DE112011102270B4

(Representative patent family member)

Actuating device for a vehicle brake system, with a first piston-cylinder unit (4), at least one working chamber of which is to be connected via at least one hydraulic line to at least one wheel brake of the vehicle, and with an electromechanical drive device and an actuating device (10, 5), wherein the actuating device has a further piston-cylinder unit (6, 41), the piston (6) of which can be actuated by means of the actuating device (10, 5) and which is connected to a piston of the first piston-cylinder unit (4) via a connecting device, characterized in that a travel simulator (8) can be actuated by means of the further piston-cylinder unit (6, 41), which travel simulator (8) is connected to the further piston-cylinder unit (6, 41) via a hydraulic line (29) by means of a cut-off valve (22), the further piston-cylinder unit (6, 41) being connected via a hydraulic line (29) and a connecting valve (30) to a further hydraulic line (28) which connects the first piston-cylinder unit (4) to the at least one wheel brake.

[1] Actuating device for a vehicle brake system, with a first piston-cylinder unit (4), at least one working chamber of which is to be connected via at least one hydraulic line to at least one wheel brake of the vehicle, and also with an electromechanical drive device and an actuating device (10, 5),

wherein

the actuating device has a further piston-cylinder unit (6, 41), the piston (6) of which can be actuated by means of the actuating device (10, 5) and which is connected to a piston of the first piston-cylinder unit (4) via a connecting device, characterized in that

a travel simulator (8) can be actuated by means of the further piston-cylinder unit (6, 41), which travel simulator (8) is connected to the further piston-cylinder unit (6, 41) via a hydraulic line (29) by means of a cut-off valve (22), the further piston-cylinder unit (6, 41) being connected via a hydraulic line (29) and a connecting valve (30) to a further hydraulic line (28) which connects the first piston-cylinder unit (4) to the at least one wheel brake.

[2] Actuating device according to claim 1, characterized in that the further piston-cylinder unit (6, 41) is arranged concentrically with respect to the first piston-cylinder unit (4).

[3] Actuating device according to claim 1, characterized in that the further piston-cylinder unit (6, 41) is arranged outside an axis of the first piston-cylinder unit (4).

[4] Actuating device according to one of the preceding claims, characterized in that the further piston-cylinder unit (6, 41) is connected to the actuating device (10) via a gear mechanism or a lever or joint connection (6a, 6b, 6c, 6d).

[5] Actuating device according to one of the preceding claims, characterized in that a currentless open valve (18) is connected in a hydraulic connection between the further piston-cylinder unit (6, 41) and a reservoir (40).

[6] Actuating device according to claim 5, characterized in that the control of the de-energized-open valve (18) is a function of the signals (distance and/or speed) of at least one pedal travel sensor (11).

[7] Actuating device according to claim 1, characterized in that a throttle (19) with a non-return valve (17) is connected in the hydraulic line (29) to the travel simulator (8).

[8] Actuating device according to one of the preceding claims, characterized in that the connecting device has at least one coupling (14, 26), namely a magnetic coupling.

[9] Actuating device according to one of the preceding claims, characterized in that a valve (30) which is closed in the absence of current is provided in each hydraulic connection between the further piston-cylinder unit (41, 6) and at least one working chamber of the first piston-cylinder unit (4).

[0001] The present invention relates to an actuating device for a vehicle brake system, with a first piston-cylinder unit, at least one working chamber of which is connected to at least one wheel brake of the vehicle via at least one hydraulic line, and also with an electromechanical drive device and an actuating device, in particular a brake pedal.

State of the art

[0002] Brake systems of the brake-by-wire type use a travel simulator. There are also so-called power braking systems with a pump and accumulator without a mechanical fall-back level, which are not used much in passenger cars.

[0003] The so-called EHB is known from the prior art in systems with a mechanical fallback level, in which a travel simulator is hydraulically actuated by the main cylinder and a non-linear travel simulator spring acts on the piston. This connection can be disconnected via a solenoid valve in order to avoid pedal loss due to the volume absorption of the travel simulator in the event of a pressure supply failure. However, if the pressure supply fails during braking, the system weakness is unavoidable and can lead to accidents. This concept is described in principle in DE 10 2006 056 907 A1. Here, the solenoid valve is open when de-energized, which means that if the power supply fails, there is a significant pedal loss due to the absorption of the piston volume in the displacement simulator.

