DE4208581A1 - Brake press control for road vehicle front and rear braking circuits - has antilocking and drive slip regulation with defined brake force ratio between front and rear braking circuits - Google Patents

Abstract

The brake press control provides antilocking regulation via magnetic valve (76, 77) associated with the wheel brakes (14, 16) and drive-slip regulation using a press setting device, the brake press regulation valves and an electrically operated function control valve (61). A sensor (49, 51) provides an output signal representing the required braking force, a second sensor (53) indicating the actual braking press in the rear braking circuit, with an electronic control (44) operating the function control valve and providing the control signals for the press setting device, with a required correlation between the brake press for the front wheel brakes and that for the rear wheel brakes. ADVANTAGE - Combined antilocking and drive slip regulation with higher braking force for rear wheels.

Description

The invention relates to a brake pressure control device for variable adjustment of the front axle / rear axle braking force distribution (EBKV) on a road vehicle with rear axle connection driven and front axle / rear axle brake circuit division of its hydraulic dual-circuit braking system.

The purpose of such a brake pressure control device is to entire braking area, but especially in the partial braking area without sacrificing dynamic stability of the vehicle rear to be able to utilize axle braking force components, which are significantly higher are than those rear axle braking force shares that are at a brake system with stability designed, fixed abge agree braking power distribution, the goal of Brake force distribution control in general is as good as possible Approaching the ideal brake force distribution is the same Traction utilization on the front and rear wheels of the Corresponds to the vehicle.

Such brake pressure control devices are expedient each combined with an anti-lock braking system, so if the vehicle brakes on a lane area  with a lower coefficient of adhesion, one as a result Dynamic instability of the vehicle due to the anti blocking control is "caught" again.

In a known brake pressure control device of this type (DE 37 23 917 C2) for a vehicle whose braking device is two in Twin design includes master cylinders that are about a momentarily balanced rocker can be actuated, the one Master cylinder the front axle brake circuit and the other master cylinders are assigned to the rear axle brake circuit, they are Master cylinder equipped with position sensors, by means of which the piston positions, which is indirectly a measure of the brake pressure are detected. By evaluating the position transmitter off An electronic processing unit determines the output signals the current front axle / rear axle brake force distribution and compares this with an ideal value based on vehicle data. This comparison shows that the rear axle braking force share is too low, the front brakes are against them Master cylinder shut off until - with further increase Operating force - the rear axle braking force component as far as indicated grow is that almost the ideal braking force distribution is achieved is. An increase in the rear axle braking force at a given one Pedal operating force is in the known brake pressure control ung also possible in that a drive cylinder on acts on the rocker arm via that of the rear axle brake circle associated master cylinder of the braking device in the sense of a Brake pressure build-up is slidable, valve-controlled to a Auxiliary pressure source is connected, which is also called auxiliary pressure Source is used for a traction control, which works on the principle of a driving tendency to spin to retard the tool wheel by activating its wheel brake. The anti-lock braking system is realized in that in the frame  the brake device is provided with a further control cylinder, through its valve-controlled connection to the auxiliary pressure source the rocker against the operating force exerted by the driver can be pushed back, causing the pistons of the two Master cylinder in the sense of expanding its outlet pressure can move rooms and a pressure drop in each connected wheel brakes can be achieved, each with a brake pressure control valve on the assigned to the respective brake circuit Master cylinder outlet pressure chamber connectable or against this are lockable.

A disadvantage of the known brake pressure control device on the one hand, the complicated structure of the implementation required master cylinder in terms of achieving the brake and traction control functions also the Disadvantage has that opposing brake pressure changes, i. H. a Lowering the brake pressure on one wheel brake and increasing it the brake pressure on the other wheel brake of the brake circuit, are not possible, but at best keeping the Brake pressure on one wheel brake while on the other the pressure is changed.

Has essentially the same functional disadvantages is also that by DE 39 41 409 C1 for the aforementioned purpose known brake pressure control device, in the case of a braking device a simple tandem master cylinder can be used for this but a separate pressure modulator for brake pressure control must be provided through its valve-controlled connection to an auxiliary pressure source, the pressurization of the Rear axle brake circuit is done. For the rest, this is due to the pressure technical effort due to modulator.  

In a further known brake pressure control device (DE 37 06 663 C2) of the type mentioned is provided that the braking system fixed at two different values one coordinated front axle / rear axle brake circuit division is adjustable, the one value in the entire braking range corresponds to stable braking force distribution and the other value a relatively higher value of the rear axle braking force share. With the onset of braking, the braking system is in the that functional state controlled, the braking force distribution with the higher rear axle braking force proportion. Under Exploitation of the anti-return principle locking system, the brake slip on the rear axle is in a relation to the brake slip held on the front axle, which gives a slightly higher brake slip on the rear wheels than on the front wheels. As soon as on one of the front wheels Antilock braking system responds both to the front axle as on the rear axle again after the same Slip thresholds are regulated so that the vehicle is dynamically stable remains. With this type of brake pressure control the The sensitivity of the anti-lock control is not impaired, and there may be brake pressure changes to that of the anti-lock subject vehicle wheels also take place in phase opposition. However, this further known brake also has the disadvantage that pressure control device the relatively high technical effort, which results from either a special design of the braking device as between two possible output pressure com combinations of switchable master cylinders and / or a one and switchable pressure converter and / or brakes with at least two wheel brake cylinder pairs must be provided, whereby One of these wheel brake cylinder pairs can be switched on and off have to be.  

Another disadvantage is that, because of the for Brake pressure control required slip control the anti-lock braking system is activated practically with every braking, whereby at least whose electrohydraulic pressure control device is elevated Wear is exposed, and it can also be considered a disadvantage be considered that due to the one after the return the anti-lock braking system working on the brake pedal possible feedback of the ease of use of the brake system is pregnant. In addition, the driver because of the frequent Response of the anti-lock braking system more often than necessary Will have the impression that a situation of potential danger is given, or that because of one of the frequent Addressing the anti-lock braking system to get used to it at the same time loses the feeling of when a braking situation needs regulation and is therefore relatively dangerous.

