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

Abstract

Method for operating an electro-hydraulic motor vehicle braking system (100) with a main cylinder (110) that can be supplied with hydraulic fluid from a reservoir (120), an electromechanical actuator (124) for actuating a piston (112; 114) housed in the main cylinder (110), and a wheel brake that can be coupled to the master cylinder (110) and a shut-off valve (TCISO; 152, 154, 156, 158) provided between the master cylinder (110) and the wheel brake, comprehensively the steps: - Controlling the electromechanical actuator (124) to build up hydraulic pressure at the wheel brake; - Actuation of the shut-off valve (TCISO; 152, 154, 156, 158) to lock in the hydraulic pressure already built up at the wheel brake; - Controlling the electromechanical actuator (124) to draw hydraulic fluid from the reservoir (120) while monitoring the time response of a pressure drop in the main cylinder (110) associated with the drawing-in process; and - Aborting the suction process depending on a monitoring result.

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), or 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 per wheel brake also presents challenges, such as unwanted pressure equalization when both valves are open. A solution for this, based on highly dynamic control behavior, is described in WO 2010 / 091883 A1.

[0006] 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.

[0007] 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).

[0008] DE 10 2012 205 340 A1 discloses an electrohydraulic braking system for motor vehicles with at least one brake pressure regulation or brake pressure control function, which can preferably be controlled in a "brake-by-wire" operating mode. The braking system has a pressure supply device that can be controlled by an electronic control and regulation unit and is driven by an electric motor, the electric motor being connected to an electrical grid for power supply. In order to enable a rapid reversal of the direction of movement of the electric motor while maintaining specified limits for the current consumed or fed back into the electrical grid, a feedback current delivered by the electric motor into the electrical grid in generator mode and / or a current consumed by the electric motor is limited.

[0009] Also known from DE 10 2011 076 675 A1 is an electrohydraulic braking system for motor vehicles with at least one brake pressure regulation or brake pressure control function, which is preferably controllable in a "brake-by-wire" operating mode, and which has a pressure supply device controllable by means of an electronic control and regulation unit, which is connected or connectable to hydraulically actuated wheel brakes. By means of the pressure supply device, the wheel brakes are hydraulically actuated via at least one pressure control valve. The pressure supply device comprises a cylinder-piston arrangement with a hydraulic pressure chamber, the piston of which is displaceable by an electromechanical actuator.In order to enable an improvement of the pressure supply functions, it is provided that a target pressure value is determined for each wheel brake, and the cylinder-piston arrangement is controlled in such a way that a predetermined pre-pressure in the hydraulic pressure chamber is set by displacement of the piston, which is determined from the target pressure values. Brief outline

[0010] 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.

[0011] To achieve this objective, one aspect provides a method for operating an electro-hydraulic motor vehicle brake system comprising a master cylinder supplied with hydraulic fluid from a reservoir, an electromechanical actuator for actuating a piston housed in the master cylinder, a wheel brake connectable to the master cylinder, and a shut-off valve provided between the master cylinder and the wheel brake. The method comprises the steps of controlling the electromechanical actuator to build up hydraulic pressure at the wheel brake, controlling the shut-off valve to lock the hydraulic pressure already built up at the wheel brake, controlling the electromechanical actuator to draw hydraulic fluid from the reservoir while monitoring a time response of a pressure drop in the master cylinder accompanying the drawing, and terminating the drawing depending on a monitoring result.

[0012] The purpose of stopping the suction can be to prevent the hydraulic pressure in the master cylinder from dropping excessively (especially to a substantially pressureless or negative pressure state) in the event of a fault. The fault can be detected based on the temporal behavior of the pressure drop in the master cylinder and can be related, for example, to the shut-off valve, other valves, or the master cylinder.

[0013] To abort the suction stroke, the electromechanical actuator can be controlled accordingly (e.g., to perform a discharge stroke instead of a suction stroke). Alternatively or additionally, one or more valves, including the shut-off valve or a valve provided between the master cylinder and the reservoir, can be controlled, for example, to counteract the pressure drop in the master cylinder in the event of a fault.