[0004] Other solutions based on vacuum brake boosters are described in DE 10 2004 011 622 A1, which aims to ensure that a path simulator is switched on. In this case, the travel simulator is mechanically actuated, combined with the pedal interface and can be switched off by a magnet if, for example, the brake booster (BKV) fails. This also results in a loss of pedal travel. The same application describes a travel simulator (WS) that is arranged in the front part in the axis of the brake booster. Here, the travel simulator is locked by a magnet when the brake booster is intact. If the brake booster fails, this locking mechanism does not work and the brake pedal acts on the tandem master cylinder (THZ) to generate pressure with a smaller pedal loss. The disadvantage here is that if the BKV fails during braking, this pedal loss occurs again. If the system is designed with a small free travel a, the pedal tappet in the ABS system encounters a low coefficient of friction and a small THZ stroke as early as the BKV connecting tappet THZ, so that the travel simulator effect is eliminated. This solution also results in a larger overall length, which is also disadvantageous from a crash point of view, since, for example, the engine presses on the THZ with BKV and thus pushes the pedal back, which can lead to significant foot injuries.

[0005] A further solution is described in DE 10 2008 063 771 A1. Here, the travel simulator is mechanically actuated with an electromechanical travel simulator lock. This is deactivated if the BKV or the power supply fails. In this case, the pedal tappet acts directly on the HZ piston. As the pedal tappet travel and HZ piston travel are decoupled by the travel simulator, smaller piston diameters can be used, which results in lower pedal forces when the BKV fails. This solution is complex and requires a large installation length.

[0006] In the case of WS systems, it is criticized that when braking at a standstill, the hard stop when the WS is activated can be felt and irritates the driver. This is not the case during braking to a standstill, since the foot force immediately follows the vehicle deceleration and the hard stop is only reached during full braking.

[0007] Systems with a travel simulator are extremely critical in terms of safety, since the fallback level must function reliably if the BKV fails. This means that all safety-related components and functions must be diagnosable. These include, for example, the mobility of the travel simulator housing or piston, and the function of the shut-off valves. In systems where the push rod piston delivers the volume into the travel simulator piston when it is actuated, the problem is that if the BKV fails, this volume is missing in the brake circuit, resulting in correspondingly long pedal travel, which irritates the driver. This becomes particularly clear in the extreme case of ABS control set to low µ and full travel simulator activation, followed by a positive µ jump and simultaneous BKV failure. Two effects occur here: considerable pedal travel and a small distance between the DC piston and the floating piston, since the volume for the travel simulator was taken from the DC circuit. When the DC piston hits the floating piston, no further pressure can be built up in the DC circuit.

[0008] The vehicle manufacturers’ specifications call for very high pedal forces, which are about 20 times higher than the pedal force required to reach the locking pressure at high µ. In today’s systems, the ABS/ESP function is disabled, but components such as the HZ, seals, and brake lines must withstand pressures of up to 350 bar.

[0009] New vehicle concepts require a short overall length, in particular between the firewall and the brake pedal linkage.

[0010] An actuating device according to the preamble of claim 1 is indicated by DE 10 2007 062 839 A1.

[0011] DE 10 2008 035 180 A1 describes a braking system that can be used for regenerative braking in hybrid or electric vehicles. In this system, the driver also receives feedback in the form of pedal resistance during regenerative braking.

[0012] Furthermore, DE 10 2010 039 345 A1 describes a braking system in which the driver can brake directly in the event of an electronic failure.

Aim of the invention

[0013] The invention is based on the problem of creating an actuating device of the type mentioned at the beginning, which is improved in terms of overall length, fail-safe performance and pedal travel compared to the known solutions.

Solution to the problem

[0014] The problem is solved by the features characterizing patent claim 1.

[0015] The solution according to the invention, in which a further piston-cylinder unit is used to form an auxiliary piston that is actuated by the actuating device or the pedal tappet, and acts on the first piston-cylinder unit or the main cylinder, an actuating device for a vehicle brake system is created in a surprisingly expedient manner, which, with a short overall length and high level of fault tolerance, largely avoids pedal travel losses.

[0016] Functional embodiments or designs of the invention are contained in the further claims.

[0017] The further piston-cylinder unit or the auxiliary piston can preferably be coaxial with the first piston-cylinder unit or main cylinder, but can also, in particular for reasons of space, be actuated via a lever system and arranged in a staggered manner.

[0018] The auxiliary piston can be movable over the entire pedal stroke and can displace its volume into the mechanical-hydraulic path simulator. This can be connected to the reservoir via a current-controlled 2/2-way solenoid valve (MV). Depending on the pedal stroke, this MV can be switched with variable current.

[0019] If, for example, the simulator piston jams, this MV acts as a pressure relief valve, so that the auxiliary piston can move with increased foot force and, if necessary, act directly on the HZ piston. If necessary, the BKV can also be switched off. This overpressure function can be diagnosed via the armature current.

[0020] The auxiliary piston and the solenoid valve can be diagnosed by coupling the drive unit, in particular the spindle, to the auxiliary piston via a coupling. The spindle can then be moved over the entire stroke using the auxiliary piston and measured via the redundant pedal stroke sensors. In this case, the solenoid valve is open. In a second test, the solenoid valve can be closed, which should not result in any movement of the auxiliary piston; the preferably magnetic coupling will disconnect in this case.

