GB2227063A

GB2227063A - Relay valves

Info

Publication number: GB2227063A
Application number: GB8927393A
Authority: GB
Inventors: A Piancastelli
Original assignee: Bendix Ltd
Current assignee: Honeywell UK Ltd
Priority date: 1988-12-02
Filing date: 1989-12-04
Publication date: 1990-07-18
Anticipated expiration: 2009-12-04
Also published as: GB2227063B; GB8828132D0; GB8927393D0

Abstract

A variable pressure ratio relay valve for vehicle load dependent brake pressure control includes in a housing (1) a moveable variable area ratio assembly (6, 13, 14) carrying a first double valve (15, 16, 17) the ratio of the areas thereof being dependent upon the position of the assembly in the housing to communicate a proportion of an input pressure as a control pressure to a control piston (21) of a relay valve the control piston carrying an exhaust valve seat (16) of the first double valve and having adjusting means (36) for setting the lapping position thereof in the housing in response to vehicle load. The relay valve member (27) engages seats (28, 29) to control communication of a chamber (39) and outputs (42) to brakes with a fluid pressure source (25) and a vent. <IMAGE>

Description

VARIABLE PRESSURE RATIO RELAY VALVE This invention relates to a variable pressure ratio relay valve and relates more especially but not exclusively to variable load dependent valves for use in compressed air operable braking systems.

In compressed air operable braking systems for vehicles it is well known to employ fluid pressure proportioning valves having means mechanically linked to a vehicle axle to sense the displacement of the axle and therefore the load on the vehicle and to adjust the available braking pressure accordingly. Such valves can be of a type which act to proportionately reduce a compressed air signal from a drivers control valve or alternatively they may be of a relay type to relay a proportionate pressure from a supply reservoir, so as to minimise the response time of the system to changes of the drivers control valve pressure.

Valves of a relay tyt- which ha'c- trevio sly been proposed either tend to exiit undesirable hysteris or alternatively they tend to be rathel- complicated in construction and an objective of the present invention is to provide a simplified pressure ratio relay valve wherein these shortcomings are reduced.

According to the prese= invention there is provided a variable pressure ratio relay valve comprising a housing including, movable ln said osio a variable area ratio pressure responslv assembly navlr.g first area subject to pressure at a control port and an opposing area subject to pressure in a first chamber which communicates alternatively with the control port or a vent via a first double valve the ratio of said opposing area to the first area being variable in accordance with the position ct the assembly in the housing, said first double valve having a valve member engageable with one valve seat carried by the assembly and a further valve seat carried by a moveable pressure responsive relay member, said relay member having a third area communicating with the said chamber and a fourth opposing area subject to pressure in a second chamber which communicates via a second double valve alternatively with a source of fluid pressure or a vent said second double valve having a valve member engageable with a third a valve seat carried by the relay member and/fourth valve seat the valve engaging position of which in the housing is adjustable by adjustable means towards or away from the variable area ratio assembly and a fluid pressure output port communicating with said second chamber.

The second double valve member may be carried by said relay member and seatable with the third one valve seat whilst being movable therewith towards or away from the fourth seat.

Alternatively, the further double valve may comprise a double valve member carried by said means and seatable with said further seat whilst being adjustable towards or away from the one valve seat.

Preferably, the further seat is adjustable towrads or away from the latter valve member by means of a rotary cam.

In order that the invention may be more clearly understood and readily carried into effect, the same will be further described by way of example with reference to the accompanying drawings of which Fig. 1 and-Fig. 2 illustrate sectional diagrammatic views of variable pressure ratio relay valves in accordance with examples of the invention.

Referring to Fig. 1 of the drawings, the variable pressure ratio relay valve shown is designed as a variable load valve for use in a vehicle compressed air braking system.

The housing comprises two housing components denoted by references 1 nod 2 sealingly clamped together by suitable set screws which are not shown. The upper housing component 1 has a cylindrical bore 5 within which a'piston 6 is sealingly slideable, being provided with an upper sliding seal 7, presenting a fixed piston area to the pressure at a control signal port 8. The lower end of the piston 6 is provided with a diaphragm 9 the periphery of which is clamped between the housing parts 1 and 2. The effective area of the-diaphragm is variable in accordance with the position of the piston 6 in the upper part of the housing.This variable are is achieved by Virtue of the piston 6 being provided with fingers 10 which extend radially outwaidly and are freely slideably located between inwardly extending fingers 11 of an insert 12 in the hous ing. The fingers 10 and 11 haves surfaces 13 and 14 which are displaced angular5} te the axes of movement of 6, such that as the piston 6 moves downwards the diaphragm 9 is increasingly supported by the lower edges 13 of the fingers 10 and reducingly supported by the lower edges of fingers 11.

