Abstract: A hydraulic circuit for a loader vehicle includes a working machine hydraulic circuit, a steering hydraulic circuit, a variable displacement auxiliary hydraulic pump, in which the displacement volume becomes smaller as the operating oil pressure becomes higher, when the operating oil pressure exceeds a predetermined oil pressure by receiving the operating oil pressure of the working machine hydraulic circuit, and a flow dividing valve for switching and supplying oil discharge from the auxiliary hydraulic pump to either one of the hydraulic circuits with a priority being given to the steering hydraulic circuit. A pump capacity control device includes a working machine hydraulic actuator, a working machine hydraulic pump, a steering pump, a steering pump capacity servo, a working machine load sensor, and an engine speed sensor.

Abstract: A method and an apparatus for driving a hydraulic system of a construction machine, in particular a hydraulic excavator, having a plurality of control blocks which are fed via at least one pump each and each drive a plurality of hydraulically operated actuators of the construction machine. At least two control blocks are designed to drive the same actuator. The delivery capacity of the pump of the second control block can be connected up to the actuator via a delay element.

Abstract: This invention relates to a hydraulic circuit for a forklift, and intends to lift a fork for lifting in high speed, or to inch the fork little by little, as occasion demands. In this hydraulic circuit, a first electric motor for driving a first electric motor disposed on a first route extending from a tank to a lift cylinder is on-off controlled. A check valve disposed on the first route downstream of the first hydraulic pump allows only an oil-flow from the oil tank to the lift cylinder. A second motor for driving a second electric motor disposed on a second route extending from a tank to a lift cylinder is PMW-controlled. A flow controlling valve is disposed on the second route downstream of the second hydraulic pump and including an electro-magnetic valve operated associating with the PMW-controlling of said second electric motor. A separating element hydraulically separates the check valve and the electro-magnetic valve of the flow controlling valve.

Abstract: An improved pressure fluid supply and delivery apparatus is disclosed that has a pressure compensating function and yet a reduced loss in pressure. The apparatus includes a variable displacement hydraulic pump unit(10; 60, 61) having a plurality of fluid discharge ports(10a, 10b; 60a, 61a) independent each other and a common drive shaft. A plurality of fluid circuits (11, 12) are connected to the plural discharge ports (10a, 10b; 60a, 61a), respectively, and a plurality of fluid operated actuators (14, 16; 14, 14′, 16, 16′) are connected via respective operating valves (13, 15; 13, 13′, 15, 15′) to the plural fluid circuits (11, 12), respectively. Also included in the apparatus is a displacement control means (19, 20; 64, 64) operable in response to discharge pressures in the fluid discharge ports (10a, 10b; 60a. 61a) and load pressures in the actuators (14, 16; 14, 14′, 16, 16′) for controlling discharge fluid pressure of the variable displacement pump unit (10; 60, 61).

Abstract: A hydraulic drive system for a supersized hydraulic working machine such as a hydraulic excavator includes hydraulic pumps connected to main lines through a delivery line and a supply line. Branch portions from the main line include flow control valves for allowing a hydraulic fluid to flow from the hydraulic pumps toward hydraulic cylinders. A hydraulic reservoir is connected to the main lines through a reservoir line and a drain line. Other branch portions for the drain line include flow control valves for allowing a hydraulic fluid to flow from the hydraulic cylinders toward the hydraulic reservoir. A line branched for the delivery line includes a bypass valve for supplying the hydraulic fluid delivered from the hydraulic pumps to the supply line at a desired flow rate and returning the remaining hydraulic fluid to the hydraulic reservoir.

Abstract: The invention related to a drive system with at least two hydraulic actuators, which are supplied with a hydraulic fluid by means of at least one pump. The drive system comprises at least one further second pump (15′) arranged parallel to the first pump (15), wherein the pumps are bi-directionally speed-regulated, and a valve arrangement (59) with one inlet per pump (61.1, 61.2), wherein each one of the inlets is connected to a pump (15), and with a number of outlets (63.1, 63.1′, . . . 63.4, 63.4′) which are connected to the actuators (1.1 . . . 1.4), wherein the inlets (61) can be connected to the outlets (63) in a pre-determined manner.

