Pressure supply device for a vehicle's braking system and method for increasing brake fluid pressure in at least one section of a vehicle's braking system.

Abstract

Pressure supply device for a vehicle's braking system with: a pressure accumulator (10); a first valve assembly (12, 14, 60) hydraulically connected to the pressure accumulator (10), wherein the release of brake fluid from the pressure accumulator (10) can be controlled by means of the first valve assembly (12, 14, 60); and at least one pump (18) whose suction side is hydraulically connected or connectable to a brake fluid reservoir (20) belonging to or separate from the pressure supply device and whose delivery side is hydraulically connected to the pressure accumulator (10); characterized by a stepped piston (22) arranged in a stepped volume in a way that is adjustable, which with a first piston area (24) limits a first partial volume (26) of the stepped volume hydraulically connected to the at least one delivery side of the at least one pump (18), and which with a second piston area (28) smaller than the first piston area (24) limits a second partial volume (30) of the stepped volume hydraulically connected to the pressure accumulator (10), wherein the first partial volume (26) is additionally hydraulically connected to the first valve assembly (12, 14, 60) and / or to a second valve assembly (62) in such a way that a release of brake fluid from the first partial volume (26) can be controlled by means of at least a part of the first valve assembly (12, 14, 60) and / or the second valve assembly (62).

Description

[0001] The invention relates to a pressure supply device for a braking system of a vehicle. The invention also relates to a hydraulic unit for a braking system of a vehicle and a braking system for a vehicle. Furthermore, the invention relates to a method for increasing brake fluid pressure in at least one subregion of a braking system of a vehicle. State of the art

[0002] DE 10 2010 039 032 B4 describes a control device for an accumulator charging pump of a vehicle's braking system and a method for operating an accumulator charging pump of a vehicle's braking system. The respective accumulator charging pump is connected to a brake fluid reservoir with its intake side and to a pressure accumulator with its discharge side. Brake fluid can be drained from the pressure accumulator, filled by the respective accumulator charging pump, via at least one valve into a pre-chamber located upstream of a master brake cylinder. In this way, the pressure present in at least one pressure chamber of the master brake cylinder can be increased. Disclosure of the invention

[0003] The invention provides a pressure supply device for a braking system of a vehicle having the features of claim 1, a hydraulic unit for a braking system of a vehicle having the features of claim 8, a braking system for a vehicle having the features of claim 9 and a method for increasing a brake fluid pressure in at least one partial region of a braking system of a vehicle having the features of claim 10. Advantages of the invention

[0004] By means of the present invention, the emptying of the pressure accumulator for filling brake fluid from the pressure accumulator into at least one partial area of ​​the pressure build-up processes to be performed can be significantly reduced for many pressure build-up processes. For this purpose, for a large number of pressure build-up processes, the desired brake fluid displacement can be achieved simply by reducing the first partial volume. Therefore, when using the present invention, the conventional labor required to refill the pressure accumulator with its high pressure level is also significantly reduced. The brake fluid volume previously withdrawn from the first partial volume is instead refilled with a lower counterpressure.Since such refilling of the first partial volume requires less energy than filling the pressure accumulator, the present invention can significantly reduce the energy required to operate a braking system. The present invention thus contributes to minimizing energy consumption during a journey. This is particularly advantageous for electric vehicles due to their limited energy capacity.

[0005] As explained in more detail below, the use of the present invention also better protects many valves of the pressure buildup device / cooperating brake system. The present invention therefore also enables an increase in the service life of valves of the pressure buildup device / cooperating brake system.

[0006] The present invention provides an electro-hydraulic pressure supply that can be used, for example, for brake boosting. Compared to conventional pneumatic brake boosting and electromechanical brake boosting, the electro-hydraulic pressure supply according to the invention offers high energy density and greater flexibility. Furthermore, the pressure supply device according to the invention, or the hydraulic unit / brake system equipped therewith, is comparatively small and lightweight. Therefore, only a comparatively small installation volume is required for installing the pressure supply device or the hydraulic unit / brake system equipped therewith. Assembly of the pressure supply device or the hydraulic unit / brake system is therefore easy and can be carried out with comparatively little labor.

