BRAKING SYSTEM OF A MOTOR VEHICLE AND METHOD FOR CONTROLLING THE SAME

Description

[0001] The invention relates to a braking system of a motor vehicle and a method for controlling this braking system, which comprises a service braking system with pressure-medium-actuated friction brakes, a continuous braking system designed as a hydrodynamic or electrodynamic retarder, at least one electric motor which is drive-connected to the wheels on a vehicle axle and which can be operated at least as a generator, and a foot brake valve which can be actuated by means of a brake pedal, wherein the foot brake valve has a brake value transmitter and a brake pedal actuator for generating a restoring force acting on the brake pedal, and in which the said components of the braking system are controllable by means of an electronic control unit, wherein the braking force requirement signalled by a deflection of the brake pedal is satisfied in priority in the order of the electric motor in generator mode, the retarder and the service braking system.and wherein the distribution of the braking force between the components of the braking system is communicated to a driver of the motor vehicle in an appropriate manner.

[0002] In addition to a service brake system with fluid-operated friction brakes, heavy commercial vehicles usually also have a wear-free continuous brake in the form of a hydrodynamic or electrodynamic retarder, which can decelerate the vehicle without using the friction brakes. When a retarder is used, the kinetic energy of the vehicle in question is converted into heat, which is dissipated into the ambient air by a suitable cooling device. The braking force of a retarder depends on the vehicle's speed or the speed of the drive shaft, for example, the output shaft of a manual transmission, with which a retarder rotor is connected. The usable braking force of a retarder is limited by the amount of heat that can be dissipated, so the activation of the friction brakes may be necessary to prevent the retarder from overheating.In addition, a motor vehicle with a retarder cannot be braked to a standstill, so the friction brakes must be activated at the latest when a minimum driving speed is reached or exceeded.

[0003] With the increasing electrification of vehicles, commercial vehicles, whether purely electric or hybrid, are also being equipped with at least one electric motor. This motor is connected to the wheels on a vehicle axle, can be operated as a motor and as a generator, and can therefore also be used as a wear-free continuous brake in generator mode. When an electric motor is in generator mode, the vehicle's kinetic energy is converted into electrical energy, which can be used in a process known as recuperation to charge an electrical energy storage device. With an electric motor, the usable braking force is limited on the one hand by the amount of heat that can be dissipated and on the other hand by the capacity of the energy storage device. This is why the activation of the retarder and / or the friction brakes may be necessary to prevent the electric motor from overheating or the energy storage device from overloading.

[0004] In an electronically controlled braking system with an integrated continuous braking system of the type just described, the braking requirement requested by a driver via a deflection of the brake pedal and detected by a brake value sensor located on the foot brake valve is distributed among the braking system (brake blending) depending on a defined priority sequence and current operating parameters, such as the driving speed, the operating temperature of the retarder or electric motor, and the charge level of the electrical energy storage device. The priority sequence is usually defined such that during a braking operation, the electric motor is used first in generator mode to decelerate the vehicle in order to charge the electrical energy storage device, the retarder is then activated as needed, and finally, the service braking system with the friction brakes is used to decelerate the vehicle, if necessary.Since the driver of the motor vehicle expects the same resistance force curve at the brake pedal regardless of how the braking force is distributed among the aforementioned components of the braking system, a brake pedal actuator is usually present. This actuator is operatively connected to the brake pedal and generates a restoring force that is then applied to the brake pedal. This restoring force is dimensioned such that, together with the resistance forces generated within the foot brake valve, such as the spring force of a return spring acting on the brake pedal and / or the pressure force of the pressure medium acting on a control piston, a resistance force corresponding to the total braking force is established at the brake pedal.

[0005] DE 11 2007 000 071 B4 discloses a braking system for a hybrid vehicle. It comprises a service braking system with hydraulically actuated friction brakes and electric motors that are connected to the wheels of a vehicle axle and can be operated as motors and generators, as well as a foot brake valve that can be actuated via a brake pedal and a brake value transmitter designed as a pressure sensor that is connected to a main brake line. The drive train of the hybrid vehicle has an internal combustion engine coupled to an electric generator. The electric motors drive the hybrid vehicle in motor mode and brake it in generator mode. The electrical energy generated by the electric motors in generator mode is converted into heat in a heat radiator and dissipated into the ambient air.During braking, the hybrid vehicle is decelerated by the electric motors operating as generators, in addition to the friction brakes of the service brake system, depending on the deflection of the brake pedal. However, during braking with a slight deflection of the brake pedal, the hybrid vehicle is decelerated solely by the friction brakes of the service brake system to ensure precise control of the braking force.

