US2954052A

US2954052A - Pressure fluid control system and valve

Info

Publication number: US2954052A
Authority: US
Inventors: Robert D Krehbiel
Original assignee: Cessna Aircraft Co
Current assignee: Cessna Aircraft Co
Priority date: 1959-02-19
Filing date: 1959-02-19
Publication date: 1960-09-27
Anticipated expiration: 1977-09-27
Also published as: GB905608A; FR1247218A

Description

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ATTORNEY PRESSURE FLUID C'ONTRQL SYSTEM AND VALVE Robert D. Krehbiel, Hutchinson, Kane, assignor to Cessna Aircraft Company, Wichita, Karts, a corporation of Kansas Filed Feb. 19, 1959, 'Ser. No. 794,315

9 Claims. (Cl. 137---622) This invention relates to a control system for double acting hydraulic motors, whether or not the major components are grouped in a single housing, as well as to a unitary valve in which the essential components of the control are grouped in a single housing.

More particularly the invention relates to a system and valve for controlling the flow of fluid under pressure to and from a double acting hoist cylinder, such as a cylinder used to raise and lower the boom of a power shovel, in which a very appreciable inertia force is built up during fast lowering or dropping of the boom.

Under such condition of use, when a conventional con- .trol valve is moved to a position in which the flow of fluid-to and from the double acting cylinder is blocked in order to stop the downward travel of the boom, inertia forces in the boom and the load it carries cause excessive pressure to build up in that end of the cylinder from which the return of fluid to the system reservoir is blocked. Such excessive pressure causes hammer and often causes a'break in some part of the-system.

It is an important object of this invention to eliminate the above described difficulty by providing a means incorporated in the control system which affords relief of excess pressure when flow of fluid to and from the hydraulic motor is suddenly stopped by a control valve, such pressure relief also affording a slight further movement of the cylinder plunger and of the controlled boom or other controlled element, and thus providing a cushioned stop in the downward movement of the element.

Since the slightest movement of the plunger in a cylinder forces some fluid out one end of the cylinder, there must be an equivalent inflow of fluid into the other end of the cylinder else cavitation or fluid starving occurs in the cylinder. Consequently it is an additional important object of the invention to eliminate cavitation by providing an associated means which affords flow of the necessary amount of fluid into the cylinder to compensate for the slight cushioned movement of the plunger after 'flow of fluid to and from the cylinder'through the normal supply and return passages has been blocked by the fluid control valve.

It is an additional object of the invention to provide 'a unitary fluid control valve which incorporates the above described features.

Other objects and advantages of the invention will be apparent when the following description is read in con 'nection with the accompanying drawing.

The single drawing figure is a schematic view of a hydraulic system including a double acting motor for actuating the boom of a power shovel, my invention being embodied therein in the form of a unitary control valve, shown in longitudinal vertical central section.

While the valve shown in the drawing is specifically designed for cooperative association with other valves in a multiple valve bank, and consequently includes a socalled zig-zag type neutral by-pass passage 10-41 through which fluid may continuously flow from the pump discharge :backto'the reservoir when there is no demand on States Patent 2 the system, it will be understood by those "familiar with this art that the invention described hereincan be "embodied in unitary valves designed'to function independent of any association With other valves in a multiple bank.

Excepting the fluid flow control means shown in the drawing, the hydraulic system shown is considered 'conventional. A pump 12 is supplied with fluid from a reservoir 13 through a conduit 14 and delivers that fluid at an increased pressure through a relief valve 15 to a pressure fluid passage 16 in the body 17 of the "flow control valve.

Under selective control by a shiftable valve spool 18 pressure fluid may be delivered from the supply passage 16 to either end of a double acting Working cylinder 19 through motor ports 20 and 21 and lines 22 and 23, respectively, while fluid is simultaneously returned from the other end of the cylinder through the valve body, out througha return passage 24, into return line 25, and

Generally, my invention includes 'a fluid supply means 16; a fluid return means 2425; means forming two

circuit control passages

26 and 27, connectible respectively to opposite sides .of 'a double acting motor 19; a shiftable valve means 13 which has a neutral position in which flow of fluid to and from both circuit control passage is blocked, and which is capable of selectively connecting either circuit .control passage with the fluid supply means '16 whileconnecting the other circuit control pas sage with the fluid return means 24; twoseparate bypass passages 28 and 29 both openly communicating with the fluid return means 24, and each associated with and connectible to a respective one of the circuit control passages independent of the shiftable valve spool 18; and

directional valves

30 and 31, one in each of said 'by-pass passages, each directional valve beingshiftable to open in response'to differential pressure, the one valve 30 being oriented to afford flow of fluid from its associated circuit control passage '26 into its associated by-pass passage 28 and thence to the fluid return means 24, and the other directional valve 31 oriented to atford flow from the fluid return means 24 through its associated by-pass passage 29 into the associated circuit control passage 27.

