US 3073340 A
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Description (OCR text may contain errors)
Jan. 15, 1963 K. s. HANCOCK HYDRAULIC SYSTEMS 3 Sheets-Sheet 1 Filed Dec. 5, 1960 ww. m mm\ smlr my M QM mm Q g/M/MV? Jan. 15, 1963 K. s. HANCOCK HYDRAULIC SYSTEMS S Sheets-Sheet 3 Filed Dec. 5, 1960 United States Patent 3,073,340 HYDRAULIC SYSTEMS Kenneth George Hancock, Walton, Warrington, England,
This invention relates to hydraulic systems for actuating one or more services such as may be required in the functioning, e.g. of'industrial fork lift trucks, or in other industrial uses such as coal mine decking arrester gear, and to selector valve mechanisms for use in such systems.
in the co-pending applications of Kenneth George Hancock and Donald Marsh Bruce Serial No. 50,716 and Serial No. 50,727, both filed August 19, 1960 and both owned in common with the present application there are disclosed hydraulic system control means whereby one or more services, such as one or more hydraulic jacks, may be operated simultaneously and/or independently of each other in such a way that the power absorbed within the system is always the minimum necessary to operate the service required; the control means also provides improved metering of the pressure fiuid within the system, so that the optimum degree of control is obtained over the service required.
The said system control means as disclosed in the said applications include a liquid tank or reservoir, a pump for providing liquid under pressure from the tank to the system, control means comprising one or more selector valve mechanisms (hereinafter referred to as a selector), an oft-load relay valve hydraulically coupled, to the selector or selectors, a pilot relief valve positioned in the pump delivery line and connections from each selector to one of a number of services dependent upon the number of selectors.
With such a system, which is vfor use with a fixed delivery pump, the pump pressure is controlled to a figure slightly in excess of the actual pressure required to operate the service selected; Fluid surplus to the requirement for that service is passed back to tank.
In such a system there is a disadvantage in that there is considerable power wastage when a service is being operated which requires a high, pressure and a small flow, because most of the pump output at the high pressure is off-loaded to tank. The present invention overcomes this disadvantage by the use of an actuator and a variable delivery swashplate type pump in conjunction with a selector valve mechanism. Such an arrangement enables a very low power loss to be attained regardless of the service requirements in respect of pressure and flow.
An hydraulic system control means according to the present invention comprises a selector valve mechanism, a variable delivery pump of the swashplate type for supplying fluid pressure to the system and means hydraulically coupled between said selector valve mechanism and the pump for automatically varying the pump output.
The said means preferably comprises a piston, the piston rod of which is pivotally linked to the swashplate oi the pump, pressure difierence within the selector valve .means acting across said piston, to move it and hence control the pump output.
FIGURE 2 a part sectional view of another form; andl FIGURE 3 a detail view of a further for-me.
Referring to the arrangement shown in FIGURE 1- there is provided a fluid reservoir 1, a variable delivery: pump 2 ot-known typein which the delivery is varied by altering the angle of a swashplate. A link 3, pivoted at 4, has its end 5 adapted to actuate-the swashplate ofpump 2. End 6 of link 3 is connected pivotally to a piston rod 7 ofactuator 8; Actuator 3 comprises a cylinder 9 divided into two chambers 10 and. 11 by a. piston 12 rigidly connected to a piston rod 7 and adapted to slide in cylinder 9. Fluid sealing meansareprovided at 13 and 14. Spring biassing means 15' is provided whereby the swashplate is blessed to the maximum de livery position for the pump. A pipeline 16 connects the reservoir 1 to the inlet of the pump 2 and pipeline 17 connects the outlet from the pump to a non-return valve .18. Branch line 1? off the line 17. connects the pump delivery to the chamber 10; Pipeline 20 con nects the non-return valve 18 to port P'ot selector valve means generally indicatedat 21. the chamber 11 of the actuator 8 to port 23 of the selector valve means 21.
