BRAKE SYSTEM

Description

State of the art

[0001] For almost 80 years, today's dual-circuit braking system with two brake circuits has been established for safety reasons and, depending on the vehicle design, is divided into a brake circuit a) diagonal and b) black / white or front axle / rear axle applied. In the event of a brake circuit failure, the braking effect is reduced by 50% in case of a) and by up to approximately 70% in case of b). Statistics estimate a brake circuit failure rate of 10 ppm / year. Due to the reduced braking effect or total brake failure, there is a significant risk of accidents.

[0002] DE 10 2017 000472 A1 discloses a hydraulic motor vehicle brake system with redundant brake pressure control, and a method for operating and testing the same.

[0003] DE 10 20 2018 213 306 describes a system for detecting brake circuit failure due to a leak in the brake circuit by evaluating the pressure gradient.

[0004] Almost all vehicles have electronic brake control systems for all four wheels, which are usually hydraulically braked. Each wheel brake cylinder is connected to at least one or two electromagnetically controlled control valves, which are electrically controlled by an electronic control unit (ECU) to prevent the wheel from locking, for example.

[0005] In today's common brake systems with ABS / ESP function, each wheel brake cylinder is usually assigned an inlet and an outlet valve, whereby the inlet valve usually has a check valve connected in parallel so that the inlet valve, which is often also referred to as a switching valve, does not close due to the back pressure when the pressure is reduced quickly.

[0006] If an inlet valve with its associated check valve fails and becomes leaky, in today's dual-circuit braking systems, a complete brake circuit usually fails when the wheel brake cylinder fails, so that the braking effect is reduced by at least 30%. Object of the invention

[0007] The object of the invention is to prevent the failure of an entire brake circuit if only one wheel circuit fails or becomes leaky. The wheel circuit here refers to the wheel brake cylinder, including its hydraulic connection to the valve, e.g., the inlet valve, up to the wheel brake cylinder. A four-circuit braking system is understood here to be a braking system in which, if one wheel circuit, two or three wheel circuits fail, the other three or two wheel circuits, or one wheel circuit, are still functional. Advantages of the invention

[0008] To achieve the above, the number of components subject to failure must be kept to a minimum between the pressure supply, the line connection, and the output of the hydraulic control unit. This includes, for example, valves, either magnetically or mechanically actuated. Ultimately, it is crucial that only a single valve with the "normally open" design is used at the end of the line connection from the pressure supply to the respective wheel brake cylinder. An inlet valve commonly used for ABS / ESP has a parallel check valve, which is considered to be unreliable in terms of leak tightness and can no longer be used. As described above, the check valve was provided to prevent the inlet valve from closing due to back pressure in the event of rapid pressure reduction.

[0009] The SV2k valve according to the invention is understood to be the valve assigned to a wheel brake cylinder, through which hydraulic fluid flows to build up pressure in this wheel brake cylinder only. The wheel circuit here is understood to mean the wheel brake cylinder including the hydraulic connection from the valve to the wheel brake cylinder. Of course, the hydraulic fluid can also flow from the assigned wheel brake cylinder through the SV2k valve back into the BK1 or BK2 brake circuit to reduce pressure.

[0010] To avoid the problems described above, the invention uses a valve SV2k or a switching valve of the "normally de-energized" type, whose valve actuator is adjusted by means of a first electromagnetic drive from the open valve position to the closed valve position, in which the valve actuator is pressed against a valve seat. If the electromagnetic drive is not energized or is not sufficiently energized, a valve spring presses the valve actuator into the initial position, i.e., into the open valve position. In the open valve position, the invention provides an additional force device that generates an additional force on the valve actuator, which is directed towards the open valve position and thus supports or replaces the valve spring, resulting in an increased resultant force with which the valve actuator is energized into the open valve position.

[0011] The additional force device can be switchable, e.g. be formed by an electromagnet in addition to the actual valve drive. It can therefore also be referred to as an active additional force device, since the additional force generated on the valve actuator can be selectively switched on or off depending on the state of the braking system. However, it is also possible for the additional force device to act passively, e.g. by using a permanent magnet. It is also within the meaning of the invention if the additional force device has an electromagnet and a permanent magnet. In all of the embodiments described above, a force that supports the valve spring is advantageously exerted on the valve actuator by means of the additional force device in order to hold the valve in its open position so that the valve does not close unintentionally.

[0012] With only an active additional force device, the drive of the SV2k valve only has to act against the force of the valve spring to close it, which can be dimensioned smaller due to the switchable additional force device, whereby the SV2k valve closes safely and the tightness is ensured by a high contact force.

[0013] With a purely passive force-assisted device, the actual actuator of the SV2k valve only needs to apply increased force at the beginning of the stroke movement from the open to the closed position to overcome the passive and thus permanently acting additional force. As the air gap increases, the force of the passive force-assisted device will rapidly decrease and have a less pronounced effect in the closed position of the valve.

[0014] The SV2k valve is the safety gate for the BK brake circuits to the RZ wheel brake cylinder. If one of the four hydraulic connections from the hydraulic control unit to a wheel brake cylinder fails in the braking system according to the invention, or if the wheel brake cylinder is leaking, the SV2k valve according to the invention can be used to decouple the faulty hydraulic connection or the faulty wheel brake cylinder from the rest of the braking system with a high degree of safety.

[0015] The auxiliary power device only needs to be switched on or activated when rapid pressure reduction is required. In all other operating states of the braking system, the additional holding or assisting force of the auxiliary power device is not required, which advantageously saves energy. In the braking system according to the invention, if one wheel circuit fails, only the braking effect of this one failed wheel circuit is lost, while the braking effect of the remaining three wheel circuits remains available. This only results in a reduction in braking effect from four to three intact wheel circuits, so that if one wheel circuit fails on the front axle, there is only a loss of braking effect of around 35%, compared to 70%, as described above for a black / white brake circuit division, when an entire brake circuit and thus two wheel circuits always fail.

[0016] The previously described valve is claimed both alone and in combination with the braking system described below. The braking system according to the invention described below should advantageously be equipped with the previously described valve. However, it is also conceivable for the braking system according to the invention to be operated with a different type of valve.

[0017] The braking system according to the invention thus has four wheel circuits, each of which has two wheel circuits assigned to a brake circuit. If one wheel circuit fails, three wheel circuits are advantageously still available for braking.

[0018] The functional reliability of the brake system according to the invention can be further increased in the presence of dirt particles in the brake fluid by installing at least one filter with a small mesh size at the inlet and / or outlet of the valve. The mesh size should be selected so small that these small dirt particles only create small leaks and thus only small flow rates when the SV2k valve is closed. These leaks can be compensated for by the pressure supply, but can be detected by the diagnostic system based on both the pressure supply flow rate and the level in the reservoir.

[0019] To verify the function of the SV2k valve according to the invention, a measurement of the volumetric absorption and the pressure variation over time in the respective wheel circuit can be performed during diagnosis, for example, and a comparison can be made with the previously determined pressure-volume characteristic curve of the wheel circuit. The diagnosis can be performed during each braking application and / or at a standstill or during servicing.

[0020] As described above, the SV2k valve does not require a check valve, yet still meets a wide range of requirements. It must remain securely open in both directions, even at high flow rates. This means that the typical weakness of today's valves, where high flow rates cause forces on the valve seat to act on the valve cone and spring, causing the valve to close automatically, must not occur.

[0021] The SV2k valve can be advantageously optimized by appropriately designing the sealing cone, the dimensions of the return spring, and the valve tappet, in addition to the additional force device. In the closed position of the valve, which can also be called the inlet valve but can also be used to relieve pressure in the wheel brake cylinder, the pressing force should be significantly lower than when using a progressive spring, which has a higher force in this position than in the open position. This is unfavorable for the dimensioning of the magnetic circuit due to the correspondingly higher force requirement.

[0022] The braking system according to the invention can have various valve circuits: a) Four SV2k valves for each of four wheel brake cylinders, through which both the pressure build-up and the pressure reduction for the respective wheel brake cylinders take place; b) four SV2k valves for each of four wheel brake cylinders and two outlet valves; c) four SV2k valves and four outlet valves.

[0023] Using an outlet valve for a wheel circuit, individual wheel control of pressure build-up (Pauf) and pressure reduction (Pab) is possible. Should a leak occur in a wheel circuit, a diagnostic circuit can advantageously identify the faulty wheel circuit both during braking and parking and close the valve SV2k associated with that wheel circuit. This allows three wheel circuits to continue operating in the event of a single fault, and two wheel circuits to remain available in the event of a double fault—i.e., if two wheel circuits fail simultaneously—in the worst case scenario. With conventional braking systems, however, the worst case scenario results in total brake failure.

[0024] In summary, it can be stated that with the SV2k valve, a significant safety improvement can be achieved by making minor changes to the inlet valve and eliminating the check valve. With an appropriate design of the SV2k valve, a cost reduction is possible in addition to the safety improvement.

[0025] The braking system according to the invention can also be designed such that, instead of four hydraulic wheel circuits, a mixed hydraulic-electric braking system is used, with, for example, hydraulic lines to the hydraulically operated front wheel brakes and only electrical connections to the electric motor-operated brakes (EMB) on the rear axle, the design of which is known. Here, too, the same advantages arise if the hydraulic wheel circuits are designed according to the previously described embodiments.

[0026] In addition to the valve concepts described, different pressure supply concepts are also possible, e.g. a single pressure supply for Level 2 of automated driving or two pressure supplies for Levels 3 to 5 of automated driving, whereby the second, redundant, pressure supply can contain a piston pump or a rotary pump. Rotary pumps offer a significant cost advantage. With the piston pump, a simple check valve can be used at the pressure supply outlet instead of the solenoid valve. This offers the same advantages in the event of a pressure supply failure and is more cost-effective. In this braking system, pressure reduction during normal braking cannot be achieved by controlling the pressure supply piston, but rather by controlling the outlet valves using the pressure sensor signal from the pressure sensor or the pressure sensor itself. Since at least two outlet valves AV are used, redundant pressure reduction is also provided.Depending on the pressure reduction rate requirement and the number of outlet valves AV, one, two or more outlet valves AV can be opened.

[0027] Solenoid valves can be provided to isolate the pressure supply from the brake circuits. However, it is also possible to dispense with such isolation valves if the pressure supply is equipped with a drive with redundant winding circuitry, e.g., 2x3-phase and / or redundant control, such that no additional valves are provided between the switching valves SV2K 1-4 assigned to the wheel circuits and the pressure supply DV. To prevent a failure of the brake system, e.g., due to a leaking piston seal or small piston clearance, compensation is provided by additional pressure.

[0028] The braking systems described above can advantageously eliminate the need for the usual vehicle adjustments in various areas such as logistics, service and homologation. Character description

[0029] In the following, various possible embodiments of the braking system according to the invention and the valves used are explained in more detail with reference to drawings.

