GB2135413A

GB2135413A - Improvements in brake force distribution

Info

Publication number: GB2135413A
Application number: GB08403514A
Authority: GB
Inventors: Hans-Christof Klein
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1983-02-25
Filing date: 1984-02-10
Publication date: 1984-08-30
Also published as: IT1173337B; FR2541642A1; SE8400965D0; GB8403514D0; DE3306611A1; GB2135413B; JPS59192659A; SE456984B; FR2541642B1; IT8419743A0; CA1248161A; SE8400965L; BR8400635A

Abstract

With a view to controlling the distribution of brake force onto the front and rear axles of an automotive vehicle in response to the momentarily prevailing static and dynamic axle load distribution, the wheel rotational behaviour (???) on the front axle (VA) and on the rear axle (HA) and the translational deceleration (-b) of the vehicle or variables proportional to said measured values are determined by way of sensors (8, 9, 10). After the said signals having been electronically processed and combined at (7), the share of the brake pressure (PHA) fed to the rear axle in response to the front wheel brake pressure (PVA) is so controlled by means of solenoid valves (4, 5) that the brake slip at the rear axle (HA) corresponds to the brake slip at the front axle (VA) or is slightly less than the front wheel brake pressure. In the event that nonetheless a locking tendency of the rear wheels occurs, e.g. as a result of rapidly changing road conditions, the brake pressure at the rear axle is reduced with the aid of another quick-acting electromagnetically operated valve (6) and is maintained constant at the low value until the front wheel pressure has decreased. If either circuit (2, 3) fails, sensor 18 actuates control 7 to permanently open valves 4, 5 and close valve 6. The circuits need not be diagonally split (Fig. 3 not shown). <IMAGE>

Description

SPECIFICATION Improvements in brake force distribution The present invention is concerned with a method and a device for controlling brake force distribution to the front axle and to the rear axle of an automotive vehicle in response to static and dynamic axle load distribution and/or other measured variables derived from the braking behaviour.

In some such braking arrangements, electric signals corresponding to wheel behaviour at the front axle and at the rear axle and to translational deceleration of the vehicle are generated, electronically combined and processed. Brake slip on the front and rear wheels and measured values proportional to the brake slip, respectively, are determined from the signals generated therefrom, and the brake slip of the rear wheels is limited with the aid of a control to the value of brake slip on the front wheels or to a slightly lower value.

Sensors are provided for measuring the rotational behaviour of the wheels and the translational deceleration, the output signals of which sensors are combined with firmly wired or programme-controlled electronic circuits, e.g. a microprocessor, and processed. The brake pressure is controlled with the aid of modulators, e.g. electromagnetically operated control valves.

A brake force distributor is already known in the art in which the static axle load distribution with the vehicle at standstill is measured by sensors and the measured data is fed into a microcomputer which, under consideration of the measured values and of the measured pressure, controls the brake force distribution pursuant to a memorized mathematical expression in the front and rear axle circuit (European patent application EP--A1 062246). It is a disadvantage of such a brake force distributor that the value of adherence between road and wheel at the rear and front axis actually prevailing at the time of the braking operation and depending on numerous parameters, cannot exert an influence on the brake force distribution.For this reason, it is imperative for the brake, in order to safely avoid dangerous overbraking of the rear axle, to be so designed that in the majority of cases, the rear axle will contribute little to the braking operation.

Moreover, it has proved to be disadvantageous that the actual values in practice considerably differ from the numerically calculated predicted values. The brake characteristics assumed to be constant in the layout of the braking force distribution and the memorized mathematical expression, in practice, are subject to substantial changes, e.g. as a result of manufacturing tolerances in the coefficient of friction, aging, contamination, changes in the spring constant in operation, defective adjustment, heavy temperature changes etc. All this might result in the actual characteristic of the brake force distribution considerably differing from the predicted values.