Abstract: A fluid control system including a valve arrangement operable for selectively, controllably supplying pressurized fluid to a work element of the system from at least two pressurized fluid sources depending on load conditions on the pressurized fluid sources. The valve arrangement is operable for directing pressurized fluid from the first pressurized fluid source to the work element when a first or low load condition is present on the first pressurized fluid source and directing pressurized fluid from the second pressurized fluid source to the work element when a second or high load condition greater than the first load condition is present on the first pressurized fluid source and a low load condition is present on the second pressurized fluid source, such that operability of the work element and other work elements supplied by the pressurized fluid sources is maintained.

Abstract: A pressurized hydraulic fluid supply apparatus capable of merging or separating a plurality of hydraulic pump lines according to the driving states of a plurality of actuators. The pressurized hydraulic fluid supply apparatus has a merge/separation valve 40 that merges or separates the hydraulic fluids delivered under pressure by the first hydraulic pump 1 and the second hydraulic pump 11. The merge/separation valve 40 is set to a flow separation state upon driving of the second hydraulic actuator 16 and is preferentially shifted to a flow merging state when the third hydraulic actuator 21 is driven. Hence, even when a manually driven operation valve is used, the merge/separation valve 40 is automatically switched between the flow separation state and the flow merging state according to the operation of the operation valve. This apparatus prevents an unintended flow rate difference between the first and second actuators from being produced upon driving of the third actuator.

Abstract: Arranged on a side of a first pump are a flow control valve for controlling a first boom cylinder, a flow control valve for an arm, said flow control valve being connected in tandem with said flow control valve and being adapted to control an arm cylinder, and a flow control valve for a second boom, said flow control valve being connected to a downstream side of the flow control valve and being adapted to control a second boom cylinder.

Abstract: A construction machine comprising two hydraulic pumps; right and left traveling motors for causing the construction machine to travel; work machine actuators for actuating a work machine of the construction machine; a control valve which makes control so that a hydraulic oil discharged from the two hydraulic pumps is fed to at least either the right and left traveling motors or the work machine actuators and so that when both traveling operation and work machine operation are performed simultaneously, the hydraulic oil discharged from one of the two hydraulic pumps is fed to the traveling motors and the hydraulic oil from the other hydraulic pump is fed to the work machine actuators, the control valve providing communication between the two hydraulic pumps through a pump communication path; a drive signal detecting device which detects drive signals with respect to the two hydraulic pumps when the traveling operation and the work machine operation are performed simultaneously; and a controller which controls

Abstract: A brake system (10) having a control member (12) through which a remotely located master cylinder (18) is selectively supplied with either a first operational fluid developed by a first pump (14), a second operational fluid developed by a second pump arrangement (500,600) or a third operational fluid from a storage system (302) as a function of a brake force applied to an input push rod (16) and a sensed flow of operational fluid through a shuttle valve (64) to the master cylinder for effecting a desired brake application. A electronic control unit (200) receives an input signal corresponding to the brake force and a sensed flow to activate the second pump arrangement (500,600). Whenever the fluid pressure of the first operational fluid is insufficient, the second pump is activated and the second operational fluid supplants the operation of the master cylinder (18) by the first operational fluid to effect the desired brake application.

Abstract: A system for supplying an implement with hydraulic fluid includes a first hydraulic pump generating a first flow, a second hydraulic pump generating a second flow and a valve assembly adapted to be coupled to the implement and coupled to the first and second flows. The valve assembly couples the first flow to the implement. The valve assembly also selectively adds the second flow to the first flow to provide a low flow or a high flow. The valve assembly couples the first flow to the implement via a first coupling in response to a first signal and via a second coupling in response to a second signal. The system further includes a manually operable control coupled to the valve assembly and movable between the first position which the first signal is generated, a second position in which the second signal is generated and a third position in which a third signal is generated. The system also includes a foot pedal control coupled to the manually operable control and to the valve assembly.