[0014] The activation of the shut-off valve to lock in the hydraulic pressure and the activation of the electromechanical actuator to draw in hydraulic fluid can occur in connection with the detection of a need to draw hydraulic fluid from the reservoir into the master cylinder as part of the hydraulic pressure build-up. The activation of the shut-off valve can precede the activation of the electromechanical actuator. The need to draw hydraulic fluid from the reservoir into the master cylinder can be detected in connection with a test phase. Alternatively or additionally, the need can be to compensate for fading during a braking operation. It is also conceivable that the necessary drawing in is accompanied by the master cylinder piston approaching (or having already reached) its delivery-side stop, while the hydraulic pressure must be further increased.

[0015] According to one implementation, suction can be aborted if the monitoring result indicates a malfunction of the shut-off valve or a malfunction of the shut-off valve control. The malfunction can be determined based on a predetermined criterion or a combination of several predetermined criteria.

[0016] For example, suction can be interrupted if the pressure drop in the master cylinder occurs more slowly than a predefined time criterion. The predefined time criterion can state that the pressure drop to a substantially pressureless state (e.g., below 5 bar or below 1 bar) must occur within approximately 5 to 50 ms. Alternatively or additionally, suction can be interrupted before the pressure drop reaches approximately 10 to 40 bar (e.g., approximately 20 bar).

[0017] In connection with the termination (e.g., simultaneously with or afterward), at least one further action can be initiated. According to one variant, the shut-off valve is controlled to open it. Alternatively or additionally, the electromechanical actuator is controlled to increase the hydraulic pressure.

[0018] The procedure can be performed during a test phase while the vehicle is stationary. This allows the operational reliability of the vehicle's braking system to be determined before a journey, and an error message can be issued if necessary. For example, the test phase can be performed after the ignition is switched on but before a gear is engaged.

[0019] Also provided is a computer program product with program code means for implementing the method presented here when the computer program product runs on a processor. The computer program product can be included in a motor vehicle control unit or motor vehicle control unit system.

[0020] To solve the problem, a further aspect is directed toward an electro-hydraulic motor vehicle brake system. The brake system comprises a master cylinder supplied with hydraulic fluid from a reservoir, an electromechanical actuator for actuating a piston housed in the master cylinder, a wheel brake connectable to the master cylinder, a shut-off valve provided between the master cylinder and the wheel brake, and a control unit or control unit system configured to control the electromechanical actuator to build up hydraulic pressure at the wheel brake, to control the shut-off valve to lock in the hydraulic pressure already built up at the wheel brake, to control the electromechanical actuator to draw hydraulic fluid from the reservoir while monitoring a time response of a pressure drop in the master cylinder accompanying the drawing, and to abort the drawing depending on a monitoring result.

[0021] The braking system may further include a valve system for vehicle dynamics control. In this case, the shut-off valve may be arranged between the master cylinder and the valve system for vehicle dynamics control or may be part of this valve system. Multiplex operation may be performed in conjunction with vehicle dynamics control. The vehicle dynamics control may include at least one of the following control systems: an anti-lock braking system (ABS), a traction control system (ASR), and an electronic stability program (ESP, also called Vehicle Stability Control, VSC).

[0022] The master cylinder can be dimensioned in such a way that it has no volume reserve to compensate for fading. For example, the master cylinder diameter can be 15 to 23 mm and the maximum actuation travel of a master cylinder piston can be 6 to 10 cm (with a tandem piston, 3 to 5 cm per piston).

[0023] The braking system may further comprise a mechanical actuator that is or can be coupled to a brake pedal for actuating the piston housed in the master cylinder. This mechanical actuator may be provided for emergency braking (e.g., in the event of failure of the electromechanical actuator).

