GB1585108A

GB1585108A - Braking apparatus with inshot

Info

Publication number: GB1585108A
Application number: GB23553/76A
Authority: GB
Original assignee: Bendix Westinghouse Ltd
Current assignee: Honeywell UK Ltd
Priority date: 1976-06-08
Filing date: 1976-06-08
Publication date: 1981-02-25
Also published as: NL181860B; ATA389977A; DE2724945A1; DE2724945C3; FR2354225B1; AT377949B; CH621298A5; ZA773073B; AU513210B2; DE2724945B2; AU2560877A; SE434493B; IT1083120B; BE855387A; FR2354225A1; SE7706595L; NL7705796A; NL181860C

Abstract

The arrangement contains a brake pressure control valve (1 to 15, 27, 28), which adjusts the feed pressure of the pressure medium from the driver's brake valve at the valve inlet (13) to an output pressure, dependent on the vehicle load (9), to the brake actuating devices of the vehicle at the brake pressure control valve outlet (27). At the start of a braking sequence, a control valve (30) applies a control pressure (50) to the brake pressure control valve (1 to 15, 27, 28) which, as a result, in a first stage delivers an output pressure which does not vary as a function of the vehicle load, and in a second stage an output pressure which varies as a function of the vehicle load. The control valve (30) contains two valve elements (19, 24), which can be moved by pressure medium, with a venting passage (23) for gradual reduction of the control pressure (50) so that the output pressure of the brake pressure control valve increases during the second pressure stage. Once an appropriate period has elapsed, the brake pressure control valve therefore delivers an output pressure, which varies as a function of the vehicle load, to the brake actuating devices of the vehicle and any trailer. <IMAGE>

Description

(54) BRAKING APPARATUS WITH INSHOT (71) We, BENDIX WESTINGHOUSE LIMITED, a Company incorporated under the Laws of Great Britain, of Douglas Road, Kingswood, Bristol, England, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to variable load valve apparatus and braking systems with inshot and relates especially to a fluid pressure operable braking apparatus employing a variable load valve for adjusting the degree of braking in a road vehicle dependent upon the loading of the vehicle.

In fluid pressure operable vehicle braking systems it has been proposed to employ load responsive proportioning valve means which operate in accordance with a signal related to the load carried by the vehicle for proportioning in accordance with load the pressure delivered to the vehicle brake actuators from or in response to brake valve output. In such a system operating under light load conditions, the pressure delivered may be low in relation to the force needed to overcome the return-springs and frictional resistances in the actuators and it has been proposed to provide "inshot" pressure in such a system whereby an initial load independent component of pressure is produced up to a given value of pressure.

According to the present invention there is provided variable load valve apparatus for use in a fluid pressure vehicle braking system including a variable load valve for adjusting the ratio of an output pressure to an input pressure in accordance with an applied loaddependent signal, the apparatus including an inshot valve operable to apply an inshot fluid pressure signal to the variable load valve to modify the operation of the variable load valve to introduce a load independent component such as to provide an initial range of output pressures the ratios of which to the corresponding input pressures do not vary and graduating means operable following attainment of a predetermined said input or output pressure to attenuate the load-independent component of the output pressure as the magnitude of the input or output pressure increases above said predetermined pressure.

The pressure responsive member of the inshot valve may have a first pressure responsive area responsive to the inshot pressure and a second pressure responsive area which is a fraction of the first area and is responsive to controlling input pressure.

In a preferred embodiment of the invention the inshot valve output is applied as an inshot biassing pressure to a pressure responsive member of a variable load valve which relays a proportion of a brake supply pressure to a brake actuator according to the loading of a vehicle on whcih the system is installed.

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: Figure 1 illustrates in diagrammatical form a variable load valve of known form together with an inshot valve connected to the variable load valve; and Figure 2 illustrates graphically the effect of a variable load valve with inshot in accordance with the present invention.

Referring to the drawing, the variable load valve is constructed with upper and lower body members denoted by references 1 and 2 respectively and which are bolted together to include a control piston 3, a flexible diaphragm 4, and a valve arrangement comprising a spring loaded valve member 5 which normally engages against a seat 6 and is further engageable by an internal tubular member 7 which is sealingly slideable in the lower body member and is engageable in turn with a ball pivot 8 carried by a pivoted lever 9 positioned by vehicle load.

