3 / 2-way valve concept for a hydraulic actuation system

Abstract

The invention relates to a method for operating a braking system, the braking system having at least two hydraulic wheel brakes (RZ1-4), each of which is associated with a switching valve (SV1-4), and an electric-motor-driven pressure supply device (DV) which has a piston-cylinder system, the double-stroke piston (DHK) of which delimits and separates two working chambers (VH, RH), wherein the one first working chamber (VH) is connected to the braking circuit (BK2, BK) via a hydraulic connection (HL2), and the one second working chamber (RH) is connected to the braking circuit (BK1, BK) via a hydraulic connection (HL1), wherein at least one hydraulic connection (HL1, HL2) contains a 3 / 2-way valve (PD1, PD2) which can selectively hydraulically connect the associated working chamber (VH, RH) to the reservoir (VB) in a first switching position (Pos b) and to a braking circuit (BK1, BK2, BK) in a second switching position (Pos a), characterised in that, before the 3 / 2-way valve (PD1, PD2) is switched into its second switching position (Pos a), in which a hydraulic connection is established between the one working chamber (VH, RH) of the pressure supply device (DV) and the hydraulic connection (L4a) leading to the switching valves (SVi=1-4), the hydraulic pressure acting at least on the valve (PD1, PD2) to be switched is lowered or reduced.

Description

[0001] Applicant:

[0002] Heinz Leiber

[0003] Theodor-Heuss-Straße 34

[0004] 71739 Oberriexingen

[0005] 3 / 2 way valve concept for hydraulic actuation system

[0006] The present invention relates to a braking system with at least two hydraulic wheel brakes, each of which is assigned switching valves, an electric motor-driven pressure supply device which has a piston-cylinder system whose pistons delimit two working chambers, wherein the first working chamber is connected to a brake circuit via a hydraulic connection, and the second working chamber is connected to one or the brake circuit via a further hydraulic connection, wherein in at least one of the two hydraulic connections a 3 / 2-way valve is arranged which serves to selectively establish a hydraulic connection of the working chamber with a hydraulic connection leading to a reservoir or with a brake circuit.

[0007] Such hydraulic actuation systems are well known. In automotive technology, 3 / 2-way valves are used in a wide variety of applications, as disclosed in DE 10 2017000472, where a 3 / 2-way valve is used to selectively connect a brake circuit to the pressure supply system or to a tandem master cylinder. Using a 3 / 2-way valve can advantageously eliminate the need for a valve if previously only 2 / 2-way valves were used. In many valve applications, the safety requirements for valve failure are high, as they can impact the braking effect and pedal characteristics.

[0008] The object of the present invention is to design a generic hydraulic actuation system, in particular for a braking system, to be more fail-safe and more cost-effective.

[0009] This object is achieved according to the invention with a hydraulic braking and actuation system having the features of claim 1 and the method according to the invention having the features of claim 11. Further advantageous embodiments of the actuation system according to claim 1 and of the method according to claim 11 result from the features of these dependent claims.

[0010] With the actuation system according to the invention, the pressure can advantageously be regulated or controlled very precisely.

[0011] The pressure supply device can advantageously comprise a piston pump. In automotive engineering, there is a wide range of applications for the actuation systems according to the invention. Compared to rotary pumps, electric motor-driven piston-cylinder systems with plunger or double-acting pistons offer significant advantages for continuous medium delivery or for controlled volume delivery using piston travel measurement or pressure measurement, and possibly also motor current measurement, in which, for example, a very specific volume of hydraulic medium is adjusted by controlled or regulated displacement of the piston. This allows, for example, a predetermined pressure in the brake circuit to be set or regulated based on a pressure-volume characteristic curve.

[0012] However, it is particularly advantageous if the pressure supply device has a double-acting piston so that hydraulic medium can be delivered in the forward and return stroke, and if each working chamber of the pressure supply device can be connected to the reservoir via a 3 / 2-way valve, in particular one assigned to it. With this valve circuit as described above, for example, each of the currently required functions of a braking system can be implemented or adjusted using the piston. This makes it possible, among other things, to adjust the double-acting piston of the pressure supply device without delivering hydraulic medium to the brake circuit(s), which is generally also referred to as an idle stroke without volume delivery to or from the hydraulic circuits or brake circuits. In some cases, this serves to improve piston positioning from the end of the stroke.

[0013] However, when using a double-acting piston pump (DHK), it is also possible to assign a 3 / 2-way valve to only one working chamber or brake circuit and only a 2 / 2-way valve to the other. With this arrangement, it is then only possible to connect one brake circuit to the reservoir via the 3 / 2-way valve in order to discharge or draw hydraulic fluid into or from the reservoir.

[0014] Even if one 3 / 2 MV fails, for example, during the forward stroke, the second 3 / 2 MV can be used to operate the brake circuit BK or both BKs via the return stroke. This is an essential redundant safety feature.

[0015] In another possible embodiment, the two working chambers of the pressure supply device can be connected to the reservoir via a single 3 / 2-way valve, whereby at least one working chamber is always hydraulically connected to the reservoir. If the 3 / 2-way valve can be held in an intermediate position by the solenoid drive, it is also possible for both working chambers of the piston-cylinder unit of the pressure supply device to be hydraulically connected to the reservoir simultaneously.

[0016] If the hydraulic actuation system according to the invention with a double-acting piston is used for pressure control in a braking system, it can pump the hydraulic medium into both the forward and return strokes of both brake circuits. In the event of a failure of one brake circuit (circuit failure), the advantageous valve circuit allows pressure control in the other, still intact brake circuit to continue using the actuation system. The braking system can advantageously have a master brake cylinder that is designed either as a tandem or single master brake cylinder. The master brake cylinder thus has at least one working chamber, which can be connected via a 3 / 2-way valve either in the fallback mode to a brake circuit or, in the normal case, to a travel simulator for adjusting pedal feel.If the master brake cylinder is designed as a tandem master brake cylinder with two working chambers, one working chamber can be connected to the brake circuit and travel simulator via a 3 / 2-way valve as described above, and the other working chamber can be decoupled from the other brake circuit by means of a 2 / 2-way valve or connected to it in the fallback level.

[0017] The double-acting piston can be advantageously used for approximately twenty different operations with the valve circuit according to the invention, provided that it is to perform these operations without compromising dynamics and positioning accuracy. In contrast to the complex valve circuits known from DE 10 20110830312 or DE 10 2018221783, the valve circuit according to the invention of the hydraulic actuation system according to the invention is significantly simpler, more cost-effective, smaller in size, and also more fail-safe.

[0018] Even if one hydraulic circuit fails, the other circuit remains operational in the actuation system according to the invention. The provision of a redundant motor winding also achieves greater reliability of the drive. The valve circuit according to the invention is also flexible in its application, allowing it to be used for a wide variety of hydraulic unit requirements in ABS, ESP with different valve circuits, and other assistance functions.

[0019] To increase safety, a safety shut-off valve, particularly one that is normally closed when de-energized, can be additionally installed in the connecting line connecting the pressure supply device to the reservoir and in which a 3 / 2-way valve is located. This shut-off valve disconnects the hydraulic connection between the reservoir and the 3 / 2-way valve, particularly in the event of a malfunction and / or leak in the 3 / 2-way valve. This advantageously allows pressure to continue to be built up or changed in at least one wheel brake by closing the additional safety shut-off valve, even if the 3 / 2-way valve is leaking.

[0020] The use of a single SiV valve only has an effect in the fallback mode in the event of a failure of the double-acting piston (DHK) of the pressure supply system. This prevents total brake failure in the event of a double fault: a) a defective double-acting piston (DHK) and b) a leaking 3 / 2 MV. If each return line from the DHK to the VB is to be protected, two SiV valves would have to be provided for the pre-stroke working chamber (VH) and the return stroke working chamber (RH).

[0021] For rapid pressure build-up in the brake circuit, a significant delivery rate / time is necessary, which is also specified in TTL (Time To Lock), e.g. 100 / bar in 150ms. The valve seats, particularly for the hydraulic connection from the pressure supply device to the brake circuit, must therefore be designed with large cross-sectional passage areas or valve flow cross-sectional areas, which become effective when switching at high pressure, as is necessary, for example, when switching from the forward stroke to the return stroke or vice versa during pressure build-up and pressure reduction. The large valve flow cross-sectional area also results in a large valve seat area, which means the opening force of the valve seat is also large. With normal switching of the valves, this means high magnetic forces, e.g. at 100 bar or a maximum of 220 bar, and corresponding dimensioning of the magnetic circuit if the pressure drop, i.e. the efficiency of the double-acting piston DHK, is to be e.g. > 90%.This would mean significantly higher construction volumes for the 3 / 2 MV, costs, and switching times.

