GB2340207A

GB2340207A - Fluid distributor device for a hydraulic remote-control system

Info

Publication number: GB2340207A
Application number: GB9917719A
Authority: GB
Inventors: Gerard Laroze
Original assignee: Mannesmann Rexroth SA
Current assignee: Bosch Rexroth SAS
Priority date: 1998-07-28
Filing date: 1999-07-28
Publication date: 2000-02-16
Anticipated expiration: 2019-07-28
Also published as: GB2340207B; GB9917719D0; DE19935101A1; IT1313240B1; FR2781845B1; ITMI991635A1; BE1014991A5; ITMI991635A0; FR2781845A1; DE19935101B4

Description

2340207 A fluid distributor device, in particular for a hydraulic

remote-control system The present invention relates to improvements made to fluid distributor devices, particularly for a hydraulic remote-control system, such as those referred to as "hydraulic manipulators", having at least one pressure reducing valve mounted in a body and a control member designed to modify the pressure setting of the reducer, said reducer having a plunger piston which is displaced by said control member in a cavity of the body which has, at the one end, a compartment in which a pressure - regulating spring of the reducer is arranged and, at the other end, a bore in which an active part of the plunger piston can be displaced as a means of reducing the fluid pressure, said plunger piston having a rod section mounted on said active part and extending substantially in said compartment, said rod section having at its free end an enlarged head defining a first shoulder and, at the end at which it adjoins said active part a second shoulder on which said pressure-regulating spring is supported, the other end being supported on a valve spring washer which is coaxial with the section of rod and which is biassed by a return spring, in support against said control member.

In conventional arrangements of a device such as that outlined above, the return spring is a conventional helical spring: a device of this type is described in documents FR 2 376 978 or FR 2 507 732, for example. The return curve obtained by these known arrangements is substantially linear and its slope is determined by the stiffness of the return spring.

In certain fields of application, users have wanted to be able to obtain more complex return curves with a variable slope (where the slope in the return curve is

2 more pronounced towards the end of the control member's travel, for example). Accordingly, one distributor device is known, in which the return curve of the plunger has a double slope: a device of this type is illustrated in figure I of the appended drawings.

This known device consists of a body 1 (which may be formed by joining several parts in order to facilitate insertion of the internal components), having at least one pressure-reducing valve 2 arranged therein. This reducer comprises a plunger piston 3 which is displaced in a cavity 4 arranged in the body 1. This cavity 4 has, at one end, a widened compartment 5 in which a pressuresetting spring 6 is arranged, being supported between a shoulder 7 of the plunger piston and a valve spring washer 8 which moves in the compartment 5 in the vicinity of the free end of the plunger piston and, at the other end, a bore 9 in which an active part 10 of the plunger piston can be displaced as a means of reducing the pressure of the fluid which is fed via an inlet orifice (not visible) connected to the bore 9 via a passage 12 opening radially therein whilst an outlet orifice 13 is located at the end of the bore 9. The active part or piston 10 of the plunger has an axial recess 22 opening at the base of the piston 10 on the side of the outlet orifice 13 and a radial orifice 23 communicating with the axial recess 22.

The plunger 3 also has a rod section 14 mounted above the active part 10 and extending substantially in the cavity 5, being coaxially surrounded by the pressuresetting spring 6; this rod section 14 passes through the valve spring washer a terminating with an enlarged head 15 defining a retaining shoulder 16 of the valve spring washer.

A return spring 17, coaxial with the rod 14, is interposed between the valve spring washer 8 and a 3 shoulder defined in the body 1, so as to push the valve spring washer upwards, i.e. into its position defining a minimum pressure setting.

Mounted above the valve spring washer 8 is a movable push rod 18 sliding freely in a bore of the body and partially projecting out from the body so as to be in contact with a cam 19 which pivots about an axis under the action of an actuating member such as a handle 21.

The way in which this device operates is known and reference may be made to documents FR 2 376 978 or FR 2 507 732 cited above for more details.

In the known device described above, the return spring 17 is a standard helical spring, comprising a metal wire of homogeneous geometry, specifically being of constant section, helically coiled at a constant pitch and a constant diameter. As mentioned above, this linear return spring provides, alone, a linear return curve, the slope of which is determined by the stiffness of said spring.

