GB2131106A - Improvements in dual brake valves - Google Patents

Abstract

A dual brake valve assembly for use in fluid pressure-operated vehicle braking systems embodies two independent braking circuits. The valve assembly 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 (30), 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. The valve assembly incorporates primary and secondary pistons (9, 10) for respectively controlling operation of the primary and secondary co-axial valves disposed in the secondary piston (10), operation of the primary piston (9) being operative to control operation of the secondary piston (10), and being initiated by a pressure plate (27) for receiving a brake-actuating force and which co-operates with the primary piston (9) through resilient means (28, 29). The brake valve assembly is provided with a releasable stop (41) for limiting movement of the pressure plate (27) in a brake-applying direction until a predetermined point is reached at which the magnitude of the brake-actuating force applied to the pressure plate (27) attains a value sufficient to overcome the load in the stop, whereafter the pressure plate (27) is adapted to co- operate directly with the primary piston (9). The stop (41) comprises a fluid- pressure biassed stop member, for example a rod (42) with a head (44) acted on by pressure in-space (46) or a sleeve (61) (Figs. 2 and 3). <IMAGE>

Description

SPECIFICATION Improvements in dual brake valves This invention relates to a dual brake valve assembly for use in fluid pressure-operated vehicle braking systems embodying two independent braking circuits, the valve assembly being of the kind comprising a housing provided with sets of primary and secondary ports associated respectively with the two braking circuits and each consisting of a supply port for connection to a source of fluid 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, and the valve assembly incorporates primary and secondary pistons for controlling operation of the primary and secondary co-axial valves respectively, operation of the primary piston being operative to control operation of the secondary piston, and operation of the primary piston being initiated by a pressure plate for receiving a brake-actuating force and which co-operates with the primary piston through resilient means.

In known brake assemblies of the kind set forth a positive stop, suitably a shoulder or other projection, in the wall of the housing limits movement of the pressure plate in a brake-applying direction in order to ensure that the pressure plate cannot engage accidently with the primary piston, with consequent risk of damage thereto. This has the disadvantage that the valve assembly cannot be operated, for example if the primary piston should become wedged in its bore, since no force sufficient to free any obstruction can be transmitted directly to the primary piston from the pressure plate due to the presence of the stop.

According to our invention a brake valve assembly of the kind set forth is provided with a releasable stop for limiting movement of the pressure plate in a brake-applying direction until a predetermined point is reached at which the magnitude of the brake-actuating force applied to the primary piston attains a value sufficient to overcome the load in the stop, whereafter the pressure plate is adapted to co-operate directly with the primary piston.

The said point is reached when the magnitude of the brake-actuating force applied to the pressure plate exceeds substantially the magnitude of the force required to operate the valve assembly normally.

After the load exerted by the stop has been overcome any increase in the magnitude of the brake-actuating force acts to overcome any resistance to movement of the primary piston in the brake-applying direction.

The stop may comprise fluid-pressure biassed stop member.

Conveniently the stop comprises an abutment face on an abutment device with respect to which both the primary piston and the pressure plate are axially movable in a brakeapplying direction, and the abutment device is movable between an advanced position in which the pressure plate is prevented from cooperating directly with the primary piston, and a retracted position at the said point and at which the pressure plate can co-operate directly with the primary piston.

The abutment device is adapted to be held in the advanced position by a holding fluid pressure acting over a pressure-responsive face on it.

The holding fluid pressure may comprise the supply pressure at one of the supply ports, or the delivery pressure at one of the delivery ports.

When the delivery pressure comprises the holding fluid pressure, the stop will be operative to arrest movement of the pressure plate only when the valve assembly is operating satisfactorily. No stop is operative unless a delivery pressure is present. This facilitates actuation of the valve assembly.

The abutment device may comprise a rod which extends axially through the valve assembly and carries at its end remote from the pressure plate an enlarged head working in a bore in a closure member at the opposite end of the housing with a face on the head exposed to pressure in the secondary delivery port to hold the rod in an advanced position in which the free end remote from the head acts as the abutment face.

In another construction the primary piston and the pressure plate are both guided to slide in the bore in a sleeve which, in turn, works in a bore in the housing, and the sleeve is provided with a face of a shoulder at a step in diameter which comprises the abutment face and is subjected at its inner end to the holding fluid pressure.

When the holding fluid pressure comprises the supply pressure the inner end of the sleeve works in an annular bore in the housing, the base of which is connected to the supply port through a suitable branch passage.

