DE102009055721A1 - Brake system with memory device with multiple function - Google Patents

Abstract

The invention relates to a brake system for a motor vehicle, comprising a master brake cylinder (4, 5) which is driven by an electric drive, a piston tappet (25) being operatively connected to a piston (3) of the master brake cylinder (4, 5), - having wheel brake valves (7) for optionally opening and closing the pressure lines (DL) connecting the wheel brakes (RB) to the master brake cylinder (4, 5), - having an actuating device (1), in particular in the form of a brake pedal, which is connected to a travel simulator ( W) acts, - whereby in the event of a fault, in particular if the drive (2) fails, the actuating device (1) acts mechanically, in particular with the pedal tappet (1a), on the piston tappet (25) to build up pressure in at least one wheel brake, and in normal operation there is an idle path (a) between the piston tappet (25) and the actuating device, in particular between the piston tappet (25) and the pedal tappet (1a), - a control device with brake-by-wire function, which controls the drive (2) and the wheel brake valves (7) for the simultaneous or sequential pressure build-up and pressure reduction in the wheel brakes (RB), - whereby at least one wheel brake (RB) or at least a fluid circuit (20, 20 ') is assigned to a brake circuit, the storage chamber of which can optionally be connected to a pressure line (BL') via a switchable storage valve (8), the pressure line (BL ') forming a working space ...

Description

The present invention relates to a brake system according to the preamble of claim 1.

State of the art

Conventional brake booster (BKV) are known as so-called. Follow-up amplifier, in which the pedal travel is proportional to the piston stroke of the master cylinder. In addition, there are increasingly systems for brake-by-wire operation with path simulator, in which the above assignment no longer applies. Such a system is called "Electrohydraulic Brake (EHB)" in Brake Manual 2nd edition, Vieweg Verlag, p. 251 and 252 , and is not yet optimized in all its features.

For different functions of the brake system Wegsimulationssysteme need a free path between pedal plunger and BKV plunger or HZ pistons to z. B. in ABS pressure modulation to produce little or no pedal feedback or recuperative braking, in spite of the generator braking effect the same assignment of pedal travel and force to the braking effect (vehicle deceleration) exists. In some systems, this free travel acts in case of failure of the brake booster or its drive as a significant pedal travel displacement, which the driver perceives as failure of the brake. This is in the WO2004 / 005095 A1 described. The main task here is in brake-by-wire operation to decouple the pedal from the brake booster. Here, an additional means is proposed, which reduces the free travel in case of failure of the brake booster. This means does not work if the BKV failure already occurs during partial braking, since the agent can not be introduced into the smaller Leerwegspalt here. Extremely critical is the case with full modulation of the path simulator and simultaneous BKV failure, since the free travel is even greater here. Here, the normal driver can not produce sufficient braking effect due to excessive pedal travel or low brake pressure, since the ergonomic limit is about 60 pedal stroke.

In the DE 10 2005 018 649.1 There is described a more advanced waysimulator system having no means for reducing idle travel, thereby having the ABS function revert to the pedal. In the DE 10 2005 059 609.6 is described a system with electromagnetic decoupling, which is only effective in the ABS function or recuperation. For this, a comparison of the Wegsimulatorweges must be carried out with the piston position. At a small distance, the coupling of pedal plunger for piston actuation is released with a free travel. If the brake booster BKV fails during a normal braking, this activation does not have a negative effect. In extreme cases, ie in case of failure of the brake booster on ice, only small blocking impressions, ie pedal travel, are required anyway, so that in this case an additional free travel does not adversely affect. This system has only one detent position.

In the DE 10 06059840.7 is a system with adaptive multi-stage Leerwegschedaltung described, which uses only the free travel and turns on mainly recuperative braking and ABS function in the low coefficient of friction range, z. By S. The effect of the extreme case is the same as above In addition, the actuating magnet is no longer movable, but arranged fixed to the housing.

Object of the invention

The present invention has for its object to provide a simple, continuous, controllable and fail-safe decoupling between pedal plunger and piston of the master cylinder or HZ piston actuation to realize the brake-by-wire functions.

This object is achieved with a braking system with the features of claim 1 advantageous. It is advantageous z. B a recuperative braking with unchanged pedal characteristics and reduction of the pedal reaction in pressure modulation of ABS possible.

The braking systems known from the prior art are relatively complex, especially in assembly, and require high investment at high production volume. In addition, it should be noted that a Wegsimulator braking system, which acts on a tandem master cylinder THZ in BKV failure, still requires additionally a lock of the WS housing. For this purpose, electromechanical and hydraulic solutions are known. Here the task is to integrate this lock in the overall construction with minimal manufacturing and investment costs.

