US RE29292 E
A pressure reducing valve mechanism maintains pressure in one of the service passages of a control valve at a desirably low value except at times when the control valve element is actuated to a position effecting flow of pressurized supply fluid to said service passage for delivery to a motor governed by the control valve.
This invention relates to control valves for governing the operation of fluid motors, and it has more particular reference to valve instrumentalities by which the speed of motor operation can be closely controlled despite load influences which tend to drive the motor at rates faster than desired.
The tendency for fluid motors such as hydraulic cylinders to be driven by the load thereon is well known. The booms of backhoes and front end loaders, for example, constitute heavy loads which are customarily raised and lowered by hydraulic cylinders at the dictate of control valves therefor. During lowering of such a boom, the control valve for its cylinder directs pressure fluid from a pump into one end of the cylinder and conducts fluid expelled from the other end thereof to the reservoir line of the system. The boom, aided by gravity, tends to descend rapidly at an accelerating and uncontrolled rate, and the boom usually attains a speed such that the expanding end of its cylinder cannot be kept filled with fluid from the pump. When that occurs, a void is drawn in the expanding end of the cylinder, and positive control over the boom is lost until its cylinder is refilled with fluid.
In situations where the load is swingable from side to side, as is the case with the boom of a backhoe, the load can actually drive the cylinder in each direction. This makes it extremely difficult to control the speed with which the boom is swung, and positive control over the boom at all times cannot be had.
Elaborate and costly throttling schemes have been proposed in the past in an effort to achieve controlled movement of heavy loads by their hydraulic cylinders. This invention provides an exceptionally simple and low cost solution to that problem.
It is the primary object of this invention to provide a control valve instrumentality for a fluid motor, wherein exceptionally good control over the speed of motor operation is achieved by means which comprises fluid pressure responsive mechanism to effectively throttle the flow of motor return fluid in one or in both service passages of the valve.
More specifically, it is an object of the invention to so combine with a more or less conventional control valve a fluid pressure .[.responsive.]. responsive exhaust throttling device which can comprise a simple pressure reducing valve mechanism for one or for both service passages of the control valve to maintain pressure therein at a substantially uniformly low value above that of fluid in the return passages of the control valve.
It is also a purpose of the invention to provide fluid motor control instrumentalities such as described in the preceding object with means to render the pressure reducing valve mechanism or mechanisms ineffective at times when pressure fluid is being directed to the service passage associated therewith for flow to the governed motor.
A further objective of the invention is to so combine a pressure reducing valve mechanism with a control valve for a fluid motor as to minimize leakage of fluid past the control spool of the valve to the return passages thereof from one or both of its service passages in the neutral position of the control valve element.
With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.
The accompanying drawings illustrate two complete examples of the embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:
FIG. 1 is a sectional view of a hydraulic control valve embodying this invention;
FIG. 2 is a fragmentary sectional view corresponding to the left hand portion of FIG. 1 but showing an operating position of the control valve spool; and
FIG. 3 is a fragmentary sectional view corresponding to a portion of FIG. 1 but showing a modified embodiment of the invention.
Referring now to the accompanying drawings, the numeral 5 generally designates a hydraulic control valve of more or less conventional construction except as to features to be described hereinafter. The control valve comprises a body 6 having a bore 7 therein and a valve spool 8 slidable axially in the bore. The spool can be shifted in either direction from the neutral or hold position thereof seen in FIG. 1 to a pair of operating positions, one of which is seen in FIG. 2, to connect either of a pair of service passages 9 and 10 of the valve with the pressure fluid inlet thereof (not shown) through what can be termed a high pressure supply or bridge passage 11, and to concurrently connect the other service passage with a reservoir port (not shown) through an exhaust passage adjacent thereto.
In the valve shown, the exhaust passages 12 and 13, open to the bore at widely spaced locations along its length. The bridge passage 11 is U-shaped, and has legs 11a and 11b which open to the bore 7 at zones spaced axially inwardly from the junctions between the exhaust passages and the bore. Each service passage connects with the bore at a zone between one of the exhaust passages and the leg of the bridge passage adjacent thereto.