[0022] This is achieved by the valve circuit according to the invention and / or the method according to the invention, in which the wheel circuits or wheel brake cylinders are decoupled from the pressure supply device or part of the brake circuit via existing valves. This occurs by closing corresponding switching valves, after which the pressure in the 3 / 2-way valve to be switched is reduced either by appropriately adjusting the piston of the pressure supply device and / or establishing a connection to the reservoir tank or, if the pressure in the master brake cylinder is below the switching pressure of the 3 / 2-way valve PD1 or PD2, the master brake cylinder. At a sufficiently low pressure, the 3 / 2-way valve can switch reliably with a small drive even with a large valve flow cross-section or large valve seat. This advantageously allows the use of a standard 3 / 2-way solenoid directional valve with a small magnetic circuit.With this switching strategy according to the invention, a small additional switching time loss occurs during pressure buildup or pressure reduction. However, this is acceptable, since the switch to the counterstroke or the subsequent pressure buildup or pressure reduction via the other stroke direction rarely occurs until the end of the stroke. Also important for the entire system is the brake circuit design with corresponding valves and the connection to the master brake cylinder, which can be designed as a single master brake cylinder (SHZ) with only one working chamber or as a tandem master brake cylinder (THZ) with two working chambers.

[0023] In the braking system according to the invention or the method according to the invention, conventional inlet switching valves with an integrated or parallel-connected check valve can be used. However, the use of switching valves is particularly advantageous. These are modified inlet valves that are connected upstream of the wheel brake cylinders and are designed without a check valve. This advantageously creates a braking system in which up to four wheel circuits are formed. With appropriate switching and control during pressure build-up and pressure reduction, this results in an enormous increase in safety and also offers the option of simplifying the valve circuit, e.g. omitting the usual circuit isolation valve KTV. Although this has disadvantages for pressure control, the 3 / 2-way solenoid directional control valve, which is used for the return stroke, can also be replaced by a more cost-effective, standard 2 / 2-way solenoid directional control valve.

[0024] The method according to the invention provides that the valve to be switched is depressurized before switching, or the pressure difference across the valve is reduced to such an extent that the valve with a large valve seat surface can be switched to the required switching position quickly and reliably using a small-sized actuator without great energy expenditure. Especially when using 3 / 2-way valves with a large flow cross-sectional area and valve seat surface for the hydraulic connection between the pressure supply device or its respective working chamber and the respective brake circuit, without the method according to the invention, the actuator of the 3 / 2-way valve would have to be very powerful, making the valve large and expensive.In the method according to the invention, the pressure difference across the 3 / 2-way valve to be switched shortly, via which further pressure build-up or release is to take place, is reduced by the appropriate valve switching and possibly by a movement of the piston of the pressure supply device, to such an extent that the valve can switch reliably with little effort. To prevent the pressure already built up in the wheel brake cylinders from dropping undesirably, it is trapped in the wheel brake cylinders by closing the switching valves already present or the at least one isolating valve present or additionally provided in the brake circuit. After this, the pressure on the valve side of the 3 / 2-way valve to be switched is reduced to such an extent that the 3 / 2-way valve can switch.

[0025] The hydraulic actuation system according to the invention and its mode of operation are explained in more detail below with reference to drawings.

[0026] They show:

[0027] Fig. 1 : A possible embodiment of the hydraulic actuation system for supplying pressure to a braking system;

[0028] Fig. la: Enlarged section of the pressure supply device with only one 3 / 2-way valve;

[0029] Fig. 2a and 2b: schematic representations of the 3 / 2-way valve according to the invention in the de-energized (Fig. 2a) and energized state (Fig. 2b);

[0030] Fig. 3: schematic representation of the actuation system according to Figure 1 with a reservoir VB, a single master brake cylinder SHZ and a 3 / 2-way valve TV, a valve circuit as with ABS but with switching valves without check valve S i - SV4 and a pressure supply DV with 3 / 2-way valves PD1 and PD2;

[0031] Fig. 4: schematic representation of the actuation system according to Fig.

[0032] 3 with additional 2 / 2-way valve MV t ;

[0033] Fig. 4a: same structure as in Figure 4, but with standard ABS inlet valves with check valves EVi - E 4 instead of the switching valves SVi - S 4 used in Figure 3, which are designed without check valves;

[0034] Fig. 4b schematic representation of the actuation system according to Fig.

[0035] 4 with a 3 / 2-way valve US instead of the 2 / 2-way valve MV t , whereby a hydraulic connection to the storage tank VB can be realized via the 3 / 2-way valve US for pressure reduction;

[0036] Fig. 5: Switching position of the 3 / 2-way valve PD1 when connecting the

[0037] Pre-stroke working chamber VH of the double-stroke piston DHK with the brake circuit BK for pressure increase;

[0038] Fig. 5a: Switching position of the de-energized 3 / 2-way valve PD1 or

[0039] PD2;

[0040] Fig. 5b: Switching position of the 3 / 2-way valve PD2 when connecting the

[0041] Return stroke working chamber RH of the double-stroke piston DHK with the brake circuit BK for pressure increase;

[0042] Fig. 6: Time sequence when switching the double-stroke piston

[0043] DHK from forward stroke to return stroke during pressure build-up;

[0044] Fig. 6a: Valve switching positions during forward stroke and return stroke of the double-acting piston when pressure builds up from Obar;

[0045] Fig. 6b: Time sequence for switching the double-stroke piston

[0046] DHK from forward stroke to return stroke during pressure reduction: Fig. 6c: Time sequence when switching the double-stroke piston DHK from forward stroke to return stroke with the 3 / 2-way valve US during pressure build-up.

[0047] Fig. 6d: Time sequence for switching the double-stroke piston

[0048] DHK from forward stroke to return stroke with switching device 3 / 2-way valve

[0049] US during pressure reduction

[0050] Figure 1 shows a system with a master brake cylinder HZ, e.g., a single master brake cylinder SHZ with one working chamber RI or a tandem master brake cylinder THZ with two working chambers RI and R2, together with a reservoir VB and pedal travel sensor 2. All valves are shown in their de-energized state. In the case of the single master brake cylinder SHZ, a hydraulic line LI leads via a 3 / 2-way valve TV (shown de-energized) and via hydraulic line L4 to the pressure supply unit DV and to the brake circuit BK1. By energizing the 3 / 2-way valve TV, the working chamber RI is connected to the travel simulator WS via the hydraulic line LI, the 3 / 2-way valve TV, and the hydraulic line L3. The hydraulic line L4 leads directly to the 3 / 2-way valve PD2 and via the circuit isolation valve KTV and, if necessary, an additional redundant circuit isolation valve KTV. rto brake circuit BK2. The pre-stroke working chamber VH of the pressure supply unit DV is connected to the second brake circuit BK2 via the energized 3 / 2-way valve PD1 and to the reservoir VB via the de-energized 3 / 2-way valve PD1 (shown as de-energized) via the return line R. In addition, if appropriate safety requirements apply, safety valves SiVvH and SiVßH can be used as a double fault if the valve seat of the suction valve SaVl or SaV2 is leaking and the DHK seal is leaking. Alternatively, both connections from the working chambers VH and RH of the double-acting piston DHK to the reservoir VB can be switched via the two safety valves SiVvH and SiVßH. The 3 / 2-way valves PD1 and PD2 are the main components of the double-acting piston DHK, which are described in detail in Figs. 2a-2b.The two brake circuits BK1 and BK2 of the pressure supply unit DV lead to the hydraulic unit HCU for ABS, ESP, and assistance functions, which are supplied with pressure by the pressure supply unit DV. The pressure supply unit DV can be used not only for pressure build-up but also for pressure reduction.

[0051] Figure 1a shows an alternative embodiment of the actuation system according to Figure 1 without master brake cylinder SHZ / THZ, wherein the second 3 / 2-way valve PD2 is replaced by a 2 / 2-way valve to reduce costs, so that the return stroke working chamber RH can no longer be connected to the reservoir VB via a solenoid valve, but with restrictions in the function, e.g. pressure reduction during the return stroke and the 3 / 2-way valve PD1 shown de-energized.

[0052] Figure 2a shows a schematic representation of a possible embodiment of a 3 / 2-way valve PD1 or PD2 according to the invention for the braking system according to the invention. The 3 / 2-way valve PD1 or PD2 has an excitation winding 5 arranged around a magnetic yoke 6, in which the magnetic armature 4 is adjustable in the axial direction relative to the connecting pin 7, 7a. A stop element 4a is arranged at the left end of the magnetic yoke 4, which abuts the inner wall of the magnetic yoke 6 in the non-energized switching state of the 3 / 2-way valve PD1 or PD2 shown in Figure 2a. The first valve closing body VSK1 is arranged at the right end of the connecting pin 7, 7a and is firmly connected to the connecting pin end 7a. The first valve closing body VSK1 interacts with the first valve seat VS1, which may be a component of the magnetic yoke 6.The magnetic yoke 6 forms a first valve chamber Kl in the region of the connecting bolt section 7a, which is connected via a hydraulic channel to the first valve connection AN1 for connecting the storage tank VB.

[0053] The 3 / 2-way valve PD1 or PD2 also has a second valve chamber K2, in which the valve spring VF and a second valve closing body VSK2 are arranged, with the valve seat VS2 having the cross-sectional area that is important for pressure build-up and which determines the TTL. The second valve chamber K2 is connected via a hydraulic channel to the second valve connection AN2, to which brake circuit BK2 or BK1 is connected. The left side of the second valve chamber K2 forms the second valve seat VS2 of the 3 / 2-way valve PD1 or PD2, which interacts with the second valve closing body VSK2. A third valve chamber K3 is arranged between the two valve seats VS1 and VS2, which is connected to the third valve connection AN3 with the pre-stroke working chamber VH and return stroke working chamber RH.On the side of the first valve closing body VSK1 facing away from the connecting pin 7, 7a, a plunger ST is molded or attached. Its length is dimensioned such that it extends through the first valve seat VS1 and the third valve chamber K3, and its free end can act on the second valve closing body VSK2 when the 3 / 2-way valve PD1 or PD2 is energized. Depending on the overall concept, the valve port AN2 of the 3 / 2-way valve PD1 or PD2 can also be connected to only one brake circuit BK, see, for example, Fig. 3.