[0021] The redundant pedal stroke sensors can also be tested during this process. The volume of the auxiliary piston can also be supplied to the push rod circuit or to further brake circuits via a further 2/2-way solenoid valve or supply valve. To obtain lower pedal forces in the event of a BKV failure, small master cylinder piston diameters are necessary. However, as is well known, small pressures require a lot of travel for the relatively flat pressure-volume characteristic curve. To this end, the volume of the auxiliary piston is utilized, especially at low pressures. The feed valve can also be tested by moving the pistons with the spindle when the control valves are closed, so that no pressure is built up in the wheel brake cylinders. When the feed valve is closed, the pressure transducer can measure a pressure increase in the DK circuit, but not when it is open.

[0022] In DE 10 2009 031 672 A1, volume is also supplied to the smaller DC cylinder via a 3/2 MV by means of a stepped piston. However, this stepped piston is firmly connected to the DC piston and not separated by a coupling, and is also not designed for a WS system.

[0023] In the critical case of a BKV failure on low µ, the auxiliary piston can also support by feeding the volume of the auxiliary piston and, if necessary, also of the travel simulator to the DK circuit and controlling it in the correct dosage via the pressure transducer. This prevents excessive pedal travel.

[0024] If, in an extreme case, the drive jams during pressure reduction, volume can be released into the reservoir via the open feed valve and pressure control valve, controlled by the pressure transducer. This can also be applied to further brake circuits by means of a further feed valve per brake circuit.

[0025] The pressure control valve can be set to a maximum pressure corresponding to a foot force in conventional systems at which the ABS/ESP no longer functions. At very high foot forces, the auxiliary piston then moves towards the HZ piston when the maximum pressure is exceeded and the path simulator is filled. It hits a stop in the process. In this way, higher pressures are only generated in the auxiliary piston in the brake circuit, only a pressure level that is necessary for the brake for fading. The braking system can therefore be designed for lower pressures, which saves costs and weight.

[0026] The auxiliary piston requires little installation space and is well suited for the articulation and attachment of the sensors in a sensor module, which includes all sensors such as pedal travel and angle of rotation. These can be mounted together with the connector or cable on a small printed circuit board.

[0027] It may also be provided for a sensor module that combines the sensors to be used with the actuating device in a single unit in a simple and advantageous manner.

[0028] The patent application DE 10 2010 045 617 A1 already describes an actuating device of the type mentioned at the beginning, which has a further piston-cylinder unit whose piston can be actuated by means of the actuating device and which is connected to a piston of the first piston-cylinder unit via a connecting device. In this case, an electromotive drive in an integrated design acts as an amplifier. Although this solution has numerous significant advantages over the prior art, it is not possible or desirable in every application. For example, there are cases in which the amplifier, e.g. in the form of an electromotively driven pump, is already present, so that in principle only a master cylinder is required. This applies, for example, to electro-hydraulic braking systems as described in the “Brake Manual”, 1st edition, Vieweg Verlag.

[0029] The invention therefore also provides an actuating device that is improved over the known solutions and that can be advantageously used in systems with an existing amplifier, such as EMS.

[0030] This solution, in which the piston of the further piston-cylinder unit is actuated by the actuating device, provides in a surprisingly practical way an actuating device for a vehicle brake system, in particular a motor vehicle brake system, which can be used in a variety of ways, in particular in cases where an amplifier device is already present or specified.

[0031] This means that the advantages of a further piston-cylinder unit (auxiliary piston), which result in particular from the fact that additional hydraulic volume can be fed into the brake circuits if the brake booster fails, can be applied in a variety of ways. Further advantages are smaller pedal travel and higher achievable pressure levels.

DE 10 2009 031 672 A1 already describes a braking system in which an additional piston-cylinder device (auxiliary piston) can be used to feed additional hydraulic medium either into an expansion tank or into a brake circuit. However, in this system, the auxiliary piston is actuated by an electromagnetic drive in particular.

[0032] Furthermore, a travel simulator can be actuated by means of the pressure in the cylinder of the second or first piston-cylinder unit. The travel simulator can be switched off, in particular via a solenoid valve.

[0033] The further piston-cylinder unit can be switched on and off by means of a solenoid valve.

[0034] As shown in the patent application DE 10 2010 045 617 A1, there are various useful embodiments for the spatial arrangement of the further piston-cylinder unit in relation to the THZ. For the purposes of disclosure, reference is made to these designs, which can be easily adapted to different spatial conditions, e.g. also to shorten the overall length.

[0035] The advantages of the invention and its embodiments are explained in more detail in the following description, with the aid of the drawing.

[0036] It shows:

Fig. 1 shows the system structure of an actuating device of a vehicle brake system;

Fig. 2 shows an alternative arrangement of the further piston-cylinder unit or the auxiliary piston;

Fig. 3 shows the pressure build-up with use of the further piston-cylinder unit or the auxiliary piston in the event of failure of the BKV;

Fig. 4 the pressure control of the solenoid valve;

Fig. 5 the arrangement of sensors used in the actuating device on a module;

Figs. 6a – Figs. 6c the course of the dual-mass piston travel and pedal tappet, pressure and BKV amplification;

Fig. 7 another design of an actuating device.

