Brake system with pressure supply for brake circuit and safety gate

Abstract

The present invention relates to two brake circuits (BK1, BK2) each including brake circuit lines (HL4, HL5) for two axles (VA, HA) and at least one hydraulically operated wheel brake (RB1 to RB4) in each brake circuit (BK1, BK2), wherein each hydraulically operated wheel brake (RB1 to RB4) can be connected to the wheel brake circuits (BK1, BK2) or to the brake circuit lines (HL4, HL5) of the wheel brake circuits (BK1, BK2) via a pair of switching valves (SV), and a pressure (P) can be accumulated in at least one wheel brake (RB1 to RB4) via the pair of switching valves (SV). auf ) and release (P ab ) and pressure is accumulated in both brake circuits (BK1, BK2) via a pressure supply device (DV). auf ) or accumulate (P auf ), at least one circuit isolation valve (BP1, BP2) that is open in a non-energized state in order to selectively cut off or release the hydraulic connection line (VL) connecting the two brake circuits (BK1, BK2), and a pressure release valve (P ab The invention relates to a brake system having at least one outlet valve (ZAV, ZAV1) capable of connecting an accumulator vessel (VB) to at least one brake circuit (BK1, BK2) for selectively closing or releasing the hydraulic lines (HL2, HL3) of the brake circuits (BK1, BK2), in particular a master cylinder (SHZ) operated by an actuator in the form of a brake pedal (1) provided with a single working chamber (110), which can be hydraulically connected to the brake circuit lines (HL4, HL5) of the brake circuits (BK1, BK2) either directly via hydraulic lines (HL2, HL3) or via circuit isolation valves (BP1, BP2), and a switching valve, in particular open in the de-energized state, is used to selectively close or release the hydraulic lines (HL2, HL3).

Description

[Technical Field]

[0001] The present invention relates to a brake system suitable for two axles, having two brake circuits each with a brake circuit line, each brake circuit being provided with at least one hydraulically operated wheel brake, each hydraulically operated wheel brake being connectable to a brake circuit of the brake system or to a brake circuit line of the brake circuit by means of a respectively assigned change-over valve, and pressure build-up and pressure reduction of each wheel brake being performed via the respectively assigned change-over valve. The brake system further comprises a pressure supply device by means of which pressure build-up is or can be performed in both brake circuits, and at least one circuit isolation valve, which is opened in particular when electrically de-energized, serves to selectively disconnect and open the hydraulic connection line connecting the two brake circuits.

[0002] Conventional technology In recent years, the trend in braking systems has been toward integrated versions, known as "one-box," that combine electrohydraulic brakes (E-Boost) with a master brake cylinder, "drive-by-wire," and ABS / ESP functions. The systems differ significantly in the structural design of the pressure supply and the valve circuit. Simplified circuits using the so-called multiplexing technology (MUX), which lack an outlet valve and incorporates pressure modulation by the pressure supply, are also known. Alternatives to tandem master brake cylinders include those with a separate chamber between the pressure supply piston and the floating piston, and more recently, single master brake cylinders without a floating piston. For diagnostic purposes, a diagnostic valve is always provided for tandem master brake cylinders. Brake systems also differ significantly in terms of fail-safes.

[0003] A wide variety of concepts and components are already known, inter alia, from the following patent documents: EP 3333031 A2 discloses a brake system with a tandem master brake cylinder (THZ), DE 102014111594 A1 and DE 102018111126 A1 disclose tandem master brake cylinders with pressure supply (THZ+DV), DE 102017201243 A1 discloses a pressure supply device (DV), DE 102017219598 A1 discloses a single master brake cylinder (SHZ), and DE 10309145 A1 discloses a diagnostic valve.

[0004] The increasing use of hydraulic systems with two or more circuits increases the safety requirements for hydraulic systems with two or more circuits. In particular, the following fault conditions and functions must be considered or provided:

[0005] a. Failure or malfunction of one hydraulic circuit must not affect the function of the other hydraulic circuit; b. Even if there is only one pressure supply, in the event of failure of the pressure supply, i.e. at an emergency level, pressure boosting by a master brake cylinder operable via the brake pedal must still be possible; c. If only one pressure supply is available, a low-power auxiliary pressure supply for so-called emergency operation is required in case of failure of the pressure supply, d. Hydraulic circuits must supply closed-loop control systems that require both open-loop and / or closed-loop controlled pressure increases and open-loop and / or closed-loop controlled pressure decreases for closed-loop control operation.

[0006] To ensure the fail-safety of hydraulic systems, it is necessary to always use diagnostic functions or diagnostic programs that can track down hydraulic system faults and implement corresponding countermeasures. It is especially important to pay attention to single faults and double faults.

[0007] Single and double faults that can occur in a hydraulic system are described below based on a dual circuit brake system.

[0008] The extent to which a vehicle can take over a driver's tasks when necessary, and how humans and machines interact on the road today and in the future, are described at various stages of development. Five levels of vehicle automation are often referenced and are described below.

[0009] Level 1: Driving assistance, where the driver assistance system assists the driver but is not yet able to control the vehicle itself.

[0010] Level 2: Partial driving automation, in which the system can, among other things, take over the steering of the vehicle, but the driver remains in charge at all times.

[0011] Level 3: High driving automation, which allows the driver to divert their attention from the driving situation for extended periods in certain circumstances.

[0012] Level 4: Full driving automation, where the vehicle primarily drives independently but the driver must still be able to drive.

[0013] Level 5: Autonomous driving, where the vehicle takes over all driving functions and the people inside the vehicle are purely passengers.

[0014] Therefore, whether single and / or double failures of the braking system can be tolerated depends on the degree of automation or the above level of the vehicle.

[0015] I. Single Fault For braking systems for Level 2 vehicles, a single failure is acceptable if a minimum braking effect of less than approximately 0.3 G is still achieved. However, such low levels of braking deceleration may already be classified as an extremely high accident risk.

[0016] Braking systems for Level 3 vehicles must achieve a braking deceleration of at least 0.5G and must also have ABS functionality.

[0017] II. Double fault with complete brake failure In many systems, double failures are acceptable if the failure probability is low based on ppm and FIT data.

