Speed ratio change control device and method for belt type continuously variable transmission

1. A speed ratio change control device for a continuously variable transmission comprising:

a continuously variable speed ratio change mechanism in which a belt is wrapped around a primary pulley and a secondary pulley and a speed ratio is varied by controlling a pressure supplied to each pulley to displace a movable sheave of each pulley;

a speed ratio change control valve which controls a primary pressure that serves as a pressure supplied to the primary pulley, using a line pressure supplied by a hydraulic pump as a source pressure; and

a link mechanism which moves the speed ratio change control valve to a position in which the primary pressure varies when a speed ratio change actuator moves to a position corresponding to a target speed ratio of the continuously variable speed ratio change mechanism, and returns the speed ratio change control valve to a position in which the primary pressure is maintained by varying the primary pressure such that the movable sheave of the primary pulley displaces,

the device comprising a controller which:

calculates a maximum thrust that can be generated by the primary pulley on the basis of an upper limit value of the line pressure;

calculates an upper limit value of a shift speed of the continuously variable speed ratio change mechanism on the basis of the maximum thrust that can be generated by the primary pulley; and

sets the target speed ratio of the continuously variable speed ratio change mechanism on the basis of the upper limit value of the shift speed.

2. The speed ratio change control device as defined in claim 1 , wherein the controller further sets the upper limit value of the shift speed of the continuously variable speed ratio change mechanism higher as a difference between a thrust of the primary pulley when the speed ratio of the continuously variable speed ratio change mechanism is in a state of equilibrium and the maximum thrust that can be generated by the primary pulley increases.

3. The speed ratio change control device as defined in claim 1 , wherein the controller sets the target speed ratio of the continuously variable speed ratio change mechanism higher as the upper limit value of the shift speed increases.

4. The speed ratio change control device as defined in claim 1 , wherein the upper limit value of the line pressure is calculated on the basis of an oil temperature and a rotation speed of the hydraulic pump.

5. A speed ratio change control method for a continuously variable transmission comprising:

a continuously variable speed ratio change mechanism in which a belt is wrapped around a primary pulley and a secondary pulley and a speed ratio is varied by controlling a pressure supplied to each pulley to displace a movable sheave of each pulley;

a speed ratio change control valve which controls a primary pressure that serves as a pressure supplied to the primary pulley, using a line pressure supplied by a hydraulic pump as a source pressure; and

a link mechanism which moves the speed ratio change control valve to a position in which the primary pressure varies when a speed ratio change actuator moves to a position corresponding to a target speed ratio of the continuously variable speed ratio change mechanism, and returns the speed ratio change control valve to a position in which the primary pressure is maintained by varying the primary pressure such that the movable sheave of the primary pulley displaces,

the method comprising:

calculating a maximum thrust that can be generated by the primary pulley on the basis of an upper limit value of the line pressure;

calculating an upper limit value of a shift speed of the continuously variable speed ratio change mechanism on the basis of the maximum thrust that can be generated by the primary pulley; and

setting the target speed ratio of the continuously variable speed ratio change mechanism on the basis of the upper limit value of the shift speed.

6. The speed ratio change control method as defined in claim 5 , wherein the calculating the upper limit value sets the upper limit value of the shift speed of the continuously variable speed ratio change mechanism higher as a difference between a thrust of the primary pulley when the speed ratio of the continuously variable speed ratio change mechanism is in a state of equilibrium and the maximum thrust that can be generated by the primary pulley increases.

7. The speed ratio change control method as defined in claim 5 , wherein the setting sets the target speed ratio of the continuously variable speed ratio change mechanism higher as the upper limit value of the shift speed increases.

8. The speed ratio change control method as defined in claim 5 , wherein the upper limit value of the line pressure is calculated on the basis of an oil temperature and a rotation speed of the hydraulic pump.

9. A speed ratio change control device for a continuously variable transmission comprising:

a continuously variable speed ratio change mechanism in which a belt is wrapped around a primary pulley and a secondary pulley and a speed ratio is varied by controlling a pressure supplied to each pulley to displace a movable sheave of each pulley;

a speed ratio change control valve which controls a primary pressure that serves as a pressure supplied to the primary pulley, using a line pressure supplied by a hydraulic pump as a source pressure; and

a link mechanism which moves the speed ratio change control valve to a position in which the primary pressure varies when a speed ratio change actuator moves to a position corresponding to a target speed ratio of the continuously variable speed ratio change mechanism, and returns the speed ratio change control valve to a position in which the primary pressure is maintained by varying the primary pressure such that the movable sheave of the primary pulley displaces,

the device comprising:

primary maximum thrust calculating means for calculating a maximum thrust that can be generated by the primary pulley on the basis of an upper limit value of the line pressure;

shift speed upper limit value calculating means for calculating an upper limit value of a shift speed of the continuously variable speed ratio change mechanism on the basis of the maximum thrust that can be generated by the primary pulley; and

target speed ratio setting means for setting the target speed ratio of the continuously variable speed ratio change mechanism on the basis of the upper limit value of the shift speed.

10. The speed ratio change control device as defined in claim 9 , wherein the shift speed upper limit value calculating means sets the upper limit value of the shift speed of the continuously variable speed ratio change mechanism higher as a difference between a thrust of the primary pulley when the speed ratio of the continuously variable speed ratio change mechanism is in a state of equilibrium and the maximum thrust that can be generated by the primary pulley increases.

11. The speed ratio change control device as defined in claim 9 , wherein the target speed ratio setting means sets the target speed ratio of the continuously variable speed ratio change mechanism higher as the upper limit value of the shift speed increases.

12. The speed ratio change control device as defined in claim 9 , wherein the upper limit value of the line pressure is calculated on the basis of an oil temperature and a rotation speed of the hydraulic pump.