US2618121A - Locking control circuit for fluid-actuated motors - Google Patents

Locking control circuit for fluid-actuated motors Download PDF

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Publication number
US2618121A
US2618121A US125877A US12587749A US2618121A US 2618121 A US2618121 A US 2618121A US 125877 A US125877 A US 125877A US 12587749 A US12587749 A US 12587749A US 2618121 A US2618121 A US 2618121A
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motor
valve
fluid
pressure
pump
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US125877A
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Warren R Tucker
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HPM DEV CORP
H-P-M DEVELOPMENT Corp
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00Details of servomotor systems ; Valves for servomotor systems
    • F15B13/01Locking-valves or other detent i.e. load-holding devices

Description

Nov. T8, 13152 W TUCKER 2,618,121

LOCKING CONTROL CIRCUIT FOR FLUID-ACTUATED MOTORS Filed Nov. 7, 1949 3/ a I II I Fllll v 7 90 FIGE:

INVENTOR. Warren R Tucker ATTOR N EY Patented Nov. 18, v 1952 UNITED STATES PATENT OFFICE LOCKING CONTROL CIRCUIT FOR FLUID- ACTUATED MOTORS Warren E. Tucker, Mount Gilead, Ohio, assignor to H-P-M Development Corporation, Mount Gilead, Ohio, a corporation of Delaware Application November 7, 1949, Serial No. 125,877

1 Claim. 1

The present invention relates generally to control circuits for fluid-actuated motors or reciprocating rams. More particularly, the present invention deals with an improved hydraulic circuit for hydraulic motors or rams of the type used to impart reciprocatory or oscillatory movement to a member or members of various types of machinery. In its more specific aspects, the present invention is concerned with a hydraulic control circuit for use in connection with a hydraulic motor or ram which is employed as an actuating member for the clamping arms or grapples of a loader or lifting machanism, although it will be understood that the present improved control circuit may be employed in connection with any type of reciprocating hydraulic motor wherein it is desirable to lock the reciprocatory member of the motor in a givenposition of extension or retraction with respect to the ram and prevent the slippage or creeping of the reciprocat-ory member after movement thereof to a said desired position.

In the past, fluid-actuated hydraulic motors or rams have been employed with facility in replacement of various typesoi mechanical movements in machinery, and for some time, it has been proposed to employ such hydraulic motors or rams as a means for actuatin the clamping or grapple members of portable lifting and elevating machines or vehicles;

However, the use of hydraulic motors in this capacity has been limited due to the tendency of the reciprocatory member-of the motor or ramto slip or creep after "being initially actuated to aload-cl'amping position, thereby allowing the load to'be dropped or released inadvertently.

In most instances, where hydraulic rams or motors are employed, the motor is under control of a multiple way hydraulic control valve which functions to direct fluid under pressure of a suitable pump into the pressure area o areas of the motor to actuate the movable plunger of the motor. Also, such control valves are usually operable to create a partial look within the fluid motor or ram while at the same time directing the pump discharge to'exhaust, in orde that free circulation of the pump is obtained when the movable member of the motor is maintained in a stationary position.

However, in most instances, the multiple way control valves employed in directing fluid to the various pressure stages of the hydraulic motor do not function to provide an efficient lock within the motor when conditioned to a neutral or pump. by-passing position. Generally, such multiple way control valves embody a movable spool as a means for establishing a look within the motor circuit.

Accordingly, it is the primary object of the present invention to provide a control circuit for hydraulic rams or motors which functions to automatically create a positive look within a hydraulic motor or ram when it is desired to maintain the plunger or reciprocatory member of theram in a desired stationary position.

It is another object of this invention to provide an improved hydraulic control circuit for hydraulic rams which comprises acontrol valve operable to introduce fluid under pressure of an associated pump into the pressure area or areas of a hydraulic motor in order to impart movement to the piston or ram member of the motor, and which is operable when occupying a neutral position to by-pass the pump discharge directly to exhaust, andwherein one or more check valves are interposedbetween the motor ports of the control valve and the pressure area of'the motor to establish a positive look within the motor when the associated control valve occupies its neutral pump by-passing position, whereby to prevent and preclude movement of the reciprocatory member. of the motor after the same is initially actuated to a desiredposition;

For a further and more detailed understanding' of the present invention and'the various additional objects and advantages derived therefrom, reference is made to the following description and the accompanying drawing, wherein:

Fig. '1 is a diagrammatic View of the present improved hydraulic control circuit, in which the control valve and motor are shown in vertical section;

Fig. 2' is a medial longitudinal vertical sectional view taken through a pilot pressure-oper'ate'd check valve employed in the present control circuit for-lockin the reciprocatory member of a hydraulic motor against slippage; and

Fig. 3 is a horizontal sectional view taken along theline '3-3 of Fig. 2.

