Transmission ratio control system for a continuously variable transmission

Claim 2

1 . A control system for a continuously variable transmission for transmitting the power of an internal combustion engine to driving wheels of a motor vehicle, having a drive pulley including a hydraulically shiftable disc and a first hydraulic cylinder for shifting the disc, a driven pulley including a hydraulically shiftable disc and a second hydraulic cylinder for operating the disc, a belt engaged with both pulleys, a transmission ratio control valve having ports and a spool, a first hydraulic circuit having a pump for supplying oil to the first and second cylinders through the transmission ratio control valve, the system comprising: first detecting means for producing a first speed signal representing input speed of the transmission; second detecting means for producing a second speed signal representing output speed of the transmission; third detecting means for detecting load on the engine and for producing a load signal; first means responsive to the first and second signals for producing an actual transmission ratio signal; second means responsive to the load signal and to the second signal for producing a desired transmission ratio signal; third means for producing a control signal in accordance with the desired transmission ratio signal and the actual transmission signal; fourth means responsive to the control signal for shifting the spool of the transmission ratio control Valve so as to provide a transmission ratio. ,

Claim 3

The control system according to claim 1 wherein the fourth means includes a second hydraulic circuit for supplying oil to the transmission ratio control valve so as to shift the spool and control valve means provided in the second hydraulic circuit for controlling the amount of oil supplied to the transmission ratio control valve.

Claim 4

The system according to claim 2 wherein the control valve means is a solenoid operated on-off valve, and the control signal is pulses for operating the on-off valve, the duty ratio of which is changed so as to control the line pressure

Claim 5

The system according to claim 3 wherein the duty ratios are stored in a look-up table.

Claim 6

The system according to claim 1 further comprising fifth means for changing the value of the desired transmission ratio signal.

Claim 7

A control system for a continuously variable transmission for transmitting the power of an internal combustion engine to driving wheels of a motor vehicle, having a drive pulley (7) including a hydraulically shiftable disc and a first hydraulic cylinder (9) for shifting the disc, a driven pulley (8) including a hydraulically shiftable disc and a second hydraulic cylinder (10) for operating the disc, a belt (11) engaged with both pulleys, a hydraulic circuit (Figure 2) having a pump (21) for supplying oil to the first cylinder (9) through a spool type valve which controls the transmission ratio, the system comprising: detecting means (71) for producing a first speed signal representing input speed of the transmission; detecting means (72) for producing a second speed signal representing output speed of the transmission; detecting means (74) for detecting load on the engine and for producing a load signal; means (75) responsive to the first and second signals for producing an actual transmission ratio signal; means (76) responsive to the load signal and to the second signal for producing a desired transmission ratio signal; means (81) for producing a control signal in accordance with the desired transmission ratio signal and the actual transmission signal; means (82, 68, 34) responsive to the control signal for shifting the spool of the transmission ratio control valve (50) so as to control the transmission ratio; means (80) for determining variation of an operating condition; and means (78) for correcting the desired transmission ratio by a correcting quantity when the determined variation of the operating condition exceeds a predetermined level.

Claim 8

A control system for a continuously variable transmission for transmitting the power of an internal combustion engine to driving wheels of a motor vehicle, having a drive pulley (7) including a hydraulically shiftable disc and a first hydraulic cylinder (9) for shifting the disc, a driven pulley (8) including a hydraulically shiftable disc and a second hydraulic cylinder (10) for operating the disc, a belt (11) engaged with both pulleys, a hydraulic circuit (Figure 2) having a pump (21) for supplying oil to the first cylinder (9) through a spool type valve which controls the transmission ratio, the system comprising: detecting means (71) for producing a first speed signal representing input speed of the transmission; detecting means (72) for producing a second speed signal representing output speed of the transmission; detecting means (74) for detecting load on the engine and for producing a load signal; means (75) responsive to the first and second signals for producing an actual transmission ratio signal; means (76) responsive to the load signal and to the second signal for producing a desired transmission ratio signal; means (81) for producing a control signal in accordance with the desired transmission ratio signal and the actual transmission signal; means (82, 68, 34) responsive to the control signal for shifting the spool of the transmission ratio control valve (50) so as to control the transmission ratio; means (80) for determining variation of an operating condition; and means (78) for correcting the desired transmission ratio by a correcting quantity when the determined variation of the operating condition exceeds a predetermined level.

Claim 9

A system as claimed in claim 6, wherein the determining means (80) is for determining the rate of change of the engine load signal.