[0024] According to a first variant, the electromechanical actuator in the brake system presented here is designed to actuate the master cylinder piston as part of a brake booster. In this case, the braking force to be boosted can be exerted on the piston by means of the mechanical actuator. According to another variant, the electromechanical actuator is designed to actuate the piston to generate braking force. This variant can be used, for example, in a brake-by-wire (BBW) operation, in which the brake pedal is (normally) mechanically decoupled from the master cylinder piston. In a brake system designed for BBW operation, the mechanical actuator is used to actuate the piston, for example, in the event of a BBW component failure (i.e., in a "push-through" mode or during emergency braking).

[0025] Depending on the design of the vehicle's braking system, a selective decoupling of the brake pedal from the master cylinder piston can be achieved using a decoupling device. In a braking system designed according to the BBW principle, permanent decoupling can be provided, except for emergency braking (in which the brake pedal is coupled to the master cylinder piston via the mechanical actuator). In a regenerative braking system, such decoupling can occur at least during regenerative braking (generator operation). In other braking systems, the decoupling device and the associated simulation device for providing pedal feedback can be completely omitted.

[0026] 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

[0027] 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. 5 is a flowchart illustrating an embodiment of a method for operating the electrohydraulic vehicle brake system according to one of the preceding figures; and Fig. 6A to Fig. 6D diagrams illustrating hydraulic pressure curves and the control of the electromechanical actuator. Detailed description

[0028] 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).

[0029] 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.

[0030] 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.

[0031] 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).

[0032] 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.

[0033] 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.

[0034] 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).

[0035] 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 selective decoupling of the brake pedal 130 from the piston arrangement 112, 114 in the master cylinder 110, for example, by interrupting a force transmission path. 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 brake 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. Accordingly, the brake pedal 130 is decoupled from the force transmission element 128 (and thus from the piston arrangement 112, 114 in the master cylinder 110), and actuation of the piston arrangement 112, 114 can occur exclusively via the electromechanical actuator 124. In this case, the usual pedal feedback 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] After the processes during service braking have been explained in more detail, the emergency braking mode (“push-through” mode) will now be briefly described. Emergency braking mode is, for example, the result of 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) in emergency braking mode enables a direct coupling of the brake pedal 130 to the master cylinder 110, namely via the force transmission element 128. Emergency braking is initiated by depressing the brake pedal 130. The brake pedal actuation is then transmitted via the force transmission element 128 to the master cylinder 110. 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.

[0039] 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.

[0040] As in Fig. 1, the brake system 100 further includes a valve 172, which is configured as a shut-off valve and can be integrated into the HCU 106. The valve 172 is operatively provided between the hydraulic chamber 116 and the unpressurized hydraulic fluid reservoir 120. In some embodiments, another such valve (not shown) can be operatively provided between the other hydraulic chamber 118 and the reservoir 120. Generally, the valve 172 is provided between the master cylinder 110 and the reservoir.

[0041] The valve 172 enables refilling of the hydraulic chambers 116, 118. Such refilling is necessary, for example, when the hydraulic fluid from the hydraulic chambers 116, 118 has been almost completely removed during an ongoing braking operation (ie the pistons 112, 114 have moved to their stop in Fig. 1 on the left) and the hydraulic pressure still needs to be increased.

[0042] For refilling, the wheel brakes VL, VR, HL and HR are controlled via assigned valves of the HCU 106 (in Fig. 1 not shown) is fluidically separated from the hydraulic chambers 116, 118. The hydraulic pressure prevailing at the wheel brakes VL, VR, HL and HR is thus "locked in". The valve 172 is then opened. During a subsequent return stroke of the pistons 112, 114 (in Fig. 3 to the right), hydraulic fluid is then sucked from the pressureless reservoir 120 into both chambers 116, 118 (due to the floating master cylinder pistons 112, 114). Finally, the valve 172 can be closed again and the hydraulic connection to at least one of the wheel brakes VL, VR, HL and HR can be opened again. During a subsequent delivery stroke of the pistons 112, 114 (in Fig. 1 to the left) the previously “locked” hydraulic pressure is then further increased.

