Abstract: A hydraulic system is disclosed for use in an automotive vehicle including an engine, a power steering gear, and a brake booster. The system includes a single engine driven pump in fluid communication with first and second fluid flow control means. The first fluid flow control means responsive to fluid inputs for discharging a small or large predetermined amount of hydraulic fluid to control the operation of the power steering gear. The second fluid flow control means supplies a constant amount of hydraulic fluid to control the operation of the brake booster.

Abstract: An agricultural harvesting combine is provided with a hydraulically positioned reel at the forward end of the combine. One single acting hydraulic cylinder is carried at each end of the reel. Hydraulic fluid is supplied to the cylinders through a rotary flow divider to cause each cylinder to synchronously be displaced to raise both ends of the reel in unison.

Abstract: The disclosure relates to improvements in a hydraulically-actuated control device used in an operation unit of treatment chair and the like in an interlocking relation with reciprocating movement of a hydraulic piston. The device is of the construction in which two control valves slow in closing and opening operation are disposed in the oil supply and discharge passages leading to a hydraulic cylinder having a hydraulic piston therein so as to prevent shock in starting and stopping of the operation unit by controlling opening and closing of the two control valves and operation of the hydraulic pump disposed in the oil supply passage.

Abstract: A hydrostatic drive system having a closed loop front wheel drive circuit and a closed loop rear wheel drive circuit. A variable displacement pump in each of the circuits is cammed to vary the displacement delivered to dual displacement wheel motors to provide two speed ranges for the drive system. A servosystem uses hydraulic fluid to cam the displacement of the variable displacement pump and a hydraulic control to selectively engage each of the drive ranges.

Abstract: A vehicle propulsion system is provided with an auxiliary hydraulic drive having a variable displacement motor connected to ground engaging wheels by a clutch. A multiple position control has a first position which causes clutch engagement and positions a motor displacement member in a position which permits fluid drive of the motor. The control has a second position which causes clutch disengagement and positions the motor displacement member in a zero displacement condition which prevents fluid drive of the motor. Preferably the control is responsive to motor output speed and reduces motor displacement as speed increases.

Abstract: A control for a variable displacement motor which utilizes a motor speed sensitive signal for moving the displacement of the motor toward a zero displacement setting position including a device for generating a conditioned variable signal representative of motor speed, circuitry for receiving said signal and upon the signal reaching a predetermined intermediate value applying the signal to the control device for motor displacement for causing reduction in motor displacement and with various devices in the circuit for modifying the variable signal to provide a desired relation between motor speed and motor displacement. Utilization of such controls individually associated with plural variable displacement motors driving vehicle wheels and driven by one pump protects against spin-out of one of the wheels.

Abstract: A steering system includes load-responsive valving which automatically routes pressure fluid to one of a pair of double-acting hydraulic actuators when steering resistance is low and which automatically routes pressure fluid to both of the actuators when the steering resistance is high.

Abstract: A control system for a hydraulic actuator comprising a first pump with large displacement capacity, a second pump with small displacement capacity, a pilot pump, a first pilot operated spring centered control valve connected at the input side thereof to the first pump, the output side of which is selectively connected to the hydraulic actuator and drain, a second pilot operated spring centered control valve connected at the input side thereof to the second pump, the output side of which is selectively connected to the hydraulic actuator and drain, and a third control valve for pilot pressure connected at the input side thereof to the pilot pump, the output side of which is connected to the first and second control valves wherein the second control valve is adapted to be actuated by a pilot pressure lower than a pilot pressure which actuates the first control valve.

Abstract: A working vehicle according to this invention comprises right and left traveling members (1a, 1b) adapted to be driven and stopped individually or simultaneously to effect traveling and turning round of the vehicle, a traveling speed changing mechanism (8) for providing a high speed drive and a low speed drive and including an operator member (8a), and a switch mechanism (13) adapted to automatically and reversibly switch the traveling speed changing mechanism (8) from a position to provide the high speed drive to a position to provide the low speed drive when the vehicle traveling straight turns round.

Abstract: An implement having a rotary flow divider controlling fluid to and from at least two independent hydraulic rams for raising and lowering the implement in a level manner. A counter monitors the revolutions of the flow divider and actuates an electric circuit which controls solenoid valves to stop the implement at the proper height. A cab mounted adjustable count selector is provided to adjust the desired height of the implement.

