Pressure-regulating Valve

Abstract

A pressure-regulating valve has a control member shiftable in a cylindrical bore of the valve housing by a lever or like actuator. The control member bears upon the valve body via a plurality of springs, at least one of which comes into play only after the control member has been displaced through a predetermined extent.

Description

FIELD OF THE INVENTION

Our present invention relates to a pressure-regulating valve and, more particularly, to a pressure regulator for a hydraulic or other fluid-responsive network.

BACKGROUND OF THE INVENTION

Pressure-regulating valves have been proposed heretofore for the manual or automatic regulation of the pressure in a line of hydraulic or other fluid-responsive network, the valve comprising essentially a valve member which is displaceable against the force of a restoring spring, the effect of which is regulated by a control member which is effective to establish the prestress of the spring. Pressure control valves of this type have generally provided springs with a linear characteristic, i.e. the relationship between the force applied by the spring to the valve member and the displacement of the valve member was generally linear. As a result, the control pressure increases linearly with the degree of displacement of the control member. When the control pressure is effective upon a piston, the degree of displacement of the piston is linearly proportional to the degree to which the control member has been displaced. This linear relationship between the input or control signal and the output pressure is desirable in many cases.

However, when the control device is to be employed to operate a stepless transmission, i.e. to displace the movable member of a stepless hydrostatic transmission, the aforedescribed linearity of the relationship between the control input and the result of this input, is often undesirable. In these cases, it is preferred that, in the region of small displacements from the null or neutral (idler) position of the control member, the transmission provide highly sensitive or fine control whereas displacements which deviate greatly from the idling condition respond with reduced sensitivity. For example, when the transmission is that of an automotive vehicle, it is desirable that control of the transmission be most sensitive with low vehicle speeds while the sensitivity is decreased for high vehicle speeds. With hydraulic controls for other purposes, a similar relationship is often desirable.

OBJECTS OF THE INVENTION

It is therefore the principal object of the present invention to provide a manual or automatic pressure control for a fluid-responsive system especially a hydraulic system, which affords greater control or sensitivity at selective areas in the response characteristic than at other regions.

Another object of our invention is to provide a control valve arrangement or a hydrostatic transmission or like hydraulic control system which provides greater sensitivity in the operational modes of the system at which increased sensitivity is desired, and is consequently more efficient, accurate and sensitive than earlier systems.

It is yet another object of our invention to provide a highly versatile control valve for hydraulic systems of various types.

It is also an object of the invention to provide a control valve whose rate of response is more sensitive at small deviations from a null or normal position, but which increases as the deviation from this null or normal position increases.

SUMMARY OF THE INVENTION

These objects and others which will become apparent hereinafter, are attained, in accordance with the present invention, in a valve system having a control or input member which, in the terms used in servomechanism practice, represents the input signal and is displaceable in a cylinder bore provided with a valve constituting the output member, the displacement of the valve representing an output signal which is controlled by the input signal.

In accordance with the principles of the present invention, a spring means is provided between the control or input member, and the valve body or output member, the spring means having at least one spring element which fails to act in force-transmitting relationship until one of the members has been displaced sufficiently toward the other member to bring that spring into play. It will be immediately apparent, therefore, that the system is more highly sensitive to displacements of the control member (or the valve member) within small deviations from a normal position, but that, as the deviation increases and the other spring is brought into play, the sensitivity is somewhat decreased.

For a predetermined degree of displacement of the input or control member in the region of the starting position, therefore, the sensitivity or control effect is greater than for the same degree of displacement of the control member at a greater deviation from the normal or starting position. With small displacements of the control member, once a small deviation from the starting position is established, therefore, a highly sensitive control of the pressure is obtainable, indeed the sensitivity may far exceed that which is available with greater offset from the starting position.

The principles of the present invention are achieved by providing a spring means between the input member and the valve body whose force/displacement characteristic increases at a faster rate, i.e. with greater slope, than the linear characteristic of a simple spring. The restoring force of the spring means according to the present invention thus rises more rapidly with compression than the restoring force of a linear spring. Hence, the characteristic of the spring means of the present invention can be described as progressive or as approximating the exponential.

It has been found, according to the invention that a substantially discontinuous increase in the restoring force should be provided, according to the present invention, with displacement of the input member and, to this end, we subdivide the spring means into at least two spring elements, one of which couples the input member to the valve body over the entire stroke of the input member, while the second spring element forms a lost-motion connection with the input member and is brought into play only after a predetermined degree of displacement of this member. For small displacements of the input member, therefore, only the first spring element is effective to couple the valve body with the input member whereas larger displacements of the input member bring into action the second spring element. With the second spring element in effect, the force supplied to the valve body increases more sharply than with the first spring element so that the force/displacement characteristic breaks sharply upward and the overall characteristic has an exponential appearance.