[0030] They show: Fig. 1: shows the structure of a braking system according to the invention with four hydraulic wheel brakes, which are connected to the hydraulic unit via four hydraulic lines, which has additional valves in addition to the four valves SV2k according to the invention assigned to the wheel brakes; Fig. 1a: shows a typical brake pressure curve in an ABS control cycle; Fig. 1b: shows the structure of a mixed braking system with hydraulically actuated brakes on the front axle and electrically actuated brakes on the rear axle; Fig. 2: shows the basic structure of a valve SV2k with an additional force device; Fig. 2a: shows the force curve of the additional force device over the valve armature stroke; Fig. 2b: shows the force curve of the electromagnetic valve force and the force of the return spring over the valve armature stroke; Fig.Fig. 2c: shows the electrical valve current during current control, the force curve of the electromagnetic valve force during current control, and the force of the additional force device over the valve armature stroke; Fig. 2d: shows the valve SV2k according to . Figure 2in a structural representation as a modification of a standard valve; Fig. 3a to 3d: various possible valve circuits for the braking system according to the invention with four wheel circuits; Fig. 4a: a diagnostic sequence during braking for the braking system according to the invention; Fig. 4b: a diagnostic sequence while the vehicle is stationary; Fig. 4c: a diagnostic sequence in the event of a leak in a wheel brake cylinder and a leak in the valve SV2k. Fig. 4d: a first alternative diagnostic sequence for single errors during braking or while the vehicle is stationary for the braking system according to the invention; Fig. 4e: a second alternative diagnostic sequence for single errors during braking or while the vehicle is stationary for the braking system according to the invention; Fig. 4f: a diagnostic sequence based on the first alternative diagnostic sequence for double errors during braking or while the vehicle is stationary for the braking system according to the invention.

[0031] Fig.1 shows the simplified structure of a brake system according to the invention with four wheel circuits with the hydraulic connections HL1 - HL4 between the wheel brake cylinders RZ1 - RZ4 and the valves SV2k1 - SV2k4. Here, for example, wheel circuit 1 consists of wheel brake cylinder RZ1 and hydraulic line HL1. The outlet valves can be provided optionally, whereby one, two or four outlet valves can be provided. The hydraulic connections between the optional outlet valves AV and the reservoir VB are shown in dashed lines. The valves SV2k have a hydraulic connection to the pressure supply DV via the brake circuits BK1 and BK2. The brake circuits BK1 and BK2 can optionally be connected via a normally open circuit isolating valve KTV, which is located in Fig. 3a - Fig. 3cwith the designation BP1 as shown in more detail in the structure. For safety reasons, this circuit isolation valve KTV can also be designed as a 3 / 2-way valve, with the pressure supply DV being connected to one connection of the valve and the other two connections to the two brake circuits, so that the pressure supply can be connected to one or the other brake circuit BK1 or BK2 as required. As is well known, piston pumps with so-called unstepped single-stroke pistons and stepped pistons as double-stroke pistons with forward and return stroke are used as the pressure supply DV. The pressure supply DV with a single-stroke piston has only one pressure outlet, whereas the pressure supply DV with a double-stroke piston has two pressure outlets. A pressure supply DV with only one pressure outlet can, for example, be formed by a motor-driven piston-cylinder unit with only one pressure chamber or, for example, by a rotary pump.A pressure supply (DV) with two pressure outputs can be formed, for example, by a motor-driven double-acting piston pump with two pressure chambers, with each pressure or working chamber then connected to or forming an output. The pressure supply (DV) with a double-acting piston is advantageously used for continuous delivery and also offers advantages for replenishment to compensate for leaks in the event of a failure in a four-circuit braking system. The pressure supply (DV) with a double-acting piston requires a valve circuit for the forward and return stroke. Both piston types also optionally use the circuit isolation valve (KTV) to separate the two brake circuits (BK1 and BK2). In a four-circuit braking system with SV2k as a safety valve and in a safe n-circuit braking system, the circuit isolation valve (KTV) and the dual-circuit supply from the pressure supply (DV) can be dispensed with. With the safety advantages of the SV2k valve in the event of a wheel circuit (RK1) failure, ..., RK4, if double fault safety is omitted, e.g. leakage from wheel brake cylinder 1 and leakage from valve SV2k1, the valve KTV can be omitted.

[0032] If a pressure supply with only one output is used, the KTV valve is used to optionally connect or disconnect the pressure supply to the brake circuits BK1 and BK2. If, on the other hand, a pressure supply with two outputs is used, a brake circuit BK1 or BK2 is connected to each output of the pressure supply DV, with the circuit isolation valve KTV then serving to optionally connect or disconnect the two brake circuits BK1 and BK2, as shown in Figure 1. The pressure supply DV preferably has an EC motor with one or two phases and a corresponding number of winding controls, thus ensuring redundant operation. One or two pressure sensors DG can be provided to determine the actual pressure, Pact, in the two brake circuits BK1, BK2.The master brake cylinder can be designed either as a single master brake cylinder (SHZ) or as a tandem master brake cylinder (THZ), through which pressure can be generated by means of the brake pedal in the event of a failure of the pressure supply (DV). The reservoir (VB) can be connected or arranged on the master brake cylinder (HZ). This reservoir has a float with a sensor target 2 mounted thereon. A sensor element 1 is provided in the control and regulation unit (ECU) to detect the fill level of the reservoir.

[0033] Fig. 1ashows the typical brake pressure curve P RZ in a wheel brake cylinder during a standard ABS control cycle. At time 1, after a brake pressure reduction due to unstable wheel slip, the brake pressure is kept constant until time 2 so that stable wheel slip can develop. At time 2, stable wheel slip is reached and the brake pressure is increased quickly, i.e. with a large gradient, with the aim of quickly returning to the maximum braking force between tire and road surface. At time 3, the braking force is just below the maximum braking force between tire and road surface. The brake pressure is now increased slowly, i.e. with a small gradient, so that the braking force remains close to the maximum braking force between tire and road surface for a long time. At time 4, the braking force between tire and road surface has dropped despite the increasing brake pressure.The wheel decelerates sharply, wheel slip is unstable and the pressure is reduced by opening the outlet valve AV. Between times 4 and 5 the brake pressure must be reduced very quickly, i.e. with a large gradient, since the wheel slip is unstable in this time period and can increase very quickly. At time 5 the wheel accelerates again, with the pressure being kept constant so that stable wheel slip can occur again. At time 6 stable wheel slip is reached and the brake pressure can be increased again. The small gradient of the brake pressure between times 3 and 4 is achieved with an electrical current control or current regulation of the valves SV2k. For this purpose the connections of the valves are as in . Fig. 1shown is absolutely necessary. The brake pressure gradient between times 4 and 5 depends on the brake pressure in the wheel brake cylinder, i.e. at high pressure in the wheel brake cylinder P RZ the gradient is large and at low pressure in the wheel brake cylinder P RZ the gradient is small. At low brake pressures in the wheel brake cylinder, e.g. P RZ = 10 bar, the hydraulic resistance of the outlet valve AV should be low for a large gradient. For high brake pressures in the wheel brake cylinder, e.g. P RZ = 100 bar, the gradient should not be too large and the hydraulic resistance of the outlet valve AV should be larger for precise pressure setting and low noise. It follows from this that the hydraulic resistance of the outlet valve can only ever be a compromise.

[0034] As already mentioned, the small gradient of the brake pressure build-up in the wheel brake cylinder between times 3 and 4 is achieved by an electrical current control or current regulation of the valves SV2k. For this purpose, the hydraulic connections of the valves SV2k, as shown in Fig. 1 , e.g. SV2k1, shown, mandatory.

[0035] During gradient control of the brake pressure build-up in, for example, wheel brake cylinder RZ1, the hydraulic resistance of valve SV2k1 is influenced by means of electrical current control or current regulation. When valve SV2k1 is open, when brake pressure builds up in wheel brake cylinder RZ1, volume flows from brake circuit BK1 into wheel brake cylinder RZ1. The volume flows through the narrow valve gap between the valve armature (ball in the figure of SV2k1) and the valve seat of valve SV2k1. As a result, the brake pressure upstream of the valve gap, i.e. on the brake circuit BK1 side, is greater than downstream of the valve gap. This pressure difference acts on the valve armature, exerting a pressure difference force on the valve armature which acts in the direction of valve opening. If valve SV2k1 is energized, a magnetic force is generated on the valve armature in the direction of the valve closing.This magnetic force causes the armature to move toward valve closing, and the valve gap decreases, reducing the volumetric flow and thus the pressure buildup gradient in wheel brake cylinder RZ1. The greater the electrical current to valve SV2k1, the smaller the brake pressure buildup gradient in wheel brake cylinder RZ1. In this way, the brake pressure buildup gradient in wheel brake cylinder RZ1 can be influenced by current control or current regulation of valve SV2k1.

[0036] Fig. 1b shows a mixed braking system with hydraulically operated brakes on the front axle and electrically operated brakes EMB on the rear axle. The hydraulic circuit of the front axle with the SV2k valves is identical to the embodiment according to Figure 1 , with simple connections to the pressure supply DV. In the connecting line HL5 there is an additional isolating valve to the single master cylinder SHZ, which is also used in the Fig. 1The valve shown in the embodiment shown can be provided. This valve is closed during normal operation. The pressure supply DV is driven by an EC motor, which is preferably redundantly driven via a 2x3-phase winding control. This allows approximately 70% of the braking effect to be provided in the event of a single fault in one winding.

[0037] Fig. 2shows the special valve SV2k required in the previously described embodiments, which functions reliably in both flow directions, ie even with large flow rates, such as 100cm 3 < / s - 120cm 3 < / s, and large pressure differences across the valve, such as 160bar - 220bar. In particular, for the previously described range, this valve SV2k ensures that it does not close automatically. The valve SV2k according to the invention has the typical structure of a solenoid valve with electromagnetic circuit EM1 with armature 6, valve actuator or valve stem 7 and valve seat 8 as well as the return spring 13. The return spring 13 can be dispensed with if the additional force device, which in Figure 2 formed by the electromagnetic circuit EM2, is designed accordingly. The valve actuator EM1 generates (see Figure 2a) over the stroke h a strong progressive force FM1 and the return spring 13 for resetting the armature a progressive restoring force FRF over the stroke h. The armature 6 is shown in the left part of the picture by Fig. 2 coupled to a second force-generating element, which forms the additional force device according to the invention. This can consist of a second electromagnetic circuit EM2 with armature 6a, whose switchable force FM2 counteracts the force FM1 of the first magnetic circuit EM1. As a more cost-effective variant, a permanent magnetic circuit can also be used as a passive additional force device, consisting of a small permanent magnet 9 with pole plate 10. The force effect of FM2 counteracts FM1 and acts with a relatively strong force when the valve is open, with a strong desired drop in force over the stroke h. The force FM2 is (see Figure 2b) at the end of the stroke is still large enough to take over the usual armature return and can therefore replace the usual return spring 13. Figure 2c shows the interaction of the power sources FM1 as a function of the current intensity and FM2 for the permanent magnet. In the closed valve position, the pressure difference P2-P1 acts on the valve seat with the force FP, which is directed towards the valve opening when the pressure P2 is greater than the pressure P1. In the open valve position, the hydraulic force FH described above acts on the valve seat due to the volume flow Q through the valve, which can tear the valve closed without countermeasures, both during pressure build-up Pauf and during pressure reduction Pab depending on how the valve SV2k is connected to the pressure supply DV and the wheel brake cylinder RZ, and depending on the direction of the volume flow, which is described in the following Figures 3 to 3b is explained in more detail.