Abstract: Pressure sensors sense a pilot pressure Pa corresponding to the amount of boom raising operation of a boom operation lever and a pilot pressure Pb corresponding to the amount of arm pulling operation of an arm operation lever. When the condition of Pa>Pb is met during the horizontal pulling operation, the rate of supply of the working fluid to an arm actuating cylinder is reduced to a rate corresponding to the amount of operation of the operation lever. Conversely, when the condition Pa<Pb is met, the rate of supply of the working fluid to the boom actuating cylinder 5 is reduced to a rate corresponding to the amount of operation of the operating lever. Horizontal pulling operation for levelling the ground can be conducted without requiring high level of skill. The horizontal pulling work can be done easily and smoothly, while preventing the bucket from cutting into the ground and from floating above the ground.

Abstract: A power machine has a base, an operator support portion, and a hydraulic slew motor coupled to move the operator support portion relative to the base. A boom, an arm, and a tool are all coupled to one another and to the operator support portion and are powered by hydraulic actuators. A slew valve is coupled to receive hydraulic fluid under pressure from a hydraulic power circuit and is also coupled to the slew motor to provide hydraulic fluid to the slew motor and receive hydraulic fluid from the slew motor. A first power actuator valve is coupled to receive hydraulic fluid from the slew valve and is coupled to provide hydraulic fluid to one of the hydraulic boom actuator, the hydraulic arm actuator and the tool actuator. The slew valve is coupled in series with the power actuator valve.

Abstract: A power machine includes a pair of traction motors to provide for travel of the machine. The power machine also includes a boom, an arm and a tool (such as a bucket). The power machine includes a hydraulic power circuit which has a valve stack that enables the boom and at least one of the arm and tool to be operated simultaneously.

Abstract: A boom and drive train hydraulic system is described having a pressure source, preferably a pump operated by a motor, said pressure source providing hydraulic fluid at a high pressure to a first set of valves used to operate the drive train of the system. The first set of valves is equipped with a power beyond for allowing the hydraulic fluid to flow from the first set of valves to a second set of valves. At the second set of valves a pressure control is provided to reduce the pressure to a desired lower pressure. The second set of valves provides the hydraulic fluid at this reduced pressure to the boom portion of the system. The differential of the pressures is approximately 5,000 psi for the track system and approximately 2,500 psi for the boom system.

Abstract: A cut-off valve is mounted so that it can open and close an oil passage which leads a pressure oil discharged from a first pump into a hydraulic oil tank in a neutral state of a spool valve for boom. When an operating lever for boom and an operating lever for arm have simultaneously been operated to a boom raising side and an arm pulling side, respectively, the cut-off valve is closed in proportion to a boom raising or arm pulling pilot pressure. The cut-off valve is controlled using as a parameter a differential pressure between the arm pulling pilot pressure and the boom raising pilot pressure. By doing so, there is obtained a low gain operability in the crane work, while in the parallel pulling work there is obtained an operability of a relatively high gain which matches a quick motion of the arm.

Abstract: An anti-stall and bias control for a hydrostatic drive train system is disclosed. The system is used on a hydrostatic drive vehicle with an engine coupled to a first and second hydraulic pump. The first and second hydraulic pumps are coupled to first and second drive motors which drive wheels of the vehicle. The power to the drive motors is controlled by a control unit which output signals proportional to the desired power output from the motors. An engine speed sensor determines the speed of the engine. The control circuit reads the engine speed and determines whether the engine is in a stall condition. If the engine is in a stall condition, the control circuit scales the control signals of the first and second motor to reduce power output. A bias control is also provided to allow the vehicle operator to select greater relative power to either the first or second motor. The bias control outputs a bias signal which is read by the control unit.

Abstract: Pilot change-over valves for operating actuators are connected in a center bypassing form and a cut-off valve is disposed downstream of each such pilot change-over valves. Commands which are in a proportional relation to each other are outputted from a controller to a pilot port of the cut-off valve and a pilot port of a pilot change-over valve for boom. Both valves are closed synchronously. Operation commands for both valves can be altered with a volume control for setting operation characteristics. Hydraulic pump oils for arm are joined together by a confluent valve. Consequently, highly responsive operations can be attained in operating the attachment of a hydraulic excavator. This is effective in the ground hardening work with a bucket, the work for removing mud from the machine body and the work for scattering soil.

