GB2136542A - Hydraulic flow control valve - Google Patents

Abstract

The regulator valve has a first restriction (7) of fixed size in series with a second, variable restriction defined between a tilting wall (1) and an annular valve seat (11) provided on a fixed wall (2). The tilting wall (1) is sealed around its periphery to the fixed wall (2) by an elastomeric membrane (3) to define between the walls (1,2) a first chamber (4), and the walls (1,2) are biassed apart by a compression spring (15). A second chamber (8) is defined on the opposite side of tilting wall (1) to chamber (4) such that tilting wall (1) is subject to the pressure differential between the first and second chambers (4,8) and the first restriction connects the two chambers (4,8). The size of the second restriction is thereby made dependent upon the pressure difference between the two chambers (4,8). The tilting wall (1) tilts about a fulcrum line (19). The valve seat (11) may be pressure-balanced by a balancing member (22) (Figure 4) (not shown). <IMAGE>

Description

SPECIFICATION Hydraulic flow control valves This invention relates to hydraulic flow control valves and particularlyto a regulator valve of the kind in which a first restriction of predetermined size is connected in series with a second restriction defined between two relatively movable members, relative movementofthe members being controlled by the difference in fluid pressure acrossthefirst restriction such that an increase in the pressure difference causes a reduction in the size ofthe second restriction. Such a valve will hereinafterbe referred to as a 'regulator valve of the kindsetforth'.

Known regulatorvalves ofthe kind setforth generally employ a match ground closefitting cylindrical valve memberwhich is not only expensive to produce with sufficient accuracy but has a significant probability of failure due to sticking. A regulator valve ofthis kind is shown for example in Specification G.B.

No. 2045372A.

An attempt at designing a less expensive regulator valve is shown in U.K. Specification No. 1409304. The valve has a valve plate slidably mounted in a housing, the plate being provided with an orifice constituting the first restriction and biassed away from a valve seat byan O-ring which also acts as a seal between the plate and the housing. The spacing between the valve plate and the valve seat provides the second restriction of variable size. A problem with that arrangement is that because the valve plate is slidably mounted in the housing, failure ofthe valve can occur with the platejammed in a position in which the plate is closing the valve seat, and this would be dangerous in certain situations, for example in some vehicle hydraulic systems such as brake systems.The pressure differential across the valve plate may also move the O-ring radially away from the adjacent housing wall which could lead to irregularities in the valve characteristics.

According to one aspect ofthe invention in a regulator valve ofthe kind setforth the relatively movable members comprise two opposing rigid walls which have a rocking engagement with each other and are sealed together around their peripheries by a sealing membrane which accommodates limited relative rocking movement ofthe walls, the confronting inner faces ofthe wallstogetherwith the sealing membrane bound a first chamber, an outerface of a first of said walls is exposed to the pressure in a second chamber, and the first restriction is arranged to connectthefirst and second chambers, the second restriction provides communication between the first chamber and a transfer passage which is provided in the second wall, the second restriction being defined between a valve member portion of the first wall spaced from the rocking engagement and a valve seat portion of the second wall surrounding one end ofthe first transfer passage, and resilient means biases the walls in the direction to increase the size of the second restriction.

The use of a rocking engagement between the walls and a membrane seal reduces the risk of the valve failing in the condition in which the valve seat is closed.

Since the sealing ofthefirst chamber is effected by a membranethe need for match grinding of the relatively movable members is avoided.

The membrane conveniently comprises an annular elastomeric sleeve which sealingly engages at its opposite axial ends with the peripheries ofthe respective walls.

Preferablythesleeve is provided bythewall of a cup-shaped elastomeric member in which the first wall isseated,the rim ofthecup-shaped member being sealingly secured to the periphery ofthe second wall.

The intended direction offlowthrough the valve is from the second chambertothetransfer passage.

In orderto minimise any change in flow rate th rough the regulatorwith applied fluid pressure the diameter ofthe valve seat portion is preferably made as small as possible in relation to the overall transverse dimen sionsofthefirstwall.

Alternatively, or in addition, a pressure balancing projection may be provided on the second wall which comprises a stem extending through the valve seat into the transfer passage, and a head which is received in a recess in the outerface of the first wall thereby to reduce the effective area of said outer face by the area ofthe head. The area ofthe head may then be made substantially equal to the effective cross-sectional area of the valve seat.

The resilient means is preferably arranged in a position which is off-set from the valve seat.

Conveniently the resilient means is housed in a bore in the second wall that is on the opposite side of the axis ofthe valve seat to the rocking axis.

Preferably the rocking engagement is provided by a fulcrum line defined on the inner surface of the second wall by suitable shaping of said inner surface.

The shaping to provide the fulcrum line is preferably a chamferofthe said inner surface.

