Transmission ratio control system for a continuously variable transmission

Claim 2

An improved control system for a continuously variable transmission for transmitting the power of an internal combustion engine, the system comprising a drive pulley having a hydraulically shiftable disc and a hydraulic cylinder for operating the disc, a driven pulley having a hydraulically shiftable disc and a hydraulic cylinder for operating the disc, a belt engaged with both pulleys, a first hydraulic circuit having a pump for supplying oil to both the hydraulic cylinders, a transmission ratio control valve having a spool for controlling the oil supplied to the cylinder of the drive pulley to change the transmission ratio to a desired transmission ratio, wherein the improvement comprises: first means for shifting the spool; sensing means for sensing operating conditions of the engine and the transmission and for producing a first signal dependent on the conditions; a control unit responsive to the first signal for producing a control signal for operating the first means to shift the spool at a speed to control transmission ratio changing speed; second means for detecting changing speed of the desired transmission ratio and for producing a second signal; third means responsive to the second signal for correcting the transmission ratio changing signal.

Claim 3

The control system according to claim 1 wherein the control signal is produced in dependence on the difference between a desired transmission ratio and an actual transmission ratio.

Claim 4

The control system according to claim 1 wherein the transmission ratio control valve has chambers at both ends of the spool, the first means includes a second hydraulic circuit for supplying oil to the chambers, and control valve means provided in the second hydraulic circuit for controlling flow rate of control oil supplied to the chambers of the transmission ratio control valve.

Claim 5

The control system according to claim 3 wherein the transmission ratio control valve has a spring for urging the spool to a drain position.

Claim 6

The control system according to claim 3 wherein the transmission ratio control valve is arranged to supply the control oil to a small area portion of the spool.

Claim 7

The control system according to claim 3 wherein the control valve means is a solenoid operated on-off valve, and the control signal of the control unit is pulses the duty ratio of which is changed so as to control the transmission ratio changing speed.

Claim 8

The control system according to claim 3 wherein the second hydraulic circuit is provided with a regulator valve for maintaining the pressure of oil at a constant value.

Claim 9

The control system according to claim 1 wherein the sensing means comprises a drive pulley speed sensor, driven pulley speed sensor and throttle valve position sensor.

Claim 10

A control system for a continuously variable transmission for transmitting the power of an internal combustion engine, which has a drive pulley (7) having a hydraulically shiftable disc and a hydraulic cylinder (9) for operating the disc, a driven pulley (8) having a hydraulically shiftable disc and a hydraulic cylinder (10) for operating the disc, a belt (11) engaged with both pulleys, a first hydraulic circuit having a pump for supplying oil to both the hydraulic cylinders, a spool valve (50) for controlling transmission ratio by controlling the oil supply to the cylinder of the drive pulley (7) in order to change the transmission ratio towards a desired transmission ratio, the system comprising: first control means (34, 68, 82) for controlling the operation of the transmission ratio control valve; means (71, 72, 74) for sensing operating conditions of the engine and the transmission and for producing a first signal dependent on the conditions; control means (70) responsive to the first signal for producing a transmission ratio control signal for operating the first means (34, 68, 82) to shift the spool of the transmission ratio control valve, to control transmission ratio changing speed and thereby the transmission ratio towards a desired transmission ratio; means (80, 78) for determining the changing speed of the desired transmission ratio and for correcting the transmission ratio control signal in response to the determined speed of change of the desired transmission ratio.

Claim 11

A control system for a continuously variable transmission for transmitting the power of an internal combustion engine, which has a drive pulley (7) having a hydraulically shiftable disc and a hydraulic cylinder (9) for operating the disc, a driven pulley (8) having a hydraulically shiftable disc and a hydraulic cylinder (10) for operating the disc, a belt (11) engaged with both pulleys, a first hydraulic circuit having a pump for supplying oil to both the hydraulic cylinders, a spool valve (50) for controlling transmission ratio by controlling the oil supply to the cylinder of the drive pulley (7) in order to change the transmission ratio towards a desired transmission ratio, the system comprising: first control means (34, 68, 82) for controlling the operation of the transmission ratio control valve; means (71, 72, 74) for sensing operating conditions of the engine and the transmission and for producing a first signal dependent on the conditions; control means (70) responsive to the first signal for producing a transmission ratio control signal for operating the first means (34, 68, 82) to shift the spool of the transmission ratio control valve, to control transmission ratio changing speed and thereby the transmission ratio towards a desired transmission ratio; means (80, 78) for determining the changing speed of the desired transmission ratio and for correcting the transmission ratio control signal in response to the determined speed of change of the desired transmission ratio.

Claim 12

A control system as claimed in claim 9, wherein the transmission ratio control signal is produced in dependence on the difference between a desired transmission ratio and an actual transmission ratio.