The selector valve means 21 comprises a body 24 bored to take a spindle 25 adapted to slide in the body 24. The spindle has fluid sealing means 26 at-each end and has reduced diameters 27, 2d, 29, (ill. Lands 31-, 32, 33, 34 and 35 are provided for control of fluid ilow. Metering means such as flats or grooves are preferably provided on lands 33, 34. Radial drillings 36, 37 and 38 communicate with a longitudinal drilling 39in spindle 25. Ports S1 and S2 in the selector valve body 24 are connected to a service, for example an hydraulic jack to be operated. Ports T1, T2, T3 are connected by pipelines (not shown) to the resorvoir 1. A lever 4b, pivoted at 41, is connected pivotally to the spindle 25 and is used to move said spindle 25 in the body 24 to control the supply of fluid to the service to be operated.
The spindle 25 is shown in the neutral position. Initially the piston 12 of actuator 8' is biassed t0 the right so that the pump is set for maximum delivery. When pump 2 is started fluid flows through pipe line 17, nonreturn valve 18, port P- to the annulusaround the reduced diameter 23. Fluid also flows through the branch line 19 to the chamber 10 of the actuator 8. There being no escape path for the fluid, the pressure rises. The increased pressure acting on the piston 12- moves the latter to the left against the spring 15"whereby the rod 7 causes movement of the link 3 to vary the angle of the swashplate so that the pump delivery is reduced to a level which will maintain suflicient pressure in the chamber 10 to hold the piston l2 over to the left. This pressure will be low and may be of the order of 20 psi; thus the power loss, when the pump is not running on load, is reduced to a minimum.
It will be appreciated that as shown the area of piston rod 7 is small compared with the area of piston 10 so that the eifect of the hydraulic unbalance is minimized, as an alternative arrangement hydraulic balance of the actuator piston can be obtained by providing a tail rod r second piston rod similar to piston rod 7 and extending through the chamber #10 and the end of the cylinder 9 in known manner.
When the selector valve means is operated by movement of the lever 40, initial movement of the spindle 25 to the left brings the land 32 over the port 23 whereby communication between ports 23 and T1 via the annulus around the reduced portion 27 is broken. With further movement of the spindle to the left, the land 34 uncovers the port S1, which is then in communication with port T3 via the annulus around the reduced diameter 33. Further very small movement of the spindle, to the left,
Pipeline 22 connects I 3 brings radial drilling 37 into communication with the port S2, so that the pressure in the service line connected to the port S2 is now led through drillings 37, 39, 36
port 23 and pipeline 22 to chamber 11 of actuator 8. The pump delivery will now be automatically adjusted to a predetermined value, for example, 20 p.s.i., above the service line pressure. spindle 25 to the left brings port P into communication with port S2 via the metering means, for example flats or grooves, in land 33. The pressure at port P being in excess of that at port S2, there will consequently be a flow from P to S2 and the service will be operated. The pump output will be automatically adjusted by the actuator 8 so that, for any position of the selector spindle, the pressure drop due to the flow from P to S2 is maintained at, for example, 20 p.s.i.; hence a small Opening between P and S2 due to the metering means will allow only a small flow for a pressure drop of, for example, 20 p.s.i., whilst a larger opening will allow a correspondingly larger flow for the same pressure drop.
If the pump output is less than that required to give the requisite pressure drop from P to S2 for a given position of the selector spindle, the spring in the actuator 8 will move the piston 12 and piston rod 7 to the right; the link 3 will thus be moved to adjust the swashplate to increase the output from the pump.
If the pump output flowing from P to S2 generates a larger pressure drop than, for example, p.s.i., the pump output pressure acting on the piston 12 of the actuator will move the piston to the left, whereby the pump output is reduced.
When the spindle has been moved fully to theleft it is arranged that the radial drilling 37 is still in register with port S2, whereby pump output control is maintained.
