Belt-and-pulley type continuously variable transmission and method for controlling the same

A method for controlling a speed ratio of a belt-and-pulley type continuously variable transmission having an input shaft, a drive pulley mounted on said input shaft and comprising a stationary conical member and a movable conical member, an output shaft, a driven pulley mounted on said output shaft and comprising a stationary conical member and a movable conical member, a V-belt trained around said drive and driven pulleys, first and second hydraulic pressure chambers for axially moving said movable conical members to vary effective diameters of said drive and driven pulleys for thereby controlling a speed ratio, and an oil pressure source and an oil reservoir operatively coupled to said first and second hydraulic pressure chamber, said method comprising the steps of:

• first communicating the hydraulic pressure chamber of one of said drive and driven pulleys, the effective diameter of which is to increase at a time, with said oil pressure source;
• and
• then communicating the hydraulic pressure chamber of the other of said drive and driven pulleys, the effective diameter of which is to reduce at the time, with said oil reservoir, for thereby starting to move said movable conical members of said drive and driven pulleys in synchronism with each other;
• wherein the method includes the step of bringing said oil pressure source and the hydraulic pressure chamber of said one pulley, and said oil reservoir and the hydraulic pressure chamber of said pulley into communication with each other by first and second valves, respectively, actuatable in unison by a speed ratio varying signal generating mechanism and having oil supply grooves, respectively, and oil drain grooves, respectively, which are offset with respect to each other.

A belt-and-pulley type continuously variable transmission comprising:

• an input shaft;
• a drive pulley mounted on said input shaft and comprising a stationary conical member and a movable conical member;
• an output shaft;
• a driven pulley mounted on said output shaft and comprising a stationary conical member and a movable conical member;
• a V-belt trained around said drive and driven pulleys;
• first and second hydraulic pressure chambers for axially moving said movable conical members to vary effective diameters of said drive and driven pulleys for controlling a speed ratio;
• an oil pressure source and an oil reservoir operatively coupled to said first and second hydraulic pressure chambers;
• a first opening communicating with said first hydraulic pressure chamber;
• a first slide valve having a first oil supply groove communicating with said oil pressure source and a first oil drain groove communicating with said oil reservoir, and actuatable for communicating said first opening selectively with said first oil supply groove and said first oil drain groove;
• a second opening communicating with said second hydraulic pressure chamber;
• a second slide valve having a second oil supply groove communicating with said oil pressure source and a second oil drain groove communicating with said oil, reservoir and actuatable for communicating said second opening selectively with said second oil supply groove and said second oil drain groove;
• and
• a first mechanism responsive to a speed ratio varying signal for axially sliding said first and second slide valves in synchronism with each other, such that the hydraulic pressure chamber of one of said drive and driven pulleys, the effective diameter of which is to become larger at a time, is communicated with the oil supply groove of an associated one of said slide valves, and the hydraulic pressure chamber of the other of said drive and driven pulleys, the effective diameter of which is to become smaller at the time, is communicated with the oil drain groove of the associated other of said slide valves no earlier than said communication of the hydraulic pressure chamber of said one pulley to said oil supply groove of said associated slide valve, for thereby starting to move said movable conical members of said drive and driven pulleys move in synchronism with each other.

A belt-and-pulley type continuously variable transmission comprising:

• an input shaft;
• a drive pulley mounted on said input shaft and comprising a stationary conical member and movable conical member;
• an output shaft;
• a driven pulley mounted on said output shaft and comprising a stationary conical member and a movable conical member;
• a V-belt trained around said drive and driven pulleys;
• first and second hydraulic pressure chambers for axially moving said movable conical members, respectively, to vary effective diameters of said drive and driven pulleys for thereby controlling a speed ratio;
• an oil pressure source and an oil reservoir;
• a first slide valve movable in a first predetermined direction for selectively communicating said first hydraulic pressure chamber with one of said oil pressure source and said oil reservoir;
• and a second slide valve movable in a second predetermined direction for selectively communicating said second hydraulic pressure chamber with the other of said oil pressure source and said oil reservoir;
• wherein:
• said transmission further comprising a servomechanism responsive to a speed ratio varying signal for sliding said first and second slide valves in synchronism with each other in said first and second predetermined directions, respectively, such that the hydraulic pressure chamber of one of said drive and driven pulleys, the effective diameter of which is to become larger at that time, is communicated with said oil pressure source, and the hydraulic pressure chamber of the other of said drive and driven pulleys, the effective diameter is to become smaller, is communicated with said oil reservoir no earlier than said communication of the hydraulic pressure chamber of said one pulley to said oil pressure source, for thereby starting to move said movable conical members of said drive and driven pulleys in synchronism with each other.