GB2057080A

GB2057080A - Anti-skid systems

Info

Publication number: GB2057080A
Application number: GB8026395A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-08-16
Filing date: 1980-08-13
Publication date: 1981-03-25
Also published as: DE2933085A1; JPS5628035A; JPS6363422B2; GB2057080B; DE2933085C2

Abstract

An anti-skid system is provided for a passenger vehicle which has split brakes (1a, 1b and 2a, 2b) on a first axle and two brake circuits (5a, 5b), one brake circuit including one compartment brake (1b, 2a) of each of the two wheels (1, 2) of one axle (Fig. 2) and optionally (Fig. 1) the brake (3a) of one wheel (3) of the second axle, and the other brake circuit including the remainder (1a, 2b, 4a) of the brakes. The four modulator valves (6, 7, 8, 9) of the anti-wheel-lock system are connected such that a first respective valve (6 or 8) in each brake circuit is associated with a brake (3a or 4a) of the second axle and a component brake (1b or 2b) of the first axle which is located at the same side of the vehicle, is in each case controlled in dependence upon the behaviour of that wheel of the wheels of the associated side of the vehicle at which the sensor (1c, 2c, 3c or 4c) is the first to indicate a tendency to lock (select low), and a second respective valve (7 or 9) in each brake circuit is associated with the other component brake (1a or 2a) and responds to the sensor at the wheel it controls. With this system only four valve arrangements are provided for regulating the pressures at six brakes or component brakes. <IMAGE>

Description

SPECIFICATION Anti-skid systems The invention relates to an anti-skid system for a motor vehicle having two brake circuits and split brakes on the wheels of one of the axles; a measured value sensor associated with each of the wheels, an evaluation circuit for processing the signals from the sensors, and valve arrangements which vary the brake pressures at the brakes of the individual wheels in dependence upon the behaviour of the wheel movement.

A dual-circuit brake system, in which the first component brakes of the two wheels of the first vehicle axle and the brake of one wheel of the second vehicle axle are associated with one brake circuit, and the second component brakes of the two wheels of the first vehicle axle and the brake of the other wheel of the second axle are associated with the second brake circuit, is described in At'70 (1968), Issue 10, page 341.

To enable an anti-skid system of known principle to be used in a brake system of this kind, it might occur to one to associate a separate valve arrangement with each brake (including the component brakes) This would imply the use of six valve arrangements, wherein the valve arrangements associated with the two component brakes of one wheel could be controlled in parallel.

A disadvantage is the high expenditure on valves required for this purpose.

An object of the invention is to provide an antiskid regulator for a brake system in which the brake circuits are split up in this manner and which is less expensive than the known system and which, nevertheless, is equally efficient.

The present invention provides an anti-skid system for a motor vehicle having two brake circuits and split brakes on the wheels of one axle, in that the first component brakes of the two wheels of the first vehicle axle and the brake of one wheel of the second vehicle axle are associated with one brake circuit, and the second component brakes of the two wheels of the first vehicle axle and the brake of the other wheel of the second axle are associated with the second brake circuit, the anti-skid system comprising a measured value sensor associated with each of the wheels, an evaluation circuit for processing the signals from the sensors, and valve arrangements for varying the brake pressure at the brakes of the individual wheels in dependence upon the behaviour of the wheel movement, a first respective valve arrangement being located in each of the first and second brake circuits for common regulation of the brake pressure at one wheel the second axle and of that component brake of the first vehicle axle which is located in the same brake circuit and at the same side of the vehicle, a second respective valve arrangement being located each of the two brake circuits for regulating the pressure at the other component brake associated with this brake circuit, the second respective valve arrangements which regulate the pressure only at one component brake of the first axle being controllable in dependence upon the movement behaviour of only the associated vehicle wheel, and the first respective valve arrangements associated with the two brakes at one side of the vehicle being each controllable in dependence upon the behaviour of that wheel of the wheels of the associated side of the vehicle which is the first to indicate a tendency to lock.

The object set forth above, and the features specified for achieving this object, can also be associated with brake circuits which are split up in a slightly different manner from that described.

