Electro-hydraulic vehicle braking system and method for operating the same

Abstract

Electro-hydraulic motor vehicle braking system (100), comprising a main cylinder (110); an electromechanical actuator (124) for actuating a first piston (112; 114) housed in the master cylinder (110) in a “brake-by-wire”, BBW, mode of the braking system (100); a mechanical actuator (126) operable by means of a brake pedal (130) for actuating the first piston (112; 114) in a “push-through”, PT, mode of the brake system (100); - wherein in BBW mode a gap (190) with a gap length (d) is present in a force transmission path between the brake pedal (130) and the first piston (112; 114) to decouple the brake pedal (130) from the first piston (112; 114), - wherein the brake system (100) is configured such that in BBW mode the gap length (d) is dependent on a pedal travel of the brake pedal (130), and - wherein the dependence of the gap length (d) on the pedal travel is defined by a translation ratio between a distance traveled by a pedal-side limit of the gap (190) and a distance traveled by a piston-side limit of the gap (190).

Description

Technical area

[0001] The present disclosure generally relates to the field of vehicle braking systems. Specifically, an electrohydraulic vehicle braking system with an electromechanical actuator for actuating the braking system is described. background

[0002] Electromechanical actuators have been used in vehicle braking systems for some time, for example, to implement an electric parking brake (EPB) function. In electromechanical braking systems (EMB), they replace conventional hydraulic cylinders on the wheel brakes.

[0003] Due to technological advances, the performance of electromechanical actuators has continuously increased. Therefore, the use of such actuators in the implementation of modern vehicle dynamics control systems has been considered. Such control systems include anti-lock braking systems (ABS), traction control (ASR), and electronic stability programs (ESP), also known as vehicle stability control (VSC).

[0004] WO 2006 / 111 393 A1 teaches an electrohydraulic brake system with a highly dynamic electromechanical actuator that handles pressure modulation during vehicle dynamics control. The electromechanical actuator described in WO 2006 / 111 393 A1 is designed to act directly on a master cylinder of the brake system. Due to the high dynamics of the electromechanical actuator, the hydraulic components of the brake system known from WO 2006 / 111 393 A1 can be reduced to a single 2 / 2-way valve per wheel brake. To implement wheel-specific pressure modulation, the valves are then controlled individually or in groups in multiplex mode.

[0005] However, minimizing the number of valves to just one per wheel brake also results in challenges, such as unwanted pressure equalization when both valves are open at the same time.

[0006] A solution based on a highly dynamic control behavior is given in WO 2010 / 091 883 A1.

[0007] WO 2010 / 091883 A1 discloses an electrohydraulic brake system with a master cylinder and a tandem piston accommodated therein. The tandem piston is actuated by an electromechanical actuator. The electromechanical actuator comprises an electric motor arranged concentrically with the tandem piston and a gear assembly that converts a rotational movement of the electric motor into a translational movement of the piston. The gear assembly consists of a ball screw drive with a ball screw nut that is non-rotatably coupled to a rotor of the electric motor and a ball screw spindle acting on the tandem piston.

[0008] Another electrohydraulic brake system with an electromechanical actuator acting on a master cylinder piston is known from WO 2012 / 152352 A1. This system can operate in a regenerative mode (generator operation).

[0009] DE 10 2010 045 617 A1 discloses an actuating device for an electrohydraulic motor vehicle brake system with an electromechanical actuator for actuating a master brake cylinder. To improve the overall length, reliability, and pedal travel, an auxiliary piston is used, which is actuated by the actuating device or a pedal tappet and acts on the piston-cylinder unit of the master brake cylinder. The auxiliary piston serves to actuate a mechanically hydraulic travel simulator, for which purpose the volume displaced by the auxiliary piston is fed to the travel simulator via a line. However, the auxiliary piston must be connected to the piston of the master brake cylinder via a connecting device, such as a coupling.

[0010] DE 10 2009 055 721 A1 discloses an electrohydraulic motor vehicle brake system with an electromechanical actuator for actuating a master brake cylinder. In contrast to the brake system disclosed in DE 10 2010 045 617 A1, the travel simulator is arranged coaxially with the master brake cylinder rather than separately via a line. To provide a simple, continuously variable, adjustable, and fail-safe decoupling between a pedal tappet and a piston of the master brake cylinder, it is proposed, firstly, to provide at least one fluid reservoir with an upstream solenoid valve in the brake circuit of the brake system to adjust the amount of free travel between the pedal tappet and the piston of the master brake cylinder.On the other hand, a piston-cylinder system is proposed as a locking device, such that the housing of the travel simulator is supported on a piston of the piston-cylinder system, and the working space of the piston-cylinder system can be shut off by means of a shut-off valve for locking the housing. Brief outline

[0011] Based on the prior art, the invention is based on the object of specifying an electro-hydraulic motor vehicle brake system and a method for operating such a brake system, which have a functionality that is advantageous, in particular from a safety perspective.

[0012] To achieve the object, according to one aspect, an electro-hydraulic motor vehicle brake system is specified, which comprises a master cylinder, an electromechanical actuator for actuating a first piston accommodated in the master cylinder in a "brake-by-wire" (BBW) mode of the brake system, and a mechanical actuator actuated by a brake pedal for actuating the first piston in a "push-through" (PT) mode of the brake system. In BBW mode, a gap with a gap length is present in a force transmission path between the brake pedal and the first piston in order to decouple the brake pedal from the first piston. The brake system is configured such that in BBW mode, the gap length is dependent on a pedal travel of the brake pedal. The dependence of the gap length on the pedal travel is defined by a transmission ratio.The transmission ratio is determined between a distance traveled by a pedal-side gap limitation and a distance traveled by a piston-side gap limitation.