[0006] US 2004 / 0251095 A1 describes a braking system for an electric vehicle, which comprises a service braking system with hydraulically actuated friction brakes and an electric motor that is drive-connected to the wheels of a vehicle axle and can be operated as a motor and as a generator, as well as a main brake valve that can be actuated via a brake pedal, a brake value sensor arranged on a brake lever of the brake pedal, and a brake pedal actuator for generating a restoring force acting on the brake pedal. In a first embodiment, the brake pedal actuator is designed as an electric motor that is actuated by a rack and pinion gear to the brake lever. In a second embodiment, the brake pedal actuator is designed as a hydraulic or pneumatic actuating cylinder whose piston rod is actuated by a brake lever.During braking, the braking force requested by the deflection of the brake pedal is distributed between the friction brakes of the service brake system and the electric motor operating as a generator. The brake pedal actuator generates a restoring force and transmits it to the brake lever. This force corresponds to the portion of the braking force generated by the generator, so that the driver perceives the same restoring force on the brake pedal as during a purely hydraulic braking operation.

[0007] DE 10 2012 209 157 A1 discloses a braking system for an electric or hybrid vehicle, comprising a service braking system with fluid-operated friction brakes and at least one electric motor that is drive-connected to the wheels of a vehicle axle and can be operated as a motor and a generator, as well as a foot brake valve that can be actuated by a brake pedal and has a brake value sensor and a brake pedal actuator for generating a restoring force acting on the brake pedal. During braking, the motor vehicle is initially decelerated by the electric motor operating as a generator. Before the electric motor reaches its maximum braking torque, the service braking system with the friction brakes is activated.A control system determines a restoring force based on the deflection of the brake pedal and the maximum or currently available or recuperable braking torque of the electric motor. This restoring force is adjusted using the brake pedal actuator. Before the electric motor reaches its maximum braking torque, the service brake system with the friction brakes is activated, which is communicated to the driver via an increased restoring force on the brake pedal.

[0008] DE 10 2018 114 848 A1 discloses a foot brake valve for an electronically controllable pneumatic brake system. The valve comprises a brake signal transmitter configured as a travel sensor and an electropneumatic brake pedal actuator for generating a restoring force acting on the brake pedal. The brake pedal actuator is flanged to the housing of the foot brake valve with an open pressure chamber, which can be ventilated via an inlet valve and vented via an outlet valve, adjacent to a spring plate. The spring plate is guided axially displaceably within the housing of the foot brake valve and primarily serves to support a return spring, against which a plunger piston, which can be axially displaced via the brake pedal, rests. A partially or gradually increased return force can be introduced into the brake pedal via the brake pedal actuator.During a braking process with ABS control activated, pressure pulses can be introduced into the brake pedal via the brake pedal actuator, which are perceived by the driver as a vibration and are intended to indicate the currently effective ABS control.

[0009] In a motor vehicle with a braking system comprising a service brake system with friction brakes, a retarder, and at least one electric motor that can be operated as a generator, the distribution of braking force among the components of the braking system can be shown to the driver during a braking operation, for example, on a display in the dashboard. The driver can then influence the braking process by actuating the brake pedal in such a way that, for example, the application of the friction brakes of the service brake system is avoided, thus preventing wear on the friction linings, brake discs, or brake drums.However, since the driver should not take his eyes off the road ahead during heavy braking in order to keep the vehicle on the road, avoid a collision with another vehicle or avoid an obstacle, additional haptic information on the current distribution of the braking force on the brake pedal is desirable.

[0010] The present invention is therefore based on the object of presenting a method for controlling a braking system of a motor vehicle of the type mentioned above, with which the driver can be appropriately informed of the distribution of his braking request among the components of the braking system. Furthermore, a braking system is to be presented and described with which the aforementioned method can be operated.