The spring means, therefore, in its most general sense, may comprise a plurality of springs effective in series and with different stiffnesses. In this system, the softest spring will be compressed predominantly prior to the development of sufficient force to compress the stiffer springs, thereby producing the increasing characteristic without a sharp demarcation between two distinct slopes. More generally, however, the springs will be provided in parallel, i.e. each spring will couple the input member with the valve body independently of the other spring. These springs may, therefore, have different lengths, corresponding to the displacement threshold of the particular characteristic and any spring without lost-motion relationship with the input member may be prestressed to the desired stiffness level. The short springs, therefore, need not be prestressed and only need be brought into play after an initial displacement of the input member.

DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is an axial cross-sectional view of a valve system embodying the present invention;

FIG. 1a is a section along the line IA--IA of FIG. 1;

FIG. 2 is a fragmentary cross section of a portion of this valve;

FIGS. 3 and 3A are diagrammatic illustrations of other spring arrangements in accordance with the invention; and

FIG. 4 is a graph illustrating the spring relationships of the present invention.

SPECIFIC DESCRIPTION

In FIGS. 1 and 2, we show a valve arrangement according to the present invention which comprises a housing 1 in the form of a cylinder mounted upon a panel or control board 1a and provided with an axially extending bore 2 in which an input member 3 is axially shiftable.

The upper end of the bore 2 is closed by a guide bushing 5 whose O-rings 5a sealingly engage the wall of bore 2 and which is held in place by a backing sleeve 5b. A lip type gland or seal 5c is received in a groove 5d of bushing 5 to hug a pin 4 whose lower end 4a bears upon the input member 3. The upper end 4b of the pin 4 projects beyond the bushing 5 and abuts, via a ball bearing 4c, a control plate 31 to which a handle 28 is affixed. The surface 31a of control plate 31, against which the pin 4 bears, extends transversely to the axis of the cylinder housing 1 and parallel to the pivot axis 27a defined by a swivel joint generally represented at 27. The swivel joint comprises a generally spheroidal shoe 27b which surrounds a ball 27c, the latter being attached to member 1a via a pedestal 27d. The socket 27b is, in turn, attached to the plate 31 by a connecting bar 27e.

As is described in greater detail hereinafter, therefore, the plate 31 is pivotable about the axis 27a to actuate pin 4b and about the axis 27f perpendicular to the plane of the pin 4b and the pivot axis 27a which enables the valve to operate a pair of further pins represented at 29 in FIGS. 1 and IA.

The member 3 comprises a spring seat or plate 3a defining a shoulder against which abuts an outer helical compression spring 14 which may be held under prestress and serves to restore members 3 and 4 to the rest position illustrated in FIG. 1. The spring 14, therefore, acting to swing the handle or lever 28 about the pivot axis 27a in the clockwise sense. At its lower end, the spring 14 bears against a shoulder 17 formed in the housing 1 and fixed with respect to the latter.

The spring seat 3 is provided with a boss 6 which is coaxial therewith and serves as a centering member for the springs 14 and 15, the latter being coaxially received within spring 14 and bearing axially upon the shoulder 3a. At its lower end, the spring 15 is seated against a shoulder 18 formed on a valve body 9 which is axially shiftable within the bore 2. The spring 15, consequently, is continuously in contact with both the input member 3 and the valve body 9 so that it serves as a continuously effective force-transmitting and coupling member. In FIG. 4, the characteristic of the spring 15 is represented at K.sub.1 and has a slope which is relatively shallow.

From the boss 6 a stud 8 projects axially downwardly and defines an angular shoulder 7 with this boss. The shoulder 7, moreover, defines a spring seat for a coil spring 16, coaxially surrounded by the spring 15 and guided on the stud 8 and a similar stud 20 formed on the boss 19 of valve member 9. The boss 19 defines the aforementioned shoulder 18 with the valve member 9 and, moreover, has a shoulder 20a at the base of the stud 20 against which the spring 16 may be compressed.

With the input member 3 in its illustrated position, the shoulder 7 is spaced from the upper end of the spring 16 upon a lost-motion play .DELTA.x, corresponding to the stroke of the input member 3 prior to its engagement with the spring 16. The spring 16 lies in parallel with spring 15 as a coupling between the input member and the valve body 9, the collective characteristic of the two parallel springs being represented at K.sub.2 in FIG. 4. It will be appreciated that the force/displacement characteristic as seen at the springs, increases sharply at the point .DELTA.x corresponding to engagement of the input member 3 with spring 16.