[0038] The hydraulic force acting on the valve armature FH when flowing through the valve with volume flow Q always acts in the open position of the valve. Therefore, the force of the additional force device FM2 should act primarily in this position. Therefore, due to the decreasing force of FM2 over the armature movement toward the valve closing, it can be dimensioned higher in the open position than when using a spring with increasing force FRF during the armature movement toward the valve closing.

[0039] The valve tappet 7 can also have a special shape which provides the counterforce through hydraulic flow forces and can reduce the closing force.

[0040] Figure 2cshows the electrical control of valve i. The current i1 is selected in the closed valve position so that FM1 is greater than FM2. The current can then be varied in the closed valve position, i2, depending on the hydraulic differential pressure P2-P1 across the valve. Since the force FM2 in this position is in the range of the usual spring force for the reasons described, the valve can also be operated, for example, with a current control or current regulation. In order to keep the valve in the closed position, the differential force FV , zu = FM 1 , zu − FM 2 , zu be greater than the force FP resulting from the differential pressure P2-P1 across the valve in the closed position.

[0041] Fig. 2dshows the design of the inventive switching valve SV2k based on a series inlet valve. The parts present in the series part are all marked with S. The check valve integrated in the series valve is omitted. Only four additional parts are required for the additional power device. These are 1. The permanent magnet 9 2. the pole plate 10 3. the electromagnetic return 11 and 4. a plastic body 12, which connects the parts together including the armature.

[0042] The Fig. 3a-3dshow various valve circuits for the ABS / ESP functions, which depend on the pressure control system for pressure build-up Pauf and pressure reduction Pab. The respective designs differ in the number of valves, whereby the differentiating feature is the outlet valve AV and thus the pressure reduction control. The arrows show the volume flows at which there is a risk of the valve SV2k1, ..., SV2k4 closing. Closing or tearing the valve is understood to mean the automatic closing of the normally open valve by a volume flow through the valve. An example is shown in Fig. 3a The pressure build-up Pauf in wheel brake cylinder 2, RZ2, is shown, where hydraulic volume flows from the brake circuit BK1 through the open valve SV2k2 into the wheel brake cylinder 2, RZ2. When the valve SV2k2 is open, the volume flows through the narrow valve gap between the valve armature (ball in the Figure 2of SV2k 2 ) and valve seat. As a result, the brake pressure in front of the valve gap is greater than behind the valve gap. This pressure difference acts on the valve armature, exerting a pressure differential force on the valve armature that acts in the direction of valve closure. If this pressure differential force is greater than the force exerted by the valve spring on the valve armature, the valve closes, which is referred to as closing the valve by volume flow. This automatic closing is unwanted because the valve is not controlled to close.

[0043] Fig. 3b shows a valve circuit similar to Fig. 1a which means that a standard ABS control, as in Fig. 1a described, is possible.

[0044] Fig. 3cshows a possible embodiment with diagonal brake circuit distribution, in which outlet valves AV are used only on the wheel brake cylinders on the front axle VA. In this application, the front wheel brake cylinders can be operated with the standard ABS control, as in Fig. 1a The pressure reduction Pab at the two rear brake cylinders is only possible if pressure is not built up at the same time at any of the front brake cylinders. Since the pressure reduction is time-critical, as detailed in Fig. 1a As described, the mixed operation of standard ABS control, e.g. on the front wheel brake cylinders, and Pauf and Pab control via the SV2k valve on the rear wheel brake cylinders is associated with disadvantages in the ABS control on the rear wheel brake cylinders.

[0045] Fig. 3cshows an application where pressure build-up Pauf and pressure reduction Pab on the rear axle via the valves SV2k3 and SV2k4 is possible by modified ABS control. Through current control of the valves SV2k3 and SV2k4, the pressure gradient during pressure reduction can be adjusted because the valve connections allow this. The current control is similar to the control of the pressure build-up gradient, as is the case with Fig. 1a described. The Fig. 1a The compromise of gradients described during pressure reduction via the outlet valve AV is not necessary here.

[0046] For example, closing the valves SV2k1, ..., SV2k4 could result in this situation at the valves in Fig. 3coccur, e.g. with the valves SV2K 1 in BK1 and SV2k 2 in BK2 during pressure reduction Pab, if the pressure reduction Pab is triggered by the DV, and with the valves SV2k 3 in BK2 and SV2k 4 in BK1 during Pauf, if the Pauf is triggered by the DV. In Fig. 3b The contraction of all SV2k could only occur when the pressure Pab is reduced via the control of the pressure supply DV. In Fig. 3a For all valves SV2k it could only occur when the pressure Pauf is built up via the control of the pressure supply DV.

[0047] The embodiment according to Fig. 3d corresponds to that according to Fig. 1a and Fig. 3b, with additions of the single master brake cylinder SHZ, the isolating valve 9, the optional circuit isolating valve BP1, the optional safety valve MVDV1 and, in the case of a dual-circuit pump, the safety valve MVDV2, and the pressure supply DV. In many systems, e.g. DE 10 2017 219 598 A1, the normally closed safety valve MVDV1 / MVDV2 is used at the outlet of the pressure supply DV. The safety valves MVDV1 / MVDV2 are normally closed valves and correspond in design to the outlet valve AV in Fig. 3bThis safety valve MVDV1 / MVDV2 is closed in the event of a failure of the pressure supply DV, e.g. in the event of a failure of the pressure supply motor or a failure of the piston seal D1 during a pressure build-up, in order to prevent an uncontrolled backflow of volume from the wheel brake cylinders into the pressure supply DV and thus an unwanted and uncontrolled reduction in pressure in the wheel brake cylinders. When using a pressure supply DV with a double-acting piston that seals off two working chambers, two solenoid valves MVDV and MVDV2 can be used in the hydraulic connections that connect the two outputs of the working chambers to the brake circuits BK1 and BK2, to selectively open and shut them off. Here, too, both brake circuits BK1 and BK2 can be optionally connected via a valve BP1.

[0048] Instead of a piston pump, a rotary pump, such as a gear pump, can be used, whereby a simple check valve RVDV1 can be provided at the pump outlet instead of a solenoid valve MVDV1. This check valve RVDV1 performs the same function in the event of a pressure supply DV failure as the solenoid valve MVDV1. In contrast to the solenoid valve MVDV1, where pressure can be reduced via the pressure supply DV when the valve is open, this is not possible with the check valve RVDV1. The pressure reduction Pab in a system with a rotary pump therefore takes place via the outlet valves AV. During slow pressure reduction, the outlet valves AV can be controlled individually or all together via the pressure sensor DG1 to reduce the pressure Pab. The combination of a rotary pump with a check valve RVDV1 at the pump outlet represents a cost-effective solution for a pressure supply DV.For some rotary pumps, the combination of a pressure supply with a solenoid valve MVDV1 is also possible, with advantages in easily controllable pressure reduction speed via the rotary pump, e.g. with gear pumps.

[0049] As in Fig. 1a As shown, some brake systems with two brake circuits BK1 and BK2 have a normally open circuit isolation valve KTV, in construction like isolation valve BP1 in Fig. 3a , which is activated and thus closed in the event of a fault, e.g. if the brake circuit BK1 is leaking, so that the other brake circuit BK2 can still be pressurized by the pressure supply DV.

[0050] The optional switching valves BP1 and MVDV1 can be used in various designs: 1. Both valves are used; 2. Only the MVDV1 safety valve is used, without the BP1 circuit isolation valve; 3. Only the BP1 circuit isolation valve is used, without the MVDV1 safety valve.

[0051] Of all three embodiments, embodiment No. 1 is the most expensive braking system, with the advantage of high safety in the event of failure of the pressure supply DV or a brake circuit BK1 or BK2, as already described above.

[0052] In embodiment 2, the failure of a brake circuit, e.g., a leak in brake circuit BK1, can be detected using diagnostics. This also allows the diagnosis to determine which wheel circuit has failed, e.g., a leak in wheel brake cylinder RZ1, whereupon the corresponding valve SV2k1 can be closed. The other wheel brake cylinders RZ2, RZ3, and RZ4 can continue to be pressurized via the pressure supply DV.

[0053] In embodiment 3, i.e., without the MVDV1 safety valve, if the pressure supply DV fails, e.g., due to a leak in the piston seal of the pressure supply DV, the switching valve 9 can be opened and the circuit isolation valve BP1 closed. The driver can then control the pressure in brake circuit BK1 using the brake pedal. Only brake circuit BK2 will then fail. If the pressure supply fails during braking, the pressure in the wheel brake cylinders RZ1, ..., RZ4 can be reduced via the AV valves when the valves SV2k1, ..., SV2k4 are closed.

[0054] The Figures 4a and 4b show test cycles for checking the tightness of the brake system in the diagnosis. Fig. 4ashows tests T0 - T4 during braking. At the start of braking, from point A0 to point A, during test T0, the pressure and volume absorption V of the wheel brake cylinders are continuously measured during pressure build-up, e.g. via the piston travel Sk of the pressure supply DV. The target value of the piston travel Sk soll is supplied by the stored pressure-volume characteristic curve of the brake, PV characteristic curve, as a function of the pressure and is compared with the actual value of the piston travel Sk ist. At point A, the pressure is kept constant. If no difference was measured between Sk soll and Sk ist at point A, this comparison remains throughout the entire braking phase up to point A1, and test T0 is negative. If test T0 is negative, further tests (T1, T2, T3, T4) are not necessary. If a difference is measured, there is a leak in a wheel circuit, i.e.between a wheel brake cylinder RZ and the associated valve SV2k, and test T0 is positive. If the test is positive, but at the time of point A only a very small difference was measured between Sk soll and Sk ist, then further tests (T1, T2, T3, T4) are not necessary. A warning on the display should advise the driver to visit the workshop at the earliest opportunity. The difference between Sk soll and Sk ist is very small if the volume in the reservoir is sufficient for many further braking operations, e.g. 1000, despite volume loss from the brake system due to the leak in the wheel circuit and the volume loss can be compensated by volume delivery of the pressure supply DV. If test T0 is positive and at the time of point A more than a very small difference was measured between Sk soll and Sk ist, it must be determined in which wheel circuit the leak is.For this purpose, test T1 is carried out at the time of point A by closing valve SV2k1 assigned to wheel brake cylinder RZ1. If wheel circuit 1 is leaking, then after valve SV2k1 closes, no piston movement Sk is necessary to keep the measured pressure constant, and test T1 is positive. If test T1 is positive, valve SV2k1 remains closed until the end of braking A01; from point A to point A1, piston travel Sk of the pressure supply DV remains constant, and further tests (T2, T3, T4) are not necessary. The test time of test T1, the test phase, is chosen to be short, e.g. 20 ms, so that the braking process and possibly the driver are not disturbed by the test. If, for example, the driver wants to reduce the pressure during the test phase, this is done via the piston movement of the pressure supply DV only after the test phase has been concluded or immediately if a wheel circuit has already been identified as leaking.If the driver wants to increase the pressure during the test phase, the test is aborted. If test T1 was negative, i.e. despite valve SV2k1 being closed, an increase in the piston travel Sk of the pressure supply DV is necessary to keep the pressure constant, then there is no leak in wheel circuit 1 but in another wheel circuit, and so after point A the leakage flow and thus the piston travel Sk of the pressure supply DV continues in the limiting case until test T4 of wheel circuit 4. The piston travel Sk actual of the pressure supply DV then increases during test phase T1 from point A to point B, and point B is reached. After the negative test T1, valve SV2k1 is opened. If test T1 is positive, no further tests are carried out, valve SV2k1 remains closed during subsequent braking applications, and the difference between Sk target and Sk actual at point A is maintained throughout the entire braking phase up to time A01.