Abstract: A fluid motor control system (11) assures that automatic changes of motor displacement, which are initiated by occurrence of a predetermined operational condition in the system (11), result in a change of motor speed of the desired magnitude. Flow adjustment elements (76) respond to a displacement increase by reducing the flow of working fluid available to the motor or motors (12, 13) and respond to a motor displacement reduction by increasing the available flow. In one specific form, the system (11) controls a pair of right and left side vehicle drive motors (12, 13) and automatically increases motor displacements while reducing the fluid flow supplied to the motors (12, 13) to reduce travel speed during a turn of travel direction.

Abstract: A multi-segment farm implement flexible tool bar or frame is provided with a hydraulic system including a rotary flow divider for raising and lowering each segment of the sectional frame in synchronous movement with the other sections. A mechanical linkage associated with a ground wheel positioning cylinder also activates the hydraulic fluid control system limiting the downward movement of the implement mounted to the sectional frame on its supporting gear.

Abstract: A vacuum supply system for automotive vehicles having vacuum powered accessories and driven by an engine with an air intake system in which vacuum is developed that may be inadequate to operate the accessories under some conditions. A vacuum pump, which may be engine driven, is connected between the engine and the accessories to supplement the operating vacuum. Flow limiting orifices in a junction connecting with secondary accessories provide for continued operation of a primary accessory such as a vacuum brake booster in spite of the disconnection of a vacuum hose or other massive air leak in one of the secondary accessory lines.

Abstract: A number of systems exist wherein a plurality of hydraulic motors (28a, 28b, 28c) receive pressurized fluid from a single pump (14) which is itself driven by an electric motor (12). Apparatus has been available for adjusting the power supplied to the electric motor (12), and thereby adjusting the pump (14) flow rate, in response to the operator activating one or more of the hydraulic motors (28a, 28b, 28c). However, such apparatus has generally been bulky, complicated and/or difficult to install and/or service. An improvement is provided wherein a single switch (22) is placed in either an open or closed position as an elongated member (34) placed transversely to a plurality of generally parallel rod member (20a, 20b, 20c) is rotated in response to longitudinal travel in either direction from a neutral position (32) of one of the rod member (20a, 20b, 20c).

Abstract: An improvement is disclosed in a hydraulic system (10) having a variable displacement pump (12) and being capable of delivering pressurized fluid from the pump (12) to selectively engage at least three work circuits (18) with a first (20) of the circuits (18) being normally operable up to a first pressure and a second (22) of the circuits (18) being normally operable up to a second and lower pressure. The improvement comprises circuitry (80, 92, 94, 98, 108, 120, 122, 124, 126) for selectively operating a third (24) of the circuits (18) at one of the first or second pressures or at an upstaged pressure which exceeds the first pressure and circuitry (128) for reducing the displacement of the pump (12) in response to the third circuit (24) being operated at the upstaged pressure. Such upstaged pressure is available in a controlled manner for working against particularly heavy loads. Thus, a third and higher operating level is added to a system which already operates at at least two pressure levels.

Abstract: A steering circuit for an articulated farm tractor having front and rear frame sections pivotally interconnected with steering cylinders pivotally connected between the frame sections. An open center hydrostatic steering unit selectively directs hydraulic fluid from a pump to the steering cylinders and a pilot-operated, alternating check valve is interposed in the conduit connecting the steering mechanism with the steering cylinders.

Abstract: A hydraulic power and control system which includes a pump which is mounted n a sealed housing. The pump is mounted in the sealed housing along with a pilot operated power valve. The pump has an inlet within the housing for intaking oil therein and is connected to the pilot operated power valve for operating components in a functional system, such as a submersible docking apparatus. The pilot operated power valve discharges oil into the sealed housing and is connected to a control valve which is located exterior of the housing. The control valve will pilot operate the power valve and discharges oil within the sealed housing. The control valve may be mounted within a pressure casing which receives a reduced oil pressure from the pump within the sealed housing. The sealed housing may be pressure compensated to ambient so that the pressure casing is maintained at a specific pressure level above ambient.

Abstract: A vehicle drive system providing abrupt turning capability under control of local or remote steering commands. The vehicle consists of a platform supported by two drive wheels and at least one castor wheel. An engine powers a hydraulic pump which drives two independently controlled hydraulic motors transmitting power to the drive wheels. Hydraulic fluid flows from the pump to the motor and is controlled through a network of valves to provide torque limiting capabilities to the drive wheels which prevents slippage with the ground. Free wheeling capability is also selectively applied during dynamic turning maneuvers to permit minimal energy changes and resulting in a short turning radius.