Thus the present invention also provides an anti-skid system for a motor vehicle having two brake circuits and split brakes on the wheels of one axle, in that the first component brakes of the two wheels of the first vehicle axle and the brakes of the two wheels of the second vehicle axle are associated with one brake circuit, and the second component brakes of the two wheels of the first vehicle axle are associated with the second brake circuit, the anti-skid system comprising a measured value sensor associated with each of the wheels, an evaluation circuit for processing the signals from the sensors, and valve arrangements for varying the brake pressure at the brakes of the individual wheels in dependence upon the behaviour of the wheel movement, first respective valve arrangements being located in the first brake circuit respectively for common regulation of the brake pressure at one wheel of the second axle and at one component brake of the first vehicle axle which is located at the same side of the vehicle as that one wheel and common regulation of the brake pressure at the other wheel of the second axle and at one component brake of the first axle at the same side of the vehicle as that other wheel, second respective valve arrangements being located for separate regulation of the pressure at the component brakes associated with this brake circuit, the second respective valve arrangements which regulate the pressure only at one component brake of the first axle being controllable in dependence upon the movement behaviour of only the associated vehicle wheel, and the first respective valve arrangements associated with the two brakes at on one side of the vehicle being each controllable in dependence upon the behaviour of that wheel of the wheels of the associated side of the vehicle which is the first to indicate a tendency to lock.

Thus, the same principles are also used in this system.

It may be mentioned that "valve arrangement" refers to a valve or a combination of valves which, in addition to permitting the build-up of pressure permits at least a reduction of pressure at the brake or brakes, although, preferably, it also renders it possible to maintain the pressure constant. By way of example, a respective threeport, two-position valve, two-port, two-position valves, a three-port, three-position valve etc. can be used.

With differing coefficients of friction of the roadway for the wheels at both sides of the vehicle, high yawing moments can act upon the vehicle during anti-skid regulation. In the anti-skid systems in accordance with the invention, these yawing moments can be avoided by providing a pressure differential detector for theregulated pressure at both sides of the vehicle. At a predetermined differential pressure, the pressure differential detector produces a signal which is dependent upon the sign of the difference. This signal is used to avoid a further pressure rise at the brakes of the wheels having the higher pressure provided that the pressure at the other brakes is correspondingly low. The higher pressure can then be maintained constant or it can be reduced.Preferably, however, to differentiaipressure thresholds are provided, the pressure being maintained constant upon reaching the lower threshold and the pressure being reduced upon reaching the higher threshold. Thus, the pressure difference does not exceed a predetermined level.

Preferably, in order to avoid particularly high requirements with respect to sealing, the pressure differential detector will be connected to the two outlets of the valve arrangements incorporated in one brake circuit.

In order to utilise the braking action of the rear wheels to a maximum extent, the pressure reduction gradient of the solely regulated component brakes of the front wheels (associating the component brakes with the front wheels is the preferred solution) will preferably be made greater than the pressure reduction gradient of the commonly regulated brakes of the wheels at one side of the vehicle. Thus, pressure is preferably reduced at the solely regulated component brake when there is a tendency for the front wheel to lock. The pressure reduction at the other component brake and at the rear wheel lags and is stopped at a higher pressure value, so that a relatively high pressure is still effective at the rear wheel brake.

The invention will be further described, by way of example, with reference to the drawings, in which: Figure 1 is a schematic circuit diagram of one embodiment of dual brake system fitted with an anti-skid device, in which the brake circuits are split up in one way, and Figure 2 is a similar diagram af an embodiment in which the brake circuits are split up in another way.

Referring to Fig. 1 , the two front wheels of a vehicle are designated 1 and 2, and the rear wheels are designated 3 and 4. Split or component brakes 1 a, 1 b and 2a, 2b are associated with the front wheels. These component brakes are of identical construction, that is to say, each of them contributes to 50% of the braking action (without regulation). Brakes 3a and 4a are associated with the rear wheels. A dual-circuit brake system is assumed.

