Hydraulic control apparatus for hydraulically-operated power transmitting system having continuously variable transmission

Claim 1

A hydraulic control apparatus for controlling a hydraulically-operated power transmitting system for an automotive vehicle, the transmitting system having a continuously variable transmission of the belt-and-pulley type and an auxiliary transmission incorporating a frictional coupling assembly and coupled to the output side of the continuously variable transmission, the continuously variable transmission including a first variable-diameter pulley, a second variable-diameter pulley, a transmission belt connecting the first and second variable-diameter pulleys, and first and second hydraulic actuators for changing the effective diameters of the first and second variable-diameter pulleys, respectively, said hydraulic control apparatus comprising: (a) first pressure-generating means for generating a first line pressure exclusively used to operate one of the first and second hydraulic actuators of the continuously variable transmission, primarily for controlling the tension of the transmission belt; (b) second pressure-generating means for generating a second line pressure exclusively used to operate the frictional coupling assembly, said second pressure-generating means generating said second line pressure based on an output torque of an engine of the automotive vehicle and on a speed ratio of the continuously variable transmission, wherein: (c) said hydraulic control apparatus includes a manual valve which has at least two shift positions including a forward-drive position, and (d) said second pressure-generating means comprises: (i) an input port to which said first line pressure is applied while said forward-drive position is selected; (ii) an output port from which said second line pressure is generated while said forward-drive position is selected; and (iii) a valve spool for controlling a cross sectional area of fluid communication between said input and output ports, said valve spool receiving a speed-ratio pressure corresponding to said speed ratio, a feedback pressure corresponding to said second line pressure, and a throttle pressure corresponding to an angle of opening of a throttle valve of the engine, said speed-ratio pressure and said feedback pressure acting on said valve spool so as to move said valve spool in one of opposite directions, and said throttle pressure acting on said valve spool in the other direction.