[0013] The dependence of the gap length on the pedal travel can be configured differently depending on the given requirements. According to one implementation, the gap length increases when the brake pedal is depressed. This increase can occur continuously or discontinuously (e.g., in steps). Furthermore, the increase can be proportional (e.g., linear) or non-proportional to the pedal travel. Additionally or alternatively, the gap length can decrease when the brake pedal is released. The dependence of the gap length on the pedal travel can be the same or different when the brake pedal is depressed and released. For different dependencies, a hysteresis, for example, can be configured.

[0014] Conveniently, the gear ratio may be in the range between approximately 1:1.25 and 1:5 (for example, between approximately 1:1.5 and 1:4).

[0015] The length of the gap in an unactuated position of the brake pedal can be between approximately 0.5 mm and 2 mm (for example, approximately 1 mm). In general, the gap can be limited between a first end face of the first piston or a first actuating element movable with the first piston on one side and a second end face of a second actuating element coupled to the brake pedal on the other side. In PT mode, the first end face and the second end face can be brought into contact by overcoming the gap. In this way, the first piston can be actuated mechanically by means of the brake pedal.

[0016] The dependence of the gap length on the pedal travel can be achieved by controlling the electromechanical actuator based on pedal travel and / or pedal force. For this purpose, a pedal travel sensor and / or a pedal force sensor can be installed. The corresponding output signals can be evaluated by a control unit controlling the electromechanical actuator.

[0017] According to one variant, the electromechanical actuator can be controlled in such a way that, when the brake pedal is depressed, the first piston is moved by the electromechanical actuator faster than a pedal-side gap limiter lags behind the first piston. In this way, a gap length that increases with the depressing of the brake pedal can be achieved.

[0018] The electromechanical actuator can be controlled to cause a return stroke of the first cylinder toward the brake pedal when the brake pedal is at least partially depressed. Such a return stroke can occur for various purposes, for example, to draw hydraulic fluid from a reservoir in the master cylinder. According to one implementation, such a return stroke is performed in vehicle dynamics control mode when it is detected that the volume of hydraulic fluid still available in the master cylinder is no longer sufficient. The return stroke of the first cylinder can be accompanied by a hydraulic decoupling of wheel brakes from the master cylinder. Furthermore, a valve between the master cylinder and the reservoir can be opened for this purpose.

[0019] In one embodiment of the brake system, in addition to the master cylinder, another hydraulic cylinder with a second piston accommodated therein is provided. The brake pedal can be coupled to the second piston to displace hydraulic fluid from the hydraulic cylinder when the brake pedal is depressed. The second piston can be rigidly coupled to an actuating element forming a pedal-side boundary of the gap. This actuating element can have a generally rod-shaped configuration.

[0020] The brake system may further comprise a hydraulic simulation device for pedal feedback. This simulation device may be configured to receive hydraulic fluid displaced from the hydraulic cylinder by actuating the second piston.

[0021] A shut-off valve can be provided between the master cylinder and the simulation device. To limit pedal travel, the hydraulic cylinder can be designed so that it can be separated from the simulation device by means of the shut-off valve. Pedal travel limitation can be provided for various purposes. For example, pedal travel limitation can be activated during vehicle dynamics control mode. In this way, haptic feedback can be given to the driver by shortening the pedal travel (compared to regular braking). The haptic feedback can indicate the onset or end of vehicle dynamics control. According to one variant, pedal travel in vehicle dynamics control mode is limited depending on the coefficient of static friction of a road surface. The lower the coefficient of static friction, the shorter the pedal travel can be (i.e., the faster the pedal travel limitation can kick in).

[0022] To achieve the object, according to a further aspect, a method is provided for operating an electro-hydraulic motor vehicle brake system, which comprises a master cylinder, an electromechanical actuator for actuating a first piston accommodated in the master cylinder in a BBW mode of the brake system, and a mechanical actuator actuatable by means of a brake pedal for actuating the first piston in a PT mode of the brake system, wherein in the BBW mode a gap with a gap length is present in a force transmission path between the brake pedal and the first piston in order to decouple the brake pedal from the first piston.The method comprises the step of adjusting, in BBW mode, the gap length as a function of a pedal travel of the brake pedal, wherein the dependence of the gap length on the pedal travel is defined by a transmission ratio between a traveled distance of a pedal-side limitation of the gap and a traveled distance of a piston-side limitation of the gap.

[0023] Also specified is a computer program product with program code means for implementing the method presented here when the computer program product runs on at least one processor. The computer program product can be included in a motor vehicle control unit or motor vehicle control unit system.

[0024] Depending on the design of the vehicle's braking system, the gap can be used to decouple the brake pedal from the master cylinder piston for different purposes. In a braking system generally designed according to the brake pedal-to-brake principle, continuous decoupling can be provided, except for emergency braking, in which the PT mode is activated. In a regenerative braking system, such decoupling can occur at least during regenerative braking (generator mode) on at least one vehicle axle.

[0025] To control the electromechanical actuator and optional additional components of the vehicle's braking system, the braking system can include suitable control devices. These control devices can comprise electrical, electronic, or program-controlled assemblies, as well as combinations thereof. For example, the control devices can be provided in a common control unit or in a system of separate control units (Electronic Control Units, ECUs). Short description of the drawings

[0026] Further advantages, aspects, and details of the hydraulic vehicle braking system presented here are evident from the following description of exemplary embodiments and from the figures. They show: Fig. 1 shows a first embodiment of an electro-hydraulic vehicle braking system; Fig. 2 shows a second embodiment of an electro-hydraulic vehicle braking system; Fig. 3 a third embodiment of an electro-hydraulic vehicle braking system; Fig. 4 a fourth embodiment of an electro-hydraulic vehicle braking system; Fig. 5A is a schematic view of the unactuated basic position of the brake system according to one of the Fig. 1 to Fig. 4; Fig. 5B is a schematic view of the actuating position of the brake system according to one of the Fig. 1 to Fig. 4; and Fig. 6A and Fig. 6B schematic diagrams illustrating the dependence of a gap length on a brake pedal travel. Detailed description

[0027] Fig. Figure 1 shows a first embodiment of a hydraulic vehicle braking system 100 based on the brake-by-wire (BBW) principle. The braking system 100 can optionally be operated in a regenerative mode (e.g., in hybrid vehicles). For this purpose, an electric machine 102 is provided, which offers generator functionality and can be selectively connected to wheels and an energy storage device, e.g., a battery (not shown).