Some embodiments of our invention are illustrated in the accompanying drawings in which: Figure 1 is a longitudinal section through substantially one half of a dual brake valve asembly for use in a fluid pressure-operated vehicle braking system; Figure 2 is a portion of the upper part of the valve asembly of Fig. 1 showing a modification; and Figure 3 is a view similar to Fig. 2 but showing another modification.

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 5 and 6 connected to different sources or to 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 works in the counterbore 3, and a secondary piston 10 or annular outline works in the counterbore 4.

Primary and secondary valves 11 and 1 2 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 1 3 and 14. The primary valve 11 is carried by the upper component 1 3 and the secondary valve 1 2 is carried by the lower component 14.

The primary valve 11 comprises a valve member 1 5 of top-hat section which is guided to slide in a cylindrical guide 1 6 carried by the component 1 3. The member 1 5 has a radial valve head 1 7 which is normally urged by a spring 1 8 into engagement with a seating 1 9 defined by the inner face of an inwardly directed radial flange at the end of the component 1 3 which is adjacent to the primary piston 9. In that inoperative position the engagement of the head 1 7 with the seating 1 9 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 of top-hat section 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 inner face of an inwardly directed radial flange at the end of the component 14 which is adjacent to the counterbore 4. In the inoperative position the engagement of the head 23 with the seating 25 isolates the secondary supply port 6 from the secondary delivery port 8 through a communicating radial passage 26 in the component 14.

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

A radial exhaust port 30 is provided in the wall of the housing and the through-bore in the secondary piston is in permanent communication with the exhaust port 30 through a diametral passage 31 in the secondary piston 1 0. The diametral passage 31 is de fined between seals 32 and 33 in the respec tive components 1 3 and 14 of which the axial spacing is such that permanent communi cation is maintained irrespective of the posi tion of the piston 10.

The primary piston 9 is urged away from the secondary piston 10 by means of a com pression spring 34 and in an inoperative posi tion determined by the spring 34 a valve seating 35 on the primary pisotn 9 is spaced from the valve head 1 7 to place the delivery port 7 in communication with the exhaust port 30 through the communicating bores of the valve members 1 5 and 21, the bore of the piston 10, and the passage 31.

Similarly the secondary piston 10 is urged away from a closure plate 36 at the end of the 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 annular seating 38. The seating 35 surrounds a central aperture 39 in the plate 36. In that position that 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 piston 10, and the pas sage 31.

The bore in the piston 9 in which the pressure plate 27 is guided to slide is of stepped outline and a shoulder 40 at a step at the change in diameter defines an abutment with which the plate-37 is engagable to affect direct operation of the piston 9.

The engagement of the plate 27 with the shoulder 40 is controlled by a pressure-oper ated stop 41. As illustrated the stop 41 comprises a rod 42 which extends longitudi nally of the housing 1 through the pistons 9 and 10. The rod 42 normally projects at its upper end above an abutment plate 43 for the springs 28 and 29 and at its lower end carries an enlarged head 44 of stepped out line which works in a complementary stepped bore 45 in the closure 36. A pressure space 46 defined between complementary steps on the head 44 and the bore 45 communicates with the delivery port 8 through a passage 48.

When the pressure space 46 is pressurised the head 44 is held in an advanced position in which the upper end of the rod 42 projects above the abutment plate 43 to act as a stop for engagement by a domed abutment portion 50 on the plate 27 in order to prevent the plate 27 from engaging with the shoulder 40.

In the inoperative position shown in the drawings, as described above the supply ports 5 and 6 are isolated from the corresponding delivery ports 7 and 8 by the 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 27 is depressed, for example by foot pressure, that force is transmitted to the primary piston 9 through the graduated springs 28 and 29. The piston 9 moves inwardly and the seating 35 engages with the head 1 7 initially to isolate the delivery port 7 from the exhaust port 30, and subsequently to urge the secondary piston 10 downwardly until the head 23 engages with the seating 38 to isolate the delivery port 8 from the exhaust port 30. Further displacement of the primary piston 9 causes the two valve heads 1 7 and 23 and the seatings 1 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 other through the respective communicating passages 20 and 26.Theoretically this give substantially no pressure differential.

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

The primary piston 9 is provided intermediate its axial length with a radial shoulder 51.

In the event of failure of a source of pressure connected to the primary supply port 5, the shoulder 51 is engagable with the adjacent end of the secondary piston 10 to operate the secondary valve 1 2 as described above.

In the event of the mechanism sticking in operation, for example by the primary piston 9 sticking in the counterbore 3, an increase in the pedal-load applied to the piston 9 acts through the domed portion to overcome the load applied to the rod by any pressure in the pressure space 46 acting on the head 44, and the plate 27 can move into engagement with the shoulder 40. An increase in the load applied to the plate 27 is transmitted dierectly to the piston 9 to overcome the resistance to brake-applying movement and the piston 9 is moved inwardly to operate the valve assembly as described above.