If it is desirable to obtain a return curve with a double slope (two successive linear sections with dif f erent slopes) a known approach is to arrange a second spring, having different characteristics, adjoining the above-mentioned spring 17.

In view of the small amount of space available inside the pressure reducer, it has proved necessary to arrange the second regulating spring 24 around the spring 17 and coaxially therewith.

As illustrated in figure 1, a sleeve 25 is placed around the foot of the push rod 18 and the valve spring washer 8, conforming to the contour of the wall of the compartment 5, bearing against a shoulder of the body 1 (in this case against the bottom of a plug 49 closing off the compartment 5 and acting as a guide for the push rod 18). The second return spring 24 is then inserted between 4 the lower end of the sleeve 25 and a second shoulder 26 provided in the wall of the compartment 5.

When the device is in the rest position (illustrated in figure 1), the lower end 27 of the sleeve 25 is located substantially underneath the valve spring washer 8 and is provided with an internal radial flange which acts as a stop for the valve spring washer 8. The distance between the valve spring washer 8 and the lower end 27 of the sleeve 25 may correspond approximately to the greater part of the travel of the valve spring washer and hence the push rod.

As the inclination of the cam 19 causes the push rod 18 to be pushed back downwards, it drives the valve spring washer 8 against the return force of the single return spring 17. When the valve spring washer 8 comes into contact with the end 27 of the sleeve 25, displacement continues against the return force produced by the two springs 17 and 24. The user manipulating the lever 21 will be able to feel the transition. An assembly of this type can therefore serve to indicate to the user that he is crossing a predetermined threshold and/or that that he is entering a specific working zone. For example, this assembly can indicate to the user that the device is reaching the end of its travel (lever 21 close to its maximum inclination) and that a locking means (not illustrated in figure 1) will be activated to lock the device into its position of maximum inclination.

An assembly of this type therefore meets all practical requirements and is satisfactory in terms of the result obtained.

However, the structure of the device is complicated since the body 1 has to be machined in a special way (the compartment 5 is no longer standard) and it is also necessary to provide additional components (second spring 24, sleeve 25). This makes the device more expensive.

Furthermore, whilst an arrangement of this type does enable a return curve with a double slope to be obtained whilst remaining relatively simple in terms of structure, it is nevertheless impossible, in practice, to construct means of this type in a manner that will produce a return curve having at least three linear segments or a gradually rising curvilinear return curve, for example, should it be desirable.

It should be pointed out that the small dimensions of the component parts of the device (figure 1 is somewhat larger than the actual size) and the close proximity of the pressure reducing valves to one another within the body (four reducers arranged in a cross design and in opposing pairs) does not leave any room free to insert additional return springs. In practical terms, figure 1 illustrates the only feasible layout in a space as limited and as encumbered as this.

An underlying objective of the invention is to overcome or ameliorate one or more of the disadvantages outlined above. The inventor proposes an improved layout that will enable a return curve of a desired pattern to be obtained without the need for additional components and/or witho ' ut modifying the existing components (retaining in particular a standard body which does not require specific machining). A further objective is to keep manufacturing costs to a level that differs little from that of a conventional device used to obtain linear return curves having a single slope.

A fluid distributor device proposed by the invention is characterised in that each pressure -reducing valve has single return spring which is a helical spring having variable stiffness, as a result of which the return curve obtained when the control member is activated to cause at least a partial compression of the return spring will exhibit a variable slope.

6 In order to implement the invention, it is therefore preferable to use a helical spring wherein at least one characteristic, in particular a geometric characteristic, varies.

In practical terms, therefore, in order to retain the same components as used in a device of the prior art and in view of the fact that it is very difficult, not to say impossible, to provide any extra free space in a radial direction, a preferred embodiment is proposed in which the return spring is a helical spring, the coil pitch of which is variable.

However, if necessary, it is also possible to make use of other characteristics of the spring. In particular, it may be that the return spring is a helical spring in which the section of the wire is variable or, alternatively, the return spring may be a helical spring of a variable diameter.