Abstract: In order to accomplish many tasks of a machine efficiently, a motion planning system predetermines the response of the machine to a given set of motion commands. With two or more actuators being driven by a single hydraulic pump, there may not be adequate hydraulic pressure to drive both of the actuators at the speed requested. In order to determine the non-linear response of the actuators and the optimal combination of motions of the moving parts driven by the actuators, a controller for the machine is modeled as a linear dynamic system. The non-linear response of the actuators is modeled using a look-up table that is a function of internal variables of the machine's actuators and hydraulic system. The number of input, or independent, variables that are supplied to the table look-up functions is proportional to the number of actuators being driven by a single pump. Sensors provide data regarding the internal state of each actuator including variables such as spool valve position and cylinder force.

Abstract: Disclosed is an apparatus for increasing the operating capability of a construction machine during a fine operation mode and a method for the same. The apparatus being capable of preventing a merged hydraulic fluid from being supplied into a hydraulic actuator and increasing the pressure of the hydraulic fluid being supplied into the hydraulic actuator during the fine operation mode. The apparatus includes a detector that detects the RPM count of the engine of the construction machine and determines whether the engine is switched into the fine operation mode. A first anti-confluence valve and a second anti-confluence valve prevent a first hydraulic fluid supplied into the first actuator and a second hydraulic fluid supplied into the second actuator from merging while either the first actuator or the second actuator is operating. An anti-confluence relay turns the first anti-confluence valve and the second anti-confluence valve on/off.

Abstract: The present invention relates to a hydraulic circuit for a hydraulically driven working vehicle which allows the vehicle to travel at an almost constant speed during high-speed traveling, provides a great digging force during working, does not need a charging pressure for preventing cavitation, loses a small amount of energy, and has a simple structure. To this end, the hydraulic circuit has a hydraulic travel pump (2) and a working machine hydraulic pump (4) which are driven by the power of an engine (1) for discharging pressurized oil to a HST travel circuit and a working machine-driving hydraulic circuit, respectively, wherein pressurized oil from the working machine hydraulic pump (4) joins pressurized oil from the hydraulic travel pump (2) to effect high-speed traveling, while pressurized oil from the hydraulic travel pump (2) joins pressurized oil in the working machine hydraulic pump (4) to generate a large digging force to effect digging.

Abstract: A pilot pressure sensor detects a pilot pressure from an arm operating unit and outputs a pilot pressure signal. A drive signal corresponding to the pilot pressure signal is then outputted from a controller to a solenoid-operated proportional valve. Through the solenoid-operated proportional valve, a pilot pressure is fed to an auxiliary selector valve so that an opening of said auxiliary selector valve becomes greater. Of pressure oil delivered from a first hydraulic pump, a flow rate of the pressure oil to be branched to a side of a by-pass circuit is hence increased. The pressure oil fed through the by-pass circuit passes through a merging directional control valve and is caused to merge with pressure oil fed from a second hydraulic pump. The thus-merged pressure oil is then fed to a hydraulic arm cylinder.

Abstract: A hydraulic drive assembly includes a variable displacement pump fluidly connected in a closed loop circuit with a motor for driving an ancillary device, such as a fan. An auxiliary pump can be operatively connected to the pump, the motor and a reservoir for replenishing fluid losses in the closed loop circuit. An auxiliary circuit connected to the pump has a recirculating passage fluidly connected to the closed loop circuit downstream of the motor to reduce the necessary reservoir volume. A method for smoothly and continuously adjusting the output of the pump to drive the ancillary device is also disclosed.

Abstract: A fluid joining device for construction vehicles is disclosed. The device has a bypass line control valve which is mounted to a second center bypass line of the second pump. The bypass line control valve normally opens the second center bypass line but selectively closes the second center bypass line in response to a pilot pressure. A second pilot line control valve is mounted to a second pilot line and controls the second pilot line in response to an outside signal. The second pilot line extends from the first pilot line control valve and selectively drives the first pilot line control valve. The device selectively performs the fluid joining function in accordance with operational conditions of the actuators, thus smoothly operating the actuators and improving operational effect of the construction vehicle.