[0037] Fig. 1 shows in a transparent manner the structure of the system with the known basic components such as electric motor 1, rotor with spindle nut 1 a, spindle 2, push rod piston (DK) 3, tandem master cylinder 4, return spring for DK piston 23, SK piston 21, 2 x switching valves 13, (storage chamber 24 with 2/2 MV 27 according to DE 10 2009 055 721 A1 with DK brake circuit 28), motor-rotation-angle-encoder 15 with redundant pedal-travel sensors 11, brake pedal 11 with pedal tappet 5. These components are described, for example, in DE 10 2005 018 649 A1, which is fully referenced here for the sake of simplicity.

[0038] The brake pedal 10 acts on the auxiliary piston 6 via the pedal tappet 5, with the volume displaced by the auxiliary piston being conveyed to the mechanical-hydraulic travel simulator 8 via a line 45. Redundant pedal-travel sensors 11 are coupled to the movement of the auxiliary piston 6. These sensors control the motor and at the same time actuate the normally-open 2/2 pressure-control solenoid valve 18, i.e. close it.

[0039] The desired reaction to the pedal force is generated by the travel simulator 8. The auxiliary piston 6 is blocked in an intermediate position at about 40% of the total piston stroke S_HK when the travel simulator piston 8a reaches the stop. The solenoid valve 18 has a pressure control function for safety reasons. A pedal-travel-dependent pressure is generated in the auxiliary piston 6 in accordance with the travel simulator spring 8b, which corresponds to the pressure control function shown in Fig. 4. If the travel simulator piston 8a jams, the pedal travel-pressure function is disrupted, i.e. pressure medium flows via solenoid valve 18 to the reservoir 40 via line 29 a.

[0040] With appropriate refinement of the response and switching behavior, e.g. opening of solenoid valve 18 when the pedal movement of the solenoid valve 18 corresponding control is withdrawn, the feedback function of the displacement simulator 8 with piston and spring can be replaced, so that it can be omitted. If necessary, a non-drawn check valve to the reservoir is necessary parallel to the solenoid valve 18 in order to avoid vacuum during the return movement of the auxiliary piston.

[0041] The pressure control function is also used when the extreme pedal forces described are applied. If a corresponding pressure is exceeded, the pressure medium escapes and the auxiliary piston 6 moves after passing through the stroke S_HK to a stop in the housing 41. Depending on the position of the DK piston 3 and the coupled transmission tappet 5 b, the auxiliary piston 6 hits them and generates an additional pressure in the THZ 4, which, however, due to its dimensioning corresponds to the maximum necessary braking pressure, but not to an excess pressure due to the high pedal forces. This means that weight and costs can be saved for the dimensioning. In the event of this overloading, the motor and thus also the ABS/ESP function are switched off. The higher pressure acts exclusively on the auxiliary piston 6 and the path simulator 8.

[0042] It is known to incorporate speed- and direction-dependent throttling of the actuation in order to achieve a good response characteristic. For this purpose, a throttle 19 is incorporated in the line to the displacement simulator 8 and a non-return valve 17 is incorporated for the fast return. The auxiliary piston 6 is reset by the return spring 20. The auxiliary piston 6 with seals is guided and mounted in a corresponding housing 41. This housing 41 can be connected to the motor 1 via a multi-part intermediate housing 42, preferably made of plastic. Housing 41 and intermediate housing can also be in one piece.

[0043] At high pedal speeds, the throttle 19 creates a higher pressure. Accordingly, the setting of the pressure control valve 18 must be correspondingly higher up to the point of movement.

[0044] The auxiliary piston 6 can continue to be used to optimize the braking effect if the BKV fails. If the BKV fails, the pedal force should be as low as possible, which requires small main cylinder piston diameters. If these are used, large pedal strokes are necessary in the low pressure range due to the flat pressure-volume characteristic.

[0045] Via a currentless closed 2/2-way solenoid valve or feed valve 30 (S_E), pressure medium can be conveyed by the auxiliary piston 6 in the lower pressure range to build up pressure in the DK circuit 28. When the pressure is reduced, pressure medium can be conveyed back to the auxiliary piston via the pressure transducer 12.

[0046] Another critical case is described in the introduction, when the BKV fails during ABS operation on ice and a positive µ jump then occurs during braking. In this case, the pressure in the brake circuits is low, in the limit 1 – 2 bar, so that the initial area of the pressure volume characteristic curve at the control point of the path simulator begins with approx. 40% pedal travel, which at the same time represents a piston path and thus a loss of volume.