[0043] Valve 172 can also be used for regenerative braking and to relieve hydraulic pressure in the event of system failures. These uses will be explained in more detail later.

[0044] 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 valves disclosed in WO 2010 / 091883 A or WO 2011 / 141158 A (cf. Fig. 15) with only four valves 152, 154, 156, 158 (and the corresponding control). The hydraulic pressure modulation in control mode is then also carried out by means of the electromechanical actuator 124. In other words, the electromechanical actuator 124 is in this case not only controlled to generate braking force during service braking, but also, for example, for the purpose of vehicle dynamics control (i.e., e.g., in ABS and / or ASR and / or ESP control mode). Together with the control of the electromechanical actuator 124, the valves 152, 154, 156, 158 are controlled individually for each wheel or wheel group in multiplex mode. 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.

[0045] The multiplex operation can be a time-division multiplex operation. In general, individual sub-slots can be specified. One or more of the valves 152, 154, 156, 158 can be assigned to a single time slot, which are actuated one or more times during the corresponding time slot (for example, by changing the switching state from open to closed and / or vice versa). 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 not shown pressureless hydraulic fluid reservoir (reference numeral 120 in Fig. 1) can be connected.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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).

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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).

[0068] In the exemplary embodiments described above, the master cylinder size, and thus the maximum deliverable volume of hydraulic fluid, is selected such that, for a given pedal transmission ratio (distance / force) at 500 N pedal force, a vehicle deceleration of approximately 0.6 g can still be achieved. This requirement results in a typical diameter of the master cylinder 110 of approximately 18 to 20 mm. In order to provide a sufficient reserve of hydraulic fluid volume with such a master cylinder diameter, the master cylinder stroke would have to be selected to be disproportionately long. Excessive volume reserves, which are only needed in special cases (e.g., in the case of fading), are therefore often dispensed with. The brake system 100 must therefore refill hydraulic fluid from the unpressurized reservoir 120 into the master cylinder 110 when additional volume is required, as explained above.

[0069] Refilling becomes necessary when, for example, it is detected during an ongoing braking operation that the volume of hydraulic fluid (still) present in the hydraulic chambers 116, 118 is not sufficient to further increase the hydraulic pressure at one, several or all of the wheel brakes VL, VR, HL and HR.

[0070] During the refilling process, the hydraulic pressure in the master cylinder 110 drops sharply for a short time. On the other hand, the hydraulic pressure already built up at the front, front, rear, and rear wheel brakes must be maintained. For this reason, the shut-off valves provided in the HCU 106 (e.g., the multiplex valves 152, 154, 156, and 158 according to Fig. 2 or the TCISO valves according to Fig. 4) are closed to include the hydraulic pressure at the front, front, rear, and rear wheel brakes. In this context, both the functionality of these shut-off valves and their control (particularly with regard to control unit 150) must be ensured. Otherwise, there would be a risk that the hydraulic pressure at one or more of the front, front, rear, and rear wheel brakes would collapse during the suction process in master cylinder 110, thus reducing vehicle deceleration.

[0071] In the event of a fault, the deceleration decrease should not exceed 0.1 to 0.3 g within approximately 200 ms. For this reason, a faulty non-closing of the shut-off valves to the front, front, rear, and rear wheel brakes must be detected while the hydraulic pressure in the master cylinder 110 is being reduced after the refilling process has been initiated. Such detection must occur before the pressure drop in the master cylinder 110 reaches approximately 20 bar (which would correspond to a deceleration decrease of approximately 0.2 g).

[0072] Fig. 5 illustrates in a flow chart 500 an embodiment for the operation of the electro-hydraulic brake system 100 according to one of the Fig. 1 to Fig. 4 for error detection when refilling hydraulic fluid from the reservoir 120 into the master cylinder 110.

