System for controlling transmission ratio of a continuously variable transmission for a motor vehicle

Claim 2

A control system for a continuously variable transmission for transmitting the power of an internal combustion engine to driving wheels of a motor vehicle through a clutch, 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 of the driven pulley, a belt engaged with both pulleys, a transmission ratio control valve having ports and a spool, a hydraulic circuit having a pump for supplying oil to the first hydraulic cylinder through the transmission ratio control valve, the system comprising: first means for shifting the spool of the transmission ratio control valve in dependency on operating conditions of the engine so as to provide a transmission ratio; a drive pulley speed sensor for producing a drive pulley speed signal dependent on the speed of the drive pulley; a driven pulley speed sensor for producing a driven pulley speed signal dependent on the speed of the driven pulley; first abnormality detecting means for producing a first abnormality signal when the drive pulley speed signal represents an abnormal value compared with the value of the drive pulley speed signal; second abnormality detecting means for producing a second abnormality signal when the driven pulley speed signal represents an abnormal value compared with the value of the drive pulley speed signal; second means responsive to the first abnormality signal for producing a fail-safe transmission ratio signal; said first means being responsive to the fail-safe transmission ratio signal for controlling the transmission ratio dependent on the fail-safe transmission ratio signal; third means responsive to the second abnormality signal for producing a fail-safe signal; said first means being responsive to the fail-safe signal for controlling the transmission ratio dependent on the fail-safe signal.

Claim 3

The system according to claim 1, wherein the first means comprises another hydraulic circuit for applying oil to the transmission ratio control valve so as to shift the spool and a control valve for controlling the oil applied to the transmission ratio control valve.

Claim 4

In a control system for a continuously variable transmission having a continuously variable transmission ratio for transmitting power of an internal combustion engine to driving wheels of a motor vehicle through a clutch, the transmission 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 of the driven pulley, and a belt engaged with both pulleys, the control system having a transmission ratio control valve having ports and a shiftable spool, and a first hydraulic circuit having a pump for supplying oil to the first hydraulic cylinder via the transmission ratio control valve and to the second hydraulic cylinder, the improvement in the system comprising: first means for shifting the spool of the transmission ratio control valve in dependency on operating conditions of the engine so as to provide a transmission ratio; a drive pulley speed sensor for producing a drive pulley speed signal dependent on the speed of the drive pulley; a driven pulley speed sensor for producing a driven pulley speed signal dependent on the speed of the driven pulley; first abnormality detecting means for producing a first abnormality signal when the drive pulley speed signal has an abnormal value; second abnormality detecting means for producing a second abnormality signal when the driven pulley speed signal has an abnormal value; second means responsive to the first abnormality signal for producing a fail-safe transmission ratio signal; said first means being responsive to the fail-safe transmission ratio signal for shifting the spool of the transmission ratio control valve in dependency on said fail-safe transmission ratio signal for controlling the transmission ratio dependent on the fail-safe transmission ratio signal; third means responsive to the second abnormality signal for producing another fail-safe signal; said first means being responsive to the fail-safe signal for shifting the spool of the transmission ratio control valve in dependency on said fail-safe signal for controlling the transmission ratio dependent on said fail-safe signal.

Claim 5

In a control system for a continuously variable transmission having a continuously variable transmission ratio for transmitting power of an internal combustion engine to driving wheels of a motor vehicle through a clutch, the transmission 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 of the driven pulley, and a belt engaged with both pulleys, the control system having a transmission ratio control valve having ports and a shiftable spool, and a first hydraulic circuit having a pump for supplying oil to the first hydraulic cylinder via the transmission ratio control valve and to the second hydraulic cylinder, the improvement in the system comprising: first means for shifting the spool of the transmission ratio control valve in dependency on operating conditions of the engine so as to provide a transmission ratio; a drive pulley speed sensor for producing a drive pulley speed signal dependent on the speed of the drive pulley; a driven pulley speed sensor for producing a driven pulley speed signal dependent on the speed of the driven pulley; first abnormality detecting means for producing a first abnormality signal when the drive pulley speed signal has an abnormal value; second abnormality detecting means for producing a second abnormality signal when the driven pulley speed signal has an abnormal value; second means responsive to the first abnormality signal for producing a fail-safe transmission ratio signal; said first means being responsive to the fail-safe transmission ratio signal for shifting the spool of the transmission ratio control valve in dependency on said fail-safe transmission ratio signal for controlling the transmission ratio dependent on the fail-safe transmission ratio signal; third means responsive to the second abnormality signal for producing another fail-safe signal; said first means being responsive to the fail-safe signal for shifting the spool of the transmission ratio control valve in dependency on said fail-safe signal for controlling the transmission ratio dependent on said fail-safe signal.