Abstract: The invention relates to a drive system for a hydraulic press. The drive system is of the type of secondary controlled system maintaining an impressed pressure of substantially constant magnitude in a pressure system. A hydraulic transformer comprises a pair of mechanically coupled hydrostatic machines each having a variably capacity. The first machine is connected to the pressure system and the second machine to the press cylinder. The invention provides a drive system in which biasing the press cylinder, rapid tranverse and pressing stroke, decompressing the fluid and flushing of hot fluid is accomplished in a closed loop free of throttling losses. The hydraulic transformer further allows to recover energy to the pressure system.

Abstract: A fluid power control system for use in a mini-excavator, in which a first control section (S2) includes first and second control valves respectively connectable to first (2) and second (4) implement functions; and in tandem with one another. A first gear pump (P2) supplies the actuator connected principally to the first implement (2), and a second gear pump (P3) supplies working fluid to the interconnection between the first and second control valves. The advantage of this arrangement is that, as the first control valve switches from its neutral position to a position selecting its associated implement (2), progressively more of the fluid passing through the second control valve is supplied by the second pump (P3) until, when the implement (2) to which the first control valve is principally connected is fully selected, the two implements (2, 4) are supplied separately by the respective gear pumps (P2, P3).

Abstract: Hydraulic control circuit for working components, in particular in earth-moving machines, said machines comprising a front group provided with actuators controlled by first hydraulic distributors (1,2) and a rear excavator group provided with actuators controlled by second hydraulic distributors (3-8), in said rear excavator group there being present a main arm actuated by a main actuator (13) controlled by a main distributor (3) located upstream of the remaining second distributors (4-8). The main actuator (13) supplies in series the remaining second distributors (4-8) when the pressure downstream thereof is less than a predetermined value and instead discharges the fluid under pressure when said pressure downstream thereof reaches or exceeds said predetermined value. In the front group there is also provided an additional distributor (A-B) which sends the fluid under pressure immediately downstream of the main distributor (3) of the rear excavator group via a bypass line (23).

Abstract: Pump ports 9p, 10p, 11p, 13p of boom, arm, bucket and first travel directional control valves 9-11, 13 are connected to first and second hydraulic pumps 1a, 1b through feeder lines 93a, 93b; 103a, 103b; 113a, 113b; 133a, 133b. Auxiliary valves 91a, 91b; 101a, 101b; 111a, 101b; 131a, 131b controlled respectively by proportional solenoid valves 31a, 31b; 32a, 32b; 33a, 33b; 34a, 34b are disposed in those feeder lines. The auxiliary valves each have a function as a reverse-flow preventing function and a variable resisting function including a flow cutoff function, whereby a joining circuit and a preference circuit can be realized in the closed center circuit with a simple structure and further, a preference degree and metering characteristics can be set independently of each other during the combined operation of plural actuators.

Abstract: An apparatus for controlling the lifting operation comprising an operation mode selection switch which is selectively set to an ordinary operation mode or to a lifting operation mode and a hydraulic circuit isolating means. The hydraulic circuit isolating means isolates the hydraulic circuit into a running drive hydraulic circuit which feeds the pressurized fluid of one of the variable-capacity hydraulic pumps to the actuators of the running apparatuses when the operation mode selection switch is set to the lifting operation mode and a hydraulic circuit for driving the apparatus on the side of the turning body, which feeds the pressurized fluid of the other variable-capacity hydraulic pump to the actuators other than those of the running apparatuses.

Abstract: A straight travelling apparatus for heavy construction equipment, equipped with a travel supplement circuit, including a variable orifice disposed in a fluid line connected to the supply-side of the control valve of a bucket and controlled to vary an opening degree thereof by a predetermined pilot signal that is applied to the variable orifice in response to an operation of at least one of right and left travel motors in order to keep the variable orifice at a relatively closed state while being released in response to the travel motors not operating in order to keep the variable orifice in a relatively opened state, thereby capable of supplementing a sufficient amount of fluid to a travelling system when the bucket is operated during, thereby preventing an abrupt reduction in travelling speed caused by operatings the straight travelling apparatus.

Abstract: In a displacement control system for a variable displacement type hydraulic pump for supplying a discharge pressurized fluid of the variable displacement type hydraulic pump to an actuator via a direction control valve and then controlling a displacement of said variable displacement type hydraulic pump for maintaining a pressure difference between a discharge pressure of said variable displacement type hydraulic pump 1 and a load pressure at a portion between a direction control valve and an actuator, wherein an inlet side pressure of said direction control valve is detected as said discharge pressure.