[0073] First, by controlling the electromechanical actuator 124 in step 502, a hydraulic pressure is built up at one or more of the wheel brakes VL, VR, HL and HR (e.g., during service braking and / or a vehicle dynamics control process). In this case, the fluid connection between the hydraulic chambers 116, 118 on the one hand and the corresponding wheel brakes VL, VR, HL and HR is opened. This corresponds, for example, in the exemplary embodiment according to Fig. 2 an open state of one or more of the multiplex valves 152, 154, 156, 158. In the embodiment according to Fig. 4 at least one of the TCISO valves is open (and the remaining valves are in the position shown in Fig. 4 illustrated position).

[0074] The following steps are performed for error detection when, as part of the hydraulic pressure buildup in step 502, hydraulic fluid must be drawn from the reservoir 120 into the master cylinder 110 (refilling process). As already explained, such a drawing process can occur, for example, in the case of fading when there is insufficient volume reserve in the master cylinder 110.

[0075] First, the open shut-off valves (multiplex valves 152, 154, 156, 158 according to Fig. 2 or TCISO valves according to Fig. 4) to close them and lock in the hydraulic pressure already built up at the front, front, rear, and rear wheel brakes (step 504). After the shut-off valves are closed, the electromechanical actuator 124 is activated to draw hydraulic fluid from the unpressurized reservoir 120 into the hydraulic chambers 116, 118 (step 506). At the same time as or shortly after the activation of the actuator, at least one of the valves 170, 172 is opened to establish a fluid connection between at least one of the hydraulic chambers 116, 118 and the reservoir 120. As already explained, due to the floating mounting of the master cylinder pistons 112, 114, opening one of the valves 170, 172 is sufficient.

[0076] The activation of the electromechanical actuator 124 causes the master cylinder pistons 112, 114 to move to the left (cf. Fig. 1 to Fig. 4). Due to the very high stiffness of the brake lines, the hydraulic pressure (in master cylinder 110) drops very sharply within a few milliseconds. Typically, a drop in hydraulic pressure to approximately 0 bar or a negative pressure occurs within 10 to 20 milliseconds.

[0077] The temporal behavior of the pressure drop in the master cylinder 110 associated with suction is continuously monitored (for example, using pressure sensor 122). If one of the shut-off valves is not closed or not fully closed, the stiffness of the braking system 100 is significantly reduced. This reduced stiffness results in a slower pressure reduction in the master cylinder 110. Thus, in a typical fault scenario, 100 ms or more are required for the hydraulic pressure in the master cylinder 110 to drop to essentially 0 bar or to a negative pressure. This means that an abnormal pressure drop in the master cylinder 110 can be detected after 10 to 20 ms at the latest.

[0078] Therefore, if an error is detected during monitoring of the temporal behavior of the pressure drop in the master cylinder, the intake process is aborted (step 508). In the event of an error, the open valve 170, 172 can then be closed again immediately or not opened at all. Furthermore, the electromechanical actuator 124 can be controlled to raise the hydraulic pressure in brake circuits I and II as quickly as possible, at least to the previous level. This control of the electromechanical actuator 124 is preceded by the opening of the closed shut-off valves to the front, front, rear, and rear wheel brakes. As a result, a substantial reduction in vehicle deceleration can be prevented in the event of an error. Furthermore, an error message can be output to the driver.

[0079] The following is based on the Fig. 6A to Fig. 6D explains the course of various hydraulic pressures under normal conditions and in the event of a fault.

[0080] Fig. Figure 6A shows an exemplary refill scenario for a stationary vehicle during a test phase. The scenario concerns the vehicle braking system according to Fig. 3, which is connected to the four multiplex valves 152, 154, 156 and 158 according to Fig. 2. The switching states of the multiplex valves 152, 154, 156, and 158 are shown at the top of the diagram, followed by the switching states of the valves 170, 172 for refilling operation. This is followed by the characteristic curve of a travel of the power transmission element 128, which illustrates the actuation of the electromechanical actuator 124. The travel of the power transmission element 128 corresponds here to the travel of the threaded spindle 138. The following characteristic curves show the hydraulic pressure at the rear wheel brakes (HR, HL) of the rear wheel axle, the front wheel brakes (VR, VL) of the front wheel axle, and the hydraulic pressure in the master cylinder 110.

