BRAKING SYSTEM WITH A PRESSURE SUPPLY DEVICE AND A SAFETY GATE FOR THE BRAKING CIRCUITS

Description

[0001] The present invention relates to a braking system with two brake circuits, each having a brake circuit line, and which is suitable for two vehicle axles, wherein at least one hydraulically actuated wheel brake is provided in each brake circuit, and each hydraulically actuated wheel brake can be connected to its brake circuit or its brake circuit line via an associated switching valve, wherein the pressure build-up and pressure release in the respective wheel brake is effected via the associated switching valve. The braking system also has a pressure supply device, wherein pressure build-up in both brake circuits occurs or can occur via the pressure supply device, and wherein at least one circuit isolation valve, in particular a normally open valve, is provided, which serves to selectively shut off or open a hydraulic connecting line connecting the two brake circuits. State of the art

[0002] In recent years, a trend has emerged in brake systems towards integrated versions, the so-called 1-box, which integrate electro-hydraulic brakes (E-Boost) with a master cylinder, drive-by-wire, and ABS / ESP functionality. These systems differ primarily in the design of the pressure supply unit and the valve configuration. Simplified circuits using multiplex technology (MUX) without an outlet valve and pressure modulation via the pressure supply unit are also known. Alternatives to the tandem master cylinder also exist, such as those with a separating chamber between the pressure supply and floating pistons, and more recently, single master cylinders without a floating piston. A diagnostic valve is always provided for diagnosing the tandem master cylinder. Furthermore, the brake systems exhibit significant differences in their reliability.

[0003] Various concepts and components are already known from the following patent documents, among others. For example, EP3333031 discloses a brake system with a tandem master cylinder (THZ), DE102014111594 and DE102018111126 disclose a tandem master cylinder with pressure supply (THZ + DV), DE102017201243 discloses a pressure supply device (DV), DE102017219598 discloses a single master cylinder (SHZ), and DE10309145 discloses a diagnostic valve. Documents EP 1 175 322 B1, DE 10 2006 035913 A1, and DE 10 2013 224783 A1 can also be considered prior art.

[0004] Hydraulic systems with two or more circuits are increasingly being used, and the safety requirements for these systems are rising. In particular, the following fault scenarios and functions must be considered and / or provided: a. The failure or malfunction of one hydraulic circuit must not affect the function of the other hydraulic circuit; b. If only one pressure supply device is present, pressure build-up must still be possible in the event of a failure of the pressure supply device, i.e., in the emergency level, by means of a master brake cylinder actuated by the brake pedal; c. If only one pressure supply device is present, a low-power auxiliary pressure supply must be available for emergency operation in the event of its failure; d. The hydraulic circuits must supply control systems that require both controlled pressure increases and controlled pressure decreases for normal operation.

[0005] To ensure the reliability of the hydraulic system, it is essential to continuously detect faults using diagnostic functions and programs and to take appropriate corrective action. It is particularly important to consider both single and multiple faults.

[0006] Possible single and double faults in a hydraulic system are explained below using a dual-circuit braking system as an example.

[0007] The extent to which a vehicle can take over the driver's tasks when needed, and how humans and machines interact on the road today and in the future, is determined in the various development stages. These stages are often described as the five levels or stages of vehicle automation, which are listed below: Level 1: Assisted driving, where driver assistance systems support the driver but cannot yet control the vehicle themselves; Level 2: Partially automated driving, where systems can, among other things, take over the control of the vehicle, but the driver always remains responsible; Level 3: Highly automated driving, where the driver can take their eyes off the road for longer periods in certain situations; Level 4: Fully automated driving, where the vehicle drives itself for the majority of the time, but the driver must be fit to drive; Level 5: Autonomous driving, where the vehicle takes over all driving functions and the people in the vehicle are merely passengers.

[0008] Whether single and / or double faults in a braking system are tolerable therefore depends on the degree of automation or the aforementioned level of the vehicle. I. Single error

[0009] In a Level 2 vehicle braking system, individual faults are permitted as long as the minimum deceleration of approximately < 0.3 g is still achieved. However, such a low deceleration can already be classified as extremely dangerous.

[0010] For a Level 3 vehicle braking system, a braking deceleration of at least 0.5 g should be achieved, while also ensuring the ABS function. II. Double fault with total brake failure

[0011] Many systems accept double failures if the probability of failure based on ppm and FIT data is low.

[0012] A particular risk is posed by dormant defects if no appropriate diagnosis is carried out.

[0013] For applications with high safety requirements, critical individual failures, such as those that reduce braking performance to less than 0.5g, should be preventable through redundancies and detectable using diagnostic functions.

[0014] A typical case of a dormant fault is outlined below: The braking system, for example, has only one pressure supply unit, which supplies two brake circuits with four wheel brakes via feed valves. As soon as one of the four wheel brakes fails, this fault cannot be located. Consequently, the entire pressure supply fails. Only one brake circuit can be supplied with a reduced pressure level via auxiliary pressure supplies, such as the master cylinder, which is actuated by the brake pedal. Due to the critically low pressure level, only a very weak and therefore dangerous braking effect is achieved. Often, important components cannot be diagnosed. For example, a solenoid valve, which is normally always open, cannot be diagnosed for leaks, as the leakage and thus the fault only occurs when the system switches to a different operating state.