Abstract: An auxiliary drive apparatus which comprises an engine, a first hydraulic pump driven by the engine, a second hydraulic pump driven by the engine and integrally connected to the first hydraulic pump, a third hydraulic pump driven by the engine and integrally connected to the second hydraulic pump, a first pressure limiting valve connected in parallel to the first hydraulic pump, a first vacuum breaking valve connected in parallel to the first hydraulic pump, a first hydraulic motor connected in series to the first hydraulic pump, a second pressure limiting valve connected in parallel to the second hydraulic pump, a second vacuum breaking valve connected in parallel to the second hydraulic pump, a second hydraulic motor connected in series to the second hydraulic pump, a third pressure limiting valve connected in parallel to the third hydraulic pump, a third vacuum breaking valve connected in parallel to the third hydraulic pump, and a third hydraulic motor connected in series to the third hydraulic pump.

Abstract: Straight travelling apparatus for construction vehicles capable of keeping the construction vehicle travelling straight even when a work implement of the construction vehicle is manipulated during travelling. The apparatus includes hydraulic circuitry for making the hydraulic oil of first and second pumps be supplied to left and right travelling motors respectively when only the left and right travelling motors are operated, and making the oils be confluent together and equally distributed and supplied to the left and right travelling motors when even one work implement is to be manipulated at the same time as operating the left and right travelling motors. The hydraulic circuitry includes left and right directional selecting valves and a confluent line extending between the directional selecting valves for selectively making the hydraulic oil confluent together.

Abstract: A hydraulic circuit is disclosed for a tractor in which a steering circuit and an implement circuit are utilized to provide a high flow capability to the implement valve stack. A series of priority valves are operable to divert hydraulic flow from the steering circuit to the implement circuit under conditions where the steering mechanism is not being operated and the implement circuit pump is operating at full capacity. The first priority valve diverts the hydraulic flow from the steering circuit to a second priority valve that is controlled by a pressure differential valve that senses the implement circuit pump working at full displacement, whereupon the second priority valve directs the diverted hydraulic flow into the implement circuit. The first priority valve retains hydraulic flow within the steering circuit whenever the steering mechanism is being operated.

Abstract: A straight travelling apparatus for heavy construction equipment such as excavator or crane, including a straight travel valve disposed in both lines respectively branching from first and second hydraulic pumps and switched between a first state at which a fluid delivered from the first hydraulic pump is supplied to a right travel motor and a part of the actuators of a working system while a fluid delivered from second hydraulic pump is supplied to a left travel motor and the remaining part of the actuators of the working system and a second state at which the fluid delivered from the first hydraulic pump is supplied to both the right and left travel motors while the fluid delivered from the second hydraulic pump is supplied to all actuators of the working system, first and second pilot fluid lines both branching from the pilot pump, a connecting fluid line adapted to communicate the first and second pilot fluid lines with each other, a fluid line branching from the connecting fluid line, and a relief check v

Abstract: A hydraulic drive system comprises a check valve cb1 for detecting a pressure on the outlet side of a pressure compensating device VB1, a maximum load pressure detecting line SL1 for selecting higher one of the pressure detected by the check valve cb1 and a load pressure of an actuator associated with a hydraulic pump P1 and supplying it as a signal pressure, a check valve cb2 for detecting a pressure on the outlet side of a pressure compensating device VB2, a maximum load pressure detecting line SL2 for selecting higher one of the pressure detected by the check valve cb2 and a load pressure of an actuator associated with a hydraulic pump P2 and supplying it as a signal pressure independently of the maximum load pressure detecting line SL1, and a passage 300 for joining hydraulic fluids supplied from the hydraulic pumps P1, P2 and passing through variable restrictors RB1, RB2 with each other and supplying it to an actuator B. Mutual independence between the two hydraulic pumps P1, P2 can be thereby ensured.