Brake force distributors commonly used nowadays are limited to an invariably adjusted pressure-responsive control. Load-responsive or deceleration-responsive brake force regulators are similarly known in a great number of variants. For the before mentioned reasons, even with careful assembly and adjustment, a satisfactory adaptation can at best only be attained, with these prior art devices, in one of the two extreme "unloaded/loaded" conditions so that, in a multiplicity of operating conditions, the exploitation of the adherence value at the front and rear axles, that is theoretically possible, will not be attained.

The present invention seeks to avoid or at least substantially reduce the afore-mentioned disadvantages of such prior art systems and to improve the brake force distribution in automotive vehicles such that both in the extreme "unloaded/ioaded" conditions and in every braking operation of the vehicle, the brake force distribution will be adapted in close approximation to the actual static and dynamic axle load distribution thereby attaining an optimum brake function, i.e. road stability, short stopping distance and a uniform load on the two axles. Moreover, high importance has been given to meeting a requirement of simplicity in the manufacture and assembly of the brake system.

According to one aspect of the invention there is provided a method of controlling the distribution of brake force onto the front axle and the rear axle of an automotive vehicle in response to the static and dynamic axle load distribution and/or to other measured variables derived from the braking behaviour, wherein electric signals are generated that correspond to the wheel rotation behaviour at the front axle and at the rear axle and to the translational deceleration of the vehicle, the said signals are electronically combined and processed to thereby derive control signals proportional to the brake slip at the front and rear wheels, with the brake slip at the rear wheels with the aid of a control being limited to the value of the brake slip at the front wheels or to a value slightly lower, characterised in that upon occurrence of a signal indicative of a tendency of the rear wheels to lock, which signal is generated by comparing the rear wheel deceleration with the vehicle deceleration or with a reference signal representative of the vehicle deceleration, the braking pressure at the rear axle is reduced.

According to another aspect of the invention there is provided a brake force distributor for carrying out the method comprising sensors for generating electric signals proportional to the wheel rotational behaviour at the front axle and at the rear axle of the vehicle, comprising electronic circuit for combining, processing and evaluating the sensor signals and for generating control signals, and comprising at least one modulator for controlling the brake pressure at the rear axle in response to the brake slip at the front and rear axles, characterised in that one or several modulators are provided to decrease the pressure at the rear axis upon occurrence of the signals indicative of a tendency to lock.

The method and distributor as previously defined may be incorporated into the invention as defined in our German Patent Application No.

P3301 9487. By measuring wheel and vehicle velocities and time-responsive changes in the said measured variables, respectively, by processing the said measured values to form a control signal in an electronic circuit, e.g. in a microprocessor, and by using simple control valves as pressure modulators, a brake force distributor can be realised which, under consideration of the conditions actually prevailing at the time of the brake operation, inclusive of the road conditions, condition of the brake system, static and dynamic axle load distribution etc., in almost ideal manner distributes the brake force onto the front and rear wheels thereby, above all, attaining a short stopping distance, a low locking risk and, hence, a high road stability and a uniform load of the braking system.Owing to the fact that only in exceptional cases, the pressure on the rear axle is required to be decreased, also the relatively rare driving situations caused e.g. by rapidly changing road conditions, will be taken into account. For, in such situations, after attaining an initially proper wheel cylinder pressure and a constantly maintained braking pressure, a wheel locking on the rear axle could subsequently occur. As opposed to brake slip control systems, in the brake force distributor of the present invention, no renewed brake pressure build-up will occur within a braking operation; and in contrast to brake slip control systems, no external energy supply, for rebuilding the brake pressure, is normally required. In the light of the required manufacturing complexity for the brake system and the operational safety thereof, this will be of special importance.