[0054] Figure 2b shows the "energized" state of the 3 / 2-way valve PD1 or PD2, in which the armature 4 is displaced to the right by the magnetic field of the excitation coil 5, whereby the first valve closing body VSK1 presses to the right and, with the tappet ST, against the second valve closing body VSK2, pushing it away from the second valve seat VS2 against the spring force of the valve spring VF, whereby the pressure supply device DV is now connected to the brake circuit BK1 / BK2. The hydraulic connection HV2 between the second valve chamber K2 and the third valve chamber K3 is opened, whereby the pre-stroke working chamber VH or the return stroke working chamber RH of the pressure supply device is connected to the brake circuit BK2 or BK1, respectively, and the hydraulic connection HV1 between the first valve chamber K1 and the third valve chamber K3 is closed, and the reservoir VB is disconnected.

[0055] The valve spring VF should be dimensioned so that when the 3 / 2-way valve PD1 or PD2 is de-energized, the solenoid armature 4 is safely reset and the valve closing body VSK2 is pressed securely against the second valve seat VS2.

[0056] Fig. 3 shows a braking system as previously known from PCT / EP 2022 / 059069, which has, among other things, four wheel circuits RK1-RK4, the reservoir VB, a single master brake cylinder SHZ with the third seal D3 and throttle Drl as well as pedal travel sensors Sp. In the de-energized state, the 3 / 2-way isolating valve TV connects the hydraulic line LI with the hydraulic line L4, and thus the single master brake cylinder SHZ with the brake circuit BK, and blocks the connection of the hydraulic line LI to the hydraulic line L3, thus blocking the connection from the single master brake cylinder SHZ to the travel simulator WS. When energized, the 3 / 2-way isolating valve TV connects the hydraulic line LI with the hydraulic line L3, thus connecting the single master brake cylinder SHZ with the travel simulator and blocks the connection of the hydraulic line LI with the hydraulic line L4, thus blocking the connection from the single master brake cylinder SHZ to the brake circuit BK.A pressure sensor DG1 is located in the hydraulic line LI, which connects the single brake master cylinder SHZ to the 3 / 2-way isolating valve TV. It monitors the pedal characteristics. Together with the pedal travel sensors Sp, it also monitors the single brake master cylinder SHZ, the travel simulator WS, and the 3 / 2-way isolating valve TV. The current values ​​from the pedal travel sensors Sp and the pressure sensor DG1 are continuously compared with the values ​​stored in the electronic control unit ECU. The 3 / 2-way isolating valve TV is connected to the brake circuit BK and to the pressure supply unit DV and the 3 / 2-way valves PD1 and PD2 via the hydraulic line L4. The brake circuit BK is in turn connected to the wheel brake cylinders RZ1-RZ4 via the switching valves SV1-SV4, which are modified standard ABS inlet valves EV without check valve RV in the version SVi=i-4, and via the hydraulic lines of the wheel circuits RK1-RK4.In the line from the switching valves SV1-SV4 to the wheel brake cylinders RZ1-RZ4, an outlet valve AV is provided for pressure relief, particularly for the ABS function. The switching valves SVi=i-4 are of great importance for the four-circuit function of the wheel circuits RK1-RK4, as described in particular in Figure 2 of PCT / EP 2022 / 059069.

[0057] The four-circuit system with its four switching valves SV1-SV4 without a respective check valve is of great importance for the inventive double-stroke piston valve circuit with its 3 / 2-way valves PD1 and PD2. Figures 6, 6a, 6b, and 6c describe in more detail the various switching strategies and process strategies for switching the 3 / 2-way valves PD1 and PD2, each with a large flow cross-section, in interaction with the pre-stroke working chamber VH and the return stroke working chamber RH, respectively, and their connection to the brake circuit BK. The large valve opening cross-section is necessary to achieve small time-to-lock values, so-called TTL values, of e.g. 150 ms. With this switching strategy, an additional volume absorption / volume change of the wheel brake cylinders RZ1-RZ4 must be avoided when switching the 3 / 2-way valves PD1 and PD2. For this purpose, the switching valve SVi = l-4 is suitable, which separates the wheel circuits RK1-RK4.As a result, the switching strategy according to the invention, which is described in more detail later in Figures 6, 6a, 6b, 6c and 6d, can be successfully used for the 3 / 2-way valves PD1 and PD2.

[0058] Many variants are conceivable for the 3 / 2-way isolating valve TV, depending on the high safety requirements. For example, failure of the electronic control unit (ECU) due to high pressure in the master brake cylinder (HZ) and high or low pressure in the brake circuit (BK). In this case, a connection from the master brake cylinder (HZ) to the brake circuit (BK) is always required in the event of a failure of the pressure supply unit (DV) or the electronic control unit (ECU). One of the variants is shown here, with a pressure relief valve (ÜV).

[0059] Figure 4 shows a further concept, based on Figure 3. Here, for the switching strategy of the 3 / 2-way valves PD1 and PD2, in addition to the switching valves SV1-SV4, a separating valve MV twhich, in the switching strategy of the 3 / 2-way valves PD1 and PD2, separates the connection from the brake circuit BK to the 3 / 2-way valves PD1 and PD2. Optionally, standard ABS inlet valves with check valve EVi - EV4 can be used instead of the switching valves SVi - SV4, as shown in Figure 4a. With this concept, too, the pressure reduction function of the failed outlet valve AV in ABS mode can be replaced or taken over by the switching valves SV1-4 and the pressure supply device DV thanks to the four-circuit system with the four switching valves SV1-SV4 without a check valve, e.g. in the event of a fault in the control of an outlet valve AV.

[0060] The safety valve SiV described in Fig. 1 can be used in the return line R from the pressure supply device DV to the reservoir VB. Furthermore, it is advisable to adapt the electronic control unit ECU to the reservoir VB by integrating the brake fluid level sensor into the electronic control unit ECU, rather than as a separate component with a cable harness.

[0061] Figure 4b shows another concept, based on Figures 4 and 4a. Here, for the switching strategy of the 3 / 2-way valves PD1 and PD2, instead of the isolating valve MV tA 3 / 2-way valve US can be used, which, when the 3 / 2-way valves PD1 and PD2 are switched on, disconnects the connection from the brake circuit BK to the 3 / 2-way valves PD1 and PD2, thereby connecting the 3 / 2-way valves PD1 and PD2 to the reservoir VB. Optionally, standard ASV inlet valves EVi - EV4 with a check valve can also be used in this brake system configuration instead of the switching valves SVi - SV4.

[0062] Figures 5, 5a and 5b show a possible design of a PD1 or PD2 valve and its various switching positions. Figure 5 shows the energized state of the 3 / 2-way valve PD1, via which the pre-stroke working chamber VH is connected to the brake circuit BK (position a). The pre-stroke of the double-stroke piston DHK then causes a volume flow through the 3 / 2-way valve PD1 and a pressure build-up in the brake circuit BK. Fig. 5a shows the de-energized state of the 3 / 2-way valve PD1 or PD2, with the pre-stroke working chamber VH connected to the reservoir VB, or with the return stroke working chamber RH connected to the reservoir VB (position b). Fig.Figure 5b shows the volume flow from the return stroke working chamber RH to the brake circuit BK via the 3 / 2-way valve PD2 during pressure build-up or pressure reduction, when the 3 / 2-way valve PD1 is also switched (position a), by return stroke of the double-stroke piston DHK, whereby the 3 / 2-way valve PD2 is in its switching position "a" like the valve PD1 shown in Figure 5.

[0063] To build up pressure P aUf the pre-stroke of the double-stroke piston DHK (Figure 5) energises the 3 / 2-way valve PD1 (position a), while the 3 / 2-way valve PD2 can either be energised (position a) or remains de-energised (position b). If the 3 / 2-way valve PD2 is energised (position a), then part of the pre-stroke volume of the double-stroke piston DHK flows from the pre-stroke working chamber VH through the 3 / 2-way valve PD1, via the brake circuit BK and via the 3 / 2-way valve PD2 into the return stroke working chamber RH, whereby only a lower motor torque is required to adjust the double-stroke piston DHK than if the 3 / 2-way valve PD2 remains de-energised. This type of control advantageously enables motor downsizing. This switching combination, in which both valves PD1 and PD2 are both in their position a), is therefore preferably used for high pressures PBK in the brake circuit BK.If the 3 / 2-way valve PD2 remains de-energized (position b), the entire displacement of the double-stroke piston DHK flows from the pre-stroke working chamber VH into the brake circuit BK, and the pressure in the brake circuit BK is then higher than when the 3 / 2-way valve PD2 is energized (position a). This switching combination "PD1 in position a and PD2 in position b" is therefore preferably used for low TTL values.

