US3620129A - Hydraulic power circuit with emergency lowering provisions - Google Patents

Hydraulic power circuit with emergency lowering provisions Download PDF

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Publication number
US3620129A
US3620129A US55028A US3620129DA US3620129A US 3620129 A US3620129 A US 3620129A US 55028 A US55028 A US 55028A US 3620129D A US3620129D A US 3620129DA US 3620129 A US3620129 A US 3620129A
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United States
Prior art keywords
pressure
remote control
control system
pump
cylinder
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US55028A
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English (en)
Inventor
Waldo G Fruehauf
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ICM ACQUISITIONS Inc A DE CORP
Hydreco Inc
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General Signal Corp
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Assigned to CONTINENTAL ILLINOIS NATIONAL BANK AND TRUST COMPANY OF CHICAGO reassignment CONTINENTAL ILLINOIS NATIONAL BANK AND TRUST COMPANY OF CHICAGO SECURITY INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ICM ACQUISTIONS INC.
Assigned to CONTINENTAL ILLINOIS NATIONAL BANK AND TRUST COMPANY OF CHICAGO reassignment CONTINENTAL ILLINOIS NATIONAL BANK AND TRUST COMPANY OF CHICAGO SECURITY INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ICM ACQUISITIONS, INC., A CORP. OF DE
Assigned to HYDRECO, INC. reassignment HYDRECO, INC. CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). EFFECTIVE DATE: SEPTEMBER 11, 1987 Assignors: ICM ACQUISTIONS INC.
Assigned to ICM ACQUISITIONS, INC., A DE. CORP. reassignment ICM ACQUISITIONS, INC., A DE. CORP. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: GENERAL SIGNAL CORPORATION, A NY CORP.
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00—Details of servomotor systems ; Valves for servomotor systems
    • F15B13/02—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors
    • F15B13/04—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor
    • F15B13/042—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor operated by fluid pressure
    • F15B13/0422—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor operated by fluid pressure with manually-operated pilot valves, e.g. joysticks
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/226—Safety arrangements, e.g. hydraulic driven fans, preventing cavitation, leakage, overheating

