DE4401995C1 - Brake pressure control device - Google Patents

Abstract

In a brake pressure control device for a road vehicle with hydraulic dual-circuit brake system with front axle/rear axle brake circuit division, which is equipped with a device for vehicle dynamics control (FDR), a device for electronic control of the front axle/rear axle brake power proportioning (EBKV) and with an antilock brake system (ABS), which functions on the front axle brake circuit on the return principle, a high-pressure pump assigned to the rear axle brake circuit and the return pump of the front axle brake circuit, which on the inlet side can be subjected to the relatively low outlet pressure of a precharge pump, which can be fed to the high-pressure pump by way of a precharge control valve and to the return pump by way of a precharge cylinder, are utilised as pressure sources from which, in the event of FDR or EBKV operation, the wheel brakes utilised for the respective type of control can be subjected to brake pressure. In brake pressure reduction phases the rear axle brake circuit is operated as open brake circuit. From a comparison of output signals from a pressure sensor detecting the brake pressure in the rear axle brake circuit with the output signals from a pressure sensor monitoring the pressure in the front axle brake circuit, an electronic control unit generates the control signals necessary for compensatory adjustment of the brake pressure in the rear axle brake circuit.

Description

The invention relates to a brake pressure control device device for a road vehicle with hydraulic More circuit brake system, which has a device for driving Dynamic control (FDR), a device for electro control of the front axle / rear axle brakes power distribution (EBKV) and with an anti-lock system stem (ABS) is equipped and with the other, in Preamble of claim 1, generic defining characteristics.

Such a brake pressure control device is counter status of your own, older, not previously published Patents DE 43 29 139 C1 and for a road trip stuff with front axle / rear axle brake circuit division and closed brake circuits, being designed as Brake pressure control unit with a tandem master cylinder two, individually assigned to the brake circuits - stati output pressure spaces is provided. The driving Dynamic control device of the vehicle works the z. B. principle known from DE 41 23 235 C1, through automatic, electronically controlled activation one or more wheel brakes on the longitudinal and side slip the vehicle wheels within those limits to keep up with the vehicle's dynamic stability overall are tolerated. The electronic tax Distribution of the braking force on the front and The rear wheel brakes are designed so that at one driver-controlled braking of the rear wheel brake brake pressure to be coupled in according to a setpoint  is carried out according to the ideal, the same Use of traction on the front and rear the corresponding brake force distribution by means of a electronic control unit from a comparative Processing the output signals of at least one of the Brake pressure in the rear axle brake circuit sensors with the output signals of the output pressure at one of the pressure outputs of the tandem master cylinder monitoring pressure sensor is continuously generated, such as B. known from DE 42 08 581 A1.

The anti-lock braking system, which is Brake circuit as well as rear axle brake circuit after Return principle works, includes the vehicle wheels individually assigned brake pressure control valves, by means of brake pressure reduction, maintenance and reconstruction phases the anti-lock control can be controlled, as well as two, return pumps individually assigned to the brake circuits, the brake pressure control valves of the ABS for the brake power distribution control and for driving dynamics Regulations are used analogously and in the sense of the respective regulation or control purpose controllable by means of an electronic control unit are.

As a pressure source (s) from the / those in the case of the brake force distribution control or driving dynamics rain for the respective control or regulation Art used wheel brake (s) with brake pressure is / can be beat the return pump (s)  exploited, the inlet side with the outlet pressure one at a low outlet pressure level of e.g. B. 15 bar working, electrically powered precharge pump can be opened, as by EP-0 460 408 A1 Traction control in one with an ABS equipped vehicle known for itself, the pressure output of the pre-charge pump via a 2/2-way magnet valve-designed precharge control valve to the never the pressure side of the high pressure pump can be connected.

For hydraulic separation of the two brake circuits these are assigned individually, in one by the DE 40 35 462 A1 known plunger construction realized precharging cylinders provided, each one Pistons have an outlet pressure chamber, which over a precharge control valve with the low pressure connection the return pump of the respective brake circuit ver is binding against a drive pressure chamber to which the Pressure outlet of the precharge pump is connected, pressure closely delimited and two axially apart has arranged flanges, between which a one of the pressure outputs of the brake device in constant com communicating connection kept trailing space stretches, the piston with a check valve is provided, the one the trailing area with the off flow passage connecting the piston locks as long as the pressure in the outlet pressure chamber of each because the precharge cylinder is larger than in the night running space and clears this flow path when the Master cylinder outlet pressure is greater than the pressure in  Output pressure space of the respective precharge cylinder. Two the pressure output of the respective precharge cylinder and the main brake line of this pressure-ver brake circuit is electrically controlled switchable valve that is open when de-energized and is locked when excited. The one for both Pre-charging cylinder jointly provided drive pressure space is by actuation of a normally open magnetic valve tils against the brake fluid reservoir Lockable brake system.

