Control device and control method for continuously variable transmission

1. A control device for a belt type continuously variable transmission including an input side primary pulley, a groove width of which is varied in accordance with a first oil pressure, an output side secondary pulley, a groove width of which is varied in accordance with a second oil pressure, and a belt wound around the primary pulley and the secondary pulley such that a contact radius thereof with the primary pulley and the secondary pulley varies in accordance with the groove width, which controls the continuously variable transmission such that a torque transmitted from an output side of an engine of a vehicle is transmitted from the primary pulley to the secondary pulley via the belt and a gear ratio determined in relation to the contact radius varies continuously, the control device comprising:

a vehicle speed detecting unit that detects a vehicle speed;

a shift actuator;

a shift control valve that controls the first oil pressure by being switched between a position in which the first oil pressure is supplied to the primary pulley, a position in which the first oil pressure is discharged, and a neutral position in accordance with a physical positional relationship between a position of a movable flange of the primary pulley and a position of the shift actuator;

a secondary pulley pressure control unit that controls the second oil pressure; and

a stationary Low return control unit that varies the gear ratio to a Low side when the vehicle is stationary by controlling the shift control valve in accordance with the position of the shift actuator such that the first oil pressure is discharged and controlling the secondary pulley pressure control unit to increase the second oil pressure to a predetermined oil pressure, whereby the contact radius between the belt and the primary pulley is displaced in a decreasing direction and the contact radius between the belt and the secondary pulley is displaced in an increasing direction while the primary pulley and the secondary pulley are non-rotational,

wherein the stationary Low return control unit controls the position of the shift actuator such that the shift control valve is controlled to a position in which the first oil pressure shifts toward the neutral position by a predetermined amount from a maximum discharge side position during a state wherein torque is transmitting to the primary pulley from the engine.

2. The control device defined in claim 1 , further comprising a primary pulley rotation speed detecting unit that detects a rotation speed of the primary pulley by detecting a rotation angle of the primary pulley,

wherein, when the rotation angle of the primary pulley exceeds a predetermined amount while the vehicle is stationary, the stationary Low return control unit controls the position of the shift actuator such that the shift control valve is controlled to the position in which the first oil pressure is supplied.

3. A control method for a belt type continuously variable transmission comprising an input-side primary pulley, a groove width of which is varied in accordance with a first oil pressure, an output-side secondary pulley, a groove width of which is varied in accordance with a second oil pressure, and a belt wound around the primary pulley and the secondary pulley such that a contact radius thereof with the primary pulley and the secondary pulley varies in accordance with the groove width, which controls the continuously variable transmission such that a torque transmitted from an output-side of an engine of a vehicle is transmitted from the primary pulley to the secondary pulley via the belt and a gear ratio determined in relation to the contact radius varies continuously, a shift actuator and a shift control valve which controls the first oil pressure by being switched between a position in which the first oil pressure is supplied to the primary pulley, a position in which the first oil pressure is discharged, and a neutral position in accordance with a physical positional relationship between a position of a movable flange of the primary pulley and a position of the shift actuator, the control method comprising:

a vehicle speed detecting step for detecting a vehicle speed;

a secondary pulley pressure control step for the second oil pressure; and

a stationary Low return control step for varying the gear ratio to a Low side when the vehicle is stationary by controlling the shift control valve in accordance with the position of the shift actuator such that the first oil pressure is discharged and executing the secondary pulley pressure control step to increase the second oil pressure to a predetermined oil pressure, whereby the contact radius between the belt and the primary pulley is displaced in a decreasing direction and the contact radius between the belt and the secondary pulley is displaced in an increasing direction while the primary pulley and the secondary pulley are non-rotational,

wherein the stationary Low return control step controls the position of the shift actuator such that the shift control valve is controlled to a position in which the first oil pressure shifts toward the neutral position by a predetermined amount from a maximum discharge side position during a state wherein torque is transmitting to the primary pulley from the engine.

4. The control method defined in claim 3 , further comprising a primary pulley rotation speed detecting step for detecting a rotation speed of the primary pulley by detecting a rotation angle of the primary pulley,

wherein, when the rotation angle of the primary pulley exceeds a predetermined amount while the vehicle is stationary, the stationary Low return control step controls the position of the shift actuator such that the shift control valve is controlled to the position in which the first oil pressure is supplied.

5. A control device for a belt type continuously variable transmission including an input-side primary pulley, a groove width of which is varied in accordance with a first oil pressure, an output-side secondary pulley, a groove width of which is varied in accordance with a second oil pressure, and a belt wound around the primary pulley and the secondary pulley such that a contact radius thereof with the primary pulley and the secondary pulley varies in accordance with the groove width, which controls the continuously variable transmission such that a torque transmitted from an output-side of an engine of a vehicle is transmitted from the primary pulley to the secondary pulley via the belt and a gear ratio determined in relation to the contact radius varies continuously, the control device comprising:

vehicle speed detecting means for detecting a vehicle speed;

a shift actuator;

a shift control valve which controls the first oil pressure by being switched between a position in which the first oil pressure is supplied to the primary pulley, a position in which the first oil pressure is discharged, and a neutral position in accordance with a physical positional relationship between a position of a movable flange of the primary pulley and a position of the shift actuator;

secondary pulley pressure control means for controlling the second oil pressure; and

stationary Low return control means for varying the gear ratio to a Low side when the vehicle is stationary by controlling the shift control valve in accordance with the position of the shift actuator such that the first oil pressure is discharged and controlling the secondary pulley pressure control means to increase the second oil pressure to a predetermined oil pressure, whereby the contact radius between the belt and the primary pulley is displaced in a decreasing direction and the contact radius between the belt and the secondary pulley is displaced in an increasing direction while the primary pulley and the secondary pulley are non-rotational,

wherein the stationary Low return control means controls the position of the shift actuator such that the shift control valve is controlled to a position in which the first oil pressure shifts toward the neutral position by a predetermined amount from a maximum discharge side position during a state wherein torque is transmitting to the primary pulley from the engine.

6. The control device for a belt type continuously variable transmission as defined in claim 5 , further comprising a primary pulley rotation speed detecting means for detecting a rotation speed of the primary pulley by detecting a rotation angle of the primary pulley,

wherein, when the rotation angle of the primary pulley exceeds a predetermined amount while the vehicle is stationary, the stationary Low return control means controls the position of the shift actuator such that the shift control valve is controlled to the position in which the first oil pressure is supplied.