DE102009043484B4

Description

State of the art

[0001] So-called auxiliary power systems with closed brake circuits are used almost exclusively in passenger cars. The exception is the electro-hydraulic brake system EHB, in which the brake circuit is opened to reduce pressure for the ABS/ESP function. If the pressure supply fails, the brake circuit is also closed in the EHB system. For the usual systems with brake force vacuum booster, with tandem master cylinder THZ and separate hydraulic unit, a storage chamber SPK is used for ABS/ESP in the low-pressure circuit.

[0002] In Reimpell Fahrwerktechnik, Radschlupfsysteme, Vogel Business Media Verlag, 1993, p. 285, an ABS system with a low-pressure accumulator, the so-called accumulator chamber SPK, is described between the exhaust valve and the pump. The accumulator chamber is thus switched on in the suction line of the pump. In this system, a check valve is also provided. The accumulator chamber is advantageous for rapid pressure reduction from the wheel brake cylinder, especially when the pressure gradient is high. This is no longer the case when the pressure gradient is low, e.g. on ice with a blocking pressure of approx. 10 bar and a storage chamber pressure of 5 bar. The volume drained into the storage chamber is pumped back into the master cylinder by the pump.

[0003] In the 2003 brake manual, the entire hydraulic ESP system is shown on p. 78. Here, too, the accumulator chamber is installed in the pump circuit between the exhaust valve and the pump, and thus also in the low-pressure circuit in the suction line. A pilot valve is arranged between the pump and the master cylinder HZ, which is necessary if, for ASR or ESP function, the pump draws volume from the master cylinder to build up brake pressure in the wheel cylinder without the brake pedal being depressed. The function of the accumulator chamber is equivalent to ABS. One accumulator chamber is used for each brake circuit.

[0004] An additional accumulator chamber is used in brake systems for hybrid vehicles. Here, this accumulator chamber is located in the primary circuit between HZ and ABS control valves and absorbs the volume from the master cylinder in the phase when the braking torque of the generator during recuperation is high and no or only low brake pressure is allowed. Since the pedal characteristics (displacement and force) should be the same or similar to normal braking without generator, this accumulator chamber acts together with a so-called fluidic pedal force counter-simulation, as known from DE 10 2008 005 145 A1. This pedal force counter-simulation and accumulator chamber are fixed to a value of displacement and counter-force curve. Other solutions with storage chambers are known from WO2009/083217 A2 and WO2009/083216 A2. In the braking system known from WO2009/083217 A2, a certain volume is stored in the accumulator chamber at approx. 5 bar, which is injected or returned to the braking circuit at a certain travel of the HZ piston or pressure. The advantage, especially in a brake system with displacement simulator, is that a master cylinder with a smaller diameter can be used, which means that the required spindle forces and the required motor torque are smaller. This accumulator chamber is used in the braking system according to WO2009/083216 A2 for an adjustment of the brake release clearance in order to eliminate the residual friction of the brake lining, which amounts to approx. 300 W. For this purpose, also in a displacement simulator system according to WO2006/111392 A1, the generic prior art, the HZ piston is steered out and a small volume is stored in the storage chamber. When the pistons are subsequently retracted, a negative pressure is created, which is measured by the pressure transducer. When negative pressure is reached, the subsequent piston movement is in relation to the movement of the brake piston. Preferably, the individual brake pistons are adjusted in succession for clearance.

[0005] The described applications of the low pressure accumulator chambers are either for conventional brake systems with separate brake booster with tandem master cylinder and pressure modulation with the described return pump or a brake system with travel simulator, where pedal movement and HZ piston movement are unequal and are only equal when the brake booster fails.

[0006] A vacuum brake booster is known from DE 10 2006 055 766 A1.

[0007] Based on WO 2006/111 392 A1, it is a task of the present invention to disclose an improved brake system for use in a hybrid vehicle.

[0008] According to the invention, the task is solved by the braking system of independent claim 1 or by the methods according to claims 14 to 17.