[0064] To build up pressure P aU f Due to the return stroke of the double-stroke piston DHK, the 3 / 2-way valve PD1 is de-energized (position b - Figure 5a), while the 3 / 2-way valve PD2 is energized (position a - Figure 5b). The return stroke volume of the double-stroke piston DHK then flows from the return stroke working chamber RH via the 3 / 2-way valve PD2 into the brake circuit BK. At the same time, volume is sucked in from the reservoir VB through the suction valve SaV of the pre-stroke working chamber VH and through the 3 / 2-way valve PD1.

[0065] To reduce pressure P ab The return stroke of the double-acting piston DHK energizes the 3 / 2-way valve PD1 (position a), while the 3 / 2-way valve PD2 can either be energized (position a) or remains de-energized (position b). If the 3 / 2-way valve PD2 is energized (position a), the return stroke volume of the double-acting piston DHK flows from the return stroke working chamber RH through the 3 / 2-way valve PD2, via the brake circuit BK and the 3 / 2-way valve PD1 into the pre-stroke working chamber VH, whereby only a smaller motor torque is required to adjust the double-acting piston DHK, in contrast to valve control, in which the 3 / 2-way valve PD2 remains de-energized (motor downsizing). This switching combination "PD1 and PD2 both in position a" is therefore preferably used for high pressures PBK in the brake circuit BK.If, however, the 3 / 2-way valve PD2 remains de-energized (position b), the entire return stroke volume of the pre-stroke working chamber VH of the double-stroke piston DHK flows from the brake circuit BK into the pre-stroke working chamber VH, and the pressure in the brake circuit BK is then lower than when the 3 / 2-way valve PD2 is energized (position a). Volume then flows from the return stroke working chamber RH into the reservoir VB via the 3 / 2-way valve PD2. This switching combination "PD1 in position a and PD2 in position b" is therefore preferably used for low pressures in the brake circuit PBK.

[0066] To reduce pressure Pab through the forward stroke of the double-acting piston DHK, the 3 / 2-way valve PD1 is de-energized (position b), while the 3 / 2-way valve PD2 is energized (position a). The return stroke volume of the return stroke working chamber RH of the double-acting piston DHK then flows from the brake circuit BK via the 3 / 2-way valve PD2 into the return stroke working chamber RH. At the same time, volume flows from the pre-stroke working chamber VH through the 3 / 2-way valve PD1 into the reservoir VB.

[0067] If both 3 / 2-way valves PD1 and PD2 are de-energized, no volume is pumped from the working chambers VH and RH of the double-acting piston DHK into or out of the brake circuit BK during the forward or return stroke. Therefore, as already mentioned, the stroke of the double-acting piston is called the idle stroke. The idle stroke can be used to position the double-acting piston DHK without pumping any volume into or out of the brake circuit BK. This is used in the event of a fault in the pressure supply device DV, e.g., a leak in the DHK piston seal.

[0068] Figure 6 shows the previously mentioned switching strategy of the 3 / 2-way valves PD1 and PD2 for the system diagram of Fig. 3 when changing from double-stroke piston pre-stroke to double-stroke piston return stroke during a pressure build-up P from Obar, with the time sequence of the pressure in the brake circuit PBK, the pressure PRH in the return stroke working chamber RH, the pressure PVH in the pre-stroke working chamber VH, the pressure in the wheel brake cylinder PRZI-RZ4, the piston stroke hk, the signals of the switching valves SV1-SV4, and the signals of the 3 / 2-way valves PD1 and PD2, where signal = 0 means that the valve is de-energized and signal = 1 that the valve is energized. Figure 6 also shows the switching strategy for the system diagram of Fig. 4, however, instead of the switching valves SV1 - SV4, only the isolating valve MV t The switching valves SVi - SN remain de-energized (open) throughout the entire process.

[0069] When using the isolation valve MV tInstead of the switching valves SVi - SV4, standard ABS inlet valves with check valve E i - EV4 can also be used as an option, whereby the timing shown in Figure 6 does not change.

[0070] At time t=0, the pre-stroke of the double-stroke piston DHK is hi<=0mm. If the 3 / 2-way valve PD1 is energized (signal = 1, position a, see Fig. 5), the 3 / 2-way valve PD2 is de-energized (signal = 0, position b, see Fig. 5a), and the switching valves SV1-SV4 (or isolating valve MV t ) de-energized (signal = 0), ie the switching valves SV1-SV4 (or the isolating valve MV t ) are open, the pressure in the pre-stroke working chamber VH PvH=0bar, the pressure in the return stroke working chamber RH P RH =0bar, the pressure in the brake circuit BK PßK=0bar, and the pressure in the wheel brake cylinders RZ1-RZ4 PRzi-RZ4=0bar.

[0071] From time t=0, the forward stroke of the double-stroke piston DHK begins with stroke hx, and thus the brake pressure build-up in the pre-stroke working chamber VH PVH, in the brake circuit BK PBK and in the wheel brake cylinders RZ1-RZ4, PRZI-RZ4, whereby the pressure in the return stroke working chamber RH PRH is adjusted to suction pressure when sucked from the reservoir VB, via the suction valve SaV and via the de-energized valve PD2, which connects the return stroke working chamber RH with the reservoir VB.

[0072] At time t=t1, the switching of the double-stroke piston movement from forward stroke to return stroke is initiated. The movement of the double-stroke piston DHK is initially stopped, i.e., the stroke of the double-stroke piston hk remains constant, whereby the pressure PVH in the pre-stroke working chamber VH, the pressure PBK in the brake circuit BK, and the pressure PRZI-RZ4 in the wheel brake cylinders remain constant. Also at time t=t1 or shortly thereafter or before, the switching valves SV1-SV4 and the isolating valve MV are tenergized, ie the valves SVi- SV4 or the isolating valve MV t are closed and thus disconnected from the pressure supply. Because no more volume is sucked in, the pressure in the return stroke working chamber RH rises to PRH = 0 bar. At time t = tz, the switching valves SV1-SV4 and the isolating valve MV t closed. Now the reversal of the movement of the double-stroke piston DHK begins with a slight return stroke hx. In the process, the pressure PVH in the pre-stroke working chamber VH and the pressure PBK in the brake circuit BK, or in the hydraulic line L4a (Fig. 4), decrease very quickly, because on the one hand the hydraulic system is closed by the closed switching valves SV1-SV4 and the energized 3 / 2-way isolating valve TV, which separates the connection between the single master brake cylinder SHZ and the brake circuit BK, or by the closed isolating valve MV t, is very stiff. Due to the return stroke hx of the double-stroke piston DHK, volume flows from the return stroke working chamber RH through the de-energized 3 / 2-way valve PD2 (position b, see Fig. 5a) to the reservoir VB, and the pressure in the return stroke working chamber RH rises to back pressure P RH =Zbar of the 3 / 2-way valve PD2.

[0073] At time t=ts, the pressure PBX=X bar, e.g. X bar=20 bar, is reached in the brake circuit BK or in the hydraulic line L4a (Fig. 4), at which pressure the magnetic force of the 3 / 2-way valve PD2 is sufficient to switch the valve, whereby the pressure PBX in the brake circuit BK or in the hydraulic line L4a (Fig. 4) is measured with the pressure sensor DG2 or estimated based on the motor current. The pressure must therefore be reduced to the pressure Pwelding(value), where Pwelding^Xbar, whereby in Fig. 6 it is assumed that Pwelding=Xbar, so that with an appropriate design of the 3 / 2-way valve PD1, PD2 with a large valve seat or large flow cross-sectional area the force of the valve spring is sufficient to switch the 3 / 2-way valve PDA, PD2. At time t=t3, the current supply to the 3 / 2-way valve PD1 is switched off so that it reaches position b (see Fig. 5b), and the connection between brake circuit BK and hydraulic line L4a (Fig.4) and pre-stroke working chamber VH is separated, and the connection between pre-stroke working chamber VH and reservoir VB is established via the 3 / 2-way valve PD1. The pressure PVH in the pre-stroke working chamber VH at time t=t3 drops to suction pressure due to the continued slight return stroke of the double-stroke piston DHK. At time t=ts the 3 / 2-way valve PD2 is also energized and switched to position a (see Fig. 5b), whereby the brake circuit BK, or the hydraulic line L4a (Fig. 4), is connected to the return stroke working chamber RH, the pressure PRH in the return stroke working chamber RH and the pressure PBX in the brake circuit BK, or in the hydraulic line L4a (Fig. 4), thereby equalize to a value Ybar, which lies between the back pressure PRH = Zbar in the return stroke working chamber RH and the pressure PBK = Xbar in the brake circuit BK, or in the hydraulic line L4a (Fig. 4), PRH = PBK = Ybar. Due to the continued slight return stroke hk of the double-stroke piston DHK, the pressure PBK in the brake circuit BK, orin the hydraulic line L4a (Fig. 4), due to the already mentioned high rigidity of the hydraulic system, increases very quickly again.

[0074] After the pressure in the brake circuit BK, or in the hydraulic line L4a (Fig. 4), PBK, has reached the pressure PRZI-RZ4 in the wheel cylinders at time t=t4, PBK = PRZI-RZ4, the current of the switching valves SV1-SV4 or the isolating valve MV t switched off. The return stroke hK of the double-stroke piston DHK continues at time t=t4, now according to the pressure increase specified, which is, for example, specified by the driver and measured with the pedal travel sensor Sp or derived from the measurement, whereby the pressures PBK, PRH, PRzi-RZ4 in the wheel brake cylinders, in the brake circuit BK, and in the return stroke working chamber RH follow the driver's command. The pressure PVH in the pre-stroke working chamber VH remains at the suction pressure level during suction from the reservoir VB.