[0055] A warning on the display should prompt the driver to visit the workshop immediately.

[0056] After a positive test T0 (at the time of point A, more than a very small difference was measured between Sk target and Sk actual) and a negative test T1, test T2 is carried out for wheel circuit 2 at the time of point B. Test T2 proceeds in a similar way to test T1. For this purpose, test T2 is carried out at the time of point B by closing the valve SV2k2 assigned to the wheel brake cylinder RZ2. If wheel circuit 2 is leaking, then after the valve SV2k2 closes, no piston movement Sk is necessary to keep the measured pressure constant, and test T2 is positive. If test T2 is positive, then valve SV2k2 remains closed until the end of braking A01. From point B to point B1, the piston travel Sk of the pressure supply DV remains constant, and further tests (T3, T4) are not necessary. The test time of test T2, the test phase, is selected to be short, e.g. 20 ms, so that the braking process and, if applicable, the driver are not disturbed by the test. For example, ifIf the driver wants to reduce the pressure during the test phase, this is done via the piston movement of the pressure supply DV only after the test phase has been completed or immediately if a wheel circuit has already been identified as leaking. If the driver wants to increase the pressure during the test phase, the test is aborted. If test T2 was negative, i.e. despite the valve SV2k2 being closed, an increase in the piston travel Sk of the pressure supply DV is necessary to keep the pressure constant, then there is no leak in wheel circuit 2 but in another wheel circuit, and so after point B the leakage flow and thus the piston travel Sk of the pressure supply DV continues in the limiting case until test T4 of wheel circuit 4. The piston travel Sk of the pressure supply DV then increases during test phase T2 from point B to point C, and point C is reached. After the test T2 is negative, valve SV2k2 is opened.If test T2 is positive, no further tests are performed, valve SV2k2 remains closed during subsequent braking applications, and the difference between Sk target and Sk actual at point B remains constant throughout the entire braking phase until point A01. A warning on the display should prompt the driver to visit the workshop immediately.

[0057] After a positive test T0 (at the time of point A, more than a very small difference was measured between Sk target and Sk actual) and negative tests T1 and T2, test T3 is carried out for wheel circuit 3 at the time of point C. Test T3 proceeds in a similar way to test T1. For this purpose, test T3 is carried out at the time of point C by closing the valve SV2k3 assigned to the wheel brake cylinder RZ3. If wheel circuit 3 is leaking, then after the closure of valve SV2k3, no piston movement Sk is necessary to keep the measured pressure constant, and test T3 is positive. If test T3 is positive, then valve SV2k3 remains closed until the end of braking A01. From point C to point C1, the piston travel Sk of the pressure supply DV remains constant and a further test (T4) is not necessary. The test time of test T3, the test phase, is selected to be short, e.g. 20 ms, so that the braking process and, if applicable, the driver are not disturbed by the test. For example, ifIf the driver wants to reduce the pressure during the test phase, this is done via the piston movement of the pressure supply DV only after the test phase has been completed or immediately if a wheel circuit has already been identified as leaking. If the driver wants to increase the pressure during the test phase, the test is aborted. If test T3 was negative, i.e. despite valve SV2k3 closing, an increase in the piston travel Sk of the pressure supply DV is necessary to keep the pressure constant, then there is no leak in wheel circuit 3 but in another wheel circuit, and so after point C the leakage flow and thus the piston travel Sk of the pressure supply DV continues in the limiting case until test T4 of wheel circuit 4. The piston travel Sk of the pressure supply DV then increases during test phase T3 from point C to point D, and point D is reached. After the negative test T3, valve SV2k3 is opened.If test T3 is positive, no further tests are performed, valve SV2k3 remains closed during subsequent braking applications, and the difference between Sk target and Sk actual at point C remains constant throughout the entire braking phase up to point A01. A warning on the display should prompt the driver to contact the workshop immediately.

[0058] After a positive test T0 (at the time of point A more than a very small difference was measured between Sk target and Sk actual) and negative tests T1, T2 and T3, it can be concluded that wheel circuit 4 is leaking and valve SV2k4 is closed immediately. On the other hand, test T4 can also be carried out for wheel circuit 4 at the time of point D in order to rule out leaks elsewhere in the braking system. Test T4 proceeds in a similar way to test T1. For this purpose, test T4 is carried out at the time of point D in which the valve SV2k4 assigned to wheel brake cylinder RZ4 is closed. If wheel circuit 4 is leaking, after valve SV2k4 is closed, no piston movement Sk is necessary to keep the measured pressure constant, test T4 is positive and point D1 is reached.If test T4 is positive, valve SV2k4 remains closed until the end of braking A01. From point D to point D1, the piston travel Sk of the pressure supply DV remains constant; a further test is not necessary. The test time of test T4, the test phase, is selected to be short, e.g. 20 ms, so that the braking process and, if applicable, the driver are not disturbed by the test. If, for example, the driver wants to reduce the pressure during the test phase, this is done via the piston movement of the pressure supply DV only after the test phase has been concluded or immediately if a wheel circuit has already been identified as leaking. If the driver wants to increase the pressure during the test phase, the test is aborted. If test T4 was negative, e.g.despite the valve SV2k4 closing, an increase in the piston travel Sk of the pressure supply DV is necessary to keep the pressure constant. This means that there is a leak somewhere else in the braking system. So after point D the leakage flow and thus the piston travel Sk of the pressure supply DV continues. The piston travel Sk of the pressure supply DV then increases during test phase T4 from point D to the end of braking A01 (not shown). After the negative test T4, the valve SV2k4 is opened. If test T4 is positive, the valve SV2k4 remains closed during subsequent braking applications, and the difference between Sk soll and Sk ist at point D is maintained throughout the entire braking phase up to time A01. The test cycle is completed when test T4 is carried out.In both the positive (leak in wheel circuit 4) and the negative (leak is elsewhere in the brake system) test T4, a warning on the display should prompt the driver to visit the workshop immediately.

[0059] With T4, the test cycle ends at point D1, and the braking process with pressure reduction ends at point E. This diagnosis requires appropriate accuracy and dynamics from the sensors, e.g., piston travel and pressure.

[0060] In Fig. 4b The test cycle is shown with the vehicle stationary, which corresponds almost entirely to 4a, with the small difference that the pressure is determined by the DV and not the driver. For simplicity, the leak in RZ4 is only detected in test 4. The test time can also be increased from 20 ms, for example, by a factor of 2.

[0061] Another situation arises if, in addition to a leak in the wheel circuit, which is not very small, the associated valve SV2k also has a leak, e.g., due to dirt particles between the valve armature and the valve seat. If this applies to wheel circuit 1 and valve SV2k1, for example, then the piston travel Sk does not remain constant during test T1 to keep the pressure constant. Volume losses due to leaks in valve SV2k are small and can be compensated by the pressure supply, so that wheel circuit 1 fails, but the other wheel circuits do not. A warning on the display should prompt the driver to visit the workshop immediately.

[0062] The Figures 4c1 to 4c3 show the basic test procedures.

[0063] Fig. 4c1 shows the piston travel Sk of the DV piston when there is no leak. Tests T0, ..., T4 are then not required.

[0064] Fig. 4c2 shows the piston path Sk of the DV piston when, for example, wheel brake cylinder RZ1 is leaking, without activation of the associated valve SV2k1, possibly with a high leakage volume flow, Q SV2k,leak, which is not throttled by the associated closed SV2k

[0065] Fig. 4c3 shows the piston travel Sk of the DV piston when, for example, wheel brake cylinder RZ1 is leaking, where the leakage flow rate, Q SV2k1,leak, is small, due to the closure of the leaking valve SV2k1. A similar piston travel Sk as in Fig. 4c3 occurs when a conventional inlet valve EV1 with a parallel check valve RV1 is used instead of valve SV2k1, whereby either the inlet valve EV1 or the check valve RV1 is leaking, or when both are leaking. By controlling the leaking inlet valve EV1, for example if the wheel brake cylinder RZ1 is leaking, the leakage volume flow Q EV1,leak through the leaking wheel brake cylinder RZ1 is not reduced to 0 cm 3 < / s but to a small value, e.g. in the worst case scenario, EV1 and RV1 are both leaking, and the leakage flow, for example, Q EV1,leak = 20 cm 3 < / s at a 50 bar pressure difference across the valve EV1.

[0066] If the difference between Sk soll and Sk ist during test T0 at time A0 is very small, braking can be maintained as under normal conditions. However, if the difference is not very small, then the failure of a wheel circuit, e.g. due to a leak in a wheel brake cylinder seal, and the closure of the associated valve SV2k, the vehicle deceleration is less than under normal conditions and a yaw moment occurs on the vehicle during braking. The electronic stability program ESP is generally able (except during emergency braking) to match the vehicle deceleration to the vehicle deceleration under normal conditions. This means that the braking feel for the driver remains largely normal and startle reactions from the driver are avoided. Furthermore, the electronic stability program ESP is able to partially compensate for the yaw moment, so that startle reactions from the driver can also be reduced.

