CA1203735A - Proportioning valve - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An axial flow proportioning valve for use in auto-motive hydraulic brake systems employs a stepped elongated piston enclosed having an axial bore therein. Input hy-draulic fluid is conducted through the axial bore exiting into an area forming an annular chamber about the piston.
When the input fluid pressure reaches a predetermined level the piston moves from its initial open position to a closed position until system forces cause the valve to again open.
Thus a modulating effect results whereby the output pressure to input pressure relationship follows a predetermined curve.

Description

3~3~ii This lnven-tion relates to vehicular fluidic brake systems and particularly to a brake pressure proportioning valve adapted -to modulate the fluid pressure at one or more hrake cy]lnders with respect to the Eluid pressure generated by a fluid pressure source.
The device of the present inven-tion is adapted to reduce the relative pressuriza-tion of the rear brakes of a motor vehicle with respect to the pressurization of the front brakes in the higher ranges of applied brake pres-sure. This is desirable in view o:E -the fact that a portion of the weight borne by the rear wheels of the vehicle is -transEerred to the front wheels of -the vehicle during rapid deceleration. ~s a result of this weight transfer, the maximum braking effort of which rear wheels are capable is reduced and -the maximum braking effort of -the front wheels is increased. It is therefore desirable to deliver a higher level of fluid pressure to the front wheels -than to the rear wheels cduring the high rates of deceleration. This will avoid premature rear wheel skidding, help main-tain the vehicle under control and reduce the to-tal distance re~uired to stop the vehicle.
The front and rear brake cylinders of a vehicle are ordinarily designed to apply forces to the front and rear brakes which are of the desired ratio for light braking or ordinary stopping. During extremely rapid deceleration or panic brake applications, however, the "buil-t-in" ratio :is no longer satisfac-tory and the ratio should be changed for maximum braking efficiency. The grea-ter -the rate of decelera-tion the greater should be the difference of fron-t brake pressure to rear brake pressure. While a bare measure-ment of -the applied brake pressure is not a completely ac-cura-te index o:E the rate of deceleration of -the vehicle, .it has been found to be a practical guide which may be use-:Eully employed in determining the poin-t at which the rela-tive pressuri.zation of the front and rear brake cylindersshoul.d be altered. The device o:E the present invention makes use o.E the applied brake pressure for such purpose.
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The presen-t invention provides a pressure pro-portioning valve for fluidic systems which comprises an elonga-ted housing having an inlet por-t and an outlet port and having an axial lnternal chamber communicating the inlet port wi-th -the outlet port; an elonga-te piston member con-~ained by the housing and axially slidable therein having a first diame-ter defining a body por-tion near -the housing outlet por-t and having a smaller second diameter which enters the chamber inlet portion, the pis-ton member having an external circumferential groove near the housin~ ou-tlet port de~ining a piston head, the pis-ton member fur-ther having a bore communicating -the ln:Le-t por-t wi-th the surface of the piston body portion; seal means within -the housing which permits axial movement of the piston member in-terposed be-tween openings of the piston bore, the piston member beingurged toward the inle-t por-t when inlet pressure increases, valve means retained by the pis-ton annular groove which cooperates with the piston head such that the flow of fluid from -the inlet port to the outlet port is restric-ted when a predetermined inlet pressure valve is reached and adapted to relieve pressure at the outlet upon a reduction of pres-sure at the inlet port.
Preferably, the valve means comprises a circular uni-tary elastomeric valve member having a plurality of cir-cum~erentially spaced projec-tions on both of i-ts circular planar surfaces and on its radiall~ outward surEace and including a flared shoulder directed toward -the inlet port of the housing, -the projections providing spaces there-between for the free flow o~ fluid from the inlet port to -the outlet por-t when the piston member is moved -toward -the outlet por-t and -the piston head movable agains-t the valve member to restric-t fluid flow when the pis-ton member is moved toward the inle-t por-t. The present propor-t:ioning va:Lve may be manufactured so as -to be particularly suitable for :in-line installa-tion wi-th o-ther brake components, for exarnple, for direct "screw-in" ins-tallation -to the outle-t port oF a master cy]lnder.