Referring'now to the'drawing, the numeral 5 generally designates a double-acting hydraulic motor or ram which embodies a cylinder 6 in which is carried a piston I having a longitudinally extended plunger 8. The side of the piston l opposite the plunger 8 is provided with a relatively large fiat pressure-responsive face which defines with the side and end walls of the cylinder 6 a piston-advancing pressure area. The side of the piston 'i connected with the plunger 8 defines with the side and end walls of the cylinder 6 a second piston-retracting chamber or area into which fluid may be introduced to retract the plunger with respect to the cylinder. The cylinder 6 is provided at either end with inlet ports 9 for the introduction and release of fluid pressure to and from the separate chambers or pressure areas of the motor.

Fluid pressure for operating the motor 5 and for imparting feciprocatory movement to the plunger 8 is derived from a fluid displacement pump Iii of any suitable type, but which preferably comprises a constant delivery non-reversible type. The pump I is provided with an intake or inlet conduit II which is in communication with a body of fluid contained in a reservoir l2. The discharg outlet of the pump is connected with a conduit I3 which is connected with the pump inlets [4 of a spool-type control valve i by way of the branched conduits IS.

The control valve I5, as shown in detail in Fig. 1, comprises a casing l! which is formed with an internal chamber 18 and a relatively smaller valve chamber l9. slidably carried within the valve chamber is is a spool-type valve member 20 having end extension shafts 2| extending through the ends of the casing l1 and joined with the armatures of a pair of solenoids 22. Preferably, the rod or shaft 2| of the movable valve member 20 is maintained under spring tension to center the valve member in its full line position as shown in Fig. l. The valve member 23 may be actuated either to th left or right by selective energization of the solenoids 22.

In its neutral position, the valve member 20 functions to connect the pump ports I4 with a relatively enlarged exhaust chamber 23 formed in the middle of the valve chamber l9. The enlarged chamber or area 23 is provided with an exhaust port 24 which in turn is in communication with the larger chamber N3 of the valve which has communication with a main exhaust port 25 extending through the wall of the casing I1. Upon energization of the left hand solenoid 22 of the control valve, the spool member 28 is shifted leftwardly to connect the left hand pump port l4 with a first motor port or outlet 26, while uncovering a second motor port or outlet 21 to connect the same by way of the right hand end of the chamber l9 with the larger exhaust chamber l8 of the valve.

Simultaneously, the right hand spool of the member 20 covers the right hand pump port [4 to interrupt communication between the latter and the enlarger exhaust area 23. Also, the valve member 20 is provided with an intermediate spool which moves leftwardly into the smaller valve chamber I9 to interrupt communication between the left hand pump port [4 and the exhaust area 23. Upon energization of the right hand solenoid 22, the member 20 is shifted in the opposite direction whereupon fluid under pressure of the pump is directed outwardly through the motor port 21 While connecting the opposite motor port 26 to exhaust. It will be seen that, in its neutral position, the member 20 provides for the free circulation of fluid displaced by the pump through the control valve by way of the enlarged area 23, the port 24 and the main outlet 25 of the valve which is connected by way of an exhaust conduit 28 with the reservoir I2.

Extending between the motor port 26 of the valve [5 and the plunger advancing area of the motor 5 is a conduit 29, and interposed within the conduit 29 is a pilot-operated check valve 30. This check valve 30 is shown in detail in Figs. 2 and 3 of the drawing, and will be seen to comprise an outer casing 3| in which is formed an inlet port 32 which is connected with the conduit 29 on the control valve side, and an outlet port 33 which communicates with the conduit 29 at its motor-connecting side. The casing 3| is further formed with a plurality of internal interconnected chambers, the uppermost of which slidably receives a movable check valve member 34 which is formed with a tapered lower end 35 for cooperative seating engagement with a valve seat region 36 provided between the uppermost and intermediate chambers or bores of the casing.