[0015] A double fault with a dormant fault occurs, for example, when one brake circuit fails, which is connected to the other brake circuit via only one circuit isolator valve. The circuit isolator valve, which is normally open, must close when the brake circuit fails. However, due to a (dormant) fault, it does not close completely, so that as a consequence, the other brake circuit also fails, leading to a total failure of the brake system.

[0016] The main costs of a braking system arise from the (tandem) master brake cylinder, the pressure supply device, as well as the number and type of valves required, the pressure sensor and the control and regulating device. Object of the invention

[0017] The object underlying the invention is to reduce costs and construction volume and to provide a braking system with better safety or probability of failure.

[0018] This problem is solved according to the invention with a braking system having the features of claim 1. Advantageous further developments of the braking system according to claim 1 result from the features of the dependent claims. Advantages of the invention

[0019] The braking system according to the invention is advantageously characterized by requiring only a small number of valves, particularly switching valves, which simplifies the design, reduces the required installation space, and also makes it cost-effective. This is made possible in particular by the special design of the safety gate, which allows the two brake circuits to be selectively separated or connected. At the same time, the braking system according to the invention exhibits a very high level of fault tolerance and a low probability of failure. Furthermore, the braking system according to the invention offers numerous diagnostic options for detecting faults, especially dormant faults. Even when faults occur, the braking system generally still provides sufficient braking pressure and / or a sufficiently high braking deceleration.

[0020] Due to the special valve circuit, the master brake cylinder can still be used to provide pressure in the event of a failure of the pressure supply system. In case of danger or wheel lockup, pressure reduction can be advantageously controlled or regulated via an exhaust valve. Here, the pressure reduction, and in particular its timing, can be precisely controlled or regulated by means of a valve actuated by a pulse-width modulated signal. During the pressure reduction phase, the master brake cylinder is disconnected from the brake circuit via a valve. After the pressure reduction phase, the master brake cylinder can then be reconnected to the brake circuit so that pressure can be rebuilt.

[0021] As already explained, the brake system according to the invention is diagnostic-capable, so that it can, for example, detect the complete or partial failure of a component. Furthermore, monitoring of the brake fluid level can advantageously be carried out, whereby this can be done by means of a level sensor in the reservoir, thereby enabling the detection of even small leaks in the hydraulic brake system, in particular from the brake system to the outside, and allowing appropriate action to be taken.

[0022] Furthermore, the single master brake cylinder can be designed to be fail-safe. Thanks to the special valve circuit, the functionality of the remaining three wheel brake cylinders can be ensured by closing a valve if one wheel brake cylinder fails.

[0023] Depending on the valve circuit used, different levels of safety can be achieved, with level 2 / 2+ being the basis for the braking system according to the invention.

[0024] The braking system according to the invention exhibits a significantly higher level of fault tolerance compared to previously known braking systems with regard to faults occurring in the event of a wheel brake cylinder failure, a single master brake cylinder failure with travel simulator failure, and also a supply valve failure. By providing an additional redundant winding, the motor of the pressure supply unit can be connected to the motor control via 2 x 3 phases, which increases the fault tolerance of this component in particular, resulting in a lower failure probability for the pressure supply than the failure probability for a wheel brake cylinder failure.

[0025] The brake system according to the invention advantageously has at least one central outlet valve, via which a reservoir can be connected directly or via a circuit isolator valve to at least one wheel brake cylinder for pressure reduction. The pressure can be reduced in one wheel brake cylinder via the outlet valve, whereby pressure reduction can occur simultaneously or overlapping in another wheel brake cylinder. In the event of a failure of the pressure supply device, both brake circuits can also be supplied by the master brake cylinder.

[0026] The braking system according to the invention has only a single pressure supply device, which is driven by an electric motor.

[0027] If the pressure supply system includes a pump, such as a piston-cylinder pump, which can both build up and release pressure, a switchable feed valve is advantageously installed between the brake circuit and the pump. This valve prevents hydraulic fluid from flowing back into the pump in the event of pump failure. If the pressure supply system uses a pump solely for pressure build-up, a simple check valve is sufficient to prevent unwanted backflow from the brake circuit into the pump.

[0028] To enable braking even in the event of a failure of the pressure supply system, the braking system according to the invention comprises a master brake cylinder with a piston that can be actuated by an actuating device, in particular in the form of a brake pedal, and which is connected to a brake circuit or the safety gate via a hydraulic line that can be selectively shut off by means of a switching valve, in particular one that is normally open. Optionally, the working chamber of the master brake cylinder can be connected to a travel simulator.

[0029] In an advantageous further development of the braking system described above, electric wheel brakes are provided for braking a vehicle wheel of a vehicle axle, in particular one wheel of each axle. These electric wheel brakes can advantageously each also have a hydraulic connection, which is hydraulically connected to a brake circuit line via a hydraulic connecting line that can be selectively closed by means of a switching valve. By means of the pressure generated by the pressure supply device or the master brake cylinder, an additional braking torque can thus be advantageously generated for the associated vehicle wheel, which acts alone or in conjunction with the electric motor-generated braking force.