In practice, users' requirements more often than not tend towards return curves with two successive linear sections having differing slopes. This being the case, the helical return spring will have at least two successive sections of different coil parameters (pitch, diameter, wire section).

It should be pointed out that the general conditions under which the invention is implemented make it possible if necessary, in a simple manner and without modifying the environment inside the device, to meet requirements for more complex return curves having multiple linear segments of differing slopes or even a curvilinear contour or a combination of linear sections and curvilinear sections: to this end, it is proposed that the helical return spring have successive sections of different winding parameters or a winding pitch which is continuously variable over at least a part of its 'Length so that the return curve is curvilinear across at least 7 a part of its length.

By virtue of the features of the invention, the desired return curve is obtained by using a single helical spring having turns wound in an appropriate manner, this spring simply being provided instead and in the place of the basic helical spring conventionally used. The other components of the device may remain identical to those which have always been used and do not require any modification. In other words, all the remote control devices may be constructed in the same manner, with the same component parts and the return curve of each pressure-regulating valve is adapted solely by selecting the appropriate single return spring.

This makes for a significant saving not only in manufacturing terms but also as regards assembly and maintenance.

The invention will be more readily understood from the detailed description below of various embodiments, given purely as illustrative examples.

Throughout the description, reference will be made to the appended drawings, of which:

- figure 2 is a simplified partial diagram, in section, of a distributor device with a layout as proposed by the invention; - figures 3A, 3B and 3C are simplified views showing respectively various types of helical springs enabling a return curve with two linear segments of differing slopes to be obtained; - figure 4 is an example of a return curve with two linear segments of differing slopes which can be obtained by means of a spring illustrated in figures 3A-C; - figures 5A and 5B are simplified views showing respectively two helical springs capable of producing complex return curves; and - figure 6 is a graph showing two complex return 8 curves which can be obtained by the springs illustrated in figures 5A, 5B respectively.

Figure 2 illustrates, in section, a part of a distributor device constructed as proposed by the invention. The device in figure 2 differs from that illustrated in figure 1 by dint of the fact that in this instance, the return spring 17 of figure 1, of the helical type, has been replaced by a helical spring of a specific type 28, examples of which will be given below. Since the single spring 28 is capable of producing the desired return curve alone, the second return spring 24 and the requisite corresponding layout (enlarged compartment 5, sleeve 25) illustrated in figure 1 are no longer necessary: the compartment 5 is therefore a standard compartment and it is no longer necessary to provide a body 1 machined in a specific manner.

This being the case, it may be noted that the regulating device illustrated in figure 2 is similar in structure to that of a conventional device as illustrated in the drawings accompanying documents FR 2 376 978 or FR 2 507 732; the return spring 28 is itself of essentially the same overall geometry (length, external diameter), having been modified in terms of its coil design only.

In order to produce a return curve with a double slope 29 such as that illustrated in figure 4 (load plotted on the ordinate, winding height of the spring plotted on the abscissa on an inverse, oriented axis with increasing values to the left), i.e. comprising, for example, a first linear section 30 with a predetermined slope corresponding to the greater part of the return path followed at the end section of the return path by a second linear section 31 having a steeper slope - a return spring 28 is used in which one characteristic varies with effect from a predetermined threshold.

For practical purposes, the preferred characteristic 9 is the winding pitch of the spring wire, as illustrated in fig. 3A: the spring 28A has a first section 33 with relatively close turns and a second section 34 in which the turns are relatively less close together, all the turns being substantially of the same coil diameter and being made from the same metal wire, the composition and section being the same throughout.

When the spring 28A is initially compressed, the first section 33 with relatively close turns, which is less stiff, is for all practical purposes acting alone and produces a return force which varies linearly as shown in the first section 30 of curve 29 in figure 4. Once all the turns of the first section 33 are edge to edge, the second section 34 with the turns spaced relatively farther apart, and hence of a higher stiffness, becomes active and produces a return force as shown in the second section 31 of curve 29 in figure 4, having a steeper slope.

A spring with a double winding pitch as illustrated in figure 3A can be manufactured without any particular difficulty and at an acceptable cost. It is therefore possible to manufacture a regulating device at a cost that is no higher than that of a conventional device.