Abstract: PCT No. PCT/US79/00664 Sec. 371 Date Aug. 30, 1979 Sec. 102(e) Date Aug. 30, 1979 PCT Filed Aug. 30, 1979 PCT Pub. No. WO81/00600 PCT Pub. Date Mar. 5, 1981A lock valve (10) for use in a hydraulic system (90) for positioning the work implement of an earth working machine which includes first and second check valves (28, 30) and a piston section (60, 70, 62, 72) for each operable by pilot fluid. In a first mode, the piston sections (60, 70, 62, 72) permit seating of both check valves, while in a second mode, the piston sections interlock so that only one check valve can seat. The lock valve (10) operates in a hydraulic system (90) to lock a work implement, such as a blade for a motor grader, in a fixed position during a first operating mode, while providing a connection from one end of an implement actuator to vent during a second operating mode to insure that a shock absorbing means for the implement hydraulic system maintains a full shock absorbing capacity.

Abstract: A rotary regenerator is provided with a hydraulic drive system to vary the rotational speed in relation to the temperature scanned. The hydraulic control system provides accurate operation at low rotational speeds.

Abstract: A vehicle is provided with right and left traction drives powered by first and second reversible two-speed hydraulic motors. A solenoid-operated speed control valve is coupled to the motors for shifting the latter to high speed operation in response to the valve being energized. Travel control valves for the motor are coupled to switches connected in the circuitry for controlling the speed control valve such that during high speed operation of the vehicle the motors will be automatically downshifted in response to the travel control valves being operated to cause the vehicle to be turned.

Abstract: The steerable wheels of a hydraulically driven vehicle are provided with fixed displacement type auxiliary motors which are connected in parallel both with each other and with the motor which powers the main drive wheels. A selector valve permits the motors for the steerable wheels to be optionally connected and disconnected from the reversible, variable displacement main pump. Flow dividers in the hydraulic lines limit the maximum flow of fluid to any one auxiliary drive motor. To prevent large power losses when the steerable wheel assist mode is not being utilized, the selector valves are placed in close proximity to each fixed displacement motor. This allows the motors to circulate large quantities of fluid around a closed loop at minimum pressure drop.

Abstract: The steerable wheels of a hydraulically driven vehicle are provided with auxiliary motors which are connected in parallel both with each other and with the motor which powers the main drive wheels. A selector valve permits the motors for the steerable wheels to be optionally connected and disconnected from the reversible, variable displacement main pump. Flow dividers in the hydraulic lines limit the maximum flow of fluid to any one hydraulic motor. The auxiliary motors are of the variable displacement type, enabling them to be destroked to neutral when disconnected from the main pump. Destroking to neutral eliminates energy loss due to the pumping of large quantities of hydraulic fluid through a closed loop when the motors are driven by the wheels.

Abstract: A hydraulic synchronous driving mechanism provided with at least two piston-cylinder assemblies, each having a bottom chamber and a ring chamber and the piston rods of which engage a counterdevice adapted to synchronously load piston rods mutually in opposite directions, a hydraulic fluid circuit provided with at least a pump and a reservoir, whereby there are pair-wise arranged volumetric pump-motors in fluid lines throughconnected to the bottom chamber of the one cylinder and the ring chamber of the other cylinder, which pump-motors are mutually coupled for a constant supply ratio, while the fluid line sections extending from the pump-motors to the cylinders are throughconnected to only one cylinder chamber.

Abstract: The invention relates to cranes or the like in which two hoist lines control a clamshell bucket. If the winch for one line is operated to draw in this line, it closes the clamshell bucket and hoists it. During this hoisting, the winch for the other line must also be operated to pull in the slack. If this other line is reeled in excessively, it will dump the bucket. A system is provided for automatic control of the winch being used for slack-takeup, thus avoiding the need for great care and delicate finesse by an experienced hand on a second control lever. The system puts the slack-takeup winch in hydraulic series or tandem with the discharge from the hoisting winch, but limits the hydraulic pressure supplied to the slack-takeup winch so that it is barely enough to accomplish the takeup of its line, and cannot cause dumping.