[0018] Risks arise especially from dormant disorders if the corresponding diagnosis is not carried out.

[0019] For high safety requirements, a critical single fault, for example causing the braking effect to be reduced to less than 0.5 g, must be able to be prevented by redundancy and identified by diagnostic functions.

[0020] A typical case of dormant failure is outlined below.

[0021] A braking system may have only one pressure supply device, for example, supplying two brake circuits with four wheel brakes via a supply valve. If one of the four wheel brakes fails, it is not possible to immediately identify the location of the fault in the four wheel brakes. As a result, the entire pressure supply fails. A reduced level of pressure can still be supplied to only one brake circuit by an auxiliary pressure supply, such as a master brake cylinder that can be activated by the brake pedal. Due to the extremely low pressure level, only a very weak and therefore dangerous braking effect may be achieved. Critical components may also not usually be able to be diagnosed. For example, it is not possible to diagnose the leak tightness of a solenoid valve, which is normally always open, because it leaks and therefore fails only when the operating state changes to another state.

[0022] A double fault with a resting fault occurs, for example, when one brake circuit fails, which is connected to the other brake circuit only through one circuit isolation valve. The circuit isolation valve, which is normally open, must close in the event of a brake circuit failure. However, due to the (resting) fault, the circuit isolation valve does not close completely, which results in the other brake circuit also failing, leading to a complete failure of the brake system.

[0023] The major costs of a braking system arise from the (tandem) master brake cylinder, the pressure supply, the number and type of valves required, the pressure transducers, and the open and closed loop controls.

[0024] Object of the invention The object underlying the present invention is to provide a braking system that reduces costs and structural volume and improves safety and / or failure probability caused by faults.

[0025] This object is achieved according to the invention by a braking system having the features of claim 1. Advantageous refinements of the braking system according to claim 1 are evident from the features of the dependent claims.

[0026] Advantages of the invention The brake system according to the present invention is advantageously characterized by operating with a small number of valves, in particular switching valves, which simplifies the design, requires less structural space, and is less expensive. This is possible in particular due to the special design of the safety gate, which allows the two brake circuits to be selectively isolated or connected to each other. At the same time, the brake system according to the present invention has an extremely high level of fail-safety and a low probability of failure. Furthermore, the brake system according to the present invention offers numerous diagnostic options for identifying faults, in particular faults in the idle state. Even in the event of a fault, the brake system generally still provides sufficient brake pressure or a sufficiently high level of brake deceleration.

[0027] Thanks to the special valve circuit, the master brake cylinder can be used to supply pressure even if the pressure supply device fails, and in the event of a critical situation or wheel lock, pressure reduction can be advantageously carried out via the outlet valve in an open-loop or closed-loop controlled manner. Here, a valve controlled by a pulse-width modulated signal allows the pressure reduction, and in particular the progression of the pressure reduction over time, to be precisely controlled in an open-loop or closed-loop manner. During the pressure reduction, the master brake cylinder must then be isolated from the brake circuit by the valve. After the pressure reduction phase, the master brake cylinder can then be reconnected to the brake circuit and pressure buildup can be carried out again.

[0028] As already mentioned, the braking system according to the invention has diagnostic capabilities, for example, to identify complete or partial failures of components. Furthermore, brake fluid level monitoring can be advantageously performed, which can be performed using a level sensor in the reservoir, so that even small leaks in the hydraulic braking system, especially leaks to the outside of the braking system, can be identified and responded to accordingly.

[0029] Furthermore, single master brake cylinders can be designed to be fail-safe: a special valve circuit advantageously ensures the function of the other three wheel brake cylinders by closing the valves in the event of a failure of one wheel brake cylinder.

[0030] Depending on the valve circuit used, different levels of safety can be achieved, Level 2 / Level 2+ being the basis for the braking system according to the invention.

[0031] The brake system according to the invention has a significantly higher fail-safety than previously known brake systems with respect to faults occurring in the event of failure of a wheel brake cylinder, failure of a single master brake cylinder with stroke simulator, and failure of a supply valve. By providing an additional redundant winding, the motor of the pressure supply device can be connected to the motor controller in a dual three-phase manner, which significantly increases the fail-safety of this component, and therefore the probability of failure of the pressure supply is lower than the probability of failure of the wheel brake cylinder.

[0032] The brake system according to the present invention advantageously has at least one central outlet valve by which the reservoir can be connected to at least one wheel brake cylinder for pressure reduction, either directly or via a circuit isolation valve. Pressure in one wheel brake cylinder can be reduced via the outlet valve, and pressure reduction can be performed simultaneously or overlappingly in another wheel brake cylinder. Furthermore, in the event of a pressure supply device failure, a master brake cylinder can be used to supply pressure to both brake circuits.

[0033] The braking system according to the invention has only a single electrically driven pressure supply device.

[0034] If the pressure supply device has a pump, such as a piston-cylinder pump, which can perform not only pressure boosting but also pressure reduction, a switchable supply valve is advantageously arranged between the brake circuit and the pump, which prevents working medium from flowing back into the pump in the event of a pump failure.If a pump is used as the pressure supply device only for pressure boosting, a simple check valve is sufficient to prevent unwanted backflow from the brake circuit to the pump.

[0035] In order to be able to carry out braking even in the event of failure of the pressure supply device, 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, which is connected via hydraulic lines to the brake circuit or to the safety gate and can be selectively blocked by a switching valve that is open in the electrically de-energized state, in particular. The working chamber of the master brake cylinder can optionally be connected to a stroke simulator.

[0036] In an advantageous refinement of the above-mentioned braking system, electric wheel brakes are provided for braking the vehicle wheels of the axles, in particular One Axle each The electric wheel brakes are provided for braking the vehicle wheels. These electric wheel brakes can advantageously each have an additional hydraulic connection, and are connected or connectable to the hydraulic connection or the brake circuit line via a hydraulic connection line that can be selectively closed by a switching valve. Thus, by means of the pressure generated by the pressure supply device or the master brake cylinder, an additional braking torque can be advantageously generated at the assigned vehicle wheel, which acts alone or to supplement the electrically generated braking force.

