GB2121496A - Improvements in dual brake valves - Google Patents

Abstract

A dual brake valve assembly for use in fluid pressure-operated vehicle braking systems embodying two independent braking circuits comprises a housing (1) provided with sets of primary and secondary ports associated respectively with the two braking circuits and each consisting of a supply port (5, 6) for connection to a source of fluid under pressure and a delivery port (7, 8) for connection to a brake actuator, an exhaust, and two co-axial primary and secondary valves (11, 12) which are operative, when actuated, to isolate the delivery ports from the exhaust and connect them to the respective supply ports. A primary piston (9) operates the primary valve (11) directly and acts on a secondary piston (10) to operate the secondary valve (12). The exhaust comprises a radial exhaust port (30) in the wall of the housing (1) intermediate opposite ends thereof, and the secondary piston (12) is provided with an exhaust passage (21) which is in communication at all times with the exhaust sides of both the primary and secondary valves (11, 12), and with the exhaust port (30) irrespective of the axial position of the secondary piston (10) in the housing (10). <IMAGE>

Description

SPECIFICATION Improvements in dual brake valves This invention relates to a dual brake valve assem blyfor use in fluid pressure-operated vehicle braking systems embodying two independent braking cir cuits, the valve assembly being of the kind comprising a housing provided with sets of primary and secon dary ports associated respectively with the two braking circuits and each consisting of a supply port for connection to a source offluid under pressure and a delivery port for connection to a brake actuator, an exhaust, and two co-axial primary and secondary valves which are operative when actuated to isolate the delivery ports from the exhaust and connect them to the respective supply ports.

Known brake valve assemblies of the kind set forth incorporate primary and secondary pistonsforcontrolling operation ofthe primary and secondary co-axial valves respectively, and the exhaust comprises an exhaust port, located in one end wall ofthe housing, conveniently an end wall at the end ofthe housing which is remote from the primary piston. The housing includes a portion of additional length in order to accommodate the exhaust port and additional space in a longitudinal sense is required also to accommodate any pipe-connection extending from the housing and surrounding the exhaust port.

According to our invention a dual brake valve assemblyofthe kind setforth incorporates a primary piston to operate the primary valve, and a secondary piston to operate the secondary valve, and the exhaust comprises a radial exhaust port in a wall of housing intermediate opposite ends thereof, the secondary piston being provided with exhaust passage means which is in communication at all times with the exhaustsidesofboththe primary and secondary valves and with the exhaust port irrespective of the axial position ofthe secondary piston in the housing.

Providing a radial exhaust port enables us to reduce the overall length of the housing, and facilitates installation since any pipe-connection from the ex haustportcan be accommodated in a radial sense where more space is normally available and such a pipe-connection is normally more readily accessible.

Preferablytheprimarypiston operatesthe primary valve directly and acts through the primary valve and the secondary piston to operatethesecondaryvalve, the secondary piston also being provided with supply passage means through which the respective supply and delivery ports are placed in communication when the primary and secondary valves are operated.

When both valves are operated opposite ends ofthe secondary piston are exposed to the pressure in the primary and secondary delivery ports so that valve assembly is held in a balanced position.

The secondary valve is carried by the secondary piston, and the primary valve may also be carried by the secondary piston. When both valves are carried by the secondary piston this provides a sub-assembly which facilitates manufacture since the secondary piston with both valves so installed can be inserted into a bore in the housing in which the secondary piston works and which is common with the bore in which the primary piston works.

Since ourvalve assembly does not depend on the generation of a pressure for operating the second valve it follows that the valve assembly is operable to provide low pressure differentials.

The housing may be constructed from a one-piece component, suitably a casting, into opposite ends of which the primary and secondary pistons are adapted to be inserted to work in the common bore in the housing, and the ends ofthe housing are closed by closure members ofwhich the member adjacent to the primary piston is guided to slide in the bore and acts as a pressure plate to transmit an actuating force to the primary piston through at least one spring, and the member adjacent to the secondary piston is rigid with the housing and is provided with a annular seating with which a valve member of the secondary valve is engageable to isolatetheexhaustportfromsecon- dary delivery port.

One embodiment of our invention is illustrated in the single Figure of the accompanying drawings which is a longitudinal section a dual brake valve assemblyforuse in afluid pressure-operated vehicle braking system.

The dual brake valve illustrated in the drawings comprises a housing 1 which is provided with longitudinally extending bore 2 having counterbored portions 3 and 4 at its opposite ends.

The housing 1 is provided with axially spaced primary and secondary supply ports 5and 6 connectedto different sources orto a common source of pneumatic pressure, and with complementary primary and secondary delivery ports 7 and 8 connected to the actuators of different or common brakes to form different braking circuits.

A primary piston 9 and a secondary piston 10 of annular outline both work in the bore 2.

Primary and secondary valves 11 and 12 are carried by the secondary piston 10, being located in a central through-bore. As illustrated the piston 10 comprises a symmetrical assembly of upper and lower components 13 and 14. The primaryvalve 11 is carried bythe upper components 13 and the secondary valve 12 is carried by the lower component 14.