In the brake pressure control device according to the patent DE 43 29 139 C1 is regarding the EBKV tax to be regarded as disadvantageous in that not too rare Driving situations, e.g. B. braking when cornering, the required reduction in brake pressure the inside of the vehicle wheels, especially on the cure inside the rear wheel a return flow of brake fluid liquid in the outlet pressure chamber of the rear axle Brake circuit associated precharge cylinder requires what turn to a pushing back of brake fluid in the master cylinder of the brake system and therefore one noticeable pulsation of the brake pedal does what one is uncomfortable on the one hand and the driver on the other Can simulate the response of the anti-lock control, so that this gives the impression of a "dangerous" brake situation wins and therefore unnecessarily brakes behavior changes. The one through the two precharging cylinders conditional technical effort and space requirement is, not respects the multitude of functions that can be achieved with the Brake pressure control device can be represented, significant  Lich. In addition, one with the so far explained brake pressure control device equipped Brake system because of the additional pre-charging cylinder too there are additional chambers from which Gasbla sen, which is subject to strong thermal stress Can form wheel brakes, can only escape with difficulty, which is especially true when the two preloading cycles linder together to a "symmetrical" unit are summarized and therefore the for a reasonably good Ent ventilation of both precharging cylinders most favorable arrangement the same at best in the sense of the best possible com promisses can be made.

The object of the invention is therefore to provide a brake pressure Control device of the type mentioned initially hend to improve that at the same time easier on build the same and reliable representability of the various regulation and control functions as well increased ease of use is achieved.

This object is achieved by the in the kenn drawing part of claim 1 mentioned times solved.

After that, the pressure output of the precharge pump is above that preload control assigned to the rear axle brake circuit valve "direct", d. H. without an intermediary loading cylinder to the low pressure inlet of the high pressure pump of the rear axle brake circuit connected where through a considerable structural simplification  is aimed.

The fact that the rear brakes each have an elec trically controllable brake pressure control valve to a Brake fluid reservoir leading return line device can be connected, which makes the rear axle brake circle both in the EBKV control mode and in the An tiblock control operation as an open brake circuit is drivable, repercussions in this regard Control and regulation processes on the master cylinder and the brake pedal are largely excluded what the "braking" comfort increased significantly.

The safety of the braking system is ensured by this type of Opening of the rear axle brake circuit to the brake fluid The storage container is not impaired because in a malfunction of the electronic control, d. that is, if the control systems are not work, the brake system automatically in an emergency drive state passes in which the brake circuits again are closed. Because the anti-lock braking system - because of the explained opening of the rear axle brake circuit ses - on this according to the principle of pressure reduction operated by draining brake fluid, one is not required for operation of the anti-lock braking system  intermediate feed required according to the return feed principle cher, so that a structural simplification of the slip control system is achieved overall. It Added to this is that caused by the EBKV dynamic operation of the rear axle brake circuit in the a constant exchange of brake fluid between the brake fluid reservoir of the brake system and the rear brakes takes place, which makes them at longer braking processes under changing brakes pressure can be cooled better than with static pressure impact, which also causes fading of the rear wheel braking is largely excluded.

If to monitor the by means of the master cylinder Generable brake pressure only a pressure sensor is seen, it is particularly advantageous if the water, as provided according to claim 2, to the Hin terachs brake circuit II assigned secondary pressure gear of the Tan provided as brake pressure control unit the master cylinder is connected, so that also in If the front brake circuit is defective, otherwise however intact brake system, which delays the vehicle Driver request still reliable recognizable and by means of the electronic control unit in the required control signals for the brake drive of the rear axle brake circuit can be implemented.

