detecting an acceleration of the vehicle,

wherein, in case the detected acceleration is equal to or greater than a predetermined acceleration, the engagement control means allow the friction element to be set in the engaged condition on the basis of the determination result without having the prohibiting means determine whether or not the predetermined condition is established.