Abstract: There is described a servo-control system incorporating a double-acting ram which is responsible for compensating electro-hydraulically for the imbalance in a servo-controlled load in order to achieve a high performance. To this end, a compensating loop is produced which slaves a balancing pressure P.sub.e to the variations in the imbalance. This pressure is exerted in one of the chambers of the ram, separately from the control pressure. It is governed by a pneumatic accumulator whose load is a function of the lack of balance between the pressure exerted by the imbalance and the balancing pressure.

Abstract: In an hydraulic power system for operating a vehicle levelling system and braking system, an accumulator supplies both the levelling system and the braking system. The accumulator is connected indirectly to the braking system through a pressure limiting device, which disconnects the braking system from the accumulator when a predetermined pressure is reached.

Abstract: An apparatus for delivering power to a marine propulsion device comprises an engine, a propeller, and a transmission which operatively connects the engine with the propeller and which is operative between a neutral position and a drive position. The apparatus further includes a source of pressurized fluid, a cylinder and a differential piston movable within the cylinder in response to pressurized fluid. A first conduit continuously conducts pressurized fluid from the source to the cylinder to locate the piston in a first position in the cylinder, and a second conduit conducts pressurized fluid from the source to the cylinder to locate the piston in a second position in the cylinder which second position is spaced from the first position. A flow control device communicates with the second conduit for selectively permitting the flow of pressurized fluid through the second conduit to displace the piston from the first position to the second position.

Abstract: A hydraulic control circuit especially for use with multi-function hydraulic devices, such as for industrial lift truck attachments, in which a combination of valve means are adapted to operate two or more hydraulic systems, the valve system being designed such that a minimum number of hydraulic conduits are required to connect the main hydraulic system to the hydraulic devices, as from a lift truck to an attachment supporting carriage on a lift truck upright, and no electric lines are required to be connected to switching devices between the hydraulic devices, such as to solenoid operated valves.

Abstract: A hydraulic control arrangement for hydraulic consumer includes a multiple position valve having a control slide movable by proportional magnets between a neutral position and a plurality of working positions, in which the magnets may be remote controlled from an analog desired value signal and in which a stop valve is provided in a control circuit leading from the consumer to an over-pressure valve, which in turn is connected, upstream of the multiple position valve, parallel to the consumer between a pressure conduit connected to a source of pressure and a return conduit connected to a tank.

Abstract: Priority valve system with pressure-flow compensation and signal control having first, a restricted orifice which can be satisfied when flow requirements therethrough are sufficiently large in combination with, second, a closed center primary control valve equipped with an hydraulic detent unlatch mechanism and hydraulically disposed downstream of the orifice to receive the flow directed thereto by the orifice, all to provide appropriate signals controlling the priority valve.Through this intervening, novel two component control combination, the priority valve is controlled to supply flow to a priority load and, in addition, has an auxiliary outlet chamber connected to an auxiliary motor with the purpose to cut off the auxiliary chamber flow whenever the priority flow is sufficient to satisfy only the restricted orifice.

Abstract: A hydraulic system having a reservoir fed charge pump supplying pressurized fluid through a charge passage and a filter to the inlet of a supply pump for direction controlled fluid devices includes a reservoir connected unloading valve assembly connected to the charge passage and parallel with the filter. The fluid devices return fluid through a return passage connected to the unloading valve assembly which maintains back pressure on the devices at charge passage pressure. The unloading valve assembly includes an unloading valve movable in response to a predetermined fluid pressure at the inlet of the supply pump to unload the charge and return passage by connecting them to the reservoir. As the devices require more fluid from the supply pump causing the pressure at the inlet of the supply pump to drop, the unloading valve proportionately blocks the charge and return passages from the reservoir to circulate return fluid into the charge passage.

Abstract: Auxiliary control of fluid actuated steering apparatus for ships, boats and the like (hereinafter, "water vessels") includes isolating the existing steering control system from the steering apparatus and providing flow-communication between fluid under pressure and the steering apparatus through an auxiliary directional control sub-system enabling control of the steering apparatus independently of the main steering control system. According to a preferred embodiment, the source of the fluid includes a quantity of fluid stored under pressure and another quantity of fluid adapted to be provided under pressure. Isolation of the existing steering control system is carried out by coupling the source of fluid to a by-pass control sub-system preferably adapted both to isolate the main steering control system and to couple the auxiliary directional control sub-system to the steering apparatus.

Abstract: A three-circuit fluid system has at least one work element served by a pressurized fluid source and a plurality of work elements connected in interruptible series in each of the second and third circuits. A control system is provided for selectively diverting excess fluid from the pressurized fluid source of the first circuit to the second and third circuits in one mode of the control system and diverting excess fluid from the pressurized fluid source of the first circuit to only preselected work elements of the second and third circuits in a preselected order in another mode of the control system.

