US 6,547,694 B2Granted

Hydraulic control system for a continuously variable transmission

AssigneeJatco Transtechnology Ltd.

InventorsYoshikazu Miyagawa, Satoshi Sakakibara

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Abstract

A CVT has primary and secondary pulleys, and a control unit for controlling the transmission ratio by controlling the line pressure applied to the first and secondary pulleys. The control unit calculates a standard step position of a step motor corresponding to the target transmission ratio and provides a command signal representative of the difference between the standard step position and the current position of the step motor. A shift control valve actuated by the step motor controls the pressure to be applied to the primary pulley. The control unit compares the actual transmission ratio with the target transmission ratio, and if the shift is not completed, the control unit commands an additional step number. Unless the shift to the HI side is accomplished when the additional step number reaches the threshold value, the line pressure is increased to achieve the shift.

Claims9

Dependent claims

A hydraulic control system for a continuous variable transmission comprising:

a transmission mechanism having a set of adjustable first and second pulleys having first and second cylinder chambers, respectively, width of respective pulleys being variable according to hydraulic pressure applied to said cylinder chambers, and a belt entraining the pulleys to transmit torque therebetween;
means for producing a line pressure and continuously supplying the line pressure to said second chamber;
a shift control valve adapted to be operated under the action of an actuator associated therewith to supply a pressure that is reduced from said line pressure to the first cylinder chamber;
and
shift control means for generating a shift command to the actuator depending on a driving condition and modifying the line pressure,
wherein said shift control means includes means for determining whether or not said shift is accomplished, said shift control means being operable to raise the line pressure from a first level to a second level when said determining means determines that the shift to a HI side is not accomplished.

3 more elements

Dependencies are inferred from the claim text.