Hydrostatic transmission drive system

Claim 1

An apparatus comprising a hydrostatic transmission, said hydrostatic transmission including a pump unit, a motor unit adapted to be connected with an output member, and first conduit means having one passage for conducting relatively high pressure fluid from said pump unit to said motor unit and another passage for conducting relatively low pressure fluid from said motor unit to said pump unit, charge pump means for supplying fluid to said hydrostatic transmission, actuator means for varying the effective displacement of at least one of said units of said hydrostatic transmission to vary the speed at which the output member is driven by said motor unit, said actuator means including pressure responsive motor means for effecting a variation in the displacement of said one unit in response to a variation in control fluid pressure, second conduit means for conducting control fluid pressure to said motor means, pressure controller means for varying the control fluid pressure conducted to said motor means to vary the speed at which the output member is driven by said first motor unit, said pressure controller means being operable from a neutral setting in which said motor unit is substantially ineffective to drive the output member to any one of a plurality of operating settings in each of which said pressure controller means is effective to port a different fluid pressure to said motor means, and control means for varying the control fluid pressure ported to said motor means in response to a decrease in the fluid pressure output of said charge pump means while maintaining the setting of said pressure controller means substantially constant to effect a reduction in the speed at which said output member is driven, said control means including pressure responsive valve means for decreasing the relatively high fluid pressure in said one passage in response to a decrease in the charge pressure during operation of said hydrostatic transmission, said valve means including a valve operable from a closed condition to an open condition enabling relatively high pressure fluid to flow from said one passage and means for effecting operation of said valve from the closed condition to the open condition in response to a decrease in the charge pressure.

Claim 2

An apparatus comprising a hydrostatic transmission, said hydrostatic transmission including a pump unit, a motor unit adapted to be connected with an output member, and first conduit means having one passage for conducting relatively high pressure fluid from said pump unit to said motor unit and another passage for conducting relatively low pressure fluid from said motor unit to said pump unit, charge pump means for supplying fluid to said hydrostatic transmission, actuator means for varying the effective displacement of at least one of said units of said hydrostatic transmission to vary the speed at which the output member is driven by said motor unit, said actuator means including pressure responsive motor means for effecting a variation in the displacement of said one unit in response to a variation in control fluid pressure, second conduit means for conducting control fluid pressure to said motor means, pressure controller means for varying the control fluid pressure conducted to said motor means to vary the speed at which the output member is driven by said first motor unit, said pressure controller means being operable from a neutral setting in which said motor unit is substantially ineffective to drive the output member to any one of a plurality of operating settings in each of which said pressure controller means is effective to port a different fluid pressure to said motor means, and control means for varying the control fluid pressure ported to said motor means in response to a decrease in the fluid pressure output of said charge pump means while maintaining the setting of said pressure controller means substantially constant to effect a reduction in the speed at which said output member is driven, said control means including pressure responsive valve means for decreasing the relatively high fluid pressure in said one passage in response to a decrease in the charge pressure during operation of said hydrostatic transmission, said valve means including a valve operable from a closed condition to an open condition enabling relatively high pressure fluid to flow from said one passage and means for effecting operation of said valve from the closed condition to the open condition in response to a decrease in the charge pressure.

Claim 3

An apparatus comprising a hydrostatic transmission, said hydrostatic transmission including a pump unit, a motor unit adapted to be connected with an output member, and first conduit means for conducting fluid from said pump unit to said motor unit, charge pump means for supplying fluid to said hydrostatic transmission, actuator means for varying the effective displacement of at least one of said units of said hydrostatic transmission to vary the speed at which the output member is driven by said motor unit, said actuator means including pressure responsive motor means for effecting a variation in the displacement of said one unit in response to a variation in control fluid pressure, second conduit means for conducting control fluid pressure to said motor means, pressure controller means for varying the control fluid pressure conducted to said motor means to vary the speed at which the output member is driven by said first motor unit, said pressure controller means being operable from a neutral setting in which said motor unit is substantially ineffective to drive the output member to any one of a plurality of operating settings in each of which said pressure controller means is effective to port a different fluid pressure to said motor means, control means for varying the control fluid pressure ported to said motor means in response to a decrease in the fluid pressure output of said charge pump means while maintaining the setting of said pressure controller means substantially constant to effect a reduction in the speed at which said output member is driven, and brake means operable between a release condition and an activated condition in which said brake means retards movement of a vehicle associated with said hydrostatic transmission, said control means including means for effecting operation of said brake means from the release condition to the activated condition in response to a decrease in the fluid pressure output of said charge pump means.