[0028] As in Fig. 1, the braking system 100 comprises a master cylinder assembly 104 that can be mounted on a vehicle firewall. A hydraulic control unit (HCU) 106 of the braking system 100 is functionally arranged between the master cylinder assembly 104 and four wheel brakes (front, front, rear, and rear) of the vehicle. The HCU 106 is designed as an integrated assembly and comprises a plurality of individual hydraulic components as well as several fluid inlets and outlets. Furthermore, a simulation device 108, shown only schematically, is provided for providing a pedal reaction behavior during service braking operation. The simulation device 108 can be based on a mechanical or hydraulic principle. In the latter case, the simulation device 108 can be connected to the HCU 106.

[0029] The master cylinder assembly 104 has a master cylinder 110 with a piston slidably received therein. In the exemplary embodiment, the piston is designed as a tandem piston with a primary piston 112 and a secondary piston 114 and defines two separate hydraulic chambers 116, 118 in the master cylinder 110. The two hydraulic chambers 116, 118 of the master cylinder 110 are each connected to a pressureless hydraulic fluid reservoir 120 via a connection for supplying hydraulic fluid. Each of the two hydraulic chambers 116, 116 is further coupled to the HCU 106 and defines a respective brake circuit I and II. In the exemplary embodiment, a hydraulic pressure sensor 122 is provided for brake circuit I, which could also be integrated into the HCU 106.

[0030] The hydraulic assembly 104 further includes an electromechanical actuator (i.e., an electromechanical control element) 124 and a mechanical actuator (i.e., a mechanical control element) 126. Both the electromechanical actuator 124 and the mechanical actuator 126 enable actuation of the master cylinder piston and, for this purpose, act on an input-side end face of this piston, more specifically, the primary piston 112. The actuators 124, 126 are configured such that they can actuate the master cylinder piston independently of one another (and separately or jointly).

[0031] The mechanical actuator 126 has a force transmission element 128, which is rod-shaped and can act directly on the input-side end face of the primary piston 112. As in Fig. 1, the force transmission element 128 is coupled to a brake pedal 130. It is understood that the mechanical actuator 126 may include additional components functionally arranged between the brake pedal 130 and the master cylinder 110. Such additional components may be either mechanical or hydraulic in nature. In the latter case, the actuator 126 is designed as a hydraulic-mechanical actuator 126.

[0032] The electromechanical actuator 124 has an electric motor 134 and a gear 136, 138 following the electric motor 134 on the output side. In the exemplary embodiment, the gear is an arrangement comprising a rotatably mounted nut 136 and a spindle 138 that engages with the nut 136 (e.g., via rolling elements such as balls) and is movable in the axial direction. In other exemplary embodiments, rack and pinion gears or other gear types may be used.

[0033] In the present embodiment, the electric motor 134 has a cylindrical design and extends concentrically to the power transmission element 128 of the mechanical actuator 126. More precisely, the electric motor 134 is arranged radially outwardly with respect to the power transmission element 128. A rotor (not shown) of the electric motor 134 is rotationally fixedly coupled to the gear nut 136 in order to set it in rotation. A rotational movement of the nut 136 is transmitted to the spindle 138 in such a way that an axial displacement of the spindle 138 results. Fig. 1 The left end face of the spindle 138 can be (if necessary via an intermediate link) brought into contact with the Fig. 1 right end face of the primary piston 112 and consequently the primary piston 112 (together with the secondary piston 114) in Fig. 1 to the left. Furthermore, the piston arrangement 112, 114 can also be moved by the force transmission element 128 of the mechanical actuator 126 extending through the spindle 138 (which is designed as a hollow body) in Fig. 1 to the left. Moving the piston assembly 112, 114 in Fig. 1 to the right is accomplished by means of the hydraulic pressure prevailing in the hydraulic chambers 116, 118 (when the brake pedal 130 is released and, if necessary, when the spindle 138 is moved to the right by the motor).

[0034] As in Fig. 1, a decoupling device 142 is functionally provided between the brake pedal 130 and the force transmission element 128. The decoupling device 142 enables a selective decoupling of the brake pedal 130 from the piston arrangement 112, 114 in the master cylinder 110. The functional functions of the decoupling device 142 and the simulation device 108 are explained in more detail below. In this context, it should be noted that the Fig. 1, the braking system 100 is based on the brake-by-wire (BBW) principle. This means that during normal service braking, both the decoupling device 142 and the simulation device 108 are activated.

[0035] Accordingly, the brake pedal 130 is connected to the force transmission element 128 (and thus to the piston arrangement 112, 114 in the master cylinder 110) via a Fig. 1, and actuation of the piston arrangement 112, 114 can only occur via the electromechanical actuator 124. In this case, the usual pedal reaction behavior is provided by the simulation device 108 coupled to the brake pedal 130.

[0036] During service braking, the electromechanical actuator 124 assumes the function of generating the braking force. A braking force requested by depressing the brake pedal 130 is generated by the electric motor 134 moving the spindle 138 into Fig. 1 is shifted to the left, thereby also moving the primary piston 112 and the secondary piston 114 of the master cylinder 110 to the left. In this way, hydraulic fluid is pumped from the hydraulic chambers 116, 118 via the HCU 106 to the front, front, rear, and rear wheel brakes.