Clearly, the regulating curve of figure 4 may be obtained using springs wherein a characteristic other than the winding pitch is modified. However, such springs are more difficult to manufacture and are therefore more expensive and/or require extra radial space.

For example, spring 28B in f igure 3B comprises a metal wire wound with a single pitch and having a single external diameter. However, the section of the wire varies at a certain point: the section is smaller over a first segment 35 (less stiff) and becomes larger at a second segment 36 (more stiff).

In another example, spring 28C in figure 3C comprises a metal wire of identical section, wound at a single pitch on two different diameters: a first segment 37 with a larger diameter (less stiff) and a second segment 38 with a smaller diameter (more stiff).

The features proposed by the invention may also be applied as a means of producing much more complex return curves, still retaining the simple structure illustrated in figure 2.

For example, the spring 28D illustrated in figure SA extends the layout illustrated in figure 3A to a greater number of sections of different pitch (here, the pitch size increases and there are four such sections) 39, 40, 41 and 42 respectively. A spring of this type will produce a return curve 43 such as that illustrated in figure 6, which is made up of four successive linear sections 44, 45, 46 and 47, each having a different and more steeply rising slope.

As another example, the spring 28E illustrated in figure 5B is made from a wire of identical section, wound on a single diameter, with a gradually variable pitch. A spring of this type will produce a curvilinear regulating curve 48 (fig. 6) without a single point (continuous curvature)- Clearly, the features described above may be combined in order to produce any desired return curve (combination of linear and curvilinear section(s)). Adapting a return curve of this type may track the changes in a complex regulating curve so as to transmit to the user a tactile sensation of variation in the regulating curve.

Claims

1. A fluid distributor device, in particular for a hydraulic remotecontrol system, having at least one pressure-reducing valve (2) mounted in a body (1) and a control member (19) capable of modifying the pressure setting of the reducer, said reducer (2) having a plunger (3) which can be displaced by said control member in a cavity (4) of the body (1) which has, at one end, a compartment (5) in which a pressure-setting spring (6) of the reducer is arranged and, at the other end, a bore (9) in which an active part (10) of the plunger (3) can be displaced as a means of reducing fluid pressure, said plunger (3) having a rod section (14) mounted on said active part (10) and extending substantially in said compartment, said rod section (14) having, at its free end, an enlarged head (15) defining a first shoulder (16), said plunger having at the end of the rod section (14) where it adjoins said active part (10), a second shoulder (7) on which said pressure-setting spring (6) is supported, the other end of said pressure-setting spring being supported on a valve spring washer (8) coaxial with the rod section (14) and which is biassed by a return spring in support against said washer, characterised in that there is a single return spring (28) in each pressure-reducing valve and it is a single helical spring having a variable stiffness, as a result of which the return curve, obtained when the control member is activated to cause the return spring to compress at least partially, has a variable slope.

2. A device as claimed in claim 1, characterised in that the return spring (28A) is a helical spring, the winding pitch of which is variable.

3. A device as claimed in claim 1, characterised 12 in that the return spring (28B) is a helical spring, the wire section of which is variable.

4. A device as claimed in claim 1, characterised in that the return spring (28C) is a helical spring, the diameter of which is variable.

5. A device as claimed in any one of claims 2 to 4, characterised in that the helical return spring (28) has at least two successive sections (33, 34; 35, 36; 37;38) having differing winding parameters (pitch, diameter, wire section), as a result of which the return curve (29) is made up of at least two successive straight-line segments (30, 31) of differing slopes.

6. A device as claimed in claim 5, characterised in that the return spring (28) is arranged so that the second section which is compressed in second place is shorter than the first so that said second section is compressed towards the end of travel of the plunger and has a stiffness that is greater than that of the first section, as a result of which the person manipulating the control member will have a tactile sensation of the control member reaching the end of its travel.

7. A device as claimed in any one of claimg 2 to 4, characterised in that the helical return spring (28E) has a continuously variable winding parameter across at least a part of its length, as a result of which the return curve (48) is curvilinear across at least a part of its length.

8. A fluid distributor device substantially as herein described and/or as illustrated in any of Figures 2 to 6.

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