The stop will be operative only when a delivery pressure, suitably 8 bar, is present in the delivery port 8.

In the construction illustrated in Fig. 2 of the drawings the rod 42 and the head 44 are omitted, and the closure 44 and the piston 9 are both in perforate. The piston 9 and the plate 27 both work in a stepped bore 60 of a sleeve 61 which is guided to slide in the counterbore 3. The inner end of the sleeve 61 is normally spaced from a shoulder 62 in the housing and is therefore exposed to pressure in the delivery port 7 to which the adjacent face of the primary piston 9 is also exposed.

When the valve assembly 1 is operating normally with a pressure in the delivery port 7, the sleeve 61 is held in an advanced position with a shoulder 63 at the step in diameter acting as a stop to arrest movement of the plate 27 in a brake-applying direction.

As in the construction of Fig. 1 the stop is inoperative when no delivery pressure is present, and the plate 27 is free to engage directly with the piston 9.

The construction and operation of the embodiment of Fig. 2 is otherwise the same as that of Fig. 1 and corresponding reference numerals have been applied to corresponding parts.

In the modified construction illustrated in Fig. 3 the inner end of the sleeve 61 works in an annular cylinder 70 in the housing 1 which is in permanent communication through a branch passage 71 with the supply port 5. Thus the sleeve 61 is normally held in its advanced position when the supply, suitably at a pressure of 11 bar, is operative.

In the event of the components sticking in operation, an increased load applied to the plate 27 carries the sleeve 61 inwardly to overcome the force of the supply pressure acting on the sleeve 61, by the engagement with the shoulder 63. This enables the plate 27 to engage with the piston 7, whereafter the valve assembly can be opeated as described above.

The construction and operation of the modification of Fig. 3 is otherwise the same as that of Fig. 2 and corresponding references have been applied to corresponding parts.

Claims (12)

1. A brake valve assembly of the kind set forth provided with a releasable stop for limiting movement of the pressure plate in a brake-applying direction until a predetermined point is reached at which the magnitude of the brake-actuating force applied to the pressure plate attains a value sufficient to overcome the load in the stop, whereafter the pressure plate is adapted to co-operate directly with the primary piston.

2. A brake valve assembly as claimed in Claim 1, in which the stop comprises a fluidpressure biassed stop member.

3. A brake valve assembly as claimed in Claim 1 or Claim 2, in which the stop comprises an abutment face on an abutment device with respect to which both the primary piston and the pressure plate are axially movable in a brake-applying direction, and the abutment device is movable between an advanced position in which the pressure plate is prevented from co-operating directly with the primary piston, and a retracted position at the said point and at which the pressure plate can co-operate directly with the primary piston.

4. A brake valve assembly as claimed in Claim 3, in which the abutment device has a pressure-responsive face, and a holding fluid pressure is adapted to act over the pressureresponsive face to hold the abutment device in the advanced position.

5. A brake valve assembly as claimed in Claim 4, in which the holding fluid pressure comprises the supply pressure at one of the supply ports.

6. A brake valve assembly as claimed in Claim 4, in which the holding pressure comprises the delivery pressure at one of the delivery ports.

7. A brake valve assembly as claimed in any of Claims 3-6, in which the abutment device comprises a rod which extends axially through the valve assembly and carries at its end remote from the pressure plate an enlarged head working in a bore in a closure member at the opposite end of the housing with a face on the head exposed to pressure in the secondary delivery port to hold the rod in an advanced position in which the free end remote from the head acts as the abutment face.

8. A brake valve assembly as claimed in any of Claims 3-6, in which the primary piston and the pressure plate are both guided to slide in the bore of a sleeve which, in turn, works in a bore in the housing, and the sleeve is provided with a face at a shoulder at a step in diameter which comprises the abutment face, the sleeve being subjected at its inner end to the holding fluid pressure.

9. A brake valve assembly as claimed in Claim 8, in which the inner end of the sleeve works in an annular bore in the housing, and the annular bore is connected to the primary supply port through a suitable branch passage.

10. A brake valve assembly substantially as described herein with reference to and as illustrated in Fig. 1 of the accompanying drawings.

11. A brake valve assembly substantially as described herein with reference to and as illustrated in Fig. 2 of the accompanying drawings.

12. A brake valve assembly substantially as described herein with reference to and as illustrated in Fig. 3 of the accompanying drawings.