The object of the invention is therefore a brake pressure control to indicate direction of the type mentioned at the same time probably a simple overall structure of the brake system and one with it combined brake and traction control system Utilization of high rear axle braking force shares enables and at least not reduce the ease of use of the brake system.

This task is accomplished through the overall combination of features of claim 1 solved.

This is for the implementation of the brake according to the invention pressure control device provided that the vehicle is both an anti-lock braking system (ABS) as well Drive slip control device (ASR) with a common, by means of a electronic control unit controllable pressure control device has the basic structure of that of a  four-channel ABS working according to the return principle speaks, with the as the auxiliary pressure source for the ASR Rear axle brake circuit assigned return pump of the ABS or a can be used with this rechargeable pressure accumulator. Individually assigned to the vehicle's wheel brakes, as a magnet Valves trained brake pressure control valves are at the rear axle brake circuit for both the anti-lock and the Drive slip control used, where in Drive-slip control operation of the rear axle brake circuit against the braking device is shut off and a pressure relief valve-controlled by draining from brake fluid to the reservoir of the brake system he follows.

The function of the brake pressure control device is implemented in such a way that even when braking is controlled by the driver, the rear brakes are pressurized by means of the functional part of the pressure control device of the slip control system provided for the drive slip control, that is to say the rear axle -Brake circuit assigned output pressure space of the braking device against the rear axle brake circuit II remains blocked, this also in the event that the anti-lock control is activated on the rear axle. As a result, the brake pressure control only reacts to the brake pedal if the anti-lock braking system on the front axle is active, ie only if there is a situation requiring anti-lock braking. This significantly improves the ease of use of the brake system. The additional technical effort required to implement the brake pressure control device according to the invention compared to a brake system with anti-lock and traction control device is thus, apart from adapting the electronic control unit to the additional function of tracking the brake pressure as a function of output signals from two sensors mediate, essentially limited to these two additionally required sensors, which, however, can be implemented as pressure sensors in the design indicated by the features of claims 2 and 3 as comparatively cheap functional elements which can be inserted into the overall system with only a small amount of electrical and hydraulic circuitry. If the pressure in the output pressure chamber of the brake device assigned to the rear axle brake circuit II is monitored by means of the pressure sensor whose output signals are processed by the electronic control unit as brake pressure setpoint information, this has the advantage that the brake force distribution control also then can still remain active if the front axle brake circuit should drop out. A failure of the front axle brake circuit can be recognized from the fact that the vehicle deceleration α _x which can be determined on the basis of output signals from the wheel speed sensors is smaller than would be expected after the detected rear axle brake pressure.

If, on the other hand, the pressure P _V in the output pressure chamber of the brake device assigned to the front axle brake circuit I is monitored with the pressure sensor used for the brake pressure setpoint formation for the rear axle brake circuit, which is also coupled as brake pressure into the front wheel brakes, it can be logical Linking the output signals of this pressure sensor with the brake light switch output signal in a simple way before the axle brake circuit failure can be detected. In this case, the braking force distribution control is switched off and the locking of the rear axle brake circuit against the braking device is released so that braking can still be carried out with the rear axle brake circuit which is still intact.

By a compensation valve arrangement provided according to claim 4 with which the directly on the rear brakes closed end portions of the brake line branches of the rear axle brake circuit in brake pressure control mode with each other are connectable, it is ensured that the only one Rear wheel brake as the actual brake pressure measured value is sensitive to the rear axle brake circuit as a whole.

For example, a pressure comes as a compensation valve arrangement controlled 2/2-way valve with blocking basic position in Consider that generated by means of the braking device Output pressure in its the two rear brakes with each other connecting flow position is controlled. A Anti-lock control is then only in the sense of an in-phase Regulation possible on both rear brakes. Is more advantageous however, the training of the off provided according to claim 5 same valve as an electrically controllable solenoid valve that if its associated with the de-energized state of its control magnet nete basic position suitable for brake pressure control operation Nete flow position is for the traction control system can be switched to its locked position as an excited position have to be. A suitable control signal can be used for for example from a NAND function of the brake light switch output signal with an OR operation of all Control signals for those assigned to the rear axle brake circuit Brake pressure control valves can be obtained.

On the other hand is the basic position of the compensating solenoid valve that required for the traction control operation Locked position exploited, so for a needs-based Control of the compensating valve z. B. that Brake light switch output signal can be used. Here is of each  assumed that the control in the anti-lock control mode with a common - in phase - brake pressure change on both Rear brakes are applied.

When to control the brake pressure build-up in the rear wheel brakes One inlet valve is provided, via which the outlet pressure the auxiliary pressure source can be coupled into the rear wheel brakes, as well as an exhaust valve, through which the rear brakes individually or can be connected together to a return line which in turn connectable to the brake fluid reservoir and can be locked against it, so - against the front storage tank shut off return line - the pressure compensation between the two rear brakes that the rear brakes by means of their exhaust valves with the Return line can be connected.

An anti-lock control system based on the return flow principle However, rear axle is then no longer possible because of the Brake circuit for pressure reduction phases of both a normal and controlled braking must also be opened.

In addition to controlling the pressure increase by e.g. B. pulsed control of the brake pressure control valves in their brakes pressure build-up positions, it is advantageous if the Pressure increase rate through speed control of the high pressure pump Rear axle brake pressure source is controllable. The Brake pressure control valves then do not have to be switched too often, which both wear-promoting and with annoying noises can be linked.

If the vehicle, as provided according to claim 11, with a Longitudinal inclination sensor is equipped, so can fall for  characteristic starting signal nale for an automatic calculation of the for Brake force distribution control to be considered axle load distribution and relocation can be exploited.

For the same purpose, the output signals from according to Claim 12 intended axle load sensors are used, by means of which the loading condition of the vehicle can also be determined is.

By means of a sensor device provided according to claim 13, the lateral forces acting on the vehicle by amount and direction detected and according to the features of claim 14 with simple technical means is feasible, it is possible, for. B. in Cornering situations in which the vehicle on the outside of the curve wheels - dynamic - are more heavily loaded than the inside of the curve Vehicle wheels, also through one on the respective vehicle page-related braking force distribution that the in the wheel brakes of the vehicle wheels inside the curve coupled brake pressures are kept lower in amount than in the wheel brakes of the outside vehicle wheels coupled brake pressures.