The solution provides, in a multiplex brake system with travel simulator, in which simultaneously or successively the setting of a pressure in the individual wheel brakes, provided in the primary brake circuit between HZ and switching valves at least one fluid reservoir with an upstream solenoid valve. Now enters the case, especially for small Reibbeiwerten that the pedal damper in the pressure modulation for ABS on the HZ piston or a connecting member strikes or threatens to hit, so from the brake circuit or the brake circuits pressure medium is introduced into the memory, so that the Extended piston stroke, and a meeting with the pedal plunger and thus the pedal reaction in ABS is prevented. Optionally, especially in the first control cycle, a act small pedal reaction. Good ABS pressure modulation requires large pressure gradients, especially in the multiplex system. For this purpose, it is proposed to use a switching valve with a large cross-section in front of the fluid reservoir and to achieve the further pressure reduction by rapid return movement of the piston at a low pressure level. This creates a small pedal reaction.

Subsequently, when the wheel brake valves are closed, additional pressure medium is conveyed into the storage chamber (SPK) or the fluid reservoir by corresponding piston movement, in order to ensure the necessary distance from the piston to the pedal tappet.

Another possibility is to continue to fill the fluid reservoir immediately after the pressure reduction in the fluid reservoir then by closing all Radbremsventile by the piston of the HZ. Again, the distance from piston to pedal ram is increased accordingly and can be variably controlled.

If the distance from the piston plunger to the pedal plunger is too large, follows by appropriate piston control emptying of the fluid reservoir in the brake circuits, so that in case of failure of the brake booster or the drive of the master cylinder only a small free travel. This is advantageously a fully adaptive and stepless Leerwegeinstellung the pedal plunger possible.

In recuperative braking, a certain pressure is adjusted depending on the generator braking effect by pressure medium is introduced into the fluid reservoir, so that no contact of HZ piston or link to the pedal ram takes place. The realization of the functions by the fluid reservoir SPK and the associated solenoid valve are similar to known valve blocks for known ABS systems and is effected by slight modification of standard components such as solenoid valve and storage chamber. This results in only small investment costs and the assembly takes place on existing facilities of the ABS / ESP line.

Similarly, the locking of the Wegsimulatorgehäuses via a small piston with cylinder with hydraulic line to the valve block with connection to a standard solenoid valve. At the start of braking, the solenoid valve is turned on, so that the hydraulic line to the valve block / reservoir is interrupted and the piston acting on the Wegsimulatorgehäuse prevents further movement of the Wegsimulatorgehäuses upon actuation of the pedal plunger. In case of failure of the brake booster BKV or its drive, the lock is turned off or the solenoid valve is not energized, so that the hydraulic line is released to the reservoir, and the piston of the locking device can retreat due to the force acting on it from Wegsimulatorgehäuse force. With regard to costs the same applies as for the o. G. Leerwegschaltung. All components, such as. B. THZ, motor with drive, WS with housing, WS-lock, valve block ECU and sensors are advantageously combined in an integrated unit.

However, the used for Leerwegeinstellung fluid reservoir SPK can also for those from the WO2009 / 083216 known functions are used. In the from the WO2009 / 083217 known brake system is stored in the storage chamber a certain volume of about 5 bar, which is fed or returned to the brake circuit at a certain distance of the HZ-piston or pressure. The advantage lies in particular in a brake system with displacement simulator in that a master cylinder can be used with a smaller diameter, whereby the required spindle forces and the required engine torque are smaller. Furthermore, this storage chamber in the brake system according to WO2009 / 083216 be used for a setting of the brake clearance, to eliminate the residual friction of the brake pad, which makes up about 300 W. For this purpose, the HZ piston is also controlled in a Wegsimulatorsystem according to WO2006 / 111392 and stored a small volume in the storage chamber. Subsequent retraction of the pistons creates a negative pressure, which is measured via the pressure transducer. When negative pressure is reached, the subsequent piston movement is related to the movement of the brake piston. Preferably, the individual brake pistons are set in succession to clearance. For all the functions described above, the fluid reservoir SPK used for setting the idle travel can advantageously also be used.