In order that the invention and its various other preferred features may be understood more easily, some embodiments thereof will now be described, by way of example only, with reference to the drawings, in which: Figure 1 is a schematically simplified block diagram of an embodiment of brake force distributor in accordance with the invention for a double-circuit brake system having split force diagonal braking, Figure 2 is graphical representation of the time-responsive curve of pressure when using a brake force distributor in accordance with the invention, and Figure 3 is a schematic block diagram similar to Figure 1, showing an embodiment of the invention having a double-circuit brake system with one brake circuit for the front axle and another for the rear axle.

In the double-circuit brake system of Figure 1, the brake circuits are diagonally split. In a standard construction-type tandem master cylinder 1 as symbolically shown, on which-as symbolised by the arrow-brake force F is exerted via a pedal, the lefthand front wheel VR, and the righthand rear wheel HRr are connected to a brake circuit 2. The second brake circuit 3 will act upon the two other wheels VRr and HR,.

In the illustrated form of embodiment of the invention, there are pressure modulators formed by quick-acting, two-way, two-position valves 4, 5, 6. While the two front wheels are directly connected to the associated braking circuit 2 and 3, respectively, of the tandem master cylinder 1, a pressure build-up on the rear wheels will be possible only after the two control valves, 4, 5 are energized. Activation of these valves is effected via an electronic control 7, to which measured variables generated with the aid of sensors 8, 9 and 10 are fed via signal lines 8', 9', 10' in the form of electric signals and which, by a logic combination, will compute the required control signal and will control the brake pressure modulators. Control 7 may contain e.g. a microprocessor for processing the sensor signals and for generating the control signals.

In the form of embodiment as described here, by sensor 8, an average value csVR of the wheel speed at the front axles determined; by sensor 10, an average value ,oHR of the wheel speeds at the rear axle is determined; and by sensor 9, the translatory deceleration-b of the vehicle during the braking operation, or measured values proportional to the wheel speeds and the deceleration, respectively, are determined.If the vehicle is already equipped with an electronic sensor for the speedometer the same may, at the same time, be used for generating the measured variable VR The pressure curve PHA on the rear axle generated with the aid of the modulators and control valves 4, 5, respectively, and the brake pressure curve PVA on the front axle on which PHA is dependent, is illustrated by Figure 2. In that example of embodiment, control 7 will generate-laterally delayed over the rise in the front axle pressure PVAactivation pulses for control valves 4, 5, with the pressure rise PHA required for an ideal pressure distribution, being adjusted at the rear wheels by pulsating or clock controlled alternation of valves 4, 5 between closing position (shown) into a through-flow position.

Moreover, another two-way two-position valve 6 is provided for decreasing the rear wheel pressure. By hydraulically connecting the two rear wheel circuits via a line having two series connected and oppositely directed non-return valves 11, 12, a single two-way, two-position valve 6 will be sufficient for the pressure decrease in the two rear wheel circuits. The illustration of Figure 1 shows that via an electrical connection of the electronic control 7 leading to the operating magnet of valve 6, the normally closed two-way, two-position valve 6 for the pressure decrease can be switched into the through-flow position whereupon both rear wheel circuits are connected to a pressure compensating unit 13, which forms part of the brake system, via non-return valves 11,12.

As shown in Figure 2, as soon as a locking tendency is indicated, the pressure is reduced in steps to a lower value at which the brake slip at the rear axle corresponds to the brake slip at the front axle or lags behind that slip. The pressure decrease starts at a time t1 after control 7 has detected a locking tendency at the rear wheels at the time to by comparing the wheel deceleration at the rear axle with the vehicle deceleration.

Non-return valves 14, 15 provided in parallel with the pressure build-up valves 4, 5 will accelerate the decrease in the brake pressure when releasing the brake.

In a split double-circuit brake in which one circuit acts upon the front axle, while the other circuit acts upon the rear axle, a brake force distributor in accordance with the invention may employ less components. As shown in Figure 3, individual electromagnetically operated two-way, two-position valves 1 6 and 17, are sufficient for enabling the build-up of braking pressure at the rear axle and for pressure reduction released as soon as control 7' has concluded a locking tendency of the rear wheels from the sensor signals fed to it via signal lines 8', 9', 10'. The non-return valves 11, 12 in the embodiment of Figure 1 which are disposed in the feedline to the pressure reducing valve 6, are eliminated in the embodiment of Figure 3.