[0075] As already mentioned, the high hydraulic stiffness of the system must be taken into account, so that even small changes in the stroke FIK of the double-acting piston result in a pressure change, as long as the switching valves SV1-SV4 or the isolating valve MV t are energized (closed) and the 3 / 2-way isolating valve TV is energized, thus breaking the connection between the master brake cylinder HZ and the brake circuit BK. The switching time of the pressure build-up, the pressure curve and the noise level can be optimized by overlapping the valve switching times with the corresponding piston stroke hK of the double-stroke piston DHK.

[0076] Fig. 6a shows the corresponding valve circuit for the switching times and controls described in Figure 6. The upper half of Fig. 6a, above the dashed line, shows, as an example, the circuit and volume flows of the 3 / 2-way valves PD1 and PD2 during pressure buildup from 0 bar by the forward stroke of the double-acting piston DHK. Alternatively, the 3 / 2-way valve PD2 can also be energized to reduce the motor torque required for pressure buildup. The lower half of Fig. 6a shows the circuit of the 3 / 2-way valves PD1 and PD2 during pressure buildup by the return stroke of the double-acting piston DHK.

[0077] Figure 6b shows the previously mentioned switching strategy of the 3 / 2-way valves PD1 and PD2 for the system diagram of Fig. 3 when changing from double-stroke piston pre-stroke to double-stroke piston return stroke during a pressure reduction, with the time sequence of the pressure PBK in the brake circuit, the pressure PRH in the return stroke working chamber RH, the pressure PVH in the pre-stroke working chamber VH, the pressure Pßzi-RZ4 in the wheel brake cylinder, the piston stroke hk, the signals of the switching valves SV1-SV4, and the signals of the 3 / 2-way valves PD1 and PD2, where signal = 0 means that the valve is de-energized and signal = 1 that the valve is energized. Figure 6b also shows the switching strategy for the system diagram of Fig. 4, although only the isolating valve MV t instead of the switching valves SVi - SV4, which remain open during the entire process. As already explained above, in this embodiment, using the valve MV tThe switching valves SVi - SV4 are replaced with standard ABS inlet valves with check valve EVi - EV4. The timing sequences shown and explained do not change.

[0078] At time t=0, a) the 3 / 2-way valve PD2 is energized (signal = 1, position a, see Fig. 5), b) the 3 / 2-way valve PD1 is de-energized (signal = 0, position b, see Fig. 5a), c) the switching valves SV1-SV4 or the isolating valve MV t de-energized (signal = 0), ie the switching valves SV1-SV4 (or the isolating valve MV t ) are open, where d) the pressure in the pre-stroke working chamber VH PvH=0bar, e) the pressure in the return stroke working chamber RH PRH=Pobar, f) the pressure in the brake circuit BK PßK=Pobar, and g) the pressure in the wheel brake cylinders RZ1-RZ4 PRzi-RZ4=Pobar.

[0079] From time t=0, the pre-stroke of the double-stroke piston DHK begins with stroke hx, and thus the brake pressure reduction in the return stroke working chamber RH PRH, in the brake circuit BK PBK and in the wheel brake cylinders RZ1-RZ4, PRZI-RZ4, whereby the pressure in the pre-stroke working chamber VH PVH adjusts to back pressure when conveyed into the reservoir VB via the de-energized valve PD1, which connects the pre-stroke working chamber VH with the reservoir VB.

[0080] At time t=ti, the switching of the double-stroke piston movement from forward stroke to return stroke is initiated. The movement of the double-stroke piston is stopped, i.e., the stroke of the double-stroke piston hk remains constant, whereby the pressure PRH in the return stroke working chamber RH, the pressure PBK in the brake circuit BK, and the pressure PRZI-RZ4 in the wheel brake cylinders remain constant, and the switching valves SV1-SV4 and the isolating valve MV t energized, ie the valves SV1-SV4 or the isolating valve MV tare closed. Because no more volume is pumped from the pre-stroke working chamber VH into the reservoir VB via the de-energized valve PD1, the pressure in the pre-stroke working chamber VH drops to PVH = 0 bar.

[0081] At time t=tz the switching valves SV1-SV4 are closed or the isolating valve MV t closed and the pressure PRZI-RZ4 in the wheel brake cylinders remains constant. Now the forward stroke hx of the double-stroke piston DHK is continued slightly. The pressure PRH in the return stroke working chamber RH and the pressure in the brake circuit PBK, or in the hydraulic line L4a (Fig. 4), decrease very quickly because the hydraulic system is supplied by the energized 3 / 2-way isolating valve TV, which separates the connection between the single master brake cylinder SHZ and the brake circuit BK, and by the closed switching valves SV1-SV4 and / or by the closed isolating valve MV t, is very stiff. Due to the pre-stroke hx of the double-stroke piston DHK, volume flows from the pre-stroke working chamber VH through the de-energized 3 / 2-way valve PD1 (position b, see Fig. 5a) to the reservoir VB, and the pressure in the pre-stroke working chamber VH rises to the back pressure PvH=Zbar of the 3 / 2-way valve PD1.

[0082] At time t=ts, the pressure of PßK=Xbar, e.g. Xbar=20bar, is reached in the brake circuit BK or in the hydraulic line L4a (Fig. 4), at which the magnetic force of the 3 / 2-way valve PD1 is sufficient to switch the valve, whereby the pressure PBK in the brake circuit BK or in the hydraulic line L4a (Fig. 4) is measured with the pressure sensor DG2 or estimated based on the motor current. At time t=ts, the power supply to the 3 / 2-way valve PD2 is switched off so that it reaches position b (see Fig. 5b), and the connection between brake circuit BK, or hydraulic line L4a (Fig. 4), and return stroke work chamber RH is severed, and the connection between return stroke work chamber RH and reservoir VB is established via the 3 / 2-way valve PD2, and the pressure PRH in the return stroke work chamber RH drops to suction pressure at time t=t3 due to the continued slight forward stroke of the double-stroke piston DHK. At time t=t3, the 3 / 2-way valve PD1 is energized and moves to position a (see Fig.5b) is switched, whereby the brake circuit BK, or the hydraulic line L4a (Fig. 4), is connected to the pre-stroke working chamber VH, the pressure in the pre-stroke working chamber VH PVH and the pressure in the brake circuit BK, or in the hydraulic line L4a (Fig. 4), PBK, thereby equalize to a value Ybar which lies between the dynamic pressure PVH = Zbar in the pre-stroke working chamber VH and the pressure PßK = Xbar in the brake circuit BK, or in the hydraulic line L4a (Fig. 4), PvH = PBK = Ybar. Due to the continued slight pre-stroke of the double-stroke piston DHK, the pressure in the pre-stroke working chamber, in the brake circuit BK, or in the hydraulic line L4a (Fig. 4), PBK, increases again very quickly due to the already mentioned high rigidity of the hydraulic system.

[0083] After the pressure in the brake circuit BK, or in the hydraulic line L4a (Fig. 4), PBK, has reached the pressure PRZI-RZ4 in the wheel cylinders at time t=t4, PBK = PRZI-RZ4, the flow of the valves SV1-SV4 (or the isolating valve MV t) is switched off. The return stroke movement of the double-stroke piston DHK hK is initiated at time t=t4, now according to the pressure reduction specification, which is specified, for example, by the driver, and is measured with the pedal travel sensor Sp or derived from the measurement, whereby the pressures in the wheel brake cylinders PRZI-RZ4, in the brake circuit BK PBK and in the pre-stroke working chamber VH PVH are reduced according to the driver's command. The pressure in the return stroke working chamber RH PVH rises to the back pressure level during pumping from the return stroke working chamber into the reservoir VB.

[0084] Figure 6c shows, for the system diagram of Fig. 4b, the previously mentioned switching strategy of the 3 / 2-way valves PD1 and PD2 when changing from a double-stroke piston pre-stroke to a double-stroke piston return stroke during a pressure build-up from Obar, with the temporal sequence of the pressure in the hydraulic line L4a Pi_4a, the pressure PRH in the return-stroke working chamber RH, the pressure PVH in the pre-stroke working chamber VH, the pressure in the wheel brake cylinder PRZI-RZ4, the piston stroke hk, the signal of the 3 / 2-way valve US, and the signals of the 3 / 2-way valves PD1 and PD2, where signal = 0 means that the valve is de-energized and signal = 1 that the valve is energized. Both the switching valves SVi - SV4 and the optional standard ABS inlet valves with check valve EVi - EV4 remain de-energized (open) throughout the entire process.

[0085] The 3 / 2-way valve US is designed as shown in Fig. 2a (de-energized) and Fig. 2b (energized). In the 3 / 2-way valve US, the hydraulic line L4 or the brake circuit BK is connected to the AN1 port, the hydraulic line L4a is connected to the AN3 port, and the reservoir VB is connected to the AN2 port. In the de-energized position, the 3 / 2-way valve US connects the hydraulic line L4a with the hydraulic line L4 or the brake circuit BK. In the energized position, the 3 / 2-way valve US connects the hydraulic line L4a with the reservoir VB.

