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

1. A speed ratio change control device for a belt type 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 serving as the pressure supplied to the primary pulley; 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 is displaced,

the device comprising a controller which:

estimates a minimum generated pressure of the primary pressure on the basis of a displacement speed of the movable sheave of the primary pulley and an opening area of a drain side passage of the speed ratio change control valve, which discharges the primary pressure;

calculates an upper limit value of a shift speed of the continuously variable speed ratio change mechanism on the basis of the minimum generated pressure of the primary pressure; 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 the primary pressure when the speed ratio of the continuously variable speed ratio change mechanism is in a state of equilibrium and the minimum generated pressure of the primary pressure increases.

3. The speed ratio change control device as defined in claim 1 , wherein the controller further 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. A speed ratio change control method for a belt type 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 serving as the pressure supplied to the primary pulley; 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 is displaced,

the method comprising:

estimating a minimum generated pressure of the primary pressure on the basis of a displacement speed of the movable sheave of the primary pulley and an opening area of a drain side passage of the speed ratio change control valve, which discharges the primary pressure;

calculating an upper limit value of a shift speed of the continuously variable speed ratio change mechanism on the basis of the minimum generated pressure of the primary pressure; 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.

5. The speed ratio change control method as defined in claim 4 , wherein the calculating action sets the upper limit value of the shift speed of the continuously variable speed ratio change mechanism higher as a difference between the primary pressure when the speed ratio of the continuously variable speed ratio change mechanism is in a state of equilibrium and the minimum generated pressure of the primary pressure increases.

6. The speed ratio change control method as defined in claim 4 , 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.

7. A speed ratio change control device for a belt type 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 serving as the pressure supplied to the primary pulley; 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 is displaced,

the device comprising:

minimum generated pressure estimating means for estimating a minimum generated pressure of the primary pressure on the basis of a displacement speed of the movable sheave of the primary pulley and an opening area of a drain side passage of the speed ratio change control valve, which discharges the primary 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 minimum generated pressure of the primary pressure; 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.

8. The speed ratio change control device as defined in claim 7 , 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 the primary pressure when the speed ratio of the continuously variable speed ratio change mechanism is in a state of equilibrium and the minimum generated pressure of the primary pressure increases.

9. The speed ratio change control device as defined in claim 7 , 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.