• a) Nachförderung von Volumen aus dem Fluidspeicher SPK in den Bremskreis bei Fahrzeugen mit großer Volumenaufnahme entsprechend DE 10 2007062839.2 mit dem Vorteil der Verwendung eines kleinen HZ-Kolben-Durchmessers mit kleinen Betätigungskräften. Hierzu wird bereits die SPK vor der Bremsung mit einem kleinen Volumen vorgefüllt und wird dann für die Leerwegfunktion weiter gefüllt.
• b) Für die Bremslüftspielsteuerung wird entsprechend der WO2009/083216 ein kleines Volumen im Fluidspeicher gespeichert, bei dem sich zunächst das 2/2-Wege-Magnetventil des Fluidspeichers öffnet und später schließt. Bei der anschließenden Rückstellung des Hauptzylinder-Kolbens kann dann über Unterdruck in den Kolbenkammern nacheinander das Lüftspiel der Bremskolben eingestellt werden, da auch hier der Unterdruck zur Verstellung des Bremskolbens wirkt. Hierzu sind zusätzlich je ein Absperrventil zwischen Vorratsbehälter und Hauptzylinder bzw. Tandem-Hauptzylinder THZ notwendig, damit nicht über die Kolbendichtung Bremsflüssigkeit angesaugt wird.
• c) Es kann eine Vorfüllung des Fluidspeichers bei Bremsbetätigung erfolgen. Da die Lüftspieleinstellung ein kleines Zusatzvolumen an Fluid erfordert, kann sich dies unter Umständen negativ bei der anschließenden Bremsbetätigung im Pedalweg bemerkbar machen. Um dies zu vermeiden, kann nach der Lüftspieleinstellung ein entsprechendes kleines Volumen in der Speicherkammer durch entsprechende Kolben- und Schaltventil-Steuerung abgespeichert werden. Dieses wird nach Bremsbeginn bei einer entsprechenden Kolbenstellung nach Schließen des Schnüffellochs in den Hauptzylinder-Kreis eingespeist.
• d) Bei rekuperativer Bremsung wird die Speicherkammer ebenfalls genutzt. Damit im Vergleich zur normalen Bremsung dieselbe Pedalcharakteristik gegeben ist, erfolgt ein vom Generatorbremsmoment abhängiger Bremsdruck, der vom Bremsenmanagement entsprechend der vom Fahrer vorgegebenen Bremswirkung bestimmt wird. Hierbei erfolgt eine Drucksteuerung im Bremskreis unter Einschaltung der Speicherkammer, damit keine Berührung von Pedalstößel zum HZ-Kolben oder Verbindungsmittel stattfindet – vorzugsweise mit einem kleinen Leerweg.

In the brake system according to the invention, the fluid reservoir with its associated 2/2-way solenoid valve can thus be used for the following additional functions. These are listed below:

• a) Nachförderung of volume from the fluid reservoir SPK in the brake circuit in vehicles with large volume intake accordingly DE 10 2007062839.2 with the advantage of using a small HZ piston diameter with small actuating forces. For this purpose, the SPK is already pre-filled before braking with a small volume and is then filled for the Leerwegfunktion on.
• b) For the brake clearance control is according to the WO2009 / 083216 a small volume stored in the fluid reservoir, in which initially opens the 2/2-way solenoid valve of the fluid reservoir and closes later. During the subsequent return of the master cylinder piston can then be adjusted by means of negative pressure in the piston chambers successively the clearance of the brake piston, since also here the negative pressure acts to adjust the brake piston. For this purpose, in addition ever a shut-off valve between reservoir and master cylinder or tandem master cylinder THZ necessary so that is not sucked on the piston seal brake fluid.
• c) There may be a pre-filling of the fluid reservoir during brake application. Since the Lüftspieleinstellung requires a small additional volume of fluid, this may be negative in the subsequent brake operation in the pedal travel may be noticeable. To avoid this, a corresponding small volume can be stored in the storage chamber by appropriate piston and switching valve control after the Lüftspieleinstellung. This is fed after the start of braking at a corresponding piston position after closing the Schnüffellochs in the master cylinder circuit.
• d) For recuperative braking, the storage chamber is also used. Thus, in comparison to the normal braking the same pedal characteristic is given, a dependent of the generator braking torque brake pressure, which is determined by the brake management according to the braking effect predetermined by the driver. Here, a pressure control in the brake circuit with the involvement of the storage chamber, so that no contact of pedal plunger to HZ piston or connecting means takes place - preferably with a small free travel.

The storage chamber thus has a multiple function for the aforementioned functions. It is sufficient in principle a fluid reservoir in the primary circuit of the push rod piston. However, it is also possible to arrange a fluid reservoir with associated storage valve in the secondary circuit of the floating piston.

The fluid reservoir used advantageously has a piston-cylinder system, wherein in particular a fluid storage drive or at least one spring acts on the piston for its adjustment, wherein the spring pressurizes the piston of the fluid reservoir, in particular biases. Thus, in one possible embodiment, the fluid in the brake line can only adjust the piston at a pressure which is greater than a preset or adjustable pressure and thus flow into the storage chamber of the fluid reservoir. At zero pressure in the brake circuit, the fluid reservoir can also be fully emptied via the storage valve.