Claim 4

An apparatus comprising a hydrostatic transmission, said hydrostatic transmission including a pump unit, a motor unit adapted to be connected with an output member, and first conduit means for conducting fluid from said pump unit to said motor unit, charge pump means for supplying fluid to said hydrostatic transmission, actuator means for varying the effective displacement of at least one of said units of said hydrostatic transmission to vary the speed at which the output member is driven by said motor unit, said actuator means including pressure responsive motor means for effecting a variation in the displacement of said one unit in response to a variation in control fluid pressure, second conduit means for conducting control fluid pressure to said motor means, pressure controller means for varying the control fluid pressure conducted to said motor means to vary the speed at which the output member is driven by said first motor unit, said pressure controller means being operable from a neutral setting in which said motor unit is substantially ineffective to drive the output member to any one of a plurality of operating settings in each of which said pressure controller means is effective to port a different fluid pressure to said motor means, control means for varying the control fluid pressure ported to said motor means in response to a decrease in the fluid pressure output of said charge pump means while maintaining the setting of said pressure controller means substantially constant to effect a reduction in the speed at which said output member is driven, and brake means operable between a release condition and an activated condition in which said brake means retards movement of a vehicle associated with said hydrostatic transmission, said control means including means for effecting operation of said brake means from the release condition to the activated condition in response to a decrease in the fluid pressure output of said charge pump means.

Claim 5

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, said first hydrostatic transmission including a first pump unit adapted to be driven by the engine, a first motor unit adapted to be drivingly connected with the first output member, first conduit means for conducting fluid under pressure from said first pump unit to said first motor unit to effect operation of said first motor unit to drive the first output member, and second conduit means for conducting fluid to said first pump unit, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, said second hydrostatic transmission including a second pump unit adapted to be driven by the engine, a second motor unit adapted to be drivingly connected with the second output member, third conduit means for conducting fluid under pressure from said second pump unit to said second motor unit to effect operation of said second motor unit to drive said second output member, and fourth conduit means for conducting fluid to said second pump unit, a first charge pump adapted to be driven by the engine, fifth conduit means for connecting said first charge pump in fluid communication with said second conduit means to enable said first charge pump to supply fluid to said second conduit means during operation of said first hydrostatic transmission, a second charge pump adapted to be driven by the engine, sixth conduit means for connecting said second charge pump in fluid communication with said fourth conduit means to enable said second charge pump to supply fluid to said fourth conduit means during operation of said second hydrostatic transmission, and control means for effecting a decrease in the speeds at which both the first and second output members are driven by said first and second hydrostatic transmissions in response to a decrease in the fluid pressure output of either one of said charge pumps.

Claim 6

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, said first hydrostatic transmission including a first pump unit adapted to be driven by the engine, a first motor unit adapted to be drivingly connected with the first output member, first conduit means for conducting fluid under pressure from said first pump unit to said first motor unit to effect operation of said first motor unit to drive the first output member, and second conduit means for conducting fluid to said first pump unit, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, said second hydrostatic transmission including a second pump unit adapted to be driven by the engine, a second motor unit adapted to be drivingly connected with the second output member, third conduit means for conducting fluid under pressure from said second pump unit to said second motor unit to effect operation of said second motor unit to drive said second output member, and fourth conduit means for conducting fluid to said second pump unit, a first charge pump adapted to be driven by the engine, fifth conduit means for connecting said first charge pump in fluid communication with said second conduit means to enable said first charge pump to supply fluid to said second conduit means during operation of said first hydrostatic transmission, a second charge pump adapted to be driven by the engine, sixth conduit means for connecting said second charge pump in fluid communication with said fourth conduit means to enable said second charge pump to supply fluid to said fourth conduit means during operation of said second hydrostatic transmission, and control means for effecting a decrease in the speeds at which both the first and second output members are driven by said first and second hydrostatic transmissions in response to a decrease in the fluid pressure output of either one of said charge pumps.