Such a malfunction of the front axle brake circuit is by means of the control unit by a logical Ver Linking the output signals from according to claims 3  and / or 4 provided pressure or displacement sensors with the Output signals of the to detect the in the rear provided axle brake circuit coupled brake pressure Pressure sensor easily recognizable and how provided according to claim 5 to increase the Pressure setpoint output signals for the still functional capable rear axle brake circuit before being used moves in indicated by the features of claim 6 benen frame, so that even if the front derachs brake circuit in the partial braking area for a be pedal actuation force practically did the same thing Talk behavior of the brake system results as with fully intact brake system.

It is useful if the high pressure pump of the rear axle brake circuit designed as a self-priming pump is, which results in a more sensitive response of the EBKV control can be achieved.

By the features of claim 8 is simple Way achieved that the brake pressure in the rear axle brake quickly as needed under the initial pressure of the Pre-charge pump can be lowered.

By an operating mode provided according to claim 9 Switch valve with the provided according to claim 10, preferred design is achieved in normal Brake operation the entire delivery rate of the preload pump pe for a sensitive brake pressure control in the back axle brake circuit is available.

Further structural and functional details of the brake pressure control device according to the invention derive from the following description of a special len embodiment with reference to the drawing, the one electrohydraulic circuit diagram one with an invent equipped brake pressure control device according to the invention hydraulic dual-circuit braking system of a road vehicle shows.

The hydraulic dual-circuit brake system 1 shown in the drawing, which has a front-axle / rear-axle brake circuit division, represents a road vehicle which also has an anti-lock braking system (ABS), a device for driving dynamics control (FDR), which can also convey the function of a traction control system and is equipped with a device for electronic control of the brake force distribution (EBKV) on the front axle brake circuit I and the rear axle brake circuit II.

These various control functions are controlled by a "common" electronic control unit 2 which, from processing output signals, the vehicle wheels individually assigned wheel speed sensors 3 , at least one electronic or electromechanical pressure sensor 4 , the electrical output signal of which is a measure of the Brake circuit I when the brake system 1 is applied is brake pressure P _VA , and a further pressure sensor 6 , the electrical output signal of which is a measure of the brake pressure P _HA coupled into the rear axle brake circuit II and, if appropriate, further sensors, such as, for. B. a pedal position sensor 7 , the output signal from which is a measure of the instantaneous position of the brake pedal 8 , by means of which the driver actuates a tandem master cylinder 11 provided for brake pressure control 9 , and / or further sensors, not shown such as a steering angle sender, a yaw sensor or axle load sensors, which generates control signals for brake pressure actuators and / or power actuators to be activated in the individual control types in the respective control purpose in a corresponding sequence and combination.

It is assumed that the description of the functions of the electronic control unit 2 also adequately explains their implementation in terms of circuitry, which, with knowledge of the functions mentioned, is possible to a relevant pre-trained specialist on the basis of his specialist knowledge using common means of electronic circuitry.

The front axle brake circuit I is designed as a static - closed brake circuit, the wheel brakes 12 and 13 both in normal braking operation, in which the electronic brake force distribution control is effective, and in the case of an emergency braking operation, in which, because of a fault in the electronic control unit 2 or the brake pressure actuators, the control systems are switched off, with the output pressure P _VA provided at the primary pressure outlet 14 of the tandem master cylinder 11 .

The rear axle brake circuit II is operated in normal Bremsbe - with the control electronics 2 intact - operated as an open brake circuit and thereby fed with the output pressure of an electrically driven high pressure pump 16 , the high pressure output 17 of which via an output check valve 18 to a main brake line 19 of the rear axle -Brake circuit II is connected, to which the brake line branches 19 'and 19 ''are connected via an inlet valve 21 and 22, respectively, which lead to the rear wheel brakes 23 , 24 , which in turn have an outlet valve 26 and 27, respectively a return line 29 connected to the brake fluid reservoir 28 of the brake system 1 can be connected, via which brake pressure can be reduced in normal braking operation.

The inlet valves 21 and 22 are designed as 2/2-way solenoid valves, the basic position 0 is the open position, in which a brake pressure build-up is possible and the energized position I is the blocking position, the z. B. brake pressure maintenance and brake pressure reduction phases of the anti-lock control and also the EBKV operation and the FDR operation is assigned.

The outlet valves 26 , 27 are also designed as 2/2-way solenoid valves, the basic position O of which is, however, the blocking position, the brake pressure build-up phases and brake pressure holding phases on the rear wheel brakes 23 and / or 24 are / are assigned, and their excited position I is the open position, which is assigned to the braking phases and control phases with brake pressure reduction.

