Fluid pressure control system for a compound transmission comprising an adjustable hydrostatic transmission part and a secondary mechanical load change-over transmission

Claim 1

A control for a compound transmission of the kind comprising an adjustable hydrostatic transmission part and a secondary mechanical load changeover gear part, and in which the pump and/or the hydromotor of the hydrostatic transmission part is adjusted by a displacement volume adjusting member by means of a control oil pressure which is variable by the control, and the control clutches of the load changeover transmission part are actuated against spring forces by means of a shift control unit with shift oil pressure which can be turned on or off, and the control comprises an adjustable throttle point for adjusting the control oil pressure, said control comprising, a shift control unit having a slide piston moveable within the shift control unit to control the flow of the shift oil to the control clutches of the mechanical load changeover gear part, shift oil conduits for conducting oil from the shift control unit to the control clutches, a throttle sliDe control unit having, two fixed abutments, first and second moveable members which are moveable relative to each other and in relation to the two fixed abutments and which are effective to form an adjustable throttle point between the two members. the first moveable member delimiting two pressure chambers in coaction with the two fixed abutments, each pressure chamber being connected with one of the shift oil conduits of the control clutches for the load change-over gear, and wherein, when one of the pressure chambers is supplied with pressure, said first moveable member abuts against one of the fixed abutments to determine its starting position in the adjustable throttle point for subsequent adjustment of the control oil pressure which determines the displacement volume of the hydrostatic transmission part, and wherein the second moveable member is adjustable from the outside and is coupled with the slide piston of the shift control unit for the control clutches so that adjustment of the second moveable member to displace the slide piston and produce a speed shift of the mechanical gear part simultaneously adjusts the throttle point to vary the displacement of the hydrostatic transmission part in reverse ratio to the transmission jump caused by the mechanical gear shift.