[0067] Fig. 4dshows an example of a first alternative diagnostic procedure for testing for individual errors with the piston travel curve Sk of the pressure supply DV, which increases from time 0 to time t0 and remains constant from time t0, and the target pressure curve, Psoll, which is derived from the piston travel curve Sk using the PV characteristic curve (pressure-volume characteristic curve) of the brake system. It also shows Fig. 4d the actual pressure curve, Pist, which is measured with the pressure sensor DG (see Fig. 3a). At time t0, a difference between the target pressure, Psoll, and the actual pressure, Pist, is detected, which suggests a malfunction of the braking system. For this reason, at time t0 all valves SV2k1, ..., SV2k4 are closed, and the actual pressure curve Pist is observed in the test period from time t0 to time t1. If the actual pressure Pist drops from time t0 to time t1, which is indicated by the dashed line 1, then the malfunction of the braking system is not caused by a leak in a wheel circuit, RK1, ..., RK4, but for example by a leak in the piston seal of the pressure supply DV. The valves SV2k1, SV2k2, SV2k3 and SV2k4 can be opened again and via a piston movement of the pressure supply DV the actual pressure Pist can be increased to the target pressure Psoll, which is reached at point A.Due to the leak in the piston seal of the pressure supply DV, a constant piston movement is required even after point A to maintain the actual pressure Pactual at the target pressure level Pset. This has the advantage that, despite the fault, normal braking action is maintained in all wheel brake cylinders. However, if the leak rate of the piston seal exceeds the maximum delivery rate of the pressure supply DV at the target pressure level Pset, the system switches to a fallback level without the pressure supply DV.

[0068] If the actual pressure Pist does not drop during the test period t0 to t1, which is indicated by the solid line 2 for the actual pressure Pist from time t0 to t1, valve SV2k1 is opened at time t1, and the actual pressure curve Pist is observed in the test period from time t1 to time t2. If the actual pressure Pist drops from time t1 to time t2, which is indicated by the dashed line 3, the malfunction of the braking system is caused by a leak in wheel circuit 1. Valve SV2k1 is then closed at time t2, while valves SV2k2, SV2k3, and SV2k4 are reopened, and via a piston movement of the pressure supply DV, the actual pressure Pist can be raised to the target pressure Psoll, which is reached at point B.

[0069] If the actual pressure Pist does not drop in the test period t1 to t2, which is indicated by the solid line 4 for the actual pressure Pist from time t1 to time t2, then valve SV2k2 is opened at time t2, and the actual pressure curve Pist is observed in the test period from time t2 to time t3. If the actual pressure Pist drops from time t2 to time t3, which is indicated by the dashed line 5, then the malfunction of the braking system is caused by a leak in wheel circuit 2. Valve SV2k2 is then closed at time t3, while valves SV2k1, SV2k3 and SV2k4 are opened again, and via a piston movement of the pressure supply DV, the actual pressure Pist can be increased to the target pressure Psoll, which is reached at point C.

[0070] If the actual pressure Pist does not drop during the test period from time t2 to time t3, which is indicated by the solid line 6 for the actual pressure Pist from time t2 to t3, then valve SV2k3 is opened at time t3, and the actual pressure curve Pist is observed in the test period from time t3 to time t4. If the actual pressure Pist drops from time t3 to time t4, which is indicated by the dash-dotted line 7, then the malfunction of the braking system is caused by a leak in wheel circuit 3. Valve SV2k3 is then closed at time t4, while valves SV2k1, SV2k2 and SV2k4 are opened again, and via a piston movement of the pressure supply DV, the actual pressure Pist can be increased to the target pressure Psoll, which is reached at point D.

[0071] If the actual pressure Pist does not drop during the test period from time t3 to time t4, which is indicated by the solid line 8 for the actual pressure Pist from time t3 to t4, then valve SV2k4 is opened at time t4, and the actual pressure curve Pist is observed in the test period from time t4 to time t5. If the actual pressure Pist drops from time t4 to time t5, which is indicated by the dash-dotted line 9, then the malfunction of the braking system is caused by a leak in wheel circuit 4. Valve SV2k4 is then closed at time t5, while valves SV2k1, SV2k2 and SV2k3 are opened again, and via a piston movement of the pressure supply DV, the actual pressure Pist can be increased to the target pressure Psoll, which is reached at point E.

[0072] If the actual pressure Pactual does not drop during the test period from time t4 to time t5, which is indicated by the solid line 10 for the actual pressure Pactual from time t4 to time t5, the malfunction of the braking system is not caused by a leak in a wheel circuit, RK1, ..., RK4, but rather, for example, by air bubbles in the brake fluid. At time t5, the valves SV2k1, SV2k2, SV2k3, and SV2k4 can be reopened, and via a piston movement of the pressure supply DV, the actual pressure Pactual can be raised to the target pressure Ptarget, which is reached at point F.

[0073] The order in which the valves are opened and the size of the leaks in the wheel circuits, RK1, ..., RK4, and piston seal of the pressure supply DV is chosen here as an example and is not binding. The order can be selected, for example, based on driving dynamics. As with a leak in the piston seal of the pressure supply DV, if a wheel circuit, e.g. wheel circuit 1, is leaking, the associated valve SV2k1 can remain open in order to keep the actual pressure Pist at the target pressure level Psoll with a constant piston movement. As already mentioned, this has the advantage that the normal braking effect is maintained in all wheel brake cylinders despite errors. In this case too, if the leak rate of wheel circuit 1 exceeds the maximum delivery rate of the pressure supply DV at the target pressure level Psoll, the target pressure Psoll is not reached and the actual pressure Pist would remain lower than the target pressure Psoll.In this case, valve SV2k1 is closed. If brake fluid flows out of the brake system when valve SV2k1 is open, this is noticeable by a reduction in the level in reservoir VB. This means that compensation for the leakage flow can be limited in time and valve SV2k1 can be closed in time to ensure that sufficient brake fluid remains in the reservoir VB for subsequent braking applications. If brake fluid flows out of the brake system, the risk that the environment could be polluted with brake fluid and the risk of fire if the highly flammable brake fluid comes into contact with hot parts, such as the brake disc, must be taken into account. This risk can be reduced by not opening valve SV2k1.

[0074] Fig. 4eshows an example of a second alternative diagnostic procedure for testing for individual errors with the piston travel curve Sk of the pressure supply DV, which increases from time 0 to time t0 and remains constant from time t0, and the target pressure curve Psoll, which is derived from the piston travel curve Sk using the PV characteristic curve (pressure-volume characteristic curve) of the brake system. It also shows Fig. 4e the pressure curve, Pist, which is measured with the pressure sensor DG (see Fig. 3a ). At time t0, a difference between the target pressure, Psoll, and the actual pressure, Pact, is detected, which indicates a malfunction of the braking system. For this reason, at time t0, the valve BP1 (see Fig. 3a ) is closed, and the actual pressure curve Pact in brake circuit BK2 (see Fig. 3a), during the test period from time t1 to time t2. Valves SV2k3 and SV2k4 remain open. Valves SV2k1 and SV2k2 are closed so that in the event of a leak in the wheel circuits in brake circuit 1, RK1 or RK2, during the test period from time t1 to time t2, brake fluid does not flow out of both wheel circuits, RK1, RK2.

[0075] For the further course of the diagnosis, a distinction is now made as to whether the pressure Pist drops in the time period from time t0 to time t1 or not. 1. If the actual pressure in brake circuit 2, measured with the pressure sensor DG, drops from time t0 to time t1, which is indicated by the fine dashed line 1, then the malfunction of the braking system is caused by a leak in a wheel circuit in brake circuit BK2, RK3 or RK4. Therefore, at time t1, the valve SV2k3 is closed, and the actual pressure curve Pist in brake circuit BK2 is observed in the test period from time t1 to time t2. If the actual pressure Pist drops from time t1 to time t2, which is indicated by the coarse dashed line 2, then the malfunction of the braking system is caused by a leak in wheel circuit 4. Then, at time t2, the valve SV2k4 is closed and the valve BP1 and the valves SV2k1, SV2k2 and SVk3 are opened.Via a piston movement of the pressure supply DV, the actual pressure Pist in the wheel brake cylinders RZ1, RZ2 and RZ3 can be increased from time t2 to the target pressure Psoll, which is reached at point A. If the actual pressure Pist does not fall from time t1 to time t2, which is indicated by the finely dashed line 1a for the actual pressure from time t1 to t2, then wheel circuit 3 is leaking and valve BP1 and valves SV2k1 and SV2k2 are opened at time t2. Via a piston movement of the pressure supply DV, the actual pressure Pist in the wheel brake cylinders RZ1, RZ2 and RZ4 can be increased from time t2 to the target pressure, which is reached at point B. 2. If the actual pressure Pist in brake circuit 2, measured with the pressure sensor DG (see . Fig. 3a), from time t0 to time t1, which is indicated by the solid line 3, then the malfunction of the braking system is not caused by a leak in a wheel circuit in brake circuit BK2, RK3 or RK4. Therefore, at time t1, valve BP1 is opened, and the actual pressure curve Pist in brake circuit BK2 is observed in the test period t1 to t2. If the actual pressure Pist drops from time t1 to time t2, which is indicated by the slightly less finely dashed line 4, then the malfunction of the braking system is not caused by a leak in wheel circuit 1 or wheel circuit 2, because valves SV2k1 and SV2k2 are still closed, but for example by a leak in the pressure supply DV.In this case, at time t2, valves SV2k1 and SV2k2 are opened, with valves SV2k3 and SV2k4 still being open, and from time t2 onwards, the actual pressure Pact in all wheel brake cylinders RZ1, RZ2, RZ3 and RZ4 can be raised to the target pressure Psoll via a piston movement of the pressure supply DV, which is reached at point C. Due to the leak in the piston seal of the pressure supply DV, a constant piston movement is required even after point C in order to keep the actual pressure Pact at the target pressure level Psoll. As already mentioned, this has the advantage that the normal braking effect is maintained in all wheel brake cylinders despite errors. However, if the leakage rate of the piston seal exceeds the maximum delivery rate of the pressure supply DV at the target pressure level Psoll, the system switches to a fallback level without the pressure supply DV.If the actual pressure Pact does not drop from time t1 to time t2, which is indicated by the solid line 5 for the actual pressure Pact from time t1 to time t2, then wheel circuit 1 or wheel circuit 2 is leaking. Therefore, valve SV2k1 is opened at time t2, and the actual pressure curve Pact is observed during the test period from time t2 to time t3. If the actual pressure Pact drops from time t2 to time t3, which is indicated by the slightly less finely dashed line 6, then the malfunction of the braking system is caused by a leak in wheel circuit 1. At time t3, valve SV2k1 is then closed and valve SV2k2 is opened, with valves SV2k3 and SV2k4 still being open, and via a piston movement of the pressure supply DV, from time t3, the actual pressure Pact in the wheel brake cylinders RZ2, RZ3 and RZ4 can be raised to the target pressure Psoll, which is reached at point D.If the actual pressure Pact does not drop from time t2 to time t3, which is indicated by the solid line 7, then the brake system malfunction is not caused by a leak in wheel circuit 1. Therefore, at time t3, valve SV2k2 is opened, and the actual pressure curve Pact is observed during the test period from time t3 to time t4. If the actual pressure Pact drops from time t3 to time t4, which is indicated by the dot-dash line 8, then the brake system malfunction is caused by a leak in wheel circuit 2. At time t4, the valve SV2k2 is then closed, while the valves SV2k1, SV2k3 and SV2k4 are still open, and from time t4 onwards, the actual pressure Pact in the wheel brake cylinders RZ1, RZ3 and RZ4 can be raised to the target pressure Psoll, which is reached at point E, via a piston movement of the pressure supply DV.If the actual pressure Pact does not drop from time t3 to time t4, which is indicated by the solid line 9 for the actual pressure Pact from time t3 to t4, the malfunction of the braking system is not caused by a leak in a wheel circuit, RK1, ..., RK4, but rather, for example, by air bubbles in the brake fluid. At time t4, with valves SV2k1, SV2k2, SV2k3, SV2k4 open, the actual pressure Pact can be raised to the target pressure Psoll via a piston movement of the pressure supply DV, which is reached at point F.