Initial movement of thespindle to the right causes the land 31 to blank port T1. Further movement of the spindle to the right brings the port S2 in communication with the port T2 via the annulus around the reduced diameter 28. Further very small movement brings the radial drilling 38 in communication with the port S1. The pressure in the service line connected to the port S1 is now led to the chamber 11, via the drillings 39, 36 and port 23, and the pump output is adjusted as described above so as to maintain a pressure of, for example 20 p.s.i. above the service line pressure. Further movement of the spindle to the right brings ports P and S1 into communication with one another via the annulus around reduced diameter 29 and-the metering means in land 34. The pressure at port P is in excess of that at port S1 and consequently there is a flow of fluid from P to S1. The pump output is automatically adjusted so that the requisite pressure drop is maintained between ports P and S1 in the same way as has been described when ports P and S2 are in communication. I
When the spindle 25 has moved fully to the right it is arranged that the radial drilling 28 is still in register with port S1 whereby pump output control is maintained.
It will thus be appreciated that the output of the pump in terms of pressure and flow is automatically controlled in accordance with the requirements of the service to be operated and the power loss is kept to a minimum.
In this construction, the invention has been described with reference to a single selector valve mechanism. It will be appreciated however that it may equally well be used with a plurality of selector valve mechanisms.
By way of example, FIGURE 2 shows improved by;- draulic'system control means as already described, but including two selector valve mechanisms, S L1 and SL2. Similanpartsare indicated with the same numerals as on F RE 1 he P s PZ..;S d r Terao S espo d qpor 1, 22 nd I1. I?
and-T3 -on selector SLLrespectivelye Ports S1, S2, may be connected to one service to be controlled by selector SL1, ports S3, S4 may be connected to a further service to be controlled by selector SL2. i Each selector SL1, SL2
Continued movement of 4 and the actuator 8 function as previously described with reference to FIGURE 1.
If the selector SL1 remains in the neutral position and the selector SL2 is operated, then the pump delivery is controlled with reference to the pressure in service port S3 or S4 whichever is connected through port P2 to the pump delivery.
It will be appreciated that if the selectors SL1 and SL2 are moved so as to select the two services simultaneously then the pump delivery and pressure will be controlled by the setting of the selector SL1. If, for example, the selector SL1 connects pump delivery through port P1 to service port S1 and selector SL2 connects pump delivery through port P2 to service port S3, then the pump delivery pressure will be controlled to say 20 p.s.i. above the pressure in service port S1. If the pressure in service port S3 is less than the pressure in service port S1 then both services will be operated simultaneously. If however the pressure in service port S3 is greater than the pressure in port S1 then the service connected to port S1 alone will be operated.
The improve'd hydraulic system control'means described may also incorporate a further feature. It may be desirable to limit the speed of operation of a heavy load to avoid overloading the driving motor and to obtain an increased speed of operation of a lighter load. This may be obtained with the modified actuator shown in FIG- URE 3.
FIGURE 3 shows the reservoir 1, pump 2, linkage actuator and pipelines as in FIGURES 1 and 2, but with the addition of pressure responsive stop means for the piston 12 in the chamber 10 of the actuator 8. The body 9 of actuator 8 is extended on the side of chamber 10. In the extended portion is slidably mounted a piston 42 attached to a rod 43 which is engageable by and forms a stop for the piston 12 in the chamber 10. Fluid sealing means are provided at 44, 45. A spring 46 biases the piston 42 to the right. The piston 42 divides the extension of body 9 into two chambers 47, 48. Chamber 47 is vented. A branch line 49 off the line 18 connects into chamber 48.
The piston 12 is shown fully to the right, that is, the pump swashplate is in the maximum delivery position. The pump delivery and pressure are regulated auto matically as previously described. As the pump pressure increases, an increasing fluid force acts on piston 42 urging it and its rod 43 to the left against spring 46. As the piston 42 and rod 43 move to the left, the piston 12 is thereby moved to the left, thus reducing the pump delivery, whereby the load on the driving motor does not exceed a safe value.