[0037] By means of the outlet valve, the brake circuit depressurization or wheel brake depressurization can advantageously be effected directly via the brake circuit line to the reservoir. In this way, the depressurization can advantageously be effected in at least one hydraulically actuated wheel brake by the pressure supply device or via the outlet valve in a manner that depends on the state of the hydraulic system and / or the closed-loop pressure control situation.

[0038] The pressure supply device can comprise either a piston-cylinder pump or a rotary pump, especially in the form of a gear pump.

[0039] When only one circuit isolation valve is provided, thereby hydraulically connecting or isolating two brake circuits from one another, the supply hydraulic line and the brake circuit line of the first brake circuit can be connected to a connection on the circuit isolation valve, particularly to the valve seat side. The brake circuit line of the second brake circuit is then connected to the other connection on the circuit isolation valve. However, it is equally possible to interchange the brake circuit connections. This configuration results in a particularly inexpensive, fail-safe brake system requiring only a few switching valves. In this brake system, the direct connection to the master brake cylinder is advantageously realized via a hydraulic line connected to the brake circuit, which is connected to the pressure supply device via a single circuit isolation valve. In this way, the master brake cylinder and the pressure supply device are isolated from each other by at least two valves, thereby advantageously providing redundancy.

[0040] The circuit isolation valves form a safety gate (SIG). If an additional isolation valve is provided to selectively isolate the brake circuit lines, this isolation valve can also be considered to belong to the safety gate SIG.

[0041] An additional outlet valve for the first brake circuit can be provided, allowing the pressure in that circuit to be reduced in the same way. This is especially true when the pressure reduction is not possible using the pump in the pressure supply device itself. This is the case, for example, when a rotary pump is used as the pump. The working medium can then be discharged from the brake circuit line directly into the reservoir via the additional outlet valve.

[0042] In the braking system according to the invention, the switching valves assigned to each wheel brake cylinder can be used for controlled pressure reduction, particularly preferably by pulse-width modulated signals, so that the rate of pressure change can be advantageously controlled in an open-loop or closed-loop manner. In this way, the pressure change over time or its progression can be set or can be set by closed-loop control, for example, in a manner that depends on the brake state or vehicle situation. For this purpose, a pressure transducer can also be used to determine the current pressure in the brake circuit and use it as an input variable for the closed-loop controller.

[0043] The ABS function can also be depressurized or realized by the switching valve and the outlet valve. Here, the switching valve can be controlled by a pulse-width modulated signal. If the pressure reduction is also implemented to the pressure supply or reservoir via the circuit isolation valve, the circuit isolation valve can also be controlled by a pulse-width modulated signal. The remaining valves through which the flow passes in the hydraulic connection between the wheel brake cylinder and the reservoir are permanently open during the pressure reduction.

[0044] To increase the reliability of the function, an additional isolation valve, which opens in particular when electrically de-energized, can be arranged in the brake circuit line of the first brake circuit, and this additional isolation valve serves to isolate the first brake circuit with respect to the safety gate and the pressure supply device.

[0045] In the present invention, if a fault or leak occurs in the switching valve that could isolate the master brake cylinder from the rest of the brake system, the single or two circuit isolation valves are closed, advantageously preserving the function of the stroke simulator. In the event of a complete failure of the switching valve, the pressure supply device can then be used to boost only the first brake circuit, so that in the case of diagonal distribution, 50% of the braking system's braking effort remains available. Even if the front axle is assigned to the first brake circuit, 60% is still available. In contrast, if the switching valve leaks only slightly, the actuator and master brake cylinder can provide additional brake pressure boost in the second brake circuit, thus leaving approximately 75% of the actual braking effort available for emergency braking. In this case, the pedal characteristic does not change significantly with respect to the stroke simulator. In this case, the ABS function cannot be used. Wheel locking is possible, especially with low friction coefficients. Even with a low leakage rate through valve FV, closing valve FV and supplying P via valves SV and ZAV are possible. reduction In this case, the valve FV of the brake circuit BK2 remains closed. build-up In this case, to prevent new locks, reduction A smaller pressure difference is selected for . During the remaining braking action, both valves SV remain closed. Thus, in this particular case, maneuverability is maintained.

[0046] Then, as described above, pressure reduction can be carried out in the second brake circuit via the outlet valve, in particular also for the ABS function.

[0047] The second circuit isolation valve BP2 provides additional safety in the event of a malfunction of valve FV, for example, due to a leak or fault in an electrical connection. In this case, the two circuit isolation valves BP1 and BP2 are closed, thereby advantageously maintaining the stroke simulator function of the stroke simulator WS. In this case, braking is performed by the pressure supply device DV of the first brake circuit BK1, which provides approximately 50% braking force in the case of a diagonal brake circuit distribution. In the case of an emergency braking operation with a higher braking force desired by the driver, the circuit isolation valve BP2 can optionally be opened, in which case additional pressure can be generated in the second brake circuit BK2 by the force applied by the foot, increasing the braking force by 75% or more. In this case, the pedal characteristic change to the stroke simulator is also not significant. However, if valve FV fails, the ABS function cannot be used. In this case, the wheels may lock, especially in low friction conditions. However, even if the leakage rate of only the valve FV is low, the valve FV can be closed and the pressure reduction P can be reduced through each of the switching valves SV and the outlet valve ZAV. reduction In this case, the valve FV remains closed. build-up In this case, the pressure is reduced to prevent further locking of the vehicle wheels. reduction A smaller pressure difference is selected for SV. During the remaining braking action, both directional control valves SV remain closed. Thus, in this particular case, maneuverability is maintained.

[0048] In the above failure scenario, a diagonal brake circuit distribution is more preferable because it increases the braking effort by 50% for the front / rear axle brake circuit distribution. However, if the front axle VA fails, only about 30% is available for the rear axle HA. In the case of circuits with so-called emergency braking, about 75% is applied regardless of the VA / HA brake circuit distribution and the diagonal brake circuit distribution.