[0011] The method-related problem is solved by a method having the features of claim 5. The features of the independent device claim (claim 1) characterize a braking system that solves the device-related problem. Advantageous embodiments and further developments are defined in the respective associated dependent claims.

[0012] A braking system of a motor vehicle is claimed, which comprises a service braking system with pressure-medium-actuated friction brakes, a continuous braking system, designed as a hydrodynamic or electrodynamic retarder, at least one electric motor which is drive-connected to the wheels on a vehicle axle and which can be operated at least as a generator, and a foot brake valve which can be actuated by means of a brake pedal, wherein the foot brake valve has a brake value transmitter and a brake pedal actuator for generating a restoring force acting on the brake pedal, and in which the said components of the braking system are controllable by means of an electronic control unit, wherein the signalled braking force requirement is satisfied in priority in the order of the electric motor in generator mode, the retarder and the service braking system,and wherein the distribution of the braking force between the components of the braking system can be communicated to a driver of the motor vehicle in a suitable manner.

[0013] To achieve the device-related task, this brake system is provided with the brake pedal actuator being electrically effective and having a rotatable or axially displaceable drive element, and with the drive element of the brake pedal actuator being directly or indirectly connected to a brake lever of the brake pedal or to a tappet piston of the foot brake valve.

[0014] In a preferred embodiment, the braking force is signaled by deflecting the brake pedal. In another preferred embodiment, the braking force requirement is automatically signaled by electronically controlled braking requests. For example, in advanced braking systems such as ESP (Electronic Stability Program), ESC (Electronic Stability Control), and ASR (Anti-Slip Regulation), the vehicle deceleration and / or braking force requirement can be controlled or calibrated independently of the driver's braking request, which is indicated by deflecting the brake pedal.

[0015] Compared to the prior art designs as hydraulic or pneumatic actuating cylinders, this electrically effective design of the brake pedal actuator has the advantages of better or faster response behavior and more precise dosing of the restoring force and the signal force acting on the brake pedal.

[0016] According to a first refinement of this braking system, the brake pedal actuator is designed as an electric motor with a rotatable rotor shaft. The rotor shaft of the electric motor is connected directly or indirectly to the brake lever of the brake pedal or to the plunger piston of the foot brake valve via a spindle gear.

[0017] Alternatively, it can be provided that the brake pedal actuator is designed as an electromagnet with an axially displaceable armature, wherein the armature of the electromagnet is directly or indirectly connected to the brake lever of the brake pedal or to the tappet piston of the foot brake valve.

[0018] Accordingly, the invention initially relates to a method for controlling a braking system of a motor vehicle, which comprises a service braking system with pressure-medium-actuated friction brakes, a continuous braking system, designed as a hydrodynamic or electrodynamic retarder, at least one electric motor which is drive-connected to the wheels on a vehicle axle and which can be operated at least as a generator, and a foot brake valve which can be actuated by means of a brake pedal, wherein the foot brake valve has a brake value transmitter and a brake pedal actuator for generating a restoring force acting on the brake pedal, and in which the said components of the braking system are controllable by means of an electronic control unit, wherein the braking force requirement signalled by means of a deflection of the brake pedal is satisfied in priority in the order of the electric motor in generator mode, the retarder and the service braking system,and wherein the distribution of the braking force between the components of the braking system is communicated to a driver of the motor vehicle in an appropriate manner.

[0019] In order to solve the process-related problem, this braking system is provided with the feature that, when the distribution of the braking force to the components of the braking system is changed at least once by means of the brake pedal actuator, the restoring force acting on the brake pedal is briefly superimposed with a haptically perceptible signal force.

[0020] The advantage of this is that the driver of the vehicle is only informed about a change in the distribution of braking force among the components of the braking system for a very short period of time, meaning that no permanent change in the restoring force acting on the brake pedal is noticeable. Since this information is also transmitted via the brake pedal to the driver's foot, the driver can continue to focus his or her attention on the road ahead.