[0030] The aforementioned outlet valve allows for advantageous pressure reduction in a brake circuit or wheel brake directly into the reservoir via the brake circuit line. This makes it advantageously possible for the pressure reduction in at least one hydraulically actuated wheel brake to occur either via the pressure supply device or via an outlet valve, depending on the state of the hydraulic system and / or the pressure regulation situation.

[0031] The pressure supply device can either have a piston-cylinder pump or a rotary pump, in particular in the form of a gear pump.

[0032] If only a single circuit isolator valve is provided, by means of which the two brake circuits can be hydraulically connected or disconnected, the hydraulic supply line and the brake circuit line of the first brake circuit can be connected to one port, in particular the valve seat-side port, of the circuit isolator valve. The brake circuit line of the second brake circuit is then connected to the other port of the circuit isolator valve. However, it is also possible to reverse the connections for the brake circuits. This configuration results in a particularly cost-effective and simultaneously fail-safe brake system that requires only a few switching valves. In this brake system, the direct connection of the master brake cylinder is advantageously achieved via a hydraulic line connected to the brake circuit that is connected to the pressure supply system via the single circuit isolator valve.This separates the master brake cylinder and the pressure supply device from each other via at least two valves, advantageously creating redundancy.

[0033] The circuit isolation valve(s) form a safety gate (SIG). If an additional isolation valve is provided for the optional isolation of a brake circuit line, this isolation valve can also be included in the safety gate SIG.

[0034] An additional outlet valve can be provided for the first brake circuit, allowing pressure relief in this circuit as well. This additional outlet valve is particularly necessary if pressure relief is not possible via the pump of the pressure supply system itself. This can occur, for example, if a rotary pump is used. The additional outlet valve then allows hydraulic fluid to be diverted directly from the brake circuit line into the reservoir.

[0035] In the braking system according to the invention, the switching valve assigned to the respective wheel brake cylinder can be used for controlled pressure reduction, preferably by means of a pulse-width modulated signal, thereby advantageously controlling or regulating the rate of pressure change. This allows, for example, the pressure change or its temporal profile to be set or regulated depending on the braking situation or vehicle condition. A pressure sensor can also be used to determine the current pressure in the brake circuit and to use this as an input for a controller.

[0036] Pressure reduction for the ABS function is also possible via the switching valves and an outlet valve. The switching valve can be controlled by a pulse-width modulated (PWM) signal. If pressure reduction also occurs via a circuit isolating valve to the pressure supply or reservoir, this valve can also be controlled by a PWM signal. The remaining valves in the hydraulic connection between the wheel brake cylinder and the reservoir are then permanently open during pressure reduction.

[0037] To increase functional reliability, an additional, in particular normally open, isolating valve can be arranged in the brake circuit line of the first brake circuit, which serves to shut off the first brake circuit from the safety gate and the pressure supply device.

[0038] In the invention, the function of the travel simulator can be advantageously maintained in the event of a failure or leakage of the switching valve that decouples the master brake cylinder from the rest of the brake system, by closing the single circuit isolating valve or the two circuit isolating valves. In the event of a total failure of the switching valve, pressure can then be built up only in the first brake circuit by means of the pressure supply device, thus providing 50% of the braking effect of the brake system with diagonal distribution. If the front axle is assigned to the first brake circuit, at least 60% is still available. In contrast, in the event of only a slight leakage of the switching valve, additional brake pressure can be built up in the second brake circuit by means of the actuating device and the master brake cylinder, thus providing approximately 75% of the actual braking effect for emergency braking.In this case, the change in pedal characteristics compared to the travel simulator is also minimal. ABS is not possible in this scenario. Particularly with a low coefficient of friction, the wheels can lock up. If the brake valve has a small leakage rate, ABS can be activated by closing the brake valve and transferring power (P) via the safety valves (SV) and the central electric valve (ZAV). In this case, the brake valve remains closed in brake circuit 2 (BK2). For the initial parking (P) transfer, a smaller differential pressure is selected relative to the initial parking (P) transfer to prevent wheel lock-up. Both safety valves remain closed for the remainder of the braking process. Thus, steering control is maintained in this specific case.

[0039] The pressure reduction can still take place in the second brake circuit, as described above, especially for the ABS function, via the outlet valve.

[0040] An additional safety feature is the second circuit isolation valve, BP2, in the event of a failure of valve FV, which could be caused, for example, by a leak or a fault in the electrical connection. In this case, both circuit isolation valves, BP1 and BP2, close, thus advantageously preserving the position simulator function of the WS position simulator. In this case, braking is applied via the pressure supply unit DV to the first brake circuit, BK1, with approximately 50% braking effect due to diagonal brake circuit distribution. For emergency braking requiring a higher braking effect, the circuit isolation valve BP2 can optionally be opened. This allows additional pressure to be generated in the second brake circuit, BK2, via pedal force, increasing the braking effect to over 75%. In this case, the change in pedal characteristics compared to the position simulator is minimal. However, ABS functionality is not possible if valve FV fails.Particularly with a low coefficient of friction, the wheels can lock up in this case. However, if the brake valve (FV) has only a small leakage rate, the ABS function is still possible by closing the FV valve and releasing the pressure Pab via the respective switching valve SV and the outlet valve ZAV. In this case, the FV valve remains closed. A smaller differential pressure is selected relative to the pressure reduction Pab to prevent the wheels from locking up again. For the remainder of the braking process, both switching valves SV remain closed. Thus, steering is maintained in this special case.