[0086] As already mentioned, for short TTL times, e.g., TTL=150ms, the first hydraulic connection HV1 of the 3 / 2-way valve US (Fig. 2a) should have a large cross-sectional area. However, in the energized state (Fig. 2b), the pressure PBK in chamber K1 can be high, e.g., PßK=100bar, while the pressure Pi_4a in chamber K3 is low, e.g., Pi_4a=Ybar. To operate the 3 / 2-way valve US at this large pressure difference P BK-PL4a = 100-Ybar, and to open this large cross-sectional area of ​​the hydraulic connection HV1 when switching to the de-energized state, a large force of the spring VF would be necessary. To reduce this required force of the spring VF, a similar switching strategy is used to open the 3 / 2-way valve US as the switching strategy of the 3 / 2-way valves PD1 and PD2, by increasing the pressure Pi_4a in the chamber K3 so that the pressure difference PBK-PL43 Z . reaches the small value Xbar, PBK-Pi_4a = Xbar and the force of the spring is sufficient to switch the 3 / 2-way valve US to the de-energized state. For switching the 3 / 2-way valve US, values ​​of the differential pressure PBK-PL43 between Obar and Xbar can be selected. The pressure Xbar thus represents a lower threshold for which the valve spring must be designed, or the pressure must be reduced to at least this pressure so that the valve spring can reliably switch the valve. In Fig. 4c, for example,The 3 / 2-way valve US is only de-energized when the difference PBK-Pi_4a=0 bar, i.e., X=0, because the switching noise of the 3 / 2-way valve US is at its lowest at this point. The pressure Pi_4a in chamber K3 can be generated by the pressure supply DV through a volume flow through the second hydraulic connection HV2, which results in a back pressure.

[0087] The timing and valve signals of the 3 / 2-way valves PD1 and PD2 are similar to those shown in Fig. 6. The timing of the 3 / 2-way valve US is also similar to that of the 2 / 2-way valve MV t . The main exception is the piston stroke h K and the switching strategy of the 3 / 2-way valve US. Therefore, the focus here is primarily on the piston stroke sequence hK and the switching of the 3 / 2-way valve US.

[0088] At time t=ti, the switchover of the double-stroke piston movement from forward stroke to return stroke is initiated. The movement of the double-stroke piston DHK is stopped, i.e., the stroke hk of the double-stroke piston remains constant, whereby the pressure PVH in the pre-stroke working chamber VH, the pressure in the brake circuit BK PBK, and the pressure PRZI-RZ4 in the wheel brake cylinders remain constant.

[0089] At time t=ti, the 3 / 2-way valve US is also energized, ie the connection between the hydraulic lines L4a and L4 or brake circuit BK is interrupted, while the hydraulic line L4a is connected to the reservoir VB (see Figure 2b).

[0090] By connecting the hydraulic line L4a to the reservoir VB at time t=t1 via the 3 / 2-way valve US, the pressure PVH in the pre-stroke working chamber VH and the pressure in the hydraulic line L4a (Fig. 4a), Pi_4a, decrease very quickly. This is because the hydraulic system is very stiff, on the one hand due to the separate connection between the hydraulic line L4a and the hydraulic line L4, and on the other hand due to the energized 3 / 2-way isolating valve TV, which separates the connection between the single master brake cylinder SHZ and the brake circuit BK. The second hydraulic connection HV2 (see Fig. 2b) or a downstream throttle (not shown) can therefore be selected with a very small cross-sectional area. Because the piston no longer moves, the pressure in the return stroke working chamber RH drops to PRH=0 bar. To accelerate the pressure drop in the hydraulic line L4a, a slight DHK piston return stroke can be initiated to support this, but this is not considered below.

[0091] At time t=t3, the pressure in the hydraulic line L4a (Fig. 4a) reaches Pi4a=Xbar, e.g. Xbar=20bar, at which the magnetic force of the 3 / 2-way valve PD2 is sufficient to switch the valve, whereby the pressure in the hydraulic line L4a (Fig. 4a) Pi_4a is measured with the pressure sensor DG2 or estimated based on the motor current. At time t=t3, the current supply to the 3 / 2-way valve PD1 is switched off so that it reaches position b (see Fig. 5b), and the connection between hydraulic line L4a (Fig. 4a) and pre-stroke working chamber VH is separated, and the connection between pre-stroke working chamber VH via the 3 / 2-way valve PD1 with the reservoir VB is established, and the pressure in the pre-stroke working chamber VH PVH drops to Obar at time t=ts.

[0092] At the time t=ts, the 3 / 2-way valve PD2 is also energized and switched to position a (see Fig. 5b), whereby the hydraulic line L4a (Fig. 4a) is connected to the return stroke working chamber RH, the pressure in the return stroke working chamber RH PRH and the pressure in the hydraulic line L4a (Fig. 4a), Pi_4a, thereby equalize to a value Ybar which lies between the pressure PRH =0bar in the return stroke working chamber RH and the pressure Pi_4a=Xbar in the hydraulic line L4a (Fig. 4a), PRH = Pi_4a=Ybar. Due to the subsequent slight return stroke of the double-stroke piston DHK, the pressure supply DV delivers brake fluid via the 3 / 2-way valve US to the reservoir VB and the pressure in the hydraulic line L4a (Fig. 4a), Pi_4a, increases very quickly due to the back pressure via the second hydraulic connection HV2 of the 3 / 2-way valve US, due to the already mentioned high rigidity of the hydraulic system.Due to the slight return stroke of the double-stroke piston hx, the pressure in the pre-stroke working chamber VH PVH reaches the suction pressure level when sucking from the storage tank VB.

[0093] After the pressure Pi_4a in the hydraulic line L4a (Fig. 4a) has reached the pressure PRZI-RZ4 in the wheel cylinders at time t=t4, Pi_4a = PRZI-RZ4, the flow of the 3 / 2-way valve US is switched off and the force of the spring of the 3 / 2-way valve US is sufficient to switch the valve to the de-energized state at a pressure difference Pi_4a-PRzi-RZ4=0bar. The return stroke movement of the double-stroke piston DHK hx is continued at time t=t4, now according to the specified pressure increase, which is specified, for example, by the driver, and is measured with the pedal travel sensor Sp or derived from the measurement, whereby the pressures in the wheel brake cylinders PRZI-RZ4, in the brake circuit BK PBK and in the return stroke working chamber RH PRH follow the driver's command. The pressure in the pre-stroke working chamber VH PVH remains at the suction pressure level when sucking from the storage tank VB.

[0094] Figure 6d shows, for the system diagram of Fig. 4a, the previously mentioned switching strategy of the 3 / 2-way valves PD1 and PD2 when changing from a double-stroke piston pre-stroke to a double-stroke piston return stroke during a pressure reduction, with the time sequence of the pressure in the hydraulic line L4a Pi_4a, the pressure PRH in the return-stroke working chamber RH, the pressure PVH in the pre-stroke working chamber VH, the pressure in the wheel brake cylinder PRZI-RZ4, the piston stroke hk, the signal of the 3 / 2-way valve US, and the signals of the 3 / 2-way valves PD1 and PD2, where signal = 0 means that the valve is de-energized and signal = 1 that the valve is energized. Both the switching valves SVi - SV4 and the optional standard ABS inlet valves with check valve EVi - EV4 remain de-energized (open) throughout the entire process.

[0095] The timing and valve signals of the 3 / 2-way valves PD1 and PD2 are similar to those shown in Fig. 6b. The timing of the 3 / 2-way valve US is also similar to the timing of the 2 / 2-way valve MV. t The main exception is the sequence of the piston stroke hx and the switching strategy of the 3 / 2-way valve US. Therefore, the focus here is on the sequence of the piston stroke hx and the switching of the 3 / 2-way valve US.

[0096] With the energized 3 / 2-way valve PD2 (position a) and the de-energized 3 / 2-way valve PD1 (position b), pressure reduction initially occurs via the forward stroke of the double-stroke piston DHK. At time t=ti, the switchover of the double-stroke piston movement from forward stroke to return stroke is initiated. The movement of the double-stroke piston DHK is stopped, i.e., the stroke of the double-stroke piston hk remains constant, whereby the pressure PVH in the return stroke working chamber RH, the pressure PBK in the brake circuit BK, and the pressure PRZI-RZ4 in the wheel brake cylinders remain constant.

[0097] At time t=ti, the 3 / 2-way valve US is energized, ie the connection between the hydraulic lines L4a and L4 or brake circuit BK is interrupted, while the hydraulic line L4a is connected to the reservoir VB via the valve US (see Figure 2b).

[0098] By connecting the hydraulic line L4a to the reservoir VB at time t=tl via the 3 / 2-way valve US, the pressure PRH in the return stroke working chamber RH and the pressure Pi_4a in the hydraulic line L4a (Fig. 4a) decrease very quickly. This is because the hydraulic system is very rigid, on the one hand due to the separate connection between the hydraulic line L4a and the hydraulic line L4, and on the other hand due to the energized 3 / 2-way isolating valve TV, which separates the connection between the single master brake cylinder SHZ and the brake circuit BK. The second hydraulic connection HV2 (see Fig. 2b) or a downstream throttle (not shown) can therefore be selected with a very small cross-sectional area. Because the double-stroke piston DHK no longer moves, the pressure in the pre-stroke working chamber VH drops to PRH=0 bar. To accelerate the pressure drop in the hydraulic line L4a, a slight DHK piston pre-stroke can be initiated, which is not taken into account below.