Consequently, the brake-pressure generator 5, illustrated as a tandem master cylinder, has two outlet lines 5a and Sb. The line 5a leads to two valve arrangements 6 and 7. It is assumed that each valve arrangement 6 and 7 is a three-port, three-position valve which is open when in its normal state (build-up of pressure), interrupts the pressure line between the pressure generator 5 and the connected brakes when in a second position (maintaining the pressure constant), and, when in a third position, connects the valve outlet (such as 6a or 6b) to a return-flow line (not illustrated) (pressure reduction).The line 5a is connected by way of the valve 6 and the valve outlet 6a to the component brake 1 b and to the brake 3a. Furt51ermore, the line 5a is connected to the component brake 2a by way of the valve 7 and the valve outlet 6b.

Correspondingly, the line 5b is connected on the one hand to the component brake 2b and to the brake 4a by way of a valve arrangement 8 and, on the other hand, to the component brake 1 a by way of a valve arrangement 9.

The outlets of the valves 6 and 7 are also connected to the two chambers of a differential pressure sensor 10 in the form of a piston 1 Oa which is biased at both sides to a central neutral position in a cylinder 1 orb. The piston 10 is deflected when there is a pressure difference.

After a predetermined deflection (pressure threshold) in one direction or the other, the piston puts a contact 11 or 1 2 into a first position with a predetermined output signal and, after an increase in the pressure difference, into a second position with another, for example, larger output signal.

Measured valve sensors 1 c, 2c, 3c, 4c for determining the wheel velocity are associated with the four wheels 1 to 4. The signals from the measured value sensors 1 C and 2c are fed to signal-processing circuits 13 and 14 respectively where retardation signals, acceleration signals and/or skid signals are produced. Upon the appearance of predetermined skid values, retardation values and/or accleration values, the valves 9 and 7 are triggered by way of respective logic circuits 17 and 1 8 and the pressures at the respective component brakes 1 a and 2a are varied.

The measured value sensors 1 c, 3c are connected to a signal-processing circuit 15 by means of a circuit component 21 and the sensors 2c, 4c are connected to a signal processing circuit 1 6 by means of a circuit component 22. A tendency to lock at a wheel 1 or 3 or at a wheel 3 or 4 initiates a pressure drop (select-low) by way of logic circuits 1 9 and 20 respectively by triggering the valves 6 and 8 respectively.

The signals from the switches 11 and 12 are fed to the logic circuits 1 7 and 1 9 or 1 8 and 20 respectively. These signals put the valves 6 and 9 or 7 and 8 into their second or third position according to, for example, the value of the signals.

When, for example, there is tendency for wheel 1 to lock, the measured value sensor 1 C causes a reduction in pressure at the brake 1 a by way of the valve 9, although at the same time it causes a reduction in pressure at the brakes 1 b and 3a by way of the circuit component 21 and the valve 6.

Preferably, the pressure reduction gradient at the brakes 1 b and 3a is smailer than that at the brake 1 a, so that the tendency to lock is chiefly eliminated by the reduction of pressure at the brake 1 a and a substantial pressure still exists at the brakes 1 b and 3a. If, as a result of asymmetrical conditions of the roadway, there is a substantial difference between the pressures at the brakes 1 b, 3a and 2a, the piston 1 Oa moves to the left and finally actuates the switch 11 whose signal then first puts the valves 7 and 8 into their pressure-stabilizing positions by way of the circuit components 1 8 and 20 and thus prevents a further build-up of pressure at the brakes 2a, 2b and 4a, and, upon a further pressure drop at the brakes 1 b and 3a, also causes a pressure drop at the brakes 2a and 2b and 4a by corresponding triggering of the valves 7 and 8, so that the pressure difference cannot increase. This avoids large yawing moments.

A tendency for only wheel 3 to lock would cause a pressure drop at the brakes 1 b and 3a, but not at the brake 1 a which would remain fully effective.

Since the two chambers of the cylinder 1 Ob are connected to brakes located in the same circuit, only a relatively simple seal is required between the piston and the cylinder.

Fig. 2 shows the same elements which are shown in Fig. 1 and which are provided with reference numerals which differ from the corresponding reference numerals of Fig. 1 by 30.