The main brake line 19 of the rear axle brake circuit II is connected to the secondary pressure output 32 of the tandem master cylinder 11 assigned to the rear axle brake circuit II by means of a changeover valve 31 , which is also in the form of a 2/2-way solenoid valve, the changeover valve 31 in its being not excited to stand its control magnet 33 corresponding basic position O is open, that is, the main brake line 19 of the rear axle brake circuit II connects to the secondary pressure output 32 of the tandem master cylinder 11 , and in its excitation of its control magnet 33 with an output signal of the electronic control unit 2 assumes its blocking position I, in which the main brake line 19 is blocked against the tandem master cylinder 11 . This blocking position I is assigned to the normal braking operation, while the basic position O, in which the switching valve 31 "falls back" when there is a fault in the electronic system, is assigned to the emergency braking operation, in which the rear axle brake circuit II is also used as a static brake circuit is operable.

The high pressure pump 16 used in normal braking operation as a pressure source for the rear axle brake circuit II can be connected on the low pressure side via a precharge control valve 34 to the pressure outlet 36 of a further electrically drivable and controllable pump 37 , which at a low output pressure level of e.g. B. works 15 bar and in normal brake operation brake fluid from the reservoir 28 to the low pressure side of the high pressure pump 16 of the rear axle brake circuit II för, whereby this high pressure pump 16 , which is provided for safety reasons with an input check valve 38 , reliably with sufficient braking liquid supply can be operated. The Vorla de-control valve 34 is in turn designed as a 2/2-way Magnetven valve, which has a blocking basic position O and upon excitation of its control magnet 39 with an output signal from the electronic control unit 2 passes into its flow position I, which is the normal braking operation and the FDR operation of brake system I is assigned.

The working as a pre-charge pump for the high pressure pump 16 of the rear axle brake circuit II low pressure pump 37 , the output pressure through a pressure relief valve 40 to the said maximum value of z. B. 15 bar is limited, is also a functional element of the auxiliary pressure source, from which the front wheel brakes 12 and / or 13 can be acted upon individually or jointly with brake pressure in the control phases of the driving dynamics control, with the auxiliary pressure source being the one in the front wheel brakes 12 , 13 provides connectable brake pressure, the Rückförderpum pe 41 of the anti-lock braking system working on the front axle brake circuit according to the return conveyor is used, which has a high pressure pump 16 of the rear axle brake circuit II corresponding design and together with this, for. B. can be driven via an eccentric drive, not shown.

Also in the front axle brake circuit I the Radbrem sen 12 and 13 each individually assigned inlet valves 42 and 43 and exhaust valves 44 and 46 are provided, which are analogous to those of the rear axle brake circuit II in terms of structure and function.

Different from this, however, is that in the front axle brake circuit I to the return line 47 , to which for the purpose of reducing the pressure in the front wheel brakes 12 , 13 these can be connected individually or together via the outlet valves 44 and / or 46 , a never derdruckspeicher 48 connected is, the storage capacity is dimensioned so that it can accommodate the maximum possible amount of brake fluid that can be displaced into the front wheel brakes 12 , 13 and is charged to a pressure level of about 25 bar, and that this low-pressure accumulator 48 or Return line 47 is connected via two hydraulically connected check valves 49 and 51 to the low-pressure input 52 of the return pump 41 , by means of which the anti-lock control and / or the driving dynamics control from the wheel brakes 12 and 13 of the front axle brake circuit during pressure reduction phases I drained brake fluid into the main brake line 53 of the front axle Br Emskreises I is recoverable, from which the two by means of the inlet valves 42 and 43 individually or ge jointly lockable brake line purposes, about which during normal braking and in driving dynamics control mode and also in brake pressure reconstruction, the pressure build-up in the front wheel brakes 12 , 13 takes place .

The directly connected to the return line 47 or the never derdruckspeicher 48 input check valve 49 is controlled by its higher pressure in Niederdruckspei cher 48 or in the return line 47 than at the center tap 54 of the two check valves 49 and 51 in its open position , the force of its valve spring against which the valve comes into its open position is equivalent to a pressure of about 2 to 5 bar.

Located between the center tap 54 and the low-pressure input 52 of the return pump 41 connected non-return valve 51 is designed accordingly and, as controlled by relatively higher pressure at the center tap 54 on the low-pressure inlet 52 of the return pump 41 in its open position.