When the vehicle makes a curve, this corresponds to a yaw movement, that is, a rotation of the vehicle about its rear axis, with an angular velocity that is equal to the angular velocity ϕ = V _F / 2π / γ (V _F = vehicle speed, γ = curve radius) with which the vehicle makes the curve.

The characteristic value of this yaw rate, which is characteristic of the dynamically stable behavior of the vehicle, can be continuously determined from the output signal of a steering angle sensor - as a measure of the curve radius γ - and the output signal of at least one wheel speed sensor - as a measure of the vehicle speed V _F - and as a target Value for the situation-appropriate yaw rate can be used, from whose comparison with an output signal of a yaw speed sensor which is characteristic of the actual yaw rate of the vehicle, a control signal can be obtained which, in the case of cornering braking, conveys a reduction in the proportion of the rear axle brake force when the yaw rate detected by the yaw rate sensor whose target value exceeds more than a threshold value. This also makes a noticeable gain in driving stability achievable.

So far a "left-right" brake force distribution control rea lized, it is of course necessary that during the brake pressure compensation under braking between the rear brakes is excluded and therefore advantageous if one for each of the two rear brakes Own pressure sensor for actual value detection of the brake pressure is available.

Further details of the invention emerge from the following description of exemplary embodiments with reference to Drawing. Show it:

Fig. 1 shows the hydraulic diagram of a hydraulic dual-circuit brake system drive of a road vehicle with rear axle, front axle / rear axle brake circuit division, an ABS and a TCS, and with a erfindungsge MAESSEN brake pressure control device, the latter in specific matically simplified representation,

Fig. 2 is a braking force distribution diagram for explaining the brake pressure control device according to Fig. 1 and

Fig. 3 and 4 each show a hydraulic diagram for explaining two embodiments of a spe cial as part of the brake system of FIG. 1 usable braking pressure control device, in one of the Fig. 1 representation corresponding.

In Fig. 1, to the details of which reference is first made, a total of 10 denotes a hydraulic dual-circuit brake system of a road vehicle represented by it, which is equipped with a brake pressure control device, the purpose of which is, according to the invention, designated 11 in total to achieve a defined distribution of the vehicle via the front brakes 12 and 13 braking forces F _Bv and the braking forces F _Bh exertable via the rear brakes 14 and 16 , especially the so-called ideal braking force distribution, utilizing the same adhesion on the front wheels when braking the vehicle and the rear wheels of the vehicle corresponds, at least to this very well approximated.

In a Fig. 2, to the details of which are also referred to for explanation, the brake force distribution diagram is shown, in which the front axle braking force F _Bv / G related to the vehicle weight G and the ordinate also related to the vehicle weight G as the abscissa Rear axle braking force F _Bh / G is plotted, the course of the ideal braking force distribution is given by a parabola 17 which begins with a positive slope in the coordinate origin of the diagram corresponding to vehicle _deceleration 0 (F _Bv = 0, F _Bh = 0) Because of the dynamic axle load shift to the front axle, which increases with increasing vehicle deceleration, the values of the vehicle deceleration are increasingly flat and, after passing through a maximum, decreases again towards even greater vehicle decelerations. The straight lines 18 falling below 45 ° in the diagram for larger values of the front axle braking force component F _Bv / G represent within the range limited by the traction coefficients that can be used between the roadway and the braked vehicle wheels, respectively, the stock of values, the front axle related to the vehicle weight. and rear axle braking force value pairs, from the addition of which the respective braking can be achieved.

The in the diagram of FIG. 2 to larger values of the front axle braking force portion down flat line 19 corresponds to braking with constant use of traction on the rear axle, while in the diagram of FIG. 2 steeply on rising straight lines 21 braking situations with constant power use of the front axle. Para bel 17 , the shape of which is determined by the parameters ψ (rear axle load component related to the vehicle weight) and χ (wheelbase-related center of gravity = h _s / l; h _s = center of gravity of the vehicle above the contact area, l = center distance), 2 in the diagram of FIG. 2, as it were, marks the boundary between the stable braking area represented by the field "below half" of the parabola 17 and the unstable braking area represented by the field above the parabola 17 .

"Stable" means that with an increase in the braking forces, which are in a fixed ratio F _Bv / F _{Bh to} each other, the front wheel brakes first reach the blocking limit, "unstable" that in the same situation the rear wheels of the vehicle lock first would.

In the diagram, an installed braking force distribution is represented by a straight line 22 , which corresponds to a fixed adjustment thereof on a rear axle braking force component of approximately 38%.

The parabola 17 of the ideal brake force distribution shown in the diagram in FIG. 2 applies within the accuracy of the representation for a fully occupied vehicle with a total weight of 21.4 kN, a rear axle brake force component ψ of 0.52 and a wheelbase-related center of gravity height χ of 0 , 21 In such a vehicle, the critical deceleration marked by the intersection 23 of the straight line 22 of the installed braking force distribution with the parabola 17 of the ideal braking force distribution has a value of around 1.17, with 0.84 on the front axle braking force component and on the vehicle weight Rear axle braking force share 0.33 is eliminated. One of the well-known decelerations, which corresponds to the utilization of a force-locking coefficient of 1.17, can easily be achieved with modern vehicle tires on dry, grippy roads.

In the partial braking area, however. B. at a deceleration of 0.6, which corresponds to the point 24 of the straight line 22 , the power utilization on the front wheels would be about 0.7, while the force utilization on the rear wheels would be significantly less with about 0.4. If instead the brake force distribution were ideal, ie 0.6 on the front wheels and on the rear wheels, corresponding to the intersection 26 of the straight line 18 corresponding to the deceleration 0.6 constant braking with the parabola 17 of the ideal braking force distribution, this would result in a for the front axle based on the vehicle weight of 0.36 braking force and 0.24 for the rear axle, ie it could be used in the partial braking area, without sacrificing dynamic stability of the vehicle, a higher proportion of rear axle braking force, both with regard to the achievable Bremsver delays as well as in view of a more uniform loading of the front and rear brakes 12 and 13 and 14 and 16 would be an advantage.

