Abstract: A transmission control system includes a plurality of hydraulic pressure operated control elements for engaging a gear of the transmission in response to actuation of a shift control lever having neutral and non-neutral positions, a plurality of control valves for controlling pressurization of the control elements and a pump for supplying pressurized fluid to the control valves. An engagement override system includes a switch which is coupled to the shift lever and which energizes a solenoid when the shift lever is in its neutral position and de-energizes the solenoid when the shift lever is in its non-neutral position. In a preferred embodiment, an engagement override valve includes a pilot operated valve which controls communication between the pump, a reservoir and the pressure operated control elements. The solenoid controls the pilot operated valve.

Abstract: A control system for a multi-speed powershift gear transmission having multiple hydraulically actuated speed range clutches and directional clutches includes a control valve module having solenoid operated valves for conducting pressure fluid to a selected one of the speed range clutches and a selected one of the directional clutches. A pressure regulator valve is in circuit with the directional clutch control valves and is acted on by pilot pressure fluid controlled by a proportional solenoid type control valve wherein the pressure rate of rise in the directional clutches may be selectively controlled in accordance with the particular shift condition initiated and based on a previous transmission operating condition. The control unit provides for a predetermined pressure rate of rise signal to the pressure regulator valve based on the selected shift condition and the previous operating condition of the transmission.

Abstract: In a control apparatus, for a vehicle having a transmission and brake means wherein hydraulic passage means connects a source of fluid pressure to a fluid actuated clutch, an improved inching valve interposed in said passage means for selectively reducing the hydraulic pressure supplied to the clutch in proportion to the degree of actuation of the brake means in two successive stages wherein there is no direct initial mechanical connection between the inching valve spool and its actuating means whereby in the first stage of operation the solely hydraulical connection between the actuating means and the spool member positively restricts the operation of the improved inching valve to pressures below the maximum desired clutch slip pressure and wherein during the second stage of operation, the clutch pressure is further reduced to a minimum slip pressure.

Abstract: A fluid pressure regulating apparatus in which a conduit means connects a source of pressure fluid to a fluid pressure operated clutch for actuating the latter and in which a valve means is interposed for controlling the pressure of fluid passing therethrough in such a manner so that the fluid pressure increases from a minimum to a maximum value within a predetermined interval of time initially at the same rate as the source pressure, then at a lesser rate than the source pressure, and finally again at the same rate as the source pressure to assure shock free engagement of the clutch.

Abstract: An improved differential pressure regulator valve for a hydrostatic transmission control system wherein the valve regulates high fluid pressure versus low fluid pressure and produces a pressure differential that in turn controls the transmission. The regulator valve includes a valve body whose bore is in communication with both first and second sets of fluid inlet and outlet ports, with the valve bore containing a spool assembly that includes first and second cooperating spool members, with the second spool member being operable to control the fluid flow between the first inlet and outlet ports or the second inlet port and the first outlet port. Means, including a passage connecting the first outlet port with a spool port, fluidly unbalances the second spool member by applying the pressure of fluid in the first outlet port to one end of the second spool member in opposition to the biasing action of a regulating spring.

Abstract: An improvement in a control system, including a brake device, for a vehicle having a hydrostatic transmission which includes a hydrostatic pump and a hydrostatic motor. The hydraulic control circuit includes a control pump, a high pressure conduit, a low pressure conduit, differential pressure regulator valve means and a directional control valve means interposed in the high and low pressure conduits and a fixed orifice means interposed in the low pressure conduit upstream from the differential pressure regulator valve. The improvement takes the form of an adjustable orifice means interposed in a branch conduit, between the high and low pressure control conduits downstream from the fixed orifice means, with the adjustable orifice means permitting the adjustment of the pressure differential between the high and low pressure control conduits.