In either operating position of the control valve spool .[.9.]. .Iadd.8.Iaddend., pressure fluid from the valve inlet is diverted into the high pressure bridge passage 11 through a load holding check valve 13 in a conventional way. It should be noted, however, that the check valve is held in place in the valve body by means of a threaded plug 14 which extends down into the body and has a well 15 therein opening to the bridge passage. A stem 16 on the check valve projects up into the well 15 to be guided thereby for opening and closing motion axially of the well. As is customary, the check valve stem has an angled passageway 17 therein to communicate the inner portion of the well 15 with the bridge passage and thus enable fluid to be readily expelled to the latter during opening motion of the check valve. A light spring (not shown) is ordinarily accommodated in the well to yieldingly urge the check valve toward closed position.
Mounted on the body 6 of the control valve directly over the mouths of its service passages 9 and 10, are pressure reducing valve mechanism 20 and 21, respectively. Since the pressure reducing valve mechanisms are identical, a description of the left hand mechanism 20 will suffice for both.
The pressure reducing valve mechanism 20 comprises a body 22 having a bore 23 therethrough, closed at its opposite ends by means of plugs 24 and 25. Those portions of the bore which are axially inwardly adjacent to the plugs 24 and 25 provide chambers 26 and 27, respectively. Slidably mounted in the bore 23 with its opposite end portions received in the chambers 26 and 27 is a fluid pressure sensitive plunger 29 having a circumferential groove 30 therein intermediate its ends to normally provide communication through the bore 23 between two branches 31 and 32 of a passageway that forms a continuation of the associated service passage 9. The branch 31 communicates directly with service passage 9 and with the bore 23 at a location spaced axially a short distance from the junction of the other branch 32 with said bore. Hence, the service passage 9 and the two branches 31 and 32 of the passageway in the pressure reducing valve mechanism constitute continuous portions of a service line through which pressure fluid can flow to and from a fluid motor.
A spring 34 confined between the plug 25 and an adjacent end portion of the plunger 29 urges the latter toward a normal or inactive position defined by the plug 24. In this normal position of the plunger, its circumferential groove 30 spans the junctions between the bore and both passage branches 31 and 32 and thus communicates the branch 32 with the associated service passage 9.
The chamber 26 at the left hand end of the plunger 29 is communicated with the branch passage 31 and hence with the service passage 9 by means of a passageway in the plunger. That passageway has an axial branch 36 which opens to the chamber 26 and a radial branch 37 which opens to the branch passage 31 and at all times communicates with the service passage 9. Accordingly, the chamber 26 will contain fluid at a pressure corresponding to that in the service passage 9.
The chamber 27 at the other end of the plunger 29 is vented so that the plunger can move to the right in response to pressure of fluid in chamber 26. Chamber 27 can be communicated in any desired fashion with the reservoir of a system of which the control valve forms a part, or it can be vented to the bridge passage .[.10.]. .Iadd.11 .Iaddend.in the interior of the control valve body 6 as by means of a vent line 40 shown diagrammatically as connecting with the plugs 14 and 25 in communication with axial ports 41 and 42, respectively, in said plugs. The vent line 40 thus serves to communicate the chamber 27 with the well in the interior of the plug 14, and with the high pressure bridge 11 through the angled passage 17 in check valve 13.
One of the features of this invention resides in providing the control spool 8 with a passageway 44 having axially spaced radial branches 45 to communicate one leg 11a of the high pressure bridge passage 11 with the return passage 12 in the neutral or hold position of the control valve spool 8. By such venting of the bridge passage, the chamber 27 of the pressure reducing valve mechanism is also vented in the hold position of the valve spool 8, and the plunger 29 can respond to load pressurized fluid in the chamber 26 and be actuated to the right thereby and thus effect reduction of pressure in the service passage 9 to a value determined by the force of the spring 34 opposing such response of the plunger.