[0021] According to a first refinement of the described method, when at least one of the components of the braking system is engaged or disengaged by the brake pedal actuator, the restoring force acting on the brake pedal is briefly superimposed with a haptically perceptible signal force. The advantages just mentioned also apply to this variant of the method. However, in this refinement of the method, the driver is only informed by the additional signal force acting on the brake pedal when one of the components of the braking system is fully engaged or fully disengaged.

[0022] By generating a haptically perceptible signal force using the brake pedal actuator and introducing this signal into the brake pedal, the driver of the vehicle is informed of a change in the distribution of braking force between the components of the braking system that is currently taking place or has just occurred. For example, this can be the activation or deactivation of the electric motor in generator mode, the retarder, or the service brake system. Since this information is signaled to the driver via the brake pedal, they do not need to take their eyes off the road ahead to acknowledge the information. In response to the signal force, the driver can influence the distribution of braking force between the aforementioned components of the braking system by actuating the brake pedal accordingly.For example, during electric braking in generator mode of the electric motor, the driver can prevent the retarder from being activated by slightly releasing the brake pedal, providing the traffic situation allows for a lower braking deceleration.

[0023] In this case, it may be advantageous for the perceptibility of the current distribution of the braking force to the components of the braking system if the signal force changing the restoring force on the brake pedal is effective as at least a pulse-shaped increase in the restoring force.

[0024] To enable a distinction between the activation and deactivation of the components of the braking system during a braking operation, it is preferably provided that the pulse-shaped signal forces applied during different changes in the distribution of the braking force differ from one another in terms of their number, strength, and / or duration. This will be discussed further in the explanation of an exemplary embodiment.

[0025] According to a further method variant, the signal force is applied in the form of a vibration sequence comprising several oscillations of the restoring force, perceptible as a vibration on the brake pedal. With this embodiment of the signal force, the oscillation sequences applied during different changes in the distribution of the braking force can differ from one another in terms of their frequency, amplitude, and / or duration.

[0026] Of course, the aforementioned method variants can also be used in combination, for example, in such a way that the activation or deactivation of at least one component of the braking system, for example, the electric motor operable as a generator, is signaled by a signal force in the form of at least one pulse-shaped increase in the restoring force. In contrast, the activation or deactivation of another component of the braking system, for example, the service braking system with the friction brakes, is brought to the driver's attention by a signal force in the form of a perceptible vibration sequence comprising several oscillations of the restoring force.

[0027] The method and the braking system with the features of the invention are explained below using an exemplary embodiment shown in the attached drawing. Fig. 1 in a schematic view a motor vehicle with a braking system having the features of the invention, and Fig. 2 a force-time diagram in which the course of a braking process with an application of the control method according to the invention is illustrated.

[0028] The Fig. 1 The motor vehicle 2 shown, which is a commercial vehicle, has a single-tire front axle 4 with two wheels 6a, 6b and a double-tire rear axle 8 with a total of, for example, four wheels 10a, 10a', 10b, 10b'. The motor vehicle 2 can be driven selectively or jointly by an internal combustion engine 12 and / or by an electric machine 24 that can be operated selectively as a motor or generator. The internal combustion engine 12 is drive-connected to the wheels 10a, 10a', 10b, 10b' of the rear axle 8 via a separating clutch 14, a manual transmission 16, a cardan shaft 18, a first axle differential 20, and a respective drive shaft 22a, 22b. The electric motor 24 is connected to the wheels 6a, 6b of the front axle 4 via a drive shaft 26, a second axle differential 28, and a drive shaft 30a, 30b. During engine operation, the electric motor 24 is supplied with electrical energy from an associated electrical energy storage device 32.In generator mode, the electric machine 24 is preferably used to charge the energy storage device 32.

[0029] The braking system 34 of the motor vehicle 2 is electronically controllable and comprises, in addition to an electronic control unit 36, a service braking system 38 with fluid-actuated wheel brakes 40a, 40b, 42a, 42b designed as friction brakes, a continuous braking system or secondary brake 44 in the form of a hydrodynamic or electrodynamic retarder, which is connected to the electric motor 24 drivingly connected to the wheels 6a, 6b of the front axle 4, and a foot brake valve 48 actuated by a brake pedal 46, which can be directly or indirectly connected to a brake value transmitter 50 designed as a travel sensor and a brake pedal actuator 52. The brake pedal actuator 52 serves to generate a restoring force acting on the brake pedal 46. For its control, it is connected to the electronic control unit 36 ​​via an electrical control line 54.