Claim 12

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, said first hydrostatic transmission including a first pump unit adapted to be driven by the engine, a first motor unit adapted to be drivingly connected with the first output member, first conduit means for conducting fluid under pressure from said first pump unit to said first motor unit to effect operation of said first motor unit to drive the first output member, and second conduit means for conducting fluid to said first pump unit, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, said second hydrostatic transmission including a second pump unit adapted to be driven by the engine, a second motor unit adapted to be drivingly connected with the second output member, third conduit means for conducting fluid under pressure from said second pump unit to said second motor unit to effect operation of said second motor unit to drive said second output member, and fourth conduit means for conducting fluid to said second pump unit, first actuator means for varying the displacement of at least one of said first pump and motor units to vary the speed at which the first output member is driven by said first motor unit during operation of said first hydrostatic transmission, second actuator means for varying the displacement of at least one of said second pump and motor units to vary the speed at which the second output member is driven by said second motor unit during operation of said second hydrostatic transmission, brake means operable between a disengaged condition and an engaged condition in which said brake means is effective to retard movement of a vehicle with which said first and second hydrostatic transmissions are associated, and control means for effecting operation of said brake means from the disengaged condition to the engaged condition and for contemporaneously therewith effecting operation of said first and second actuator means to reduce the speed at which the first and second output members are driven by said first and second motor units.

Claim 13

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, said first hydrostatic transmission including a first pump unit adapted to be driven by the engine, a first motor unit adapted to be drivingly connected with the first output member, first conduit means for conducting fluid under pressure from said first pump unit to said first motor unit to effect operation of said first motor unit to drive the first output member, and second conduit means for conducting fluid to said first pump unit, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, said second hydrostatic transmission including a second pump unit adapted to be driven by the engine, a second motor unit adapted to be drivingly connected with the second output member, third conduit means for conducting fluid under pressure from said second pump unit to said second motor unit to effect operation of said second motor unit to drive said second output member, and fourth conduit means for conducting fluid to said second pump unit, first actuator means for varying the displacement of at least one of said first pump and motor units to vary the speed at which the first output member is driven by said first motor unit during operation of said first hydrostatic transmission, second actuator means for varying the displacement of at least one of said second pump and motor units to vary the speed at which the second output member is driven by said second motor unit during operation of said second hydrostatic transmission, brake means operable between a disengaged condition and an engaged condition in which said brake means is effective to retard movement of a vehicle with which said first and second hydrostatic transmissions are associated, and control means for effecting operation of said brake means from the disengaged condition to the engaged condition and for contemporaneously therewith effecting operation of said first and second actuator means to reduce the speed at which the first and second output members are driven by said first and second motor units.

Claim 19

An apparatus comprising a hydrostatic transmission having a pump unit adapted to be driven by an input member, a motor unit adapted to be connected with an output member, said motor unit including a swashplate movable between a first position in which said motor unit has a relatively large displacement and a second position in which said motor unit has a relatively small displacement, and hydrostatic loop means for conducting fluid between said pump and motor units during operation of said hydrostatic transmission, said hydrostatic loop means including first conduit means for conducting relatively high pressure fluid from said pump unit to said motor unit during operation of said hydrostatic transmission and second conduit means for conducting relatively low pressure fluid from said motor unit to said pump unit during operation of said hydrostatic transmission, swashplate motor means for moving said swashplate between said first and second positions, motor control valve means operable from a first condition to a second condition to effect operation of said swashplate motor means to move said swashplate between the first and second positions to thereby vary the displacement of said motor unit, third conduit means for conducting relatively low pressure fluid from said second conduit means to said motor control valve means, said motor control valve means being operable to port relatively low pressure fluid from said second conduit means to said swashplate motor means upon operation of said motor control valve means from the first condition to the second condition to thereby effect operation of said swashplate motor means under the influence of the relatively low pressure fluid, and control means for effecting operation of said motor control valve means between the first and second positions.