[0037] The resulting braking force of the front, front, rear, and rear wheel brakes is adjusted depending on the brake pedal actuation detected by a sensor. For this purpose, a travel sensor 146 and a force sensor 148 are provided, whose output signals are evaluated by an electronic control unit (ECU) 150 controlling the electric motor 134. The travel sensor 146 detects an actuation travel associated with the actuation of the brake pedal 130, while the force sensor 148 detects a related actuation force. Depending on the output signals of the sensors 146, 148 (and, if applicable, the pressure sensor 122), the control unit 150 generates a control signal for the electric motor 134.

[0038] In the present exemplary embodiment, the control of the electric motor 134 (and thus of the electromechanical actuator 124) is carried out in such a way that the length of the gap mentioned above for decoupling the brake pedal 130 from the master cylinder piston arrangement 112, 114 is dependent on the pedal travel of the brake pedal 130. The dependency is selected in such a way that the gap length increases with the depression of the brake pedal 130 (i.e., with increasing pedal travel). For this purpose, the control unit 150 evaluates the output signal of the displacement sensor 146 (and additionally or alternatively of the force sensor 148) and controls the electromechanical actuator 124 in such a way that the piston arrangement 112, 114 moves more quickly into the Fig. 1 is moved to the left, as a brake pedal-side limitation of the gap of the piston arrangement 112, 114 lags behind.

[0039] After explaining the processes during service braking (BBW mode) in more detail, we will now briefly describe the PT mode during emergency braking. Emergency braking may, for example, result from the failure of the vehicle battery or a component of the electromechanical actuator 124. Deactivation of the decoupling device 142 (and the simulation device 108) during emergency braking enables a direct coupling of the brake pedal 130 to the master cylinder 110, namely via the force transmission element 128.

[0040] The emergency braking is initiated by depressing the brake pedal 130. The brake pedal actuation is then transmitted to the master cylinder 110 via the force transmission element 128, overcoming the gap mentioned above. As a result, the piston arrangement 112, 114 moves in Fig. 1 to the left. This causes hydraulic fluid to be pumped from the hydraulic chambers 116, 118 of the master cylinder 110 via the HCU 106 to the front, front, rear, and rear wheel brakes to generate braking force.

[0041] According to a first embodiment, the HCU 106 has a basically conventional design with a total of 12 valves (in addition to valves used, for example, in connection with the activation or deactivation of the decoupling device 142 and the simulation device 106) with respect to vehicle dynamics control operation (brake control functions such as ABS, ASR, ESP, etc.). Since the electromechanical actuator 124 is then controlled (possibly exclusively) within the scope of braking force generation, the additional control functions are accomplished in a known manner by means of the HCU 106 (and possibly a separate hydraulic pressure generator such as a hydraulic pump). However, a hydraulic pressure generator in the HCU 106 can also be dispensed with. The electromechanical actuator 124 then additionally assumes the pressure modulation within the scope of control operation.For this purpose, a corresponding control mechanism will be implemented in the control unit 150 provided for the electromechanical actuator 124.

[0042] In a further embodiment according to Fig. 2, the special valves for vehicle dynamics control operation (e.g., ASR and ESP operation) can be omitted in the HCU 106, except for four valves 152, 154, 156, 158. In this other embodiment of the HCU 106, the valve arrangement known from WO 2010 / 091883 A or WO 2011 / 141158 A (cf. 15) with only four valves 152, 154, 156, 158 (and the corresponding control) can be used. Hydraulic pressure modulation during normal operation is also performed by electromechanical actuator 124. In other words, in this case, electromechanical actuator 124 is controlled not only to generate braking force during service braking, but also, for example, for the purpose of vehicle dynamics control (e.g., in ABS and / or ASR and / or ESP control mode). Together with the control of electromechanical actuator 124, the valves 152, 154, 156, and 158 are controlled individually for each wheel or wheel group in multiplex mode.In the in . Fig. In the implementation shown in Figure 2, there are no further valves for driving dynamics control purposes between the valves 152, 154, 156, 158 and the master cylinder.

[0043] The multiplex operation can be a time-division multiplex operation. In general, individual time slots can be specified. One or more of the valves 152, 154, 156, 158 can be assigned to an individual time slot, which are actuated during the corresponding time slot (for example, by changing the switching state from open to closed and / or vice versa once or multiple times). According to one implementation, each of the valves 152, 154, 156, 158 is assigned exactly one time slot. One or more further valve arrangements (in Fig. 2 not shown) one or more additional time slots can be assigned.

[0044] In multiplex operation, for example, several or all of the valves 152, 154, 156, 158 can initially be opened, and simultaneously, by means of the electromechanical actuator 124, hydraulic pressure can be built up at several or all of the assigned wheel brakes (front, front, rear, and rear). Upon reaching a wheel-specific target pressure, the corresponding valve 152, 154, 156, 158 closes synchronously with the time slot, while one or more other valves 152, 154, 156, 158 remain open until the respective target pressure is also reached there. Therefore, in multiplex operation, the four valves 152, 154, 156, 158 are opened and closed individually for each wheel or wheel group depending on the respective target pressure.

[0045] According to one embodiment, valves 152, 154, 156, and 158 are implemented as 2 / 2-way valves and are designed, for example, as non-adjustable shut-off valves. In this case, therefore, no opening cross-section can be adjusted, as would be the case with proportional valves, for example. In another embodiment, valves 152, 154, 156, and 158 are implemented as proportional valves with an adjustable opening cross-section.