Between a front axle brake circuit I assigned pressure supply connection 56 of the ABS, FDR and EBKV hy draulic unit explained so far, designated 57 in total, on which, in the case of braking controlled by the driver, at the primary output 14 of the Tandem master cylinder 11 provided output pressure P _VA is present and in the case of an automatically controlled braking, for. B. for the purpose of driving dynamics control a pressure corresponding to the output pressure of the precharge pump 37 is present, and the main brake line 53 of the front axle brake circuit 1 is a structurally and functionally the switching valve 31 of the rear axle brake circuit II accordingly switching valve 58 , which is connected in its the non-excited state of its control magnet 59 corresponding basic position O this pressure supply connection 56 connects to the main brake line 53 of the front axle brake circuit I and in its - lock the - energized position I this pressure supply circuit 56 against the main brake line 53 of the front axle brake circuit I cordoned off. In driving dynamics control operation, this switch valve 58 is switched to its blocking position I.

Furthermore, between these the front axle brake circuit 1 assigned pressure supply input 56 of the hydraulic unit 57 and the center tap 54 of the two input check valves 49 and 51 of the return pump 41 a structurally and functionally the precharge control valve 34 of the rear axle brake circuit II corresponding preload Control valve 61 switched, which is the non-actuated state of its control magnet 62 corre sponding basic position O is its blocking position, which is assigned to normal braking operation, and whose flow position I when driving its control magnet 62 with an output signal from the electronic control unit 2 , the driving dynamics control mode assigned.

For alternative provision of the output pressure at the front axle brake circuit I assigned Druckver supply connection 56 of the hydraulic unit 57 , on the one hand, or the output pressure of the precharge pump 37 , on the other hand, a Vorladezy designated overall with 63 is provided, which in the case of a ge controlled by the driver Braking the function of the primary pressure output 14 of the tandem master cylinder 11 with the pressure supply connection 56 of the hydraulic unit 57 connecting valve, in the case of driving dynamics control has the function of a 1: 1 pressure converter with which the output pressure of the precharge pump 37 is also provided at the Druckversor supply connection 56 and in Fahrdyna mik control operation also provides the function of a shut-off valve that shuts off the primary pressure output 14 of the tandem master cylinder 11 against this pressure supply connection 56 .

This precharge cylinder 63 is designed in the manner of a single-circuit master cylinder which has an output pressure chamber 64 in which pressure can be built up and broken down in alternate directions by axially displacing a piston designated 66 as a whole, at a pressure outlet 14 'Of the precharge cylinder 63 is provided.

This piston 66 has two axially spaced from each other arranged, slidably sealed against the cylinder bore piston flanges 67 and 68 , between which a substantially annular "trailing space" 65 extends, which via a supply connection 69 to the primary pressure outlet 14 of the tandem master cylinder 11 is communicatively connected. The piston 66 of the Vorla dezylinders 63 is urged by a return spring 71 in ne ne defined by the stop effect, the maximum volume of the outlet pressure chamber 64 corresponding basic position, which is shown in the drawing. The trailing chamber 65 against the outlet pressure chamber 64 delimiting flange 67 of the piston 66 is provided with a central valve 72 designed as a seat valve, which in the illustrated basic position of the piston 66 by a stop action between its valve body and a stop pin or tube 73 fixed to the housing of his name Valve seat is lifted off, so that there is a communicating connection between the trailing chamber 65 and the outlet pressure chamber 64 of the precharge cylinder 63 via a central channel of this piston flange 67 .

The second piston flange 68 of the piston 66 of the precharging cylinder 63 forms the axially movable, pressure-tight delimitation of the trailing chamber 65 against a drive pressure chamber 74 which can be struck by a control input 76 with the output pressure generated by the precharging pump 37 .

At a pressure space of a pressure of the actuator 74 resulting displacement of the precharge cylinder piston 66 in the sense of a displacement of the brake of the Vorladezy liquid from the output pressure chamber 64 Linders reaches 63 whose central valve 72 after a small initial portion of the piston into its closed position, so that now in the output pressure space 64 a pressure can be built up, which is the same as the output pressure of the precharge pump 37 in the configuration of the flanges 67 and 68 of the piston 66 with the same cross-sectional area.

Between the pressure output 36 of the precharge pump 37 and the control input 76 of the drive pressure chamber 74 of the precharge cylinder 63 , an operating mode changeover valve 77 is connected, the blocking basic position O of which is assigned to normal braking operation and whose excitation of its control magnet 78 with an output signal of the electronic signal Control unit 2 assumed flow position I is assigned to FDR operation.