Thus, with a 200 p.s.i. spring, for example, the pressure reducing valve mechanism will function to reduce pressure to about 200 p.s.i. in the service passage 9, whereas the pressure therein might otherwise reach a value as high as 3,000 p.s.i. if the governed cylinder is heavily loaded. Consequently, with zero pressure in the adjacent exhaust passage 12, the leakage of fluid thereto along the wall of the spool receiving bore 7 from the service passage 9 when such reduced pressure obtains in the latter could be as much as one-fifteenth .[.less than.]. .Iadd.of .Iaddend.the leakage that would occur if a non-reduced pressure of 3,000 p.s.i. were allowed to remain in the service passage in the hold position of the valve spool 8. In other words, the leakage would be far greater with a 3,000 p.s.i. pressure differential between the exhaust passage 12 and service passage 9 than it is with only a 200 p.s.i. pressure differential between said passages.
The pressure reducing valve mechanism 20 will maintain this desirably low pressure differential between passages 9 and 12 in the neutral position of the valve spool 8 as long as seepage past the left hand land of plunger 29 to the service passage 9 is no greater than the leakage from service passage 9 to the adjacent exhaust passage 12 across the control valve spool 8. .[.This can normally be taken care of.]. .Iadd.Since plunger clearance in its bore and wall area of the latter engaged by the left hand land on the plunger are factors that determine the amount of fluid at a given pressure that will seep past the plunger in neutral, it is obvious that such seepage can be reduced to a very low level either by minimizing plunger clearance, or .Iaddend.by assuring adequate land length along the wall of the bore 23 between its junctions with passage branches 31 and 32 .[...]. .Iadd.for encircling engagement with the left hand land of the plunger in what can be considered its closed position. It will also be obvious that plunger clearance in its bore need not be critical if its left hand land were enlarged and formed like a poppet, with a conical surface to engage a similarly surfaced seat formed in that portion of the bore between passage branches 31 and 32. .Iaddend.
It will thus be seen that the pressure reducing valve mechanism will function to minimize leakage of pressure fluid from either service passage to the adjacent exhaust passage, past the control valve spool 8 in the neutral or hold position of the latter.
The control valve spool 8 is shown in an operating position in FIG. 2 which, for the sake of discussion, can be considered as permitting pressure fluid to exhaust to passage 12 from a single acting hydraulic cylinder, via service passage 9. The valve spool has not been moved to a full .[.operation.]. .Iadd.operating .Iaddend.position to the left of neutral, but is in a partial operating position at which it meters flow of exhaust fluid to the return passage 12. This situation represents the heretofore commonly accepted way of governing the speed of motor operation, in this case, the rate at which the load on the cylinder is allowed to descend.
If the load on the governed cylinder is a heavy one that tends to descend at an increasing rate, exhaust fluid will be forced through the metering orifice set up by the control valve spool at correspondingly faster rates. Under such conditions, the valve spool 8 can only effect throttling over a very narrow range, through the metering notches ordinarily provided in the spool lands governing exhaust flow.
This problem is solved by the pressure reducing valve mechanism 20 for service passage 9. Again let it be assumed that the spring 34 exerts a 200 p.s.i. force upon the plunger 29 tending to hold it in its wide open or inactive position allowing free flow of fluid to service passage 9 from branch passage 32. The plunger 29 will then respond to increase in pressure in service passage 9 to a value above 200 p.s.i. and be moved to the right by such pressure in chamber 26, toward a closed position restricting communication between passage branch 32 and the service passage 9 whatever extent is necessary to restore the desired 200 p.s.i. differential in the pressures of fluid in the service passage 9 and in the adjacent exhaust passage 12. Any tendency for increase in pressure in service passage 9 due to the tendency for the load on the governed cylinder to descend at an accelerating rate will thus be manifested in further automatic adjustment of the plunger 29 in the passage closing direction, to keep the pressure in service passage 9 at a constant low value predetermined by the strength of spring 34.
Other advantages result from the use of the pressure reducing valve mechanisms described. For example, with only a 200 p.s.i. pressure differential between passages 9 and 12, the axial jet forces reacting upon the valve spool as the result of high speed fluid flow past the spool to the exhaust passage are dramatically reduced. Equally as significant, however, is the fact that the range of spool throttling movement is greatly increased.