[0041] For the aforementioned fault scenarios, diagonal brake circuit distribution is more advantageous due to its higher braking performance of 50% compared to front / rear axle brake circuit distribution. With the latter, in the event of a front axle failure, only approximately 30% of the braking force is available from the rear axle. In the emergency braking scenario, regardless of the front / rear axle brake circuit distribution or diagonal brake circuit distribution, approximately 75% braking force is available.

[0042] With the braking system according to the invention, a modified control concept for the ABS function can be used while retaining the basic algorithms, whereby significantly fewer valves are required and pressure measurement can also be carried out during pressure build-up.

[0043] The following section explains various possible embodiments of the braking system according to the invention with reference to drawings.

[0044] They show: Fig. 1: A first possible embodiment of the brake system according to the invention with a single master brake cylinder with travel simulator, valve circuit and pressure supply device with control and regulating unit as well as a safety gate with two circuit isolating valves; Fig. 2: A second possible embodiment of the brake system according to the invention with a single master brake cylinder with travel simulator, valve circuit and pressure supply device with control and regulating unit as well as a safety gate with only one circuit isolating valve, wherein hydraulically actuated wheel brakes are provided on the front axle and electromechanical brakes are provided on the rear axle; Fig.3: A third possible embodiment of the brake system according to the invention with a single master brake cylinder with travel simulator, valve circuit and pressure supply device with control and regulating unit as well as a safety gate with two series-connected circuit separating valves, wherein hydraulically actuated wheel brakes are provided on the front axle and hydraulically assisted electromechanical brakes are provided on the rear axle; Fig. 4a-c: various valve circuits for three different configurations of the pressure supply device.

[0045] Fig 1Figure 1 shows a first possible embodiment of the brake system according to the invention, wherein the single electrically driven pressure supply device DV acts from brake circuit BK1 into brake circuit BK2 via the hydraulic lines HL1, VLa, and HL5, through the switching valves SV and the circuit isolation valves BP1 and BP2, to the wheel brake cylinders RZ3 and RZ4. In contrast to the prior art, two circuit isolation valves BP1 and BP2 are used for circuit separation. The invention therefore provides two redundant valves BP1 and BP2 as safety features to enable the connection to brake circuit BK2 from the pressure supply device DV. In the event of a failure of the pressure supply device DV, e.g., a piston seal failure, feedback to brake circuit BK2 is prevented via the three redundant valves BP1, BP2, and PD1.Valves BP1 and BP2 are preferably normally open valves so that, in the event of a failure of the pressure supply unit DV, the master brake cylinder SHZ can act on both brake circuits BK1 and BK2. If pressure is reduced by opening valves ZAV and FV, the two circuit isolating valves open automatically due to the differential pressure without their own electrical control.

[0046] The switching valves have the following functions: a) Brake circuit failure at a wheel brake cylinder RZi. This failure is detected via the additional volume intake / delivery of the pressure supply unit DV compared to the so-called pv characteristic curve, which is read in as the vehicle characteristic curve during end-of-line inspection or measured at intervals in the vehicle. This detection method is known per se. However, with conventional brake systems, it is difficult to identify which wheel brake cylinder is affected or faulty. With the brake system according to the invention, however, locating this fault is relatively straightforward and quick. If the aforementioned deviation is detected, pressure is first built up, then the circuit isolation valve BP1 is closed, and the subsequent pressure profile is measured. This checks whether one or both wheel brake cylinders RZ3 and RZ4 are faulty. If the pressure changes, this indicates that at least one of the two wheel brake cylinders is faulty.To test which of the two wheel brake cylinders is faulty, the switching valve SV3 of wheel brake cylinder RZ3 is closed. If the pressure remains constant, the fault lies with wheel brake cylinder RZ4. If the pressure changes, wheel brake cylinder RZ3 has failed. If the pressure does not change, both wheel brake cylinders RZ3 and RZ4 are functioning correctly. Next, to check the wheel brake cylinders of the other brake circuit, the circuit isolating valve BP1 is opened and the switching valves SV3 and SV4 are closed. Now, the switching valve SV1 is closed. If the pressure remains constant, this indicates that wheel brake cylinder RZ2 is faulty. If the pressure changes, wheel brake cylinder RZ1 has failed. The wheel brake cylinders of the first brake circuit BK1 can also be tested simultaneously.The pressure supply unit DV can be used to measure the pressure curve in parallel with the wheel brake cylinders of the second brake circuit, BK2. If the pump moves with a constant current, this indicates a pressure drop, provided one of the switching valves SV1 or SV2 is open. b) Brake circuits BK1 and BK2 are protected by the interposed circuit isolation valves BP1 and BP2. Therefore, the braking effect remains greater than 70% even if one wheel brake cylinder fails. A triple failure would be required, meaning both valves BP1 and BP2 would also have to fail, for a total brake system failure to occur. At least one brake circuit is thus reliably protected against double failures, preventing a total brake system failure. Protection against double failures, when dormant faults can occur, is a crucial safety feature.The first brake circuit BK1 is also reliably protected against double failures when using the optional isolating valve TV1, meaning that even in the event of a double failure of one wheel brake cylinder RZi, three wheel brake cylinders can still be used thanks to the switching valves SVi.