[0046] Fig. 3 shows a more detailed embodiment of a vehicle brake system 100, which is based on the in connection with the schematic embodiments of the Fig. 1 and Fig. 2. Identical or similar elements have been given the same reference numerals as in the Fig. 1 and Fig. 2, and their explanation is omitted below. For the sake of clarity, the ECU, the wheel brakes, the HCU valve units assigned to the wheel brakes, and the generator for regenerative braking operation have not been shown.

[0047] Also the Fig. The vehicle brake system 100 illustrated in Figure 3 comprises two brake circuits I and II, wherein two hydraulic chambers 116, 118 of a master cylinder 110 are each assigned to exactly one brake circuit I, II. The master cylinder 110 has two connections per brake circuit I, II. The two hydraulic chambers 116, 118 each open into a first connection 160, 162, via which hydraulic fluid can be conveyed from the respective chamber 116, 118 into the assigned brake circuit I, II. Furthermore, each of the brake circuits I and II can be connected via a second connection 164, 166, which opens into a corresponding annular chamber 110A, 110B in the master cylinder 110, to the Fig. 3 unillustrated pressureless hydraulic fluid reservoir (reference numeral 120 in 1).

[0048] Between the respective first port 160, 162 and the respective second port 164, 166 of the master cylinder 110, a valve 170, 172 is provided, which in the exemplary embodiment is implemented as a 2 / 2-way valve. The first and second ports 160, 162, 164, 166 can be selectively connected to one another by means of the valves 170, 172. This corresponds to a "hydraulic short circuit" between the master cylinder 110, on the one hand, and, on the other hand, the unpressurized hydraulic fluid reservoir (which is then connected to the hydraulic chambers 116, 118 via the annular chambers 110A, 110B). In this state, the pistons 112, 114 in the master cylinder 110 can be moved essentially without resistance by the electromechanical actuator 124 or the mechanical actuator 126 ("free travel release"). The two valves 170, 172 thus enable, for example, regenerative braking (generator operation).Here, the hydraulic fluid displaced from the hydraulic chambers 116, 118 during a delivery movement in the master cylinder 110 is not directed to the wheel brakes, but rather to the pressureless hydraulic fluid reservoir, without causing a hydraulic pressure buildup at the wheel brakes (which is generally undesirable during regenerative braking). A braking effect is then generated during regenerative braking by the generator (see reference numeral 102 in the . Fig. 1 and Fig. 2) was achieved.

[0049] It should be noted that regenerative braking can be implemented on an axle-by-axle basis. Therefore, in the case of axle-specific brake circuit splitting, one of the two valves 170, 172 can be closed and the other open during regenerative braking.

[0050] The two valves 170, 172 also enable the reduction of hydraulic pressure at the wheel brakes. Such pressure reduction may be desired in the event of a failure (e.g., a blockage) of the electromechanical actuator 124 or during vehicle dynamics control mode to prevent a return stroke of the electromechanical actuator 124 (e.g., to prevent a reaction on the brake pedal). The two valves 170, 172 are also moved to their open position to reduce pressure, allowing hydraulic fluid from the wheel brakes to flow back into the hydraulic fluid reservoir via the annular chambers 110A, 110B in the master cylinder 110.

[0051] Finally, the valves 170, 172 also allow refilling of the hydraulic chambers 116, 118. Such refilling may be necessary during an ongoing braking operation (e.g., due to so-called brake fading). For refilling, the wheel brakes are actuated via assigned valves of the HCU (in Fig. 3 not shown) are fluidically separated from the hydraulic chambers 116, 118. The hydraulic pressure prevailing at the wheel brakes is thus "locked in". The valves 170, 172 are then opened. During a subsequent return stroke of the pistons 112, 114 provided in the master cylinder 110 (in Fig. 3 to the right), hydraulic fluid is then sucked from the pressureless reservoir into the chambers 116, 118. Finally, the valves 170, 172 can be closed again and the hydraulic connections to the wheel brakes can be opened again. During a subsequent delivery stroke of the pistons 112, 114 (in Fig. 3 to the left) the previously “locked” hydraulic pressure can then be further increased.

[0052] As in Fig. 3, in the present embodiment, both a simulation device 108 and a decoupling device 142 are based on a hydraulic principle. Both devices 108, 142 each comprise a cylinder 108A, 142A for receiving hydraulic fluid and a piston 108B, 142B accommodated in the respective cylinder 108A, 142A. The piston 142B of the decoupling device 142 is mechanically connected to a Fig. 3 brake pedal not shown (see reference numeral 130 in the Fig. 1 and Fig. 2). Furthermore, the piston 142B has an extension 142C extending axially through the cylinder 142A. The piston extension 142C runs coaxially with a force transmission element 128 for the primary piston 112 and is positioned upstream of the latter in the actuation direction of the brake pedal.

[0053] Each of the two pistons 108B, 142B is preloaded into its initial position by an elastic element 108C, 142D (here, a coil spring). The characteristic curve of the elastic element 108C of the simulation device 108 defines the desired pedal reaction behavior.

[0054] As further stated in Fig. 3, the vehicle brake system 100 in the present exemplary embodiment comprises three further valves 174, 176, 178, which are implemented here as 2 / 2-way valves. It is understood that individual or all of these three valves 174, 176, 178 can be omitted in other embodiments in which the corresponding functionalities are not required. Furthermore, it is understood that all of these valves are part of a single HCU block (cf. reference numeral 106 in the Fig. 1 and Fig. 2). This HCU block can include additional valves (see Fig. 4 below).

[0055] The first valve 174 is provided, on the one hand, between the decoupling device 142 (via a port 180 provided in cylinder 142A) and the simulation device 108 (via a port 182 provided in cylinder 108A), and, on the other hand, the unpressurized hydraulic fluid reservoir (via port 166 of the master cylinder 110). The second valve 176, which has a throttle characteristic in its through-flow position, is connected upstream of port 182 of cylinder 108A. Finally, the third valve 178 is provided between the hydraulic chamber 116 (via port 116) and brake circuit I, on the one hand, and the cylinder 142A of the decoupling device 142 (via port 180), on the other hand.