Claim 20

An apparatus comprising a hydrostatic transmission having a pump unit adapted to be driven by an input member, a motor unit adapted to be connected with an output member, said motor unit including a swashplate movable between a first position in which said motor unit has a relatively large displacement and a second position in which said motor unit has a relatively small displacement, and hydrostatic loop means for conducting fluid between said pump and motor units during operation of said hydrostatic transmission, said hydrostatic loop means including first conduit means for conducting relatively high pressure fluid from said pump unit to said motor unit during operation of said hydrostatic transmission and second conduit means for conducting relatively low pressure fluid from said motor unit to said pump unit during operation of said hydrostatic transmission, swashplate motor means for moving said swashplate between said first and second positions, motor control valve means operable from a first condition to a second condition to effect operation of said swashplate motor means to move said swashplate between the first and second positions to thereby vary the displacement of said motor unit, third conduit means for conducting relatively low pressure fluid from said second conduit means to said motor control valve means, said motor control valve means being operable to port relatively low pressure fluid from said second conduit means to said swashplate motor means upon operation of said motor control valve means from the first condition to the second condition to thereby effect operation of said swashplate motor means under the influence of the relatively low pressure fluid, and control means for effecting operation of said motor control valve means between the first and second positions.

Claim 22

An apparatus comprising a reversible hydrostatic transmission capable of driving an output member in either one of two directions, said hydrostatic transmission comprising a pump unit adapted to be driven by an output member, said pump unit including a swashplate movable between a forward actuated position and a reverse actuated positions, a motor unit adapted to be connected with the output member, said motor unit including a swashplate movable between a first position in which said motor unit has a relatively large displacement and a second position in which said motor unit has a relatively small displacement, and hydrostatic loop means for conducting fluid between said pump and motor units during operation of said hydrostatic transmission to drive the output member in either one of the two directions, said hydrostatic loop means including first conduit means for conducting relatively high pressure fluid from said pump unit to said motor unit during operation of said hydrostatic transmission to drive the output member in a first one of the two directions and for conducting relatively low pressure fluid from said motor unit to said pump unit during operation of said hydrostatic transmission to drive the output member in a second one of the two directions and second conduit means for conducting relatively low pressure fluid from said motor unit to said pump unit during operation of said hydrostatic transmission to drive the output member in the first direction and for conducting relatively high pressure fluid from said pump unit to said motor unit during operation of said hydrostatic transmission to drive the output member in the second direction, swashplate motor means for moving said motor unit swashplate between said first and second positions, motor control valve means operable from a first condition to a second condition to effect operation of said swashplate motor means to move said motor unit swashplate between the first and second positions to thereby vary the displacement of said motor unit, third conduit means for conducting relatively low pressure fluid from said second conduit means to said motor control valve means during operation of said hydrostatic transmission to drive the output member in the first direction and for conducting relatively low pressure fluid from said first conduit means to said motor control valve means during operation of said hydrostatic transmission to drive the output member in the second direction, and control means for effecting operation of said motor control valve means between the first and second positions.