[0007] Preferably, the first partial volume is hydraulically connected to the at least one delivery side of the at least one pump via at least one first check valve. Alternatively or in addition, the first partial volume can be hydraulically connected to the first valve device and / or the second valve device via at least one second check valve. This allows relatively cost-effective and space-saving valve types to be used to suppress an undesired flow of brake fluid from the first partial volume to the at least one pump, or from the first valve device and / or the second valve device into the first partial volume.

[0008] For example, a first surface area of ​​the first piston surface can be larger than a second surface area of ​​the second piston surface by a factor of between 2 and 7. In particular, the first surface area of ​​the first piston surface can be larger than the second surface area of ​​the second piston surface by a factor of between 3.5 and 6.5, preferably by a factor of between 4 and 6. As explained in more detail below, such a surface ratio on the stepped piston can optimize the interaction between the stepped piston and the pressure accumulator.

[0009] Preferably, the pressure supply device comprises at least one sensor, by means of which information regarding a position of the stepped piston within the stepped volume can be determined. In this way, it is possible to reliably determine which brake fluid volume is currently available in the first partial volume to cause an increase in the brake fluid pressure in at least one partial area of ​​the brake system.

[0010] In an advantageous embodiment, the at least one sensor comprises at least one Hall sensor and / or at least one reed switch. As an alternative or in addition to this, the at least one sensor can also comprise at least one switch element, which is closed whenever the stepped piston is in at least one specific position within the stepped volume. Thus, cost-effective sensor types requiring little installation space can be used for the pressure supply device. In order to additionally determine information about the presence / consumption of a brake fluid volume in the first partial volume sufficient to cause an increase in the brake fluid pressure in the at least one partial area of ​​the brake system, either one sensor with multiple switching points or multiple sensors with different switching points can be used.

[0011] The advantages described above are also realized in a hydraulic unit for a braking system of a vehicle with such a pressure supply device.

[0012] A braking system for a vehicle with such a pressure supply device and / or a corresponding hydraulic unit also has the advantages described above.

[0013] Furthermore, implementing a corresponding method for increasing brake fluid pressure in at least one subregion of a vehicle's brake system also provides the advantages already listed above. It should be noted that the method can be further developed according to the above-described embodiments of the pressure supply device.

[0014] For example, a brake pressure can be increased as brake fluid pressure in at least one wheel brake cylinder, which is at least one sub-area of ​​the brake system. The method described here can therefore be used advantageously. Short description of the drawings

[0015] Further features and advantages of the present invention are explained below with reference to the figures. They show: Fig. 1a and Fig. 1b schematic partial and overall representations of a first embodiment of the pressure supply device; Fig. 2 is a schematic overall view of a second embodiment of the pressure supply device; and Fig. 3 a block diagram for explaining an embodiment of the method for increasing a brake fluid pressure in at least one subregion of a brake system of a vehicle. Embodiments of the invention

[0016] Fig. 1a and Fig. 1b show schematic partial and overall representations of a first embodiment of the pressure supply device.

[0017] The Fig. 1a schematically illustrated pressure supply device has a pressure accumulator 10. The pressure accumulator 10 can be, for example, a high-pressure accumulator 10. In particular, a storage pressure p H of at least 100 bar, especially of at least 140 bar, preferably of at least 160 bar, for a longer period of time. However, it should be noted that the pressure accumulator 10 does not refer to a specific accumulator type. Instead, a variety of different accumulator types can be used as the pressure accumulator 10 for the pressure supply device. Depending on the system requirements, other pressure ranges can also be maintained by the pressure accumulator 10.

[0018] The pressure supply device also includes a first valve device 12 and 14 hydraulically connected to the pressure accumulator 10. The first valve device 12 and 14 is designed and hydraulically connected to the pressure accumulator 10 in such a way that the draining of brake fluid from the pressure accumulator 10 can be controlled by means of the first valve device 12 and 14. As explained below using several examples, the first valve device 12 and 14 does not necessarily refer to a single valve.

