GB2131107A

GB2131107A - Proportioning valve

Info

Publication number: GB2131107A
Application number: GB08330387A
Authority: GB
Inventors: Gary A Willi
Original assignee: Kelsey Hayes Co
Current assignee: Kelsey Hayes Co
Priority date: 1982-11-15
Filing date: 1983-11-15
Publication date: 1984-06-13
Also published as: FR2536147A1; BR8306270A; GB8330387D0; MX159365A; CA1203735A; IT1233248B; JPS59114150A; DE3341220A1; IT8323703A0

Abstract

An axial-flow proportioning- valve 10 especially for use in automotive hydraulic brake systems employs a stepped elongate plunger 25 enclosed in a housing 4 to 6 and having an axial bore 21 therein. Input hydraulic fluid is conducted through the axial bore 21 and a radial extension in the plunger head into a region within the housing 25 forming an annular chamber 52 about the plunger 25. When the input fluid pressure reaches a predetermined level the plunger 25 moves from an initial valve open position to a closed position engaging an annular seal 84 disposed in a groove 23 of the head until system forces cause the valve to again open. Thus a modulating effect results whereby the output-pressure relationship follows a predetermined curve. <IMAGE>

Description

SPECIFICATION Improvements in and relating to proportioning valves This invention relates to vehicular fluidic brake systems, including both pneumatic and hydraulic brake systems, and to a brake-pressure proportioning valve arranged to modulate the fluid pressure at one or more brake cylinders of such a brake system with respect to the fluid pressure generated by a fluid pressure source.

The device of the present invention is especially suited to reducing the relative pressurization of the rear brakes of a motor vehicle with respect to the pressurization of the front brakes in the higher ranges of applied brake pressure. This is desirable in view of the fact that a portion of the weight borne by the rear wheels of the vehicle is transferred to the front wheels of the vehicle during rapid deceleration. As a result of this weight transfer, the maximum braking effort of which the rear wheels are capable is reduced and the maximum braking effort of which the front wheels are capable is increased. It is therefore desirable to deliver a higher level of fluid pressure to the front wheels than to the rear wheels during the high rates of deceleration.This will tend to postpone or avoid premature rear wheel skidding, help maintain the vehicle under control and reduce the total distance required to stop the vehicle under control.

The front and rear brake cylinders of a vehicle are ordinarily designed to apply forces to the front and rear brakes which are in a ratio appropriate for light braking or ordinary stopping. During extremely rapid deceleration of panic brake applications, however, the "built-in" ratio is no longer satisfactory and the ratio should be changed for maximum braking efficiency. The greater the rate of deceleration the greater should be the ratio of front brake pressure to rear brake pressure.

While a bare measurement of the applied brake pressure is not a completely accurate index of the rate of deceleration of the vehicle, it has been found to be a practical guide which may be usefully employed in determining the point at which the relative pressurization of the front and rear brake cylinders should be altered. The device of the present invention is arranged to make use of the applied brake pressure for that purpose.

The invention provides an axial-flow proportioning valve. The valve comprises an elongate housing containing therein an elastomeric valve member and a piston which moves axially in the housing which in cooperation with the valve member forms the valve mechanism. The valve piston includes an axial fluid passage extending from the inlet end of the valve and opening out upstream of the elastomeric valve member. The axial-flow proportioning valve is especially suitable for inline installation with other brake components.

For example, the valve is suitable for direct "screw-in" installation to the outlet port of a master cylinder. The fluid may be either liquid or gaseous.

One form of axial-flow proportioning valve constructed in accordance with the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the valve; Figure 2 is a cross-sectional view taken along the line 2-2 Fig. 1, to a larger scale than Fig. 1; Figure 3 is an exploded perspective view, partly in axial cross section, showing various valve components; Figure 4 is a view of the valve member, partly in section and partly in elevation, to a larger scale than Fig. 2; Figure 5 is a fragmentary plan view of the valve member shown in Fig. 4; Figure 6 is a fragmentary cross section taken along line 6-6 in Fig. 4; and Figure 7 is a fragmentary cross section taken along line 7-7 in Fig. 4.