The fluid reservoir can be completely or partially filled or emptied by means of adjusting the piston of the piston-cylinder system for the various aforementioned functions in cooperation with the pressure sensor and the valves and the piston drive with fluid.

For the prescribed functions, it is advantageous for the piston movement to use a switch which switches with a corresponding piston travel, or a displacement sensor for determining the piston position of the fluid reservoir. Also, a pressure sensor may be provided for determining the pressure in the fluid reservoir.

The size of the volume of the storage chamber of the fluid reservoir can advantageously be adapted to the volume of fluid required for a μ jump.

The term brake booster used in connection with the brake system according to the invention is understood to mean that the control device of the brake system generates a required or required pressure change in the brake circuit or the wheel brakes by means of the drive of the master brake cylinder in cooperation with the wheel brake valves. An amplification of the foot force acting on the brake pedal does not take place, since, except in the normal case, a free travel between actuator and piston plunger is set / adjusted.

Of course, in all possible embodiments, the control device of the brake system can also control the other brake assistance functions in addition to the ABS, ESP and recuperation functions.

Hereinafter, some possible embodiments of the brake system according to the invention will be explained in more detail with reference to drawings.

Show it:

1 : Structure of the brake system according to the invention;

2 : Construction with advanced functions;

3 : time course of the various functions for the control of the fluid reservoir SPK;

3a : alternative course of the various functions for the control of the fluid reservoir SPK;

4 : time course for the adaptive Leerwegsteuerung.

The 1 shows the basic structure of the highly dynamic motor drive 2 which the piston 3 for pressure change in the wheel brakes RB moves, each wheel brake RB each a wheel brake valve 7 is assigned, so that the brake pressure in the wheel brakes sequentially, ie in multiplex mode, can be adjusted. The drive 2 adjusts the piston 3 also for ABS / ESP function. To the electric motor 2 preferably with spindle drive 2a is the push rod piston 3 preferably firmly coupled, which in the tandem master cylinder 5 in a known manner hydraulically on the floating piston 4 acts. In the brake lines BL are 2/2-way wheel brake valves 7 arranged, which together with the brake booster the in WO2006 / 111393 allow described multiplex operation. The brake pedal 1 acts on the pedal ram 1a on a Wegsimulatorfeder 16 , which in the WS housing 15 is stored. This is preferably in the center of the axle in the housing flange 33 stored.

Of course, the electric motor drive can also be replaced by a piezo element drive.

This pedal ram 1a acts on failure of the drive or brake booster BKV directly on the piston plunger 25 for actuating the HZ pistons 3 . 4 , Between spindle 2a and piston plunger 25 is a clutch 26 , which with intact engine the spindle 2a with the piston 3 connects to allow rapid pressure build-up at low pressure. The path simulator spring 16 is in the path simulator housing 15 stored. The spindle reset is done by the spring 31 , In the pedal plunger 1a can be a damping element 32 be arranged to allow a shock when hitting the plunger 25 is reduced. By appropriate speed control of the piston 3 when approaching the pedal ram 1a This can also be reduced because both positions are via the pedal travel sensor 11 and the rotation angle sensor 14 of the motor 2 are known.

The pedal travel is from the sensor 11 and the motor rotation across the sensor 14 detected. The sensor 14 can be designed as an angle sensor, which also detects the piston stroke. The motor drive 2 acts in a known manner on the spindle 2a on the piston 3 , Instead of the spindle, other drives are conceivable, as exemplified in WO2006 / 111392 are described.

The pedal travel sensor 11 is used for BKV amplification or for pressure build-up and pressure reduction and is preferably redundant. The functions brake booster and pressure modulation are also detailed in the WO2006 / 111393 and WO2006 / 111392 described.

New in the brake system according to the invention is that the fluid reservoir 20 , the piston 9 and the return spring 10 having, via the upstream solenoid valve 8th with the master cylinder 5 and the wheel brake valves 7 connecting pressure line BL is connectable. By means of the piston travel switch or sensor 24 and the central pressure sensor 12 done the fluid storage 20 different functions. Not shown is a second optional fluid store that is in 2 With 20 ' is designated, so that an emptying of both brake circuits in the fluid reservoir 20 . 20 ' is possible.