[0009] Further advantageous embodiments result from the subclaims.

[0010] The invention is advantageously characterized by the fact that a storage chamber in the form of a fluid reservoir is provided, whereby the storage chamber can be connected to the brake circuit or the pressure line to the wheel brake via a switchable storage valve and the fluid can flow out of the brake circuit or the pressure line into the storage chamber. If the pressure reduction were to take place solely via the HZ or THZ piston of the piston-cylinder system, particularly in the case of rapid pressure changes, this would possibly result in excessively rapid and large and thus disruptive pedal movements due to the reaction of the piston on the brake pedal. The brake system according to the invention advantageously has a highly dynamic electric motor that moves the push rod piston of the THZ via a gearbox or directly and thus performs the function of the BKV and, in the MUX process, enables the pressure modulation for ABS/ESP together with the shift valves. With the braking system according to the invention, very fast pressure changes are possible, which is necessary for the MUX process, since the wheel brakes are usually operated one after the other.

[0011] In the ABS and/or ESP function, the pressure reduction in a wheel brake can be performed either solely by means of the accumulator valve associated with the respective wheel brake and opened, with the fluid from the brake circuit flowing only into the fluid accumulator. However, under appropriate conditions, the control device can perform the pressure reduction by adjusting the piston of the piston-cylinder system and via the fluid accumulator. In this case, for example, the pressure reduction can be carried out first via the fluid accumulator and subsequently or the remaining pressure reduction via the piston adjustment. However, depending on the type of braking process, the pressure reduction in ABS/ESP can also be performed solely by adjusting the piston of the piston-cylinder system via the actuator.

[0012] The high dynamic response results in a correspondingly fast pedal reaction during pressure reduction, which is annoying if larger pressure changes occur during rapid braking or µ-jump, which require large pedal travel changes. The solution according to the invention is to use one fluid accumulator for each brake circuit, but preferably only one fluid accumulator for both brake circuits in the primary circuit together with a pressure transducer between the DK piston and the two 2/2-way switching valves, which are inserted in the connecting line to the wheel brake. The fluid accumulator is advantageously combined with a 2/2-way solenoid valve, i.e. filling and emptying are controlled. If a higher pressure change is now necessary in special cases, part of the brake fluid volume of the wheel cylinder(s) is fed into the fluid accumulator when the valve is open. The remainder of the pressure reduction can be achieved by appropriate piston movement with corresponding pedal reaction. This pedal reaction can hereby be controlled within certain limits by switching on the accumulator chamber of the fluid accumulator proportionally for the pressure reduction. If, for example, small friction value jumps now take place during the control, e.g. water puddles or in winter typically between snow and ice, the pedal reaction is no longer so violent. Also, the piston speed for pressure reduction, i.e. pedal reaction speed, can be varied by the engine. In particular, this method becomes especially obvious in the case of a negative µ-jump, where a strong pedal reaction is noticeable even with the present system, since the return pump has to empty the full accumulator chamber quickly for further pressure reduction cycles. In this case, the pedal reaction can be made much smaller than in the above-mentioned conventional systems according to the state of the art.

[0013] When adjusting the piston of the piston-cylinder system to change the pressure and/or the rate of pressure change in one or more wheel brakes, the pressure-volume characteristics of the individual wheel brakes are advantageously taken into account.

[0014] During continuous control, the volume stored in the fluid accumulator is gradually returned to the master cylinder in small amounts when the master cylinder pressure comes below the accumulator chamber pressure during MUX pressure modulation. In this case, the 2/2-way solenoid valve is opened briefly to inject a small volume into the main cylinder circuit. In borderline cases, such as negative and then positive µ jump, the stored volume can be fed back into the master cylinder circuit by appropriate piston control, thus the brake pedal can return to the pressure-proportional pedal position.

[0015] In addition, the fluid reservoir can be emptied via the piston movement by means of the actuator in phases of large wheel slip and closed shift valves.