[0076] The order in which the valves are opened and closed and the size of the leaks in the wheel brake circuits and piston seal of the pressure supply DV are examples chosen here and are not binding. The order can be selected, for example, based on driving dynamics aspects. As with a leak in the piston seal of the pressure supply DV, if a wheel brake circuit, e.g. wheel brake circuit 1, is leaking, the associated valve SV2k1 can remain open in order to keep the actual pressure Pact at the target pressure level Psoll with a constant piston movement. As already mentioned, this has the advantage that the normal braking effect is maintained in all wheel brake cylinders despite errors. In this case too, if the leakage rate of wheel circuit 1 exceeds the maximum delivery rate of the pressure supply DV at the target pressure level Psoll, the target pressure Psoll is not reached and the actual pressure Pact would remain lower than the target pressure Psoll.In this case, valve SV2k1 is closed. If brake fluid flows out of the brake system when valve SV2k1 is open, this is noticeable by a reduction in the level in reservoir VB. This means that compensation for the leakage flow can be limited in time and valve SV2k1 can be closed in time to ensure that sufficient brake fluid remains in the reservoir VB for subsequent braking applications. If brake fluid flows out of the brake system, the risk that the environment could be polluted with brake fluid and the risk of fire if the highly flammable brake fluid comes into contact with hot parts, such as the brake disc, must be taken into account. This risk can be reduced by not opening valve SV2k1.

[0077] Fig. 4fshows an example of the first alternative diagnostic procedure, but now for testing for double errors in the form of a logic tree, with the piston travel curve Sk of the pressure supply DV, which increases from time 0 to time t0 and remains constant from time t0 onwards, and the target pressure curve Psoll, which is derived from the piston travel curve Sk using the PV characteristic curve (pressure-volume characteristic curve) of the brake system. It also shows Fig. 4f the actual pressure curve, Pist, which is measured with the pressure sensor DG (see Fig. 3a). At time t0, at point 1, a difference is detected between the target pressure, Psoll, and the actual pressure, Pist, which suggests a malfunction of the braking system. For this reason, at time t0, all valves, SV2k1, ..., SV2k4 are closed, and the actual pressure curve Pist is observed in the test period from time t0 to time t1. If the actual pressure Pist drops from time t0 to time t1 up to point 2, then the malfunction of the braking system is caused by at least a leak other than possible leaks in the wheel circuits, RK1, ..., RK4, e.g., a leak in the piston seal of the pressure supply DV. For an additional test of the tightness of the wheel circuits, RK1, ..., RK4, the delivery rate of the pressure supply DV is adjusted at point 2 so that the leakage flow caused by the leak in the piston seal of the pressure supply DV is compensated.This is shown by the finely dashed line at piston travel Sk from time t1. However, if the leakage flow is greater than the maximum delivery rate of the pressure supply DV, the diagnosis is aborted and the system switches to a fallback level without pressure supply. Otherwise, valve SV2k1 is opened at point 2 at the same time. If the measured pressure drops, point 3 is reached at time t2, which indicates the double fault "pressure supply DV leaking and wheel circuit 1 leaking". If the measured pressure does not drop, point 4 is reached at time t2. At point 4, valve SV2k1 is closed and valve SV2k2 is opened. If the measured pressure drops, point 5 is reached at time t3, which indicates the double fault "pressure supply DV leaking and wheel circuit 2 leaking". If the measured pressure does not drop, point 6 is reached at time t3. In point 6, valve SV2k2 is closed and valve SV2k3 is opened.If the measured pressure drops, point 7 is reached at time t4, which indicates the double fault "pressure supply DV leaking and wheel circuit 3 leaking". If the measured pressure does not drop, point 8 is reached at time t4. Valve SV2k4 is opened at point 8. If the measured pressure drops, point 9 is reached at time t5, which indicates the double fault "pressure supply DV leaking and wheel circuit 4 leaking". If the measured pressure does not drop, point 10 is reached at time t5, at which only the pressure supply DV is leaking and there is no double fault because no wheel circuit, RK1, ..., RK4, is leaking. Due to the leak in the piston seal of the pressure supply DV, a constant piston movement is required after point 10 in order to keep the actual pressure Pact at the target pressure level Psoll. Even if there is an additional leak in a wheel circuit in point 3 or 5 or 7 or 9, e.g.For wheel circuit 1 at point 3, the associated valve SV2k1 can remain open to maintain the actual pressure Pactual at the target pressure level Psoll with a constant piston movement of the pressure supply DV. As already mentioned, this has the advantage that, despite errors, the normal braking effect is maintained in all wheel brake cylinders. In this case, too, if the sum of the leakage rates of the piston seal and wheel circuit 1 exceeds the maximum delivery rate of the pressure supply DV at the target pressure level, the target pressure Psoll is not reached, and the actual pressure Pactual remains lower than the target pressure Psoll. In this case, the valve SV2k1 is closed.If brake fluid flows out of the brake system when valve SV2k1 is open, this is noticeable by a reduction in the level in the reservoir. This means that the compensation of the leakage flow in wheel brake cylinder RZ1 can be limited in time and the SV2k1 valve can be closed in time so that sufficient brake fluid remains in the reservoir VB for subsequent braking applications. If brake fluid flows out of the brake system, it must be taken into account that the environment can be polluted with brake fluid and that fire can start if the highly flammable brake fluid comes into contact with hot parts, such as the hot brake disc. This risk can be reduced by not opening valve SV2k1.

[0078] If the actual pressure Pact does not drop from time t0, from point 1, until time t1, then point 11 is reached at time t1 and a check is made to see if the malfunction is caused by a leak in one or two wheel circuits, RK1, RK2, RK3 or RK4. To test the tightness of wheel circuit 1, valve SV2k1 is opened at point 11. If the measured pressure then drops, then there is a leak in wheel circuit 1 and it is reached at time t2, point 12. From time t2, point 12, a check is then carried out for a second fault, with valve SV2k1 being closed and valve SV2k2 being opened at time t2. If the measured pressure then drops, then point 13 is reached at time t3, which indicates the double fault "wheel circuit 1 leaking and wheel circuit 2 leaking". If the measured pressure does not drop after this time, point 14 is reached at time t3. This indicates that there is no leak in wheel circuit 2.At time t3, at point 14, valve SV2k2 is closed and valve SV2k3 is opened. If this causes the measured pressure to drop, point 15 is reached at time t4, which indicates the double fault "wheel circuit 1 is leaking and wheel circuit 3 is leaking". If this does not cause the measured pressure to drop, point 16 is reached at time t4. This indicates that there is no leak in wheel circuit 3. At point 16, valve SV2k3 is closed and valve SV2k4 is opened. If this causes the measured pressure to drop, point 17 is reached at time t5, which indicates the double fault "wheel circuit 1 is leaking and wheel circuit 4 is leaking". If this does not cause the measured pressure to drop, point 18 is reached at time t5, at which only wheel circuit 1 is leaking and there is no double fault.

[0079] If the actual pressure Pact does not drop from time t1, from point 11, until time t2, then point 19 is reached at time t2 and the malfunction of the braking system is not caused by a leak in wheel circuit 1. A check is carried out to see whether the malfunction is caused by a leak in one or two wheel circuits, RK2, RK3 or RK4. To test the tightness of wheel circuit 2, valve SV2k1 is closed and valve SV2k2 is opened at point 19. If the measured pressure then drops, then there is a leak in wheel circuit 2 and it is reached at time t3, point 20. From time t3, point 20, a check is then carried out for a second fault, with valve SV2k2 being closed and valve SV2k3 being opened at time t3. If the measured pressure then drops, point 21 is reached at time t4, which indicates the double fault “wheel circuit 2 leaking and wheel circuit 3 leaking”.If the measured pressure does not drop after this, point 22 is reached at time t4. This indicates that there is no leak in wheel circuit 3. At time t4, at point 22, valve SV2k3 is closed and valve SV2k4 is opened. If this causes the measured pressure to drop, point 23 is reached at time t5, which indicates the double fault "wheel circuit 2 is leaking and wheel circuit 4 is leaking." If this does not cause the measured pressure to drop, point 24 is reached at time t5. This indicates that there is no leak in wheel circuit 4 and that only wheel circuit 2 is leaking, meaning there is no double fault.

[0080] If the actual pressure Pact does not drop from time t2, from point 19, until time t3, then point 25 is reached at time t3 and the malfunction of the braking system is not caused by a leak in the wheel circuits RK1 or RK2, and a check is made to see whether the malfunction is caused by a leak in one or two wheel circuits, RK3 or RK4. To test the tightness of wheel circuit 3, valve SV2k2 is closed and valve SV2k3 is opened at point 25. If the measured pressure then drops, then there is a leak in wheel circuit 3 and point 26 is reached at time t4. From time t4, point 26, a check is then carried out for a second fault, with valve SV2k3 being closed and valve SV2k4 being opened at time t4. If the measured pressure then drops, point 27 is reached at time t4, which indicates the double fault “wheel circuit 3 leaking and wheel circuit 4 leaking”.If the measured pressure does not drop after this time, point 28 is reached at time t5. This indicates that there is no leak in wheel circuit 4, and that only wheel circuit 3 is leaking, and there is no double fault.

[0081] If the actual pressure Pact does not drop from time t3, from point 25, until time t4, then point 29 is reached at time t4 and the malfunction of the braking system is not caused by a leak in the wheel circuits RK1, RK2 or RK3, and a check is made to see whether the malfunction is caused by a leak in wheel circuit 4. To test the tightness of wheel circuit 4, valve SV2k3 is closed and valve SV2k4 is opened at point 29. If the measured pressure then drops, then there is a leak in wheel circuit 4 and point 30 is reached at time t5. However, there is no double fault. If the measured pressure does not drop after that, point 31 is reached at time t5. This indicates that there is no leak in wheel circuit 4. If point 31 is reached, there are no leaks in the wheel circuits RK1, ..., RK4 and the malfunction of the braking system must have another cause, e.g.Air bubbles in the brake fluid.