[0047] In systems in which the DC piston actuates the travel simulator 8, the distance to theSC piston is correspondingly small in this case, with the result that in this critical case, only a relatively low pressure is possible in the DC circuit during the subsequent pressure build-up, which considerably impairs the possible braking effect. DE 10 2009 055 721 A1, mentioned above, describes a system for controlling the free travel of the pistons during ABS operation. To prevent the DK piston from hitting the pedal tappet in the lower pressure range during ABS control, a corresponding piston travel and thus distance to the pedal tappet = free travel is achieved by feeding a corresponding volume into an accumulator chamber 24. The advantage of this system in the critical case is that part of the volume can be recovered back into the brake circuit.

[0048] Instead of the storage chamber 24 with solenoid valve 27, only a 2/2-way solenoid valve 27a can be used for simplification, which is used for idle travel control, i.e. when the distance between the auxiliary piston 6 or pole piece and the transmission tappet becomes too small. If the free travel is too great, volume can be drawn from the reservoir 40 by appropriate piston control, so that this solenoid valve acts in both directions.

[0049] This 2/2-way solenoid valve can also be used for the same function for one or more brake circuits, e.g. in the SC circuit, instead of the storage chamber 24 and the upstream 2/2-way solenoid valve 27.

[0050] These valves can be used for an additional function of snifting volume from the reservoir by appropriate piston control. This replaces the make-up chamber in order to feed additional volume into the brake circuits when the master cylinder piston no longer reaches the necessary pressure. To do this, it is advantageous to make the master cylinder seals thicker in order to be vacuum-tight. A switching device, e.g. a solenoid valve, can also be provided between the reservoir and the master cylinder. This is to prevent air from being sucked into the brake circuits during the above-mentioned post-delivery process. The volume that is discharged back into the reservoir via valve 27a when the pressure is reduced at the end of the braking process is calculated from the pressure and the piston position. This avoids placing too much stress on the main cylinder seals.

[0051] Both cases and solutions with an accumulator chamber or valve 27a can be further improved if necessary by using the volume of the auxiliary piston in this critical case to improve the braking effect via the feed valve S_E 30. The necessary feed and return of the auxiliary piston is controlled by the pressure transducer.

[0052] An additional feed valve can also be used for further brake circuits, e.g. the SK circuit, in order to also feed volume from the auxiliary piston into the SK circuit in the described borderline case in the fall-back level, in order to achieve a higher pressure level or shorter pedal travel.

[0053] Reliable diagnostics of valves 30 and 27a, which open the brake circuit(s) to the auxiliary piston 6 and to the reservoir, are of great importance. This can be done with the proposed diagnostic methods after opening the door by means of piston movement and pressure measurement.

[0054] In this case, the volume stored in the path simulator 8 can also be used or isolated using a separating valve 22.

[0055] The potential of the auxiliary piston makes it possible to take a decisive step towards improving fail-safe performance.

[0056] Equally important is the diagnosis of functionally relevant components. For this purpose, the system has two or at least one coupling. The first force-locking coupling 14, preferably with a permanent magnet 16 embedded in a magnet housing 16a, acts on a pole piece 2a of the spindle. This coupling is necessary on the one hand to reinforce the piston return via the spindle by means of the coupling force, especially at low pressures.

[0057] The second clutch acts on the front end of the transfer tappet 5 b, which is firmly connected to the DK piston 3 via the magnet housing. This force-locking second clutch is also preferably constructed with a permanent magnet with pole 5 a on the auxiliary piston. A small free travel is provided between the pole 5 a and the transmission tappet 5 b / 26, which is used, among other things, for the pedal characteristic and calibration of the pedal travel sensors.

[0058] To diagnose the auxiliary piston movement, spindle 2 with clutch 26 is moved back until the full clutch force is applied at a free travel of 0. In this case, the DK piston is preferably at stop 43. During the subsequent forward movement, the auxiliary piston can be moved over the full stroke S_HK and measured via the pedal travel sensors 11. If the friction force in the piston is too high or the clutch force is too low, the movement stops and the fault is detected. During this movement, valve 18 is open. During a second movement, valve 18 is closed, the movement of the auxiliary piston is stopped via 17 and measured via sensor 11.

[0059] The diagnosis of the pressure control of valve 18 is explained in Fig. 4.

[0060] The diagnosis of feed-in valve S_E 30 with path simulator 8 is carried out by building up pressure via the spindle and piston with the switching valves 13 closed.

[0061] In this case, the pressure transducer and the piston stroke can be used to test both the feed valve 30 and the path simulator. The return spring 17 is used at the spindle outlet to reset the spindle and, for structural reasons, in parallel with the tandem master cylinder 4.

[0062] The accumulator chamber 24 with switching valves 13, 27 is only shown here in the DK circuit and is described in the function for both brake circuits in DE 10 2009 055 721 A1.

[0063] The condition of the vehicle being stationary is ideal for the described diagnosis, preferably after opening the door when entering the vehicle before starting. In this case, the vehicle may have been stationary for a long time, with all the conceivable influences that affect the function, e.g. corrosion, gaskets seizing, etc.