[0056] The first valve 174 enables selective activation and deactivation of the decoupling device 142 (and indirectly also of the simulation device 108). When the valve 174 is in its open position, the cylinder 142A of the decoupling device 142 is hydraulically connected to the depressurized hydraulic reservoir. In this position, the decoupling device 142 is deactivated, corresponding to emergency braking operation. Furthermore, the simulation device 108 is also deactivated.

[0057] The opening of valve 174 causes the hydraulic fluid held in cylinder 142A to be pumped into the depressurized hydraulic fluid reservoir with virtually no resistance when piston 142B is displaced (as a result of actuating the brake pedal). This process is essentially independent of the position of valve 176, since it has a significant throttling effect even in its open position. Thus, when valve 174 is open, simulation device 108 is also indirectly deactivated.

[0058] When the brake pedal is actuated when the valve 174 is open, the piston extension 142C overcomes a gap 190 towards the force transmission element 128 and consequently comes into contact with the force transmission element 128. After overcoming the gap 190, the force transmission element 128 is captured by the displacement of the piston extension 142C and then actuates the primary piston 112 (and - indirectly - the secondary piston 114) in the master brake cylinder 110. This corresponds to the Fig. 1 explained direct coupling of brake pedal and master cylinder piston for hydraulic pressure build-up in brake circuits I., II. in emergency braking mode.

[0059] When valve 174 is closed (and valve 178 is closed), however, the decoupling device 142 is activated. This corresponds to service braking operation. When the brake pedal is actuated, hydraulic fluid is pumped from cylinder 142A into cylinder 108A of the simulation device 108. In this way, the simulator piston 108B is displaced against the counterforce provided by the elastic element 108C, resulting in the usual pedal reaction behavior. At the same time, the gap 190 between the piston extension 142C and the force transmission element 128 is maintained. This mechanically decouples the brake pedal from the master cylinder.

[0060] In the present embodiment, the gap 190 is maintained by the electromechanical actuator 124 moving the primary piston 112 at least as fast as Fig. 3 is moved to the left, just as the piston 142B moves to the left due to the brake pedal actuation. Since the force-transmitting element 128 is mechanically or otherwise (e.g., magnetically) coupled to the primary piston 112, the force-transmitting element 128 moves together with the primary piston 112 when actuated by the transmission spindle 138. This entrainment of the force-transmitting element 128 allows the gap 190 to be maintained.

[0061] Maintaining the gap 190 during service braking requires precise detection of the distance traveled by the piston 142B (and thus the pedal travel). For this purpose, a displacement sensor 146 based on a magnetic principle is provided. The displacement sensor 146 comprises a plunger 146A rigidly coupled to the piston 142B, to the end of which a magnetic element 146B is attached. The movement of the magnetic element 146B (i.e., the distance traveled by the plunger 146B or piston 142B) is detected by a Hall sensor 146C. An output signal of the Hall sensor 146C is transmitted to a Fig. 3 not shown control unit (see reference numeral 150 in the Fig. 1 and Fig. 2). Based on this evaluation, the electromechanical actuator 124 can then be controlled.

[0062] Now to the second valve 176, which is connected upstream of the simulation device 108 and can be omitted in some embodiments. This valve 176 has a predetermined or adjustable throttle function. Using the adjustable throttle function, for example, a hysteresis or other characteristic curve for the pedal feedback behavior can be achieved. Furthermore, by selectively blocking the valve 176, the movement of the piston 142B (with the valves 174, 178 closed) and thus the brake pedal travel can be limited.

[0063] In its open position, the third valve 178 enables the delivery of hydraulic fluid from piston 142A into brake circuit I or the hydraulic chamber 116 of the master cylinder 110, and vice versa. Fluid delivery from piston 142A into brake circuit I enables, for example, rapid braking (e.g., before the delivery effect of the electromechanical actuator 124 begins), with valve 178 immediately closing again. Furthermore, when valve 178 is open, a hydraulic reaction (e.g., a pressure modulation generated by the electromechanical actuator 124 during vehicle dynamics control mode) can be achieved via piston 142B on the brake pedal.

[0064] A pressure sensor 148 is provided in a hydraulic line leading into port 180 of cylinder 142A, the output signal of which allows a conclusion to be drawn about the actuating force on the brake pedal. The output signal of this pressure sensor 148 is received by a Fig. 3 is evaluated. Based on this evaluation, one or more of the valves 170, 172, 174, 176, 178 can then be controlled to implement the functionalities described above. Furthermore, the electromechanical actuator 124 can be controlled based on this evaluation.

[0065] At the Fig. 3 shown brake system 100, the Fig. 1 shown HCU 106 can be used. An exemplary implementation of this HCU 106 for the brake system 100 according to Fig. 3 is in Fig. 4. Here, a total of 12 (additional) valves are provided for the implementation of the driving dynamics control functions, as well as an additional hydraulic pump. In an alternative embodiment, Fig. 3 also the multiplex arrangement according to Fig. 2 (with a total of four valves in addition to those in Fig. 3 illustrated valves).

[0066] Even in the embodiments according to the Fig. 3 and Fig. 4 shows a pedal travel dependency of the gap 190 between the force transmission element 128 on the one hand and the piston extension 142C on the other hand. The following are described with reference to the schematic Fig. 5A and Fig. 5B the processes when operating the brake system 100 according to Fig. 3 or Fig. 4 with regard to the path dependence of a length d of the gap 190 (“gap length d”). It is understood that the corresponding technical details also apply to the brake system 100 according to Fig. 1 or Fig. 2 can be implemented.