Claim 23

An apparatus comprising a reversible hydrostatic transmission capable of driving an output member in either one of two directions, said hydrostatic transmission comprising a pump unit adapted to be driven by an output member, said pump unit including a swashplate movable between a forward actuated position and a reverse actuated positions, a motor unit adapted to be connected with the output member, said motor unit including a swashplate movable between a first position in which said motor unit has a relatively large displacement and a second position in which said motor unit has a relatively small displacement, and hydrostatic loop means for conducting fluid between said pump and motor units during operation of said hydrostatic transmission to drive the output member in either one of the two directions, said hydrostatic loop means including first conduit means for conducting relatively high pressure fluid from said pump unit to said motor unit during operation of said hydrostatic transmission to drive the output member in a first one of the two directions and for conducting relatively low pressure fluid from said motor unit to said pump unit during operation of said hydrostatic transmission to drive the output member in a second one of the two directions and second conduit means for conducting relatively low pressure fluid from said motor unit to said pump unit during operation of said hydrostatic transmission to drive the output member in the first direction and for conducting relatively high pressure fluid from said pump unit to said motor unit during operation of said hydrostatic transmission to drive the output member in the second direction, swashplate motor means for moving said motor unit swashplate between said first and second positions, motor control valve means operable from a first condition to a second condition to effect operation of said swashplate motor means to move said motor unit swashplate between the first and second positions to thereby vary the displacement of said motor unit, third conduit means for conducting relatively low pressure fluid from said second conduit means to said motor control valve means during operation of said hydrostatic transmission to drive the output member in the first direction and for conducting relatively low pressure fluid from said first conduit means to said motor control valve means during operation of said hydrostatic transmission to drive the output member in the second direction, and control means for effecting operation of said motor control valve means between the first and second positions.

Claim 26

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, said first hydrostatic transmission including a first pump unit adapted to be driven by the engine, a first motor unit adapted to be drivingly connected with the first output member, first conduit means for conducting fluid under pressure from said first pump unit to said first motor unit to effect operation of said first motor unit to drive the first output member, and second conduit means for conducting fluid to said first pump unit, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, said second hydrostatic transmission including a second pump unit adapted to be driven by the engine, a second motor unit adapted to be drivingly connected with the second output member, third conduit means for conducting fluid under pressure from said second pump unit to said second motor unit to effect operation of said second motor unit to drive said second output member, and fourth conduit means for conducting fluid to said second pump unit, first actuator means for varying the displacement of at least one of said first pump and motor units to vary the speed at which the first output member is driven by said first motor unit during operation of said first hydrostatic transmission, second actuator means for varying the displacement of at least one of said second pump and motor units to vary the speed at which the second output member is driven by said second motor unit during operation of said second hydrostatic transmission, brake means operable between a disengaged condition and an engaged condition in which said brake means is effective to retard movement of a vehicle with which said first and second hydrostatic transmissions are associated, the control means for effecting operation of said brake means from the disengaged condition to the engaged condition and for contemporaneously therewith effecting operation of said first and second actuator means to reduce the speed at which the first and second output members are driven by said first and second motor units, said first and second pump units each include a movable swashplate, said first and second actuator means each including pump actuator means for varying the displacement of the associated one of said pump units by moving the associated one of said swashplates, each of said pump actuator means including primary motor means for moving the associated one of said swashplates from an initial position, a pilot valve operable between a null position and any one of a plurality of positions enabling fluid to flow from a source of fluid to said primary motor means to effect operation of said primary motor means and movement of the associated one of said swashplates, reversible secondary motor means for operating said pilot valve between the null and actuated positions, said secondary motor means being operable from an initial position in response to variations in control fluid pressure conducted to said secondary motor means, feedback means for operating said pilot valve from any one of the plurality of actuated positions to the null position in response to movement of the associated one of said swashplates by said primary motor means to an extent which is a function of the extent of operation of said secondary motor means, and pressure controller means for varying the control fluid pressure conducted to said first and second actuator means as a function of the extent of operation of said pressure controller means from an initial condition, said pressure controller means being operable to vary the control fluid pressure conducted to said secondary motor means in each of said pump actuator means as a function of the extent of operation of said pressure controller means from the initial condition to control the extent to which the swashplates of said first and second pump units are moved.