[0099] At time t=ts, the pressure in the hydraulic line L4a (Fig. 4a) reaches Pi4a=Xbar, e.g. Xbar=20bar, at which the magnetic force of the 3 / 2-way valve PD1 is sufficient to switch the valve, whereby the pressure in the hydraulic line L4a (Fig. 4a) Pi_4a is measured with the pressure sensor DG2 or estimated based on the motor current.

[0100] At time t=ts, the current supply to the 3 / 2-way valve PD2 is switched off so that it reaches position b (see Fig. 5a), and the connection between hydraulic line L4a (Fig. 4a) and return stroke working chamber RH is separated, and the connection between return stroke working chamber RH via the 3 / 2-way valve PD2 with the reservoir VB is established, and the pressure in the return stroke working chamber RH PRH drops to Obar at time t=ts. At time t=t3, the 3 / 2-way valve PD1 is energized and switched to position a (see Fig. 5), whereby the hydraulic line L4a (Fig. 4a) is connected to the pre-stroke working chamber VH, the pressure in the pre-stroke working chamber VH PVH and the pressure in the hydraulic line L4a (Fig. 4a), Pi_4a, thereby equalize to a value of Ybar which lies between the pressure PVH =0bar in the pre-stroke working chamber VH and the pressure Pi_4a=Xbar in the hydraulic line L4a (Fig. 4a), PVH = Pi_4a= Ybar.Due to the subsequent slight forward stroke of the double-acting piston DHK, the pressure supply DV pumps brake fluid from the pre-stroke working chamber VH via the 3 / 2-way valve PD1 and the 3 / 2-way valve US to the reservoir VB. The pressure Pi_4a in the hydraulic line L4a (Fig. 4a) rises due to the back pressure via the second hydraulic connection HV2 of the 3 / 2-way valve US. This increase in pressure Pi_4a is very rapid due to the aforementioned high rigidity of the hydraulic system. Due to the slight forward stroke of the double-acting piston hx, the pressure in the return-stroke working chamber RH PRH reaches the suction pressure level when sucking from the reservoir VB.

[0101] After the pressure in the hydraulic line L4a (Fig. 4a), Pi4a, has reached the pressure PRZI-RZ4 in the wheel cylinders at time t=t4, Pi_4a = PRZI-RZ4, the flow to the 3 / 2-way valve US is shut off, and the force of the spring VF of the 3 / 2-way valve US is sufficient to switch the valve to the de-energized state at a pressure difference Pi_4a-PRzi-RZ4=0 bar. The connection between the hydraulic line L4a and the reservoir VB via the 3 / 2-way valve US is thus interrupted. The connection between the hydraulic lines L4a and L4 is then re-established via the 3 / 2-way valve US. The return stroke movement of the double-stroke piston DHK hx is initiated at time t=t4, according to the pressure reduction specification, which is specified, for example, by the driver, and is measured with the pedal travel sensor Sp or derived from the measurement, whereby the pressures in the wheel brake cylinders PRZI-RZ4, in the brake circuit BK PBX and in the return stroke working chamber RH PRH follow the driver's pressure reduction request.The pressure in the return stroke working chamber RH PRH remains at the back pressure level during pumping from the return stroke working chamber RH via the 3 / 2-way valve PD2 into the reservoir VB. This represents a key achievement: a 3 / 2-way valve with a large cross-section and low back pressure losses has been implemented without additional effort in both the PD1 and PD2, as well as the 3 / 2-way valve US.

[0102] iste:

[0103] 1 Pedal 2 Pedal travel sensor 3 Pedal tappet 4 Magnet armature 4a Stop element 5 Excitation winding 6 Magnet yoke 7, 7a Connecting bolt 9 Isolating valve 9 AN1, AN2, AN3 Valve connections AV Outlet valve of a standard ABS BK brake circuit

[0104] BK1, BK2 first and second brake circuit D3 third seal of the master cylinder DG pressure sensor DHK double-stroke piston Drl throttle DV pressure supply device ECU electronic control unit EV inlet valve of a standard ABS with check valve Fl, F2, F3 filter F PForce by hydraulic pressure H Stroke of the magnet armature HCU Hydraulic unit h K DHK-Hub HL1, HL2 Hydraulic lines HV1 First hydraulic connection HV2 Second hydraulic connection HZ Master brake cylinder Kl, K2, K3 Valve chamber LI, L2, L3, L4, L4a Hydraulic lines MV, PD1, PD2 3 / 2-way valves MV tIsolating valve for DV MVws 2 / 2-way valve Pab Pressure reduction Pauf Pressure build-up PBK Pressure in the brake circuit PHZ Pressure in the master brake cylinder SHZ or THZ Pl4a Pressure in the hydraulic line L4a PVH Pressure in the pre-stroke working chamber VH PRH Pressure in the return stroke working chamber RH PRZ1-RZ4 Pressure in the wheel brake cylinders RZ1-RZ4 R Return line RI, R2 Working chambers of the master brake cylinder RH Return stroke working chamber RK1-RK4 Wheel circuits 1 to 4 RV Check valve RZ1-RZ4 Wheel brake cylinders 1 to 4 SHZ / THZ Single or tandem master brake cylinder SiV Safety valve SiVßH Safety valve return stroke working chamber SiVvH Safety valve pre-stroke working chamber Sp Pedal travel sensor ST Tappet SV Switching valve, modified Standard ABS inlet valves EV without check valve RV

[0105] SV2k Switching valve with additional magnet SVx Switching valve T Target of brake fluid level TTL Time-To-Lock, time for pressure build-up from 0-100 bar TV 2 / 2-way isolating valve or 3 / 2-way isolating valve US 3 / 2-way changeover valve ÜV Overpressure valve VB Reservoir VF Valve spring VH Pre-stroke working chamber

[0106] VS1 first valve seat VS 2 second valve seat

[0107] VSK1, VSK2 valve closing body WS travel simulator

[0108] X Pressure in the brake circuit Y Pressure in the brake circuit Z Back pressure in the return stroke working chamber

Claims

Patent claims 1. Brake system with at least two hydraulic wheel brakes (Z1-4), each of which is assigned switching valves (SV1-4), an electric motor-driven pressure supply device (DV) which has a piston-cylinder system, the pistons (DHK) of which delimit two working chambers (VH, RH), wherein the first working chamber (VH) is connected to a brake circuit (BK2, BK) via a hydraulic connection (HL2), and that the second working chamber (RH) is connected to one or more brake circuits (BK2, BK) via a further hydraulic connection (HL1).the brake circuit (BK1, BK), wherein in at least one of the two hydraulic connections (HL1, HL2) a 3 / 2-way valve (PD1, PD2) is arranged, which serves to selectively establish a hydraulic connection of the working chamber (VH, RH) with a hydraulic connection (R) leading to a reservoir (VB) or with a brake circuit (BK1, BK2, BK), characterized in that either in the hydraulic connection (L4) connecting the switching valves (SV1-4) with the 3 / 2-way valve (PD1, PD2) a valve (US, MV. t ) is arranged, with which the hydraulic connection between the switching valves (SV1-4) and the at least one 3 / 2-way valve (PD1, PD2) can be interrupted and / or the switching valves (SV1-4) do not have any integrated or parallel-connected check valves.

2. Brake system according to claim 1, characterized in that the valve is either a 2 / 2-way shut-off valve (MV t) or a 3 / 2-way valve (US), whereby the 3 / 2-way valve (US) can be used to connect the pressure supply (DV) to the brake circuit BK or the reservoir (VB).

3. Brake system according to claim 1 or 2, characterized in that for selectively shutting off and opening a hydraulic line (R) which supplies at least one working chamber (VH, RH) of the pressure supply device (DV) with the reservoir (VB), a switching valve (SiVvH, SiV RH , SiV) and / or a suction valve (SaVl, SaV2) is arranged.

4. Brake system according to claim 3, characterized in that the suction valve (SaVl, SaV2) is arranged in series with the switching valve (SiVvH, SiVßH, SiV) arranged in the hydraulic line (R) for selectively shutting off and opening.

5. Brake system according to one of the preceding claims, characterized in that the brake system has a master brake cylinder (HZ, THZ, SHZ) which can be controlled or actuated via a brake pedal (1) and whose at least one working chamber (RI) can be connected by means of a 3 / 2-way valve (TV) optionally to a travel simulator (WS) or a brake circuit (BK, BK1, BK2).

6. Braking system according to one of the preceding claims, characterized in that the 3 / 2-way valve (PD1, PD2) is in a first switching position (Pos b) when it hydraulically connects the respective working chamber (VH, RH) to the reservoir (VB), and in that the 3 / 2-way valve (PD1, PD2) is in a second switching position (Pos a) when it hydraulically connects the respective working chamber (VH, RH) to the brake circuit (BK1, BK2, BK) or hydraulic line (L4, L4a), wherein in particular the first switching position (Pos b) is the position in which the valve is in the de-energized state.

7. Brake system according to one of the preceding claims, characterized in that by means of a drive (M) the double-stroke piston (DHK) of the piston-cylinder system of the pressure supply device (DV) is movable or adjustable in a forward stroke direction, in which the volume of the first working chamber (VH) is reduced, and in a return stroke direction, in which the volume of the other second working chamber (RH) is reduced.