[0064] The cases described with failure of the BKV are based on a functioning on-board electrical system. A total failure of the on-board electrical system while driving is not assumed by the OEM at present. However, should demands be made for the additional functions of the auxiliary piston and the switching of the MV as described, this can be solved with a separate emergency circuit via an ASIC with a small storage capacitor or auxiliary battery.

[0065] An alternative arrangement of the further piston-cylinder unit is shown in Fig. 2. In this arrangement, the auxiliary piston 6 is not concentric, but offset with respect to the axis of actuation of the pressure rod piston 3. The transmission of the pedal force from the pedal 10 via the pedal tappet 5] and transmission element 5c] is carried out by a gear mechanism. This is designed here, for example, as a three-bar linkage.

[0066] The pivot joint works as follows. The first connecting rod 6 c directs the force into the joint carrier 6 d. This rotates around the pivot 6 b. This moves the second connecting rod 6 a, which is supported on the piston 6. Thus, the fluid in the master cylinder 1 is displaced via the line 29 into the path simulator 8. This creates a counter-pressure. This in turn creates a counter-force on the pedal 10, simulating the pedal feel of a conventional braking system for the driver. The rotation of the joint carrier 6 d can be assigned to a defined pedal position. This makes it possible to detect the pedal stroke using a rotary sensor 11, for example. The two connecting rods 6 c and 6 a are preferably designed so that they are at a small angle to the actuating axis 2 and the axis of the piston 6. This means that only small transverse forces arise when the brake is applied.

[0067] The transmission element 3, which is preferably designed as a spindle, is driven by a brake booster 1, which is preferably designed as an electric motor. The booster transmits an axial force to the piston 3, which, in a not shown HZ according to the prior art, supplies the brake fluid to the not shown brake circuit.

[0068] In the fallback level, the solenoid valve 18 is opened. Thus, when the pedal is moved, the fluid is not displaced into the simulator 8, but can flow back into the reservoir 40 without counterpressure. Thus, there is no significant hydraulic loss force at the pedal. Consequently, the entire pedal force can be transmitted from the transmission element 5 to the piston 3. Preferably, an actuating tappet 5 b is located between the transmission element 5 and the piston 3, which engages through the transmission element 3 and is at a distance s from it. Thus, the piston 3 can also be actuated if, for example, the transmission element 3 were to jam.

[0069] One advantage of the offset arrangement of the master cylinder 1 to the actuation axis 2 is that the overall length can be reduced. This is advantageous in vehicles with a small distance between the pedal 10 and the firewall. This makes it possible to install the brake system closer to the brake pedal. This reduces the space required in the engine compartment, which has a particularly positive effect in the event of a crash.

[0070] Fig. 3 shows the pressure or pedal force and pedal tappet travel, S_P with pressure build-up of DK piston and auxiliary piston HK. By intermittent switching, e.g. pressure-dependent via the S_E valve, a considerably higher pressure level can be generated at the same pedal tappet travel S_D at time a than only with the DK piston at considerably lower pedal forces than with the additional auxiliary piston. On the other hand, this means that the flat part of the p – V characteristic curve does not require as much pedal travel and that the system switches to the smaller DK piston when the p – V characteristic curve becomes steeper.

[0071] Fig. 4 shows the progression of pressure, pedal force and valve closing force FM over the travel of the pedal tappet S_P. In displacement simulator systems, the pedal travel force curve is usually mapped, especially in the lower pressure range. At higher pressures, the characteristic curve is steeper in order to save pedal travel, which in turn shortens the response time in the event of a panic stop. Furthermore, the limit current curve i is shown, where, as is well known, the current acts quadratically on the magnetic force FM and thus on the valve closing force. In the S_P1 position, it is assumed that the travel simulator piston jams, which leads to an increase in pedal force and thus pressure. The switching threshold FM₁ is exceeded, which then leads to further pedal movement, since the valve allows the volume from the auxiliary piston to pass through until the magnetic force FM₂ is higher again at S_P2, which in turn leads to renewed pedal movement. The associated movement of the magnet armature produces a current or voltage change, which can be evaluated in relation to the pedal tappet movement SP for diagnostic purposes. It has already been mentioned that the pressure control is a function of the speed of the brake pedal or coupled auxiliary piston.

[0072] The actual current for closing the valve at the respective SP value can also be determined. A braking process is recommended, preferably when the vehicle is stationary. In this case, the corresponding current can be reduced from the limit value in a time-related function until the pressure force on the valve is greater than the magnetic force. This results in a pedal tappet movement that is measured and then the current is immediately increased to the limit value again. If this reaction does not occur, there is a malfunction, so that the BKV can be switched off during a repeated test.

[0073] In the S_P2 position, the path simulator is deactivated. If the high pedal force now occurs, the closing force of the valve is exceeded at the corresponding pressure. The auxiliary piston moves under this high pressure as far as it will go in the housing.