The member 7 is clamped when a brake application is made, by virtue of pressure being applied beneath a piston 10 in a cylinder 11 which is connected via an external pipe 12 to the brake supply pressure input port 13 which is above the normally closed valve 5. The control piston 3 carried radially extending fingers such as the finger 14 which move between corresponding fingers 28 against which the diaphragm rests in the position shown, the arrangement being such that on downward movement of the piston, the diaphragm is increasingly engaged by the radial fingers 14 and decreasingly engaged by the inwardly projecting fins 28 such that the effect of pressure beneath the diaphragm on the piston arrangement, increases the greater the downward deflection ofthe piston.A similar such-arrangement is previously described in the Specification of British Patent No. 1029183 and need not be further described herein.

Referring now to the inshot valve arrangement, for the purposes of connecting this to the variable load valve, a port is provided connected to the region of the body of the variable load valve which is above the diaphragm 4 and this port, denoted by reference 15 is connected to an output port 16 of the inshot valve. Additionally, the inshot valve has a supply pressure input 17 and a controlling pressure input port 18 each connected to the supply pressure input port 13 of the variable load valve as shown.The inshot valve arrangement includes a pressure responsive member 19 comprising a double piston having two pressure responsive areas, the larger of which is the underside 20 subject to inshot region pressure, namely the output pressure of the inshot valve and the other of which is the annular part 21 which is subject to input region pressure namely the magnitude of the controlling pressure at the port 18. The pressure responsive member is downwardly biassed by a spring 22 and has a lower central vent passage 23 the low extremity of which acts as an exhaust valve seat bearing against a double member 24 which is shown in the closed position against an inlet valve seat 25 under the combined effects of a light housed spring 26 and the upward effective applied pressures.

Whilst not shown in the drawing, the variable load proportioning valve receives a brake pressure at port 13 from a reservoir via a driver's brake valve which is usually a footoperated valve. The pressure delivered at port 27 is applied to the brake actuators and in the case of there also being a trailer vehicle possibly to a relay valve which controls trailer service brakes.

Referring briefly to the operation of the variable load valve itself, when a brake application is made, air at the supply pressure is applied via the input port 13 to the chamber above the valve member 5 causing downward deflection of the piston 3. At the same time, there is a flow of air from the port 13 to the cylinder 11 so that the piston 10 is upwardly deflected to clamp the ball pivot against the internal slideable stem 7 by virtue of which the movable parts within the arrangement are responsive only when braking pressures are applied and thereby avoiding unnecessary wear. Since the valve member 5 is supported by the tubular stem 7, downward deflection of the piston 3 unseats the valve member 5 from its seat 6 permitting brake supply air to pass to the brake actuators via the variable load valve output port denoted by reference 27.At the same time, this pressure is presented to the region beneath the diaphragm 4 via a passage which is not readily seen in the drawing. Furthermore, as the piston is downwardly deflected, the diaphragm moves away from the fixed support of the inwardly directed fingers carried by the housing and becomes the more partially supported by the fingers such as 14 carried by the piston. This modifies the effective area of the diaphragm supported by the moving piston until-the force beneath the diaphragm, which depends on the pressure and effective area, equalises with the force acting above the piston. At this point, the valve member 5-reseats with the -seat 6 and a balance is achieved with a lower pressure at 27 than that which is applied at 13, keeping the valve assembly in the lapped condition with the input and exhaust ways via the valve members5 closed.The pressure at which this is attained depends upon the position of the lever 9 and therefore upon the loading of the vehicle. When the brakes are released the pressure in the port 27 as applied to the brake actuators lifts the piston thereby unseating the valve member 5 from the internal tubular tem 7 to result in venting of the pressure from 27 to atmosphere through the centre of the tube 7 until balance is re-àchieved or total release is attained.

In the foregoing the fact of pressure being applied from the inshot valve above the diaphragm 4 has been ignored for the sake of initial understanding but it will be appreciated that during the initial stage of increasing supply pressure at the port 13 from zero value, the valve member 24 remains unseated from the valve seat 25 but is engaged with the central vent valve passage 23.Under progressive increase of pressure at the port 17, a corresponding pressure therefore appears at the output 16 up to a point at which assisted by the additional pressure under the fractional area 21, the piston 19 is upwardly deflected to lap off the valve member 24 against its seat 25.:Further increase of braking pressure applied to the port 17 therefore cannot reach the output port 16 but can still reach the fractional annular area connected to the port 18 with the result that the piston is further deflected to act as agraduating-means to unseat the lower end of the exhaust passage 23 and permit a graduated venting of the pressure at the port 16 to atmosphere via the port 23. Assuming that the relative areas of the fractional annular area 21 and the area under the piston at 20 are about one to seven, and assuming that the valve 24 laps-off at a pressure of approximately one bar, with increasing supply pressure at the port 18 beyond the lapping off pressure, the pressure at the port 16 will be gradually reduced over the subsequent increase of seven bar in the supply pressure.