Referring to the drawings, and initially to Figs. 1 to 3, a proportioning valve indicated generally by the reference numeral 10 includes an elongate main body 5 having an externally threaded inlet boss 6 projecting one end of the main body along its longitudinal axis. Screwed into the main body 5 at the end opposite the threaded in let boss 6 is an outlet plug 4. A fluid-tight seal between the outlet plug 4 and the main body 5 is ensured by an O-ring 1 7 incorporated into the screw connection between them.

Within the main body 5 is a central chamber or bore 52 communicating with a narrower stepped bore 53 which in turn communicates with a still narrower inlet bore 56 that extends through the inlet boss 6.

The outlet plug 4 includes an axially projecting hollow cylindrical projection 42 having an outside diameter less that the inside diameter of the central chamber 52 and extending axially into the central chamber. The inside diameter of the cylindrical projection 42 is sufficient to permit free axial translation of a piston head 22 within it. A combination bore and slot 44 extends diametrically through the cylindrical projection 42 and a piston head abutment surface 43 of the plug 4. An outlet passageway 41 extends axially from the centre of the abutment surface 43 to an outlet port 45 in the form of a threaded recess in the external end surface of the outlet plug 4.

Positioned within the main body 5 and extending through the central chamber 52, the stepped bore 53 and the inlet bore 56 is a stepped piston indicated generally by the reference numeral 25 slidably received within the stepped bore 53, having a fluid inlet portion 26 extending axially through the inlet boss 6 and sliably received within the inlet bore 56 and having the piston head 22 at its other axial end. Standard O-rings 1 8 and 1 9 provide hydraulic sealing between the piston 25 and the main body 5 preventing the flow of fluid into a chamber 14, defined by the piston 25 and the wall of the end portion of the stepped bore 53 where it meets the inlet bore 56, which is vented to the atmosphere via a radial duct 51.A further O-ring 1 5 is seated in a V-groove 54 encircling the body 5 and passing over the end of the radial duct 51 to hinder the entry of dirt and foreign objects into the atmosphere chamber 14. Any other suitable filtering means may be used in addition or instead.

The stepped piston 25 includes an inlet passage 21 extending from an inlet port 20 at the end of the fluid inlet portion 26 axially through the piston and opening out radially into the central chamber 52. A coil spring 1 6 surrounding the piston 25 is compressed between a washer 1 2 abutting the first step of the stepped bore 53 and a piston flange 27 on the piston 25 biasing the piston head 22 towards the piston head abutment surface 43 of the outlet plug 4. A valve member 84 is positioned about the piston 25 in an annular piston recess 23 formed between the flange 27 and the piston head 22.

Referring now more especially to Figs. 4 to 7, the valve member 84 has a depending lip 86 (as seen in Fig. 4) which, when the valve member 84 is in an unstressed condition, is inclined angularly, extending axially upstream and flared radially outward. When the valve member 84 is fitted into the central chamber 52, the lip 86 is deflected radially inward by engagement of its outer periphery with the wall of the central chamber. This prevents the downstream flow of fluid from the central chamber 52 around the lip 86. The outer periphery of the valve member 84 drown: stream of the lip 86 is provided with a plurality of circumferentially spaced axially extending ribs 88 of generally semi-circular cross sectional shape. The ribs 88 contact the wall of the central chamber 52 downstream of the lip 86.The piston flange 27 lies partly within the lip 86 and engages a plurality of spaced hemispherical bosses 90 projecting upstream from the valve member 84. The outer diameter of the piston flange 27 is less than the inner diameter of the lip 86, thereby permitting fluid to flow through the spaces between the bosses 90. The diameter of the piston recess 23 on the piston 25 is less than the inside diameter of an inner peripheral surface 92 of the valve member 84 so that an open fluid path exists from the space between the bosses 90 to the combination bore and slot 44 in the outlet plug 4 when the piston 25 is disposed in the position illustrated in Fig. 2 with the piston head 22 in contact with the abutment surface 43.