[0047] The pedal movement is measured via redundant pedal position sensors, which simultaneously act on a crankshaft position sensor (CPS) measuring element as described in WO2012 / 059175 A1. The signal from the pedal position sensors controls the pressure supply unit (DV), whereby the piston control regulates the volume flow in the hydraulic main line (HL1) in brake circuit BK1 and, via the redundant circuit separators BP1 and BP2, in the second brake circuit BK2.

[0048] Actuating the pedal moves piston 3, which, via pressure proportional to the pedal force, acts on the known travel simulator WS and thus determines the pedal characteristics. The travel simulator WS can typically be deactivated via a valve 14, particularly in the fallback system in case of a pressure supply failure. By providing redundant windings with 2 x 3 phase connections (P1 and P2) and, in particular, simpler rotary pumps, the failure rate of the pressure supply unit DV is significantly lower than that of a brake circuit failure in systems without drive-by-wire and with additional pedal travel. Therefore, valve 14 can generally be omitted.

[0049] The master brake cylinder (SHZ) can be connected to brake circuits BK1 or BK2 via lines HL2 and HL3. Valve FV, located in lines HL2 and HL3, separates these two sections. This connection is only effective as a fallback. If the master brake cylinder (SHZ) is connected to the connecting line VLa of the two circuit isolating valves BP1 and BP2, these two valves provide additional redundancy. A conventional connection from valve FV directly to one of the brake circuits (BK1 or BK2) would, in the event of a leak in valve FV, result in the brake circuit, and thus the pressure supply device (DV), acting on piston 3, which would conventionally shut off the pressure supply.

[0050] An additional safety feature is the second circuit isolation valve, BP2, in the event of a failure of valve FV, which could be caused, for example, by a leak or a fault in the electrical connection. In this case, both circuit isolation valves, BP1 and BP2, close, thus advantageously maintaining the position simulator function of the WS position simulator. In this case, braking is achieved via the pressure supply unit DV into the first hydraulic circuit, BK1, with approximately 50% braking effect due to diagonal brake circuit distribution. For emergency braking requiring a higher braking effect, the circuit isolation valve BP2 can optionally be opened. This allows additional pressure to be generated in the second hydraulic circuit, or brake circuit BK2, via foot pressure, increasing the braking effect to over 75%. In this case, the change in pedal characteristics compared to the position simulator is also minimal. However, ABS functionality is not possible if valve FV fails.Particularly with a low coefficient of friction, the wheels can lock up in this case. However, if the brake valve (FV) has only a small leakage rate, the ABS function is still possible by closing the FV valve and releasing the pressure Pab via the respective switching valve SV and the outlet valve ZAV. In this case, the FV valve remains closed. A smaller differential pressure is selected relative to the pressure reduction Pab to prevent the wheels from locking up again. For the remainder of the braking process, both switching valves SV remain closed. Thus, steering is maintained in this special case.

[0051] For the aforementioned fault scenarios, diagonal brake circuit distribution is more advantageous due to its higher braking performance of 50% compared to front / rear axle brake circuit distribution. With the latter, in the event of a front axle failure, only approximately 30% of the braking force is available from the rear axle. In the emergency braking scenario, regardless of the front / rear axle brake circuit distribution, approximately 50% braking force is available, while with diagonal brake circuit distribution, it is 75%.

[0052] In Figure 1 The letters a and b indicate different functions in the two brake circuits BK1 and BK2 in the event of a valve FV failure: Case a) Braking occurs only via the first brake circuit BK1 with the pressure supply unit DV when the driver requests greater deceleration, for example, during emergency braking, which is indicated by Sp1. Case b) Braking occurs via the pressure supply unit DV in the first brake circuit BK1. In this case, the valve FV is only slightly leaking. Pressure can be built up in the second brake circuit BK2 using the master brake cylinder SHZ. If the ABS function is required, a pressure reduction P ab can be achieved via the outlet valve ZAV. The pressure is then built up P auf to a reduced pressure level via the pressure supply unit DV. After a certain period, during which further pressure build-up P auf occurs, the ABS function is activated again.

[0053] Besides its function in the event of a failure of the switching valve FV, the second function is the control function (unchanged for decades) for ABS. In a first stage, pressure reduction Pab occurs. If the controller reports that a wheel, for example, meets the criterion of excessive pressure, the pressure build-up Pauf can be stopped to monitor the wheel. If the controller then sends a signal indicating "too much braking torque / pressure," pressure reduction Pab begins. In this case, the outlet valve ZAV opens, and preferably the corresponding switching valve SVi is switched via pulse width modulation (PWM), thus controlling the rate of pressure reduction Pab. The pressure reduction Pab is stopped by the controller when the valves SV and ZAV close again. During this process, the circuit isolating valves BP1 and BP2 remain open.It is also possible to control two or four wheel brake cylinders RZ simultaneously in pressure reduction mode P ab, or the pressure reduction P ab takes place in the second brake circuit BK2 via the outlet valve ZAV and in the first brake circuit via the pressure supply device DV or an optional additional outlet valve ZAV2.

[0054] The pressure reduction P can also take place in the second brake circuit BK2 via the outlet valve ZAV and in the first brake circuit BK1 via the pressure supply device DV, which here also only acts as a pressure reduction.