In order to achieve the desired approximation of the real braking force distribution to the ideal, if possible, in the entire braking range - partial braking to full braking - at least approximately, the brake system 10 and its brake pressure control device 11 are provided in more detail for the structure explained below, for the purpose the explanation for all the exemplary embodiments is provided that the vehicle has a rear axle drive, and that the front wheel brakes 12 and 13 are combined to form a front axle brake circuit I and the rear wheel brakes 14 and 16 form a rear axle brake circuit II.

As a braking device, by means of which the driver can control a braking deceleration corresponding to his assessment of the traffic situation in the brake system 10 , a - via hydraulic or pneumatic - brake booster 27 actuable by means of a brake pedal 28 master cylinder 29 is provided, which is one of the front axle brake circuit I assigned, first output pressure chamber 31 and a second output pressure chamber 32 assigned to the rear axle brake circuit II, in which - by actuating the brake pedal 28, static pressures P _V and P _{h can be built up, in} addition to the force K _p with which the driver depresses the brake pedal 28 operated, are proportional.

In the special embodiment shown in FIG. 1, the master cylinder 29 is designed as a tandem master cylinder of a design known per se, the primary outlet pressure chamber of which forms the first outlet pressure chamber and is pressure-tightly movable on one side in the axial direction by a primary piston 33 which engages the actuating force amplified by means of its brake booster 27 , and the secondary outlet pressure chamber which forms the second outlet pressure chamber 32 and which, seen in the axial direction, is fixed to the housing by an end wall 34 of the cylinder housing 36 and is pressure-tightly movable against the primary outlet pressure chamber 31 a floating piston 37 is delimited so that a prevailing pressure P _h in the secondary output pressure chamber 32 is always in a defined ratio to the pressure in the primary output pressure chamber 31 .

In the illustrated design of the tandem master cylinder 29 with the same surfaces of the piston flanges with which the floating piston 27 on the one hand limits the primary outlet pressure chamber 31 and on the other hand the secondary outlet pressure chamber 32 , pressures P _V and P _h are essentially in these outlet pressure chambers Lichen same amount generated when the braking device 29 is actuated. A z. B. the straight line 22 of the brake force distribution diagram of FIG. 2 corresponding fixed brake force distribution is achieved by the design of the front brakes 12 and 13 and the rear brakes 14 and 16 .

About the pressure outlet 38 of the primary outlet pressure chamber 31 of the tandem master cylinder 29 connected to the main brake line 39 of the front axle brake circuit I and its outgoing from the branch point 41 leading to the left front wheel brake 12 and the right front brake 13 branch lines 42 and 43 , when braking, the front wheel brakes 12 and 13 are acted upon by the pressure P _V generated in the primary outlet pressure chamber 31 of the tandem master cylinder 29 as a braking pressure, by means of which the braking forces which can be generated by the front wheel brakes 12 and 13 are determined.

The brake pressure P _H coupled during braking into the rear wheel brakes 14 and 16 is, however, in contrast to a conventional brake system, generated by the brake pressure control device 11 , which has an electronic control unit 44 and an electro-hydraulic pressure control device 46 controlled by this comprises, which is designed according to its basic structure as an independent brake pressure source with which any pressures can be generated within the brake pressure requirement, and which has a pressure output 47 assigned to the left rear brake 14 and a pressure output 48 assigned to the right rear brake 16 , at which the pressure coupled into the respective wheel brakes 14 and 16 as braking pressure is provided.

The brake pressure control device 11 conveys the function within the framework of the brake system 10 , the brake pressure P _H coupled into the wheel brake cylinders of the rear wheel brakes 14 and 16, the brake pressure P _V coupled into the wheel brake cylinders of the front wheel brakes 12 and 13 - that in the primary output pressure chamber 31 of the tandem -Main cylinder 29 generated pressure - so that overall there is the ideal braking force distribution, according to the relationship

or a brake force distribution approximating this relationship ( 1 ), such that the rear axle brake force component F _Bh is larger than that represented by the straight line 22 of the brake force distribution diagram in FIG. 2, by the construction of the front and rear wheel brakes 12 and 13 as well as 14 and 16 and the braking device 29 caused brake force distribution would correspond, but lower than it would correspond to the course represented by the parabola 17 of this brake force distribution diagram.

The information required for such a follow-up control or regulation about the front-axle braking force component F _Bv , the pressure P _V coupled into the front-axle braking circuit I by a proportionality relationship,

F _Bv = K _V P · _V (2),

linked, in which K _V is a constant determined by the brake design, the chassis design and the vehicle weight Kon, can be monitored continuously by the brake pressure P _V coupled into the front wheel brakes 12 and 13 by means of a to the pressure output 38 of the primary output pressure chamber 31 of the braking device 29 connected pressure sensor 49 can be obtained, which generates a characteristic for the front axle brake pressure P _V cha, ver ver by the electronic control unit 44 electrical output signal.

The information about the front axle braking force component F _Bv can also be obtained by means of a pressure sensor 51 analogous to the pressure sensor 49 , which is connected to the pressure outlet 52 of the secondary outlet pressure chamber 32 of the tandem master cylinder 29 , since the pressure P _h generated therein , depending on the design of the tandem master cylinder 29, is either equal to the pressure P _V generated in its primary outlet pressure chamber 31 or is strictly proportional to it.

Furthermore, for the actual value detection of the brake pressure coupled into the rear wheel, which is related to the rear axle braking force component F _Bh through a relationship analogous to relationship ( 2 ),
F _Bh = K _h · P _H (3)
is linked to see at least one further pressure sensor 53 which is connected between one of the pressure outputs 47 or 48 of the brake pressure control device and the wheel brake 14 or 16 connected to it, and thus detects the brake pressure P _H coupled into it and detects it generated for this characteristic output signal that can be processed by the electronic control unit 44 .

