IMPROVEMENT IN HYDRAULIC BRAKING SYSTEMS FOR VEHICLES

Abstract: In an hydraulic braking system for vehicles a pedal-operated booster-assisted hydraulic master cylinder assembly (1) is adapted to apply a vehicle brake (2) by the supply of hydraulic fluid under pressure to a brake actuator for operating the brake, and a proportional valve (50) is arranged to provide a quick-fill function for the brake actuator in response to a proportional pilot signal (40) from the master cylinder assembly.

Description: IMPROVEMENT IN HYDRAULIC BRAKING SYSTEMS FOR VEHICLES This invention relates to hydraulic braking systems for vehicles of the kind in which a pedal-operated booster-assisted hydraulic master cylinder assembly is adapted to apply a vehicle brake by the supply of hydraulic fluid under pressure to a brake actuator for operating the brake. In braking systems, particularly for vehicles of the "off-highway type" , such as tractors and earth moving equipment, the trend is to adopt large running clearances between the braking members of the brake, for example between friction members and rotatable discs, in order that friction loses arising from parasitic drag are reduced or substantially eliminated. According to our invention in an hydraulic braking system of the kind set forth for vehicles, a proportional valve is arranged to provide a quick-fill function for a wheel brake actuator in response to a proportional pilot signal from the master cylinder assembly. The quick-fill function compensates for additional fluid volume requirements, and ensures that the pedal is immediately responsive with such additional volume requirements. The proportional valve may be situated in any convenient location, for example in close proximity to the brake actuator. In one construction, in a normal operative mode, the booster is adapted to meter input pressure to provide a booster signal, with the metered side of the booster being connected into and at a pressure, substantially equal to the pilot signal of the proportional valve. As the pilot signal is applied to the proportional valve, the proportional valve will open, allowing hydraulic fluid to flow from available vehicle hydraulics into the brake actuator. The "quick-fill" function works until a pre-set pressure is reached, directly proportional to the pilot signal provided by the booster which is also directly proportional to the effort applied by the pedal. Preferably the setting of the proportional valve is such that all clearances are taken up by utilising available vehicle hydraulics and thereafter the proportional valve is adapted to close allowing all further braking to be applied directly from the master cylinder. The invention allows rationalisation of boosters into fewer sizes to meet customer requirements. By tuning the proportional valve or pre-setting the setting of the proportional valve, the clearances of the brake may be taken up accordingly, and higher pressure brake stiffnesses may be applied through one size of master cylinder for all applications. The invention is particularly applicable to a dual braking system in which brakes on wheels on opposite sides of the vehicle may be operated simultaneously for braking, or independently to assist steering. When operated simultaneously pressure spaces in the two master cylinder assemblies are interconnected to compensate for differential wear of linings of the brakes. One embodiment of our invention is illustrated in the accompany drawings in which:- Figure 1 is a layout of a dual hydraulic braking system for "off-highway" vehicles; Figure 2 is an exploded view of a proportional pressure port incorporated in each of a pair of pedal-operated booster hydraulic master cylinder assemblies; and Figure 3 is a layout similar to Figure 1 but showing a modification. In the braking system illustrated in the layout of Figures 1 and 2, a pedal-operated booster assisted hydraulic master cylinder assembly 1 is adapted to operate a brake actuator 2 in order to apply a brake on the right-hand side of a vehicle, and a similar pedal-operated booster assisted master-cylinder assembly 3 is adapted to operate a brake actuator 4 in order to apply a brake on a wheel on the opposite side of the vehicle. The two master cylinder assemblies are identical so that only the assembly 1 will be described in detail. The pedal-operated booster assisted hydraulic master cylinder assembly 1 comprises a housing 5 having a stepped longitudinal bore 6 which is closed at its inner end and which comprises an outer bore portion 7 of greater diameter and an inner bore portion 8 of smaller diameter. A first stepped piston 9 works in the bore 6. A closure member 10 of "top-hat" section closes the outer end of the bore portion 7 and is disposed between the piston 9 and a stop defined by a mounting bracket 11. An internal bore 12 in the piston 9 and an internal bore 13 in the closure member 10, and which is of smaller diameter than the bore 12 together constitute a stepped bore in which works a second stepped piston 14 upon which a brake pedal 15 acts through an operating rod. Normally the piston 14 is held in a retracted position in which a shoulder at the step in diameter co-operates with the closure member 10 in turn to hold it in engagement with the stop 11 as biased by the loading in an internal return spring 16. Similarly a compression spring 17 acts on the piston 9 to hold it in a retracted position in engagement with the piston 13, the spring 17 being stronger than the spring 16. A third compression return spring 18 housed in a pressure space 19 defined by the bore portion 8 which is of smaller diameter also acts on the piston 9. The pressure space 19 is connected to the brake 2 through a pipe line 20. The system is provided with a source 30 of high pressure fluid comprising a pump 31 driven by a motor 32 and which is adapted to draw hydraulic fluid from a reservoir 33 to charge an hydraulic accumulator 34 through a one-way valve 35. An outlet from the supply 30 is connected through a pipeline 36 to the master cylinder 1 through an inlet port and which, in the off position shown in the drawings, is isolated from a pressure space 38, in which the spring 16 is located, by a seal 39 carried by the piston 9. A proportional pressure port 40 in the wall of the housing 5 is normally closed by a seal 41 , also carried by the piston 9, and communication between the annular chamber 42 defined between the bore 6 and two seals 39 and 41 communicates with a space between the pistons 14 and the bore 12 through a radial port 45. In the retracted position shown in the drawings free communication is allowed through the port 45 and past a seal 46 carried by the piston 14. The proportional port 40 is connected to a proportional valve 50 through a pipe-line 51 and the proportional valve 50 is located in close proximity to the brake actuator 2. Normally the proportional valve 50 is closed to isolate the brake actuator 2 from vehicle hydraulics 52. In the retracted, inoperative, position illustrated in the drawings the components of the master cylinders 1 ,3 are at rest with all the chambers of the master cylinders connected to respective reservoirs 60 and 61 of hydraulic fluid and which, in turn, are connected to their respective pressure spaces 19 through recuperation ports 62. The high pressure source 30 is isolated from the master cylinders 1 ,3 by closure of inlet ports, and the proportional pressure ports 40 are also closed. When a master cylinder, say the master cylinder 1, is operated by the pedal the stepped pistons 10 and 9 are advanced so that fluid under pressure enters the space 42 and into the proportional pressure port 40, in turn to pressurise the pressure space 38. The piston 9 is then advanced to pressurise fluid in the pressure space 19 which, in turn, is supplied to the brake actuator 2. During this movement of the pistons 10, 9 relative movement between them also takes place, the proportional pressure port 4 is opened, and the port 45 is closed by the seal 46. A proportional pilot signal comprising hydraulic pressure in the space between the pistons 10 and 9 is therefore directed to the respective proportional valve 50 which then opens to allow hydraulic fluid to "quick-fill" into the brake actuator 2. The "quick-fill" aspect works until a pre-set pressure is reached, directly proportional to the pilot signal provided by the master cylinder 1 and which is also directly proportional the effort provided by the pedal 15. The setting of the proportional valve 50 is also such that all clearances are taken up utilising the available vehicle hydraulics. Thereafter the proportional valve closes allowing further braking to be applied directly from pressurised fluid supplied to the brake actuator 2 from the pressure space 19. The pre-set pressure is tailored to the requirements of the vehicle braking system. When braking is no longer required the pedal is released and returns to the position illustrated in the drawings, and hydraulic fluid is returned to the reservoir 16 through the recuperation port 62 in the wall of the housing 6. Since the construction and the operation of the master cylinder 3 is similar to that of the master cylinder assembly 1 any further description is considered unnecessary. When both master cylinder assemblies 1 and 3 are operated simultaneously to apply brakes on opposite side of the vehicle, respective pressure spaces 19 are interconnected by a valve controlled compensating passage 70 which is in open communication when both pedals are operated together. This compensates for differential wear of the linings of the two brakes. In the braking system illustrated in the layout of Figure 3 of the accompanying drawings the source 30 is omitted, and the volume of hydraulic fluid from the vehicle hydraulics 65 is utilised to provide the quick-fill function described above. The construction and operation of the system illustrated in the layout of Figure 3 is otherwise the same as that of Figure 1 and corresponding reference numerals have been applied to corresponding parts.

