Control device and control method for continuously variable transmission

1. A control device for a belt type continuously variable transmission in which a belt is wound around a primary pulley into which a power output by a power source is input and a secondary pulley connected to an output side of a driving system of a vehicle, and an oil pressure supplied to the primary pulley is regulated by driving a step motor, thereby modifying a groove width of the primary pulley and the secondary pulley such that a rotation speed of the power source is output while being varied continuously, comprising:

a deceleration detecting unit configured to detect a deceleration of the vehicle;

a brake operation detecting unit configured to detect an operation of a brake; and

a gear ratio control unit configured to:

set a target gear ratio on a basis of an operating condition of the vehicle,

control a drive amount of the step motor such that an actual gear ratio converges with the target gear ratio,

control the drive amount of the step motor such that a predetermined gear ratio is maintained when the deceleration of the vehicle exceeds a predetermined threshold,

determine the predetermined threshold on a basis of the actual gear ratio upon detection of the operation of the brake, and

set the predetermined threshold at a larger degree of deceleration as the actual near ratio shifts toward a high side.

2. A control method for a belt type continuously variable transmission in which a belt is wound around a primary pulley into which a power output by a power source is input and a secondary pulley connected to an output side of a driving system of a vehicle, and an oil pressure supplied to the primary pulley is regulated by driving a step motor, thereby modifying a groove width of the primary pulley and the secondary pulley such that a rotation speed of the power source is output while being varied continuously, the method comprising:

detecting a deceleration of the vehicle;

detecting an operation of a brake;

setting a target gear ratio on a basis of an operating condition of the vehicle;

controlling a drive amount of the step motor such that an actual gear ratio converges with the target gear ratio;

controlling the gear ratio by controlling the drive amount of the step motor such that a predetermined gear ratio is maintained when the deceleration of the vehicle exceeds a predetermined threshold,

wherein the predetermined threshold is determined on a basis of the actual gear ratio upon detection of the operation of the brake, and the predetermined threshold is set at a larger degree deceleration as the actual gear ratio shifts toward a high side.

3. A control device for a belt type continuously variable transmission in which a belt is wound around a primary pulley into which a power output by a power source is input and a secondary pulley connected to an output side of a driving system of a vehicle, and an oil pressure supplied to the primary pulley is regulated by driving a step motor, thereby modifying a groove width of the primary pulley and the secondary pulley such that a rotation speed of the power source is output while being varied continuously, comprising:

deceleration detecting means for detecting a deceleration of the vehicle;

brake operation detecting means for detecting an operation a brake; and

gear ratio control means for setting a target gear ratio on a basis of an operating condition of the vehicle, controlling a drive amount of the step motor such that an actual gear ratio converges with the target gear ratio, and when the deceleration of the vehicle exceeds a predetermined threshold, controlling the gear ratio by controlling the drive amount of the step motor such that a predetermined gear ratio is maintained,

wherein the gear ratio control means determines the predetermined threshold on a basis of the actual gear ratio upon detection of the operation of the brake, and sets the predetermined threshold at a larger degree of deceleration as the actual gear ratio shifts toward a high side.

4. The control device according to claim 1 , wherein the high side is higher relative to a low side.

5. The control method according to claim 2 , wherein the high side is higher relative to a low side.

6. The control device according to claim 3 , wherein the high side is higher relative to a low side.