Belt type continuously variable transmission

1. A belt type continuously variable transmission, comprising:

a primary pulley on an input side having a groove which varies according to an oil pressure;

a secondary pulley on an output side having a groove which varies according to an oil pressure;

a belt wound around the primary pulley and secondary pulley;

detecting means for detecting a vehicle running state;

pulley ratio setting means for setting a final pulley ratio achieved by a shift of the pulley ratio of the primary and secondary pulleys, based on the vehicle running state;

steady oil pressure computing means for computing a primary steady oil pressure supplied to the primary pulley and a secondary steady oil pressure supplied to the secondary pulley, according to an input torque inputted to the primary pulley and an actual pulley ratio;

target shift speed determining means for determining a target shift speed based on the final pulley ratio;

target stroke speed computing means for computing a target stroke speed of the primary pulley and/or secondary pulley from the target shift speed;

target pulley rotation speed computing means for computing a target pulley rotation speed of the primary pulley, based on the vehicle running state;

transitional oil pressure computing means for computing a transitional oil pressure correction amount which can attain the target shift speed, in response to the target pulley rotation speed of the primary pulley and the target stroke speed; and

oil-pressure control means for setting one of the oil pressure supplied to the primary pulley and the oil pressure supplied to the secondary pulley, to the sum of the steady oil pressure and transitional oil pressure correction amount, so as to attain the final pulley ratio.

2. The belt type continuously variable transmission as defined in claim 1 , comprising a target stroke change calculating means for calculating a target stroke change per pulley rotation based on a value obtained by dividing the target stroke speed by the target pulley rotation speed,

wherein the transitional oil pressure computing means computes the transitional oil pressure correction amount according to the target stroke change per pulley rotation.

3. The belt type continuously variable transmission as defined in claim 2 , wherein the transitional oil pressure correction amount has a proportional relation to the target stroke speed.

4. The belt type continuously variable transmission as defined in claim 1 , wherein the primary and secondary steady oil pressures are oil pressures required to attain a torque capacity of the belt which is larger than the input torque to the primary pulley.

5. A belt type continuously variable transmission, comprising:

a primary pulley on an input side having a groove which varies according to an oil pressure;

a secondary pulley on an output side having a groove which varies according to an oil pressure;

a belt wound around the primary pulley and secondary pulley;

a sensor for detecting a vehicle running state; and

a controller programmed to:

set a final pulley ratio achieved by a shift of the pulley ratio of the primary and secondary pulleys, based on the vehicle running state,

compute a primary steady oil pressure supplied to the primary pulley and a secondary steady oil pressure supplied to the secondary pulley based on an input torque inputted to the primary pulley and an actual pulley ratio,

determine a target shift speed based on the final pulley ratio,

compute a target stroke speed of the primary pulley and/or secondary pulley from the target shift speed,

compute a target pulley rotation speed of the primary pulley, based on the vehicle running state,

compute a transitional oil pressure correction amount which can attain the target shift speed, in response to the target pulley rotation speed and the target stroke speed, and

set one of the oil pressure supplied to the primary pulley and the oil pressure supplied to the secondary pulley, to the sum of the steady oil pressure and the transitional oil pressure correction amount, so as to attain the final pulley ratio.

6. A control method for controlling a belt type continuously variable transmission, the transmission comprising: a primary pulley on an input side having a groove which varies according to an oil pressure; a secondary pulley on an output side having a groove which varies according to an oil pressure; and a belt wound around the primary pulley and secondary pulley;

the control method comprising:

detecting a vehicle running state;

setting a final pulley ratio achieved by a shift of the pulley ratio of the primary and secondary pulleys, based on the running state;

computing a primary steady oil pressure supplied to the primary pulley and a secondary steady oil pressure supplied to the secondary pulley, according to an input torque inputted to the primary pulley and an actual pulley ratio;

determining a target shift speed based on the final pulley ratio;

computing a target pulley rotation speed of the primary pulley, based on the vehicle running state;

computing a target stroke speed of the primary pulley and/or secondary pulley from the target shift speed;

computing a transitional oil pressure correction amount which can attain the target shift speed, in response to the target pulley rotation speed and the target stroke speed; and

setting one of the oil pressure supplied to the primary pulley and the oil pressure supplied to the secondary pulley, to the sum of the steady oil pressure and transitional oil pressure correction amount, so as to attain the final pulley ratio.