[0081] Fig. 6A concerns the case of faultless operation of the multiplex valves 152, 154, 156, 158. In Fig. Not shown in Figure 6A is the initial activation of the electromechanical actuator 124 to build up hydraulic pressure at the four wheel brakes (front, front, rear, and rear). At time t1, a refilling process is then initiated for test purposes. For this purpose, the multiplex valves 152, 154, 156, and 158 are first activated to close them. This locks in the previously generated hydraulic pressure at the wheel brakes (front, front, rear, and rear).

[0082] Shortly thereafter, the electromechanical actuator 124 is activated so that the master cylinder pistons 112, 114 perform a return stroke. This is Fig. 6A through the path of the force transmission element 128. Due to the high rigidity of the brake system 100, which is related to the functionality of the closed valves 152, 154, 156, 158, the hydraulic pressure in the master cylinder drops sharply to essentially 0 bar within less than 15 ms. This temporal behavior of the master cylinder hydraulic pressure indicates that the valves 152, 154, 156, 158 are functional. For this reason, with a certain delay at time t2, the valves 170, 172 (or at least one of these two valves) can be opened to draw hydraulic fluid from the unpressurized reservoir 120. The master cylinder pistons 112, 114 are still in their return stroke.

[0083] At time t3, the intake process is essentially complete. As a result, both valves 170, 172 are again in their closed state. In other words, the master cylinder 110 is fluidically decoupled from the reservoir 120 again. Furthermore, the valves 152, 154, 156, 158 can be opened again, which is noticeable in only a slight pressure drop at the wheel brakes, front, rear, and rear. From this point on, the hydraulic pressure in the master cylinder 110 can be increased again by a corresponding delivery stroke of the master cylinder pistons 112, 114.

[0084] During the scenario according to Fig. 6A demonstrates the functionality of valves 152, 154, 156, 158, Fig. 6B shows the interruption of an intake process in the event of a fault. The fault concerns the fact that two of the four multiplex valves 152, 154, 156, 158 cannot be closed. As a result, the stiffness of the brake system 100 is significantly reduced, which is noticeable in a comparatively slow pressure drop in the master cylinder 110. The pressure drop to essentially 0 bar takes more than 100 ms. At the same time, due to the two faulty valves, a sharp pressure drop occurs at one wheel brake on the front axle and one wheel brake on the rear axle, which are assigned to these defective valves.

[0085] Fig. 6C shows a similar error case as Fig. 6B, except that here the intake process for refilling the master cylinder 110 is aborted immediately after the fault is detected. For this reason, the hydraulic pressures at those wheel brakes assigned to the two faulty multiplex valves only drop briefly and slightly. The corresponding reduction in the vehicle's deceleration is less than 0.2 g within 200 ms. Furthermore, the hydraulic pressure reduction in the master cylinder 110 is significantly less than 20 bar before the pressure drop is compensated for by a delivery stroke of the master cylinder pistons 112, 114.

[0086] Fig. 6D shows a similar scenario as Fig. 6C. Here too, the intake process is interrupted due to a too slow pressure drop in the master cylinder 110. As in both Fig. 6C as well as Fig. 6D, in both scenarios the fault is detected before any of the valves 170, 172 is opened, thus creating a “hydraulic short circuit” between the master cylinder 110 and the fluid reservoir 120.

[0087] While the Fig. 6A to Fig. 6C illustrate the test phase in the case of a stationary vehicle, concerns Fig. 6D illustrates the case of a moving and constantly decelerating vehicle. It is clearly evident that, due to the timely termination of the intake process, there is virtually no negative impact on the vehicle's deceleration.

[0088] Overall, the technology presented here can ensure that faulty valves or faulty valve control can be reliably detected. Furthermore, it increases the safety of refilling processes. Due to this increased safety, master cylinders can generally be designed with smaller volume reserves.