The effective area of diaphragm 9 thereby increases as the piston 6 moves downwards. This arrangement is of generally known form in variable load valve technology and the piston 6 carries with it a double valve having a first double valve member 15 which rests alternatively against a first vent valve seat 16, a second inlet valve seat 17 or against both 16 and 17. In the rest position shown, the double valve member 15 which is retained in the piston 6 by means of a suitable circlip 18 and a captive light spring 19, is seen to be resting against the first vent valve seat 16.

The aforementioned first vent valve seat 16 is formed by the upper end of a t1rbnlar member 20 carried by a further piston 21 which is dealingly slideable in a bore 22 of the body part 2 of the housing. The piston has two seals 23 and 24 thereby providing an annular region between these seals which communicates with a reservoir supply port denoted by reference 25 and which com nlcates through a bore 26 of the piston with the input side of a further double valve having a valve member 27 which is urged by a light spring 27a to seat as shown with a third inlet valve seat 28 and is engageable with a fourth vent valve seat 29 which is axially moveable in the housing part 2. The tubular portion 20 is rigidly retained in the piston 21 by means of a suitable circlip 30.

The fourth vent valve seat 29, associated with double valve member 27 is carried on a sealingly slideable tubular member 33 in a seal 32 and provided at its lower end with a roller 34 retained by a suitable snap-in cage 35. The roller 34 rests against a rotary cam 36 carried on a transverse shaft 37 which rotates in bushes and captive seals (not shown), in the lower part 2 of the housing. The shaft 37 is provided with a lever a fragment 40 of which is shown for connecting the shaft 38, via a linkage (not shown), to an axle the load on which is to be sensed. The shaft 37 is provided with a helical spring (not shown) which insures that the valve returns to a full-load condition in the event of the mentioned linkage separating.

The upper part 1 of the housing is additionally provided with a pressure responsive valve arrangement 38 which functions in a broadly known manner to admit increasing control pressure from port 8 via a passage 39 to the region 39 above the diaphragm. The valve cuts off at a predetermined pressure and thereafter the pressure in region 39 is progressively diminished as the pressure at port 8 further increases.

Such a diminishing inshot feature is more fully discussed in the Specification of rWnited Kingdom Patent No. 1585108 and offers the benefit of an initial load-independent output which ensures the brakes are applied after overcoming initial friction but acts thereafter in a sense to prevent the proportioning being diminished under light load conditions.

In operation of the valve arrangement shown in Fig. 1, the fluid pressure control port 8 is connected to receive a control pressure from a drivers control valve and the supply port 25 is connected to a reservoir which is charged in known manner from a compressor carried on the vehicle. Output ports are denoted by reference 42 and these are connectable to actuators or further control valves for controlling the vehicle braking. Furthermore, the interior of the tubular portion 20, and the tubular part 33 are interconnected, by an axial passage through the assembly with the region 42 within which the cam 36 rotates, this region being vented through a suitable vent cap 43.

When the driver of the vehicle operates his brake control valve, a pressure is applied to the control port 8. This pressure is transmitted initially via passage 39 to the region above the diaphragm and also via the unseated double valve 15 to the first region above the piston 21 and when the piston 21 moves c:c'nwarc'W t. a ve .ember 15 seats against the inlet seat 17 and the control pressure is then active over the area defined by the seal 7. Downward movement of the piston 6 therefore begins and shortly afterwards the-valve member 27 engages with the exhaust valve seat 29. This sequence of events is assisted by the arrangement being such that in the rest position shown, the separation between the double valve member 15 and its seat 17 is slightly less than the separation between the vent valve seat 29 and the seated double valve 27.The resulting movements and balancing pressures result in the piston 21 resting in a stable position with the valve member 27 lapped in sealing engagement with its inlet valve seat 28 and its vent -valve 29. Similarly, the piston 6 rests in a stable position at which the double valve member 15 is lapped in sealing engagement with its inlet valve seat 17 and vent valve seat 16. This stable position of piston 6 is that which affords the desired pressure ratio between the effective areas of seal 7 subject to the input pressure at port 8 and the controlling presusre in the first chamber above piston 21. Pressure proportioning begins to occur after the cut off pressure setting of the valve arrangement 38 has been reached to disconnect port 8 from passage 39.Proportioning is then determined by the setting of the tubular member 33 in the housing in accordance with the position of the lever 40 which in turn determines the balancing position for piston 6.