More specifically the valve illustrated, which embodies my control system, includes a housing 17 which has a longitudinal valve spool receiving bore 32. This bore is intersected by two cooperating branches 10 and 11 of a neutral by-pass passage, and bytwo separated but communicating fluid pressure supply ducts 33 and 34 which are delivered fluid from a fluid pressure supply passage 16 through a ball check valve 35. Bore 32 is also intersected by two

circuit control passages

26 and 27, each located adjacent a respective one of the supply ducts 33 and 34, and by two by-pass passages 28 and 29,'each located adjacent a respective one of the

circuit control passages

26 and 27. 1

The two circuit control passages 26 and '27 communicate respectively with motor ports 20 and 21, which in turn are connected by means of conduits 22 and 23 to opposite ends of a hydraulic motor or double acting cylinder 19.

In the system illustrated, by-pass passage 28 functions as a 'circuitrelief passage, while by-pass passage 29 functions as an anti-cavitation passage.

From the drawing it will be seen that the upper end of by-pass passage 29 communicates directly with return passage 24. In the preferred form of valve shown the upper end of bypass passage 28 also communicates with 0nd return passage 39, which would communicate di- 3 rectly with the upper end of passage 28 as well as with return line 25.

From the drawing it will be noted that

passages

28 and 26 are intersected and connected by a cross bore 40 and that a directional relief valve assembly 30 is sealed in this cross bore to afford flow of fluid under excessive pressure from passage 26 into passage 28.

The particular relief valve shown is pilot operated, although other types of pressure relief valves will serve the purpose of my invention provided the valve used opens only at a pressure greater than the normal operating pressure existing in control passage 26 during the raising and lowering of the boom 41 by cylinder 19. Although the specific relief valve construction shown is not essential to theoperation of the invention described in this application, and is disclosed completely and in greater detail in a separate patent application, it will be briefly described to assure that the operation of my invention is clearly understood.

Valve assembly 30 includes a housing 42 having a longitudinal bore 43 extending part Way through the housing from its inner end. A valve seat insert 44 is fixed in the inner end of bore 43. The housing has an inlet 45 which communicates with chamber 26, and has an outlet 46 which communicates with by-pass passage 28. A longitudinally bored valve head 47 is reciprocable in bore 43 and is normally maintained on seat 44 by a spring 48, which bears against an orifice plate 49 and against a combination pilot valve seat and spring tension adjusting member 50. A spring pressed pilot valve 51 is normally maintained seated on seat 50 by a spring 52. The oper- .ation of this relief valve will be described along with the description of the operation of my complete control system.

In the control valve illustrated the lower portions of passages 27 and 29 are connected by an intersecting cross bore 53 in which is sealed a differential pressure opened directional valve in the form of a simple check valve assembly 31. This includes a housing 54 having an inlet 55, a valve seat 56, a ball check 57, an outlet 58 forming a ball cage, and a fixed cross pin 59 to hold the ball in its cage.

To control fluid flow through the housing a shiftable valve means in the form of a cannelured valve spool 18 is reciprocably mounted in the bore 32 of the housing. The spool is urged toward the neutral or centered position shown in the drawing by a conventional spring centering assembly designated as a whole by the numeral 60.

The lands and grooves of spool 18 are so located that when the spool is in its neutral position communication between the fluid pressure supply means 16 and both

circuit control passages

26 and 27 is blocked. Likewise communication is blocked between both circuit control passages and the respective by-pass passages 28 and 29, and hence no fluid can be returned through spool bore 32 into the'return means 24. During normal operation this condition will positively lock the plunger in cylinder 19 against movement in either direction, thus holding boom 41 in a'desired position.

Operation It will be understood that pressure of fluid in circuit relief passage 28 is relatively low because it communicates only with the fluid return side of the system.

When boom 41 is in the raised position shown and the operator desires to lower or drop it, he moves spool l8 to the left. Pressure fluid flows from passage 16 past ball check 35, thru duct 34, bore 32, control passage 27, line 23 and into the inner end of cylinder 19 causing the plunger therein to move outward rapidly. As boom 41 drops fluid from the outer end of the cylinder 19 flows thru line 22, control passage 26, bore 32, transfer duct 36 and out thru return passage 24.

When the operator desires to stop the downward travel of the boom 41 he returns spool 18 to its neutral position,

as shown in the drawing. This stops the normal flow of fluid from the supply means 16 to the inner end of the cylinder 19 and also stops the flow of return fluid from the outer end of cylinder 19 back to the return passage 24. Ordinarily, due to the inertia forces built up during the downward travel of boom 41 the boom would come to an abrupt and complete stop which would result in an extreme pressure being built up in circuit control passage 26, and a resulting hammer throughout the entire hydraulic system shown. Such pressure and hammer could easily damage various parts of the system.

