Hydraulic speed-changing system

Claim 1

In a transmission system connected between a fuel-powered engine and an output shaft driven thereby, in combination: gear-shifting means for switching between a plurality of forward speed ratios and a reverse speed ratio of said output shaft with reference to said engine, said gear-shifting means including a fluid-operated clutch actuatable to establish one forward speed ratio and said reverse speed ratio; a speed selector having a forward position and a reverse position; an operator-controlled accelerator for varying the fuel supply to said engine; switchover means controlled by said speed selector and responsive to the position of said accelerator and to the speed of said output shaft for actuating said clutch in said reverse position and under certain load conditions in said forward position of said speed selector; and damping means responsive to said speed selector for retarding full operation of said clutch by a first delay period in said forward position and by a second delay period shorter than said first delay period in said reverse position thereof; said switchover means comprising a control valve inserted between said clutch and a source of pressure fluid therefor; said control valve including a cylinder with a piston, biasing means tending to hold said piston in a normal position enabling rapid flow of fluid from said source to said clutch, and a feedback connection from said clutch to said cylinder for shifting said piston into a throttling position against the force of said biasing means upon partial pressurization of said clutch; said damping means comprising a plunger mechanically linked with said piston and fluidically connected to said clutch for displacement in a direction restoring said piston to said normal position upon further pressurization of said clutch; said control valve being provided with an ancillary inlet connected to said source in said reverse position of said speed selector for subjecting said piston to a supplemental force aiding the force of said biasing means in said reverse position of said speed selector.