The bore 2 is provided at its lower end with an axially extending spool valve bore 10 closed at its bottom end by a fitting 21. The latter is formed with a prismatic head 21a enabling a washer 21b to be clamped against the lower wall 21c of the housing 1 while threaded socket 10a at the lower end of bore 10. The fitting 21 is connected to a fluid network, a pump 30a is connected to the reservoir 30b and is provided with an accumulator 30c to maintain constant pressure and reduce surges. The hydraulic system 30a and 30c is connected to the inlet fitting 23 by the usual passage and has been illustrated and described only in the most diagrammatic sense.

Between the fitting 21 and the valve body 9, we provide a spring 22 which serves to restore the original position of the valve member 9 against displacement by the control member 3. The spring 22 is seated within a cylindrical recess 13 of the body 9, this recess opening downwardly and having a passage 13a communicating with a transverse bore 11 of the valve member. The bore 11 opens, into an annular groove 12 along the periphery of the valve body 9 which selectively connects with radial port 25 or with radial port 24. The radial port 24 communicates in turn with a port 23 extending perpendicular to the plane of the paper and connected to the hydraulic pump 30a as represented diagrammatically in FIG. 1. The connection 26 forms a hydraulic return path including bore 25 to the reservoir 30b. The fitting 21 is, in turn, connected with the load 30d, i.e. a hydraulic vehicle transmission.

The housing 1 can be provided with two or more control valves whose pins are represented diagrammatically at 29 and one of which is illustrated on the right-hand side of FIG. 1. These systems include valve members 29a connected by single springs 29b with the input element 29c. These control valves are used for the regulation of equipment or the like which does not necessitate fine control as noted earlier. As shown in FIG. 1a, displacement of the lever 28 about the axis 27f will actuate the lower valve whereas displacement with the lever 28 in the opposite direction will actuate the upper valve. A counterclockwise displacement of lever 28 actuates pin 4 while the clockwise displacement of the lever actuates both of the pins 29. It has already been noted that the valve system of the invention is preferably employed for hydraulic transmissions in which a swash plate or tiltable control head of a hydrostatic axial-piston pump is hydraulically displaced. The springs 29b, of course, may have linear characteristics. The valve may also be used in the hydraulic controls of a forklift truck, front-end loader, excavator or like vehicle wherein the hydraulic system operates arms, lifters or other loads.

Below, we have described the operation of the valve on the left-hand side of FIG. 1, i.e. the valve structure in accordance with the present invention having a nonlinear operating characteristic. It will be apparent that the conventional valves in the right-hand side of the housing operate in accordance with conventional principles which need no elucidation.

Upon a counterclockwise displacement of the lever 28 about the axis 27a and the plate 31 rigid with this lever, the pin 4 and the spring seat 3a are shifted downardly (FIG. 1) see FIG. 2. Spring 15 is thereby compressed to increase the downward or resisting force applied to the valve body 9. The latter is thereby shifted downwardly against the force of spring 22 to connect the annular groove 12 with bore 24 and the pressure inlet 23, whereupon hydraulic fluid flows under pressure through the port 23, the bore 24, the annular groove 12, the radial port 11, the axial passage 13a, the interior chamber 13 of valve member 9 and the fitting 21 to the load 30d. A pressure is built up in the hydraulic network represented by load 30d and is effective to displace the valve body 9 upwardly against the force of spring 15 until this pressure, when taken over the effective cross section of the valve body 9, in conjunction with spring 22, suffices to balance and then exceed the spring force 15. The valve body 9 thus reaches equilibrium. When the lever 28 is then shifted to the left (counterclockwise) a limited degree further, the spring seat 3 is shifted downwardly again and the spring 15 is further compressed. The restoration of the equilibrium follows as previously described.

However, in an extreme position of the lever 28 (FIG. 2) the shoulder 7 engages the spring 16 which adds its force to that of spring 15 and bearing upon the valve body 9. The pressure buildup required to shift the member 9 back into its equilibrium position thereby increases sharply in accordance with the characteristic illustrated at K.sub.1, K.sub.2 in FIG. 4. At this threashold point therefore, each millimeter of displacement of the lever 28 and the pin 4 corresponds to a greater pressure increment in the hydraulic network 30d to which the system is connected.