Claim 27

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, said first hydrostatic transmission including a first pump unit adapted to be driven by the engine, a first motor unit adapted to be drivingly connected with the first output member, first conduit means for conducting fluid under pressure from said first pump unit to said first motor unit to effect operation of said first motor unit to drive the first output member, and second conduit means for conducting fluid to said first pump unit, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, said second hydrostatic transmission including a second pump unit adapted to be driven by the engine, a second motor unit adapted to be drivingly connected with the second output member, third conduit means for conducting fluid under pressure from said second pump unit to said second motor unit to effect operation of said second motor unit to drive said second output member, and fourth conduit means for conducting fluid to said second pump unit, first actuator means for varying the displacement of at least one of said first pump and motor units to vary the speed at which the first output member is driven by said first motor unit during operation of said first hydrostatic transmission, second actuator means for varying the displacement of at least one of said second pump and motor units to vary the speed at which the second output member is driven by said second motor unit during operation of said second hydrostatic transmission, brake means operable between a disengaged condition and an engaged condition in which said brake means is effective to retard movement of a vehicle with which said first and second hydrostatic transmissions are associated, the control means for effecting operation of said brake means from the disengaged condition to the engaged condition and for contemporaneously therewith effecting operation of said first and second actuator means to reduce the speed at which the first and second output members are driven by said first and second motor units, said first and second pump units each include a movable swashplate, said first and second actuator means each including pump actuator means for varying the displacement of the associated one of said pump units by moving the associated one of said swashplates, each of said pump actuator means including primary motor means for moving the associated one of said swashplates from an initial position, a pilot valve operable between a null position and any one of a plurality of positions enabling fluid to flow from a source of fluid to said primary motor means to effect operation of said primary motor means and movement of the associated one of said swashplates, reversible secondary motor means for operating said pilot valve between the null and actuated positions, said secondary motor means being operable from an initial position in response to variations in control fluid pressure conducted to said secondary motor means, feedback means for operating said pilot valve from any one of the plurality of actuated positions to the null position in response to movement of the associated one of said swashplates by said primary motor means to an extent which is a function of the extent of operation of said secondary motor means, and pressure controller means for varying the control fluid pressure conducted to said first and second actuator means as a function of the extent of operation of said pressure controller means from an initial condition, said pressure controller means being operable to vary the control fluid pressure conducted to said secondary motor means in each of said pump actuator means as a function of the extent of operation of said pressure controller means from the initial condition to control the extent to which the swashplates of said first and second pump units are moved.

Claim 28

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission having a pump unit adapted to be driven by the engine and a motor unit for transmitting drive forces to the first output member, a second hydrostatic transmission having a pump unit adapted to be driven by the engine and a motor unit for transmitting drive forces to the second output member, a first charge pump adapted to be driven by the engine, first conduit means for connecting said first charge pump in fluid communication with said first hydrostatic transmission, a second charge pump adapted to be driven by the engine, second conduit means for connecting said second charge pump in fluid communication with said second hydrostatic transmission, and control means for effecting a decrease in the speeds at which both the first and second output members are driven by said first and second hydrostatic transmissions in response to a decrease in the fluid pressure in either said first or said second conduits.

Claim 29

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission having a pump unit adapted to be driven by the engine and a motor unit for transmitting drive forces to the first output member, a second hydrostatic transmission having a pump unit adapted to be driven by the engine and a motor unit for transmitting drive forces to the second output member, a first charge pump adapted to be driven by the engine, first conduit means for connecting said first charge pump in fluid communication with said first hydrostatic transmission, a second charge pump adapted to be driven by the engine, second conduit means for connecting said second charge pump in fluid communication with said second hydrostatic transmission, and control means for effecting a decrease in the speeds at which both the first and second output members are driven by said first and second hydrostatic transmissions in response to a decrease in the fluid pressure in either said first or said second conduits.