The feather 10 tenses the piston 9 to a value between 2 to 4 bar, in particular 3 bar, before. Now takes the described greater pressure reduction in the fluid reservoir 20 . 20 ' for the required free travel a, the storage valve opens 8th and at the same time one or more wheel brake valves 7 , And the volume flows into the storage chamber of the fluid reservoir 20 . 20 ' , In detail, the temporal process is based on the 3 to 4 explained. The emptying can be defined - as explained later - via the storage valve 8th respectively. For the pressure modulation and also fluid storage control is a central pressure transmitter 12 built-in.

At the path simulator housing 15 lies the pestle 27a of the piston 27 with the assistance of a return spring 29 at. The piston 27 is in the cylinder 28 guided and via a supply line 30 with a 2/2 solenoid valve 13 connected. This is switched on at the beginning of braking and thus locks the Wegsimulatorgehäuse. In case of failure of the engine 2 this is turned off, and the housing moves with the pedal ram 1a that on the pistons 3 acts to generate pressure. The output line of the solenoid valve 13 is with the reservoir 6 over the master cylinder 5 connected. The cylinder 28 is small and simple and together with the Wegsimulatorgehäuse with spring and pedal plunger with storage makes the structure simple, inexpensive, easy and cheap for installation. The valve block contains the remaining components. The brake system according to the invention advantageously has only six solenoid valves 7 . 8th . 13 and a fluid reservoir 20 on. In comparison, a conventional ESP system requires twelve solenoid valves, two fluid reservoirs and a pump.

In the starting position, the system already has a small free travel a ₀ between the pedal plunger 1a and piston plunger 25 or spindle 2a , This is also in the timeline of the 3 . 3a and 4 shown. This small Leerweg a ₀ is favorable for a small initial force in the pedal characteristic. In addition, when the pedal is pressed quickly, the pedal plunger does not strike the spindle directly.

The 2 shows the structure with two fluid reservoirs 20 . 20 ' and additional valve 8th' for the additional functions.

For the function of Nachförderung, as in DE 10 2007062839.2 are preferably two fluid reservoirs 20 . 20 ' Cheap. According to the Nachfördervolumen of z. B. 2 cm ³ is the fluid reservoir 20 . 20 ' pre-filled before braking. The piston 9 is therefore in an intermediate position. For the Leerwegsteuerung a further volume intake of about 3-4 cm ^{3 is} necessary. Accordingly, the fluid reservoir 20 . 20 ' dimensioned or dimensioned by its volume. The return spring 10 is designed for this function to a pressure of 6 to 8 bar. For fast filling and emptying here are solenoid valves 8th . 8th' used with a large valve cross-section. Preferably, a position switch or sensor 24 used.

Additional brake valves may be required for the function of the brake release control 18 and 19 necessary.

In the supply lines ZL, the reservoir 6 with the tandem master cylinder 5 connect, is in each case a shut-off valve 18 . 19 arranged. The shut-off occurs when the piston 3 generates a vacuum or a low pressure for the brake clearance control and thus a Nachschnüffeln from the reservoir is not possible. Alternatively, this can be avoided by appropriate piston seals and the tandem master cylinder THZ, so that the shut-off valves are not necessary.

Instead of the piston tappet 25 The power transmission can also be applied to the shaft of the spindle 2a respectively.

The 3 . 3a and 4 show the time course of vehicle speed v _F and wheel speed v _R , wheel pressure p _R , piston s _K and pedal travel s _P with the various phases of brake pressure control and Leerwegsteuerung. At (0) is the beginning of braking and at (1) begins the first control cycle with pressure reduction in the fluid reservoir with corresponding movement of the piston s _K. During pressure reduction p _ab in the fluid reservoir 20 becomes the piston movement of the piston 3 Zero, the pedal travel s _P comes delayed and later applies to the resting piston 3 , At time (3), when low pressure level is reached and the pressure reduction gradient by the fluid storage filling is correspondingly small, the further pressure reduction takes place via the piston movement s _{K of} the piston 3 . 4 until the time (4). In this phase, a small pedal reaction occurs, the fluid storage filling is interrupted. This is followed by a fast piston movement of the piston 3 . 4 and a corresponding volume is in the fluid reservoir 20 with closed wheel brake valves 7 promoted. The piston stroke is chosen so that it is well above the locking position of the pedal piston PA, at a distance a. Here, variable - also over time - piston speeds can be used.

The pedal stroke follows here delayed to piston stroke s _K to Pedalstößelanschlag PA, ie when the pedal plunger 1a on the arrested Wegsimulatorgehäuse 15 incident. At (5), the next pressure build-p _to be made. With a small delay t _V , the piston moves 3 the stepped pressure build-up _on p. At (6), the next control cycle begins via the fast piston movement without the use of the fluid reservoir 20 , The pressure reduction times t _from or gradients are due to the large cross-sections of the solenoid valve 8th . 8th' and the rapid piston movement much faster than conventional systems, whereby the deviation of the wheel speed is small, which is the goal of each scheme to achieve high stability and short braking distances.