The opposite end of the uppermost chamber is closed by a screw threaded plug 31 which limits the movement of the member 34 within the chamber. Interposed between the member 34 and the plug 31 is a light compression spring 38 which lightly urges the member 34 toward its seated position. Thus, the member 34 normally occupies its seated position with respect to the area 36 in which communication between the inlet and outlet ports 32 and 33 is interrupted. The member 34 is further formed at its tapered end with a first pressure-responsive area 39 which is constantly in communication with the inlet port 32, and a second pressure-responsive area 40 which communicates with the outlet 33 by Way of a relatively restricted opening 4| formed in the side wall of the member adjacent the outlet 33.

The lowermost chamber of the casing 3| which is substantially larger than the upper and intermediate chambers thereof slidably receives a pressure-responsive piston member 42 having an axially extended plunger rod 43 disposed in longitudinal alignment with the valve member 34. The under face of the piston 42 is in communication with a pilot port 44 which in turn is connected by way of a pilot conduit 45 with the pump discharge conduit I3 between the pump and the control valve l5.

In Fig. 1, it will be seen that the opposite motor port 27 which is connected with the retracting area of the motor 5 by means of a conduit similar to that designated by the numeral 29, may also be provided with an identical pilotoperated check valve 33.

In operation, assuming the piston 1 of the motor 5 to be in a fully retracted position, the plunger 8 of the motor is extended or advanced by shifting the valve member 20 in a leftward direction to connect the discharge of the pump with the conduit 29 leading to the advancing area of the motor. Upon introduction of pressure fluid within the inlet 32 of the check valve 30, the valve member 34 is unseated by pump pressure acting upon the lower pressure-responsive area 39 thereof, and establishes communication between the inlet 32 and the outlet 33 of the check valve, thus allowing of passage of fluid to the advancing area of the motor 5. As the piston I of the motor starts to advance, fluid disposed within the retracting area of the ram is momentarily trapped by the seated valve member 34 of the right hand pilot-operated valve 39 thus creating a build-up in pressure within the pump discharge conduit 13 which, in turn, is transmitted through the pilot conduits 45 to the lower area of the piston member 42 which is immediately elevated to positively unseat the valve members 34 of both valves 30 to permit of circulation of pressure fluid to and from the separate areas of the motor 5.

When the plunger 8 of the motor 5 has been advanced to a desired position, the control valve I5 is neutralized and fluid from the pump is freely by-passed back to the reservoir I2. At this time, the separate valve members 34 of the check valves 35 close, thus interrupting the flow of fluid from both of the areas of the motor 5 in a direction toward the control valve [5. Thus, work-resistance forces transmitted to the plunger 8 of the motor are absorbed thereby due to the positive lock created on both sides of the piston 1 by fluid trapped between the separate pressure areas of the motor and the check valves 30. It will here be seen that any tendency of the motor to slip or creep under the resistance of a load will be positively prevented without depending upon the spool members of the associated control valve I5. When it is desired to retract the plunger 8 of the motor, the valve member 20 of the control valve I5 is shifted rightwardly by energization of the right hand solenoid 22 whereupon pressure fluid from the pump I is directed through the right hand motor port 21 of the control valve through the right hand check valve 30 and into the retracting area of the motor. When the piston 1 meets resistance to retracting movement, the pressure in line I3 immediately builds up to a point at which the piston members 42 of the check valves are elevated to unseat the associated valve members 34 to permit of passage of fluid to and. from the motor.

It will be understood that only one of the pilotoperated check valves 30 need be employed when it is desired that the plunger 8 of the hydraulic motor be held against load resistance in one direction only, that is to say, when it is desired to prevent creeping of the piston 1 in a backward direction after initial extension. In this event, it is only necessary to employ the pilot-operated check valve 30 within the line or conduit leading to the advancing pressure area of the motor.

In the example shown in Fig. 1, it will be understood that the two check valves 30 employed in each conduit connecting the control valve with the separate areas of the motor function to; prevent the possibility of creeping or slippage of the piston in either direction after extension or retraction. It will also be understood that the present improved control system may be used in connection with a single-acting hydraulic ram having a single pressure-responsive area in which it is desired to positively lock fluid to prevent accidental slippage of the ram after the same is actuated to a desired position of exten- SIOII.