Figure 1 also shows a difference pressure switch 1 8 which detects failure of a brake circuit and a pressure difference caused thereby between the two brake circuits 2, 3, to control 7 via line 19. This will cause a permanent energization of valves 4, 5 and a permanent locking of valve 6 in order that upon failure of a brake circuit, at least in the second brake circuit, the full brake pressure can be built up on the front and rear axles. The track or directional stability of the vehicle, in that case, will also be maintained with a locking of the wheels of the intact diagonal circuit by the non-braked wheels of the failing braking circuit.

Claims

1. A method of controlling the distribution of brake force onto the front axle and the rear axle of an automotive vehicle in response to the static and dynamic axle load distribution and/or to other measured variables derived from the braking behaviour, wherein electric signals are generated that correspond to the wheel rotation behaviour at the front axle and at the rear axle and to the translational deceleration of the vehicle, the said signals are electronically combined and processed to thereby derive control signals proportional to the brake slip at the front and rear wheels, with the brake slip at the rear wheels with the aid of a control being limited to the value of the brake slip at the front wheels or to a value slightly lower, characterised in that upon occurrence of a signal indicative of a tendency of the rear wheels (HR,, HRr) to lock, which signal is generated by comparing the rear wheel deceleration with the vehicle decleration or with a reference signal representative of the vehicle deceleration, the braking pressure at the rear axle is reduced.

2. A method as claimed in claim 1, characterised in that upon occurrence of the signal indicative of the tendency to lock, the braking pressure (PHA) at the rear axle (HA) is reduced to a braking pressure dependent on the wheel and vehicle deceleration values and the reduced pressure is then maintained constant until the braking pressure at the front axle (VA) has decreased.

3. A method as claimed in claims 1 or 2, characterised in that the braking pressure rise at the rear axle (HA) follows the braking pressure rise at the front axle after a delay, and that both the braking pressure rise at the rear axle and the decrease upon occurrence of a tendency to lock are effected in steps.

4. A brake force distributor for automotive vehicles, for implementing the method as claimed in any one of claims 1 to 3, comprising sensors for generating electric signals proportional to the wheel rotational behaviour at the front axle and at the rear axle of the vehicle, comprising electronic circuit for combining, processing and evaluating the sensor signals and for generating control signals, and comprising at least one modulator for controlling the brake pressure at the rear axle in response to ths brake slip at the front and rear axles, characterised in that one or several modulators (6, 16) are provided to decrease the pressure at the rear axis (HA) upon occurrence of the signals indicative of a tendency to lock.

5. A brake force distributor according to claim 4, characterised in that the modulators are quickacting, electromagnetically operated two-way, two-position valves (6, 1 6) that, in their energized condition, they connect a rear wheel (HR1, HRr) and one rear wheel braking cylinder, to a pressure compensating unit (13) and that, in a deenergized condition they block the passage.

6. A brake force distributor as claimed in claim 4, for an automotive vehicle having a hydraulic brake system and a diagonal brake circuit split-up characterised in that the hydraulic brake circuits (2, 3) of the two rear wheels (HR,, HR,) are connected to a common electromagnetically operated two-way, two-position valve (6) serving as a modulator for pressure decrease, which is blocked when de-energized and which establishes a connection with a pressure compensating unit (13) when energized, with non-return valves (11, 12) being provided one in each path from the hydraulic braking circuits (2, 3), to the two-way, two-position valve (6) for decoupling the two braking circuits.

7. A method of controlling the distribution of brake force onto the front and rear axles of an automotive vehicle substantially as described herein with reference to the drawings.

8. A brake force distributor substantially as described herein with reference to the drawings.