Hydraulic control system for a continuously variable transmission
First Claim
1. A hydraulic control system for a continuously variable transmission comprising a transmission mechanism which includes 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 provided between the pulleys so as 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 which 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, characterized in that 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 the HI side is not accomplished.
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0 Petitions
Accused Products
Abstract
A transmission mechanism of the continuously variable transmission comprises a set of primary and secondary pulleys between which a belt is provided. The CVT control unit is operable to supply line pressure directly to a secondary pulley and also to a primary pulley via a shift control valve associated with a step motor in such a manner as to control a transmission ratio. The CVT control unit calculates a standard step position of the step motor corresponding to the target transmission ratio and provides a command signal representative of a difference between the standard step position and the current position of the step motor. The shift control valve actuated by the step motor controls the pressure to be supplied to the primary pulley. The actual transmission ratio obtained on the basis of the rotation speeds of the pulleys is compared with the target transmission ratio. If the shift is not accomplished, the CVT control unit commands additional step number. Unless the shift to the HI side is accomplished at the time when the additional step number reaches the threshold value, the line pressure is increased so as to achieve the shift. Thus, the transmission normally operates with a low line pressure sufficiently to reduce a frictional loss at the contact areas of the belt and the pulleys, thereby resulting in an enhanced fuel economy.
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Citations
5 Claims
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1. A hydraulic control system for a continuously variable transmission comprising a transmission mechanism which includes 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 provided between the pulleys so as 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 which 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,characterized in that 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 the HI side is not accomplished. - View Dependent Claims (2, 3, 4, 5)
- means for producing a line pressure and continuously supplying the line pressure to said second chamber;
Specification