FR2539687A1 - METHOD AND DEVICE FOR CONTROLLING THE BRAKE FORCE DISTRIBUTION WITH THE FRONT AXLE AND THE REAR AXLE OF A VEHICLE - Google Patents

Abstract

THE INVENTION RELATES TO A BRAKING FORCE DISTRIBUTION METHOD IN WHICH THE SENSORS PROVIDE O, O DATA ON THE SPEED OF THE VEHICLE AND OF THE WHEELS, WHICH ALLOWS TO MODULATE THE BRAKING PRESSURE PROVIDED TO THE REAR WHEELS HR ACCORDING TO THAT OF THE FRONT WHEELS VR. THE DATA OBTAINED ARE USED TO DETERMINE THE BRAKE SLIP ON THE FRONT AND REAR WHEELS AND, BY MODULATOR 6, THE FRICTION COEFFICIENT AT THE REAR WHEELS IS LIMITED TO APPROXIMATELY 80 TO 100, PREFERABLY 85 TO 97, OF THE FRICTION COEFFICIENT AT THE FRONT WHEELS .

Description

The present invention relates to a method of controlling the distribution

  braking force to the front axle and the rear axle of a motor vehicle according to the static and dynamic load distribution on the axles and to other measured variables derived from the braking behavior, in

  measured quantities used for the order are obtained.

  naked by means of measuring value sensors, also known as "sensors", and are combined and processed electronically, and in which the brake pressure on the rear wheels is controlled 1 I) in relation to the braking pressure on the front wheels In

  in addition, the invention also relates to a brake force distributor

  swimming, in particular for a motor vehicle, to implement

  this method, this dispenser comprising: sensors for determining

  to reduce measured quantities that can be used to control the distribution

  braking force delivery; electronic circuits for combi-

  to use, process and exploit sensor signals and to produce

  control signals for one or more modulators of the pres-

braking pressure.

  We already know a brake force distributor of

  this kind, in which the static load distribution on the

  of the stationary vehicle is measured by sensors and stored in a microcomputer which, taking into account these measured values, according to a stored mathematical relationship, and the pressure measured Jans the circuits of the front axle and the axle -back,

  controls the distribution of braking force (European Patent

  EP-A1 062246) A disadvantage of this device is that the effective value of the adhesion between the road and the wheels at the rear axle and the front axle can not exert any influence on the distribution of braking force, so that, in order to avoid dangerous braking on the rear axle, there is a contribution from this

  last braking is usually weak.

  The braking force distributors usually used today are limited to regulation, established once and for all, made according to the pressure. Many variants of brake force distributors operating according to the load or the pressure are also known. deceleration A satisfactory adaptation is obtained, even at the cost of a great complication of assembly and adjustment, that at most in one of the two limit cases "vehicle not loaded" / "vehicle loaded", so that under many operating conditions, the rate of adhesion utilization that it would theoretically be possible to achieve at

  the front axle and rear axle is actually not reached.

  The object of the invention is therefore to improve the braking force distribution in motor vehicles so that, in both the "empty vehicle" and "loaded vehicle" limits, and during each braking, the braking force distribution be adapted, with a good approximation, to the effective distribution of dynamic and static loads The invention aims to

  also obtain this result by means of a distribution

  Striker braking force relatively uncomplicated.

  According to the invention, this object is achieved, with surprising simplicity, by measuring, directly or indirectly, the rotational behavior of the wheels at the front axle and at the rear axle, as well as the deceleration longitudinal direction of the vehicle, and one draws braking slip from the front and rear wheels, or from measured values proportional to this braking slip,

  and by the fact that with the aid of the control and the modulators of pres-

  the braking slip of the rear wheels to approximately 70 to 100% of the braking slip of the front wheels, by adjusting, by modulating the brake pressure at the rear wheels, the coefficient of friction at the rear wheels at about 80 to 100%, preferably 85 to 97%, of the coefficient of friction at the front wheels A device for implementing this method according to the invention is such that the sensors are designed and 3 () arranged to measure the behavior rotation of the wheels at the front axle and the rear axle, and such that, with the aid of the modulator, the brake pressure at the rear wheels can be controlled in a controlled manner.

  that, as long as the front wheels do not block, the coefficient of friction

  rear wheels is 80% to 100%, and preferably 85%

  97% of the front wheel friction coefficient

  its embodiments of the method and the device according to the invention.

  are also indicated below.