[0049] The braking system according to the present invention allows for a modified closed-loop control concept of the ABS function while maintaining the basic algorithm, requires significantly fewer valves in the braking system, and also allows pressure measurements to be performed during pressure buildup.

[0050] Various possible embodiments of the braking system according to the invention are discussed below with reference to the drawings. [Brief explanation of the drawings]

[0051] [Figure 1] FIG. 1 shows a first possible embodiment of a braking system according to the invention, comprising a single master brake cylinder with a stroke simulator, a valve circuit and pressure supply device with open-loop and closed-loop control units, and a safety gate with two circuit isolation valves. [Figure 2] FIG. 2 shows a second possible embodiment of a braking system according to the invention with a single master brake cylinder with a stroke simulator, a valve circuit and pressure supply with open-loop and closed-loop control units, and a safety gate with only one circuit isolation valve, in both cases the front axle is provided with hydraulically operated wheel brakes and the rear axle is provided with electromechanical brakes. [Figure 3] FIG. 3 shows a third possible embodiment of a braking system according to the invention, comprising a single master brake cylinder with a stroke simulator, a valve circuit and pressure supply device with open-loop and closed-loop control units, and a safety gate with two series-connected circuit isolation valves, in both cases the front axle is provided with hydraulically operated wheel brakes and the rear axle with hydraulically assisted electromechanical brakes. [Figure 4a] 10A-10C show different valve circuits for three different configurations of the pressure supply device. [Figure 4b] 10A-10C show different valve circuits for three different configurations of the pressure supply device. [Figure 4c] 10A-10C show different valve circuits for three different configurations of the pressure supply device.

[0052] FIG. 1 shows a first possible embodiment of a brake system according to the present invention. A single electrically driven pressure supply DV connects brake circuit BK1 to brake circuit BK2 via hydraulic lines HL1, VLa, and HL5, a switching valve SV, and circuit isolation valves BP1 and BP2, acting on wheel brake cylinders RZ3 and RZ4. In the prior art, two circuit isolation valves BP1 and BP2 are used for circuit isolation. Therefore, the present invention provides two redundant valves as safety functions BP1 and BP2 to enable connection of pressure supply DV to brake circuit BK2. In the event of a failure of pressure supply DV, for example, a piston seal failure, the three redundant valves BP1, BP2, and PD1 prevent counteracting brake circuit BK2. Valves BP1 and BP2 are preferably electrically de-energized valves that are open so that in the event of a failure of pressure supply device DV, master brake cylinder SHZ can act on both brake circuits BK1 and BK2. When pressure is reduced by opening valves ZAV and FV, the two circuit isolation valves automatically open without dedicated electrical actuation due to the pressure differential.

[0053] The switching valve has the following functions:

[0054] a) A brake circuit fault at wheel brake cylinder RZi. This fault is identified by an additional intake / delivery volume of the pressure supply device DV relative to the so-called pv characteristic curve, which is read as a vehicle characteristic curve at the end of the line test or measured at intervals in the vehicle. This method of identification is known per se. However, in the case of a normal brake system, it is difficult to determine which wheel brake cylinder is affected or has failed.

[0055] However, in the braking system according to the present invention, wheel brake cylinder failures can be located relatively easily and quickly. If such a deviation is detected, the pressure first rises, then the circuit isolation valve BP1 is closed, and the subsequent pressure progression is measured. Thus, a check is performed to determine whether one or both of the 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. Next, the switching valve SV3 of the wheel brake cylinder RZ3 is closed to determine which of the two wheel brake cylinders has failed. If the pressure remains constant, a fault exists in the wheel brake cylinder RZ4. In contrast, if the pressure changes, a fault exists in the wheel brake cylinder RZ3. If the pressure does not change, both the wheel brake cylinders RZ3 and RZ4 are functioning normally. Next, the circuit isolation valve BP1 is opened, and the switching valves SV3 and SV4 are closed to check the wheel brake cylinders of the other brake circuit. Next, the switching valve SV1 is closed. If the pressure remains constant, this indicates a fault in wheel brake cylinder RZ2. In contrast, if the pressure changes, a fault exists in wheel brake cylinder RZ1. The wheel brake cylinders of the first brake circuit BK1 can also be checked simultaneously or in parallel with the wheel brake cylinders of the second brake circuit BK2 by measuring the pressure progression using the pressure supply device DV. If the pump moves with a constant current, this is an indication of a pressure drop if either directional control valve SV1 or directional control valve SV2 is open.

[0056] b) Brake circuits BK1 and BK2 are protected by the interconnection of the two circuit isolation valves BP1 and BP2. Therefore, even if one wheel brake cylinder fails, the braking effect remains above 70%. A triple fault would be required for the brake system to completely fail, meaning both valves BP1 and BP2 would have to fail. Therefore, at least one brake circuit is reliably protected from a double fault, preventing a complete breakdown of the brake system. Double fault safety is an important safety feature when idle failures are possible. When using the optional isolation valve TV1, the first brake circuit BK1 is also reliably protected from a double fault, so that the three wheel brake cylinders can still be used by the switching valve SVi, even in the case of a double fault in the case of one wheel brake cylinder RZi failing.

[0057] The pedal travel is measured by a redundant pedal travel sensor which simultaneously acts on a force-travel sensor (KWS) measuring element, as described in WO 2012 / 059175. The pressure supply DV is controlled by a signal from the pedal travel sensor and by piston control generates a volume flow in the hydraulic main line HL1 of brake circuit BK1 and, via redundant circuit isolation valves BP1 and BP2, in the second brake circuit BK2.

[0058] Actuation of the pedal displaces piston 3, which exerts a pressure proportional to the pedal force on the known stroke simulator WS, thus determining the pedal characteristics. The stroke simulator WS can generally be shut off by valve 14, particularly at a fallback level in case of a breakdown of the pressure supply device. By providing redundant windings with dual three-phase connections (P1 and P2) and, in particular, a relatively simple rotary pump, the failure rate of the pressure supply device DV is far below the value of a brake circuit failure in a system without drive-by-wire and additional pedal folding. Therefore, valve 14 can also be omitted in principle.

