GB2183760A

GB2183760A - Vehicle antilock braking system

Info

Publication number: GB2183760A
Application number: GB08527293A
Authority: GB
Inventors: Kenneth James Bunker
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1985-11-06
Filing date: 1985-11-06
Publication date: 1987-06-10
Also published as: GB2183760B; GB8527293D0

Abstract

An antilock braking system for a vehicle has a master cylinder 20 adapted upon actuation to supply high pressure fluid to a brake actuator 11, 13, 15 and 17 on each wheel of the vehicle. Servo units 23 are provided in the lines 24, 25 between the master cylinder 20 and each of the actuators 11, 13, 15 and 17, each servo unit 23 being common at least two actuators 11 and 17 and 13 and 15. Wheel speed sensors 18, 19 are associated with each of the wheels and serve to control the servo unit 23 associated with the actuator 11, 13, 15 or 17 on that wheel, to reduce the braking effort of the actuators 11, 13, 15 or 17 associated with that servo unit 23, when the wheel deceleration increases above a predetermined limit.

Description

SPECIFICATION Vehicle antilock braking systems This invention relates to vehicle antilock braking systems.

It has been proposed, particularly for front wheel drive vehicles where the weight distribution is typically of the order of seventy per cent on the front and thirty per cent on the rear, to have a dual braking system in which the brakes of each front and the diagonally opposite rear wheels are interlinked. With this system, a sensor is fitted to each front wheel to actuate an antilock control unit in the leg of a dual braking system associated with that front wheel. There are no sensors on the rear wheels and these wheels will be controlled in accordance with the sensor associated with the front wheel on the same leg of the dual braking system.Proportioning valves, which are reactiveto some condition, for example pressure in the brake line or vehicle deceleration, are included in each leg of the dual braking system, to reduce the proportion of the braking effort applied to the rear brakes, under some pre-determined condition.

This antilock system functions well under most conditions. However, under certain extreme conditions, it is possible to lock one or both rear wheels. For example, on split IL tests, where the wheels on one side of the vehicle are on a surface of high frictional coefficient while the wheels on the other side of the vehicle are on a surface of low frictional coefficient, the front wheel on the surface of high frictional coefficient will control the effort applied to the brakes of the rear wheel on the surface of low frictional coefficient and this may result in the rear wheel locking. Also, where the surface changes from low frictional coefficient to high frictional coefficient, there is a possibility that both rear wheels will lock momentarily.

According to one aspect of the present invention a vehicle antilock braking system comprises a master cylinder which will produce a source of high pressure fluid upon brake actuation, said master cylinder being connected to a plurality of brake actuators, at least one actuator being associated with each of the braked wheels of the vehicle; servo means by which the effort applied to each brake actuator may be varied, disposed between each brake actuator and the master cylinder, at least two actuators associated with different wheels being connected to a common servo means; and control means associated with each of the braked wheels of the vehicle for sensing the rate of change of velocity of the wheel and controlling the servo means associated with the or each brake actuator on that wheel to reduce the effort to the or each brake actuator associated with that servo means, when the wheel deceleration increases above a pre-determined limit.

By this means, when the deceleration on one. of the braked wheels becomes so high that there is a danger that the wheel will lock, the braking effort will be reduced and the wheel will be permitted to accelerate. Preferably the control will be arranged to re-apply full braking effort, once acceleration of all wheels reaches a pre-determined limit.

An embodiment of the invention is now described by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates diagrammatically an antilock braking system formed in accordance with the present invention; and Figure 2 illustrates in sectional side elevation an antilock servo mechanism used in the system illustrated in Figure 1.

In the system illustrated in Figure 1, the front wheels of a vehicle are provided with disk brakes 10, 12 controlled by actuating callipers 11, 13 respectively and the rear wheels are provided with drum brakes 14, 16 being controlled by hydraulic cylinders 15, 17 respectively.

The braking system is a dual system controlled by a servo assisted dual master cylinder 20 of conventional design.