  The invention is therefore based on the recognition that the braking slip at the front axle and the rear axle of a vehicle is particularly suitable for controlling the braking force distribution, that is, for designing a braking force. effective and relatively simple braking force distributor The required measuring variables can be obtained with conventional sensors or sensors, from which signals deceleration and a reference speed can be derived, and possibly with an additional sensor. for

  measure the speed of translation of the vehicle Electronic means

  Logically combining and logically combining the signals of these sensors, generate control signals for

  solenoid valves which directly control the brake pressure

  On the one hand, the front and rear wheels contribute approximately equally to the braking of the vehicle and, on the other hand, the certainty that the rear wheels will not be able to lock only after the front wheels, which is of great importance for the directional stability of the vehicle. The different objects and characteristics of the invention

  will now be detailed in the description that follows,

  BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified block diagram of one embodiment of the braking force distributor according to the invention;

  FIG. 2 a, a diagram showing, in its right part,

  te, the relation between the coefficient of friction (in ordinates) and

  braking slip (S, in abscissae), and in its left part

  ch, the relation between coefficient of friction and braking (z, in abscissae), this diagram illustrating a distribution of braking force of a known type; FIG. 2b, a diagram of the same type as that of the

  FIG. 2a, but applied to a control according to the method of the invention.

  tion; FIG. 3, a diagram showing the evolution, over time, of the braking pressure on a front wheel and on a rear wheel, in a case of use of an embodiment according to FIG. 1; FIG. 4, a diagram illustrating, in the same mode as FIG. 3, the evolution of the pressure in another embodiment of the invention; FIG. 5, a diagram relating to the same magnitudes

  than that shown in Figure 4, but illustrating another way of

  lisation, with pressure limitation at the beginning of blocking; and FIG. 6, a simplified block diagram of an embodiment of the braking force distributor according to the invention,

  with distribution of braking circuits "diagonally".

  In the type of embodiment of the invention shown above

  1, the braking force distributor according to the invention essentially consists of a regulator 1, a plurality of sensors 2, 3 and 4, and a brake pressure modulator 5, which in FIG. the example shown, consists of a quick response valve, 6, electromagnetically actuatable ("solenoid valve"), of the two-position and two-way type, and a non-return valve 7 for the

  fast pressure drop when loosening the brakes.

  The rotational behavior of the wheels of the front axle (O Ri) and the wheels of the rear axle (a Ri) is determined by the respective sensors 2 and 3 For this, it is possible to use, in a known manner, for each sensor, to a rotation speed sensor

  inductive, with only one sensor per axle sufficient in most

  of the cases To measure the deceleration of the vehicle, the sensor

  4 can be realized, for example, in the form of an electronic sensor.

  However, a suitable reference speed can also be formed by means of wheel speed sensors and, by an appropriate combination of the signals of these sensors, or by the averaging of the measurements of the speed sensors. many

speed sensors.

  The electronic circuits for processing and combining the sensor signals, and for generating the control signals for the opening / closing valve 6 are in the circuit block 1 to form the control clock pulses of the control valve. opening / closing 6, one can use a

microcomputer in block 1.

  As long as it is current-free, the solenoid valve 6 according to FIG. 1 connects the hydraulic circuit of the front wheels,

  VR, the rear wheel hydraulic system, HR, the braking system,

  To reduce the amount of braking force attributed to the rear axle, the valve 6 is pulsatingly closed, which will be

  explained further with reference to Figures 3 and 4.

  The values of the braking characteristics, taken as constant during the study of the distribution of the braking forces, in fact undergo, in practice, significant modifications, due for example to the tolerances of realization of the coefficient of friction, to aging, to fouling, temperature variations, etc. It follows that the characteristic of distribution of forces of

  braking may differ significantly from that originally calculated.

  With the method according to the invention, these variations are nevertheless taken into account because the slip to tires, proportional to the effective adhesion, or measurement values derived from the sliding of the tires, are evaluated to control the distribution of the braking forces. Figures 2a and 2b illustrate

  this mode of action and progress achieved.

  The diagram of Figure 2a applies to conventional braking force distributors, with the brake force distribution between the front axle and the rear axle determined once and for all. In the case of a braking force of, for example, z = as shown, the front axle VR has a friction coefficient of f VR = 0.46, while for the rear axle HR the coefficient of friction is only f = 0.19; coefficient of friction expressing a ratio between the tangential and the actual force exerted on a tire at the point of contact with the rolling surface. The corresponding operating points on the friction / slip curve on the right side of the tire. figure 2 a, s thus separated by a significant difference The contribution of the rear axle

2539687.

  braking is therefore relatively low.

  In the case of a distribution of the braking forces according to the teachings of the invention, that is to say when using a brake force distributor according to the invention, such as that described with reference to FIG. 1, the two axles contribute

  almost equally under braking, since the proportion of brake pressure

  transmitted to the rear wheels is regulated so that the coeffi-

  friction at the rear axle is below that

  i the front axle only a predetermined value, a few

  percent, preferably from 3 to 15%. For a master cylinder pressure

  dre given, the braking distance is therefore significantly shorter, since it makes more use of the rear wheels, especially

during small braking.

