GB2033512A - Brake master cylinder-relay valve combinations - Google Patents

Abstract

An hydraulic master cylinder assembly 4 is operated by a pedal operated booster 5 and includes a piston 19 working in a bore 3 to pressurise fluid in a first pressure space 21. A control valve assembly 11 operable in response to pressurised fluid in the pressure space 21 controls communication between an inlet 12 for connection to a source 13 of hydraulic fluid under pressure, and an outlet 16. The booster 5 may be of the differential pneumatic pressure-operated type, or it may be of the hydraulic type operated by a supply of hydraulic fluid under pressure from a second source. The pressure space 21 and the outlet 16 may be connected to actuators for the same or different wheels of a vehicle and, when the booster is of the hydraulic type, an outlet from the booster may also be connected to actuators for brakes on front and/or rear wheels. <IMAGE>

Description

SPECIFICATION Improvements in hydraulic actuator assemblies for vehicle braking systems This invention relates to hydraulic actuator assemblies for use in vehicle hydraulic braking systems of the kind adapted to supply hydraulic fluid under pressure to respective braking circuits for operating front and rear wheel brakes.

In the Specification of our GB Patent Application No. 46114/77 we have disclosed an hydraulic actuator assembly comprising a pedal-operated master cylinder assembly including a piston working in a first cylinder bore in a housing to pressurise fluid in a first pressure space, and a control valve assembly for controlling communication between an inlet for connection to a source of hydraulic fluid under pressure and an outlet for connection to a braking circuit, the control valve assembly being operable in response to pressurised fluid in the first pressure space.

In the specific construction described in our GB Patent Application No. 46114/77 the first pressure space is adapted to be connected to a different braking circuit from that to which the outlet is connected. When the master cylinder assembly is operated one of the braking circuits is power applied, by the supply of pressure fluid from the source, suitably an accumulator, to the outlet under the control of the control valve assembly, and the other braking circuit is applied hydrostatically from the pressure space, that is to say from the master cylinder assembly itself. Should the master cylinder, the accumulator or either of the braking circuits fail for any reason the remaining braking circuit can still be applied.To reduce the pedal effort required to apply the brakes upon failure of the power applied to the hydraulic circuit, or the source of pressure fluid, the piston of the master cylinder assembly must be relatively small in diameter. This causes excessive travel of the piston to be necessary to operate the control valve assembly upon failure of the master cylinder assembly itself.

It is also known in an actuator assembly of the kind set forth to actuate tandem master cylinders of the hydrostatic type by two booster units arranged in series, one being of the differential pneumatic pressure-operated type and the other being of the hydraulic type operated by a supply of hydraulic fluid under pressure. Such an assembly comprising a tandem master cylinder and boosters in tandem are of substantial length and weight. This therefore presents a problem of installing such an assembly in the limited space normally available, and add significantly to the overall weight of a vehicle. Furthermore the displace ment of brake circuits is limited by the design of the master cylinder. For example, increasing the diameter would increase the pedal effort, whilst increasing the stroke affects the travel of the pedal.

According to our invention an hydraulic actuator assembly for a vehicle braking system comprises in combination a pedal-operated booster, an hydraulic master cylinder assembly operated by the booster and including a piston working in a first cylinder bore in a housing to pressurise fluid in a first pressure space for connection to a first braking circuit, and a control valve assembly for controlling communication between an inlet for connection to a source of hydraulic fluid and an outlet for connection to a second braking circuit, the control valve assembly being operable in response to pressurised fluid in the pressure space.

The provision of the booster enables the piston of the master cylinder relatively to be increased in diameter with consequent reduction in its stroke in the normal case and in all part failed cases. For example, with a front/ rear split, the normal pedal travel is reduced by 50%, in the fronts failed case by 62%, in the rears failed by 25%, and in the booster failed case by 50%. This means that a designer can design a car for a maximum pedal travel which is 40% less than that which would be required for a normal system. In addition it will be appreciated that assistance from the booster is provided in a failed case irrespective of whether the power applied hydraulic circuit, the source of pressure fluid, or the master cylinder assembly itself, has failed; whilst in the event of failure of the booster, both hydrostatic and hydraulic circuits can be applied.Thus relatively low pedal efforts and pedal travels, are required to operate the braking system, whichever item should fail or become inoperative.

Our assembly is substantially, compact and light in weight in comparison with known assemblies of tandem master cylinders and boosters in tandem. Thus installation in a limited space is facilitated, and the overall weight of a vehicle is not increased significantly.

Furthermore four assembly is able to supply large displacements of brake circuits from the source which is connected to the inlet. This makes it suitable to satisfy two current trends.