8. Brake system according to one of the preceding claims, characterized in that the 3 / 2-way valve (PD1) is arranged in a hydraulic connection (HL2), with which the respective Working chamber (VH) can be connected to the brake circuit (BK2, BK) or hydraulic line L4a or L4 or the storage tank (VB), and that in the other hydraulic connection (HL1) either a 2 / 2-way valve for selectively opening and shutting off the hydraulic connection (HL1) or also a 3 / 2-way valve (PD2) is arranged, with which the respective working chamber (RH) can be selectively connected to the brake circuit (BK1, BK) or hydraulic line (L4a, L4) or the storage tank (VB).

9. Brake system according to one of the preceding claims, characterized in that the switching valves (SV1-4) are modified standard inlet valves of an ABS system, which do not have a check valve or are replaced by standard inlet valves (EV1-4) of an ABS system.

10. Braking system according to one of the preceding claims, characterized in that the 3 / 2-way directional control valve (US) has two valve actuators (VSK1, VSK2) and two valve seats (VS1, VS2) interacting therewith, the first valve actuator (VSK1) being displaceably mounted in a first valve chamber (K1) and the second valve actuator (VSK2) being displaceably mounted in a second valve chamber (K2), and in that a third valve chamber (K3) is located between the first and the second valve chamber (K1, K2), and in that a hydraulic connection to the brake circuit (BK, BK1, BK2) opens into the first valve chamber (K1), and in that the second chamber (K2) is hydraulically connected to the reservoir (VB) and the third valve chamber (K3) is hydraulically connected to a hydraulic connecting line (L4a) to the pressure supply device (DV).

11. Method for operating a brake system, in particular according to the preamble of claim 1 or in particular according to one of claims 1 to 10, wherein the brake system has at least two hydraulic wheel brakes (RZ1-4), each of which is assigned a switching valve (SV1-4), and an electric motor-driven pressure supply device (DV), which has a piston-cylinder system, the Double-stroke piston (DHK) delimits and separates two working chambers (VH, RH), wherein the first working chamber (VH) is connected to the brake circuit (BK2, BK) via a hydraulic connection (HL2) and the second working chamber (RH) is connected to the brake circuit (BK1, BK) via a hydraulic connection (HL1), wherein at least in one hydraulic connection (HL1, HL2) a 3 / 2-way valve (PD1, PD2) is arranged, with which the respective working chamber (VH, RH) can be hydraulically connected in a first switching position (Pos b) to the reservoir (VB) and in a second switching position (Pos a) to a brake circuit (BK1, BK2, BK), characterized in that before switching the 3 / 2-way valve (PD1, PD2) into its second switching position (Pos a), in which a hydraulic connection then exists between the one working chamber (VH, RH) of the pressure supply device (DV) and the hydraulic connection (L4a) leading to the switching valves (SVi=i-4),the hydraulic pressure acting at least on the valve to be switched (PD1, PD2) is lowered or reduced., 12. Method according to claim 11, characterized in that the pressure reduction is carried out by adjusting the piston (DKV) of the pressure supply device (DV) and / or by establishing a connection to a storage container (VB) or a pressure relief device.

13. Method according to claim 11 or 12, characterized in that the pressure is reduced to such an extent (t2 to ts), in particular below a predetermined threshold value (Pschweii), and that only thereafter (ts) the 3 / 2-way valve (PD1, PD2) is switched into its second switching position (Pos a) by means of its drive (4, 5, 6).

14. Method according to one of claims 11 to 13, characterized in that either - both switching valves (PD1, PD2) are 3 / 2-way valves, which are suitable for hydraulically connecting the respective working chamber (VH, RH) either with the brake circuit (BK1, BK2, BK) or with the reservoir (VB) or - only one of the two switching valves is a 3 / 2-way valve (PD1) and the other is a 2 / 2-way valve (PD2), whereby the 3 / 2-way valve (PD1) is suitable for hydraulically connecting the working chamber (VH) either to the brake circuit (BK2, BK) or to the reservoir (VB), and the 2 / 2-way valve (PD2) only serves to selectively shut off or open the hydraulic connection (HL1) between the working chamber (RH) and the brake circuit (BK1, BK).

15. Method according to one of claims 11 to 14, characterized in that before the pressure is reduced, the brake circuit (BK) and / or the wheel brake cylinders (RZ1-4) are hydraulically decoupled at least from the valve (PD1, PD2) to be switched by closing at least one valve (MVt, US, SV1-4, EV1-4), such that the pressure (PRZI-PRZ4) enclosed in the wheel brake cylinders (RZ1-4) or the pressure (PBK) enclosed in the brake circuit (BK) does not change during and due to the pressure reduction.

16. Method according to one of claims 11 to 15, characterized in that before the change between forward stroke and return stroke of the piston (DHK) of the pressure supply device (DV), the valves (PD1, PD2) initially remain in their switching positions (Pos a, Pos b), and in a first method step (ti to tz) a) either all switching valves (SVi=i-4) which have not yet been closed are closed, so that the wheel brake cylinders (RZ1-4) are separated from the pressure supply device (DV) and the valves (PD1, PD2), or b) a switching valve (MV t, US) is switched in such a way that the brake circuit (BK) or the wheel brake cylinders (RZ1-4) are separated from the pressure supply device (DV) and the valves (PD1, PD2), and that in a subsequent process step, which may also slightly overlap in time with the preceding process step, a pressure reduction takes place in the part (L4a) of the hydraulic connection (L4) which is still hydraulically connected to the valves (PD1, PD2), in particular to a predetermined threshold value (Pschweii), wherein this is done either by adjusting the double-stroke piston (DHK) (tz to ts) or by establishing a short-term (tz to ts) hydraulic connection between the reservoir (VB) and the hydraulic connection (L4a), in particular via the valve (US) or via the master brake cylinder (HZ, THZ, SHZ) and the isolating valve (TV), and that after reaching the required pressure reduction, the switching positions (Pos a, Pos b) of both valves (PD1, PD2), in particular simultaneously, are changed via corresponding control at (ts), and that thereafter or slightly overlapping in time (t4) the valves (US, MV t , SVi=i-4) are opened again, after which the pressure change continues via the valve (PD1, PD2) which is now in the second switching position (Pos a).

17. The method according to claim 16, characterized in that the valve (US) is a 3 / 2-way valve which, in its first switching position, connects the pressure supply device (DV) to the brake circuit (BK) and, in its second switching position, connects the pressure supply (DV) to the reservoir (VB).

18. Method according to one of claims 11 to 17, characterized in that a switching valve (SV1-4) does not have a parallel-connected check valve or is an ABS standard inlet valve (EV1-4) with a check valve.

19. Method according to one of claims 11 to 18, characterized in that the control and regulating unit (ECU) monitors the position of the piston (DHK) of the pressure supply device (DV), and in that the ECU calculates whether the still available piston travel or stroke (hx) in the current direction of movement of the piston is sufficient to achieve the pressure to be set in the wheel brake cylinders, and in that upon detection of a necessary reversal of direction and the resulting required switching from one valve (PD1, PD2) to the other, the switching process is initiated.

20. Method according to one of claims 11 to 19, characterized in that the 3 / 2-way valve (PD1, PD2) has two valve actuators (VSK1, VSK2) and two cooperating valve seats (VS1, VS2), wherein the first valve actuator (VSK1) is displaceably mounted in a first valve chamber (Kl) and the second valve actuator (VSK2) is displaceably mounted in a second valve chamber (K2), and that a third valve chamber (K3) is located between the first and the second valve chamber (Kl, K2), and that a hydraulic connection to the reservoir (VB) opens into the first valve chamber (Kl), and that the second chamber (K2) is hydraulically connected to a brake circuit (BK1, BK2, BK) and the third valve chamber (K3) is hydraulically connected to a working chamber (VH, RH) of the pressure supply device (DV).

21. Method according to claim 19, characterized in that a valve spring (VF) located in the second valve chamber (K2) applies force to the second valve actuator against the second valve seat (VS2), and in that the first valve actuator (VSK1) can be pressed against the first valve seat (VS1) or moved away from it by means of an electric and / or electromagnetic drive (4, 5, 6), wherein a spacer element (ST), in particular arranged, fastened or molded on the first valve actuator (VSK1), keeps the two valve actuators at a minimum distance such that when the first valve actuator (VSK1) rests against the first valve seat (VS1), the second valve actuator (VSK2) is held at a distance from the second valve seat (VS2).

22. Method according to claim 20 or 21, characterized in that the opening cross-sectional area (Al) between the first valve seat (VS1) and the first valve actuator (VSK1) spaced therefrom is smaller than the opening cross-sectional area (A2) between the second valve seat (VS2) and the second valve actuator (VSK2) spaced therefrom, the ratio of the areas A2 / A1 corresponding to at least 1.5 to 2.

23. Method according to claim 20, 21 or 22, characterized in that in order to reduce the required motor torque of the pressure supply device (DV), both 3 / 2-way valves (PD1, PD2) are opened while the double-stroke piston (DHK) of the pressure supply device (DV) is in the forward stroke movement, such that part of the The hydraulic medium pumped out of the pre-stroke working chamber (VH) passes into the return stroke working chamber (RH) via the valve (PD2) and thus a higher pressure can be achieved in the brake circuit with lower engine torque.

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