While the pressure reducing valve mechanism 20 thus serves to improve the throttling action and regulation of the speed of descent of a single acting cylinder, (or of the speed of rotation of a rotary fluid motor supplied with pressure fluid from the other service passage .[.13.]. .Iadd.10.Iaddend.), it should not interfere with flow of pump fluid to a cylinder or other motor when the valve spool 8 is actuated to an operating position communicating the service passage 9 with the adjacent leg of the high pressure bridge passage 11, and the load is to be raised. For that purpose, the vent line 40 which connects the spring chamber 27 of the pressure reducing valve mechanism with the high pressure bridge passage 11 also serves to render the plunger 29 non-responsive to the high pressure of pump fluid flowing through the service passage 9 to the cylinder. This results from the fact that fluid in spring chamber 27 will then be maintained at the same high pressure as obtains in the bridge passage 11, and the plunger 29 will be held thereby in its wide open limit of motion defined by its engagement with plug 24.
Pressure reducing valve mechanisms 20 and 21, such as seen in FIG. 1, are useful for both service passages of a control valve governing the operation of reversible fluid motors such as double acting hydraulic cylinders. The operation of the pressure reducing valve 21, of course, is the same as that of the pressure reducing valve mechanism 20 described above. It will function to maintain a desirably low pressure in service passage .[.13.]. .Iadd.10 .Iaddend.in the neutral position of valve spool 8 as well as when the spool is in a position communicating service passage 10 with the adjacent branch 13 of the exhaust passage; but its vent line connection with the bridge passage 11 renders it ineffective at times when its associated service passage 10 is communicated with the leg 11b of the bridge passage by the control valve spool.
Another important feature of the invention which results from venting the chambers 27 of the two pressure reducing valves 20 and 21 to the high pressure bridge or supply passage 11 of the control valve, is that this expedient permits the pressure reducing valves to achieve a counter balancing or flow coordinating function such as is ordinarily possible only with far more sophisticated counterbalance valve mechanisms.
For example, let it be assumed that the control spool 8 is in a left hand operating position directing pump fluid from the supply bridge 11 to service passage 10 for flow to one end of a hydraulic cylinder while providing for return flow of fluid from the other end of the cylinder to exhaust passage 12 through service passage 9 and the pressure reducing valve 20 therefor. At that time, the pressure of supply fluid is manifested in the spring chambers 27 of both pressure reducing valves through the venting lines 40, 41 and 42 and the angled passage 17 in load check 13. Hence, the pressure will immediately rise in the supply bridge 11 if and when the plunger of valve 20 occupies a restricting position at which it will not allow flow of fluid out of the exhausting end of the governed cylinder at a high enough rate to match the flow of pump fluid into its other end. Such rise in pressure, of course, is also manifested in the chambers 27 of both pressure reducing valves 20 and 21. As a result, the pressures in the chambers 26 and 27 of valve 21 will be in balance at the increased pressure and the spring 34 thereof will hold the valve plunger in its open position; but the increased pressure in the spring chamber 27 of the pressure reducing valve 20 on the return side will cause the plunger thereof to be moved in the valve opening or flow coordinating direction to allow exhaust flow from the governed cylinder as fast as pump fluid is allowed to flow thereinto in any given setting of the control spool 8.
FIG. 3 shows another way of assuring flow of high pressure fluid from the pump out through either service passage 9 or 10 of the control valve to a fluid motor governed thereby, without interference from the associated pressure reducing valve mechanism, at times when the spring chambers 27 thereof are vented to a reservoir or to the opposite service passage 10, instead of to the bridge passage 11. As diagrammatically seen in FIG. 3, a check valve controlled bypass line 50 can then be provided to connect the branch passages 31 and 32, in bypass relation to the plunger 29. The check valve 51 in the bypass line is oriented to permit pressure fluid to flow substantially freely from the branch passage 31 to the branch passage 32, regardless of the position of the plunger 29 of the pressure reducing valve mechanism, while precluding reverse flow through the bypass line.
As will be appreciated, the bypass line 50 and its check valve 51 can be incorporated in the body of the pressure reducing valve mechanism if desired. Similarly, the pressure reducing valve mechanisms can be incorporated in the body 6 of the control valve, or secured thereto by screws, whichever is preferred.
From the foregoing description, together with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention provides an exceptionally simple but efficacious way of utilizing pressure reducing valve mechanisms to help govern the speed at which fluid motors are operated by their control valves.