The 3a shows an alternative when pressure reduction p _from . Here, the pressure reduction p _ab1 after the time (1) takes place only by opening the switching valve 8th in the fluid storage 20 until the time (4a), as is the case with today's ABS / ESP systems, with the difference that the fluid reservoir 20 is arranged in the primary circuit, and that in the higher pressure range due to the larger cross sections of the fluid storage valve 8th larger gradients are achieved. Again, at (1) the piston 3 still, and the pedal ram 1a Delayed on this or the piston plunger 25 , Here, the phase of greater slip takes longer correspondingly, so that at (5) again a pressure build-up with corresponding piston and Pedalstößelbewegung follows, the latter now applies to the lock PA. There is a further pressure reduction p _ab2 at (6) in the fluid reservoir 20 , Only in the next control cycle is (9) the piston 3 at a sufficient distance to the pedal plunger stop PA, so that a rapid pressure reduction p _ab3 on the piston 3 can be done.

The 4 shows a further alternative to depressurization control p _off and Leerwegsteuerung. Between times (1) and (3), the pressure reduction p _ab is again effected in the fluid reservoir 20 , In (3) now takes place a pressure maintenance phase by means of closed Radbremsventile 7 , wherein at the same time the fluid reservoir is further filled and the piston comes well over the pedal ram stop PA. Thereafter, at time (3a), a further pressure reduction p _{ab takes place} via the piston adjustment until the time (4). By this pressure reduction p _from the time duration of the larger wheel slip is greater, so that after the time (5) of the stepped pressure build-up _on p. Again, there is no pedal feedback. Previously, the piston 3 a free path of a ₁ . In (6), the pressure reduction p _ab for the next control cycle via the quick piston adjustment to time (7). Here concludes the corresponding wheel brake valve 7 if necessary with a short stop of the piston movement. The piston movement is continued with emptying of the fluid reservoir 20 until the time (8) with a free travel a ₂ . Here, the adaptive Leerwegsteuerung is shown, which allows both the distance to Pedalstößelanschlag PA and the pedal feedback controlled as desired. If the Leerwegabstand a too large, there is the disadvantage that in case of failure of the drive of the master cylinder, a large Pedalwegverlängerung arises. If in the meantime z. B. during the ABS control, a small pedal effect desired, the free travel a is controlled to zero, so that the next pressure reduction of the piston 3 the pedal ram 1a emotional. The target distance a _will directed _off to the piston movement to reduce the pressure p. When a storage chamber pressure p ₀ of 8-10 bar is reached, further pressure reduction takes place via the piston movement of the piston 3 to achieve a higher pressure gradient in the lower pressure range of about 0-1 bar. The corresponding volume, which decreases from the target pressure p ₀ to 0-1 bar wheel cylinder pressure from the piston 3 must be promoted corresponds to the maximum pedal reaction and applies in all cases where the piston position s _{K is} before the pedal stop PA. The pedal reaction can only be changed with a free travel a equal to zero by a piston movement or piston speed. Also, depending on the road, speed of the vehicle, outside temperature of the controller or the customer by appropriate programming, the described method for pressure control and pedal reaction according to 3 . 3a and 4 to be selected. In conventional systems, the pressure reduction to p _min ≈ 3-4 bar storage pressure is limited according to small pressure gradient, which is disadvantageous in particular ice and aquaplaning.

It should also be considered that, in the case of travel simulator systems, the piston travel s _{k is} greater than the pedal travel s _p , ie an idle travel a is predetermined. Thus, in a normal control in the high pressure range, a sufficient free travel exists, so that the control of the fluid reservoir is not necessary, except for a μ-jump, in which a large pressure change is necessary.

The use of the fluid reservoir for pressure reduction or pressure build-up is mainly suitable for larger pressure changes in the ABS control and in particular at low friction coefficient, in which the distance from the piston to the pedal plunger is small. The solenoid valve should be designed with a large cross-section and with short switching times, in particular short closing time. At high flow rates, however, this leads to strong pressure oscillations. It is advantageous here, the solenoid valve 8th with a stroke control over z. B. PWM, so here the closing operation is controlled by a corresponding change in cross section.

The fluid reservoir can be diagnosed via the volume displacement of the HZ pistons and the pressure transducer both in the set pressure and in the receiving volume or in the stored volume for the Nachförderung in the brake circuit. The same applies to the tightness and the valve cross-section of the switching valve 8th , In this context, the disclosure content of the DE 10 2007062839 directed.