Firstly the construction of brake calipers from aluminium, which has a lower modulus of elasticity than cast iron used hitherto, results in increased deflection of the caliper with an attendant increase in the volumetric displace ment required. Secondly there is the need to simplify anti-skid braking systems. Powered braking systems permit the use of relatively simple modulator valves through which fluid from the brake is discharged to a reservoir during a skid, and replaced with fresh fluid from the source when the skid has been corrected.

The source may comprise an hydraulic accumulator provided specifically for that purpose, or we could utilise an hydraulic accumulator which otherwise forms part of a suspension system of the vehicle.

The booster may be of the differential pneumatic pressure-operated type or it may be of the hydraulic type operated by a supply of hydraulic fluid under pressure from another source.

Conveniently for a front/rear split substantially 30% of the system is applied by the master cylinder assembly, when operated by the booster, and the remaining substantially 70% is provided from the power applied hydraulic circuit.

The control valve assembly may be of tandem construction to provide outlets for the supply of hydraulic pressure to separate hydraulic circuits from two separate sources of hydraulic fluid.

Some embodiments of our invention are illustrated in the accompanying drawings, in which: Figure 1 is a layout of a vehicle hydraulic braking system including a longitudinal section through an actuator assembly incorporating a vacuum suspended booster; Figure 2 is a layout of a modified system; Figure 3 is a layout of another system; Figure 4 is a layout of yet another system; Figure 5 is a layout of a further hydraulic braking system incorporating a tandem control valve assembly; Figure 6 is a layout of another system; and Figure 7 is a layout of a system similar to Fig. 6 but showing a modification.

In the vehicle hydraulic braking system illustrated in Fig. 1 of the accompanying drawings an actuator assembly 1 comprises a housing 2 having a first longitudinaily extending cylinder bore 3 housing a pedal-operated master cylinder assembly 4 which is operated by a vacuum-suspended booster 5. The housing 2 is provided with a first recuperation port 6 for connection to a reservoir for hydraulic fluid (not shown) and a first outlet port 7 connected to the rear wheel brakes 8 through a pipe-iine 9.A second longitudinally extending cylinder bore 10 co-axial with, and of larger diameter than, the first bore 3, houses a control valve assembly 11 and is provided with an inlet port 1 2 connected to hydraulic accumulator 13, an exhaust port 14 connected to a reservoir 1 5 and a second outlet port 16 connected to front wheel brakes 17, through a pipe-line 1 8.

The master cylinder assembly 4 comprises a piston 1 9 working in the bore 3 and carrying a seal 20 which is normally spaced to the rear of the recuperation port 6 so that the reservoir communicates with a first pressure space 21 in the part of the bore 2 in which the outlet port 7 is located. The piston 1 9 is urged towards the inoperative position shown by a return spring 22 mounted in the first pressure space 21.

The control valve assembly 11 comprises a valve spool 23 working in a sleeve 24 in the bore 9. The spool 23 is exposed at one end to the first pressure space 21 and at the other end to a second pressure space 25 at the outer end of the bore 9 and which is closed by a plug 26. The plug 26 clamps the sleeve 24 against a shoulder 27 at a step in diameter between the bores 3 and 9.

The valve spool 23 comprises a stem portion 28 of reduced diameter which is provided at opposed ends with head portions 29, 30 for controlling communication between a series of radial ports in the sleeve 24. A drilled axial passage 31 in the valve spool 23 connects a chamber 32 surrounding the stem portion 28 with the second pressure space 25.

The valve spool 23 is normally urged by a return spring 33 into the position shown in Fig. 1. In this position the valve assembly 11 is closed and the inlet port 12, which communicates with a radial passage 34 in the sleeve 24, is cut-off by the head portion 29, and the second outlet port 16, which communicates with a radial passage 35 in the sleeve 24, is in communication with the exhaust port 14 through the chamber 32 and radial passages 36 in the sleeve 24.

The vacuum-suspended booster 5 comprises a housing 40 which is rigidly mounted on the end of the housing 2 remote from the plug 26. A movable wall 41 comprising a piston 42 connected by a flexible diaphragm 43 to the peripheral wall of the housing 40 divides the housing 40 into a front constant pressure chamber 44, which is connected to a source of vacuum, suitably the engine manifold, and a rear variable pressure or energising chamber 45. The piston 42 acts on the piston 1 9 of the master cylinder assembly 4 through a force transmission rod 46 and a reaction disc 47.

Energisation of the booster 5 is controlled by a pedal-operated valve 48. The valve 48 comprises a valve member 49 which is alter nativeiy engageable with spaced seatings in a bore in the piston 42 to control communication between the chambers 44 and 45 through a passage 50 in the piston 42, and between the chamber 45 and atmosphere through a filter 51 in an open end of the piston 42 remote from the master cylinder 2.