[0059] The master brake cylinder SHZ can be connected to either the brake circuit BK1 or the brake circuit BK2 via the lines HL2 and HL3, with the valve FV located in the lines HL2 and HL3 to separate the two line sections HL2 and HL3. This connection is only effective at a fallback level. If the master brake cylinder SHZ is connected to the connecting line VLa of the two circuit isolation valves BP1 and BP2, the two valves BP1 and BP2 provide additional redundancy. A conventional direct connection from the valve FV to one of the two brake circuits BK1 and BK2 would mean that if the valve FV leaked, the brake circuit, and thus the pressure supply device DV, would act on the piston 3, which would conventionally result in the pressure supply being cut off.

[0060] The second circuit isolation valve BP2 provides additional safety in the event of a malfunction of valve FV, for example, due to a leak or fault in an electrical connection. In this case, the two circuit isolation valves BP1 and BP2 are closed, thereby maintaining the stroke simulator function of the stroke simulator WS. In this case, braking is performed by the pressure supply DV of the first hydraulic circuit BK1, which provides approximately 50% braking effort in the case of a diagonal brake circuit distribution. In the case of an emergency braking operation with a higher braking effort desired by the driver, the circuit isolation valve BP2 can optionally be opened, allowing additional pressure to be generated in the second hydraulic circuit or brake circuit BK2 by the force applied by the foot, increasing the braking effort by 75% or more. In this case, the pedal characteristic for the stroke simulator is not significantly affected. However, if valve FV fails, the ABS function cannot be used. In this case, the wheels may lock, especially in low friction conditions. However, even if the leakage rate of the valve FV is low, the valve FV is closed and the pressure reduction P is applied through the respective switching valves SV and the outlet valve ZAV. reduction The ABS function can still be used by performing the following. In this case, the valve FV remains closed. build-upIn this case, the pressure is reduced to prevent further locking of the vehicle wheels. reduction A smaller pressure difference is selected for . During the remaining braking action, both directional control valves SV remain closed. Thus, in this particular case, maneuverability is maintained.

[0061] In the above failure scenario, a diagonal brake circuit distribution is more preferable because 50% braking effort is greater for the front axle / rear axle brake circuit distribution. However, if the front axle VA fails, only about 30% is available for the rear axle HA. In the case of so-called emergency brake circuits, about 50% is applied regardless of the VA / HA brake circuit distribution, while 75% is applied for the diagonal brake circuit distribution.

[0062] In FIG. 1, the alphabetic letters a and b are used to indicate the different functions of the two brake circuits BK1 and BK2 in the event of a fault in the valve FV.

[0063] Case a) If the driver requires relatively strong braking, braking is carried out only by the first brake circuit BK1 with the pressure supply device DV, which applies in the case of emergency braking, which can be identified, for example, by Sp1.

[0064] Case b) Braking is performed by the pressure supply DV of the first brake circuit BK1. Here, there is a small leakage through the valve FV. The master brake cylinder SHZ can be used to boost the pressure in the second brake circuit BK2. If the ABS function is required, a pressure reduction P is provided via the outlet valve ZAV. reduction It is possible to achieve the boost pressure P build-up The pressure is increased to a reduced level using a pressure supply device DV. After a certain time has elapsed, the pressure is further increased by P build-up occurs, the ABS function responds again.

[0065] In addition to the function in case of a failure of the switching valve FV, the second function is the closed-loop control function of the ABS (which has remained unchanged for decades). reductionIn the first stage, if the closed-loop controller reports a criterion of overpressure at the wheel, for example, it will initiate a pressure increase P build-up When the closed-loop controller sends a signal that the braking torque / pressure is excessive, the pressure reduction P reduction In this case, the outlet valves ZAV are opened and the respective associated switching valves SVi are switched, preferably by pulse width modulation PWM, so that the pressure reduction P reduction The valves SV and ZAV are closed again, so that the closed-loop controller reduces the pressure drop P reduction In this case, the circuit isolation valves BP1 and BP2 are open. Also, two or four wheel brake cylinders RZ are simultaneously in pressure reduction mode P reduction or in the second brake circuit BK2 via the outlet valve ZAV and by the pressure supply device DV or in the first brake circuit via the optional additional outlet valve ZAV2. reduction can be implemented.

[0066] In the second brake circuit BK2 via the outlet valve ZAV and in the first brake circuit BK1 by means of the pressure supply device DV, which in this case also functions simply as a pressure sink, a pressure reduction P reduction can also be implemented.

[0067] The third function is the pressure reduction P for normal braking. reduction There are two possibilities here.

[0068] a. Because there are tolerances in the switching valves SV1 to SV4, in order to equalize the pressure in the two brake circuits, for example, a pressure reduction P is performed via all four switching valves SV1 to SV4 with a short stop according to Δt or Δp ​​between the outlet valves ZAV. reduction The pressure reduction P reduction can also be implemented in an open-loop or closed-loop controlled manner by a pulse-width modulated switching valve SV.

[0069] b. Pressure reduction P via outlet valve ZAV or by single master brake cylinder SHZ reduction When the pressure control signal is activated and the working medium is flowing, one of the circuit isolation valves BP1 / BP2 can be controlled by a pulse width modulated signal for open loop pressure control and / or closed loop pressure control.