Definitions

  • the remote control system normally receives motive 'fluid from a pump, but, when the pump is disabled or idle, the controls may be adjusted to effect lowering of an elevated load utilizing the fluid under load pressure in the cylinder.
  • the circuit includes a switch valve which alternately connects the inlet conduit of the remote control system with the pump or the cylinder depending upon whether pump output pressure is above or below a predetermined value, and a pressure regulator for reducing the pressure of the fluid delivered to the remote control system from the cylinder.
  • the pressure regulator may be arranged between the switch valve and the remote control system so that it can serve to reduce the pressure of the fluid supplied to that system from either the power pump or the lift cylinder.
  • Hydraulic power circuits employed on large construction and material-handling vehicles, such as front end loaders use high capacity, open center directional control valves which require large actuating forces. Therefore, from the standpoint of reducing operator fatigue, it is desirable that these valves be actuated through a low pressure remote control system.
  • a common remote control system includes a pair of piloted pressure motors for shifting each directional control valve, and a small, manually operated, pressure-graduating pilot valve for each set of motors which serves to furnish them with pilot fluid at a selectively variable pressure.
  • the pilot valves normally are supplied with operating fluid at a substantially constant, low pressure by a source including a pump and a relief valve.
  • the pump is driven by the propulsion engine of the vehicle, so the actuating cylinders in the power circuit cannot be operated when the engine is off. Because of this, circuits which include a lift cylinder, such as the boom-lifting cylinders on a loader, should be provided with some means which allows the load to be lowered in situations where the engine stops while the load is in an elevated position.
  • One prior solution to the engineoff lowering problem consists in providing the lift cylinder with a vent line which leads from its contracting end to the oil tank, and which is controlled by an auxiliary, manually operated throttling valve. Gradual opening of this valve allows controlled escape of oil from the contracting end of the cylinder, and thereby permits the operator to effect and regulate descent of the load under emergency conditions. While this solution is workable, it has two disadvantages. First, since the operator normally effects lowering of the load through one of the pilot valves, the use of a separate valve for emergency lowering would be inconvenient and would require additional training. The second disadvantage is the risk that the auxiliary valve will be left open inadvertently and that, therefore, proper operation of the lift circuit will be precluded.
  • a second, and better, prior proposal for effecting engine-off lowering involves use of the oil under load pressure in the cylinder as the operating fluid for the remote control system.
  • the contracting end of the lift cylinder is connected with the inlet conduit of the pilot valves through a pressure reducer, and the discharge line of the engine driven pump is provided with a check valve oriented to block flow toward the pump.
  • the output pressure of the reducer is comparable to that established by the relief valve; therefore, when the engine is olf and the load is in an elevated position, the remote control system still will be supplied with operating fluid at the proper pressure level. As a result, the operator will be able to lower the load in the usual way by merely manipulating the appropriate pilot valve.
  • the pressure reducer Under normal conditions, i.e., when the pump is running, the pressure reducer must close and isolate the lift cylinder from the remote control system in order to prevent unintended upward creeping of the load when the pilot and directional control valves are in neutral position, and to insure proper operation of the circuit when these valves are in the power down and raise positions.
  • This means that the pressure setting of the reducer must be lower than the setting of the relief valve.
  • the response characteristics of the remote control system depend upon the pressure of the fluid supplied to it, so, if substantially equal response is desired under both emergency and normal conditions, the settings of the pressure reducer and the relief valve must be fairly close to each other. Therefore, in order to correct for the effects of manufacturing tolerances and of dilferences between installations, either the reducer or the relief valve on each vehicle must be adjusted to make sure that the relief valve has the higher setting.
  • the object of this invention is to provide an improved engine-off lowering scheme which utilizes the fluid under pressure in the lift cylinder as the emergency source of operating fluid for the remote control system, but which eliminates the need for adjusting the components on a vehicle-byvehicle basis and can be incorporated in the circuit of application Ser. No. 37,200 without the need for an extra pressure reducer.