From the comparison of the output signals characteristic of a certain rear axle braking force component F _Bh with target values, which the electronic control unit 44 gains from processing the output signals of the pressure sensor 49 assigned to the front axle braking circuit I and / or the pressure sensor 51 , which wins the pressure output 52 of the secondary output pressure chamber 32 of the braking device 29 is connected, the electronic control unit generates the control signals required for the adjustment of the actual and target value for the pressure actuating device 46 , the z. B. can be realized by a pump with adjustable speed and output pressure and the rear brakes 14 and 16 individually assigned inlet and outlet valves, the brake pressure control device 46 has a supply connection 54 , which with the brake fluid reservoir 56 of the brake system 10th is connected, from which the pump (not shown) can deliver brake fluid to the wheel brakes 14 and 16 , and an outlet connection 57 , via which brake fluid can be drained to the brake fluid reservoir 56 during braking pressure reduction phases of a braking operation, with a control for this between this drain port 57 and the brake fluid reservoir 56 switched outlet control valve 58 is connected, which is formed in the illustrated, special embodiment as a 2/2-way solenoid valve, the position 0 by output signals of the electronic control unit 44 from its blocking basic position in his - excited e - Flow position I is controllable, in which the drain port 57 is connected to the brake fluid reservoir 56 of the brake system 10 .

Furthermore, the pressure control device 46 has a pressure input 59 , which can be connected by means of a function control valve 61 to the pressure outlet 52 of the secondary outlet pressure chamber 32 of the tandem master cylinder 29 , alternatively can be shut off from the latter. This function control valve 61 is designed as a 2/2-way solenoid valve, which is controllable by an output signal of the electronic control unit 44 in its - blocking - excited position I and in the de-energized state of its control magnet in its the pressure output 52 of the tandem master cylinder 29 with the pressure input 59 of the pressure adjusting device 11 connecting basic position 0 is held.

When braking, the function control valve 61 is switched into its blocking position by an output signal from the electronic control unit 44 .

The pressure control device 46 is further ausgebil det that in the event of a defect in the brake pressure Steuerein device 11 by switching back in the context of the control device 46 any existing valves and when the auxiliary pressure source is switched off its pressure input 59 with the two, the rear brakes 14 and 16 each individually assigned pressure outputs connects 47 and 48 and forms a branching point corresponding to the branching point 41 of the front axle brake circuit I, which is connected via the function control valve 61 now held in its basic position 0 to the pressure output 52 of the secondary output pressure chamber 32 of the braking device 29 , so that in this malfunction at least with the straight line 22 of the brake force distribution diagram according to FIG. 2 accordingly, firmly coordinated, designed for stable dynamic behavior of the vehicle brake force distribution can be braked.

In the exemplary embodiment of a brake pressure control device 11 according to the invention shown in FIG. 3, its pressure adjusting device is realized by components of an anti-lock and drive slip control system associated with the brake circuit II of the driven vehicle wheels and with which the vehicle is also equipped. The electronic control unit of the brake pressure control device 11 , which in this case is expediently integrated into the electronic control unit also provided for the anti-lock braking system and the drive slip control device, is not shown for the sake of simplicity.

Insofar as components and functional elements of the brake system 10 shown in FIG. 3 and its brake pressure control device 11 are assigned the same reference numerals as elements of the brake system 10 explained with reference to FIG. 1, this is intended to indicate the identical construction and function or analogy of the identically labeled elements and also include the reference to the relevant parts of the description of FIG. 1.

For the anti-lock braking system it is assumed that it works according to the return flow principle, according to which in a brake pressure reduction phase of the anti-lock control system, brake fluid discharged from a wheel brake subject to the control system is pumped back into the main brake line 39 or 62 of the respective brake circuit I or 11 . The traction control device works on the principle of retarding a vehicle wheel which tends to spin by activating its wheel brake (s) 14 and / or 16 , the return pump 63 being used as an auxiliary pressure source in this regard, which is also pressure in the brake. Control operation of the pressure control device 46 is the case.

The input supply of the return pump, usually designed as a non-self-priming piston pump, with brake fluid takes place by means of an electrically driven, self-priming, precharge pump 64 operating at a low output pressure level of approx. 10 bar, which via an output check valve 66 to the input 67 of the return pump 63 is connected, the pressure output 68 via an output check valve 69 and a provided for sound absorption buffer throttle section 71 is connected to the main brake line 62 of the rear axle brake circuit 11 , which is at the junction 72 in the to the wheel brakes 14 and 16th further brake branches 73 and 74 branches.

To control brake pressure reduction, brake pressure maintenance and brake pressure build-up phases of the anti-lock control, brake pressure control valves 76 and 77 , which are individually assigned to the rear wheel brakes 14 and 16 , are used for braking pressure for a normal brake control that is not subject to an anti-lock control. Control in the sense of achieving a desired braking force distribution and used for the purpose of traction control are analogously designed in the exemplary embodiment according to FIG. 3 as 3/3-way solenoid valves, whose control magnets 78 and 79 are taken in the de-energized state Grundstel development 0 is a first flow position in which the wheel brakes 14 and 16 are connected to the main brake line 62 , ie the brake line branches 73 and 74 are open and brake pressure can be built up. In this basic position 0, the respective wheel brake 14 or 16 is also blocked against a return line 81 , which is connected to the outlet connection 57 of the pressure actuator 46 .

The brake pressure control valves 76 and 77 are - alternatively or jointly - each defined by a control signal level, for. B. a 3A signal in a first excited position I, the brake pressure hold position switchable, in which the respective wheel brake 14 or 16 is blocked against both the main brake line 62 and the return line 81 of the rear axle brake circuit 11 , and defined by a control signal, higher signal levels, for. B. 6A signal in a further excited position 11 , the pressure reduction position switchable, in which the respective wheel brake 14 or 16 connected to the return line 81 , but is blocked against the main brake line 62 .

To the return line 81 is a z. B. connected as a piston-spring accumulator formed low-pressure accumulator 82 , which in brake pressure reduction phases of the anti-lock control in the return line 81 can receive drained brake fluid before this by means of the return pump 63 , the pump input 67 via an input check valve 83 is also connected to the return line 81 , possibly pumped back into the main brake line 62 .