Claims: CLAIMS 1. A hydraulic braking system for a vehicle in which a pedal-operated booster-assisted hydraulic master cylinder assembly (1 ,3) is adapted to apply a vehicle brake by the supply of hydraulic fluid under pressure to a brake actuator (2,4) for operating the brake, characterised in that a proportional valve (50) is arranged to provide a quick-fill function for a wheel brake actuator 2 in response to a proportional pilot signal from the master cylinder assembly. 2. A braking system according to Claim 1 , in which the proportional valve (50) is situated in any convenient location in close proximity to the brake actuator 2. 3. A braking system according to Claim 1 or Claim 2, in which the booster (1) is adapted to meter input pressure to provide a booster signal, with the metered side of the booster being connected into and at a pressure, substantially equal to the pilot signal of the proportional valve (50) so that as the pilot signal is applied to the proportional valve, the proportional valve (50) will open, allowing hydraulic fluid to flow from available vehicle hydraulics into the brake actuator (2) . 4. A braking system according to any preceding claim, in which the "quick-fill" function works until a pre-set pressure is reached, directly proportional to the pilot signal provided by the booster which is also directly proportional to the effort applied by the pedal. 5. A braking system according to any preceding claim, in which the booster includes first and second pistons (9, 10) which are relatively movable to close a port (45) leading to a reservoir (60) and to open a proportional pressure port (48) through which the pilot signal comprising hydraulic pressure in the space between the pistons (9, 10) is directed to and opens the proportional valve. 6. A braking system according to any preceding claim in which the setting of the proportional valve (50) is such that all clearances are taken up by utilising available vehicle hydraulics and thereafter the proportional valve is adapted to close allowing all further braking to be applied directly from the master cylinder. 7. A braking system according to any preceding claim in which the volume of hydraulic fluid from the vehicle hydraulics (52) is utilised to provide the quick fill function. 8. A braking system according to Claim 7, in which the fluid from the vehicle hydraulics (65) also provides the proportional pilot signal. 9. A dual braking system comprising a first and a second pedal- operated booster-assisted hydraulic master cylinder assemblies (1 ,3) each according to any preceding claim, in which the master cylinder assemblies (1 ,3) may be operated simultaneously for applying brakes on wheels on opposite sides of the vehicles, or independently to assist steering when operated simultaneously, in which pressure spaces in the master cylinder assemblies are interconnected to compensate for differential wear of linings of the brakes when the two master cylinder assemblies are operated simultaneously.

Inventors: BATCHELOR MARK, WILLIAMSON MICHAEL, BATCHELOR, MARK, WILLIAMSON, MICHAEL
Applicants: BATCHELOR MARK, MERITOR AUTOMOTIVE INC, WILLIAMSON MICHAEL, BATCHELOR, MARK, MERITOR AUTOMOTIVE, INC., WILLIAMSON, MICHAEL
Application year: 1999
Main classification: B60T13
IPC codes: B60T13