  • the power circuit is equipped with a switch valve which responds to the output pressure of the engine driven pump and serves to connect the inlet conduit of the remote control system with this pump or with the lift cylinder depending upon whether the pressure is above or below a predetermined value.
  • the predetermined value has no significance as far as performance of the remote control system is concerned, but serves merely as an indicator of whether or not the pump is operating normally. Therefore, it can be sufficiently lower than the settings of other valves in the circuit to obviate adjustment of any of the values on the vehicle.
  • the switch valve not the pressure reducer, serves to isolate the lift cylinder from the remote control system during normal operation,
  • the reducer may be located either between the cylinder and the switch valve, or between the latter and the inlet conduit of the remote control system.
  • the ability to use the last mentioned location is important in embodiments incorporating the teachings of application Ser. No. 37,200, because it allows a single pressure reducer to serve both the normal and the emergency pilot supply circuits.
  • FIG. 1 is a schematic diagram of an embodiment employing separate pilot and main pumps.
  • FIG. 1A is a schematic diagram showing a modification of the FIG. 1 circuit.
  • FIG. 2 is a schematic diagram of an embodiment wherein the main power pump serves as the normal source of supply for the remote control system.
  • the improved circuit is employed to actuate a load 11, which may represent the boom of a front end loader, and includes one or more lift cylinders 12, a main power pump 13 and oil tank 14, and an open center, sliding plunger directional control valve 15.
  • a load 11 which may represent the boom of a front end loader
  • the complete power circuit normally includes additional actuating cylinders and directional control valves, for convenience and clarity the present discussion concerns only the lift portion of the circuit.
  • the plunger of directional control valve 15 is biased to its neutral or hold position by a centering spring (not shown) and is shifted to its various actuating positions by a pair of opposed piloted pressure motors 16 and 17 which are supplied with operating fluid at a selectively variable pressure by a closed center, manually operated, pressure-graduating pilot valve 18.
  • a centering spring not shown
  • piloted pressure motors 16 and 17 which are supplied with operating fluid at a selectively variable pressure by a closed center, manually operated, pressure-graduating pilot valve 18.
  • Pilot valve 18 receives operating fluid at a relatively low pressure from either one of two sources.
  • the first includes a relief valve 19 and a small pilot pump 21 which, like main pump 13, is driven by the vehicles propulsion engine.
  • the second source includes the head end 12a of lift cylinder 12, a pressure reducing valve 22, and a relief valve 23.
  • Valves 22 and 23 may be packaged together in a unit of the type shown in application Ser. No. 37,200.
  • relief valve 19 and pressure reducer 22 are set for a pressure on the order of 200 p.s.i.
  • relief valve 23 is set for a pressure of about 500 p.s.i. Selection between the two sources is effected automatically by a switch valve 24 which responds to the output pressure of pilot pump 21.
  • Valve 24 is biased by spring 24a to the illustrated position, in which it connects the inlet conduit 25 of pilot valve 18 with the outlet conduit 27 of pressure reducer 22, and is shifted by actuating motor 24b to a second position in which it connects conduit 25 with the discharge conduit 26 of pump 21.
  • Motor 24! and spring 24a are so sized that valve 24 is held in its second position whenever the pressure in conduit 26 is above a level indicative of the fact that the pump 21 is running.
  • motor 24b shifts valve 24 to the second position at a pressure of about 40 p.s.i.
  • conduit 26 When the FIG. 1 circuit is in service and the engine is running, the pressure in conduit 26 will be well above the setting of valve 24, so this valve will assume its second position, and pump 21 will deliver operating fluid to pilot valve 18 at a pressure determined by the setting of relief valve 19. Under this condition, conduit 27 is isolated from both of the conduits 25 and 26, so there will be no flow from pump 21 to the head end 12a of cylinder 12 or from the head end to the remote control system, Because of this, the settting of reducer 22 may be higher than the setting of relief valve 19 without adverse effect.
  • the relief valve 23 is in communication with the head end 12a of cylinder 12 through pressure reducer 22, and that therefore some oil can escape from the cylinder to tank 14 at times when the head end pressure is higher than the relief valve setting.
  • the setting of relief valve 23 is higher than the setting of reducer 22, the reducer will be closed when the load pressure is this high, and consequently the volume of oil which escapes from the cylinder will be limited to the small amount which leaks across the spool of the reducer 22 from conduit 28 to conduit 27.
  • pressure reducer 22 and relief valve 23 may be connected into the circuit between switch valve 24 and the inlet conduit 25 of the remote control system, rather than between the switch valve and the lift cylinder.