~3~5 An embodiment of the invention is illustrated by way of exampl.e in the drawings, in which:
Figure 1 is a pictorial view of an axial flow proportioning valve;
Figure 2 is a cross-sectional view -taken along line 2-2 in Figure 1 and showing the relative positioning of the valve elements;
Figure 3 is an exploded pictorial showing the various valve components;
Figure 4 is an enlarged view par-tly in section and partly in elevation of the valve member;
Figure 5 is a partial -top view of -the val~e member shown in Figure 4;
Figure 6 is a sectional view taken along line 6-6 in Figure 4; and Figure 7 is a sectional view taken along line 7-7 in Figure 4.
Referring to Figures 1, 2 and 3, the new improved proportionlng valve 10 includes a main body 5 having an externally threaded inlet boss 6 axially projecting there-from. Threaded into main body 5 opposite -threaded inlet 6 is outlet plug 4.
Within main body 5 is a central chamber or bore 52 communicating with stepped bore 53 which in turn com-municates w:ith inlet bore 56.
Outlet plug 4 includes an axially projecting cy-lindrical projection 42 having an outside diame-ter less -than -the inside diameter of cen-tral bore 52 and extending axially into the bore. The inside diameter of cylindrical projec-tion 42 is sufEicient to permit free axial -transla--tion o:E piston head projection 22 -therein. ~ combination bore and slo-t 44 extends diametrically through cylindrical projection 42 and piston head abutmen-t surEace 43 o:E plug 'I .
Positioned within main body 5 and extending through central charnber 52, stepped bore 53 and ir~.~.t bore 56 is stepped piston 25 sliclably received wi-thin bore 53 and Eluid ~2~;373~i inle-t por-tion 26 ex-tending axially through inlet boss 6 and slidably recei.ved wi-thin inlet bore 56. Standard O-rings 18 and 19 provide hydraulic sealing between pis-ton 25 and the main body 5 preven-ting the flow of fluid into chamber 14 which is ven-ted to the atmosphere via duct 51.
O-ring 15: is seated in V-groove 54 acting to restrict dirt and foreign objec-ts from entering atmosphere chamber 14.
Any other flltering means known in the art may also be used.
Stepped piston 25 includes inlet passage 21 ex-tendin~ from inlet port 20 axially through the piston exit-ing radially into cen-tral bore 52. Coil spring 16 sur-rounding piston 25 is compressed between washer 12 and piston flange 27 biasing pis-ton head 22 toward -the piston head abu-tment surface 43 of ou-tlet plug 4. Valve member 84 is positioned about pis-ton 25 in annular pis-ton recess 23 be-tween flange 27 and piston head 22.
The details of construction for valve member 84 are shown in Figures 4-7. I-t will be seen tha-t valve member 84 has a depending lip 86 which, i.n the free state of valve member 84~ is inclined angularly ups-tream and radially out-ward. When valve member 84 is fitted into bore 52 lip 86 is deflec-ted radially inward by engagement of its outer periphery wi-th bore 52. This prevents the downstream flow of fluid from bore 52 around lip 86. The outer periphery of valve member 84 downs-tream of lip 86 is provided with a plurality of clrcumferentially spaced axially extending ribs 88 of generally semi-cylindrical cross-sec-tional shape.
~ibs 88 contact the wall of bore 52 downstream of lip 86.
Plston flange 27 lies partly within lip 86 and engages a plurality of spaced semispherical bosses 90 projec-ting up-stream from valve member 84. The outer diameter of piston flange 27 is less than the inner diameter of lip 86, -thereby permittlng :Eluid to flow through -the spaces between -the bosses 90. The diameter o:E pis-ton recess 23 on piston 25 is less than the inside cliame-ter of inner peripheral sur-face 92 of valve member 84 so that an open fluid path exists from the space be-tween bosses 90 to passage 44 ln ou-tlet ~ ~-p/~
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plug 4 when piston 25 is disposed in the posl-tion ill.us--trated in Figure 2.
The downstream side of valve member 84 is pro-vided with a plurality of angularly spaced bosses 94 which engage -the cylindrical projection 42 of outlet plug 4 and angularly aligned with ribs 88 thereby providing spaces -therebetween for f]ow of fluid ups-tream from passage 44 past piston head 22 and outward between cylindr-ical portion 42 and valve member 84 to the spaces between ribs 88. Thus :L0 the fluid pressure a-t outle-t port 45 also exists at the outer periphery of lip 86 such tha-t if -the ou-tle-t por-t 45 pressure is higher than the fluid pressure a-t inlet port 20 after valve closure, the outlet pressure will force lip 86 radially inward permi-t-ting reverse flow of fluid from the outle-t por-t and into chamber 52. It will be seen tha-t valve member 84 has a rounded valve seat 96 disposed at the downstream end of its inner peripheral surface 92. Seat 96 engages the piston head 22 upon upstream movement of piston 25 agai.nst spring 16. In the even-t of such upstream movement valve member 84 is kept in position through frictional engagement between depending lip 86 and central bore 52.
Thus it is seen th~ fluid enters bore 52 via inlet port 20 and passage 21. From chamber 52 fluid flows radially inward between bosses 90 of valve member ~4, axially be-tween the inner peripheral surface g2 of valve member 84 and recess 23 of pis-ton 25, and into outlet port 45 via passageway 41. Fluid also flows to ou-tlet port 45 through a pa-th radially outward between bosses 94, axially between cylindrical portion 42 of plug 4 and -the wall of bore 52 and through bore 44 and passageway 41. This fluid pa-th remains open until the fluid inle-t pressure a-ttains a precletermined value. A-t this -time piston head 22 will close against the valve member sea-t 96. Summing forces act:ing upon piston 25 when the fluid path is open and assum:ing that forces act:ing in the upst:ream directi.on is pos:it:ive we see that:

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(1) F = PlA 1- S PlA2 where:
F = Resulting force acting upon piston 25 when the fluid path is open.
PlAl = Force resul-ting from the in].et pres-sure Pl ac-ting on piston area Al.
S = Spring force PlA2 = Force resulting from -the inlet pres-sure Pl acting on piston area A2.
Atmospheric pressure does not enter into the equation for forces on piston 25 since it acts equally on all the system components and the sys-tem does not employ evacuated cavities.
During periods of brake inactivity, F is negative and -the valve elements assume the posi-tion shown in Figure

2. So long as F is negative, the fluid path around valve member 84 remains open and -the outle-t port pressure equals -the inlet port pressure. However, as the inlet pressure increases to the extent -that F becomes positive, piston 25 moves upstream until piston head 22 engages seat 96 of ~alve member 84 thereby closing off the fluid path around valve member 84.
Once valve head 22 of piston 25 closes the fluid path around valve member 84 the forces acting upon piston 25 become:
1 2 3 S PlA2 - Pl(A3-Al) where:
F~ = Resulting force acting on piston 25 ~ when the fluid path is closed.
P2A3 = Force resul-ting from the ou-tlet port pressure P2 ac-ting on the piston head area A3.
Pl(A3-~l) = Force resul-ting from inlet pressure Pl ac-ting on an area equivalent -to the piston head area A3 minus the -the piston area A, when -the piston head 22 is closed against valve member seat 96.
35 S = Spring Eorce.
So long as Fl is positive piston 25 moves upstream and the :Eluid path around valve member 84 will remain closed.

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~ ~ ~, However, when inlet ~ressure Pl increases such that Fl be-comes negative, piston 2S moves downstream thereby opening the fluid path. Equation (1~ then applies. Thus by -the movement of piston 25 upstream and downstream the working pressure of -the fluid flowing -through the valve ls propor-tionecl.
It is to be unders-tood that the form of the inven-tion shown and descrlbed is to be taken as a preferred ex-ample of the same, and that various changes in the shape, size and arrangement of the parts may be made as do not depart from -the spirit of the invention or the scope of the following claims.

Claims (4)

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

1. A pressure proportioning valve for fluidic systems comprising:
an elongated housing having an inlet port and an outlet port and having an axial internal chamber com-municating said inlet port with said outlet port;
an elongate piston member contained by said housing and axially slidable therein having a first diameter defin-ing a body portion near said housing outlet port and having a smaller second diameter which enters said chamber inlet port, said piston member having an external circumferential groove near said housing outlet port defining a piston head, said piston member further having a bore communicating said inlet port with the surface of said piston body portion;
seal means within said housing which permits axial movement of said piston member interposed between openings of said piston bore, said piston member being urged toward said inlet port when inlet pressure increases, valve means retained by said piston annular groove which cooperates with said piston head such that the flow of fluid from said inlet port to said outlet port is restricted when a pre-determined inlet pressure valve is reached and adapted to relieve pressure at said outlet upon a reduction of pressure at said inlet port.

2. The pressure proportioning valve in claim 1 wherein said valve means comprises:
a circular unitary elastomeric valve member having a plurality of circumferentially spaced projections on both of its circular planar surfaces and on its radially outward surface and including a flared shoulder directed toward said inlet port of said housing, said projections providing spaces therebetween for the free flow of fluid from said inlet port to said outlet port when said piston member is moved toward said outlet port and said piston head movable against said valve member to restrict fluid flow when said piston member is moved toward said inlet port.

3. The pressure proportioning valve of claim 2, wherein said outlet port communicates with said spaces between said projections on said radially outward surface of said valve member through a radially extending passage between said outlet port and said piston head to permit reverse flow from said outlet port to past said flared shoulder when the pressure at said outlet port is greater than the pressure at said inlet port and said piston head has moved against said valve member.

4. The pressure proportioning valve in claim 1, 2 or 3, further comprising:
spring means urging said piston member toward said outlet port such that the relationship between inlet and outlet pressure is thereby modified.