[0082] The order in which the valves are opened and the extent of the leaks in the wheel circuits RK1, ..., RK4, and the piston seal of the pressure supply DV are examples and are not binding. The order can be selected, for example, based on driving dynamics aspects such as braking distance and driving stability. As described above, in the event of a double fault «DV leaking and wheel circuit 1 leaking» the associated valve SV2k1 can remain open in order to keep the actual pressure Pact at the target pressure level Psoll with a constant piston movement of the pressure supply DV. In this way, even in the event of a double fault, e.g. «wheel brake cylinder RZ1 leaking and wheel brake cylinder RZ2 leaking» both valves SV2k1 and SV2k2 can remain open in order to keep the actual pressure Pact at the target pressure level Psoll with a constant piston movement of the pressure supply DV. As already mentioned, this has the advantage that the normal braking effect is maintained in all wheel brake cylinders despite the fault.In this case too, if the sum of the two leakage rates of both wheel circuits, RK1 and RK2, exceeds the maximum delivery rate of the pressure supply DV at the target pressure level, the target pressure Psoll is not reached and the actual pressure Pact remains lower than the target pressure Psoll. If the individual leakage rates of both wheel circuits, e.g. RK1 and RK2, are already greater than the maximum delivery rate of the pressure supply DV, then both valves SV2k1 and SV2k2 are closed. If the leakage rate only exceeds the maximum delivery rate of the pressure supply DV in one wheel circuit, e.g. RK1, then only valve SV2k1 is closed. If only the sum of the leakage rates of the two wheel circuits, e.g. RK1 and RK2, exceeds the maximum delivery rate of the pressure supply DV, then a decision can be made as to which valve SV2k1 or SV2k2 is closed based on driving dynamics aspects such as braking distance and driving stability. Here too, i.e. if e.g.Valve SV2k1 remains open despite a leak in wheel circuit 1. If brake fluid flows out of the brake system, this is noticeable by a reduction in the level in the reservoir VB. This means that the compensation of the leak flow can be limited in time and the valve SV2k1 can be closed in time so that sufficient brake fluid remains in the reservoir VB for subsequent braking applications. If brake fluid flows out of the brake system, the risk that the environment could be contaminated with brake fluid and the risk of fire if the highly flammable brake fluid comes into contact with hot parts, such as the brake disc, must be taken into account. This risk can be reduced by not opening the valve SV2k1.

[0083] In an intact braking system, each brake pedal travel corresponds to a defined pressure, the target pressure, in the master brake cylinder SHZ / HZ, see. Fig. 1 , which determines the pedal characteristics. The pressure in the master brake cylinder is measured, e.g. directly with a pressure sensor DG-SHZ, the actual pressure, or indirectly with a force-displacement sensor (not shown) which can measure, for example, the pedal force. The brake pedal travel is measured using a pedal travel sensor - not shown. In this way, a target pressure in the master brake cylinder can be determined for each brake pedal travel. If the master brake cylinder SHZ / HZ or valve 9 is leaking, see Fig. 1 , the volume in the master brake cylinder changes, which means that the actual pressure in the master brake cylinder SHZ / HZ deviates from the target pressure value.

[0084] The error is detected by continuously comparing the actual pressure with the target pressure in the master brake cylinder SHZ / HZ. In the fallback mode, if the difference between the actual pressure and the target pressure exceeds a selectable limit, valves SV2k1, ..., SV2k4 are closed and valve 9 is opened. The volume change in the master brake cylinder SHZ / HZ is compensated via the pressure supply DV. If volume is lost from the master brake cylinder, volume is supplied from the pressure supply to the master brake cylinder, or if volume in the master brake cylinder SHZ / HZ increases, volume is removed from the pressure supply to the master brake cylinder, until the actual pressure equals the target pressure. Valve 9 is then closed, and valves SV2k1, ..., SV2k4 are opened. The pressure supply DV is then supplied again for brake pressure control to the wheel brake cylinder RZ1, ...RZ4 is used until the difference between the actual and target pressure exceeds the selectable limit again, after which the fallback process repeats. The brake pedal characteristics and feel remain largely normal. However, slight vibrations of the brake pedal may occur.

[0085] The following table lists reference values ​​for diagnosis: Event Approximate value Maximum flow rate for the pressure supply from the TTL requirement. Note: TTL stands for "Time To Lock" and is the shortest time it takes to reach 100 bar of brake pressure in the wheel brake cylinders. A typical requirement is: TTL = 150 ms Q DV,max = 66 cm 3 < / s = 6.6 cm 3< / 100 ms = 1.2 cm 3< / 20 ms TD (TD = diagnostic time = 20ms) Maximum flow rate through a valve SV2k (from TTL requirement): Q SV2k,max = 22 cm 3< / s = 2.2 cm 3< / 100ms = 0.44cm 3< / 20ms TD Volume flow SV2k with dirt particles in the valve seat (leakage flow Q SV2k,leak ) at 50 bar differential pressure across the valve: Q SV2k, leak = 8 cm 3< / s = 0.8 cm 3< / 100 ms = 0.16 cm 3< / 20 ms TD Volume flow EV with dirt particles in the valve seat (leakage flow Q EV,leak ) at 50 bar differential pressure across the valve: Volume flow RV from EV with dirt particles in the valve seat (leakage flow Q RV,leak ) at 50 bar differential pressure across the valve: QSV,leak = 8 cm 3 < / s Q RV,leak = 12 cm 3 < / s DV piston area Ak = 4.4 cm 2< DV piston displacement for volume displacement of 0.16cm 3< Sk = 0.4mm DV piston speed at leakage flow Q SV2k,leak Vk leak = 0.4mm / 20ms TD List of reference symbols

[0086] 1 Sensor element 2 Target in the float 3 Return line to the VB 4 DV specific valve circuit 5 Single-circuit pressure supply 6 Armature 6 / 6a 7 / 7a Valve tappet 8 Valve seat 9 Isolating valve RZ1 - RZ4 Wheel brake cylinder BK1 / BK2 Brake circuits RK1 Wheel circuit 1 RK2 Wheel circuit 2 RK3 Wheel circuit 3 RK4 Wheel circuit 4 HCU Entire hydraulic unit with DV and valves VB Reservoir HL1 - HL4 Hydraulic lines outside the HCU to the RZ HL5 Hydraulic lines from SHZ to BV KTV Circuit isolating valve DV Pressure supply DG Pressure sensor EM1 / 2 Electrical magnetic circuit ½ EIV Electrical valve control elEM Electrical motor control of the electromechanical brake 9 Permanent magnet 10 Pole plate 11 Electromagnetic return 12 Plastic body 13 Return spring SV2k Normally open solenoid valve without check valve with a Power auxiliary device

Claims

1. Brake system with - at least two wheel brake cylinders (RZ1-4), each of which is part of separate wheel circuits (RK1-4), - at least one pressure supply (DV), which serves at least to build up pressure (pauf) in the wheel brake cylinders (RZ1-4), - at least one reservoir (VB), - at least one electronic control and regulation device (ECU) - switching valves (SV2K1-4), wherein each wheel brake cylinder (RZ1-4) is connected via a hydraulic connection line to a switching valve (SV2K1-4), which serves to disconnect and connect the hydraulic connection of the respective wheel brake cylinder (RZ1-4) and at least one further hydraulic main line, via which the switching valve (SV2K1-4) is connected or can be connected to at least the pressure supply (DV), wherein the hydraulic connecting line and the wheel brake cylinder (RZ1-4) connected thereto are each part of a wheel circuit (RK1-4), characterized in that a diagnosis of the respective leakage of the individual wheel circuits (RK1-4) is performed and that, depending on the diagnostic result, an electronic control and regulation device (ECU) decides whether a wheel circuit (RK1-4) is switched off by permanently closing the associated switching valve (SV2K1-4) or continues to be operated to generate a braking effect.

2. Braking system according to claim 1, characterized in that the degree of leakage or the leakage flow (Qleck) in a wheel circuit (RK1-4) is determined using one or more of the following methods a) to e): a) Determination of the required amount of hydraulic fluid which must be supplemented to the predetermined fluid quantity by means of the pressure supply (DV) in order to achieve a target pressure (psoll) in the respective wheel circuit (RK1-4); b) Determination of a calculated absolute pressure drop (dpab) and / or pressure drop gradient (pab / dt) in the respective wheel circuit (RK1-4); c) Determination of the pressure deviation (dp = psoll - pist) from the target pressure value (psoll) during pressure build-up in the respective wheel circuit (RK1-4) by pumping a predetermined fluid quantity (q) into the wheel circuit (RK1-4) to achieve the set pressure (psoll) and then determining the actual pressure (pist); d) Diagnosis of leaks in the wheel circuit (RK1-4) by the pressure (pist) in the hydraulic line connecting the switching valve (SV2K1-4) and the pressure supply (DV) during pressure build-up by means of the pressure supply (DV) or when the pressure supply (DV) is switched off; e) Measurement of the absorption volume (Q) of the respective wheel circuit (RK1-4) via the pressure supply (DV) to achieve a target pressure (psoll), wherein the absorption volume (Q) is determined by means of the pressure supply (DV), in particular by measuring the current of the drive motor (M) of the pressure supply (DV) and / or the piston stroke (ds) of the piston of the pressure supply (DV).

3. Braking system according to claim 1 or 2, characterized in that when an upper limit value (Qhigh) or limit value range (dQhigh) for the leakage of a wheel circuit (RK1-4) is exceeded, the respective associated switching valve (SV2K1-4) is permanently closed, thereby preventing any braking action from occurring with this wheel brake cylinder (RZ1-4), and that below the upper limit value (Qhigh) and above a lower limit value (Qlow), a temporary and / or permanent follow-up delivery takes place in order to achieve the brake pressure (psoll) to be set in the respective wheel brake cylinder (RZ1-4), whereby in particular either the upper limit value (Qhigh) is determined by the maximum delivery rate of the pressure supply (DV) for increasing the pressure and / or, in the event of a leakage flow (Qleck) of 50-90% of the maximum delivery rate of the pressure supply (DV), the leakage flow (Qleck) is compensated by the pressure supply (DV) by means of additional delivery, such that there is no or only a slight reduction in the braking effect.

4. Braking system according to one of claims 3, characterized in that, in order to optimize the braking effect and driving stability, an electronic control and regulation device (ECU) determines whether and which leaky wheel circuit(s) (RK1-4) is or are shut off by permanently closing the respective switching valve(s) (SV2K1-4).

5. Braking system according to one of the preceding claims, characterized in that either an outlet valve (AV1-4) belonging to a wheel brake cylinder is part of the respective wheel circuit (RK1-4) and / or the brake system has a brake pedal, in particular in the form of a brake pedal acting mechanically on a master brake cylinder (SHZ, THZ) or an electronic brake pedal for a brake-by-wire brake system.

6. Braking system according to one of the preceding claims, characterized in that either - with the diagnosis single faults, double faults, and the leakage rate (dQ; dQ / dt) in the brake system and / or - no check valve (RV) is connected in parallel to the switching valve (SV2K1-4) and / or - when a certain leakage flow (Qleck, min) is exceeded in at least one wheel circuit (RK1-4) or the sum of all determined leakage flows one wheel circuit (RK1-4) or the sum of all determined leakage flows (ΣQleck,1-4), the brake system issues a warning message, in particular a visual and / or acoustic warning, in particular by means of a display, indicating the failure of at least one wheel circuit (RK1-4) and / or - when diagnosing the leak in a wheel circuit (RK1-4), the pressure-volume characteristic curve (DVK) of the respective wheel circuit (RK1-4) is taken into account or used.