  • the switch valve 24 may serve to connect the inlet conduit 29 of reducer 22 with either the discharge conduit 26 of pump 21 or the conduit 28 leading from the head end of the lift cylinder, this would require that all of the oil delivered to the remote control system during normal operation pass through reducer 22. Since the pressure reducer is needed only during emergency conditions, the pressure losses accompanying flow through this device would constitute a waste of energy. Therefore, it is preferred that the switch valve 24 in the FIG. 1A embodiment deliver oil from pump 21 to conduit 25 through a conduit 31 which by-passes reducer 22.
  • FIG. 1A Inasmuch as the relief valve 23 in FIG. 1A is isolated from the lift cylinder whenever the pilot pump 21 is running, this version of the invention inherently precludes escape of any oil fro-m the head end of the cylinder to tank through that relief valve.
  • the embodiment of FIG. 1A also is desirable because it allows the valves 22-24 to be packaged as a unit which, except for minor changes in circuitry, can be employed in power circuits which use the main power pump as the normal source of operating fluid for the remote control system.
  • FIG. 2 shows the invention embodied in the power circuit of application Ser. No. 37,200.
  • the supply line 32 leading from power pump 13 to directional control valve 15' is provided with an adjustable throttling valve 33, and the pilot valve 18 normally is supplied with oil through a branch line 34 which joins the supply line at a point upstream of the throttling valve.
  • Valve 33 is controlled primarily by apparatus including a spring 33a which bias it toward a high flow-restricting position, and an opposing fluid pressure motor 33b which is connected with sup-ply line 32 through a restriction 35 and with tank 14 through a vent valve 36 operated in unison with pilot valve 18.
  • valve 33 assumes a low flow-restricting position, and imposes a minimum backpressure on pump 13, when the pilot valve is in neutral position, and shifts to the high flow-restricting position and creates a backpressure sufficient to operate the remote control system when pilot valve 18 is shifted away from neutral position to effect actuation of cylinder 12.
  • Valve 33 also is equipped with an override motor 33c which shifts it to the low flow-restricting position where the load pressure in line 32 developed during actuation of the cylinder is itself high enough to insure proper operation of the remote control system.
  • the pressure of the oil delivered to branch line 34 varies with the load pressure in conduit 3-2, so, under high load conditions, it must be reduced before the oil reaches pilot valve 18.
  • this function may be performed by the same reducer 22 which serves the emergency engine-otf lowering scheme if, as illustrated, this component is located downstream of switch valve 24.
  • the arrangement is similar to the one shown in FIG. 1A except, of course, that the bypass 31 is omitted and valve 24 is used to connect one or the other of the lines 28 and 34 with the reducer 22.
  • valve 24 will connect line 34 with pressure reducer 22, and the remote control system can be operated in the usual way utilizing a portion of the out put of pump 13 as the operating fluid.
  • the pressure in line 34 will dissipate, and valve 24 will shift to the illustrated position and connect line 28 with the pressure reducer. Therefore, if load 11 is in an elevated position, pilot valve 18 will still receive oil at the pressure needed for proper operation of the remote control system, and emergency lowering of the load can be effected as in the other embodiments.
  • a hydraulic power circuit including a lift cylinder (12) for raising a load (11), directional control valve means (15) for controlling flow from a power pump (13) to the cylinder and from the cylinder to a reservoir (14), a low pressure remote control system (1648) for actuating the directional control valve means and having an inlet conduit (25) through which it receives motive fluid, and pumping means (21 or 13) for delivering fluid under pressure to the inlet conduit, the improvement which comprises emergency means for permitting lowering of the load from an elevated position when the pumping means is disabled, the emergency means including (a) an auxiliary conduit (28) for leading fluid expelled from the cylinder (12) by the load to the remote control system;
  • switch valve means responsive to the output pressure of the pumping means for alternately connecting the inlet conduit (25) with the pumping means (21 or 13) or the auxiliary conduit depending upon whether the pressure is above or below a predetermined value;
  • the switch valve means (24-) connects the inlet conduit (.25) with the supply passage (32) at a point upstream of the throttle valve when the output pressure of the power pump is above said predetermined valve, whereby said power pump serves as said pumping means;
  • said regulating means (22) is interposed between the switch valve means (24) and said inlet conduit (25), whereby this means (22) serves to reduce the pressure of the fluid delivered to the inlet conduit through the auxiliary conduit (28) as well as the pressure of the fluid delivered thereto by the power pump (13).