Abstract: There is shown a safety control system for a self-propelled road roller having hydrostatic transmission, which includes a prime mover, an hydraulic pump driven by the prime mover and included in a main hydraulic circuit incorporating a motor with a power-off brake device, a check valve bridge with a ventable relief valve and a main control valve, and means for selecting automatically the speed and a predetermined operating speed, the speed selecting means comprise a secondary hydraulic circuit including means operatively connectible with the prime mover speed control means and controllable by the ventable relief valve in accordance with the operation of the main control valve.

Abstract: A fluid system (10, 10A, 10B) which supplies two work systems (26, 38) with respective different fluid flow rates, including a pressure-flow compensated pump (12), a first control valve (18) for delivering the fluid to one of the work systems, a second control valve (28) for receiving the fluid from the first control valve and delivering the fluid to the other of the work systems (38), a first device ([20,42,50] or [20,56,58] or [20,90,96]) coupled between the pump output and the first control valve, for providing one control signal causing the pump to produce one flow rate of fluid for activating the one work system (26), and a second device ([20,40,44,46,50] or [22,58,66,72,78] or [22,88,92,96,102]) for overriding the first device for providing another control signal causing the pump to produce another flow rate of fluid for actuating the other work system.

Abstract: More specifically, the invention includes a single lever control mechanism for controlling the operation of hydraulic cylinders and including a control housing, a manually operable lever, and a support member housed in the control housing and having a supporting surface. The single lever control mechanism also includes a pivot member rigidly connected to the lower end of the lever and supported on the supporting surface of the support member for rocking movement from a neutral position in a first pivotal direction and in a second pivotal direction transverse to the first direction. The control mechanism also includes a first cable attached to one side of the pivot member and being adapted to be operably connected to a first hydraulic cylinder for actuating that hydraulic cylinder in response to pivotal movement of the lever and the pivot member in the first direction.

Abstract: The closure and trip pilot valves of a circuit-breaker control unit are actuated by a hydraulic device controlled by a pressure drop which appears in control lines in response to the transient opening of a drain electrovalve within a control cubicle. Thus the pressure-drop hydraulic signal transmitted from a single central control cubicle for closing or tripping a circuit-breaker dispenses with the need for any electrical system and permits the control of a plurality of circuit-breakers or breaker modules solely by means of small-section lines providing hydraulic connections between the central control cubicle and each breaker control unit.

Abstract: A control mechanism for controlling a reversible pump that selectively supplies fluid to two different motors forming separate functions includes a control lever pivoted about a fixed axis and having said pump connected thereto. A control console is located adjacent the control lever and cooperates therewith to define a plurality of distinct operating positions on opposite sides of a neutral position for said control lever. The control lever and control console also have releasable interlock means defining the neutral position for the control lever and the pump.

Abstract: A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions and a variable displacement pump with loading sensing control for supplying fluid to said actuator. A meter-in valve is provided to which the fluid from the pump is supplied and a pilot controller alternately supplies fluid at pilot pressure to the meter-in valve for controlling the direction and displacement of movement of the meter-in valve and the direction and velocity of the actuator. A pair of lines extends from the meter-in valve to the respective openings of the actuator and a meter-out valve is associated with each line of the actuator for controlling the flow out of the actuator when that line to the actuator does not have pressure fluid from the pump applied thereto. Each meter-out valve is pilot operated by the pilot pressure from the controller.

Abstract: A hydraulic drive and braking system for vehicles having a pair of positive displacement pumps connected to drive axles attached to the wheels of the vehicle. Hydraulic fluid is supplied to the positive displacement motors from a reservoir by means of a variable displacement pump. The flow to the motors is controlled by a flow divider connected to the steering linkage. Braking is provided by blocking the return flow of the positive displacement motors. An antiskid system senses wheel rotation and responsive thereto prevents the blocking of the return flow of the positive displacement motors.

Abstract: A system for selectively and controllably supplying pressurized fluids to dental or surgical tools requiring high pressure air at two levels of pressure and low pressure air and/or liquid.