[0016] In the prior art described, the accumulator chamber or the fluid accumulator is located in the low-pressure suction circuit of the pump, and the discharge is also determined by the pump and cannot be variably controlled.

[0017] In the braking system according to the invention, the fluid accumulator with its associated 2/ 2-way solenoid valve can be used for all the additional functions described above. These are listed below: a) Pedal control and force feedback for hybrid vehicles and recuperative braking can be performed with the electric motor drive of the piston of the piston-cylinder system together with the fluid accumulator. Here- DE 10 2009 043 484 B4 2018.05.03 5/16 to a fluidic pedal force counter-simulation is not necessary. The electromotive brake booster can thereby advantageously act as desired in the brake force boosting also with reverse action against the pedal force. Pedal travel without hydraulic braking action is possible within wide limits by feeding the master cylinder volume into the fluid reservoir. The electrical gain is fully variable and depends on the desired braking and the available generator braking torque as well as the frictional and restoring forces of the pistons and the drive. b) For brake release control, a small volume is stored in the fluid accumulator in accordance with WO2009/083216 A2, at which the 2/2-way solenoid valve of the fluid accumulator first opens and later closes. When the master cylinder piston is subsequently reset, the clearance of the brake pistons can then be adjusted successively via negative pressure in the piston chambers, since the negative pressure also acts here to adjust the brake pistons. For this purpose, an additional shut-off valve is required between the reservoir and the master cylinder or tandem master cylinder THZ to prevent brake fluid from being drawn in via the piston seal. c) The fluid reservoir can be pre-filled when the brakes are applied. Since the clearance adjustment requires a small additional volume of fluid, this may have a negative effect on the subsequent brake application in the pedal travel. To avoid this, a corresponding small volume can be stored in the accumulator chamber by appropriate piston and switching valve control after the clearance adjustment. This is fed into the master cylinder circuit after the start of braking with an appropriate piston position after closing the sniff hole.

[0018] The accumulator chamber thus has a multiple function for the above functions. In principle, one fluid accumulator in the primary circuit of the push rod piston is sufficient. However, it is also possible to arrange a fluid accumulator with associated accumulator valve in the secondary circuit of the floating piston.

[0019] The fluid accumulator used advantageously has a piston-cylinder system, wherein in particular a fluid accumulator drive or at least one spring acts on the piston for its adjustment, wherein the spring pressurizes, in particular biases, the piston of the fluid accumulator. Thus, in one possible embodiment, the fluid in the brake line can only adjust the piston and thus flow into the fluid accumulator chamber at a pressure greater than a preset or adjustable pressure. At zero pressure in the brake circuit, the fluid accumulator can also be fully drained via the accumulator valve.

[0020] The fluid accumulator can be completely or partially filled or emptied with fluid by means of adjusting the piston of the piston-cylinder system for the various aforementioned functions in cooperation with the pressure sensor as well as the valves and the piston actuator.

[0021] For the aforementioned functions, it is advantageous for the piston movement to use a switch that switches when the piston travel is appropriate, or else a travel sensor to determine the piston position of the fluid reservoir. Also, a pressure sensor can be provided to determine the pressure in the fluid accumulator.

[0022] The size of the volume of the storage chamber of the fluid accumulator may advantageously be adapted to the volume of fluid required for a µ-jump.

[0023] In the following, some possible embodiments of the braking system according to the invention are explained in more detail with reference to drawings.

[0024] They show: Fig. 1: Structure of the braking system according to the invention; Fig. 2: Typical course of the ABS control with the most important data of the control; Fig. 3: Time course of the pressure reduction in the fluid reservoir; Fig. 3a: Time course of the emptying of the fluid reservoir; Fig. 4: Borderline cases of the ABS control; Fig. 5: Function of the brake booster MB = f(Sp) Fig. 5a: Function of the brake booster with the influence of the generator braking effect.