The brake system 10 explained so far with brake pressure control device 11 operates as follows:

From the beginning of braking, that is, with the onset of the output signal of the brake light switch 83 , the function control valve 61 is switched into its blocking position 1 and thereby the main brake line 62 is blocked against the pressure output 52 of the tandem master cylinder 29 assigned to the rear axle brake circuit 11 . At the same time, the precharge pump 64 and the high pressure pump 63 are activated and the outlet control valve 58 is switched to its flow position I. By pulsed switching of the brake pressure control valves 76 and 77 between their basic position 0 and their blocking position I, the pressure increase rate in the wheel brakes 14 and 16 , according to the brake pressure control, can be set to the respectively required value. To reduce the brake pressure, the brake pressure control valves are controlled in their second flow position II, in the Bremsflüs fluid from the wheel brakes 14 and 16 flow into the return line 81 and via the outlet control valve 58 held in its passage position I to the brake fluid reservoir 56 can flow back. Even in the pressure reduction mode, the pressure reduction rate can be set by pulsed switching between the pressure reduction position 11 and the blocking position 1 of the brake pressure control valves 76 and 77 .

In a distribution to achieve a desired VA / HA brake force distribution suitable operating mode of the pressure control device 46 , the brake pressure control valves 76 and 77 are switched simultaneously to set identical pressure ratios on both rear wheel brakes 14 and 16 . Due to differing response behavior of the brake pressure control valves 76 and 77 , however, an asymmetrical brake force development can occur on the two rear wheel brakes 14 and 16 , in particular when a large number of switching operations of these brake pressure build-up or reduction phases Valves 76 and 77 are linked.

In order to avoid such "asymmetric" braking force development at the two rear wheel brakes 14 and 16, UNMIT telbar between the wheel brakes 14 and 16 as a 2/2-way-Mag netventil formed compensating valve 84 is connected, whose basic position is 0 its blocking position, and whose excited position I, in which it is switched over in the brake pressure control mode, is its flow position in which it conveys the greatest possible pressure equality in the two wheel brakes 14 and 16 .

If the anti-lock control on the rear axle takes place "in phase" on both rear wheels, with brake pressure reduction phases taking place on both rear brakes, even if a locking tendency only occurs on one of the braked rear wheels, the compensating valve 84 can also be switched to its flow position I during the anti-lock control stay. Proper function of the pressure actuating device 46 presupposes, can on a certain, for. B. the ideal brake force distribution targeting brake pressure control can also be maintained during the anti-lock control, wherein pressure reduction phases of the same brake fluid via the outlet control valve 58 located in its open position I can flow out to the reservoir 56 out. The rear axle brake circuit is then operated as an open brake circuit as in the case of brake pressure control. However, an anti-lock control is also possible with the rear-axle brake circuit closed, ie in the return mode of operation of the return pump 63 , in which case, in the introductory phase of the anti-lock control, the brake pressure detected by the pressure sensor 53 in the rear-axle brake circuit II is reduced until it is the same the detected by means of the pressure sensor 51 or the pressure sensor 49 pressure in the brake device 29 , after which the function control valve 61 is switched back to its basic position 0 - its open position - and the outlet control valve 58 is switched to its - non-blocking - basic position 0 is, and for the rest of the anti-lock control process, the braking device 29 is also used for the brake pressure build-up on the rear axle.

This type of anti-lock control remains possible even if the brake pressure control, for. B. is not available due to a defect in the precharge pump 64 and brake pressure on the rear wheels of the vehicle must therefore be built up by means of the braking device 29 .

For the drive-slip control operation of the Druck-Stellein device 46 , the compensating valve 84 must be in its blocking position so that pressure changes are possible on the two rear wheel brakes 14 and 16 of each other and, if necessary, antiphase braking.

The necessary for the operational and regulatory changeover of the function control valve 61 , the outlet control valve 58 , the precharging pump 64 and the high pressure pump 63 and the brake pressure control valves 76 and 77 and possibly the compensation valve 84 control pulses required by the electronic control unit 44 in the case the anti-lock control and the traction control from a processing according to known criteria of level and / or frequency generates the information about the dynamic behavior of the vehicle wheels output signals from the vehicle wheels individually assigned, not shown wheel speed sensors, in the case of brake pressure control essentially from processing the output signals of the pressure sensors 49 and 51 and 53 on the basis of the basic idea with reference to FIGS. 1 and 2 according to the criteria explained.

Assuming that it is a specialist in electronic Circuit technology is possible with knowledge of these criteria the required electronic control unit with common Realizing means will be one in their circuitry Detailed explanation is considered unnecessary.

The illustrated in Fig. 4, to the details of which reference is now made, further embodiment of a brake system 10 with brake pressure control device 11 differs from the embodiment of FIG. 3 in structural terms only in that

• a) instead of a single 3/3-way solenoid valve 76 or 77 per wheel brake 14 or 16 two, each as 2/2-way solenoid valves 76 'and 76 ''or 77 ' and 77 '' are provided,
• b) the high-pressure pump 63 on the input side is only connected via the output check valve 66 to the precharge pump 64 and
• c) a memory corresponding to the buffer memory 82 according to FIG. 3 is not available - saved.

In functional terms, the execution example according to FIG. 4 differs from the embodiment according to FIG. 2 in that an anti-lock control taking place according to the recirculation principle is not possible and therefore in brake pressure reduction phases of the anti-lock control from the wheel brakes 14 and 16, the brake fluid is always drained the outlet control valve 58 to the brake fluid reservoir 56 must be drained.

As far as in Fig. 4 elements of the same are assigned the same reference numerals as elements of Figs. 3 and 1, this should again mean the reference to the structural and functional equality or analogy and also the reference to the corresponding parts of the description of these Fig. Include.