[0030] An axially or rotationally acting drive element 53 is arranged on the brake pedal actuator 52, by means of which a signal force can be exerted on the brake pedal 46 in addition to the aforementioned restoring force.

[0031] The service brake system 38 is designed as a compressed air brake system and has a compressed air supply device 56 and two brake circuits 58, 60. The compressed air supply device 56 comprises a compressor 62, a pressure regulator 64, and a multi-circuit protection valve 66. Compressed air is pumped from the compressor 62, which is driven by the internal combustion engine 12, into the two brake circuits 58, 60 via the pressure regulator 64 and the multi-circuit protection valve 66.

[0032] The first brake circuit 58 has a first pressure accumulator 70 and a first supply line 68, which leads from the multi-circuit protection valve 66 to the foot brake valve 48. A first axle brake line 72 is connected to the foot brake valve 48, into which a brake pressure is applied depending on the actuation of the brake pedal 46. The first axle brake line 72 leads to a first axle valve module 74 on the rear axle 8.

[0033] The first axle valve module 74 comprises a relay valve and preferably one ABS valve arrangement (not shown) for each wheel pair 10a, 10a'; 10b, 10b' of the rear axle 8. It should be noted that the presence of the ABS valve arrangement of the first axle valve module 74 is only an optional feature, particularly if the first axle valve module 74 is designed as an electronically controllable valve module. A wheel brake line 76a, 76b is routed from the first axle valve module 74 to the associated wheel brake 42a, 42b of the rear axle 8. The relay valve of the first axle valve module 74 is electronically controlled primarily as a function of the braking value detected by the braking value sensor 50 of the foot brake valve 48. For this purpose, the brake value sensor 50 is connected to the electronic control unit 36 ​​via an electrical sensor line 78 and the first axle valve module 74 via an electrical control line 80.In the case of redundancy, i.e. if the electronic control system fails, the relay valve of the first axle valve module 74 is pneumatically controlled depending on the brake pressure present in the axle brake line 72.

[0034] The second brake circuit 60 has a second supply line 82 and a second pressure accumulator 84, wherein the second supply line 82 is guided from the multi-circuit protection valve 66 via the second pressure accumulator 84 to the foot brake valve 48. A second axle brake line 86, into which a brake pressure is introduced depending on the actuation of the brake pedal 46, runs from the foot brake valve 48 to a second axle valve module 88. This second axle valve module 88 also includes a relay valve (not shown) and one ABS valve arrangement per wheel 6a, 6b of the front axle 4. From the ABS valve arrangements of the second axle valve module 88, one wheel brake line 90a, 90b is guided to the associated wheel brake 40a, 40b of the front axle 4.The relay valve of the second axle valve module 88 is also primarily electronically controlled depending on the braking value detected by the brake value sensor 50 of the foot brake valve 48 and is connected to the electronic control unit 36 ​​via an electrical control line 92. In the case of redundancy, the relay valve of the second axle valve module 88 is also pneumatically controlled depending on the brake pressure present in the second axle brake line 86.

[0035] The retarder 44 is drive-connected to an output shaft of the manual transmission 16 and is drive-connected to the wheels 10a, 10a', 10b, 10b' of the rear axle 8 via the propshaft 18, the axle differential 20, and the drive shafts 22a, 22b. For electronic control, the retarder 44 is connected to the electronic control unit 36 ​​via an electrical control line 94. Likewise, the electric motor 24 is connected to the electronic control unit 36 ​​via an electrical control line 96.

[0036] During a braking operation, the braking deceleration desired by the driver, which corresponds to the braking value detected by the braking value sensor 50 when the brake pedal 46 is actuated, is distributed in the electronic control unit 36 ​​among the components of the braking system 34. As mentioned, these are the service braking system 38, the retarder 44, and the electric motor 24 in generator mode, with the distribution of the braking force being prioritized in the order of electric motor 24, retarder 44, and service braking system 38.