With my invention, however, as the excess pressure builds up in control passage 26 fluid passes through orifice 61 into the bore in valve seat 50, lifts pilot valve 51 off its seat, flows through bore 62 in valve head 47 and into circuit relief passage 28. As fluid flows past the pilot valve 51 there is a resulting pressure drop in chamber 63 of the circuit relief valve 30, and valve head 47 moves to the right in the drawing against the pressure of spring 48. Thereafter fluid may flow from the lower portion of circuit control passage 26 through inlet 45 and around the valve head 47 and out through the valve seat 44 into passage 28, and thence to the return passage 24. As soon as a sufficient amount of fluid has escaped from control passage 26 to lower the pressure therein below the pressure at which the relief valve is set to open, valve head 47 again moves to the left and seats under the urging of spring 48. It will be understood that only a very minor amount of liquid actually flows through the relief valve.

As a result of the escape of this small amount of fluid from control passage 26, however, the plunger in cylinder 19 is not brought to an immediate and complete stop. The escape of fluid first slows and then stops the plunger travel and results in what is commonly termed a cushioned stop, which completely eliminates the hammer which normally accompanies the stopping of a plunger which is being subjected at the time to inertia forces.

During the described cushioned stop the plunger moves slightly in cylinder 19, creating a partial vacuum in the inner end of the cylinder, in line 23, and in circuit control passage 27, because this circuit is unable to obtain supply fluid from the duct 34. As a result of the drop in pressure in control passage 27 the pressure in anti-cavitation passage 29 causes fluid to flow from the return line through that passage past ball check 57 and thence through line 23 to the inner end of cylinder 19, thus preifllenting that end of the cylinder from being starved of uid.

It is believed that those familiar with this art will understand that by shifting spool 18 to the right of its neutral position, shown in the drawing, supply fluid will pass from supply passage 16 through duct 33, bore 32, control passage 26, line 22 and into the outer end of cylinder 19. Simultaneously fluid will return from the inner end of cylinder 19 through line 23, circuit control passage 27, bore 32 and into return passage 24.

Having described the invention with sufficient clarity to enable those familiar with this art to construct and use it, I claim:

1. A pressure fluid control system for a double acting fluid motor comprising: fluid supply and fluid return means; means forming two circuit control passages connected respectively to opposite sides of said motor; shiftable valve means for selectively connecting either circuit control passage with the fluid supply means while connecting the other circuit control passage with the fluid return means, and in one position for blocking flow of fluid to and from said circuit control passages; means openly communicating with the fluid return means and forming two separate by-pass passages, each associated with and connectible to a respective one of said circuit control passages independent of the shiftable valve means; and means responsive to an appreciable pressure fluid" motor comprising: fluid supply and fluid; re--- turn means; means forming two circuit control passages connected respectively to opposite sides of said motor; shiftable valve means for selectively connecting either circuit control passage with the fluid supply means while connecting the other circuit control passage with the fluid return means, and in one position for blocking flow of fluid to and from said circuit control passages; means openly communicating with the fluid return means and forming two separate by-pass'passages, each associated with and connectible' to a respective one of said circuit control passages independent of the shiftable valve means: and'means responsive to an appreciable pressure increase inone circuit control passage and a pressure decrease in the other circuit control passage to bypass excess fluid from the higher pressure circuit control passage through its associated by-pass passage to the fluid return means, and to bypass supplemental fluid from the fluid return means through the other bypass passage into the lower pressure circuit control passage, independent of said shiftable valve means.

3. A control system for a double acting fluid motor comprising: fluid supply and fluid return means; means forming two circuit control passages connected respectively to opposite sides of said motor; shiftable valve means for selectively connecting either circuit control passage with the fluid supply means while connecting the other circuit control passage with the fluid return means, and in one position for blocking flow of fluid to and from said circuit con-trol passages; means openly communicating with the fluid return means and forming two separate by-pass passages, each associated with and connectible to a respective one of said circuit control passage independent of the shiftable valve means; a valve interposed between and capable of by-passing excess fluid from one circuit control passage into its associated by-pass passage in response to a predetermined pressure differential in those two passages when the shiftable valve means is in its flow blocking position; and a second valve interposed between and capable of by-passing supplemental fluid from the other by-pass passage into its associated circuit control passage when pressure in the latter drops below pressure in the said other by-pass passage and in the connected fluid return means.