[0070] Figure 1 also shows the main structural units of the master brake cylinder SHZ, the valve arrangement HCU, and the open-loop and closed-loop control units ECU. Pressure is generated by the piston 3 via the brake pedal 1 and pedal plunger 2. This pressure is passed to the second brake circuit BK2 via the electrically de-energized open valve FV and to the first brake circuit BK1 via the electrically de-energized open circuit isolation valve BP1. The piston 3 includes a primary seal D2 and a secondary seal D1, which are connected to the reservoir VB via a check valve RV1 and a restrictor Dr1. These components perform an important safety function. If seal D2 fails, the leakage flow is throttled by the restrictor Dr1, resulting in a slight reduction in piston pedal travel—for example, 2 mm over 10 seconds (0.2 mm / s = 2 mm, or approximately 0.05%). The average braking time for a vehicle decelerating from 100 km / h at 1 G is approximately 3 seconds. This means that pedal travel in the event of a malfunction is extremely small. On the other hand, due to the restriction Dr1, a malfunction of seal D2 does not result in a malfunction of the single master brake cylinder SHZ. The check valve RV1 allows easy venting of the single master brake cylinder SHZ, which transfers its volume via the vent screw of the check valve RV1. Brake fluid is drawn in through the check valve RV1. Seals D2 and D1 are safety-related. Seal D2 is protected by the restriction Dr1, while seal D1 is protected by a diagnostic function. For this reason, seal D1 is diagnosed or checked for its functionality after every parking stop, for example, by the residual brake pressure passing through the release valve FV to the master brake cylinder SHZ. Here, the pressure transducer DG measures the pressure change over a period of, for example, 10 seconds, which corresponds to leakage throughout the brake system. If this is determined, a second test is performed by closing the directional control valves SV to the wheel cylinders RZ1-RZ4, generating a specific pressure (e.g., 20 bar) with the pressure supply DV, and measuring it again with the pressure sensor DG. The delivery speed can be measured, for example, from the angular movement of the drive motor. If this is greater than the known delivery speed of the throttle Dr1, the seal D1 is leaking.Instead of the restrictor Dr1 with check valve RV1, a solenoid valve MV, which is open when electrically de-energized, can also be used, but this involves significant additional costs. Under normal circumstances, the master brake cylinder (SHZ) piston 3 delivers volume to the stroke simulator WS with the valve FV closed. This is a basic component of a "drive-by-wire" system.

[0071] The function of the Stroke Simulator WS is standard. Its piston has an elastic element that generates a specific pressure-dependent force. Since the pedal force is converted into pressure and piston stroke, a specific pedal stroke force characteristic can be generated via the Stroke Sensor (WS) piston and the Stroke Sensor (WS) force.

[0072] As is known, the pedal characteristic of a travel simulator system is always the same, is independent of, for example, brake circuit failures, does not cause pedal collapse, and has great advantages in electric vehicles, for example with recovery by the electric motor. Here, the driver determines the amount of brake pressure that the pressure supply device DV must generate for the desired braking action in addition to the braking torque of the electric motor. The pedal travel is redundantly measured by a pedal travel sensor, and determines the brake pressure generated by the pressure supply device DV and measured by the pressure sensor DG.

[0073] There are various solutions for implementing redundant pedal travel sensors, which are also described, inter alia, in PCT / EP2016 / 055471 (WO 2016 / 150746).

[0074] Redundant pedal travel sensors can be coupled to the two pistons as shown and to the spring between the two pistons. This therefore has the advantage that a force-travel measurement can be realized, with the additional advantage of fault analysis, e.g. with respect to a jamming piston 3. This is disclosed inter alia in DE 10 2010 050 132 A1.

[0075] If the pressure transducer DG fails, the pressure booster P build-up and reduced pressure P reduction The current-pressure relationship for the stroke simulator WS is stored in a characteristic map, so the motor current can also be used to set the pressure. The stroke simulator WS has two seals, D3 and D3r. Downstream of seal D3, a redundant seal D3r is provided, with a restriction Dr3, which has the same function as restriction Dr1. If seal D3 fails, a leakage flow will occur, but it will be throttled by restriction Dr3 and will not lead to a failure of the master brake cylinder SHZ. Diagnosis is performed with seals D1 and D2 as described. The stroke simulator WS has a conventional restriction for pedal travel and a check valve RV for rapid emptying of the stroke simulator WS.

[0076] The seal and throttling configuration creates a fail-safe single master brake cylinder SHZ, which is crucial when a tandem master brake cylinder HZ with redundant pistons is omitted.

[0077] The pressure supply device DV is shown only in principle and is described in detail in PCT / EP2018 / 071923 (WO 2019 / 214832). The supply valve PD1 has a safety function in case of failure of the pressure supply device DV. Brake fluid can be replenished from the reservoir VB via the non-return valve RV2. If the pump of the pressure supply device DV is self-locking, there is no functioning drive, and the pump does not allow a pressure reduction in the brake circuit, the supply valve PD1 can also be omitted.

[0078] The valves, the pressure supply device DV and the master brake cylinder SHZ are combined in one block. According to the prior art, the open-loop and closed-loop control unit ECU comprises all electrical and electronic components and electrical connections to the sensors and solenoid valves via coils connected to the circuit board PCB. Connection to the on-board electrical system is achieved via (one or two) plug connectors 13.

[0079] Figure 2 shows a simplified solution for a safety gate SIG with only one circuit isolation valve BP1 for a mixed braking system with electromechanical rear axle brakes.

[0080] The master brake cylinder SHZ corresponds to the master brake cylinder shown in Figure 1. The safety gate SIG with valve BP1, together with the outlet valve ZAV, valve FV, and switching valve SV, enable almost all of the functions described for the brake system of Figure 1. However, without the second circuit isolation valve BP2, the second brake circuit BK2 would not be fail-safe in the event of a double failure of the valve FV. Here, the pressure supply device DV is separated from the brake circuit BK1 by the check valve RV3, so that if a rotary piston pump is used, no working medium can flow back from the brake circuit BK1 to the pump.

[0081] An electromagnetic brake EMB is used on the rear axle HA, which, according to the prior art, can also perform the function of a parking brake and can also be used for ABS functions. The electrical functions are contained in the open-loop and closed-loop control unit ECU. An additional outlet valve ZAV2, shown in dashed lines, can also be optionally provided in the brake circuit BK1, which allows pressure reduction by dissipation into the reservoir VB via the additional outlet valve.