[0037] As a result, the motor vehicle 2 is initially braked without wear by the electric motor 24 operating as a generator, partially recovering the kinetic energy of the motor vehicle 2 and charging the electrical energy storage device 32 (recuperation). The motor vehicle 2 is then further braked without wear by the retarder 44 before the friction brakes 40a, 40b, 42a, 42b of the service brake system 38 are actuated. In a preferred embodiment, it is also conceivable that the distribution or scheduling or sequencing with regard to the use of the braking force from the aforementioned brake components (service brake system 38, the retarder 44, and the electric motor 24 in generator mode) is determined depending on the determined driver braking request (e.g., by the electronic control unit 36).Since the driver should perceive largely the same resistance force F BP at the brake pedal 46 for a specific deflection of the brake pedal 46, regardless of the distribution of the braking force to the components 24, 38, 44 of the braking system 34, in a preferred embodiment a corresponding restoring force in the form of a signal force is generated by means of the axially or rotationally acting drive element 53 on the brake pedal actuator 52 and introduced into the brake pedal 46.

[0038] In another preferred embodiment, feedback is provided to the driver through an increased resistance sensation or resistance force on the brake pedal 46 or on the foot brake valve 48 when the driver should or must be informed about the distribution of the braking force between the components 24, 38, 44 at a specific deflection of the brake pedal 46. It should be noted that the deflection of the brake pedal 46 does not always reflect a desired vehicle deceleration. For example, in advanced braking systems such as ESP (Electronic Stability Program), ESC (Electronic Stability Control), and ASR (Anti-Slip Regulation), the vehicle deceleration and / or braking force requirement can be controlled independently of the driver's braking request.

[0039] In order to inform the driver, possibly in addition to a visual display on a display in the dashboard of the motor vehicle 2, about the distribution of the braking force between the components 24, 38, 44 of the braking system 34, it is provided according to the invention that, in the event of at least one change in the distribution of the braking force between the components 24, 38, 44 of the braking system 34, for example, when one of the components 24, 38, 44 of the braking system 34 is switched on and / or off, a brief signal force that can be perceived haptically at the driver's foot is superimposed on the restoring force by means of the brake pedal actuator 52. How this is preferably done is shown by way of example in the diagram of Fig. 2 shown.

[0040] In the diagram of the Fig. 2the curve of the resistance force F BP acting on the brake pedal 46 over time t during a braking operation is shown (F BP (t)). The resistance force F BP results from the sum of the resistance forces generated within the foot brake valve 48 and the restoring force applied by means of the foot brake actuator 52. The braking operation begins at time t0 with the driver actuating the brake pedal 46, with the motor vehicle 2 initially being decelerated only by the electric machine 24 operated as a generator. At time t1, the retarder 44 is activated, which is indicated to the driver by a haptically perceptible signal S1 in the form of a pulsed increase in the restoring force with the strength H1 and the duration T1.

[0041] The braking torque of the electric machine 24 is then continuously reduced and the braking torque of the retarder 44 is correspondingly increased until the electric machine 24 is completely switched off at time t2. The switching off of the electric machine 24 is communicated to the driver by a haptically perceptible signal force S2 in the form of a double-pulse increase in the restoring force with the strength H2 and the duration T2. ​​In the present case, for example, the strength H2 of the second signal force S2 is noticeably lower than the strength H1 of the first signal force S1 and the duration T2 of the second signal force S2 is greater than the duration T1 of the first signal force S1 (H2 < H1, T2 > T1). The switching off of the electric machine 24 and the switching on of the retarder 44 may be necessary, for example, because the electrical energy storage device 32 is largely charged and / or the electric machine 24 has reached its overheating limit.

[0042] At time t3, the service brake system 38 with the friction brakes 40a, 40b, 42a, 42b is activated, which is indicated to the driver by a haptically perceptible signal force S3 in the form of a vibration sequence comprising several oscillations of the restoring force with the amplitude A1, the frequency f1, and the duration T3. Thereafter, the braking torque of the retarder 44 is continuously reduced, and the braking torque of the friction brakes 40a, 40b, 42a, 42b is correspondingly increased by increasing the applied brake pressure until the retarder 44 is completely deactivated at time t4.