The rear brakes 14 and 16 are each one of the 2/2-way solenoid valves, namely the open in their home position 0 and in their energized position I blocking valves 76 'and 77 ' to the junction 72 of the main brake line 62 of the rear axle brake circuit 11 connected and connected to the return line 81 via the two other 2/2-way solenoid valves 76 '' and 77 '', the basic position 0 of which is their blocking position and whose excited position I is their flow position. The brake pressure build-up on the rear brakes 14 and 16 takes place in the home position 0 of the inlet valves 76 'and 77 ' and the outlet valves 76 '' and 77 ''.

The function of the compensation valve 84 described with reference to FIG. 3 can be achieved by means of the two exhaust valves 76 '' and 77 '' because these two valves are switched to their flow positions I in the brake pressure control mode of the brake pressure control device 11 .

The realizations of a explained with reference to FIGS. 3 and 4

• - Brake pressure adjusting device 11 according to the invention imply the possibility of an individual brake pressure control or
• - Control on the two rear brakes 14 and 16 . In principle, it is then also possible to use different brake force distributions on the left and right side of the vehicle, e.g. B. in a cornering situation, in which the inside of the vehicle wheels are always relieved, but the outer vehicle wheels are loaded more heavily. A prerequisite for a possible "left-right brake force distribution control" is knowledge of the lateral forces acting on the vehicle. These can be determined taking into account the track widths and the roll radii of the vehicle wheels by evaluating the output signals from the wheel speed sensors individually assigned to the vehicle wheels, which are provided in the context of the slip control systems (ABS and TCS). For the determination of lateral forces, specially provided lateral acceleration sensors can also be used.

Furthermore, a control of the Front axle / rear axle brake force distribution depending on the topographical Road conditions make sense, in the sense of a humiliation of the rear axle braking force share when the vehicle is in steep downhill descent and an elevation of the same, when the road rises steeply. Suitable Nei in this regard tion sensors are known, but are particularly in Gelän  vehicles only for displaying vehicle longitudinal and Banks exploited.

So far different on the two sides of the vehicle Braking force distributions should be adjustable, it is of course required so that at least the rear brakes each have a pressure or Brake force sensor is assigned to the actual value at the respective To be able to monitor the rear wheel.

Deviating from a braking force distribution control "along" the parabola 17 of the ideal braking force distribution, the braking force distribution, in particular in the partial braking range, ie at relatively low braking values of, for. B. 0.4 also take place in such a way that the rear axle braking force portion increases in proportion to the front axle braking force portion, but its absolute amount is higher than this, from a certain value, the absolute amount is kept essentially constant, while only the Front axle braking force is increased and only when the braking force distribution reaches the "ideal" distribution with a further increase in the front axle braking force, the further braking force distribution control takes place approximately along the parabola 17 of the ideal braking force distribution.

For example, if the adhesion coefficient µ _H usable on the rear wheel brakes 14 and 16 has a value of 0.6, which is represented by the straight line 19.6 in the braking force distribution diagram of FIG. 2, then the deceleration 0.4 of the vehicle can be represented by the Just 18.4, without the vehicle becoming unstable, can also be achieved with a front axle braking force component of 0.16 and a rear axle braking force component of 0.24, as represented by point 86 of the braking force distribution diagram, which lies in its "unstable" area .

However, such a braking force distribution control presupposes that is recognizable, wherein amount of rear axle braking force, less a safety margin, which is still usable from adhesion μ _H at the rear axle achieved. In a vehicle equipped with a slip-dependent anti-lock braking system, this limit is readily recognizable by the fact that the brake slip at the rear wheels reaches a threshold value, which however is still below the value from which there is a need for anti-lock regulation.

The determination of the parabola 17 of the ideal braking force distribution, which is valid for the respective loading condition of the vehicle, can be carried out automatically by means of a computer provided for this purpose, the electronic control unit 44 if the vehicle is equipped with e.g. B. the static deflection state of the vehicle sensors, z. B. position sensors is equipped and can be driven by the output signals of other sensors, z. B. the mentioned lateral acceleration and / or inclination sensors can be modified.

Other constraints that can be easily taken into account for situation-appropriate braking force distribution control by means of the brake pressure control device 11 are, for. B. the prevailing temperatures on the front brakes and / or the rear brakes, which can be determined either directly by means of specially provided temperature sensors or indirectly via the braking durations and pressures with which the brakes have been applied, in the second case by processing the output signals the pressure sensors 49 and / or 51 and 53 . If, for example, the temperature of the rear wheel brakes exceeds that of the front wheel brakes, it is expedient to switch to a brake force distribution control with a lower rear axle braking force component until the temperature of the rear wheel brakes has again reached a tolerable value.

The output signals of a - not shown - Yaw rate sensors can cause a situation fair reduction of the rear axle braking force share be exploited.

The brake pressure control device 11 enables the fact that the brake pressure P _H coupled into the rear axle brake circuit can be adjusted in practically any relation to the front axle brake pressure, the use of a wide variety of brake force distribution characteristics and their appropriate use depending on the situation the monitoring of the dynamic behavior of the vehicle characterizing variables "assessed" and can be used to set the most favorable braking force distribution.

Claims (16)

1. Brake pressure control device for variable adjustment of the front axle / rear axle brake force distribution (EBKV) on a road vehicle with

• a) rear-axle drive and front-axle / rear-axle brake circuit division of its hydraulic dual-circuit brake system, the braking device by means of which the driver controls the braking of the vehicle is a tandem master cylinder ( 29 ), which is delimited from one another by a floating piston ( 7 ), the brake circuits has an individually assigned output pressure chamber ( 31 and 32 ), in which static pressures P _h and P _{V are} built up when the brake system ( 10 ) is actuated;
• b) an anti-lock braking system (ABS), which is designed as a solenoid valve ( 76 , 77 ; 76 ' 76 '', 77 ', 77 '') and associated with the wheel brakes associated with brake pressure control valves by means of which brake pressure reduction, maintenance and brake pressure build-up phases of the anti-lock control are controllable;
• c) a traction control system (ASR), which works on the principle of retarding a tendency to spin vehicle wheel by automatically activating its wheel brake ( 14 or 16 ) again, in the context of at least one for traction control operation required Druck-Stellein direction ( 11 , 46 ) as an auxiliary pressure source, a rear axle brake circuit ( 11 ) assigned high pressure pump ( 63 ), if necessary a rechargeable pressure reservoir is provided and the brake pressure control valves for controlling brake pressure build-up, hold and dismantling phases on the wheel subjected to the ASR are used analogously, and the pressure output ( 52 ) of the braking device ( 29 ) associated with the brake circuit (α) of the driven vehicle wheels is at least during the traction control operation by means of an electrically controllable one Function control valve ( 61 ) blocked against the pressure input ( 59 ) of the pressure control device ( 11 , 46 ) is