In view of the foregoing, it will be seen that the present invention provides a highly eflicient control circuit for employment in connection with hydraulic motors of the type used to actuate an associated clamping or grappling mechanism to its load-engaging position, positive provision being made within the circuit to prevent slipping or retraction of the plunger 8 of the motor after inititally extended to its desired position.

While a single preferred embodiment of the present hydraulic circuit has been disclosed in detail, it will be manifest that various modifications as to constructional details may be restored to without departing from the spirit of the invention or the scope of the following claim.

I claim:

In a hydraulic control circuit; a hydraulic ram having a ram-advancing pressure area and a ram retracting pressure area; a distributing valve having a pair of outlet ports connected, respectively, with the ram-advancing and ram-detracting pressure areas of said ram, an exhaust port and a pressure inlet, and operable selectively to connect the pressure inlet with either of the outlet ports while connecting the opposite outlet port with the exhaust port or to connect the pressure inlet with the exhaust port thereof; a pump connected to circulate pressure fluid to the pressure inlet of said distributing valve; a check valve connected between one of the outlet ports of said distributing valve and the associated pressure area of said ram and having a movable valve member therein normally arranged to interrupt communication between the last-named outlet port of said distributing valve and the associated pressure area of said ram, but being movable in response to the flow of pressure fluid in a direction from said last-named outlet port toward the associated pressure area of said ram to provide free communication therebetween; and fluid-pressure-actuated means engageable with the movable valve member of said check valve and connected directly with the discharge of said pump in bypassing relation to said distributing valve and responsive to a given high pressure within the discharge of said pump for moving the valve member of said check valve to an open position independently of the flow of pressure fluid from said last-named outlet port of said distributing valve toward the associated pressure area of said ram.

WARREN R. TUCKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,590,226 Boisset June 29, 1926 1,955,154 Temple Apr. 17, 1934 2,058,377 Francis Oct. 20, 1936 2,533,833 Mott Dec. 12, 1950 2,575,507 Acton Nov. 20, 1951

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Cited By (40)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2674231A (en) * 1952-01-02 1954-04-06 Ohio Commw Eng Co Power pack for massage suits
US2739449A (en) * 1952-09-26 1956-03-27 Vickers Inc Power transmission for multiple motor operation
US2745499A (en) * 1951-12-26 1956-05-15 Gen Motors Corp Propeller control
US2750743A (en) * 1952-03-12 1956-06-19 Bosch Gmbh Robert Control devices for hydraulic motors
US2770098A (en) * 1952-03-12 1956-11-13 Bosch Gmbh Robert Hydraulic servo-motors
US2830562A (en) * 1954-01-21 1958-04-15 Cleveland Pneumatic Tool Co Hydraulic ball screw type steering motor and shimmy damper
US2841960A (en) * 1954-01-18 1958-07-08 J H Holan Corp Fluid pressure control system