  As already indicated by describing the embodiment according to FIG. 1, the variation of the proportion of braking pressure

  the rear axle can be obtained in particular

  simple, but nevertheless very accurate and finely dosable, by a rhythmic control of the opening / closing valve 6 As a result, as shown in FIGS. 3 to 5, a "pulsed" rise of the pressure PHR to the wheels of the rear axle By variation of the

  pulse ratio of the control signals fed to the valve of

  opening / closing 6, from the circuit block 1, thus by varying the maneuver from the "open" position to the "closed" position, the desired brake pressure distribution is obtained on the axle

front and rear axle.

  The evolution, over time, of the braking pressure p VR at the front axle, compared with the braking pressure PHR at the rear axle, as indicated in FIG. 3, preferably applies to the vehicles whose front axle has disc brakes and the rear axle of drum brakes With such braking systems, in order to shorten the application process

  drum brakes at the beginning of braking, it is recommended to admit

  be for a short time t 1 a non-slowed rise in the pressure at the rear axle, from the origin, and to forecast, only

  then, a phase of pressure arrest t 2 before the pulsating progression

2539687.

  pressure area at the rear axle.

  In the case of vehicles having similar brakes front and rear, a control of the increase in pressure according to Figure 4 is against preferable pressure to the front wheels, PVRP believes, again, linearly, proportionally to the force at the pedal The pressure P at the rear wheels, again established in a pulsating manner, "follows" against the pressure at the

  front wheels with an offset in time, and only reaches the

  both t 1 H its constant value which is determined by electronics,

according to the chosen criteria.

  In the case of vehicles having similar brakes front and rear, a control of the increase in pressure according to Figure 4 is against the preferable pressure to the front wheels, PVR 'increases, again, linearly , in proportion to the force at the pedal The pressure P at the rear wheels, again established in a pulsating manner, "follows" against the pressure at the front wheels with an offset in time, and only reaches the moment t H its constant value which is determined by electronics, according to

the chosen criteria.

  In addition, in another embodiment of the invention, illustrated in FIG. 5, the electronics are designed in such a way that, in the event of a detection of a risk of locking the front wheels at the instant t A instant from the start of blocking any further increment

  from the PHR pressure to the rear axle, beyond PHRO 'is avoided.

  A tendency to blockage, or a risk of blockage, can be deceived.

  for example electronically, from the variation of

  measured with sensors 2 and 3, ie from the slowed down

  If these values of the measurements exceed a threshold

  higher, this can be interpreted as a start of blocking.

  If the increase in pressure at the rear wheels is, as shown in FIGS. 4 and 5, kept back from the pressure at the front wheels, the limitation of the climb

  pressure at the rear axle allows, if there is detection of a

  preventing the rear wheels from locking up in many cases This is due to the fact that the logic deductively decides to prohibit further pressure build-up

  At the rear axle As, as already described, the rise in pressure

  rear axle "follows", with an offset in time, the pressure at the front axle, it follows that the rear wheel is still, at this time, away from the maximum of the curve adhesion-

  braking slip and so will surely not hang.

  This variant of the brake slip regulator according to the invention

  vention is very important from the point of view of

vehicle.

  In the case of the vehicle symbolically represented in FIG. 6, equipped with the braking force regulator according to the invention, two hydraulic braking circuits are provided which are assigned

  the wheels in a "diagonal" distribution. The hydraulic connection

  that 10 on a tandem master cylinder 9 actuated by the brake pedal 15 S leads directly to the brake cylinder of the right front wheel, V ht and leads, via a ball valve, 12, to the rear wheel gauging H link In the same way, the second braking circuit goes, through the connection 11, directly to the left front wheel Vlinks and, via a separating solenoid valve 13, to the right rear wheel Hht A check valve 14, for the rapid fall of the pressure when loosening the brakes, is mounted

  in parallel with the solenoid valve 13.

  The operating mode of the arrangement according to FIG. 6 corresponds to that of the arrangement according to FIG.

  central electronic combination device, 15, comprising here a micro-

  processor, receives signals corresponding to the behavior in

  rear wheels, these signals being picked up by the sensors 16, 17, and receives from a sensor 18 a signal corresponding to the average speed of the front wheels and finally receives a deceleration signal produced by means of a sensor 19 The sensor 18 is disposed, in this case, on the differential mechanism 20 by which the front wheels

are trained.