[0082] FIG. 3 shows the safety gate SIG of FIG. 1 again, with the same pressure supply device DV, outlet valves ZAV and FV, brake circuits BK1 and BK2, master brake cylinder SHZ, and open-loop and closed-loop control units ECU. In contrast to the electromechanical brake EMB shown in FIG. 2, the electromechanical brake used on the rear axle is additionally hydraulically assisted. These brakes are known from PCT / EP2019 / 061909. Here, two hydraulically assisted electromechanical brakes, EMB2 and EMB4, are assigned to the third brake circuit BK3 and perform the functions of a primary brake with ABS function and a parking brake. The EMB function, as described in PCT / EP2019 / 061909 (WO 2019 / 215278), is limited to locking the parking brake application by a corresponding structure, and the ABS function at an emergency level is limited, especially in the event of a pressure supply device failure. As with the current parking brakes, the hydraulic electromagnetic brakes EMB2 and EMB4 have the advantage of being significantly less expensive, but the motor power is increased in order to also operate the rear axle (HA) brakes and the ABS function in case of a failure of the pressure supply device DV. Here too, an additional outlet valve ZAV2, shown in dashed lines, can be optionally provided in the brake circuit BK1, through which the pressure reduction P is dissipated into the reservoir VB. reduction This makes it possible.

[0083] 4a to 4c show a variant of the pressure supply device DV, in which the valve circuit of the safety gate SIG is identical to the valve circuit of FIGS.

[0084] FIG. 4a corresponds here to FIG.

[0085] Figure 4b shows that the pressure reduction P reduction2, instead of the supply valve PD1, a check valve RV3 can also be used.

[0086] Figure 4c shows a gear pump that requires a switchable supply valve PD1 due to leakage flow. The advantage of a gear pump is that it delivers volume in two directions, allowing both closed-loop controlled pressure increase and closed-loop controlled pressure decrease. If the pump used does not have leakage flow, valve PD1 can also be omitted.

[0087] In all solutions, the pressure supply DV provides both the rotor angle signal and the EC motor current measurement. [Explanation of symbols]

[0088] SHZ Single Master Brake Cylinder ECU Open and closed loop electronic control units HCU Hydraulic Control Unit KWS Force-Stroke Sensor RV1 Check valve 1 RV2 Check valve 2 RV3~RV6 Check valve 3~Check valve 6 RF return spring Dr1~Dr3 Aperture RZ1~RZ4 wheel cylinder SV1~SV4 switching valves DV Electric pressure supply unit HL1, HL3, HL4, HL5 hydraulic line connection VB Reservoir ZAV1 / ZAV2 central outlet valve BP1 / BP2 Circuit Isolation Valves FV Supply valve from master brake cylinder SHZ to brake circuit BK SV Switching valve to wheel cylinder RZ DG pressure transducer p=f(v) V Diagnostic Valve E Valve spring WS stroke simulator, piston D1~D3 stickers Sp1, Sp2 pedal travel sensor TV1 isolation valve SIG Safety Gate EMB electric brake a) P in the event of a failure of the supply valve FV with pressure supply DV of the brake circuit BK1 build-up / P reduction b) P in the event of failure of the supply valve FV with pressure supply DV and the master brake cylinder SHZ with ABS build-up / P reduction 1 brake pedal 2 pedal plungers 3 Master brake cylinder (HZ) piston 4 Master brake cylinder (HZ) housing 5 PCB 6 Sensor element for level converter 7 Sensor Targets 8 Float in the reservoir 9 Electrical elements for a stroke simulator for force characteristics 10 Redundant electrical connections, possibly with redundant coils 11 Redundant connections to motor for dual three-phase windings 12 Redundant connections for dual three-phase motors 13 Electrical plug connector for connecting the on-board electrical system 14-stroke simulator isolation valve

Claims

1. A braking system comprising: Electromechanical wheel brakes (EMB2, EMB4) on each wheel of the rear axle (HA) of the vehicle; two brake circuits, each with one brake circuit line, each of the two brake circuits serving at least one hydraulic wheel brake cylinder (RZ1, RZ3) of a front axle (VA) of the vehicle; a pressure supply device (DV); a single master brake cylinder (SHZ) actuable by an actuator in the form of a brake pedal (1) and having only one working chamber (110), said working chamber (110) being directly connected to the brake circuit lines (HL4, HL5) of the brake circuit via hydraulic lines (HL2, HL3); an open-loop and closed-loop control unit (ECU) for controlling the pressure supply device (DV) and the electromechanical wheel brakes (EMB2, EMB4); Equipped with The pressure supply device (DV) increases the pressure (P) in the hydraulic wheel brake cylinders (RZ1, RZ3) of the front axle (VA). ｂｕｉｌｄ－ｕｐ ) can be implemented via each brake circuit, an electrically de-energized open valve (FV) serving to selectively block or open the hydraulic lines (HL2, HL3) connecting the pressure supply device (DV) or the single master brake cylinder (SHZ) with one of the two brake circuits; and / or an electrically de-energized open circuit isolation valve operative to selectively close or open a connection between the pressure supply device (DV) and one of the two brake circuits; Brake system.

2. 2. A braking system according to claim 1, characterized in that said circuit isolation valve serves to selectively cut off or open a hydraulic connection line (VL) connecting said two brake circuits.

3. 3. A brake system according to claim 1, wherein the piston (3) of the single master brake cylinder (SHZ) has a primary seal (D2) and a secondary seal (D1), and the primary seal (D2) and the secondary seal (D1) are connected to a reservoir (VB) via a check valve (RV1) and a throttle (Dr1).

4. a switching valve (SV1, SV3) is provided between each of the hydraulic wheel brake cylinders (RZ1, RZ3) and the pressure supply device (DV), and in the event of a failure of a hydraulic wheel brake cylinder (RZ1, RZ3), the switching valve (SV1, SV3) is closed to ensure the function of the hydraulic wheel brake cylinder (RZ1, RZ3) that is not failing; and / or a valve arrangement is provided between each of the hydraulic wheel brake cylinders (RZ1, RZ3) and the pressure supply device (DV), which closes a valve of the valve arrangement in the event of a failure of a hydraulic wheel brake cylinder (RZ1, RZ3) thereby ensuring the function of the non-failed hydraulic wheel brake cylinder (RZ1, RZ3); and / or the single master brake cylinder (SHZ) is connected or connectable to one or both of the brake circuits via one valve or several valves, 3. A brake system according to claim 1 or 2, characterized in that:

5. 3. A brake system according to claim 1, wherein a hydraulic supply line (HL1) is provided for hydraulically connecting the pressure supply device (DV) to the respectively assigned first brake circuit (BK1), and wherein a supply valve (PD1) serves to selectively block and open the hydraulic supply line (HL1) or a check valve (RV3) serves to prevent a reverse flow from the first brake circuit (BK1) to the pressure supply device (DV).