[0025] Fig. 1 shows the basic structure of the system with electric brake booster, which can have a highly dynamic electric motor. Piezo actuators not shown are also conceivable, which move, for example, one piston per brake circuit with two switching valves in the MUX process, and control the pressure change for the brake boosting and the ABS/ESP function. Firmly coupled to the electric motor with preferably spindle drive 2a is the push rod piston 3, which acts hydraulically on the piston 4 in the tandem master cylinder 5 in a known manner. In the brake lines 22, 2/2-way switching valves 7 are arranged DE 10 2009 043 484 B4 2018.05.03 6/16 which, together with the brake booster, enable the multiplex operation described in WO2006/111393 A1. The brake pedal 1 acts on an elastic member 15 via the pedal plunger 1a. The pedal travel is detected by the sensor 13 and the motor rotation is detected by the sensor 14. The sensor 14 can be designed as an angle sensor that also detects the piston travel. The motor drive 2 acts on the piston 3 in a known manner via the spindle 2a. Instead of the spindle, other drives are also conceivable, as described for example in WO2006/111392 A1. The elastic member 15 can serve both for damping in pressure modulation and for damping the pedal reaction in ABS, and can also be used in the differential travel evaluation between pedal travel sensor 13 and piston travel sensor 14 for BKV amplification, as described in WO 2010/ 017 998 A1. The brake force boosting and pressure modulation functions are also described in detail in WO2006/111393 A1 and WO2006/111392 A1. What is new in the brake system according to the invention is that the fluid accumulator 20 with piston 9, return spring 10 and piston travel switch or sensor 24 is arranged directly in the pressure line BL connecting the master cylinder to the switching valves 7, together with a central pressure sensor.

[0026] A second optional fluid accumulator 20' is shown dashed, which allows both brake circuits to be drained into the fluid accumulators.

[0027] The spring 10 preloads the piston 9 to a value between 2 to 4 bar, in particular 3 bar. If the described larger pressure reduction now occurs, the accumulator valve 8 and simultaneously one or more switching valves 7 open and the volume flows into the accumulator chamber of the fluid accumulator 20. The temporal process is explained in detail with reference to Fig. 2 - Fig. 5a. Draining can be performed in a defined manner - as explained later - via the accumulator valve 8, or alternatively via the check valve 16 with throttle, if the main cylinder pressure is lower than the fluid accumulator pressure. A central pressure transducer 12 is installed for pressure modulation and also fluid accumulator control. Instead of a central fluid accumulator 20, a second SPK can also be installed in the SPK circuit.

[0028] A shut-off valve 18, 19 is arranged in each of the supply lines ZL connecting the reservoir 6 to the tandem master cylinder 5. The shut-off occurs when the piston 3 for the brake release control generates a vacuum or a low pressure, and thus a post-sniffing from the reservoir is not possible. Alternatively, this can be avoided by appropriate piston seals in the tandem master cylinder 5 (THZ), so that the shut-off valves are not necessary.

[0029] Fig. 2 shows a typical course of the ABS control with the most important data of the control for the control cycles ① to ⑤. With the start of braking, the rapid pressure build-up takes place, which already triggers a controller signal for pressure reduction at P1. The controller determines the amount of pressure reduction by its setpoint, for example, which corresponds directly to the pedal reaction via the elastic link. If this determined value is above a limit value, the accumulator valve 8 is switched on over the time ΔtMV8 for partial filling of the fluid accumulator 20, which is described in detail with reference to Fig. 3. The main cylinder pressure decreases even further, so that at P2 the pressure reduction is completed. The curve Sp(t) shows the pedal travel over time. Without fluid reservoir 20, the pedal travel would be ΔsP , with fluid reservoir 20, the result is ΔsP-red. The amount of pedal travel feedback can be varied within limits by controlling accumulator valve 8 accordingly. Subsequently, the known pressure build-up begins in cycle ①, which leads to a renewed pressure reduction in cycle ②. Here the pressure reduction is small, so that the accumulator chamber is not switched on until the pressure in the master cylinder HZ is below the pressure of the fluid accumulator 20. Over a short period of time, a small volume is admitted into the main cylinder here. In the process, the accumulator chamber empties by Δss with a corresponding effect in the pedal reaction by ΔsP . This emptying is repeated in the subsequent control cycle ③. In cycle ④, a larger pressure reduction is again necessary, which again requires the activation of accumulator valve 8 over time ΔtMV8. Cycle ⑤ is again normal as in ② and ③, since only a small pressure reduction takes place, which occurs without filling the fluid accumulator 20, i.e. by the piston adjustment alone. Via the small fluid accumulator emptying, the entire fluid accumulator 20 can be emptied in the course of the control, the emptying process being essentially dependent on the degree of filling of the fluid accumulator 20 and the duration of the entire ABS control.