  When the brakes are actuated by the pedal 8, the

  pressure on both front wheels increases immediately as soon as the electro-

  valve 13 was ordered, in other words excited and switched, the

2539687.

  pressure rise in the right rear wheel Hrechts can

  At the same time, by the hydraulic connection going from the

  The solenoid valve 13 at the ball valve 12, the control piston of the latter is moved, which has the effect that the rear left wheel Hlinks is connected to the second brake circuit. Instead of the ball valve 12, it is possible to use a second solenoid valve which is then also controlled by the circuit block 15 and which is conveniently operated in parallel with

the solenoid valve 13.

  In addition, in many cases, it may be advantageous for the solenoid valve 13, like the ball valve 12, to be formed as an integral part of the tandem master cylinder 9.

-2539687

Claims (8)

REVENDICA Tl ONS   1 Control method of the force distribution of   front axle and rear axle braking of a self-   moving according to static load distribution and dynami-   than on axles and other measured quantities   braking behavior, a process in which large   The measured quantities used for the control are obtained by means of sensors, combined and processed electronically, and in which   the braking pressure on the rear wheels is controlled in relation to   with the brake pressure on the front wheels, using modulators, characterized in that the rotational behavior of the wheels at the front axle and at the rear axle is measured directly or indirectly, and longitudinal deceleration of the vehicle, and the braking slip (A) is deduced from the front and rear wheels, or measured values proportional to this braking slip, and that by means of the control and of   appropriate brake pressure modulators, the   braking of the rear wheels to approximately 70% to 100% of   braking of the front wheels by adjusting, by modulating the brake pressure at the rear wheels, the coefficient   (VR) friction at the rear wheels to approximately 80 to 100%, preferably   85 to 97%, of the coefficient of friction (f HR) to the front wheels 2 The method according to claim 1, characterized in that after the birth of a tendency to block the front wheels one   maintains constant brake pressure at the rear wheels.   3 Process according to claim 1 or 2, characterized in that, during the growth of the brake pressure, the brake pressure (P HR) at the rear wheels follows, with a delay of some   milliseconds, brake pressure (PVR) to the front wheels.   4 Brake force distributor, in particular for motor vehicles, for implementing the method according to one   any of claims 1 to 3, comprising: sensors   to determine measured quantities that can be used to control the braking force distribution; electronic circuits for   to combine, process and exploit the sensor signals and to 2539687.   to draw control signals; and one or more modulators for controlling the brake pressure at the rear axle as a function of the braking pressure at the front axle and as a function of the signals of the sensors, characterized in that the sensors (2, 3, 16, 17 , 9 18) are designed and arranged to measure the rotational behavior (WVR 'MHR) of the wheels at the front axle (VR) and at the rear axle (HR), and in that, using the modulator (5), the brake pressure (PHR) at the rear wheels can be controlled so that, as long as the front wheels do not lock, the coefficient of friction (f HR) at the rear wheels is 80 to 100%, and preferably from 85 to 97%,   coefficient of friction (f VR) to the front wheels.   Dispenser according to claim 4, characterized in that   in addition, a sensor (4) is provided for measuring the decelerating   longitudinal direction (-b) of the vehicle, a sensor whose output signals are combinable, in the electronic circuit (1), in the   signals coming from the front axle (VR) and the rear axle (HR).   Distributor according to Claim 4 or 5, characterized in that the modulator (5) consists, for the most part, of a   two-position, two-way solenoid valve (6, 13) with   pide, which, in the absence of current, connects the hydraulic circuit relating to the front axle (VR) to that relating to the rear axle   (HR), and interrupts this communication after excitation.   Distributor according to Claim 4 or 5, characterized in   the modulator (5) comprises a solenoid valve (6) with two posi-   fast response, which, when energized, establishes a hydraulic communication between the forward circuit and the backward circuit (HR) and which, when   is not excited, interrupts this communication.   Dispenser according to any one of the claims   4 to 7, characterized in that the electronic circuit (1, 15) for processing the sensor signals and for producing the control signals, i.e. the control signals driving the   modulator (5) contains, as an essential component, a microproces- sor.   Distributor according to any one of claims 4   * 35 to 8, characterized in that it is inserted in a hydraulic braking system with two circuits with "diagonal" distribution, the distribution of the brake pressure in a first circuit (Vli k H ht) being modifiable at using a solenoid valve (13) inks' Hrechts) with two positions and two channels controlled according to the slip of   braking, and the distribution of the brake pressure in the   x brake system (Vrechts, Hlinks) being modifiable by means of a hydraulically controlled ball valve separator depending on the brake pressure in the wheel circuit   rear of the first brake system (Vlinks, Hechts). - -