The downstream side of the valve member 84 is provided with a plurality of angularly spaced bosses 94 which enS9e tbP C ri.

cal projection 42 of the outlet plug 4 and are angularly aligned with the ribs OR t-hrehy providing spaces between them through which fluid can flow upstream from the bore and slot 44 past the piston head 22 and outwards between the cylindrical projection 42 and the vahzs memher to the spaces between the ribs 88. Thus the fluid pressure at the outlet port 45 is also present at the outer periphery of the lip 86, so that if the fluid pressure at the outlet port is higher than the fluid pressure at the inlet port 20 when the valve is closed, the outlet pressure will force the lip 86 radially inward permitting reverse flow of fluid 86 radially inward permitting reverse flow of fluid from the outlet port and into the central chamber 52.The valve member 84 has a rounded valve seat 96 disposed at the downstream end of its inner peripheral surface 92. The seat 96 engages the piston head 22 upon upstream movement of the piston 25 against the action of the spring 1 6. In the event of such upstream movement, the valve member 84 is kept in position through frictional engagement between the lip 86 and the wall of the central chamber 52.

Thus it is seen that fluid enters the central chamber 52 via the inlet port 20 and the inlet passage 21 in the piston 25. From the central chamber 52 fluid flows radially inwards between the bosses 90 of the valve member 84, axially between the inner peripheral surface 92 of the valve member 84 and the recess 23 of the piston 25, and into the outlet port 45 via the outlet passageway 41. Fiiii;d flows to the outlet port 45 through a path radially outwards between the bosses 94, axially bctween the cylindrical portion 42 of the plug and the wall of the central chamber 52, and through the bore and slot 40 and the outlet passageway 41.This fluid path remains opeFrr until the fluid inlet pressure attains a rrsdeter^ mined value explained in more detail below.

At that time the piston head 22 will close against the valve member seat 96. Summing the forces acting on the piston 25 when the fluid path is open and assuming that forces acting in the upstream direction are positive we see that: (1) F = P1A,-S-PtA2 where: F = resultant force acting upon piston 25 when the fluid path is open; S = spring force; P, = inlet pressure; A1 = area of piston at O-ring 18; A2 = area of piston at O-ring 19; P1A, = force resulting from the inlet pressure P, acting on piston area A2.

P1A2 = force resulting from the inlet pressure P1 acting on piston area A2 The balance of forces acting on the piston 25 is not affected by changes in atmospheric pressure, because atmospheric pressure acts on the entire brake system uniformly, and there are no evacuated cavities present. Furthermore, because the brake fluid pressures are expressed as gauge pressures, atmospheric pressure would appear in equation (1) only in express terms which would cancel out directly with one another. Accordingly, atmospheric pressure could be omitted from equation (1) without any consequential amendments being needed and, in the interests of conciseness, it has been so omitted.

When the brakes are not in use or are only used gently, P1 is low, F is negative and the valve elements assume the position shown in Fig. 2. So long as F is negative, the fluid path around the valve member 84 remains open and the outlet port pressure equals the inlet port pressure. However, if the inlet pressure P1 increases to the point where F becomes positive, the piston 25 moves upstream until the piston head 22 engages the seat 96 of the valve member 84 thereby closing off the fluid path around the valve member 84.

Once the valve head 22 of the piston 25 closes the fluid path around the valve member 84 the forces acting upon piston 25 become: (2) F1 = P2A3-S-P1A2-P1(A3-A1) where, in addition to the symbols used in equation (1): F1 = resultant force acting on piston 25 when the fluid path is closed; P2 = pressure at the outlet port; A3 = area of the piston head within the line of sealing between piston head 22 and valve member seat 96; P2A3 = force resulting from the outlet port pressure P2 acting on piston head area A3; and P (A3-A1) = force resulting from the inlet pressure P1 acting on an area equal to the difference between the piston head area A3 and the piston area A1.