[0055] The third function is pressure reduction P during normal braking. There are two possibilities here: a. The pressure reduction Pab occurs via all four switching valves SV1-4 with a brief stop, e.g., after Δt or Δp, via the outlet valve ZAV to equalize pressure in the two brake circuits, as the switching valves SV1-4 have tolerances. The pressure reduction Pab can also be controlled or regulated by pulse-width modulated switching valves SV. b. The pressure reduction Pab occurs either via the outlet valve ZAV or the single master cylinder SHZ, and one of the circuit isolation valves BP1 / BP2, provided it is energized by hydraulic fluid, can be controlled by pulse-width modulated signal for pressure control or regulation.

[0056] In Fig. 1The main components, master brake cylinder (SHZ), valve assembly (HCU), and control unit (ECU), are also shown. Pressure is generated via the brake pedal (1) and pedal plunger (2) through piston (3). This pressure is transferred via the normally open valve (FV) to the second brake circuit (BK2) and via the normally open circuit isolating valve (BP1) to the first brake circuit (BK1). Piston (3) has primary seals (D2) and secondary seals (D1), which are connected to the reservoir (VB) via check valve (RV1) and restrictor (Dr1). These components have an important safety function. If seal D2 fails, the leakage flow is throttled via restrictor (Dr1), resulting in a negligible piston-pedal movement, e.g., 0.2 mm / s = 2 mm over 10 s, i.e., approximately 0.05%. The average braking time is approximately 3 s to decelerate a vehicle from 100 km / h at 1 g.This means that the pedal movement in the event of a failure is very small, and conversely, a failure of seal D2 does not lead to a failure of the single master cylinder SHZ due to the throttle Dr1. The check valve RV1 facilitates easy bleeding by allowing the single master cylinder SHZ to transfer the volume of fluid to RV1 via the bleed screw. Brake fluid is drawn in via the check valve RV1. Seals D2 and D1 are safety-relevant. Seal D2 is protected by Dr1, and seal D1 by diagnostic functions. Therefore, seal D1 is diagnosed and its function is checked at every parking stop, for example, by measuring the residual pressure in the brake system through the open valve FV into the master cylinder SHZ. The pressure change is then measured by the pressure sensor DG, for example, over a period of 10 seconds, which would then indicate a leak in the entire brake system.If this is detected, a second test is performed by closing the switching valves SV to the wheel cylinders RZ1-4 and generating a specific pressure, e.g., 20 bar, from the pressure supply unit DV, which is then measured again by the pressure sensor DG. The delivery rate can be measured, for example, via the angular movement of the drive motor. If this is greater than the known delivery rate of the throttle Dr1, then the seal D1 is leaking. As an alternative to the throttle Dr1 with check valve RV1, a normally open solenoid valve MV can also be used, but this involves considerably higher costs. Normally, the SHZ piston 3 delivers the volume to the displacement simulator WS with the FV valve closed. This is the basic component of the "drive-by-wire" system.

[0057] The WS pedal travel simulator operates according to standard principles. Its piston contains elastic elements that generate a specific pressure-dependent force. Since the pedal force is converted into pressure and piston travel, a specific pedal travel force characteristic can be generated via the WS piston using the WS force.

[0058] As is known, the pedal characteristics in the travel simulator system are always the same and independent of, for example, the failure of a brake circuit, thus preventing pedal dips and offering significant advantages in electric vehicles with regenerative braking using the electric motor. Here, the driver determines how much brake pressure, in addition to the braking torque of the electric motor, the pressure supply unit (DV) must generate to achieve the desired braking effect. The pedal travel is measured redundantly via the pedal travel sensors, which determine the brake pressure generated by the pressure supply unit (DV) and measured by the pressure sensor (DG).

[0059] There are various solutions for implementing redundant pedal travel sensors. These are also described in PCT / EP2016 / 055471.

[0060] The redundant pedal position sensors can be coupled with two pistons, as shown, and a spring between the two pistons. This has the advantage of enabling force displacement measurement, with additional benefits for fault analysis, e.g., regarding a jammed piston 3. This is disclosed, among other places, in DE102010050132.

[0061] If the pressure sensor DG fails, the pressure can also be adjusted via the motor current, as the current-pressure relationship for pressure increase and pressure decrease (P up and P down) is stored in a characteristic map for this case. The travel simulator WS has two seals, D3 and D3r. A redundant seal, D3r, with a restrictor Dr3, is located downstream of seal D3 and performs the same function as Dr1. If seal D3 fails, a leakage occurs, which is throttled by Dr3 and does not lead to a failure of the master brake cylinder (SHZ). Diagnosis is performed together with seals D1 and D2, as described. The travel simulator WS has a standard throttle for pedal movement along with a check valve RV for rapid drainage of the travel simulator WS.

[0062] The sealing and throttling configuration creates a fail-safe SHZ, which is of great importance when foregoing a tandem HZ with redundant piston.

[0063] The pressure supply unit DV is shown only in principle and is described in detail in PCT / EP2018 / 071923. The feed valve PD1 has a safety function in case of failure of the pressure supply unit DV. Brake fluid can be replenished from the reservoir VB via the check valve RV2. The feed valve PD1 can also be omitted if the pump of the pressure supply unit DV is self-locking and the pump does not allow pressure reduction in the brake circuit even without a functioning drive.