[0030] Fig. 3 shows the time course of the pressure reduction P in the wheel brake RB by means of the fluid accumulator 20 and the piston adjustment of the piston 3. In addition, the path course ss (t) of the piston of the fluid accumulator 20 is shown. At the time ①, the command for pressure reduction is issued by the controller, and at the same time the accumulator valve 8 and the switching valve 7 are actuated, i.e. switched to the open position. After the delay time tvMV/M, the pressure is now reduced via the accumulator valve 8 over the time ΔtMV8. At time ②, accumulator valve 8 closes. This can be followed by a short pressure holding phase, which is used to evaluate the pressure level. The controller compares the pressure difference ΔPMV with the setpoint Δp. After a small time difference of Δt to ②, the motor and thus the piston can be adjusted again by means of the drive DE 10 2009 043 484 B4 2018.05.03 7/16 so that after ΔpK the setpoint value at ④ is reached. In the phase ΔtMV8, the fluid reservoir 20 fills up. In some cases, the entire pressure reduction can be taken care of by ΔtMV8, especially in the higher pressure range. In the low pressure range, the filling pressure of the fluid accumulator 20 of approx. 2 - 5 bar limits the pressure reduction, so that piston adjustment by means of a drive is unavoidable here. It is well known that pressure control via the timing of the solenoid valves is inaccurate. The system has, for example, created or determined a pressure volume map during commissioning, i.e. pressure volume travel characteristics of the entire brake and each wheel brake have been recorded, according to which the pressure control is then carried out via the piston adjustment, i.e. a quotient ΔV/bar is available for the entire control range 100 to 1 bar. On this basis, a further characteristic map for the wheel brakes Δp = f(ΔT, po ) can then be applied, so that pressure control is optionally possible and accurate from one wheel to four wheels simultaneously.

[0031] Fig. 3a shows the temporal process of fluid accumulator emptying. After ①, the solenoid switching valve 7 and the drive motor are activated, preferably simultaneously, and the accumulator valve 8 is activated with a time delay. The pressure reduction via piston adjustment without fluid accumulator filling Sk is initiated when smaller Δp are required by the controller. The dash-dotted course of the main cylinder pressure in the primary circuit of piston 3 falls below the pressure level of the accumulator chamber, particularly at low blocking pressure level of p0. At ②, the PHZ falls below the filling pressure PS of the fluid reservoir 20. Here, the switching valve 7 opens and a selectable small volume is transferred to the primary circuit by the fluid reservoir drain Δss. As already described with reference to Fig. 2, this is repeated for small Δp values until the fluid reservoir 20 is empty. A characteristic diagram ΔS = f(ΔT, pS ) can also be applied for this timing of the accumulator valve 8.

[0032] Fig. 4 shows borderline cases of ABS control: the so-called µ-jump from high to low and back to high. Similar to Fig. 2, the course of vR, vF , pR, sP and ss is shown. At time ① the control starts as described in Fig. 2 and Fig. 3. At time ③, the µ-jump occurs with a large pressure change Δp. As described in Fig. 3, the pressure reduction occurs in stages.