The valve 48 is operated by a pedal-operated rod 52 which projects through the filter 51. Return springs 53 and 54 act to hold the movable wall 41 and the rod 52 in the retracted position illustrated in which the valve member 49 cuts-off communication between atmosphere and the chamber 45, and places the chambers 44 and 45 in communication through the passage 50.

When the brake pedal is depressed to operate the booster, the rod 52 is advanced, initially to cause the valve member 49 to isolate the chamber 45 from the chamber 44.

Further movement of the valve member 49 in the same direction admits air into the chamber 45 to energise the booster and the movable wall 41 is advanced in the housing 40 against the force in the return spring 53 to apply a force to the piston 1 9 of the master cylinder assembly 4. The piston 1 9 is advanced in the bore 3 initially to close the recuperation valve 6 and isolate the reservoir from the first pressure space 21. Thereafter, upon further movement of the piston 1 9 in the same direction, fluid in the pressure space 21 is pressurised and is supplied to the rear wheel brakes 8 through the first outlet port 7.

Pressurised fluid in the pressure space 21 also acts on the valve spool 23 to urge it towards the plug 26. The head portion 30 covers the radial port 36 in the sleeve 24 to cut-off communication from the exhaust port 1 4 and the head portion 29 uncovers the radial port 34 to connect the inlet port 1 2 to the second outlet port 1 6 so that pressurised fluid from the accumulator 1 3 is supplied to the front wheel brakes 17.

After the valve assembly 11 opens, pressurised fluid supplied to the second outlet port 1 6 through the chamber 32 is also fed through the drilled passage 31 to the second pressure space 25 where it acts on the spool 23 in opposition to the pressurised fluid in the pressure space 21. The pressure in the pressure space 21 provides a reaction or "feel" at the pedal in proportion to the braking effort which is fed back to the pedal through the reaction disc 47 and the valve member 49.

When the applied force on the pedal is released, the piston 1 9 is urged rearwardly by the return spring 22 and the movable wall 41 is retracted by the spring 53. This exhausts the first pressure space 21 to the reservoir through the recuperation port 6, and the booster 5 is restored to a balanced condition with both chambers 44 and 45 connected to vacuum. Upon relief of the pressure in the space 21 the valve spool 23 is then returned to the inoperative position shown by the force in the return spring 33.

Should the front brakes 1 7 fail, the rear brakes 8 can still be applied with booster assistance by pressurisation of the pressure space 21. Similarly, should the rear brakes 8 fail, the front brakes 1 7 can still be applied with booster assistance, by the engagement of an extension 55 on the piston 1 9 with the adjacent end of the valve spool 23.

Should the booster 5 fail, the master cylinder 4 and the control valve assembly 11 can still be operated by a force transmitted mechanically from the pedal to the rod 46 and through the reaction disc 47.

The system described above is of the 'closed-centre' type in which the control valve assembly 11 acts normally to cut off communication between the accumulator 1 3 and the reservoir 15, and to isolate the accumulator 1 3 from the reservoir 1 5 and place it in communication with the brake 1 7 when the pedal is operated. In a modification the system may be of the 'open-centre' type in which the control valve assembly 11 is adapted normally to permit fluid at low pressure to be circulated in a closed circuit from a pump to the reservoir 1 5. When the pedal is operated the control valve assembly 11 throttles the supply from the pump and the fluid at increased pressure is applied to the brakes 1 7.

In the system shown in the layout of Fig. 2 the outlet port 1 6 is connected to actuators 62 and 63 of front and rear wheel brakes respectively, and the outlet port 7 from the pressure space 1 8 is connected to further actuators 64 for the front wheel brakes. In this system the front wheel brakes can be applied upon failure either of the accumulator 1 2 or the pressure space 21.

In the system shown in Fig. 3 each of the actuators 63 for the rear wheel brakes is connected to a different one of the outlet ports 16 and 7.

The layout of Fig. 4 shows a diagonal split with an actuator 64 for each front wheel brake connected to either outlet port 1 6 or 7 and to actuator 63 for the brakes on the rear diagonal wheel. In the event of failure of the supply of pressure fluid from one outlet port 16, 7 the brakes on one diagonal pair of wheels can still be applied.

The layout of Fig. 5 incorporates a tandem control valve assembly provided with spaced outlets 71 and 72 for connection, respectively, to actuators 73 and 74 for front and rear wheel brakes. Operations of the control valve assembly causes fluid under pressure to be supplied to the outlets 71 and 72 from respective hydraulic accumulators 75 and 76.