Claim 6

A control system according to claim 3, wherein said first and second abnormality detecting means produce said first and second abnormality signals when said abnormal values are zero, respectively.

Claim 7

A control system according to claim 3, wherein said second means produces said fail-safe transmission ratio signal as a function of said driven pulley speed signal upon occurrence of said first abnormality signal.

Claim 8

A control system according to claim 5, wherein said second means produces said fail-safe transmission ratio signal as a function of said driven pulley speed signal upon occurrence of said first abnormality signal such that as said driven pulley speed signal increases said fail-safe transmission ratio signal is representative of a decreasing transmission ratio.

Claim 9

A control system according to claim 3, wherein said second means produces said fail-safe transmission ratio signal as a function of said driven pulley speed signal and position of a throttle valve of the engine upon occurrence of said first abnormality signal.

Claim 10

A control system according to claim 3, wherein said second means produces said fail-safe transmission ratio signal as representative of a maximum transmission ratio upon occurrence of said first abnormality signal when said driven pulley speed is at least as high as a predetermined low value, and said second means produces said fail-safe transmission ratio signal as a changing function of said driven pulley speed signal upon occurrence of said first abnormality signal when said driven pulley speed is higher than said predetermined low value.

Claim 11

A control system according to claim 8, wherein said changing function is also dependent on position of a throttle valve of the engine.

Claim 12

A control system according to claim 8, wherein said changing function is such that, said fail-safe transmission ratio signal as said changing function multiplied by said driven pulley speed signal is substantially constant.

Claim 13

A control system according to claim 3, wherein said second means produces said fail-safe transmission ratio signal as representative of a minimum transmission ratio upon occurrence of said first abnormality signal when said driven pulley speed is higher than a predetermined high value.

Claim 14

A control system according to claim 3, wherein said third means produces said fail-safe signal as a function of said drive pulley speed and position of a throttle valve of the engine upon occurrence of said second abnormality signal.

Claim 15

A control system according to claim 3, wherein said third means produces said fail-safe signal as a function of position of a throttle valve of the engine upon occurrence of said second abnormality signal.

Claim 16

A control system according to claim 3, wherein said fail-safe signal is representative of the transmission ratio as a function of opening degree of the throttle valve such that as the opening degree increases said fail-safe signal is representative of an increasing transmission ratio.

Claim 17

A control system according to claim 14, wherein said fail-safe signal is representative of the transmission ratio also as a function of drive pulley speed such that, driven pulley speed multiplied by the transmission ratio represented by said fail-safe signal is substantially a constant, said constant being different depending on the opening degree of the throttle valve.

Claim 18

A control system according to claim 15, wherein said constant increases as the opening degree of the throttle valve increases.

Claim 19

In a control system for a continuously variable transmission having a continuously variable transmission ratio for transmitting power of an internal combustion engine to driving wheels of a motor vehicle through a clutch, the transmission 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 of the driven pulley, and a belt engaged with both pulleys, the control system having a transmission ratio control valve having ports and a shiftable spool, and a first hydraulic circuit having a pump for supplying oil to the first hydraulic cylinder via the transmission ratio control valve and to the second hydraulic cylinder, the improvement in the system comprising: first means for shifting the spool of the transmission ratio control valve in dependency on operating conditions of the engine so as to provide a transmission ratio; a pulley speed sensor for producing a pulley speed signal dependent on the speed of one of the pulleys; abnormality detecting means for producing an abnormality signal when the pulley speed signal has an abnormal value; second means responsive to the abnormality signal for producing a fail-safe transmission ratio signal; said first means being responsive to the fail-safe transmission ratio signal for shifting the spool of the transmission ratio control valve in dependency on said fail-safe transmission ratio signal for controlling the transmission ratio dependent on the fail-safe transmission ratio signal.

Claim 20

In a control system for a continuously variable transmission having a continuously variable transmission ratio for transmitting power of an internal combustion engine to driving wheels of a motor vehicle through a clutch, the transmission 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 of the driven pulley, and a belt engaged with both pulleys, the control system having a transmission ratio control valve having ports and a shiftable spool, and a first hydraulic circuit having a pump for supplying oil to the first hydraulic cylinder via the transmission ratio control valve and to the second hydraulic cylinder, the improvement in the system comprising: first means for shifting the spool of the transmission ratio control valve in dependency on operating conditions of the engine so as to provide a transmission ratio; a pulley speed sensor for producing a pulley speed signal dependent on the speed of one of the pulleys; abnormality detecting means for producing an abnormality signal when the pulley speed signal has an abnormal value; second means responsive to the abnormality signal for producing a fail-safe transmission ratio signal; said first means being responsive to the fail-safe transmission ratio signal for shifting the spool of the transmission ratio control valve in dependency on said fail-safe transmission ratio signal for controlling the transmission ratio dependent on the fail-safe transmission ratio signal.