The primary valve 11 comprises a valve member 15 oftop-hat section which is guided to slide in a cylindrical guide 16 carried by the component 13. The member 15 has a radial valve head 17 which is normally urged by a spring 18 into engagement with a seating 19 defined by the innerface of an inwardly directed radial flange at the end ofthe component 13 which is adjacentto the primary piston 9. In that inoperative position the engagement ofthe head 17 with the seating 19 isolates the primary supply port 5 from the primary delivery port 7 through a communicating radial passage 20 in the component 13.

The secondary valve comprises a valve member 21 oftop-hatsection which is guided to slide in a cylindrical guide 22 carried by the component 14. The member 21 has a radial valve head 23 which is normally urged by a spring 24 into engagement with a seating 25 defined by the innerface of an inwardly directed radial flange atthe end ofthe component 14 which is adjacent to the counterbore 4. In that inoperative position the engagement of the head 23 with the seating 25 isolates the secondary supply port 6from the secondary delivery port8through a communicating radial passage 26 in the component 14.

A pressure plate 27 for receiving a brake actuating force is guided to slide in the counterbore 3 on the side ofthe primary piston 9 which is remote from the secondary piston 10, andthe pressure plate 22 acts on the primary piston 9through a pairof concentric graduating springs 28 and 29.

A radial exhaust port 30 is provided in the wall of the housing 1 andthethrough-bore in the secondary piston 10 is in permanent communication with the exhaust port 30 through a diametral passage 31 in the secondary piston 10. The diametral passage is defined between seals 32 and 33 in the respective components 13 and 14 of which the axial spacing is such that permanent communication is maintained irrespective ofthe axial position ofthe piston 10 in the bore 2.

The primary piston 9 is urged away from the secondary piston 10 by means of a compression spring 34 and in an inoperative position determined bythe spring 34 a valve seating 35 on the primary piston 9 is spaced from the valve head 17 to place the delivery port7 in communication with the exhaust port30through the bore of the valve members 15, and the bore ofthe secondary piston 10, and the passage 31.

Similarlythe secondary piston 10 is urged away from a closure plate 36 at the end ofthe housing 1 remote from the plate 27 by means of a compression spring 37 and this acts to hold the valve head 23 away from an innerannularseating 38 which projects inwardly from the plate 36 and which is concentric with the seating 25. In that position the secondary delivery port 8 is placed in communication with the exhaust port 30 through the bore of the valve member 21 the bore of the secondary piston 10, and the passage 31.

In the inoperative position shown in the drawings, as described abovethe supply ports 5 and 6 are isolated from the corresponding delivery ports 7 and 8 bythe closed primary and secondary valves 11 and 12, and the delivery ports 7 and 8 are in communication with the exhaust port 30.

When the pressure plate is depressed, for example by foot pressure, that force is transmitted to the primary piston 9through the graduated springs 28 and 29. The piston 9 moves inwardly and the seating 31 engages with the head 17 initiallyto isolate the delivery port7 from the exhaust port 30, and subsequently, through the spring 34,to urge the secondary piston 10 downwardly until the head 23 engages with the seating 25 to isolate the delivery port 8fromtheexhaustport30. Furtherdisplacementof the primary piston 9 cau sthetwo valve heads 17 and 23 and the seatings ;9 and 25 to move relatively away from each other simultaneously so that the supply and delivery ports 5,7 and 6,8 are placed in communication with each otherthrough the respective communicating passages 20 and 26. Theoretically this gives substantially no pressure differential.

The valve balance is maintained by the pressures in the two delivery ports 7 and 8 acting on opposite ends ofthe secondary piston 10. The valve loading can be substantially high provided the balance is maintained.

Priority can be given to either system by selecting suitable loadingsforthe springs 18 and 24 such that the valves 11 and 12 can be operated sequentially.

The primary piston 9 is provided intermediate the axial length ofthe seating 35 with a radial shoulder 40.

In the event of failure of a source of pressure connectedtothe primarysupplyport5,theshoulder 40 is engageable with the adjacent end of the secondary piston 10 to operate the secondary valve 12 as described above.

Claims (5)

1. A dual brake valve assembly of the kind setforth incorporating a primary piston to operate the primary valve, and a secondary piston to operate the secon- dary valve, and the exhaust comprises a radial exhaust port in a wall of housing intermediate opposite endsthereof, the secondary piston being provided with exhaust passage means which is in communication at all times with the exhaust sides of both the primary and secondaryvalves and with the exhaust port irrespective of the axial position ofthe secondary piston in the housing.

2. Avalve assembly as claimed in Claim 1, in which the primary piston operates the primaryvalve directly and acts through the primary valve and the secondary piston to operatethesecondaryvalve,the secondary piston also being provided with supply passage means through which the respective supply and delivery ports are placed in communication when the primary and secondary valves are operated.

3. Avalve assembly as claimed in Claim 1 or Claim 2, in which the secondaryvalve is carried bythe secondary piston.

4. Avalve assembly as claimed in any preceding claim inwhich both valves are carried bythe secondary piston.

5. Avalve assembly as claimed in any preceding claim, in which the housing is constructed from a one-piece component into opposite ends of which the primary and secondary pistons are adapted to be inserted to work in the common bore in the housing, and the ends ofthe housing are closed by closure members of which the member adjacentto the primary piston is guided to slide in the bore and acts as a pressure plate to transmit an actuating force to the primary piston through at least one spring, and the member adjacent to the secondary piston is rigid with the housing and is provided with a annular seating with which a valve member of the secondary valve is engageableto isolate the exhaustportfrom secondary delivery port.