The outlet 7 is connected to other actuators 77 of the front wheel brakes.

The layout of Fig. 6 is similar to that of Fig.

2 except that the vacuum-suspended booster 5 has been replaced by an hydraulic booster 78 which is energised by an hydraulic accumulator 79.

The layout of Fig. 7 is similar to that of Fig.

6 except that an outlet port 80 from the booster 78 is connected to the actuators 63 of the rear wheel brakes and the communication between the outlet port 14 and the rear wheel brakes is omitted.

In a modification of the construction described above the master cylinder may be of tanden construction with the booster 5, 78 operating on a primary piston to pressurise fluid in a first pressure space which, in turn, acts on a secondary or floating piston, and the secondary or floating piston pressurises fluid in a second pressure space which operates the control valve assembly. In such a construction the first pressure space may also be connected to a third hydraulic circuit.

Claims (20)

1. An hydraulic actuator assembly for a vehicle braking system comprising in combination a pedal-operated booster, an hydraulic master cylinder assembly operated by the booster and including a piston working in a first cylinder bore in a housing to pressurise fluid in a first pressure space for connection to a first braking circuit, and a control valve assembly for controlling communication between an inlet for connection to a source of hydraulic fluid and an outlet for connection to a second braking circuit, the control valve assembly being operable in response to pressure fluid in the pressure space.

2. An hydraulic actuator assembly as claimed in claim 1, in which the source comprises an hydraulic accumulator specifically for that purpose.

3. An hydraulic actuator assembly as claimed in claim 1, in which the source comprises an hydraulic accumulator which otherwise forms part of a suspension system for the vehicle.

4. An hydraulic actuator assembly as claimed in any preceding claim in which the booster is of the differential pressure-operated type.

5. An hydraulic actuator assembly as claimed in any of claims 1 to 3, in which the booster is of the hydraulic type, and the booster is operated by a supply of hydraulic fluid under pressure from another source.

6. An hydraulic actuator assembly as claimed in any preceding claim in which the control valve assembly is of tandem construction to provide outlets for the supply of hydraulic pressure to separate hydraulic circuits from two separate sources of hydraulic fluid.

7. A vehicle hydraulic braking system incoporating an actuator assembly as claimed in any of claims 1 to 5, in which the first pressure space is connected to the first braking circuit, and the outlet is connected to the second braking circuit.

8. A vehicle braking system as claimed in claim 7, in which the first pressure space is connected to rear wheel brakes, and the outlet is connected to front wheel brakes.

9. A vehicle braking system as claimed in claim 7, in which the first pressure space is connected to actuators for the front wheel brakes, and the outlet is connected to actuators for both the front and the rear wheel brakes.

10. A vehicle braking system as claimed in claim 7, in which the first pressure space is connected to actuators for the front wheel brakes and to an actuator for one of the rear wheel brakes, and the outlet is also connected to actuators for the front wheel brakes and to an actuator for the other of the rear wheel brakes.

11. A vehicle braking system as claimed in claim 7, in which the pressure space is connected to a brake on one front wheel and to a brake on a rear wheel on the opposite side of the vehicle, and the outlet is connected to a brake on the other of the front wheels and to a brake on the other of the rear wheels.

1 2. A vehicle braking system incorporating an hydraulic actuator assembly as claimed in claim 6, in which the outlets from the control valve assembly are connected to actuators for the front wheel brakes and the rear wheel brakes, and the pressure space is connected to other actuators for the front wheel brakes.

1 3. A vehicle braking system as claimed in claim 7, in which the booster is of the hydraulic type, and the booster is operated by a supply of hydraulic fluid under pressure from a second source, the booster having an outlet connected to the rear wheel brakes, and the outlet from the control valve assembly and the pressure space being connected to actuators for the front wheel brakes.

14. A vehicle hydraulic braking system substantially as described herein with referen ce to and as illustrated in Fig. 1 of the accompanying drawings.

1 5. A vehicle hydraulic braking system substantially as described herein with reference to and as illustrated in Fig. 2 of the accompanying drawings.

1 6. A vehicle hydraulic braking system substantially as described herein with reference to and as illustrated in Fig. 3 of the accompanying drawings.

1 7. A vehicle hydraulic braking system substantially as described herein with reference to and as illustrated in Fig. 4 of the accompanying drawings.

1 8. A vehicle hydraulic braking system substantially as described herein with reference to and as illustrated in Fig. 5 of the accompanying drawings.

1 9. A vehicle hydrualic braking system substantially as described herein with reference to and as illustrated in Fig. 6 of the accompanying drawings.

20. A vehicle hydraulic braking system substantially as described herein with reference to and as illustrated in Fig. 7 of the accompanying drawings.