[0067] In the Fig. 5A and Fig. 5B are the components of the brake system 100 which are relevant for explaining the path dependence of the gap length d according to Fig. 3 or Fig. 4 shown. Fig. 5A illustrates the unactuated basic position of the brake system 100 in BBW mode (i.e. with the brake pedal not actuated), while Fig. 5B shows the operating position in BBW mode.

[0068] As in Fig. 5A, the gap 190 is formed between mutually facing end faces of the force transmission element 128 on the one hand and the piston extension 142C on the other hand. In the unactuated basic state according to Fig. 5A, the gap length d has a predetermined minimum value d MIN of approximately 1 mm.

[0069] When the brake pedal is actuated, the piston 142B in the cylinder 142A is Fig. 5A shifted to the left and creates a path s EINIn BBW mode, the valve 176 between the cylinder 142A and the cylinder 108A of the simulation device 108 is normally open. The hydraulic fluid displaced from the chamber 142A when the piston 142B is displaced can thus be displaced into the cylinder 108A and thereby displaces the piston 108B in Fig. 5A against a spring force downwards (see element 108C in the Fig. 3 and Fig. 4). This spring force creates the pedal feedback behavior familiar to the driver.

[0070] The way s EIN , which the piston 142B in the cylinder 142A can travel when the brake pedal is actuated, is limited to a maximum value s EIN , MAX typically 10 to 20 mm (e.g., approximately 16 mm). This limitation also limits the brake pedal travel.

[0071] In the embodiment according to Fig. 5A results in the limitation to the maximum value s EIN , MAXdue to a stop in the cylinder 108A for the piston 108B, which limits the path s SIM of the piston 108A to a maximum value s SIM , MAX limited. Between the maximum values ​​s EIN , MAX and s SIM , MAX There is a functional relationship which is determined by the volume of hydraulic fluid displaced between the two cylinders 142A, 108A and the hydraulically effective working surfaces of the two cylinders 142B, 108B.

[0072] As already explained above, it is possible to take the path s EIN to a lower maximum value than by s SIM , MAX This limitation is achieved by closing the valve 176 before the piston 108B reaches its stop in the cylinder 108A (it is assumed here that the hydraulic fluid displaced from the cylinder 142A cannot escape otherwise, for example the valves 174, 178 in the Fig. 3 and Fig. 4 are closed).

[0073] The limitation of the path s EIN By closing valve 176, the pedal travel is thus limited. In the present exemplary embodiment, such pedal travel limitation is implemented when ABS control is activated. By shortening the pedal travel when valve 176 is closed, the driver is haptically alerted to a low static friction value of the road surface and the activation of ABS control. The lower the static friction value, the faster the pedal travel limitation can be activated (i.e., the shorter the maximum pedal travel). This pedal reaction behavior is familiar to the driver from conventional braking systems that are not based on the BBW principle.

[0074] When the brake pedal is actuated in BBW mode, the electromechanical actuator 124 is activated to act on the primary piston 112 in the master cylinder 110 by means of the spindle 138, and thus also on the secondary piston 114. The piston arrangement 112, 114 then moves by a distance s HBZ in Fig. 5A to the left (or to the right when releasing the brake pedal). The path s HBZ is also limited to a maximum value s HBZ , MAX of approximately 35 to 50 mm (e.g., approximately 42 mm). This limitation results from a stop in the master cylinder 110 for at least one of the two pistons 112, 114.

[0075] As already mentioned above, the force transmission element 128 is fixedly or detachably coupled (e.g., by magnetic forces) and mechanically coupled to the primary piston 112. A displacement of the primary piston 112 (and the secondary piston 114) in the master cylinder 110 therefore causes the same displacement of the force transmission element 128, both in direction and distance.

[0076] The control of the electromechanical actuator 124 is now carried out in such a way that between s EIN and s HBZ a specific transmission ratio is defined. In the exemplary embodiment, the transmission ratio is selected to be > 1 and is, for example, 1:3 (cf. Fig. 6A). Due to the rigid coupling of the force transmission element 128 to the primary piston 112 and of the piston extension 142C to the piston 142B, the same transmission ratio is established between a traveled path of the end face of the piston extension 142C facing the force transmission element 128 and a traveled path of an end face of the force transmission element 128 associated with the piston extension 142C.

[0077] The transmission ratio is therefore selected such that the gap length d increases continuously when the brake pedal is depressed. This ensures that the force transmission element 138 moves more quickly into Fig. 5B moves to the left as the piston extension 142C follows it. Therefore, a translation between the path s EIN of the piston 142B on the gap length d, whereby the transmission ratio, as in Fig. 6B, approximately Fig. 2 (and can generally be between 1:1.5 and 1:4.

[0078] The gap length d, which increases with depressing the brake pedal, is advantageous from a safety perspective, since with increasing brake pedal travel a “stronger” mechanical decoupling of the brake pedal from the piston arrangement 112, 114 in the master cylinder 110 is achieved.

[0079] The increasing gap length d is also advantageous from another point of view. As already explained above, in the brake system 100 according to Fig. 3 or Fig. 4 In certain situations, it may be necessary to draw hydraulic fluid from the reservoir into the master cylinder 110 during service braking (e.g., after the activation of a vehicle dynamics control system). For this purpose, as already explained, the fluid lines to the wheel brakes are closed and the refill valves 170, 172 are opened. Furthermore, a return stroke of the pistons 112, 114 is initiated by means of the electromechanical actuator 124 in order to draw hydraulic fluid from the reservoir into the hydraulic chambers 116, 118. As a result of the return stroke, the piston arrangement 112, 114, and thus also the force transmission element 128, moves in Fig. 3 to the right.