When the pressure in the bore 30 increases sufficiently to overcome the force of the spring 15 or of the springs 15 and 16 together, the valve body 9 is shifted upwardly until the bore 11 and the annular groove 12 communicate with the bore 25 to bleed pressure from the load to the reservoir 30b, thereby maintaining the pressure associated with the position of lever 28. The out-flow from the load 30d is, of course, throttled by the lever edge of the groove 12.

In FIG. 3, we have shown a modified spring arrangement between the input member 103 and the valve member 109. In this system, the springs are provided, not in parallel, but in cascade; the springs include a spring 116a of relatively low stiffness (i.e. a relatively soft spring), a spring 116b of moderate stiffness and a spring 116c of high stiffness. As a consequence, the entire spring assembly will compress upon the displacement of member 103 with force/displacement characteristic and shown at 100 in FIG. 4. It will be evident that the system of FIG. 3 may be simply interposed between the input member and valve member of the valve illustrated in FIG. 1. The single spring 216 has a similar characteristic but is of progressively varying cross section and stiffness and is composed of synthetic resin. The spring is received between members 203 and 209 as previously described. The spring may be designed so that a portion thereof (216a) will have its turns compress into contacting relation prior to other portions.

Claims

We claim:

1. A hydraulic system comprising a pump, a reservoir, and a pressure regulator connecting said pump and said reservoir to a load, said pressure regulator comprising:

a housing provided with a bore;

a manually controlled input member slidable in said bore and actuatable from a starting position to control the pressure at said load;

a valve member slidable in said bore and defining a controllable passage therein;

means connecting said passage in a hydraulic network with said pump, said reservoir and said load;

first spring means interposed between said members and having a force/displacement characteristic increasing with displacement at a rate greater for a larger displacement of said input member than for a smaller displacement of said input member from the starting position of the latter, said first spring means comprising at least two parallel springs rendered successively effective between said members upon displacement of said input member, said parallel springs including inner and outer coaxial springs, the outer spring being prestressed and bridging said members in all positions thereof, the inner spring being shorter than said outer spring and forming a lost-motion coupling with at least one of said members; and

second spring means in said bore biasing said valve member toward said input member, said valve member being constructed and arranged for biasing against said first spring means by the fluid pressure at said load, said input member including:

a spring seat slidably mounted in said bore, said outer spring bearing upon the said seat,

a shoulder carried by said input member and axially entrained with said seat in the direction of said valve member for engagement with said inner spring, and

a pin connected to said spring seat and to said shoulder and extending outwardly of said housing;

a control plate swivelably mounted on said housing and engageable with said pin while being provided with a control lever; and

a spring received in said bore and bearing at an end upon said housing and at the other end against said spring seat, said means for connecting said passage in said hydraulic network including a first fitting connecting said bore on the side of the valve member opposite said input member with said load, said passage including a channel in said valve member opening into said

side of said bore and a circumferential groove formed in the periphery of said valve member and communicating with said channel,

an inlet port communicating with said bore and formed in said housing while being connected to said pump, and

an outlet port formed in said housing and opening into said bore while being connected with said reservoir, said groove selectively communicating with said ports upon axial displacement thereof.

2. The hydraulic system defined in claim 1 wherein the hydraulic network is a vehicle transmission.

3. The hydraulic system defined in claim 1 wherein the hydraulic network is the hydraulic circuit of a machine having hydraulic load-operating means.

4. A hydraulic system comprising a pump, a reservoir, and a pressure regulator connecting said pump and said reservoir to a load, said pressure regulator comprising:

a housing provided with a bore;

a manually controlled input member slidable in said bore and actuatable from a starting position to control the pressure at said load;

a valve member slidable in said bore and defining a controllable passage therein;

means connecting said passage in a hydraulic network with said pump, said reservoir and said load;

first spring means interposed between said members and having a force/displacement characteristic increasing with displacement at a rate greater for a larger displacement of said input member than for a smaller displacement of said input member from the starting position of the latter,

second spring means in said bore biasing said valve member toward said input member, said valve member being constructed and arranged for biasing against said first spring means by the fluid pressure at said load, said means for connecting said passage in said hydraulic network includes a first fitting connecting said bore on the side of the valve member opposite said input member with a hydraulic load, said passage including a channel in said valve member and opening into said side of said bore and a circumferential groove formed in the periphery of said valve member and communicating with said channel, an inlet port communicating with said bore and formed in said housing while being connected to a source of hydraulic pressure, and an outlet port formed in said housing and opening into said bore while being connected with a fluid reservoir, said groove selectively communicating with said ports upon axial displacement thereof.