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mining & Mineral Resources (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • Fluid-Pressure Circuits (AREA)
US55028A 1970-07-15 1970-07-15 Hydraulic power circuit with emergency lowering provisions Expired - Lifetime US3620129A (en)

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US5502870A 1970-07-15 1970-07-15

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US3620129A true US3620129A (en) 1971-11-16

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US55028A Expired - Lifetime US3620129A (en) 1970-07-15 1970-07-15 Hydraulic power circuit with emergency lowering provisions

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US (1) US3620129A (de)
JP (1) JPS564762B1 (de)
DE (1) DE2130655C3 (de)
FR (1) FR2098423B1 (de)
GB (1) GB1297761A (de)
SE (1) SE371263B (de)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3805678A (en) * 1972-04-17 1974-04-23 Caterpillar Tractor Co Hydraulic control system for load supporting hydraulic motors
US3817153A (en) * 1971-09-29 1974-06-18 Rexroth Gmbh G L Hydraulic control circuit
US3935792A (en) * 1973-02-26 1976-02-03 Caterpillar Tractor Co. Pilot pump bleed control for earthmoving scrapers
DE2536126A1 (de) * 1974-08-12 1976-02-26 Caterpillar Tractor Co Hydrauliksteuerung
WO1981003685A1 (en) * 1980-06-16 1981-12-24 Caterpillar Tractor Co Pressure reducing valve for dead engine lowering
US4487106A (en) * 1983-11-04 1984-12-11 Towmotor Corporation Fluid operated system
US4509406A (en) * 1980-06-16 1985-04-09 Caterpillar Tractor Co. Pressure reducing valve for dead engine lowering
US5095804A (en) * 1990-04-09 1992-03-17 Asea Brown Boveri Ltd. Drive for a steam servo valve
EP0668407A1 (de) * 1994-02-22 1995-08-23 Clark Equipment Company Hydraulische Verriegelung mit Aufhebungsfähigkeit für bremsgelenkten Lader
US20110158830A1 (en) * 2009-12-29 2011-06-30 Volvo Construction Equipment Holding Sweden Ab. Negative control type hydraulic system
CN109312569A (zh) * 2016-04-11 2019-02-05 德国施维英有限公司 用于大型操纵器的电液控制回路

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5226311B2 (de) * 1973-08-24 1977-07-13
US4799420A (en) * 1987-08-27 1989-01-24 Caterpillar Inc. Load responsive control system adapted to use of negative load pressure in operation of system controls
US5060475A (en) * 1990-05-29 1991-10-29 Caterpillar Inc. Pilot control circuit for load sensing hydraulic systems

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3817153A (en) * 1971-09-29 1974-06-18 Rexroth Gmbh G L Hydraulic control circuit
US3805678A (en) * 1972-04-17 1974-04-23 Caterpillar Tractor Co Hydraulic control system for load supporting hydraulic motors
US3935792A (en) * 1973-02-26 1976-02-03 Caterpillar Tractor Co. Pilot pump bleed control for earthmoving scrapers
DE2536126A1 (de) * 1974-08-12 1976-02-26 Caterpillar Tractor Co Hydrauliksteuerung
US3987703A (en) * 1974-08-12 1976-10-26 Caterpillar Tractor Co. Combined restrictor and dead engine lowering valve
US4509406A (en) * 1980-06-16 1985-04-09 Caterpillar Tractor Co. Pressure reducing valve for dead engine lowering
WO1981003685A1 (en) * 1980-06-16 1981-12-24 Caterpillar Tractor Co Pressure reducing valve for dead engine lowering
US4487106A (en) * 1983-11-04 1984-12-11 Towmotor Corporation Fluid operated system
US5095804A (en) * 1990-04-09 1992-03-17 Asea Brown Boveri Ltd. Drive for a steam servo valve
EP0668407A1 (de) * 1994-02-22 1995-08-23 Clark Equipment Company Hydraulische Verriegelung mit Aufhebungsfähigkeit für bremsgelenkten Lader
US20110158830A1 (en) * 2009-12-29 2011-06-30 Volvo Construction Equipment Holding Sweden Ab. Negative control type hydraulic system
US8713930B2 (en) * 2009-12-29 2014-05-06 Volvo Construction Equipment Holding Sweden Ab Negative control type hydraulic system
CN109312569A (zh) * 2016-04-11 2019-02-05 德国施维英有限公司 用于大型操纵器的电液控制回路

Also Published As

Publication number Publication date
DE2130655A1 (de) 1972-01-20
JPS564762B1 (de) 1981-01-31
DE2130655B2 (de) 1973-05-24
FR2098423B1 (de) 1974-06-21
GB1297761A (de) 1972-11-29
DE2130655C3 (de) 1973-12-13
SE371263B (de) 1974-11-11
FR2098423A1 (de) 1972-03-10

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Owner name: CONTINENTAL ILLINOIS NATIONAL BANK AND TRUST COMPA

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Effective date: 19870911

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Owner name: CONTINENTAL ILLINOIS NATIONAL BANK AND TRUST COMPA

Free format text: SECURITY INTEREST;ASSIGNOR:ICM ACQUISITIONS, INC., A CORP. OF DE;REEL/FRAME:005156/0501

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Effective date: 19870911