[0033] The storage chamber stroke of the fluid reservoir Δss is correspondingly large, yet there is only a relatively small pedal motion of ΔsP-red. This is considerably smaller compared to the dashed curve of p. To reduce the pedal reaction, the rate of pressure change and thus the rate of pedal change can be reduced at ③a. This can also be applied throughout the control range, especially when the pressure change specified by the controller is small. After pressure reduction, the wheel speed accelerates back to the smaller slip range, so that at ④ the next control cycle already starts at low µ. At ⑤, the positive µ jump now occurs, which can be detected by correspondingly high wheel acceleration. This is immediately followed by a larger pressure buildup +Δp. To ensure that a further necessary pressure buildup subsequently does not lead to large pedal travels, the fluid reservoir is emptied between ⑤ and ⑥ by appropriate piston control until the pressure level is reached again at ⑥ in order to start the control cycles on high µ.

[0034] Alternatively or in addition to this emptying, the fluid accumulator can also be emptied earlier, e.g. after ③a - as shown by the dashed line - at ⑦, in particular if the switching valves 7 are closed due to higher slippage. The emptying can also be implemented in stages to optimize the pedal reaction in any time function. The draining takes place in the interaction of the piston control, control of the switching valves and the accumulator valve.

[0035] With this solution, a considerable improvement in pedal performance is possible compared to today's ABS/ESP. The annoying pedal shocks in rain puddles, ice patches are significantly reduced.

[0036] In the following, another second function "pad clearance adjustment with negative pressure" by means of the fluid reservoir, as known from WO2009/083216 A2, is now described. As is known, a friction power averaging 300 W ≈ 8g CO2 is associated with the lightly contacting brake pads. With the braking system according to the invention, this can be improved in a simple manner. When the braking process is completed, the sequence of air clearance adjustment follows when the driver preferably depresses the accelerator pedal and a speed of more than 10 km/h is present.

[0037] At the beginning of the lining clearance adjustment, piston 3 is advanced by a small distance or volume via motor drive 2. This is dimensioned in such a way that, when pistons 3 and 4 are subsequently moved back, the vacuum for the clearance adjustment of all brake pistons is possible. With valve 8 open, the fluid accumulators 20, 20' are then filled accordingly. The accumulator valves 8 are then closed. After closing the accumulator valves 8, one of the switching valves 7 is opened. The piston 3, which is still in the extended position, is retracted a short distance by the motor spindle drive towards the starting position. This creates negative pressure, which is transmitted via the brake lines 22 to the wheel brake RB with the brake piston whose switching valve 7 is open. Now the remaining three wheel brakes RB are retracted by sequentially opening the respective control valves. The travel of piston 3 is proportional to the travel of the brake piston via the area ratio with the brake piston. In this phase, the vacuum is evaluated via the pressure transmitter 12 so that the piston movement is only evaluated under a pressure level or temporal pressure progression. By temporal pressure progression is meant that if the vacuum is constant over the piston friction, this is equivalent to a movement of the brake piston. Finally, the accumulator valves 8 are opened again. Thus, the negative pressure in the tandem master cylinder THZ is cancelled. The task of the shut-off valves 18 is to prevent brake fluid from entering the working chambers A1 and A2 of the THZ from the reservoir via the THZ seals during the vacuum phase in the THZ. It is also possible to retract all brake pistons of the wheel brakes RB simultaneously by opening all switching valves 7 during the vacuum phase.

[0038] Another third function "pre-filling or post-filling" can also be realized by means of the fluid accumulator. The previously described clearance adjustment requires a small stroke of the brake pistons, which means a small pedal travel extension. This can be eliminated by pre-filling the fluid reservoir after the second function has been completed. For this purpose, when the driver is not braking, the piston 3 is briefly moved over a small distance or up to a certain pressure via the motor drive 2, similar to the second function, but with the switching valves 7 closed. After the corresponding volume has been fed into the fluid accumulator 20, the accumulator valve 8 is closed and the piston 3 is moved back to its initial position. During the following braking, this volume is fed from the fluid accumulator 20 into the braking circuits by switching the accumulator valve 8 when the pistons 3 and 4 have passed over the snuff hole. This procedure can be extended, for example, to use smaller HZ diameters and to reduce the load on the entire drive. For this purpose, a larger volume is stored in the fluid accumulator 20 and preferably delivered to the brake circuits by appropriate piston control when the pedal stroke is larger. This is preferably done at a larger pedal stroke, if necessary also in steps. For the second and third functions, it is advantageous to use a piston travel switch or sensor 24, which is also useful for diagnostics, such as map adjustment.