According to a second aspect of the invention in a regulatorvalve ofthe kind setforth the relatively movable members comprise two opposing rigid walls which are sealed together around their peripheries by a sealing membrane which accommodates limited relative movement apart of the walls, the confronting inner faces of the wallstogetherwith the sealing membrane bound a first chamber, an outerface of a first of said walls is exposed to the pressure in the second chamber, and the first restriction is arranged to connectthefirst and second chambers, the second restriction provides communication between the first chamber and a transfer passage which is provided in the second wall, the second restriction being defined between a valve member portion ofthefirstwall and a valve seat portion of the second wall surrounding one end ofthe first transfer passage, one ofthe walls is provided with a series of recesses extending substantially radially from adjacent to the radially outer margin ofthe valve seat, and resilient means biases the walls in the direction to increase the size of the second restriction.

The radial recesses can be dimensioned to control the degree of damping produced by the squish action between the confronting faces ofthe walls.

The valve seat is preferably encircled by a co-axial annular recess into which the radial recesses lead at their radially inner ends.

Preferably the radial recesses are provided in the inner faces of the second wall.

The walls ofthe regulator valve in accordance with the second aspect ofthe invention may be relatively movable withouttilting, but preferably the walls are arranged to have a rocking engagement with each other in accordance with the first aspect ofthe invention.

The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: Figure 1 schematically illustrates the principle of regulator valves in accordance with the invention; Figure2is a schematic longitudinal cross-sectional view of a practical regulator valve assembly in accordance with the invention, but with the valve clearance exaggerated for illustration; Figure 3 is a view looking from the left in Figure 2 of the valve wall provided with the annular valve seat; Figure 4 is a schematic longitudinal cross-section of a modification ofthe regulator valve assembly of Figure2; and Figure 5is a drawing indicating the important dimensions ofthe assembly of Figure 4.

The principle of operation of regulator valves in accordance with the invention will first be explained.

With reference to Figure 1, first and second rigid walls 1,2 are connected around their peripheries by an annular elastomeric membrane 3 which is sealingly secured in suitable manner to both walls 1, 2. Afirst chamber4 is defined between confronting inner faces 5,6 respectively of the walls 1, 2. Afirst, fixed restriction in the form of an orifice7 providesfluid communication for hydraulic fluid between a high pressure second chamber 8 bounding the outerwall 9 ofthefirstwall 1. Atransfer passage 10, in this case the outlet passage ofthe assembly connecting with a low pressure chamber 12, extends through the second wall 2 from a valve seat 11, between which and a valve member 13 is defined a second, variable restriction 14.

Valve member 13 is indicated schematically as a cone valve, but in practice the wall 1 is arranged to act as a plate valve member, as described hereafter.

A compression spring 15 urges walls 1,2 relatively apart and provides a balancing force to create a defined pressure dropthrough thefirst restriction 7.

Figures 2 and 3 show a practical construction utilising the principles of Figure 1. Parts corresponding ofthose of Figure 1 have been given corresponding reference numerals. The tilt ofthe wall 1 in Figure 2 is exaggerated for the purposes of illustration.

The first wall is in the form of a rigid circularvalve plate 1 and is held in contact with the face of a second wall in the form of a rigid plug 2 by a rubber cup 3, the rim 1 ofthe cup being formed as a bead 3' which is seated in an external annular recess in the plug 2. The surface 6 is pierced bythe central outlet passage 10, and an annular land 11 encircles the passage lOto provide a valve seat.

The land 11 is encircled by an annular recess 1 6from which extend six radial recesses 17. Damping to inhibitvibration is produced bythesquish action generated by the flat surfaces 5,6 in close proximity.

The degree of damping produced bythesquish action can be optimised by choosing an appropriate area for the grooves 17.

A small segment 18 ofthe surface 6 is chamfered to define a fulcrum line 19 about which the valve plate 1 is rockable to define the variable second restriction between the land 11 and the confronting surface 5 of the plate 1. A spring 15 is housed in a bore 20 ofthe plug 2 positioned diametrically opposite to the fulcrum 19.

The operation oftheassembly of Figure 2 is essentiallythe same asthat of Figure 1 when inlet po'trt.

21 is connected to a high pressure supply, except that it will be appreciated thatthe valve plate 1 simply tilts aboutfulcrum line 19 in response to changes in the pressure at inlet21.

It will be appreciated thatthere is virtually no possibility of the valve plate 'jamming in use. In addition the only surfaces requiring accurate machining are the flat areas of opposing surfaces 5,6 of the valve plate 1 and plug 2, and this presents no difficulties.

The cup 3 performs the various functions of retaining the plate 1 in a generally central position with respecttotheaxisofpassage 10, holding the plate againstthefulcrum line 19, and also sealing the chamber 4.

All ofthese features help to reduce manufacturing costs.

The assembly of Figure 4 is essentially the same as that of Figure 2 exceptforthe provision of a pressure balancing projection 22 which comprises a stem 23 having a reduced end 24 loosely received in a bore of the plug 2, the stem 23 extending through the portion 10' ofthe passage 10 and through the centre of valve seat 11, and a head 25 received in a recess 26 in the outerface 9 of valve plate 1. The head 25 is made of a diameter substantially equal to the effective diameter of valve seat 11 and transfers to the plug 2 the force of the pressure in chamber 8 applied to cup 3 overthe area of head 25, therebyto balance the valve action between plate 1 and seat 11.