4. A pressure fluid control system for a double acting fluid motor comprising: fluid supply and return means; means forming two circuit control passages connected respectively to opposite sides of said motor; shiftable valve means for selectively connecting either circuit control passage with the fluid supply means while simultaneously connecting the other circuit control passage with the fluid return means, and in one position for blocking flow of fluid to and from both said circuit control passages; a separate by-pass passage between each circuit control passage and the fluid return means; a directional valve in each of said by-pass passages, each valve shiftable in response to differential pressure, one oriented to aflord flow of fluid from its associated circuit control passage into its associated by-pass passage and to the fluid return means, and the other oriented to aflord fluid flow from the fluid return means through its associated by-pass passage into its associated circuit control passage.

5. The system described in claim 4 in which the said one directional valve is of the relief type and opens only at a pressure in excess of that norm-ally supplied by the fluid supply means, and the said other directional valve is a simple check valve.

6. A valve for controlling the flow of fluid to and from both ends of a. double-acting hydraulic. working cylinder". or motor comprising: a. housing having a bore. therein; fluid pressure supply and fluid return. means. defined? by thehousing, for connection with a. source of fluidrunder; pressure and with. a reservoir, respectively, bothcthefluid: supply andreturn means communicating with. said bore;

means in the housing defining two circuit controlpassages for connection: respectively to opposite endsofisaid; motor, both saidpassages communicating with said: bore; shiftable valve meansinsaidbore eflective in one: position to block flow of fluid to and from both. circuit control: passages, and shiftable to selectively connect either: circuit control passage withthe fluid supply means while.

simultaneously connecting the other circuit control pas sage with the fluid return means; means in the housing: defining by-pass passages in open communication with the fluid return means and respectively connecting the. circuit control passages with said fluid. return means; a directionalvalve in each by-pass passage openable in response to differential pressure, one oriented to. aflord' flow offluid from its associated control passage into its associated by-pass passage in response to a pressure in. that control passage greater than the pressure required to operate the motor under a loaded condition, the other directional valve being oriented to aflord fluid flow from.

the fluid return means into its associated circuit control passage in response to the slightest excess of pressure in the fluid return means.

7. The valve described in claim 6 in which each of said by-pass passages is closely associated with a respective one of said circuit control passages, and is capable of connecting its associated control passage with the fluid return means independent of the bore and the shiftable valve means therein, through the opening of its respective directional valve.

8. A valve for controlling the flow of fluid to and from both ends of a double acting hydraulic working cylinder or motor comprising: a housing having a valve spool receiving bore therein; a pressure fluid inlet passage in said housing in communication with said bore and connectible to a source of fluid under high pressure; a fluid outlet passage in the housing in communication with said bore and connectible to a reservoir; a pair of circuit control passages in communication with said bore for com nection to the respective opposite ends of the cylinder; a cannelured flow controlling valve spool reciprocable in said bore, effective in a neutral position to block the flow of fluid from the inlet to both circuit control passages and to block flow from both circuit control passages into said outlet through the bore, said spool being shiftable to selectively connect either circuit control passage with the inlet while simultaneously connecting the other circuit control passage with the outlet; a circuit relief bypass passage in open communication with the outlet and in valve controlled communication with one of said circuit control passages independent of said valve spool; a

pressure opened circuit relief valve interposed between the circuit relief passage and its connected circuit control passage and oriented to by-pass fluid from the control passage into the circuit relief passage in response'to a 7 pressure increase in the said control passage to a value greater than the pressure supplied by the inlet; an anticavitation by-pass passage in open communication with the outlet and in valve controlled communication with the other circuit control passage independent of said valve spool; and a check valve interposed between the anti-cavitation passage and the said other circuit control passage and affording flow of fluid from the former into passage in the housingfor connection'to a sourceof high pressure liquid; a liquid return passage in the housing for connection to a liquid reservoir; a circuit relief by-pass passage in the housing; an anti-cavitation by-pass passage in the housing; a pair of circuit control passages in the housing; two motor ports communicating respectively with said circuit control passages and constituting means to connect the valve with the opposite ends of a double acting hydraulic hoisting cylinder, all said passages communicating with said bore, said by-pass passages both being in open communication with the liquid return passage, each by-pass passage being connectible directly with a respective one of said circuit control passages through said bore and also at a location spaced from said bore, said circuit control passages being connectible selectively with said pressure passage and with said liquid return passage through said bore; a cannelured liquid flow controlling valve spool reciprocable in said bore and movable to a neutral position in which liquid flow from both circuit control passages through the bore and to the return passage is blocked, and in which flow from the pressure passage into both circuit control passages is blocked; a circuit relief valve interposed between cavitation passage and in the connected liquid return;

passage.

References Cited in the file of this patent UNITED STATES PATENTS 1,807,191 Boyle May 26, 1931 1,807,231 Weeks May 26, 1931 2,193,736 Onions Mar. 12, 1940 2,387,777 Stanton et al. Oct. 30, 1945 l 2,742,880 Ball Apr. 24, 1956 2,755,741 Erskine July 24, 1956 2,783,742 Shafer Mar. 5, 1957