With such a given setting of the lever 40, if the drivers brake valve pressure output is increased, piston 6 is urged downwards sufficiently further to permit unseating of valve member 15 from seat 17 te enhance the pressure in the first chamber above piston 21. Acting in its pressure relay mode this piston therefore moves downwards to admit further source pressure to the second chamber beneath piston 21 and at output ports 42 and the pistons return to their position of equilioriuw with stable output pressure. The reverse occurs if the drivers brake valve pressure output reduces, by virtue of temporary upward movement of both pistons permitting partial venting via the respective vent valve seats of valve members 15 and 27 following which the lapped condition is restored with a lower stable output pressure.

In the alternative example of the variable pressure ratio relay valve shown in Fig. 2, the upper part 51 of the housing is substantially identical with the part 1 of Fig. 1. The variable effective area diaphragm 59 is the same as diaphragm 9 of Fig. 1 and a first double valve member 65 with respective seats 66 and 67 is the same as the first double valve member 15 with its seats 16 and 17. However the further double valve of the example of Fig. 2 is now carried not by the relay member such as piston 21 (Fig. 1) but by the means which is adjustable towards and away from the relay member.

Thus, respective vent valve seats 66 and 79 of the first and second double valves are now each carried by a piston 71 with a single seal 73 slideable in a bore 72. The further double valve with valve member 77 is sealingly carried in a sealingly axially adjustable member 81 having seals 83 and 84 the annular region 86 between which is in permanent communication with a happily port 75. The annular region 85 is connected with t input side of the further double valve member 77 relay in member 81 against the force of a light spring 77a hv its annular seat member 78 which is retained by a circlip 80.The member 81 has a downwardly projecting tubular stem, wnich is sealingly slideable in the lower housing part 52 and carries a roller 89 as in Fig. 1 resting against a rotary cam 88 operated identically to cam 36 of Fig. 1, namc-ly by a lever (not shown).

The operation of the pressure proportioning valve of Fig.

2 is substantially eauivalcnt to that of the valve of Fig.

1, the double valve 77, 78, 79 operating to relay pressure from the source at port 75 via second chamber 91 to the output ports 92 in accordance with setting of cam 88 and the pressure in first chamber 93. However the valve arrangement of Fig. 2 has a relay piston 71 which may present larger areas to the controlling pressures than the piston of Fig. 1 and therefore the arrangement of Fig. 2 can have the greater control sensitivity.

Claims

1. A variable pressure ratio relay valve comprising a housing and including moveable In said housing a variable area ratio pressure responsive assembly having a first area subject to pressure at a control port and an opposing area subject to pressure in a first chamber which communicates alternatively with the control port or a vent via a first double valve, the ratio of said opposing area to said first area being variable in accordance with the position of the assembly in the noising, said first double valve having a valve member engageable with one valve seat carried by the assembly and a further valve seat carried by a moveable pressure responsive relay member, said relay member having a third pressure responsive area in communication wit the salo chamber and a fourth opposing area subject to pressure in a second chamber which communicates via a second double valve alternatively with a source of fluid pressure of a vent, said second double valve having a second double valve member engageable with a third valve seat carried by the relay member and with a fourth valve seat the valve engaging position of which in the housing is adjustable towards or away from the variable area ratio assembly and a fluid pressure output port communicating with said second chamber.

2. A variable pressure ratio relay valve as claimed in claim 1, wherein the secod double valve member is carried by said relay :rb::r and is seatable with the third valve seat whilst being moveable tnerewith towards or away from the fourth valve seat.

3. A variable pressure ratio relay valve as claimed in claim 1 wherein the second double valve member is carried with the third valve seat by said adjustable means to be moveable therewith towards or away from the fourth valve seat.

4. A variable pressure ratio relay valve as,claimed in claim 1, 2, or 3 said adjustable means being adjustable by a cam arrangement in the housing.

5. A variable pressure ratio valve as claimed in claim 1, 2, or 3 said cam being a rotary cam.