7. Braking system according to one of the preceding claims, characterized in that - between the pressure supply (DV) and a switching valve (SV2K1-4) a maximum of two further valves (BP1, MVDV1, MVDV2), in particular switching valves, are arranged in the hydraulic connecting line and / or - between the pressure supply (DV) and a switching valve (SV2K1-4) at least one wheel circuit (RK1, RK2), a maximum of two additional valves (MVDV1, MVDV2, BP1), in particular switching valves, are arranged in the hydraulic connecting line, and that between the pressure supply (DV) and at least one additional switching valve (SV2K1-4) of another wheel circuit (RK3, RK4), only one further valve (MVDV1, MVDV2), in particular a switching valve, is arranged in the hydraulic connecting line.

8. Brake system according to one of the preceding claims, characterized in that all wheel circuits (RK1, RK2, RK3, RK4) belong to one brake circuit (BK) and are connected via a common hydraulic main line (HL) either a) to the single working chamber (A) of a plunger system of the pressure supply (DV) or, via at least one valve (MVDV1) from the working chamber (A), or b) connected to both working chambers (A1, A2) of a double-acting piston-cylinder-system of the pressure supply (DV) or can be connected, whereby in both stroke directions of the double-acting piston, pressure reduction and / or pressure build-up can occur in at least one wheel circuit (RK1-4), whereby optionally at least one wheel brake cylinder (RZ1-4), in particular two or all wheel brake cylinders, can be assigned one outlet valve (AV) each.

9. Brake system according to one of claims 1 to 8, characterized in that two wheel circuits (RK1, RK2; Rk3, RK4) belong to one brake circuit (BK1, BK2), wherein the brake circuits each have hydraulic brake circuit lines (HL1, HL2), wherein in particular - the brake circuits (BK1, BK2) can be hydraulically connected to each other or hydraulically separated from each other via a circuit separation valve (BP1) and / or - each brake circuit (BK1, BK2) has a separate hydraulic line with a respective working chamber (A1, A2) of a double-acting - each brake circuit (BK1, BK2) is or can be connected via a separate hydraulic line to a respective working chamber (A1, A2) of a double-acting piston-cylinder-system of the pressure supply (DV), wherein a separating valve can optionally be arranged in each hydraulic line.

10. Brake system according to one of claims 5 to 9, characterized in that at least one wheel brake cylinder (RZ1-4), in particular one wheel brake cylinder per brake circuit (BK1, BK2), is assigned an outlet valve (AV) or only a single outlet valve (AV) is provided for the entire brake system.

11. Brake system according to one of the preceding claims, characterized in that in addition to the diagnosis of the wheel circuits (RK1-4) a) a diagnosis of the valves (MVDV1, MVDV2, BP1, BP2) arranged between the switching valves (SV2K1-4) and the pressure supply for function and / or tightness and / or b) a diagnosis of the function and / or tightness of the switching valves (SV2K1-4) is performed and / or c) a diagnosis of the function and / or tightness of the pressure supply (DV) is performed and / or for diagnosing leakage in one or more wheel circuits (RK1-4) all switching valves (SV2K1-4) of all wheel circuits (RK1-4) are first opened and the pressure supply (DV) is used to set a target pressure (psoll) in the wheel circuits, whereby the actual pressure (pist) is compared with the target pressure (psoll), and that if a certain deviation is exceeded, a further diagnosis of the individual wheel circuits (RK1-4) is carried out one after the other until either a) a leak is detected in a wheel circuit (RKi), in particular for the deviation between the previously determined actual pressure (pist) and the set pressure (psoll) or b) all wheel circuits (RK1-4) have been checked for leaks one after the other.

12. Braking system according to claim 11, characterized in that, in order to check the tightness of an individual wheel circuit (RKi), all switching valves (SK2k1-4) of all wheel circuits of one or all brake circuits (s) (BK1, BK2) are first closed, then the switching valve (SV2Ki) belonging to the wheel circuit (RKi) to be checked is opened, and then either a) a target pressure (psoll) in the respective wheel circuit (RKi) or its brake cylinder (RZi) using the pressure supply, whereby the actual pressure (pist) is determined using a pressure sensor (DG) and / or on the basis of the measured drive current of the drive motor (M) of the pressure supply (DV), and that on the basis of a deviation from the determined set pressure (psoll) and the determined actual pressure (pist), the degree of leakage is determined or estimated, or b) no pressure change is made by means of the pressure supply (DV) and the actual pressure in the respective wheel circuit or brake circuit is determined, in particular by means of a pressure sensor (DG), and that the degree of leakage is determined or estimated on the basis of a determined pressure drop.

13. Brake system according to one of the preceding claims, characterized in that the pressure supply (DV) has an electric motor drive (M) which a) drives a piston-cylinder system either with aa) a single-stroke piston and a working chamber or bb) a double-stroke piston with two working chambers, or b) drives a rotary pump, wherein, optionally, when using a rotary pump or a piston pump for the pressure supply (DV), a solenoid valve (MVDV) or a check valve (RV) is provided to separate the pressure output of the pump from the brake circuit, in particular the pressure reduction (Pab) is carried out via the outlet valves (AV) assigned to the wheel brake cylinders (RZi), whereby one, two, or more outlet valves (AV) are opened, in particular to achieve a target gradient of the pressure reduction (Pab).

14. Brake system according to one of the preceding claims, characterized in that the diagnosis for checking for leaks in the brake system or in the individual wheel circuits (RK1-4) is or can be performed at one of the following times or driving situations: a) during braking, b) while the vehicle is stationary or at speeds lower than a maximum speed (vmax), in particular, for example, lower than or equal to 30 km / h, c) at specific time intervals, d) each time the vehicle is started.

15. Brake system according to one of the preceding claims, characterized in that a) during diagnosis, each wheel circuit of the brake system is checked for failure, and / or b) during diagnosis, the actual piston position (Skist) of the pressure supply (DV) and the actual pressure (pist) in the brake system are checked, and / or during the diagnosis, the stored pressure-volume characteristics (DKV) of the brake system and / or the wheel circuits are used, and / or c) a target piston position (Sksoll) of the pressure supply (DV) is derived from the pressure in the brake system using the pressure-volume characteristics (DKV), and / or d) a malfunction of the brake system is derived from the difference between the actual piston position and the target piston position, and / or e) in the event of a malfunction due to leakage, the leakage volume flow is compensated by corresponding replenishment using the pressure supply (DV).

16. Brake system according to one of the preceding claims, characterized in that either - one or both hydraulic main lines (HL1, HL2) of the brake circuit (BK) or brake circuits (BK1, BK2) are connected to one or more working chambers of a master brake cylinder, in particular in the form of a single master brake cylinder (SHZ) or a tandem main brake cylinder (THZ), wherein this connection or these connections can be interrupted by means of one or two, in particular "normally open," switching valve or switching valves (9) and / or - at least one brake circuit (BK, BK1) or the brake circuits (BK1, BK2) can be disconnected from the pressure supply (DV) by means of one or two, in particular "normally closed," switching valves (MVe, BP1, BP2), in particular in the event of a fault, and / or - the electromagnetic switching valves (SV2K1-4) and / or drives of the pressure supply (DV) have at least double redundant windings and / or controls.

17. Braking system according to one of the preceding claims, characterized in that the wheel circuits (RK14) are distributed over two brake circuits (BK1, BK2), and that the two brake circuits (BK1, BK2) are connected by means of a hydraulic line which can be shut off by means of a circuit isolating valve (BP1), and that one brake circuit (BK2) is permanently connected to the pressure supply without an intermediate solenoid valve, and that the other brake circuit (BK1) is connected to the master brake cylinder (SHZ, THZ) via a hydraulic connection (HL5), whereby this hydraulic connection (HL5) can be shut off by means of a "normally open" switch valve (9).

18. Brake system according to one of the preceding claims, characterized in that the brake system a) has exclusively purely hydraulically acting wheel brake cylinders (RZ1-4) and / or b) both purely hydraulically acting wheel brake cylinders (Rz1, RZ2) and electromotively actuated wheel brakes (EMB1, EMB2) and / or c) has or replicates an anti-lock braking system (ABS) and / or an electronic stability program (ESP).

19. Braking system according to one of the preceding claims, characterized in that either - in the event of failure of at least one wheel circuit (RK1-4) when a yaw moment occurs, the yaw moment control of the electronic stabilization system (ESP) is used or intervenes in the pressure control and / or - a detection of a volume change in the master brake cylinder (SHZ / HZ), in particular due to leaks in the master brake cylinder (SHZ / HZ) or leaks in the valve (9) by permanently comparing the target pressure in the master brake cylinder (SHZ / HZ), which is derived from the measured pedal travel, with the actual pressure in the master brake cylinder (SHZ / HZ), and / or that if a selectable limit value is exceeded, compensation for the change in volume is carried out by means of the pressure supply (DV) to maintain the normal brake pedal characteristics, whereby during compensation the pressure control in the wheel brake cylinders is stopped, and / or - no further valves are provided between the switching valves (SV2K1-4) assigned to the wheel circuits (RK1-4) and the pressure supply (DV).

20. Braking system according to one of the preceding claims, characterized in that the braking system comprises a switching valve (SV2K1-4), wherein the switching valve (SV2K1-4) is a solenoid valve with an electromagnetic drive (EM1) via which a valve actuator or valve tappet (7) between an open valve position and a closed valve position, characterized in that the switching valve (SV2K1-4) has an additional force device (EM2, 9) which exerts a force (FM2) on the valve actuator or valve tappet (7) by means of its own magnetic field, wherein in particular the switching valve (SV2K1-4) has a return spring (RF) which exerts a force on the valve actuator or valve tappet (7) which prevents the valve from closing abruptly, wherein the valve (SV2K1-4) is optionally a normally open valve or a normally closed valve, wherein normally open means that the electromagnetic drive (EM1) is not energized and / or the force (FM2) of the force-adding device (EM2, 9) can be generated or is generated by means of an energizable electromagnet and / or a permanent magnet.

21. Braking system according to claim 20, characterized in that the force (FM2) of the additional force device (EM2, 9) is directed opposite to the force (FM1) of the electromagnetic drive (EM1), wherein in particular the force (FM2) of the additional force device (EM2, 9) is equivalent to the force (FRF) of a possible return spring (RF), and no return spring (RF) is required if the magnetic circuit is dimensioned accordingly.

22. Braking system according to one of claims 20 to 21, characterized in that the force-adding device (EM1) only generates a force (FM2) by energizing the coil if the state of the brake system indicates that the switching valve (SV2K1-4), so that the force addition device (EM1) only consumes energy in such a state and / or the electromagnetic holding force is diagnosed via the current and movement of the armature by means of diagnostic functions.