Abstract: Simultaneous operation efficiency in a case where a plurality of actuators are operated by one or a plurality of hydraulic pumps is improved. A delivery pressure passage (1a) of one hydraulic pump (1) and that (1a) of the other hydraulic pump (1) communicate with each other through a first short-circuit passage (39) via a pair of check valves (38, 38), and an unload valve (40) is provided in this first short-circuit passage (39). The load pressure introduction passages (6, 6) on the left and right hydraulic pumps (1, 1) communicate with each other through a second short-circuit passage (36) via a pair of check valves (35, 35), and a relief valve (37) is provided in this short-circuit passage (36).

Abstract: A hydraulic drive system for actuating a reciprocating member such as a polished rod in a pump jack device, and for acting as a counterbalance and/or for energy conservation. The system has two hydraulic circuits and a prime mover. A first circuit includes a cylinder for driving an output member which may be connected to the polished rod, a first pump of the variable displacement, reversible flow type, together with a pair of fluid lines forming with the cylinder a closed-loop circuit. A controller is programmed to control the setting of the first pump so as to establish the velocity profile of the output member. A second hydraulic circuit is also in the form of a closed-loop containing first and second pumps, at least one of which is of the variable displacement type and is also controlled by the controller.

Abstract: An improvement in a multiple intensifier system having two intensifier units with reciprocating piston assemblies to supply very high pressure water. When one of the piston assemblies travels faster than the other, so that these reached an end stroke position at the same time, there can be an abrupt pressure drop. To alleviate this, a first embodiment isolates the compensator control lines of the pumps of the two intensifier units so as to maximize volumetric flow rates during such pressure drops to give the slower moving piston assembly a boost at the beginning of its subsequent stroke. Another embodiment provides an accumulator in the fluid control line for the compensators, and a further embodiment provides a pressure reference supply pump to alleviate pressure variations in the fluid control line.

Abstract: A combined hydraulic circuit to be used with a hydraulically powered implement of a motorized equipment and its engine-driven host vehicle. The combined hydraulic circuit allows the implement to be operated with a vehicle, such as a tractor, which does not have the adequate capacity to power the implement without the usual requirement of using an hydraulic fluid reservoir and a filter in the independent hydraulic circuit of the implement. Instead, the implement uses the tractor hydraulic circuit to clean, cool and pressurize in part the hydraulic fluid in its hydraulic circuit which has a hydraulic motor or a hydraulic cylinder driven by a hydraulic pump. This hydraulic pump can be a generated orbital rotor pump since the supplied fluid entering the pump is already pressurized unlike a circuit that uses a hydraulic fluid reservoir. The implements may be rotary brooms, mowers, portable saw mills, hoeing machines, loaders or snowblowers.

Abstract: A hydraulic circuit for a working vehicle comprising a first pump, a second pump, a first actuator, a second actuator, and a selector valve having a plurality of control positions. The selector valve is switchable between a first position for connecting the first pump to the first actuator and the second pump to the second actuator, and a second position for connecting the first pump and the second pump to the second actuator. This circuit includes a first relief valve disposed between the selector valve and the first pump, and a second relief valve disposed between the selector valve and the second pump. The first relief valve is set to a higher relief pressure than the second relief valve.

Abstract: A hydraulic drive system consists of a first partial system I and a second partial system II. Each partial system has a pump regulated by the stream required (1,9) and a hydraulic energy consumer connected to its output line (2,10). Load pressure lines (7,13) that sense the maximum load pressure are also provided in each partial system I and II; they are connected with the required flow regulators (8,14) of the pumps (1,9). A coupling device III is provided for connecting the feed lines (2,10) and the load pressure lines (7,13) of the two partial systems I and II. The coupling device III can be switched as a function of a consumer designed for driving and is connected with a circuit logic IV that supervises the driving of this consumer. The circuit logic consists of a NAND (not-and-) element (19) and an UND (and-) element (22).

Abstract: A variable gain control apparatus for a servo assist system includes a position sensor, a valve, a controller and an actuator. The valve has an actuated member and a variable flow orifice to communicate hydraulic fluid between the high pressure supply line and a reservoir of hydraulic fluid. The position of the actuated member determines the cross sectional area of the variable flow orifice. The position sensor determines the present position of the actuated member. The controller determines a position error between the present position of the actuated member and a varying predetermined position of the actuated member. The actuator in response to the position error actuates the actuated member to eliminate the position error so that assist pressure to the servo assist system is varied as a function of the varying predetermined position.

