Pump controlled pressure modulator for reversing clutches

Claim 1

A clutch shift modulation system for vehicular hydraulic transmissions comprising a rotatable torque input member, a torque receiving output member rotatable in a forward direction and in a reverse direction, a pressure actuated forward clutch having one portion thereof connected to be rotated by said input member and another portion thereof connected to rotate said output member, said forward clutch connecting said input member to rotate said output member in said forward direction when said forward clutch is supplied with a predetermined pressure, a pressure actuated reverse clutch having one portion thereof connected to be rotated by said input member and another portion thereof connected to rotate said output member, said reverse clutch connecting said input member to rotate said output member in said reverse direction when said reverse clutch is supplied with a predetermined pressure, pressure supply means including a first hydraulic pump driven by said input member for supplying said selected pressure, direction-selecting valve means having forward and reverse positions, first conduit means connecting said pressure supply means with said valve means, second conduit means connecting said valve means with said forward clutch, third conduit means connecting said valve means with said reverse clutch, said valve means connecting said first conduit means with said second conduit means when said valve means is in said forward position and connecting said first conduit means with said third conduit means when said valve means is in said reverse position, and modulating means to effect a gradual, programmed change from the hydraulic pressure actuation of one of said clutches to the other of said clutches when said valve means is operated to select a reversal in vehicle direction, said modulating means comprising a second hydraulic pump driven reversibly by said output member and having first and second outputs, one output being connected directly to said second conduit means for hydraulic communication therewith and the other output being connected directly to said third conduit means for hydraulic communication therewith whereby said second pump effects an hydraulic pressure which opposes the pressure applied to the newly selected clutch by the first pump as long as the output member rotates in the previously selected direction and which adds to the pressure applied to the newly selected clutch by the first pump when said output member reverses direction to the newly selected direction, the pressure supplied by the first pump being less than the predetermined pressures when opposed by the second pump pressure, but at least equal to the predetermined pressures when aided by the second pump pressure, the clutches being responsive to the resulting gradual pressure increase applied thereto during a direction reversal to engage gradually thereby to prevent sudden engagement of either clutch during a direction reversal, and means for venting pressure supplied by the first pump to the previously engaged clutch upon operation of said valve means to effect a direction reversal.