Claims

[1] Method for operating an electro-hydraulic motor vehicle brake system (100) with a master cylinder (110) supplied with hydraulic fluid from a reservoir (120), an electromechanical actuator (124) for actuating a piston (112; 114) received in the master cylinder (110), and a wheel brake which can be coupled to the master cylinder (110) and a shut-off valve (TCISO; 152, 154, 156, 158) provided between the master cylinder (110) and the wheel brake, comprehensive the steps: - controlling the electromechanical actuator (124) to build up hydraulic pressure at the wheel brake; - Control of the shut-off valve (TCISO; 152, 154, 156, 158) to lock the hydraulic pressure already built up at the wheel brake; - controlling the electromechanical actuator (124) to suck hydraulic fluid from the reservoir (120) while monitoring a time response of a pressure drop in the master cylinder (110) associated with the sucking; and - Aborting suction depending on a monitoring result. [2] Method according to claim 1, wherein the suction is interrupted when the result of the monitoring indicates a lack of functionality of the shut-off valve (TCISO; 152, 154, 156, 158) or a control (150) of the shut-off valve (TCSIO; 152, 154, 156, 158). [3] Method according to claim 1 or 2, wherein the suction is interrupted when the pressure drop occurs more slowly than a predetermined time criterion. [4] The method of claim 3, wherein the predetermined time criterion states that the pressure drop to a substantially pressureless state must occur within approximately 5 to 50 ms. [5] A method according to any one of the preceding claims, wherein the suction is stopped before the pressure drop is approximately 10 to 40 bar. [6] Method according to one of the preceding claims, wherein in connection with the termination of the suction, the shut-off valve (TCISO; 152, 154, 156, 158) is controlled in order to open it. [7] Method according to one of the preceding claims, wherein in connection with the termination of the suction, the electromechanical actuator (124) is controlled to increase the hydraulic pressure. [8] Method according to one of the preceding claims, wherein the method is carried out during a test phase in which the vehicle is at a standstill. [9] Computer program product with program code means for carrying out the method according to one of the preceding claims when the computer program product runs on a processor. [10] Motor vehicle control unit or control unit system comprising the computer program product according to claim 9. [11] Electro-hydraulic motor vehicle braking system (100), comprising: a master cylinder (110) supplied with hydraulic fluid from a reservoir (120), an electromechanical actuator (124) for actuating a piston (112; 114) accommodated in the master cylinder (110), a wheel brake that can be coupled to the master cylinder, a shut-off valve provided between the master cylinder (110) and the wheel brake, and a control device or control device system (150) which is designed to - controlling the electromechanical actuator (124) to build up hydraulic pressure at the wheel brake; - Control of the shut-off valve (TCISO; 152, 154; 156; 158) to lock the hydraulic pressure already built up at the wheel brake; - controlling the electromechanical actuator (124) to suck hydraulic fluid from the reservoir (120) while monitoring a time response of a pressure drop in the master cylinder (110) associated with the sucking; and - Aborting suction depending on a monitoring result. [12] Brake system according to claim 11, further comprising a valve system (106) for controlling vehicle dynamics, wherein the shut-off valve (TCISO; 152, 154, 156, 158) is arranged between the master cylinder (110) and the valve system (106) for controlling vehicle dynamics or is a part of this valve system (106). [13] Brake system according to claim 11, wherein the shut-off valve (152) can be operated in multiplex mode together with further shut-off valves (154, 156, 158) assigned to further wheel brakes in order to carry out driving dynamics control. [14] Braking system according to claim 12 or 13, wherein the driving dynamics control comprises at least one of the following control systems: an anti-lock braking system, ABS, a traction control system, ASR, and an electronic stability program, ESP. [15] Brake system according to one of claims 11 to 14, wherein the master cylinder (110) is dimensioned such that it has no volume reserve to compensate for fading. [16] Brake system according to one of claims 11 to 15, further comprising a mechanical actuator (126) which can be coupled or is coupled to a brake pedal (130) for actuating the piston (112, 114) accommodated in the master cylinder (110).

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