Furthermore, a relief valve 79 , also designed as a 2/2-way solenoid valve, is provided which, by energizing its control magnet 81 with an output signal from the electronic control unit 2 from its open basic position O, in which the drive pressure chamber 74 with the brake fluid reservoir 28 is connected, can be switched into its blocking position I, which is assigned to the precharging operation of the precharging cylinder 63 , in which this brake fluid can convey to the return pump 41 of the front axle brake circuit I, if at the same time the operating mode switch valve 77 is switched to its excited position I. . In the illustrated, special embodiment, the relief valve 79 is connected to its own relief output 82 of the precharge cylinder 63 .

The brake system 1 , as far as its structure is concerned, operates in a normal braking operation controlled by the driver with electronically controlled front axle / rear axle brake force distribution as follows:

The precharge pump 37 is switched on, the precharge control valve 34 of the rear axle brake circuit II is switched to its flow position I, the changeover valve 31 of the rear axle brake circuit II is switched to its blocking position I and the high pressure pump 16 is switched on and delivers brake fluid into the main brake line 19 of the rear axle brake circuit II. The operating mode switch valve 77 is in its blocking basic position O, so that the output pressure of the precharge pump 37 is not coupled into the drive pressure chamber 74 of the precharge cylinder 63 of the front axle brake circuit I, the drive pressure Room 74 through which in its basic position O - the discharge position-held by relief valve 79 is connected to the reservoir tank 28 of the brake system 1 . Since the piston 66 of the precharge cylinder 63 takes its ver with maximum volume of the outlet pressure chamber 64 linked basic position, in which the check valve 72 is held by stop action in its open position. Via the changeover valve 58 of the front axle brake circuit I held in its open basic position O, the brake pressure P _{VA provided} by actuation of the master cylinder 11 at its primary pressure outlet 14 can be coupled into it, which also prevails in the secondary output pressure chamber of the tandem master cylinder 11 and is detected by means of the pressure sensor 4 . In response to this front axle brake pressure P _VA , the electronic control unit 2 generates the target value for the brake pressure to be coupled into the rear wheel brakes 23 and 24 in the sense of an ideal brake force distribution, its actual value by means of the pressure connected to the main brake line 19 of the rear axle brake circuit II sensors 6 detected and the electronic control unit 2 is reported back. The braking pressure actual value can be adjusted by pulsed actuation of the inlet valves 21 and 22 . Alternatively or in addition, the increase in brake pressure in the rear wheel brakes 23 and 24 can also be achieved by pulsed activation of the precharge pump 37 and / or the high pressure pump 16 or, if possible, by a continuous change in the delivery capacity of these pumps. It is also possible to control the increase in brake pressure in the rear axle brake circuit II by pulsing the precharge control valve 34 . Maintaining the rear axle brake pressure P _HA at a certain value can be done by shutting off the inlet valves 21 and 22 and / or by locking the precharge control valve 34 of the rear axle brake circuit II and / or by switching off the high pressure pump 16 and possibly the precharge pump 37 be achieved. Brake pressure reduction phases can be controlled by opening the exhaust valves 26 and 27 , while the remaining functional elements of the rear axle brake circuit 11 remain in a functional state suitable for maintaining brake pressure.

Aufanaloge way, in vehicle-dynamics control operation of brake pressure increase valves, -Halte- and brake pressure reduction phases controlled at one or both wheel brake (s) 23 and / or 24 of the Hinterachsbremskreises. 11

In the event of a subsequent activation of one or both wheel brakes (s) 12 and / or 13 of the front axle brake circuit I for the purpose of driving dynamics control, the precharge pump 37 is switched on, the relief valve 79 is switched to its blocking position I, the operating mode switch valve 77 is in whose flow position I, the changeover valve 58 of the front axle brake circuit I in his ne blocking position I and the precharge control valve 61 of the front axle brake circuit I switched to its flow position I. When the precharge pump 37 is switched on or these valves of the front axle brake circuit I are switched on, its return pump 41 is also switched on, which now feeds brake fluid under increasing pressure into the main brake line 53 of the front axle brake circuit. The selection of the driving tool wheel that should not be braked is made by locking its inlet valve.