The master cylinder 20 has two outlets 22, 22' which provide a source of hydraulic pressure for the two legs of the dual system, one seving the calliper 11 of the off side front wheel and the cylinder 17 of the near side rear wheel and the other leg serving the calliper 13 of the near side front wheel and cylinder 15 of the off side rear wheel.

The two legs of the system are identical in arrangement and operation, and only one leg is described in detail beiow. Similar components have been identified with similar references.

The outlet 22 of master cylinder 20 is connected to the hydraulic fluid inlet port 36 of an antilock servo mechanism 23 and the outlet port 37 from said servo mechanism 23 is connected via line 25 to the near side front calliper 13 and off side rear cylinder 15.

As illustrated in greater detail in Figure 2, the servo mechanism 23 comprises a cylinder body 35 having an inlet port 36 in a screw-in end plug 38 and an outlet port 37 opening into a bore 39. A valve seat member 40 is secured by the end of plug 38 and has a control port 41 which can be closed by a ball 42. A control plunger 43 is slidable in the bore 39 and in the position shown in Figure 2 is operative to unseat the ball 42 against a light compression spring 44 and open communication between the inlet port 36 and outlet port 37. The cylinder body 35 is secured to a casing portion 45 which is itself secured at its outer rim to the outer rim of another casing portion 46. A flexible diaphragm 47 is secured at its outer periphery between the outer rims of the casing portions 45 and 46 and at its inner periphery to a piston portion 48.

Two helical compression springs 49, 50 act between the end wall of casing portion 46 and a dished plunger 51 which is coaxial with the cylinder body 35 and reacts on the end of the cylinder body 35 and the end of plunger 43 remote from the end plug 38.

The diaphragm 47 and piston portion 48 separate two chambers 26, 27 within the casing portions 45, 46. Chamber 26 is connected to a vacuum reservoir 29 via line 30 whilst chamber 27 is selectively connected to the vacuum reservoir 29 through line 30 or to atmosphere, through solenoid control valve 28.

Under normal braking conditions, the servo mechanism 23 will be as illustrated in Figure 2. The solenoid valve 28 will be switched to connect chamber 27 to the vacuum reservoir 29, so that pressure on either side of the diaphragm 47will be equal and the springs 49 and 50 will act through plunger 51 on control plunger 43 to keep the inlet port 36 and outlet port 37 in communication. Switching of the solenoid valve 28 to connect chamber 27 to atmosphere will provide a pressure differential across piston 48 and the resulting force re-enforces the force applied to plunger 43 caused by brake pressure at the outlet port 37, the combined forces moving the plunger 51 against the force of springs 49, 50, and allowing the ball 42 to seat against valve seat member 40 closing control port 41 and thus reducing brake pressure.

Toothed wheels 18 are mounted for rotation with each of the wheels of the vehicle and electro-magnetic pick-ups 19 are associated with each of the toothed wheels 18 to provide a signal which alternates at a frequency proportional to the rotational speed of the wheel with which it is associated.

The pick-ups 19 associated with the near side front wheel and off side rear wheel of the vehicle are connected to an electronic control module 31, which processes the signals from the pick-ups 19 to provide a measure of the deceleration or acceleration of each of the wheels. An output is provided from the control module 31 to solenoid valve 28, by means of which the solenoid valve 28 may be energised to open chamber 27 to atmosphere and thus reduce the braking effort applied to the brake calliper 13 and cylinder 15 connected thereto, when the deceleration of either the near side front wheel or off side rear wheel rises above a pre-determined limit, locking of the wheel being liable to occur above this limit.The solenoid valve 28 remains energised until the acceleration of both wheels rises above a pre-determined limit, when it will be de-energised and the servo mechanism 23 will re-apply normal braking.

In the embodiment illustrated in Figure 1 a proportioning valve 34 is provided in line 25 between the servo mechanism 23 and brake cylinder 15, said valve 34 being responsive to certain conditions, for example pressure in the brake line or deceleration of the vehicle, to vary the proportion of braking effort applied to the rear brake cylinder 15, under certain predetermined conditions. This proportioning valve 34 compensates for the shift in vehicle weight distribution during braking. While proportioning valves are extremely desirable in systems where there is no antilock braking system on the rear wheels, it will still provide energy saving advantages in the present system, although the system will perform adequately without such means.