US2872903A (en) * 1956-11-13 1959-02-10 Emhart Mfg Co Fluid lock valve
US2914087A (en) * 1958-03-21 1959-11-24 Mead Specialties Company Inc Valve
US2915332A (en) * 1956-07-03 1959-12-01 Cleveland Crane Eng Material handling apparatus
US2946319A (en) * 1956-11-07 1960-07-26 Otis Elevator Co Hydraulic control system for elevators
US2984985A (en) * 1959-02-16 1961-05-23 Macmillin Hydraulic Engineerin Hydraulic operating and control system
US3009660A (en) * 1958-09-08 1961-11-21 Nordberg Manufacturing Co Release and adjustment for gyratory crushers
US3033001A (en) * 1958-05-05 1962-05-08 Crane Carrier Corp Hydraulic system for cranes and the like
US3039271A (en) * 1959-02-28 1962-06-19 Newton & Bennett Ltd Hydraulic pressure intensifier
US3048981A (en) * 1959-05-21 1962-08-14 Massey Ferguson Inc Control mechanism for tractor hydraulic systems
US3058676A (en) * 1960-02-23 1962-10-16 Charles E Hermann Rock crusher
US3060688A (en) * 1959-09-18 1962-10-30 John T Gondek Hydraulic systems
US3099440A (en) * 1960-09-26 1963-07-30 Ritter Co Inc Apparatus for controlling the flow of fluids
US3127189A (en) * 1964-03-31 Automatic control for vehicle suspension
US3151455A (en) * 1963-05-16 1964-10-06 Hydraulic Unit Specialities Co Pilot operated control valve mechanism
US3213874A (en) * 1961-06-02 1965-10-26 Parker Hannifin Corp Pressure responsive flow control valve for directional control valve
US3404650A (en) * 1965-04-14 1968-10-08 Manitowoc Shipbuilding Inc System and apparatus for translating and discharging a load
DE2050761A1 (en) * 1969-10-15 1971-05-27 Matairco Sa
US3703850A (en) * 1970-04-03 1972-11-28 Redman Ind Inc Hydraulic control system
US3728941A (en) * 1970-11-23 1973-04-24 Caterpillar Tractor Co Flow control valve
US3800962A (en) * 1968-11-26 1974-04-02 Byron Jackson Inc Electrohydraulic control system
US3800670A (en) * 1969-10-21 1974-04-02 Caterpillar Tractor Co High pressure implement hydraulic circuit
US3800537A (en) * 1969-10-15 1974-04-02 Matairco Sa Control systems for operating jack units
US3805678A (en) * 1972-04-17 1974-04-23 Caterpillar Tractor Co Hydraulic control system for load supporting hydraulic motors
US3943825A (en) * 1972-04-17 1976-03-16 Caterpillar Tractor Co. Hydraulic control system for load supporting hydraulic motors
US3943824A (en) * 1975-01-22 1976-03-16 Deere & Company Hydraulic system
US3967532A (en) * 1974-01-07 1976-07-06 Caterpillar Tractor Co. Forward-reverse valve for elevating scraper drive
US4006663A (en) * 1973-02-07 1977-02-08 Danfoss A/S Hydraulic control means, especially a steering means
US4026231A (en) * 1976-01-26 1977-05-31 Fedorko Irvin E Device for controlling boat speed
US4667570A (en) * 1984-12-21 1987-05-26 The Boeing Company Integral hydraulic blocking and relief valve
US4697498A (en) * 1985-09-10 1987-10-06 Kabushiki Kaisha Toyoda Jidoshokki Seisakusho Direction control valve fitted with a flow control mechanism
EP0414984A1 (en) * 1989-08-31 1991-03-06 Nissan Motor Co., Ltd. Active suspension system with enhanced response characteristics hydraulic circuit
US5067389A (en) * 1990-08-30 1991-11-26 Caterpillar Inc. Load check and pressure compensating valve
US6131610A (en) * 1996-11-22 2000-10-17 Smc Kabushiki Kaisha Speed controller with pilot check valve