Brake pressure holding phases can be controlled both by blocking the inlet valves 42 and / or 43 and by switching off the return pump 41 and / or the precharge pump 37 , and by blocking the precharge control valve 61 . In pressure reduction phases of the driving dynamics control operation on the front axle brake circuit I, this is operated as in the return operation with an anti-lock control subjected to braking, the changeover valve 58 and the precharge control valve 61 of the front axle brake circuit again in their respective Basic positions O, in one case the passage position, in the other case the blocking position is switched back and the return pump 41 via the outlet valve (s) 44 and / or 46 from the wheel brake (s) 12 and / or 13 drained brake fluid back into the output pressure chamber 64 of the precharge cylinder 63 , the relief valve 79 in the pressure reduction operation of the front axle brake circuit I in its basic position 0, its flow position, is switched back and expediently also the operating mode switchover valve 77 in its - locking - basic position is switched back.

In the changeover valves 31 and 58 of the rear axle brake circuit II and the front axle brake circuit I pressure limit valves 83 are integrated, which in the blocking positions I of the changeover valves 31 and 58 the prevailing pressure in the main brake line 19 and 53 to a value limit by 150 bar.

In the illustrated embodiment, a pressure sensor 84 is also provided, which monitors the output pressure provided at the primary pressure output 14 of the tandem master cylinder 11 . The output signal of this additional pressure sensor 84 , which can be designed as a simple pressure switch, enables in combination with the output signals of the pressure sensor 4 , which is connected to the secondary pressure output of the tandem master cylinder 11 , to detect a failure of the front axle brake circuit I. In this malfunction, the electronic control unit 2 generates setpoint signals for the rear axle brake circuit II when the braking is controlled by the driver, which corresponds to higher brake pressures than in the trouble-free operation of the brake system 1 , so that the driver continues to experience a desired vehicle deceleration with approximately can control the force that he has to exert with the brake system 1 intact in order to achieve the expected vehicle deceleration.

Claims (11)

1. Brake pressure control device for a road vehicle with a hydraulic multi-circuit brake system, which has a device for driving dynamics control (FDR), a device for electronic control of the front / rear axle brake force distribution (EBKV) and an anti-lock braking system (ABS ) is equipped, whereby

• a) the brake system ( 1 ) has a front axle / rear axle brake circuit division and as a brake pressure control unit a tandem master cylinder ( 11 ) with the brake circuits (I and II) individually assigned pressure outputs ( 14 , 32 ) is provided,
• b) the FDR works according to the principle, by self-activating, electronically controlled activation of one or more wheel brakes ( 12 , 13 , 23 , 24 ) the longitudinal and transverse slip of the vehicle wheels within tolerable limits with dynamic stability of the vehicle hold,
• c) the EBKV works according to the principle, in the case of braking controlled by the driver, to adjust the brake pressure to be coupled into the rear wheel brakes ( 23 , 24 ) to a setpoint value which, based on comparative processing of the output signals, at least one of the brake pressure in the rear axle brake circuit (I) Detecting pressure sensor ( 6 ) with the output signals of a pressure sensor ( 4 , 84 ) continuously monitoring the output pressure at one of the pressure outputs ( 14 , 32 ) of the tandem master cylinder ( 11 ),
• d) the ABS on the front axle brake circuit (I) works according to the return feed principle,
• e) as a pressure source (s) from which, in the case of FDR or EBKV operation, the wheel brake (s) used for the respective control system (s) can be subjected to brake pressure, the brake circuits (I and II ) each individually assigned high-pressure pumps ( 16 , 41 ) are provided, the one on the aisle side via a 2/2-way solenoid valve designed, normally-off precharge control valve ( 34 , 61 ) with the outlet pressure of a precharge pump working at a low outlet pressure level ( 37 ) can be acted upon,
• f) for the hydraulic separation of the front axle and the rear axle pressure supply circuit, the front axle brake circuit (I) is assigned to a precharging cylinder ( 63 );
• f1) the precharge cylinder ( 63 ) has a drive pressure chamber ( 74 ) and an outlet pressure chamber ( 64 ), which are separated from one another by a pressure-tight piston ( 66 );
• f2) the drive pressure chamber ( 74 ) can be connected to the pressure outlet of the precharge pump ( 37 );
• f3) the outlet pressure chamber ( 64 ) can be connected via the assigned precharge control valve ( 61 ) to the input side ( 52 ) of the return pump (high pressure pump 41 ) of the front axle brake circuit I;
• f4) the piston ( 66 ) is provided with two flanges ( 67 , 68 ) arranged axially from one another, between which there is a trailing space ( 65 ) which communicates with the front axle pressure outlet ( 14 ) of the master cylinder ( 11 ) in a constantly communicating manner ) extends;
• f5) of the piston (66) has a check valve (72) blocks a the supply chamber (65) connected with the output pressure chamber (64) flow passage of the piston (66), so long as the pressure in the main pressure chamber (64) is greater than in Trailing space ( 65 ) and the sen flow path releases when the master cylinder outlet pressure is greater than the pressure in the outlet pressure chamber ( 64 );
• g) individually assigned brake pressure control valves are provided for the vehicle wheels, by means of de brake pressure reduction, holding and rebuilding phases of the anti-lock control and the brake pressure metering required on the individual wheel brakes in operating phases of the EBKV and FDR ,
• h) an electronic control device ( 2 ) processes the output signals of the pressure sensors ( 4 , 6 ) and processes the necessary control signals for the activation of the precharge pump ( 37 ), the high pressure pumps ( 16 , 41 ), the excitation of the precharge control valves ( 34 , 61 ) and the pressure control signals for the brake pressure control valves ( 21 , 22 , 26 , 27 , 42 , 43 , 44 , 45 ) of the wheel brakes ( 12 , 13 , 23 , 24 )