characterized in that

• d) a first sensor ( 49 and / or 51 ) is provided which generates an output signal which is a measure of the force with which the driver actuates the braking device in the sense of specifying a target value for the vehicle deceleration; that
• e) a second sensor ( 53 ) is provided which generates an output signal which is a measure of the actual value of the braking force generated in the rear axle brake circuit ( 11 ), and that
• f) an electronic control unit ( 44 ) is provided which, even when the driver triggers braking, generates an output signal controlling the function control valve ( 61 ) from a flow position into its blocking position, and control signals for the pressure control device from processing the sensor output signals ( 11 , 46 ) generated in such a way that the pressure coupled into the rear wheel brakes via the brake pressure control valves is tracked in a correlation corresponding to a desired development of the braking force distribution with the pressure coupled into the front wheel brakes.

2. Brake pressure control device according to claim 1, characterized in that as the setpoint sensor (s) a pressure (P _h ) in the rear axle brake circuit ( 11 ) assigned output pressure chamber ( 32 ) of the master cylinder ( 29 ) detecting pressure sensor ( 51 ) and / or the pressure (P _V ) which prevails in the output pressure chamber ( 31 ) of the master cylinder ( 29 ) associated with the front axle brake circuit ( 1 ), is / are provided pressure sensor ( 49 ). 3. Brake pressure control device according to claim 1 or claim 2, characterized in that at least one pressure sensor ( 53 ) is provided as the actual value sensor, the one for the brake pressure (P _H ) in one of the rear wheel brakes ( 14 or 16 ) characteristic output signal generated. 4. Brake pressure control device according to claim 3, characterized in that the directly to the rear wheel brakes ( 14 and 16 ) connected end portions of the brake line branches ( 73 and 74 ) via a compensation Ven valve arrangement ( 84 ) can be connected to each other. 5. Brake pressure control device according to claim 4, characterized in that the compensation valve arrangement ( 84 ) is designed as a 2/2-way solenoid valve with a blocking and a flow position. 6. Brake pressure control device according to claim 5, characterized in that the excited position ( 1 ) of the compensating valve ( 84 ) is its flow position. 7. Brake pressure control device according to claim 5, characterized in that the excited position ( 1 ) of the compensating valve ( 84 ) is the blocking position. 8. Brake pressure control device according to claim 4, characterized in that for the rear wheel brakes ( 14 and 16 ) as brake pressure control valves for the drive slip control and / or an anti-lock control each have an inlet valve ( 76 'or 77 ') is provided, through which the rear wheel brakes ( 14 and 16 ) can be acted upon by the outlet pressure of the auxiliary pressure source ( 63 , 64 ) of the ASR, and an exhaust valve ( 76 '' and 77 ''), via which the rear wheel brakes ( 14 and 16 ) can be connected to a return line ( 81 ) which can be connected to the brake fluid reservoir ( 56 ) of the brake system ( 10 ) via an outlet control valve ( 58 ) and that the two outlet valves ( 76 '' and 77 'ß) , whose basic position (0) is its blocking position, can be controlled by output signals from the electronic control unit ( 44 ) together in their rear wheel brakes ( 14 and 16 ) with the return line ( 81 ) connecting flow position (I) are. 9. Brake pressure control device according to claim 8, wherein the inlet and outlet valves ( 76 ', 77 ', 76 '' and 77 '') are also used as brake pressure control valves of an anti-lock braking system (ABS), characterized in that this ABS works on the brake circuit ( 11 ) of the rear wheel brakes ( 14 and 16 ) according to the principle of lowering the brake pressure by opening the rear axle brake circuit ( 11 ) to the reservoir ( 56 ) of the brake system ( 10 ). 10. Brake pressure control device according to one of claims 1 to 9, characterized in that the brake pressure build-up rate in the rear axle brake circuit (II) by speed control of a high pressure pump ( 63 ) is controllable. 11. Brake pressure control device according to one of claims 1 to 10, characterized in that the vehicle is equipped with a longitudinal inclination sensor which generates processable electrical output signals by means of the electronic control unit ( 44 ) which contain the information about the inclination and sense of inclination Seen in the longitudinal direction of the vehicle, and processed by the electronic control unit ( 44 ) in the sense of a reduction in the rear axle brake force part when the road, viewed in the direction of travel, drops and in the sense of an increase in the rear axle brake force share when the roadway increases. 12. Brake pressure control device according to one of claims 1 to 11, characterized in that a front axle load sensor and a rear axle load sensor are provided which generate processable electrical output signals by means of the electronic control unit ( 44 ). 13. Brake pressure control device according to one of claims 1 to 12, characterized in that a sensor device is seen before that detects the transverse forces acting on the vehicle according to direction and amount and for this characteristic, by means of the electronic control unit ( 44 ) processable, electrical Output signals generated. 14. Brake pressure control device according to claim 13, characterized in that at least one of the sensor combinations mentioned below or at least one of the sensors mentioned below is provided which / which generates electrical output signals which can be processed by the electronic control unit:

• a) at least one wheel speed sensor assigned to one of the front wheels of the vehicle and at least one wheel speed sensor assigned to one of the rear wheels of the vehicle, which generate characteristic output signals for the wheel circumference speeds according to level and / or frequency;
• b) a steering angle sensor and at least one wheel speed sensor;
• c) a lateral acceleration sensor;
• d) a bank sensor.
• e) a yaw rate sensor

15. Brake pressure control device according to one of claims 12 to 14, characterized in that a pressure sensor ( 53 ) is provided for both rear wheel brakes ( 14 and 16 ), the output signals of which can be processed by means of the electronic control unit ( 44 ).