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1590226A (en) * 1921-02-10 1926-06-29 Boisset Charles Leon Hydraulic steering apparatus for tractors
US1955154A (en) * 1932-11-08 1934-04-17 Cash A W Co Valve mechanism
US2058377A (en) * 1931-05-07 1936-10-20 Chas E Francis Co Hydraulic press control
US2533833A (en) * 1946-08-10 1950-12-12 Int Harvester Co Opposed hydraulic ram power transmission, including hydraulically operated power transmission stop
US2575507A (en) * 1949-05-13 1951-11-20 Russel D Acton Hydraulic power device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1590226A (en) * 1921-02-10 1926-06-29 Boisset Charles Leon Hydraulic steering apparatus for tractors
US2058377A (en) * 1931-05-07 1936-10-20 Chas E Francis Co Hydraulic press control
US1955154A (en) * 1932-11-08 1934-04-17 Cash A W Co Valve mechanism
US2533833A (en) * 1946-08-10 1950-12-12 Int Harvester Co Opposed hydraulic ram power transmission, including hydraulically operated power transmission stop
US2575507A (en) * 1949-05-13 1951-11-20 Russel D Acton Hydraulic power device

Cited By (42)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3127189A (en) * 1964-03-31 Automatic control for vehicle suspension
US2745499A (en) * 1951-12-26 1956-05-15 Gen Motors Corp Propeller control
US2674231A (en) * 1952-01-02 1954-04-06 Ohio Commw Eng Co Power pack for massage suits
US2750743A (en) * 1952-03-12 1956-06-19 Bosch Gmbh Robert Control devices for hydraulic motors
US2770098A (en) * 1952-03-12 1956-11-13 Bosch Gmbh Robert Hydraulic servo-motors
US2739449A (en) * 1952-09-26 1956-03-27 Vickers Inc Power transmission for multiple motor operation
US2841960A (en) * 1954-01-18 1958-07-08 J H Holan Corp Fluid pressure control system
US2830562A (en) * 1954-01-21 1958-04-15 Cleveland Pneumatic Tool Co Hydraulic ball screw type steering motor and shimmy damper
US2915332A (en) * 1956-07-03 1959-12-01 Cleveland Crane Eng Material handling apparatus
US2946319A (en) * 1956-11-07 1960-07-26 Otis Elevator Co Hydraulic control system for elevators
US2872903A (en) * 1956-11-13 1959-02-10 Emhart Mfg Co Fluid lock valve
US2914087A (en) * 1958-03-21 1959-11-24 Mead Specialties Company Inc Valve
US3033001A (en) * 1958-05-05 1962-05-08 Crane Carrier Corp Hydraulic system for cranes and the like
US3009660A (en) * 1958-09-08 1961-11-21 Nordberg Manufacturing Co Release and adjustment for gyratory crushers
US2984985A (en) * 1959-02-16 1961-05-23 Macmillin Hydraulic Engineerin Hydraulic operating and control system
US3039271A (en) * 1959-02-28 1962-06-19 Newton & Bennett Ltd Hydraulic pressure intensifier
US3048981A (en) * 1959-05-21 1962-08-14 Massey Ferguson Inc Control mechanism for tractor hydraulic systems
US3060688A (en) * 1959-09-18 1962-10-30 John T Gondek Hydraulic systems
US3058676A (en) * 1960-02-23 1962-10-16 Charles E Hermann Rock crusher
US3099440A (en) * 1960-09-26 1963-07-30 Ritter Co Inc Apparatus for controlling the flow of fluids
US3213874A (en) * 1961-06-02 1965-10-26 Parker Hannifin Corp Pressure responsive flow control valve for directional control valve
US3151455A (en) * 1963-05-16 1964-10-06 Hydraulic Unit Specialities Co Pilot operated control valve mechanism
US3404650A (en) * 1965-04-14 1968-10-08 Manitowoc Shipbuilding Inc System and apparatus for translating and discharging a load
US3800962A (en) * 1968-11-26 1974-04-02 Byron Jackson Inc Electrohydraulic control system
DE2050761A1 (en) * 1969-10-15 1971-05-27 Matairco Sa
US3800537A (en) * 1969-10-15 1974-04-02 Matairco Sa Control systems for operating jack units
US3800670A (en) * 1969-10-21 1974-04-02 Caterpillar Tractor Co High pressure implement hydraulic circuit
US3703850A (en) * 1970-04-03 1972-11-28 Redman Ind Inc Hydraulic control system
US3728941A (en) * 1970-11-23 1973-04-24 Caterpillar Tractor Co Flow control valve
US3805678A (en) * 1972-04-17 1974-04-23 Caterpillar Tractor Co Hydraulic control system for load supporting hydraulic motors
US3943825A (en) * 1972-04-17 1976-03-16 Caterpillar Tractor Co. Hydraulic control system for load supporting hydraulic motors
US4006663A (en) * 1973-02-07 1977-02-08 Danfoss A/S Hydraulic control means, especially a steering means
US3967532A (en) * 1974-01-07 1976-07-06 Caterpillar Tractor Co. Forward-reverse valve for elevating scraper drive
US3943824A (en) * 1975-01-22 1976-03-16 Deere & Company Hydraulic system
US4026231A (en) * 1976-01-26 1977-05-31 Fedorko Irvin E Device for controlling boat speed
US4667570A (en) * 1984-12-21 1987-05-26 The Boeing Company Integral hydraulic blocking and relief valve
US4697498A (en) * 1985-09-10 1987-10-06 Kabushiki Kaisha Toyoda Jidoshokki Seisakusho Direction control valve fitted with a flow control mechanism
EP0414984A1 (en) * 1989-08-31 1991-03-06 Nissan Motor Co., Ltd. Active suspension system with enhanced response characteristics hydraulic circuit
US5067389A (en) * 1990-08-30 1991-11-26 Caterpillar Inc. Load check and pressure compensating valve
US6131610A (en) * 1996-11-22 2000-10-17 Smc Kabushiki Kaisha Speed controller with pilot check valve
US6293180B1 (en) 1996-11-22 2001-09-25 Smc Kabushiki Kaisha Speed controller with pilot check valve
US6296015B1 (en) 1996-11-22 2001-10-02 Smc Kabushiki Kaisha Speed controller with pilot check valve

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