6. 3. A brake system according to claim 1, wherein the electromechanical wheel brakes further comprise hydraulic connections which are hydraulically connected or can be hydraulically connected to brake circuit lines (HL4, HL5) via hydraulic connection lines which can be selectively closed by a switching valve, and wherein the pressure generated by the pressure supply device (DV) or the single master brake cylinder (SHZ) can generate a braking torque for the assigned vehicle wheel, which braking torque acts alone or supplements the electromechanically generated braking force.

7. At least one outlet valve is provided, by means of which the brake circuit lines (HL4, HL5) of the brake circuit are provided with a reduced pressure (P ｒｅｄｕｃｔｉｏｎ 3. A brake system according to claim 1, wherein the brake fluid is directly connectable to a reservoir (VB) for the brake fluid.

8. The reduced pressure (P ｒｅｄｕｃｔｉｏｎ 8. A braking system according to claim 7, characterized in that the pressure control is implemented in at least one hydraulically operated wheel brake (RB1-RB4) either by the pressure supply device (DV) or via an outlet valve depending on the state of the braking system and / or the closed-loop pressure control situation.

9. 3. Brake system according to claim 1 or 2, characterized in that the pressure supply device (DV) comprises a piston-cylinder pump or a rotary pump.

10. Only one circuit isolation valve (BP1) is provided, by means of which the two brake circuits can be hydraulically connected to each other or hydraulically isolated from each other, the supply hydraulic line (HL1) and the brake circuit line (HL4) of the first brake circuit (BK1) are connected to the connection of one of the circuit isolation valves (BP1), and the brake circuit line (HL5) of the second brake circuit (BK2) is connected to the other connection of one of the circuit isolation valves (BP1). ＳＧ 6. The brake system according to claim 5, wherein the brake system is connected to a brake circuit.

11. 11. Brake system according to claim 10, characterized in that one hydraulic line (HL2) is connected to the brake circuit line (HL5) of the second brake circuit (BK2).

12. 11. A brake system according to claim 10, characterized in that, when the pressure supply device (DV) is provided with a rotary pump, an additional outlet valve is provided which is used to selectively block and open a hydraulic connection line which connects the first brake circuit (BK1) directly, i.e. without further intervening valves, to a reservoir (VB).

13. In the ABS function of the brake system, pressure reduction (P ｒｅｄｕｃｔｉｏｎ 3. The brake system according to claim 1, wherein the hydraulically actuated wheel brakes (RB1-RB4) are connected to the associated switching valves (SV) and outlet valves.

14. 6. A brake system according to claim 5, characterized in that an additional isolation valve (TV) is arranged in the brake circuit line (HL4) of the first brake circuit (BK1), which is open when electrically de-energized.

15. 3. A braking system according to claim 1 or 2, characterized in that the working chamber (110) of the single master brake cylinder (SHZ) is connected to a stroke simulator (WS).

16. In the event of a failure or leakage of the valve (FV) that is open when de-energized, the single circuit isolation valve or both circuit isolation valves are closed, thereby maintaining the function of the process simulator (WS); If the valve (FV) that opens when de-energized completely fails, the pressure increase (P ｂｕｉｌｄ－ｕｐ ) is implemented only in the first brake circuit (BK1) by the pressure supply device (DV), If the valve (FV) that opens when de-energized has only a small leakage, the additional brake boost pressure (P ｂｕｉｌｄ－ｕｐ ) is implemented in the second brake circuit (BK2) by the actuating device and the single master brake cylinder (SHZ), and pressure reduction (P ｒｅｄｕｃｔｉｏｎ ) is implemented in the second brake circuit (BK2) via an outlet valve for the ABS function of the brake system.

16. The braking system of claim 15, wherein:

17. 4. A brake system according to claim 3, characterized in that the reservoir (VB) has at least one level converter (7, 8), a sensor (6) is provided to detect the position of the level converter (7, 8), the sensor (6) is arranged in the open-loop and closed-loop control unit (ECU), and the level of the hydraulic fluid in the reservoir (VB) can be or is continuously checked by the level converter (7, 8) and the sensor (6) in order to identify leaks.

18. 3. A brake system according to claim 1, further comprising a pressure transducer (DG) for ascertaining the prevailing pressure (p) in at least one brake circuit, the pressure transducer (DG) ascertaining the pressure (p) in one of the brake circuit lines (HL4, HL5).

19. 18. A braking system according to claim 17, characterized in that the motor (M) of the pressure supply device (DV) is connected to the open-loop and closed-loop control units (ECU) of the pressure supply device (DV) via a dual three-phase connection.

20. 3. A brake system according to claim 1, wherein the hydraulic wheel brake cylinders (RZ1, RZ3) of the front axle (VA) are assigned to or belong to different brake circuits.

21. 4. A braking system according to claim 3, characterized in that the valve and / or the circuit isolation valve, the pressure supply device and the single master brake cylinder (SHZ) are combined into one structural unit.

22. 3. A brake system according to claim 1, wherein the valve (FV) that opens when de-energized is connected between two of the hydraulic lines (HL2, HL3), one of the hydraulic lines (HL3) being hydraulically connected to the working chamber (110) of the single master brake cylinder (SHZ).

23. Pressure reduction (P) of all hydraulically operated wheel brakes (RB1 to RB4) ｒｅｄｕｃｔｉｏｎ 2. The brake system according to claim 1, wherein the braking force is controlled by a respective one of the switching valves (SV).

24. 2. A braking system according to claim 1, wherein an electromechanical wheel brake is provided for braking at each vehicle wheel of one axle.

25. The braking system of claim 9 , wherein the rotary pump is in the form of a gear pump.

26. The supply hydraulic pressure line (HL1) and the brake circuit line (HL4) of the first brake circuit (BK1) are connected to a valve seat side connection (BP1) of one of the circuit isolation valves (BP1). ＶＳ 11. The brake system of claim 10, wherein the brake system is connected to a

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