[0039] The fourth possible function "pedal characteristic for hybrid vehicle" is described below. As is known, the same pedal characteristic with respect to pedal travel and pedal force is desirable both with normal braking and with additional braking action of the generator, e.g., with recuperation. DE 102008005145 A1 describes a solution with an accumulator chamber in cooperation with a fluidic pedal force counter-simulation device with fixed setting of force and travel. This solution is complex and not variable for strongly fluctuating generator braking torques in order to achieve the same pedal characteristics as the normal brake in every case. A pedal travel or piston travel sensor is also missing here, for example. A pressure sensor is arranged e.g. in the floating piston circuit without detailed description of the function and not in the primary circuit of the push rod piston, where also a storage chamber with solenoid valve and a storage chamber without sensor is provided to achieve a pedal travel and a pedal force without effect of the hydraulic brake in case of recuperative braking. In parallel, pressurized fluid is injected into the pedal force counter-simulation device and accumulator chamber to achieve pedal travel characteristics similar to those without generator braking effect.

[0040] In the inventive solution, the pedal force counter-simulation via the electric drive is fully variable in cooperation with the controllable fluid accumulator 20 together with the measurement of the pressure in the primary circuit as well as the pedal travel.

[0041] Fig. 5 describes the function of the normal brake MB = f(sP ) with pedal force and piston force applied by the electric drive in addition to the pedal force. The ratio FK /FP gives the gain.

[0042] Fig. 5a shows in simple illustration the function with action of the generator braking effect MG. The driver applies the brake, where a generator braking effect MG is called up according to the desired deceleration. As the braking torque MB (deceleration) increases, the MB controlled by the driver via pedal force and pedal travel increases. The braking torque MB from the hydraulic brake is only effective after ①. Here, the desired deceleration is greater than the generator braking torque MG, so that pressure is now built up in the brake circuit by closing the accumulator valve and a hydraulic braking torque MP is generated by the braking pressure. In this phase, the usual pedal travel and pedal force are generated up to ① by means of the fluid accumulator 20 and the variable gain of the electric drive. Since this force of the electric drive may not act on the piston 3 with a corresponding counterforce, the volume displacement ss takes place into the fluid reservoir 20. The motor force FM is generated here by the electric drive, which in the first phase up to ① has a correspondingly weaker amplifying effect for the pedal force than DE 10 2009 043 484 B4 2018.05.03 9/16 without generator braking effect MG. Only from ① does FM have a strong reinforcing effect at higher deceleration. Here, from ①, the MP from the pressure in the wheel brakes also acts in accordance with the higher deceleration. In special cases, the force from the electric drive can also act against the pedal force. The dash-dotted lines show the force effect of the electric drive over the pedal travel with and without generator braking effect MG.

[0043] In the present example, MG is constant, but in practice may increase on a case-by-case basis over the deceleration period. In this undrawn case, pressure must be reduced from the wheel brakes by injecting appropriate volume into the fluid reservoir. For this purpose, in addition to the correspondingly controlled piston movement of pistons 3, 4, a pressure measurement via pressure sensor 11 is necessary. The different conditions for the hybrid vehicle with a good brake dosage require a variable pedal force simulation, which is possible with a highly dynamic electric drive.

[0044] These possible functions of high complexity can be realized with a small effort in a highly dynamic electric drive by means of an accumulator valve 8 and the fluid accumulator 20.

List of reference signs