characterized by the following features:

• i) the low-pressure side of the high-pressure pump ( 16 ) of the rear axle brake circuit is connected directly to the pressure outlet ( 36 ) of the precharge pump ( 37 ) via the associated precharge control valve ( 34 );
• j) the rear wheel brakes ( 23 , 24 ) - for the control of brake pressure reduction phases - via an electrically controllable brake pressure control valve ( 26 , 27 ) to a brake fluid reservoir ( 28 ) leading return line ( 29 ) can be connected.

2. Brake pressure control device according to claim 1, characterized in that the output pressure of the tandem master cylinder ( 11 ) monitoring pressure sensor ( 4 ) to the rear axle brake circuit (II) associated pressure output ( 32 ) of the tandem master cylinder ( 11 ) is connected. 3. Brake pressure control device according to claim 2, characterized in that a pressure sensor ( 84 ) is provided which generates a characteristic electrical output signal for the primary pressure output space of the tandem master cylinder, which generates the electronic control unit (I) is supplied as an information signal. 4. Brake pressure control device according to one of claims 1 to 3, characterized in that a the position of the brake pedal ( 8 ) or a position of the primary piston of the tandem master cylinder ( 11 ) of the brake system ( 1 ) detecting electronic cal or electromechanical Position transmitter ( 7 ) is provided, the electrical output signals of the electronic control unit ( 2 ) are fed as information signals. 5. Brake pressure control device according to claim 3 or claim 4, characterized in that the electronic control unit ( 2 ) in the event of a failure of the front axle brake circuit (I) increased values of the brake pressures to be coupled into the rear axle brake circuit (II) corresponding to the desired value - Output signals generated. 6. Brake pressure control device according to claim 5, there characterized in that the increased setpoints two to three times that for the malfunction target values generated in free fall. 7. Brake pressure control device according to one of claims 1 to 6, characterized in that the high pressure pump ( 16 ) of the rear axle brake circuit (II) is designed as a self-priming pump. 8. Brake pressure control device according to one of claims 1 to 7, characterized in that an electrically controllable relief valve ( 79 ) which connects the drive pressure chamber ( 74 ) of the precharge cylinder ( 63 ) with the unpressurized brake fluid reservoir ( 28 ) in its basic position and in brake pressure build-up phases of an automatically controlled or driver-controlled braking is switched to its blocking position, in brake pressure reduction phases of normal braking it can be switched back to its basic position if the brake pressure P _HA in the rear axle brake circuit (II) falls below the target value. 9. Brake pressure control device according to one of claims 1 to 8, characterized in that an operating location switch valve ( 77 ) is provided, by means of which the pressure output ( 36 ) of the precharge pump ( 37 ) against the drive pressure chamber ( 74 ) of the precharge cylinder ( 63 ) can be locked. 10. Brake pressure control device according to claim 9, characterized in that the operating location order switching valve ( 77 ) as a 2/2-way solenoid valve is formed, the blocking basic position 0 the normal braking operation and its excited function position I the FDR - Operation assigned by flow position is.