Abstract: A load sensing hydraulic system is disclosed of the type in which a load signal is communicated from downstream of a main flow control orifice to a device which is operable to vary the fluid delivery rate in response to changes in the load signal. Disposed in the load signal conduit is a load signal modulating valve which, in one position, communicates the load signal, substantially unchanged, to the variable fluid source. In another position of the modulating valve, the load signal chamber of the variable fluid source is drained to tank, while in intermediate positions of the modulating valve, a portion of the load signal is communicated to the variable fluid source, and a portion is bled to tank. Modulation of a load signal permits flow control in an hydraulic system, independent of the position or movement of the main spool valve. The input to the modulating valve may be manual or electric, and if electric, may be remote, or may be automatic in response to certain predetermined system conditions.

Abstract: A hydraulic control system is provided including a fluid reservoir, a variable displacement pump having a fluid input in fluid communication with the reservoir and having a fluid output, and a fluid actuated displacement control mechanism for controlling the displacement of the pump. A control valve is placed in fluid communication with the fluid output of the variable displacement pump and with the reservoir and is adapted to control the flow of fluid to a fluid actuated device. The control valve includes means for developing a control pressure signal.

Abstract: A vehicle drive system including a rotary output, variable displacement, hydraulic motor (22) adapted to drive a wheel or the like, a pump (10) for providing hydraulic fluid under pressure to the motor, a pressure control valve (30) connected to the motor for regulating the displacement thereof to achieve a desired system pressure and having a pressure responsive surface (34) receiving a signal representative of system pressure and a biasing spring (36) acting in opposition thereto. The invention contemplates the improvement wherein a variable, settable, pressure reducing device (60,106) is connected to the pump and to the pressure control valve to apply hydraulic fluid under reduced pressure to the pressure control valve in bucking relation to the system pressure signal.

Abstract: A two speed valve and bi-directional motor system is provided having a pair of motors, means for delivering pressure fluid selectively to either side of said motors, a two speed valve means receiving fluid on one side of said motors to selectively direct the fluid to one or both motors to provide high or low speed operation thereof and flow sensing means automatically connecting the discharge from the motors to the one motor not receiving fluid when the two speed valve is shifted to divert all fluid to one motor so that fluid is recirculated through said motor.

Abstract: A fluid control system includes a directional control valve assembly adapted for use in either an open-center or a closed-center configuration. The system is capable of incorporating one or more control sections, each with a manual control valve and its own individually variable flow control mechanism. Each flow control mechanism is independently responsive to section load pressure, and is capable of controlling the flow rate delivered to its section when the control valve spool is biased to a full power position. Each section contains a kickout mechanism for returning the control valve spool to its neutral position at a predetermined pressure.

Abstract: The engine comprises a base having a spool fastened thereon, the spool including a hub symmetrical about a first axis and having a pair of side plates normal to and having inside faces spaced apart along the first axis. There are plate ports in the inside faces. A cylinder rotor includes a second hub rotatable on the first hub about the first axis and includes a pair of side discs normal to the first axis and having outside faces spaced apart axially between said side plates to establish first and second axial clearances between the side plates and the adjacent side discs. There are cylinders mounted radially on the cylinder rotor with ducts extending from the cylinders to the disc ports in the outside faces radially opposite the plate ports. A driven shaft symmetrical about a second axis is eccentrically journalled in and extends through the hub. A rotor is fast on the driven shaft and carries pivot pins.

Abstract: A motor displacement control system (10) has a variable displacement drive motor (38), an auxiliary motor (30), a source (12) of fluid under pressure for operating the motors (30, 38), a first valve (50) for controlling the displacement of the drive motor (38) and maintaining at least a first pressure level thereto, and a second valve (98) for controlling the displacement of the drive motor (38) in response to operation of the auxiliary motor (30) at a second pressure level and overriding the first valve (50). The system is particularly useful on a motor grader.

Abstract: A vehicle engine accessory drive system is disclosed including a hydraulic fan motor (41) and a power steering gear mechanism SG in series flow relationship. The vehicle power steering pump P is the sole source of fluid for the system and has its flow control setting at a flow rate X, which is substantially greater than the flow rate Z required by the power steering gear SG. The motor-valve apparatus includes a valve portion (43), including a bypass valve portion (43), including a bypass valve piston (113) connected in parallel across the fan motor (41), and operable to permit fluid flow from the inlet passage (83) to the outlet passage (91) at a flow rate which is at least a portion of X. The bypass valve piston (113) is biased toward the bypass position by the fluid pressure in the inlet passage (83), and is biased toward the closed position by fluid pressure in a signal chamber (115).