[0080] Due to the comparatively large gap length d = s HBZ - s EIN + s MINA significant return stroke (and thus a significant volume of hydraulic fluid in the master cylinder 110) can take place without the force transmission element 128 striking the piston extension 142C by overcoming the gap 190. This avoids unwanted haptic feedback on the brake pedal. At the same time, it is ensured that in the unactuated basic position, only a small gap length d MIN is present. If it is necessary to switch to PT mode, the gap 190 of the length d MIN quickly overcome, which leads to a largely delay-free coupling of the piston extension 142C with the force transmission element 128.

[0081] In the embodiments according to the Fig. 3, Fig. 4, Fig. 5A and Fig.5B, the gap 190 is provided between the force-transmitting element 128 and the piston extension 142C. It should be noted that in other embodiments, the gap could also be provided at a different location in the force-transmitting path between the brake pedal 130 and the master cylinder piston assembly 112, 114. For example, it is conceivable to form the piston extension 142C and the force-transmitting element 128 as a single, gap-free component. In this case, a gap could then be provided between the end face of the primary piston 112 facing the brake pedal and the end face of the integrated element 128, 142C facing the primary piston 112.

Claims

[1] Electro-hydraulic motor vehicle brake system (100), comprising a master cylinder (110); an electromechanical actuator (124) for actuating a first piston (112; 114) received in the master cylinder (110) in a “brake-by-wire”, BBW, mode of the braking system (100); a mechanical actuator (126) operable by means of a brake pedal (130) for actuating the first piston (112; 114) in a push-through, PT, mode of the braking system (100); - wherein in the BBW mode, a gap (190) with a gap length (d) is present in a force transmission path between the brake pedal (130) and the first piston (112; 114) in order to decouple the brake pedal (130) from the first piston (112; 114), - wherein the brake system (100) is configured such that in the BBW mode the gap length (d) is dependent on a pedal travel of the brake pedal (130), and - wherein the dependence of the gap length (d) on the pedal travel is defined by a transmission ratio between a traveled path of a pedal-side limitation of the gap (190) and a traveled path of a piston-side limitation of the gap (190). [2] Brake system according to claim 1, wherein the gap length (d) increases with depressing of the brake pedal (130). [3] A brake system according to claim 1 or 2, wherein the gear ratio is in the range between approximately 1:1.25 and 1:

6. [4] Brake system according to one of the preceding claims, wherein the gap (190) is delimited between a first end face of the first piston (112; 114) or a first actuating element (128) movable with the first piston (112; 114) on the one hand and a second end face of a second actuating element (142C) coupled to the brake pedal (130) on the other hand. [5] Brake system according to claim 4, wherein in the PT mode the first end face and the second end face can be brought into contact by overcoming the gap (190) in order to actuate the first piston by means of the brake pedal (130). [6] Brake system according to one of the preceding claims, wherein the dependence of the gap length (d) on the pedal travel is realized by a pedal travel-dependent and / or a pedal force-dependent controllability of the electromechanical actuator (124). [7] Brake system according to one of the preceding claims, wherein the electromechanical actuator (124) can be controlled in such a way that the first piston (112; 114) is moved faster by means of the electromechanical actuator (124) when the brake pedal (130) is depressed than a brake pedal-side limitation of the gap (190) lags behind the first piston (112; 114). [8] Brake system according to one of the preceding claims, wherein the electromechanical actuator (124) is controllable in order to effect a return stroke of the first cylinder (112; 114) in the direction of the brake pedal (130) when the brake pedal (130) is at least partially depressed. [9] Brake system according to claim 8, wherein the return stroke serves to suck hydraulic fluid from a reservoir (120) into the master cylinder (110). [10] Brake system according to one of the preceding claims, wherein a hydraulic cylinder (142A) is provided with a second piston (142B) received therein, wherein the brake pedal (130) is coupled to the second piston (142B) in order to displace hydraulic fluid from the hydraulic cylinder (142A) when the brake pedal (130) is depressed. [11] Brake system according to claim 10, wherein the second piston (142B) is rigidly coupled to an actuating element (142C) forming a pedal-side boundary of the gap (190). [12] Brake system according to claim 10 or 11, wherein a hydraulic simulation device (108) for a pedal reaction behavior is provided, which is designed to receive hydraulic fluid displaced from the hydraulic cylinder (142). [13] Brake system according to one of claims 10 to 12, wherein a shut-off valve (176) is provided between the hydraulic cylinder (142A) and the simulation device (108). [14] Brake system according to claim 13, wherein the hydraulic cylinder (142A) can be separated from the simulation device (108) by means of the shut-off valve (176) in order to limit the pedal travel. [15] Method for operating an electro-hydraulic motor vehicle brake system (100) with a master cylinder (110), an electromechanical actuator (124) for actuating a first piston (112; 114) accommodated in the master cylinder (110) in a “Brake-By-Wire”, BBW, mode of the brake system (100), and a mechanical actuator (126) operable by means of a brake pedal (130) for actuating the first piston (112; 114) in a "push-through", PT, mode of the brake system (100), - wherein in the BBW mode, a gap (190) with a gap length (d) is present in a force transmission path between the brake pedal (130) and the first piston (112; 114) in order to decouple the brake pedal (130) from the first piston (112; 114), and - wherein the dependence of the gap length (d) on the pedal travel is defined by a transmission ratio between a traveled path of a pedal-side boundary of the gap (190) and a traveled path of a piston-side boundary of the gap (190), comprising the step: - Adjusting, in BBW mode, the gap length (d) depending on the pedal travel of the brake pedal (130). [16] Computer program product with program code means for carrying out the method according to claim 15, when the computer program product runs on at least one processor. [17] Motor vehicle control unit or control unit system comprising the computer program product according to claim 16.

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