Reverting again to the variable load valve, the inshot pressure at port 16, being applied above the piston initially gives rise to a load independent output pressure component corresponding to the portion AD of the graph shown in Figure 2. For a fixed value of load, and therefore of position of the lever 9, the output of the port 27 varies with supply pressure according to the curve ADB. The point B being the point corresponding to load proportioned supply pressure with no inshot, achieved by virtue of the graduable venting of the inshot pressure above the diaphragm 4 over the range of operation following the point D.

In contrast, the curve ADE illustrates the output which would occur in the event of the inshot pressure not being so graduably removed but being maintained throughout the range of operation.

In the foregoing the inshot valve which is operable to provide an initial range of pressure output independent of the load-dependent signal, namely the position taken-up by lever 9, receives the variable load valve input pressure to cause the inshot component to be progressively reduced. Novertheless, it will be appreciated that an alternative pressure may be employed to achieve a similar result. For example, the delivered pressure of the variable load valve may be used to cause this graduable reduction of the inshot components, it being understood that appropriate adjustment of the dimensions of the stepped piston arrangement of the inshot valve may be required.

Whilst the delivered pressure may be used to perform the function within the inshot valve arrangement which in the above illustrated arrangement is performed by the input pressure from the brake valve, the delivered pressure may be arranged to perform the graduating function only, the input to the inshot valve being derived from the input to the variable load valve.

WHAT WE CLAIM IS: 1. Variable load valve apparatus for use in a fluid pressure vehicle braking system including a variable load valve for adjusting the ratio of an output pressure to an input pressure in accordance with an applied load-dependent signal, the apparatus including an inshot valve operable to apply an inshot fluid pressure signal to the variable load valve to modify the operation of the variable load valve to introduce a load independent component such as to provide an initial range of output pressures the ratios of which to the corresponding input pressures do not vary and graduating means operable following attainment of a predetermined said input or output pressure to attenuate the load-independent component of the out put pressure as the magnitude of the input or output pressure increases above said predetermined pressure.

2. Variable load valve apparatus as claimed in Claim 1, the graduating means being integral with the inshot valve, the inshot valve comprising a self-lapping valve device which has a first pressure responsive area, pressure on which acts in a sense to close-off an input passage at said predetermined pressure and an extra pressure responsive area for receiving a graduating signal pressure acting in a sense to cause opening of a vent passage to reduce said inshot fluid pressure signal.

3. Variable load valve apparatus as claimed in Claim 2, said graduating signal pressure being the input pressure to the variable load valve apparatus.

4. Variable load valve apparatus as claimed in Claim 1, wherein the graduating means is integral with the inshot valve.

5. Variable load valve apparatus as claimed in Claim 1 or 4, the inshot valve having a biassed pressure responsive means, an input pressure region connected to a first area of the pressure responsive member, an inshot pressure region connected to a second area of a pressure responsive member and an exhaust port, a selflapping double valve controlled by said biassed pressure responsive means to connect the inshot pressure region to the input pressure region or to the exhaust port, the pressures on said areas acting in like senses such that increasing input pressure produces progressive venting of the inshot pressure.

6. Variable load valve apparatus as claimed in any of Claims 1,2,3,4 or 5, the inshot valve comprising a spring-loaded valve member, a stepped piston arrangement providing two separate pressurable regions, one to receive a brake pressure signal and the other to receive resultant inshot pressure, said piston being spring-loaded against said first mentioned spring in a sense to hold the inshot valve open and retain a vent passage closed by engagement with the valve member in the absence of input pressure.

7. Variable load valve apparatus as claimed in any of Claims 1 to 6, wherein the fluid pressure signal forms an additional control signal to the variable load valve by acting upon a pressure responsive member thereof to partially counteract the effect of the delivered pressure acting on said member.

8. Variable load valve apparatus with an inshot valve substantially as described herein with reference to Figure 1 of the accompanying drawings.

9. A fluid pressure braking system including variable load valve apparatus as claimed in any

Claims

preceding claim.