[0074] Fig. 5 shows the combination of several sensors into one module. It was described in Fig. 1 that the system requires a rotation angle sensor to detect the movement of the rotor and thus the position of the piston and two pedal travel sensors (redundant). These are arranged spatially in the pedal interface. It makes sense to combine these into one module with a common electrical connection 39 (plug or multi-core cable) to the ECU, provided that the pedal interface is designed accordingly.

[0075] The sensor component 33/33 a, e.g. a Hall IC, is mounted on the printed circuit board 32. On the other side of the LP32, a rotor 35 is mounted in the housing 31. The permanent magnet 34 is arranged in the rotor with the appropriate polarity to activate the sensor. The sensor optionally provides an analog or digital signal. The rotor can be connected to the spindle nut via a gear wheel 36, for example, or a rack 37 connected to the auxiliary piston can be moved. The sensor module is attached to the intermediate housing part and is arranged within a shielding plate 39 or housing.

[0076] Fig. 6 a shows the relationship between the DK piston travel S_K and the pedal tappet travel with and without the BKV. After the BKV response value, which is essentially dependent on the pedal travel sensor, has been passed through, the DK piston S_K moves very quickly. This rushes ahead of the pedal tappet with the BKV. In the event of a BKV failure, an idle travel 1 is performed until the pedal tappet meets the DK piston and moves it.

[0077] Fig. 6 b shows the pressure curve with and without the BKV. After the response value of the BKV, the pressure builds up suddenly (so-called spring function) and then rises in line with the WS design. Without a BKV, a free travel is necessary until the DK piston closes the snifting hole and the pressure then rises.

[0078] Fig. 6 c shows the BKV amplification as a function of the pedal tappet travel at the top at v > 0 with WS, i.e. the normal function. It is now possible to switch from the WS function at X to the conventional follow-up amplifier function when the vehicle is stationary.

[0079] At this point, the pedal tappet meets the DK piston. After the free travel 1 the amplification is activated, so that the reset forces of the piston and spindle are less noticeable and after the free travel 2 with pressure build-up, it is increased further. The amplification can be selected so that the same pedal feel as with WS is created, but without impact.

[0080] This describes the processes that take place when the vehicle is stationary and braking.

[0081] At X₂ in Fig. 6 a and Fig. 6 c, it is shown when the vehicle is braked from v > 0. In the range between the free travel 1 and 2 of the SK piston, it is steered to the value of the pedal tappet. If a certain pressure, e.g. braking with 10 bar at a standstill, is maintained, the DK piston travel S_K is also synchronized with the SPS value at this value.

[0082] Fig. 7 shows an actuating device 110 for a vehicle brake system. The actuating device 110 has a tandem master cylinder (THZ) 102 whose pressure chambers 103, 104 are connected to a pressureless equalizing reservoir 105. In the housing 106 of the THZ2, pistons 109, 110 are arranged so that they can be pushed axially, supported and sealed by springs 107, 108. At one end of the THZ 102, a further piston-cylinder unit 111 is connected to the THZ 102 or integrated in it. This second piston-cylinder unit 111 can, for example, for reasons of a reduced overall length, also be arranged outside the axis of the THZ 102, as for example in DE 10 2010 045 617.9 of the same applicant, to which full reference is made here for disclosure purposes, or in the form of a stepped piston, which forms a second piston-cylinder unit with a part of the extended diameter and an annular space formed by the part of the smaller diameter, from which additional volume can be supplied, as shown in DE 10 2009 031672 by the same applicant. A piston 113 is arranged axially displaceable in the cylinder part 112 of this second piston-cylinder unit 111, which piston has an extension 114 that passes in a sealed manner through an opening 115 in a partition 116 and rests against the piston 110 in order to act on it.

[0083] An actuating device 117 in the form of a brake pedal 118 is connected to the piston 113 via a rod 122.

[0084] A hydraulic line 125, in which a pressureless open 2/2-way valve 26 is connected, leads from the pressure chamber 112a formed by the cylinder of the second piston-cylinder unit 111 to the equalizing reservoir via an annular groove 127 formed in the THZ 102. Another hydraulic line 128 branches off from this hydraulic line 125, in which a non-return valve 129 is arranged, and leads to the pressure chamber of the THZ. Alternatively, a normally-closed solenoid valve 142 can be used.

[0085] This alternative has the advantage that both the supply of volume from the additional piston-cylinder unit 111 at a pressure level above the pressure transducer 133 and the pressure reduction are controlled. In this case, the volume enters the reservoir via line 128 and solenoid valve 261.

[0086] A hydraulic line 129 branches off from the hydraulic line 128 and leads to a hydraulic path simulator 131 via a pressure-less closed 2/2-way valve 130.