So long as F, is positive the piston 25 is urged upstream and the fluid path around the, valve member 84 will remain closed. However, if the inlet pressure P, increases to the point where F, becomes negative, the piston 25 moves downstream thereby opening the fluid path. Equation (1) then applies. Thus by the movement of the piston 25 upstream and downstream the working pressure of the fluid flowing through the valve is proportioned.

When the inlet pressure P, decreases again as the brakes are released, the fluid path around the valve member 84 will initially remain closed, but the resilience of the valve member 84 will allow the fluid on the outlet side of the valve to expand to some extent, maintaining the proportioning action of the valve.

Claims

1. A pressure-proportioning valve comprising: a housing having an inlet port and an outlet port and having an internal chamber communicating with the said inlet port and the said outlet port; a piston member axially slidable in the housing having a body portion of a first diameter near the housing outlet port and having an inlet portion of a second diameter smaller than the first diameter which enters the said inlet port, the piston having an external circumferential groove near the housing outlet port defining a piston head, the piston having a passage within it connecting the inlet port with the surface of the piston body portion; seal means within the housing which permits axial movement of the piston engaging the piston between the said openings of the passage within the piston, the piston being urged toward the said inlet port when inlet pressure increases; and valve means retained by the said annular groove of the piston which so cooperates with the piston head that the flow of fluid from the said inlet to the said outlet is restricted when the pressure of fluid at the inlet reaches a predetermined value and is arranged to relieve pressure at the outlet upon a reduction of the pressure at the inlet.

2. A pressure-proportioning valve as claimed in claim 1, wherein the valve means comprises: an annular unitary elastomeric valve member having a plurality of circumferentially spaced projections on both of its axial end surfaces and on its radially outward surface and including a flared shoulder extending axially towards the inlet port of the housing, the projections providing spaces between them for the free flow of fluid from the inlet to the outlet when the piston is moved towards the outlet and the piston head being movable against the valve member to restrict fluid flow when the piston is moved towads the inlet port.

3. A pressure-proportioning valve as claimed in claim 1 or claim 2, comprising: spring means urging the piston towards the outlet in such a manner as to influence the relationship between the inlet pressure and the outlet pressure.

4. A pressure-proportioning valve as claimed in any one of claims 1 to 3, wherein the said seal means comprises seals engaging portions of the piston of the first diameter and of the second diameter and defining between them a region not exposed to the pressure of the fluid within the valve.

5. A pressure-proportioning valve as claimed in claim 4, wherein the region between the seals is in communication with the atmosphere.

6. A pressure-portioning valve as claimed in any one of claims 1 to 5, wherein the housing inlet port and the housing outlet port open into the internal chamber through opposite axial ends thereof, and the valve means is between the housing outlet port and the said opening of the passage within the piston through the surface of the piston body portion.

7. A proportioning valve having a housing containing a slidable piston element wherein fluidic pressure at the inlet port is greater by some desired ratio as compared to the fluidic pressure at the outlet port, wherein: the piston element includes an elongate portion which protrudes into the inlet port and a passageway through the piston element which conducts fluid from the inlet port to an area within the housing separated from the inlet port by sealing means.

8. A brake system comprising a source of fluid pressure, a proportioning valve as claimed in any one of claims 1 to 7, and at least one pressure-operated brake that in operation is supplied with fluid under pressure from the source through the proportioning valve.

9. A brake system as claimed in claim 8 which is a hydraulic brake system.

10. A brake system as claimed in claim 8 which is a pneumatic brake system.

11. A wheeled vehicle having a brake system as claimed in any one of claims 8 to 10, the said at least one brake of which system is arranged to brake at least one rear wheel of the vehicle.