[0043] The deactivation of the retarder 44 is communicated to the driver by a haptically perceptible signal force S4 in the form of a vibration sequence comprising several oscillations of the restoring force with the amplitude A2, the frequency f2 and the duration T4.

[0044] In this case, for example, the amplitude A2 of the fourth signal force S4 is greater than the amplitude A1 of the third signal force S3, the frequency f2 of the fourth signal force S4 is less than the frequency f1 of the third signal force S3, and the duration T4 of the fourth signal force S4 is less than the duration T3 of the third signal force S3 (A2 > A1, f2 < f1, T4 < T3). Switching off the retarder 44 and engaging the service brake system 38 may be necessary, for example, if the retarder 44 can no longer generate usable braking torque due to a reduced driving speed of the motor vehicle 2 and / or has reached its overheating limit.

[0045] The signal forces S1, S2, S3, S4, which are applied to the brake pedal 46 by means of the drive element 53 on the brake pedal actuator 52 and superimposed on the restoring force, inform the driver about the respective processes for distributing the braking force, such as the activation of the retarder 44 or the service brake system 38 or the deactivation of the electric motor 24 or the retarder 44, without having to take their eyes off the road ahead. The different designs of the signal forces S1, S2, S3, S4 make the respective activation and deactivation processes clearly identifiable. Unless there is an emergency braking situation, the driver can influence the distribution of the braking force between the components 24, 38, 44 of the braking system 38 by actuating the brake pedal 46, for example by partially releasing the brake pedal 46 to return to the previous distribution of the braking force. List of reference symbols (part of the description)

[0046] 2 Motor vehicle, commercial vehicle 4 Vehicle axle, front axle 6a, 6b Wheels on the front axle 8 Vehicle axle, rear axle 10a, 10a' Wheels on the rear axle, right side of the vehicle 10b, 10b' Wheels on the rear axle, left side of the vehicle 12 Combustion engine 14 Disconnect clutch 16 Manual transmission 18 Propshaft 20 Axle differential on the rear axle 22a, 22b Drive shafts on the rear axle 24 Electric motor 26 Drive shaft 28 Axle differential on the front axle 30a, 30b Drive shafts on the front axle 32 Energy storage device, battery 34 Brake system 36 Electronic control unit 38 Service brake system 40a, 40b Wheel brakes, friction brakes on the front axle 42a, 42b Wheel brakes, friction brakes on the rear axle 44Continuous braking system, retarder 46Brake pedal 48Foot brake valve 50Brake value sensor,Travel sensor 52 Brake pedal actuator 53 Drive element on the brake pedal actuator 54 First control line 56 Compressed air supply device 58 First brake circuit 60 Second brake circuit 62 Compressor 64 Pressure regulator 66 Multi-circuit protection valve 68 First supply line 70 First pressure accumulator 72 First axle brake line 74 First axle valve module 76a, 76b Wheel brake lines 78 Second sensor line 80 Third control line 82 Second supply line 84 Second pressure accumulator 86 Second axle brake line 88 Second axle valve module 90a, 90b Wheel brake lines 92 Fourth control line 94 Fifth control line 96 Sixth control line A1 Amplitude of signal force S3 A2 Amplitude of signal force S4 ECU Electronic control unit f1 Frequency of signal force S3 f2Frequency of the signal force S4 F BP Resistance force H1Strength of the signal force S1 H2Strength of the signal force S2 S1Signal force, restoring force increase S2Signal force, restoring force increase S3Signal force, oscillation sequence S4Signal force, oscillation sequence tTime t0Time point,Start time t1First time T1Duration of signal force S1 t2Second time T2Duration of signal force S2 t3Third time T3Duration of signal force S3 t4Fourth time T4Duration of signal force S4,