Claim 32

An apparatus for use in transmitting drive forces from an engine to first and second output members used to propel a vehicle, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, a first charge pump adapted to be driven by the engine, first conduit means for connecting said first charge pump in fluid communication with said first hydrostatic transmission, a second charge pump adapted to be driven by the engine, second conduit means for connecting said second charge pump in fluid communication with said second hydrostatic transmission, brake means operable between a release condition and an activated condition in which said brake means is capable of retarding movement of the vehicle independent of said first and second hydrostatic transmissions, and means for effecting operation of said brake means from the release condition to the activated condition in response to a decrease in the fluid pressure in either one of said first or second conduits.

Claim 33

An apparatus for use in transmitting drive forces from an engine to first and second output members used to propel a vehicle, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, a first charge pump adapted to be driven by the engine, first conduit means for connecting said first charge pump in fluid communication with said first hydrostatic transmission, a second charge pump adapted to be driven by the engine, second conduit means for connecting said second charge pump in fluid communication with said second hydrostatic transmission, brake means operable between a release condition and an activated condition in which said brake means is capable of retarding movement of the vehicle independent of said first and second hydrostatic transmissions, and means for effecting operation of said brake means from the release condition to the activated condition in response to a decrease in the fluid pressure in either one of said first or second conduits.

Claim 36

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, a first charge pump adapted to be driven by the engine, first conduit means for connecting said first charge pump in fluid communication with said first hydrostatic transmission, a second charge pump adapted to be driven by the engine, second conduit means for connecting said second charge pump in fluid communication with said second hydrostatic transmission, first actuator means for varying the speed at which the first output member is driven by said first hydrostatic transmissions, second actuator means for varying the speed at which the second output member is driven by said second hydrostatic transmission, and means for effecting operation of both said first and second actuator means to reduce the speeds at which both the first and second output members are driven in response to a decrease in the fluid pressure output of either one of said charge pumps.

Claim 37

An apparatus for use in transmitting drive forces from an engine to first and second output members, said apparatus comprising a first hydrostatic transmission for transmitting drive forces from the engine to the first output member, a second hydrostatic transmission for transmitting drive forces from the engine to the second output member, a first charge pump adapted to be driven by the engine, first conduit means for connecting said first charge pump in fluid communication with said first hydrostatic transmission, a second charge pump adapted to be driven by the engine, second conduit means for connecting said second charge pump in fluid communication with said second hydrostatic transmission, first actuator means for varying the speed at which the first output member is driven by said first hydrostatic transmissions, second actuator means for varying the speed at which the second output member is driven by said second hydrostatic transmission, and means for effecting operation of both said first and second actuator means to reduce the speeds at which both the first and second output members are driven in response to a decrease in the fluid pressure output of either one of said charge pumps.

Claim 38

An apparatus comprising a hydrostatic transmission, said hydrostatic transmission including a pump unit, a motor unit adapted to be connected with an output member, and first conduit means for connecting said pump unit in fluid communication with said motor unit, fluid actuator means for varying the effective displacement of at least one of said units of said hydrostatic transmission to vary the speed at which the output member is driven by said motor unit, brake means separate from said hydrostatic transmission and operable between a disengaged condition and an engaged condition in which said brake means is effective to retard movement of a vehicle with which said hydrostatic transmission is associated, and fluid control means for effecting operation of said brake means from the disengaged condition to the engaged condition and for contemporaneously therewith effecting operation of said fluid actuator means to reduce the speed at which the output member is driven by said motor unit.

Claim 39

An apparatus comprising a hydrostatic transmission, said hydrostatic transmission including a pump unit, a motor unit adapted to be connected with an output member, and first conduit means for connecting said pump unit in fluid communication with said motor unit, fluid actuator means for varying the effective displacement of at least one of said units of said hydrostatic transmission to vary the speed at which the output member is driven by said motor unit, brake means separate from said hydrostatic transmission and operable between a disengaged condition and an engaged condition in which said brake means is effective to retard movement of a vehicle with which said hydrostatic transmission is associated, and fluid control means for effecting operation of said brake means from the disengaged condition to the engaged condition and for contemporaneously therewith effecting operation of said fluid actuator means to reduce the speed at which the output member is driven by said motor unit.