[0064] The valves, the pressure supply unit (DV), and the master brake cylinder (SHZ) are integrated into a single unit. The electronic control unit (ECU), according to current technology, comprises all electrical and electronic components and electrical connections to the sensors and solenoid valves via coils connected to the printed circuit board (PCB). Connection to the vehicle's electrical system is made via connector 13 (single or double).

[0065] The Fig. 2 shows a simplified solution of the safety gate SIG with only one circuit isolation valve BP1 for a mixed braking system with electromechanical rear axle brake.

[0066] The master brake cylinder SHZ corresponds to the one in Fig. 1 The depicted master brake cylinder. The safety gate SIG with its valve BP1, together with the outlet valve ZAV, the valve FV and the switching valves SV, enables almost all functions of the brake system according to [relevant standard / regulation]. Fig. 1 as described. Without the second circuit isolating valve BP2, the second brake circuit BK2 is not doubly fail-safe in the event of a faulty valve FV. The pressure supply device DV is separated from brake circuit BK1 via the check valve RV3, so that if a rotary piston pump is used, no hydraulic fluid can flow back from brake circuit BK1 into the pump.

[0067] The rear axle (HA) uses electromagnetic brakes (EMB), which, according to current technology, can also function as the parking brake and can be used for the ABS function. The electrical functions are integrated into the control unit (ECU). Optionally, an additional outlet valve (ZAV2), shown with a dashed line, can be provided for brake circuit BK1, allowing pressure relief (Pab) to the reservoir (VB).

[0068] The Fig. 3 The security gate SIG is shown again Fig. 1 with the same pressure supply device DV, outlet valve ZAV and valve FV, with brake circuits BK1 and BK2 and the master brake cylinder SHZ and the control and regulation unit ECU. In contrast to the in Fig. 2The electromechanical brakes EMB shown are the electromechanical brakes used on the rear axle, which are additionally hydraulically assisted. These brakes are known from PCT / EP2019 / 061909. The two hydraulically assisted electromechanical brakes EMB2 and EMB4 are assigned to the third brake circuit BK3 and perform the function of the primary brakes with ABS function and the function of the parking brake. The EMB function is limited to fixing the braking effect of the parking brake via a correspondingly designed configuration (see PCT / EP2019 / 061909) and to the ABS function in the emergency level, particularly in the event of a failure of the pressure supply system.The advantage lies in the significantly lower costs of the hydraulically assisted electromagnetic brake EMB2, EMB4, which is similar to today's parking brake. However, the motor has a higher power output for emergency operation of the rear axle brake and also the ABS function in the event of a failure of the pressure supply unit DV. Here, too, an additional outlet valve ZAV2, shown with a dashed line, can be optionally provided for brake circuit BK1, allowing pressure relief Pab to the reservoir VB.

[0069] The Fig. 4a - 4c show variants of the pressure supply device DV, where the valve circuits of the safety gate SIG are those of the Figs. 1 to 3 same.

[0070] Fig. 4a This corresponds to the Fig. 1 .

[0071] Fig. 4bFigure 1 shows a version with a piston pump and an additional central outlet valve (ZAV) for pressure reduction (P), as the piston pump's outlet valves do not allow for this. As an alternative to the feed valve (PD1), a check valve (RV3) can be used (see figure 1). Fig. 2 .

[0072] The Fig. 4c The diagram shows a gear pump which requires the switchable feed valve PD1 due to leakage. The advantage of the gear pump is its ability to deliver volume in both directions, allowing for controlled pressure build-up and pressure drop. If the pump used does not exhibit leakage, the valve PD1 can be omitted.

[0073] In all solutions, the pressure supply unit DV provides both an angle signal of the rotor and the current measurement of the EC motor. Reference symbol list

[0074] SHZ Single master brake cylinder ECU Electronic control unit HCU Hydraulic control unit KWS Force displacement sensor RV1 Check valve 1 RV2 Check valve 2 RV3-6 Check valve 3-6 RF Return spring Dr 1-3 Throttles RZ1-4 Wheel cylinders SV 1-4 Switching valves DV Electromotive pressure supply unit HL 1,3, 4,5 Hydraulic line connections VB Reservoir ZAV1 / 2 Central outlet valve BP1 / 2 Circuit isolation valve FV Feed valve from SHZ to BK SV Switching valve to RZ DG Pressure sensor p = f (v) V Diagnostic valve E Valve spring WS Position simulator, piston D1-3 Seals Sp1,2 Pedal position sensors TV1 Isolation valve SIG Safety gate EMB Electromotive brake a) P on / P off in case of fault FV with DV in BK1 b) P on / P off in case of fault FV with DV and SHZ with ABS 1Brake pedal 2Pedal plunger 3HZ piston 4HZ housing 5PCB 6Sensor element for level sensor 7Sensor target 8Float in reservoir 9Electrical elements for travel simulators for force characteristics 10Redundant electrical connection, if applicablewith redundant coil 11 redundant connection to motor for 2 x 3 phase winding 12 redundant connection for 2 x 3 phase motor 13 electrical plug for on-board power supply connection 14 path simulator isolating valve.