[0087] A pressure sensor or pressure transmitter 133 is arranged in the hydraulic line 132. A hydraulic line leads from the line 128 to a unit (HCU) 35, which may contain valves in configurations not shown in more detail, in order to control or regulate the pressure in the wheel brakes (also not shown).

[0088] Furthermore, the HCU contains an amplifier that has at least one pressure generator, such as an electric motor and pump with corresponding control elements, and thus forms an electro-hydraulic braking device (EHB).

[0089] The operating principle of the embodiment shown in Fig. 7 is described below:

[0090] When the actuating device or the brake pedal 118 is actuated, the piston 113 in Fig. 1 is displaced to the left, thereby displacing hydraulic fluid via the line 128 and the opened valve 126 into the equalizing tank. At the same time, the pressure rod piston (DK) 109 is moved to the left via the extension 114. When the 2/2-way valve 130 is open, the pressure that builds up in the pressure chamber 103 can pressurize the piston of the path simulator 131 that is working against spring pressure. In other words, in this demonstration, the path simulator 131 is controlled by the pressure in the dual-circuit chamber and can be switched off via the 2/2-way valve. In this case, the pressure built up is measured by the pressure transducer and the measured values are fed to an evaluation unit (ECU) (not shown). The pressure desired by the driver or the resulting braking effect is determined, for example, by a displacement sensor 119 on the brake pedal, the measured values of which are fed to the ECU and compared with the values of the pressure transducer. The functionality of the travel simulator 131 can be checked by means of a device with two elements that can be moved relative to each other between the brake pedal 118 and piston 113 and are supported against each other by an elastic element, the relative movement of which is measured by two travel sensors (only one of which is shown here) and evaluated by the ECU. Alternatively, the signal of the position sensor 119 can also be compared with the signal of the pressure transducer 133 and, if the assignment is not plausible, the BKV function can be switched off and reported as a warning.

[0091] In the event that the amplifier fails (fallback level), the 2/2-way valve 128 can be closed so that the volume displaced by the pistons 109 and 113 is used in full for pressure generation, with the hydraulic volume displaced in the further piston-cylinder unit 111 being supplied to the brake circuits as additional volume. The control of the solenoid valve 128 can be done via the pressure transducer 133, so that, for example, a supply of hydraulic fluid to the brake circuit is only up to about 20 bar. Also, the control of the pressure reduction can be done via this solenoid valve, as already mentioned.

[0092] The piston-cylinder unit can also be represented by two units parallel to the axis, e.g. outside the THZ, which has a favorable effect on the overall length.

List of Reference Symbols

1 Electric motor

1a Rotor with spindle nut

2 Spindle

2a Pole piece of spindle

3 Pressure rod piston DK

4 Tandem master brake cylinder

5 Pedal tappet

5 a Pole on the auxiliary piston

5 b Transfer tappet

5 c Transfer element

6 Auxiliary piston

6 a First connecting rod

6 b Pivot axis of the joint carrier

6 c Second connecting rod

6 d Joint carrier

7 Free travel (s) at the pedal tappet

8 Travel simulator or travel simulator housing

8a Travel simulator piston

8b Travel simulator spring

10 Brake pedal or actuation device

11 Pedal travel sensor

12 Pressure transducer

13 Switching valves

14 First clutch

15 Rotation angle sensor

16 Permanent magnet

16 a Magnet housing

17 Spindle return spring

18 Pressure control MV S_D

17 Check valve

19 Throttle

20 Return spring for auxiliary piston

21 Floating piston SK

22 Cut-off valve for path simulator

23 Return spring for pressure-rod piston

24 Accumulator chamber

26 Second clutch

27 2/2-way solenoid valve for accumulator chamber

27 a 2/2-way solenoid valve for empty path control

28 DC brake circuit

29 Line to the path simulator

29 a Line to the reservoir

30 Supply valve S_E or 2/2-way valve

31 Sensor housing

32 Printed circuit board or film

33 Sensor BE of angle of rotation sensor

33 a Sensor BE of pedal travel sensor

34 Magnet

35 Rotor

36 Gear wheel

37 Gear rack

38 Shielding plate

39 Electrical connection

40 Reservoir

41 Housing for auxiliary piston

42 Intermediate housing part

43 DK piston stop

45 Line

101 Actuating device

102 Piston-cylinder unit or tandem master cylinder (THZ)

103 Pressure chamber

104 Pressure chamber

105 Equalizing reservoir

106 Housing

107 Spring

108 Spring

109 Piston (DK)

110 Piston (SK)

111 Piston-cylinder unit

112 Cylinder part

112a pressure chamber

113 piston

114 extension

115 opening

116 intermediate wall

117 operating device

118 brake pedal

119 pedal travel sensor

122 linkage

125 Hydraulic line

126 2/2-way valve

127 Annular groove

128 Hydraulic line

129 Non-return valve

130 2/2-way valve

131 Travel simulator

132 Hydraulic line

133 Pressure sensor or pressure transducer

135 HCU