There now follows with reference to Figure 5 a calculation which demonstrates th e the characteristics of the assembly of Figure 4, butwhich is also relevant to the arrangement of Figure 2 Notation: A0 - area ofvalve plate 7 including area of head 25 of balancing projection A, - effective area of valve seat 11 A2 -- balancing area of head 25 A3 - cross-sectional area of fixed orifice 7 P0 - outlet pressure in transfer passage 10 P, - supply pressure in chamber 8 P2 - intermediate pressure in chamber 4 W - load of spring 15 R - spring mechanical advantage when referred to valve seat 11 Q - quantity of flow per sec.

The calculations will assumethatthe orifice is short and has a square law characteristic (P1 - P2) = (QIA3)2K . . (1) (where K is a constant) Suitable allowance must be madefor any other characteristics ofthe orifice.

At load balance on the valve plate 1: P1(A0-A2) + PO(A2 - A1) = P2(A0-A,) + WR P2 = [P,(A0-A2) + PO(A2-A1) - WR]/(A0-A1) (2) Substituting (2) in (1): Q = A3 V[(P, -P0) (A2-A,) + WR]/(A0-A,)K (3) note that if A2 = A, (for perfect pressure balancing) Q=A3VWR/(-A,)K ... ...... ......... (4) which showsthatthe flow rate is independentofthe inlet and outlet pressures (i.e. constantflow). If, as in Figure 2, the is no balancing projection. A2 = 0 and; Q = A3 V[(P1 - P0) (-A1) + WR]i(A0 - A1)K This shows the obvious case where if the pressure difference causes a valve load [(Pa - Po)A11 greater than the spring load WR the valve snaps shut uncontrollably. The spring 15 musttherefore have a load greater than W = (P1 - P0)A1/R

Claims (12)

1. A regulator valve comprising first and second opposing rigid walls, portions of the walls having a rocking engagement with each other, a sealing membrane sealingly connecting together the walls around their peripheries and permitting limited relative rocking movement ofthe walls, the confronting innerfaces of the walls togetherwith the sealing membrane bounding a first chamber, the outerface ofthefirstwall being exposed to pressure in a second chamber, a first restriction of predetermined size connecting the first and second chambers,the second wall being formed with a transfer passage, the innerface of the second wall being provided with a valve seat portion surrounding the end of the transfer passage adjacent to the first wall, the valve seat portion being spaced from the rocking engagement, a valve member portion of the innerface of the first wall defining with the valve seat portion a second restriction of variable size, and resilient means acting between said walls in the direction to increase the size ofthe second restriction, the arrangement being such that aniincrease in the pressure in the second chamber relative to the pressure in the transfer passage brings about a reduction in the size ofthe second restriction.

2. A regulator valve as claimed in claim 1 in which the membrane comprises the rim ofacup-shaped elastomeric member in which the first wall is seated.

3. A regulator valve as claimed in claim 1 or claim 2 in which the innerface of one ofthe walls is formed with a chamferto define a fulcrum line providing the rocking engagement.

4. A regulatorvalve as claimed in claim 2 which comprises a pressure balancing projection, the projection comprising a head which is received in a recess provided in the outerface of the first wall in engagement with the cup-shaped member, and a stem extending into the transfer passage.

5. A regulatorvalve comprising first and second opposing rigid walls, a seal sealing together the walls around their peripheries and permitting relative movement of the walls towards and away from each other, confronting innerfaces ofthe walls together with the seal bounding a first chamber, the outer face ofthefirstwall being exposed to pressure in a second chamber, a first restriction of predetermined size connecting the first and second chambers, the second wall being formed with a transfer passage, the inner face of the second wall being provided with a valve seat portion surrounding the end of the transfer passage adjacentto the first wall, valve member portion ofthe inner face ofthe first wall defining with the valve seat portion a second restriction of variable size, and resilient means acting between the walls in the direction to increase the size ofthesecond restriction, the arrangement being such that an increase in the pressure in the second chamber relativeto the pressure in the transfer passage brings about a reduction in the size ofthe second restriction, and the innerface of one of the walls being formed with a series of recesses extend ing substantially radiallyfrom adjacent to the valve seat portion.

6. A regulatorvalve as claimed in claim 5 in which the inner face provided with the radial recesses is also provided with an annular recess co-axial with the valve seat portion, the radial recesses leading into the annular recess.

7. A regulator valve as claimed in claim 5 or claim 6 in which radial recesses are provided in the inner face ofthe second wall.

8. A regulatorvalve as claimed in any of claims 5 to 7 in which portions ofthewalls have a rocking - engagement with each other at a position spaced from the valve seat portion.

9. A regulatorvalve is claimed in claim 1 and substantially as described with reference to Figures 2 and 3 ofthe accompanying drawings.

10. A regulatorvalve as claimed in claim 1 and substantially as described with reference to Figures 4 and 5 of the accom pa nyi ng drawings.

11. A regulator valve as claimed in claim 5 and substantially as described with reference to Figures 2 and 3 ofthe accompanying drawings.

12. A regulator valve as claimed in claim 5and substantially as described with reference to Figures 4 and 5 ofthe accompanying drawings.