Claims

1. A brake system for a vehicle having a front axle (VA) and a rear axle (HA), wherein the brake system comprises: - one electromechanical wheel brake (EMB2, EMB4) on each wheel of the rear axle (HA); - a first brake circuit (BK1) and, optionally, a second brake circuit (BK2), each with a brake circuit line (HL4, HL5) for a hydraulically acting wheel brake (RB1, RB3) for a wheel of the front axle (VA) of the vehicle, - a third brake circuit (BK3) with a third brake circuit line (HL6) for at least one hydraulically acting wheel brake (RB2, RB4) for a wheel of the rear axle (HA), - a pressure supply device (DV), - a control unit (ECU) for controlling the pressure supply (DV) and the electromechanical brakes (EMB2, EMB4), - wherein the pressure supply device (DV) is used to perform pressure build-up (Pauf) in the hydraulic wheel brakes (RB1, RB2, RB3, RB4) via each brake circuit (BK1, BK2, BK3), characterized in that the control unit (ECU) is configured to control the electromechanical wheel brakes (EMB2, EMB4) and the at least one hydraulically acting wheel brake (RB2, R4) of the third brake circuit (BK3) such that ∘ the electromechanical wheel brakes (EMB2, EMB4) are hydraulically assisted and have both the functionality of a primary brake with ABS functionality and the functionality of a parking brake; and / or ∘ the electromechanical wheel brakes (EMB2, EMB4) have ABS functionality in emergency mode, in particular in the event of failure of the pressure supply device (DV).

2. The brake system according to claim 1, characterized in that the pressure supply device (DV) comprises a pump, in particular a piston-cylinder pump, which may be used to perform pressure build-up (Pauf) and pressure reduction (ab), wherein a feed hydraulic line (HL1) is provided as a hydraulic connection from the pressure supply device (DV) to the brake circuits (BK1, BK2, BK3), wherein a feed valve (PD1) is used to selectively close and open the feed hydraulic line (HL1).

3. The brake system according to claim 1 or 2, characterized in that at least one outlet valve (ZAV) is provided, through which a brake circuit line (HL4, HL5, HL6) of a brake circuit may be connected directly to a reservoir (VB) for pressure reduction (Pab).

4. The brake system according to claim 3, characterized in that the pressure reduction (Pab) in at least one hydraulically acting wheel brake (RB1-4) is performed depending on the state of the hydraulic system and / or the pressure control situation, either via the pressure supply device (DV) or via an outlet valve (ZAV).

5. The brake system according to claim 3 or 4, characterized in that the valves, pressure supply device (DV), master cylinder (SHZ) and reservoir (VB) are combined in a single assembly.

6. The brake system according to any one of the preceding claims, characterized in that the control unit (ECU) is connected to the on-board network in a redundant manner via a dual connection (B1, B2).

7. The brake system according to any one of the preceding claims, characterized in that the pressure supply device (DV) includes a motor (M) connected to the control unit (ECU) of the pressure supply device (DV) via 2 x 3 phases.

8. The brake system according to any one of the preceding claims, characterized in that individual brake circuits (BK1, BK2) are provided for each hydraulically acting wheel brake (RB1, RB3) for the wheels of the front axle (VA), wherein a control valve (SV1, SV3) is provided for each hydraulically acting wheel brake (RB1, RB3) of the front axle (VA).

9. The brake system according to any one of the preceding claims, characterized by a single master cylinder (SHZ), which is operable via an operating unit configured as a brake pedal (1), and which has only one working space (110), wherein the working space (110) is connected or connectible to the third brake circuit (BK3) via a hydraulic line (HL3) with a normally open isolation valve (TV).

10. The brake system according to claim 9, characterized in that the working space (110) of the master cylinder (SHZ) is connected or connectible to a reservoir (VB) via a check valve (RV1) and a throttle valve (Dr1).

11. The brake system according to claim 10, characterized in that the reservoir (VB) includes at least one level sensor (7, 8) and that a sensor (6) is provided for detecting the position of the level sensor (7, 8).

12. The brake system according to claim 11, characterized in that the level of the hydraulic fluid in the reservoir (VB) may be or is continuously determined by means of the level sensor (7, 8) and the sensor (6) in order to detect a leak.

13. The brake system according to any one of the preceding claims, characterized in that a pressure transducer (DG) is provided to determine the pressure (p) present in at least one brake circuit (BK1, BK2, BK3), wherein the pressure transducer (DG) is configured to determine the pressure (p) in one of the brake circuit lines (HL4, HL5, HL6).

14. The brake system according to any one of the preceding claims, characterized in that a normally open control valve (FV) is used to selectively close or open a connection between a hydraulic wheel brake cylinder (RZ1, RZ3) and one of the brake cylinders (BK1, BK2, BK3).

15. The brake system according to any one of the preceding claims, characterized in that at least one normally open circuit isolation valve (BP1, BP2) is provided, which is provided to selectively close or open a hydraulic line (HL2, HL3) connecting the pressure supply device (DV) or the single master cylinder (SHZ) to one of the brake cylinders (BK1, BK2, BK3).

16. The brake system according to any one of the preceding claims, characterized in that the working space (110) of the master cylinder (SHZ) is connected to a travel simulator (WS).

17. The brake system according to any one of the preceding claims, characterized in that pressure reduction (Pab) is performed in all hydraulic wheel brakes (RB1, RB3) of the front axle (VA) via a respectively associated control valve (SV1, SV3).