Considering the limiting means shown in FIGURE 3 more particularly in connection with FIGURE 1, it is re called that the piston 12 primarily controls the pump output or delivery rate under the conjoint influences of the pump delivery pressure and the service pressure, for example the pressure extant at the port 23, the two pressures opposing one another on opposite sides of the piston 12. Accordingly, for normal serviceor load conditions, the opposite faces of the piston 12 and the biasing spring15 satisfactorily control the pump delivery rate. However, when the load on the service connected to the port 23 is abnormally large, the pressure responsive control means 8 would not alone be capable of preventing the pump from delivering at a high rate and high pressure such as to operate the service faster than would be desired. Consequently, the stop means or limiting device illustrated in FIGURE 3 may be used to advantage when such abnormally large load conditions are anticipated. When the load is normal, the spring 46 maintains the piston rod 43, which acts asa stop for the piston 12, in
its right most position as viewed in FIGURE 3 due to relatively low pressure acting on the right hand face of the piston 42. Under such conditions, the piston 12 of the primary pressure responsive-control means 8 will adjust the pump delivery rate in dependence upon the relation of the pump delivery pressure to the service load, the piston 12 moving back and forth according to fluctuations in the relation of the delivery pressure to the service pressure without restraint by the stop rod 43. However, when an abnormally heavy load is imposed upon the service connected to the port 23, the pump pressure rises sufficiently within the auxiliary piston chamber 48 to move the piston and the stop rod 43 toward the left against the bias of the spring 45, the cylinder chamber 47 being vented as previously stated. The stop rod 43 Will therefore move to a position for limiting the rightward movement of the main pressure responsive piston 12 such as to limit the maximum pump discharge rate which may be determined by the relative pressures acting on the opposite sides of the piston 12.
To obtain hydraulic balance of the piston 12 the piston rod 43 may be made of the same diameter as the rod 7 and be carried by the piston 12.
What is claimed is:
1. Control means for an hydraulic system wherein a variable delivery pump accepts fluid from a tank and delivers fluid under pressure to service means to be operated, said control means comprising pressure responsive means hydraulically connected to the pump delivery and being operable for varying the pump delivery; and a manually operable selector valve mechanism including a body having five ports or" which the first port is hydraulically coupled to said pressure responsive means, the second port is connected to the tank, the third port is connected to a service to be operated, the fourth port is connected to the pump delivery and the fifth port is connected to said tank, and a valve member movable in said valve body and formed with intercommunicating passage means opening outwardly through said selector valve member, said ports and passage means being so related that in a first position of said valve member said third port is in communication with said pressure responsive means through said first port via said passage means whereby pressure in said service acts on said pressure responsive means in opposition to pump pressure.
2. Control means according to claim 1 in which said selector valve body further includes a sixth port connected to a service to be operated, and a seventh port connected to said tank, said ports and said passage means being so related that in a second position of said valve member said sixth portis in communication with said pressure responsive means through said first port and said third port is in communication with said fifth port.
3. Control means according to claim 1 further including means for limiting the controlling of the pump by said pressure responsive means.
4. Control means according to claim 1 in which said pressure responsive means comprises a first piston slidable in a first cylinder, and said control means further includes a second cylinder formed as an extension of said first cylinder, a second piston 'slidable in aid second cylinder and having a piston rod providing a stop for limiting movement of said first piston, and means hydraulically connecting said second cylinder to the pump discharge.
5. Control means according to claim 1 including a plurality of selector Valve mechanisms, said second port of the selector valve body defined in claim 1 being hydraulically coupled to a port of the next succeeding selector valve body which corresponds to said first port of said selector valve body defined in claim 1, and a port of the last succeeding selector valve body which corresponds to said second port of said selector valve body defined in claim 1 being hydraulically coupled to said tank.
References Cited in the file of this patent UNITED STATES PATENTS 2,572,390 Righton Oct. 23, 1951