Claims

1. Brake system (23) of a motor vehicle (2), which comprises a service brake system (38) having friction brakes (40a, 40b, 42a, 42b) which can be actuated by a pressure medium, a sustained-action brake system (44), designed as a hydrodynamic or electrodynamic retarder, at least one electric machine (24) which is drivingly connected to the wheels (6a, 6b) on a vehicle axle (4) and can be operated at least as a generator, and a foot brake valve (48) which can be actuated by means of a brake pedal (46), wherein the foot brake valve (48) has a brake value transmitter (50) and a brake pedal actuator (52) for generating a restoring force acting on the brake pedal (46), and in which said components (24, 38, 44) of the brake system (23) can be controlled by means of an electronic control device (36), wherein the braking force requirement is requested, in the order of priority, by the electric machine (24) in generator mode, the retarder (44) and the service brake system (38), and wherein the distribution of the braking force between the components (24, 38, 44) of the brake system (23) can be suitably communicated to a driver of the motor vehicle (2), characterized in that the brake pedal actuator (52) is designed to be electrically effective and has a rotatable or axially movable drive element (53), and in that the drive element (53) of the brake pedal actuator (52) is directly or indirectly connected in an actuating manner to a brake lever of the brake pedal (46) or to a plunger piston of the foot brake valve (48).

2. Brake system according to claim 1, characterized in that the brake pedal actuator (52) is designed as an electric motor having a rotatable rotor shaft, and in that the rotor shaft of the electric motor is directly or indirectly connected in an actuating manner to the brake lever of the brake pedal (46) or to the plunger piston of the foot brake valve (48) via a spindle gear.

3. Brake system according to claim 1, characterized in that the brake pedal actuator (52) is designed as an electromagnet having an axially movable armature, and in that the armature of the electromagnet is directly or indirectly connected in an actuating manner to the brake lever of the brake pedal (46) or to the plunger piston of the foot brake valve (48).

4. Brake system according to any of claims 1 to 3, wherein the braking force requirement is signaled by means of a deflection of the brake pedal (46).

5. Method for controlling a brake system (34) of a motor vehicle (2), which has a service brake system (38) having friction brakes (40a, 40b, 42a, 42b) which can be actuated by a pressure medium, a sustained-action braking system (44), designed as a hydrodynamic or electrodynamic retarder, at least one electric machine (24) which is drivingly connected to the wheels (6a, 6b) on a vehicle axle (4) and can be operated at least as a generator, and a foot brake valve (48) which can be actuated by means of a brake pedal (46), wherein the foot brake valve (48) has a brake value transmitter (50) and a brake pedal actuator (52) for generating a restoring force acting on the brake pedal (46), and in which said components (24, 38, 44) of the brake system (34) can be controlled by means of an electronic control device (36), wherein the braking force requirement is satisfied, in order of priority, by the electric machine (24) in generator mode, the retarder (44) and the service brake system (38), and wherein the distribution of the braking force between the components (24, 38, 44) of the brake system (34) is suitably communicated to a driver of the motor vehicle (2), characterized in that in the case of at least one change in the distribution of the braking force between the components (24, 38, 44) of the brake system (34) by means of the brake pedal actuator (52), the restoring force acting on the brake pedal (46) is briefly overlaid with a haptically perceptible signaling force (S1, S2, S3, S4).

6. Method according to claim 5, characterized in that when at least one of the components (24, 38, 44) of the brake system (34) is activated or deactivated by means of the brake pedal actuator (52), the restoring force acting on the brake pedal (46) is briefly overlaid with a haptically perceptible signaling force (S1, S2, S3, S4).

7. Method according to either claim 5 or claim 6, characterized in that the signaling force (S1, S2) that changes the restoring force acts as at least one pulsed increase in the restoring force.

8. Method according to claim 7, characterized in that the pulsed signaling forces (S1, S2) that are activated in the case of different changes in the distribution of the braking force differ from one another in terms of their number and / or strength (H1, H2) and / or duration (T1, T2).

9. Method according to any of claims 5 to 8, characterized in that the signaling force (S3, S4) is applied in the form of a oscillation sequence which comprises a plurality of oscillations of the restoring force and which can be perceived as a vibration on the brake pedal (46).

10. Method according to claim 9, characterized in that the oscillation sequences applied in the case of different changes in the distribution of the braking force differ from one another in terms of their frequency (f1, f2) and / or amplitude (A1, A2) and / or duration (T3, T4).

11. Method according to any of claims 5 to 10, characterized in that the braking force requirement is signaled by means of a deflection of the brake pedal (46).