The only difference is that the valves 36 and 37 located in one brake circuit now influence the pressures at the brakes 31 b, 33a located at one side of the vehicle and the brakes 32b, 34b located at the other side of the vehicle respectively, while the valves 38 and 39 located in the other brake circuit each influence only the pressure at one respective component brake of the front axle.

Claims

1. An anti-skid system for a motor vehicle having two brake circuits and split brakes on the wheels of one axle, in that the first component brakes of the two wheels of the first vehicle axle and the brake of one wheel of the second vehicle axle are associated with one brake circuit, and the second component brakes of the two wheels of the first vehicle axle and the brake of the other wheel of the second axle are associated with the second brake circuit, the anti-skid system comprising a measured value sensor associated with each of the wheels, an evaluation circuit for processing the signals from the sensors, and valve arrangements for varying the brake pressure at the brakes of the individual wheels in dependence upon the behaviour of the wheel movement, a first respective valve arrangement being located in each of the first and second brake circuits for common regulation of the brake pressure at one wheel of the second axle and of that component brake of the first vehicle axle which is located in the same brake circuit and at the same side of the vehicle, a second respective valve arrangement being located in each of the two brake circuits for regulating the pressure at the other component brake associated with this brake circuit, the second respective valve arrangements which regulate the pressure only at one component brake of the first axle being controllable in dependence upon the movement behaviour of only the associated vehicle wheel, and the first respective valve arrangements associated with the two brakes at one side of the vehicle being each controllable in dependence upon the behaviour of that wheel of the wheels of the associated side of the vehicle which is the first to indicate a tendency to lock.

2. An anti-skid system for a motor vehicle having two brake circuits and split brakes on the wheels of one axle, in that the first component brakes of the two wheels of the first vehicle axle and the brakes of the two wheels of the second vehicle axle are associated with one brake circuit, and the second component brakes of the two wheels of the first vehicle axle are associated with the second brake circuit, the anti-skid system comprising a measured value sensor associated with each of the wheels, an evaluation circuit for processing the signals from the sensors, and valve arrangements for varying the brake pressure at the brakes of the individual wheels in dependence upon the behaviour of the wheel movement, first respective valve arrangements being located in the first brake circuit respectively for common regulation of the brake pressure at one wheel of the second axle and at one component brake of the first vehicle axle which is located at the same side of the vehicle as that one wheel and common regulation of the brake pressure at the other wheel of the second axle and at one component brake of the first axle at the same side of the vehicle as that other wheel, second respective valve arrangements being located for separate regulation of the pressure at the component brakes associated with this brake circuit, the second respective valve arrangements which regulate the pressure only at one component brake of the first axle being controllable in dependence upon the movement behaviour of only the associated vehicle wheel, and the first respective valve arrangements associated with the two brakes at one side of the vehicle being each controllable in dependence upon the behaviour of that wheel of the wheels of the associated side of the vehicle which is the first to indicate a tendency to lock.

3. An anti-skid system as claimed in claim 1 or 2, further comprising a pressure differential detector for measuring the difference between the brake pressures at least two brakes at opposite sides of the vehicle, switching means for producing upon occurrence of a predetermined pressure difference, a signal in dependence upon the sign of the difference, and further switching means for preventing, upon the appearance of such a signal, a pressure rise at the brake or brakes at that side of the vehicle which has or have the higher pressure.

4. An anti-skid system as claimed in claim 3, in which the pressure differential detector is connected to the outlets of the two valve arrangements which are located in the one brake circuit.

5. An anti-skid system as claimed in claim 3 or 4, in which the pressure differential detector and the associated switching means are adapted to produce differing signals at two different differential pressures, and the switching means to which these signals are fed are adapted to maintain the pressure constant upon the appearance of the signal at the smaller pressure difference and to reduce the pressure upon the appearance of the signal at the larger pressure difference.

6. An anti-skid system as claimed in any of claims 1 to 5, in which each second respective valve arrangement which regulates only the pressure at one component brake of the first axle has a larger pressure reduction gradient than the first respective valve arrangement which is associated with the other component brake.

7. An anti-skid system for a motor vehicle.

constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the drawings.