LIST OF REFERENCE NUMBERS

1

brake pedal

1a

pedal tappet

2

motor drive

2a

spindle

3

Push rod piston DK

4

floating piston

5

Brake cylinder HZ

6

reservoir

7

wheel brake valves

8th

Solenoid valve for fluid storage

9

piston

10

Return spring

11

Pedal travel sensor

12

pressure sensor

13

Solenoid valve for locking pistons 27

14

Incremental encoder motor / angle sensor

15

Wegsimulatorgehäuse

16

travel simulator

17

18

shut-off valve

19

shut-off valve

20

Fluid storage / storage chamber

21

22

brake circuit

23

24

plunger sensor

25

plunger rod

26

clutch

27

lock piston

27a

Plunger of the piston 27

28

cylinder

29

Return spring

30

hydraulic line

31

Spindle return spring

32

damping element

33

housing flange

BL

brake line

ZL

supply line

RB

wheel brake

v _R

wheel speed

v _F

vehicle speed

p _R

wheel pressure

S _P

pedal travel

s _K

Piston stroke DK

Δ _{sp red}

reduced pedal stroke with SPK

t _V

Delay time for pressure build-up

a

Distance piston to pedal ram

t _from

Pressure reduction time

PA

Pedalstößelarretierung

p ₀

Storage chamber pressure when switching to piston control

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2004/005095 Al [0003]
• DE 102005018649 [0004]
• DE 102005059609 [0004]
• DE 1006059840 [0005]
• WO 2009/083216 [0015, 0015, 0016]
• WO 2009/083217 [0015]
• DE 102007062839 [0016, 0041, 0051]
• WO 2006/111393 [0031, 0035]
• WO 2006/111392 [0034, 0035]

Cited non-patent literature

• "Electrohydraulic Brake (EHB)" in Brake Manual 2nd Edition, Vieweg Verlag, p. 251 and 252 [0002]

Claims (15)