Abstract: An hydraulic actuator composed of a double-acting actuator, a mobile switching member disposed in a housing connected hydraulically to the actuator, two fluid inlet and outlet pipes and a control member adapted to command the mobile switching member to move between a neutral configuration and an active service configuration. A variable speed pump system is connected to the housing by an auxiliary circuit; the mobile switching member has an active second configuration in which the actuator communicates with the auxiliary circuits, whereby the actuator, the pump system and the auxiliary circuit constitute a hydrostatic transmission.

Abstract: A brake valve (45) is disclosed of the type which permits communication from a source (11) of pressurized fluid to a brake actuator (47) in response to manual movement of a valve spool (57) from a neutral position (FIG. 2) to a power brake position (FIG. 5). In the power brake position, the valve spool permits fluid communication between a work port (53), which communicates with a brake actuator, and a brake load signal chamber (87), the brake load signal controlling the fluid output of the source. As the valve spool moves toward a manual brake position (FIG. 6) communication between the work port and the brake load signal chamber is blocked. In the manual brake position, movement of the valve spool causes a large piston (63) to displace fluid from its piston bore (73) into a piston bore (75) in which is disposed a small piston (61), the small piston being operable in response to movement of the valve spool to build brake pressure in the work port (53).

Abstract: An active hydraulic pressure control system includes a sensor, a valve, a controller and an actuator. In accordance with a broad aspect of the present invention, the controller determines a pressure differential between the pressure sensed by the sensor in a high pressure supply line of a hydraulic system and a predetermined pressure. In response to such pressure differential, the actuator drives the valve which has a variable flow orifice to communicate hydraulic fluid between the high pressure supply line and a reservoir of hydraulic fluid to eliminate the pressure differential.

Abstract: A hydraulic circuit apparatus for use in construction vehicles which is arranged to reduce pressure losses that occur when all the implement operating valves are kept at their neutral positions, to reduce the power consumption by all hydraulic pumps when the hydraulic circuit for implements require only a small amount of pressurized fluid, and to transmit a command signal to unload the surplus pressurized fluid when occasion demands. The circuit comprises a surplus pressurized fluid control circuit (50) to facilitate the regulation of changes in the fluid flow rate when changing over valves. The surplus pressurized fluid control circuit (50) has a pilot actuated type unloading valve (11) provided in a surplus pressurized fluid supply conduit (51) which is connected through a check valve 20 to a hydraulic pump (P.sub.1). The hydraulic pump (P.sub.1) is for the exclusive use of the implement. The conduit (51) is also connected to a drain conduit (Ct).

Abstract: A control system having a flow-dividing selector valve mechanism (52) for changing the channels for causing a pressure fluid to flow from two main pumps (40), (50) into two control valve groups (60), (70) therethrough, and confluent selector valve mechanisms (80), (90) for causing the pressure fluid flowing into each group to flow into a working device control valve of the other group. The confluent selector valve mechanism (80) of the group wherein the working device control valve (62) has a need to compensate for the flow of fluid thereinto cancels the confluence function. The system has a mechanism for restricting the stroke of the spool of a working device control valve (160) to be subjected to varying loads to cause the fluid discharged from the actuator connected thereto to flow into the actuator again when the load is small. A sequence valve (170) operates the spool stroke restricting mechanism (190) by a pilot primary pressure.

Abstract: A hydraulic control circuit adequate to control a main hydraulic actuator and auxiliary hydraulic actuators. The main actuator drives farm machinery mounted to an agricultural tractor or the like. The auxiliary actuators drive farm attachments independent of said farm machinery. At least two hydraulic pumps and at least two sets of control valves are connected in series. The exit of one hydraulic pump is connected with the other hydraulic pump via a check valve. Said one hydraulic pump is connected with a tank via an openable valve upstream of the check valve. The upstream set of control valves is used to control the auxiliary hydraulic actuators needing more flow rate than the downstream set of control valves. The openable valve has an offset valve at its one end to determine the direction of flow. The openable valve is either opened or closed by the pressure admitted from the downstream side of the upstream set of control valves.