Various modifications may be made without departing from the invention. For example, while. a dual braking system is described above, the invention may be applied to single circuit braking systems where a single antilock servo would be controlled by sensors on all four wheels. Also, with dual braking systems the wheels need not be linked diagonally, but may be linked for example, two fronts/two rears, two fronts and one rear/two fronts and other rear, or even have all four wheels on each separate circuit.

Claims

1. A vehicle antilock braking system comprising a master cylinder which will produce a source of high pressure fluid upon brake actuation, said master cylinder being connected to a plurality of brake actuators, at least one actuator being associated with each of the braked wheels of the vehicle; servo means by which the effort applied to each brake actuator may be varied, disposed between each brake actuator and the master cylinder, at least two actuators associated with different wheels being connected to a common servo means; and control means associated with each of the braked wheels of the vehicle for sensing the rate of change of velocity of the wheel and controlling the servo means associated with the or each brake actuator on that wheel to reduce the effort to the or each brake actuator associated with that servo means, when the wheel deceleration increases above a pre-determined limit.

2. A vehicle anti-lock braking system according to Claim 1 in which the control means reapplies full braking effort, once the acceleration of all the wheels reaches a pre-determined limit.

3. An antilock braking system according to Claim 1 or 2 in which the system is divided into two separate legs, a plurality of brake actuators being served by each leg, each leg including individual servo means and a control means responsive only to the wheels associated with the brake actuators served by that leg.

4. A vehicle antilock braking system according to Claim 3 in which each leg serves the brake actuator associated with one front wheel and the brake actuator associated with the diagonally opposite rear wheel.

5. A vehicle antilock braking system according to any one of Claims 1 to 4 in which the control means includes a sensor on each of the braked wheels of the vehicle which provides a signal indicative of the wheel speed, processing means for providing a measure of wheel acceleration or deceleration and means responsive to the measure of wheel acceleration or deceleration to control the servo means.

6. A vehicle antilock braking system according to Claim 5 in which the servo means is controlled by means of a solenoid actuated valve.

7. A vehicle antilock braking system according to any one of the preceding claims in which one or more proportioning valves are provided to control the proportion of braking effort applied to the rear brakes in response to some pre-determined condition.

8. An antilock braking system substantially as described herein with reference to, and as shown in, Figures 1 and 2 of the accompanying drawings.

8. A vehicle antilock braking system substantially as described herein with reference to, and as shown in, Figures 1 and 2 of the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. An antilock braking system for a vehicle having a plurality of braked wheels, said system comprising a master cylinder which upon actuation will produce a source of high pressure fluid, at least one actuator for each of the braked wheels of the vehicle, each of the actuators being connected to the master cylinder via servo means by which the effort ap piied to the actuators may be varied, the actuators associated with at least two different wheels being connected to a common servo means, and control means associated with each of the braked wheels for sensing the rate of change of velocity of the wheel and controlling the servo means associated with the actuator on that wheel to reduce the effort to each actuator associated with that servo means, when the wheel deceleration increases above a pre-determined limit.

2. An antilock braking system according to Claim 1 in which the control means reapplies full braking effort, once the acceleration of all the wheels reaches a pre-determined limit.

4. An antilock braking system according to Claim 3 in which each leg serves the brake actuator associated with one front wheel and the brake actuator associated with the diagonally opposite rear wheel.

5. An antilock braking system according to any one of Claims 1 to 4 in which the control means includes a sensor on each of the braked wheels of the vehicle which provides a signal indicative of the wheel speed, processing means for providing a measure of wheel acceleration or deceleration and means responsive to the measure of wheel acceleration or deceleration to control the servo means.

6. An antilock braking system according to Claim 5 in which the servo means is controlled by means of a solenoid actuated valve.

7. An antilock braking system according to any one of the preceding claims in which one or more proportioning valves are provided to control the proportion of braking effort applied to the rear brakes in response to some predetermined condition.