Brake system for a motor vehicle, - a master cylinder ( 4 . 5 ), which is driven by an electric drive, wherein a piston tappet ( 25 ) and / or a spindle ( 2a ) with a piston ( 3 ) of the master cylinder ( 4 . 5 ), - wheel brake valves ( 7 ) for selectively opening and closing the wheel brakes (RB) with the master cylinder ( 4 . 5 ) having connecting pressure lines (DL), - an actuating device ( 1 ), in particular in the form of a brake pedal, which acts on a travel simulator (W), - being in case of failure, in particular in case of failure of the drive ( 2 ), the actuating device ( 1 ) mechanically, in particular with the pedal ram ( 1a ), on the piston plunger ( 25 ) acts to build up pressure in at least one wheel brake, and in normal operation, in particular a small free travel (a ₀ ) between the piston plunger ( 25 ) and the actuating device, in particular between the piston plunger ( 25 ) and the pedal ram ( 1a ), comprising - a control device with brake-by-wire function having the drive ( 2 ) with piston ( 3 ) and the wheel brake valves ( 7 ) in particular for selectively simultaneous or successive pressure buildup and pressure reduction in the wheel brakes (RB) for the ABS, ESP, and recuperation function controls, - wherein at least one wheel brake (RB) or at least one brake circuit, a fluid reservoir ( 20 . 20 ' ), whose storage chamber is connected via a switchable storage valve ( 8th ) is selectively connectable to a pressure line (BL '), wherein the pressure line (BL') a working space (A ₁ , A ₂ ) of the piston-cylinder system ( 5 ) and at least one wheel brake valve ( 7 ), characterized in that the fluid reservoir ( 20 . 20 ' ) for adjusting the size of the free travel (a) is used. Brake system according to claim 1, characterized in that the control device with active ABS function, ESP function and / or recuperation function, the storage chamber of the fluid reservoir ( 20 . 20 ' ) uses for the supply and discharge of fluid from or into the brake circuit, wherein the free travel (a) increases in the absorption of fluid into the storage chamber and the discharge of fluid in the brake circuit, the free travel (a) decreases. Brake system according to claim 1, characterized in that the fluid reservoir ( 20 . 20 ' ) is arranged in particular in the pressure piston circuit and the filling and emptying of the fluid reservoir ( 20 . 20 ' ), in particular also for setting a brake pad clearance in a wheel brake (RB) and for refilling the brake circuit with fluid, by means of the switching valves ( 7 ) and the storage valve ( 8th ) and by means of appropriate control of the piston drive ( 2 ) he follows. Braking system according to one of claims 1 to 3, characterized in that in the ABS, ESP and / or recuperation function, the pressure reduction in a wheel brake (RB) either a) solely by means of the respective wheel brake (RB) associated and open storage valve ( 8th ) takes place and the fluid from the brake circuit only in the fluid reservoir ( 20 . 20 ' ) flows ( 3a ) or b) by in particular additional adjustment of the piston ( 3 . 4 ) of the piston-cylinder system ( 5 ) in the lower pressure range, in particular at a pressure of less than 10 bar, with simultaneously closed storage valve ( 8th ) he follows ( 3 ), or c) by sole adjustment of the piston ( 3 . 4 ) of the piston-cylinder system ( 5 ) with simultaneously closed storage valve ( 8th ) he follows ( 3 , Time (6), or d) first by filling the fluid reservoir ( 20 . 20 ' ) in the first stage and then in a second stage by the piston movement of the master cylinder ( 4 . 5 ) a further pressure reduction takes place, wherein between the first stage and the second stage, an interruption of the pressure reduction P _ab takes place, during which the fluid reservoir ( 20 . 20 ' ) is filled further, so that the free travel (a) is increased. Brake system according to one of the preceding claims, characterized in that a pressure sensor, the fluid pressure in the storage chamber of the fluid reservoir, in particular for pressure control and diagnosis, or in a brake circuit or a sensor ( 24 ) the piston adjustment of the piston of the fluid reservoir ( 20 . 20 ' ). Brake system according to one of the preceding claims, characterized in that the control device for the adjustment of the piston ( 3 . 4 ) of the piston-cylinder system ( 5 ) takes into account, and in particular determines, the pressure-volume characteristics of the individual wheel brakes (RB). Brake system according to one of the preceding claims, characterized in that the control device by means of the piston drive ( 2 ) regulates or controls a variable pressure gradient in the brake circuit or the piston speed for pedal feedback. Brake system according to one of the preceding claims, characterized in that the travel simulator housing ( 15 ) on a piston ( 27 ) of a piston-cylinder system ( 27 . 28 . 29 ), and the working space of the piston-cylinder system ( 27 . 28 . 29 ) by means of a, in particular in or on the valve block arranged, shut-off valve ( 13 ) for locking the Wegsimulatorgehäuses ( 15 ) can be shut off. Brake system according to one of the preceding claims, characterized in that the master cylinder ( 4 . 5 ), the drive ( 2 ), in particular coaxial with the master cylinder ( 4 . 5 ) path simulator (W), the Wegsimulatorgehäuse ( 15 ) arresting piston cylinder system ( 27 . 28 . 29 ), together with all switching valves, storage chamber with sensors and pressure transducer in the valve block are combined as a unit. Method for operating a brake system according to one of the preceding claims, characterized in that the fluid reservoir ( 20 . 20 ' ) with appropriate control of the switching valves ( 7 ) and the storage valve ( 8th ) and that in the fluid reservoir ( 20 . 20 ' ) stored fluid volume is fed at the beginning of braking in the brake circuit, in particular the Schnüffelloch or the sniffer holes of the master cylinder ( 5 ) by the piston (s) ( 3 . 4 ) is closed or are. Method for operating a brake system according to one of the preceding claims, characterized in that the brake system is arranged in a vehicle with full or partial electric drive, wherein the pedal characteristic of force and travel of the brake pedal while acting on a generator braking torque (recuperation) by filling the fluid reservoir ( 20 . 20 ' ) and the variable gain via the drive ( 2 ) is determined. Method for operating a brake system according to one of the preceding claims, characterized in that in recuperative braking or similar brake-by-wire function to achieve an optimal pedal characteristic of the brake management certain pressure by filling the fluid reservoir ( 20 . 20 ' ) and pressure control in the brake circuit, so that a certain free travel (a) arises. Method for operating a brake system according to one of the preceding claims, characterized in that the travel simulator housing ( 15 ) at each braking by closing the shut-off valve ( 13 ) is locked and in case of failure, the shut-off valve ( 13 ) remains open. Method for operating a brake system according to one of the preceding claims, characterized in that the adjustment of the free travel (a) is variable and adaptive, wherein a free travel a equal to zero a reaction of the piston plunger ( 25 ) on the actuating device ( 1 ) causes. Method for operating a brake system according to one of the preceding claims, characterized in that the solenoid valve ( 8th ) has a large valve cross-section, wherein by means of a stroke control of the valve ( 8th ), in particular by PWM method, the closing characteristic of the valve ( 8th ) can be influenced so that no excessive pressure vibrations in the brake circuit.

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