[0019] Preferably, the pressure accumulator 10 is connectable / connectable via the first valve device 12 and 14 to at least one sub-region 16 of a brake system equipped with the pressure supply device such that brake fluid can be drained from the pressure accumulator 10 via the first valve device 12 and 14 into the at least one sub-region 16. By draining brake fluid from the pressure accumulator 10 via the first valve device 12 and 14 into the at least one sub-region 16, at least one brake fluid pressure in the at least one sub-region 16 can be increased. The at least one sub-region 16 can, for example, be at least one wheel brake cylinder of the brake system, so that by filling the at least one sub-region 16 with brake fluid, at least one brake pressure can be increased as brake fluid pressure.Alternatively or in addition, the at least one sub-area 16 can also be a pre-chamber located upstream of a master brake cylinder of the brake system, which is why a pressure chamber pressure present in at least one pressure chamber of the master brake cylinder can be increased by filling the respective sub-area 16 with brake fluid. It is expressly pointed out here that the usability of the pressure supply device is not limited to a specific configuration of the at least one sub-area 16.

[0020] The pressure supply device also comprises at least one pump 18, the intake side of which is / can be hydraulically connected to a brake fluid reservoir 20 and the delivery side of which is hydraulically connected to the pressure accumulator 10. The brake fluid reservoir 20 can, for example, be a brake fluid reservoir 20 belonging to the pressure supply device, to which the at least one intake side of the at least one pump 18 is connected. Likewise, however, the at least one pump 18 can also be connected to a brake fluid reservoir 20 that is external to the pressure supply device (i.e., formed as a separate component). Furthermore, it is pointed out that the design of the at least one pump 18 is not limited to a specific pump type. Fig. The design of the at least one pump 18 as the only pump 18 shown in Figure 1a is to be understood as an example only.

[0021] In addition, the pressure supply device comprises a stepped piston 22 which is adjustable in a stepped volume and which Fig. 1b is shown enlarged. With a first piston surface 24, the stepped piston 22 delimits a first partial volume 26 of the stepped volume, which is hydraulically connected to the at least one delivery side of the at least one pump 18. The stepped piston 22 also has a second piston surface 28, which is smaller than the first piston surface 24, i.e. a first surface area A1 of the first piston surface 24 is greater than a second surface area A2 of the second piston surface 28. The second piston surface 28 of the stepped piston 22 delimits a second partial volume 30 of the stepped volume, which is hydraulically connected to the pressure accumulator 10. In particular, the second partial volume 30 is hydraulically connected to the pressure accumulator 10 in such a way that, while a first pressure p1 present in the first partial volume 26 is not equal to the accumulator pressure p H in the pressure accumulator 10, a second pressure p2 present in the second partial volume 30 is equal to the accumulator pressure pH in the pressure accumulator 10.

[0022] The first partial volume 26 is additionally hydraulically connected to the first valve device 12 and 14 and / or to a second valve device such that a draining of brake fluid from the first partial volume 26 can be controlled by means of at least a portion of the first valve device 12 and 14 and / or the second valve device. This preferably means that a draining of brake fluid from the first partial volume 26 into the at least one partial region 16 can be controlled by means of at least the portion of the first valve device 12 and 14 and / or the second valve device.

[0023] The pressure supply device can always drain brake fluid from the first partial volume 26 into the at least one partial region 16 when a slow pressure increase and / or a pressure increase up to a target pressure below the first pressure p1 in the at least one partial region 16 is sufficient. Due to the fact that the pressure supply device is equipped with the stepped piston 22 arranged in the stepped volume, there is therefore no need to drain a corresponding volume of brake fluid from the pressure accumulator 10 into the at least one partial region 16, even for a slow pressure increase and / or a pressure increase up to a target pressure below the first pressure p1. This eliminates the need to drain brake fluid from the pressure accumulator 10 for many pressure increases in the at least one partial region 16.Accordingly, there is no need to refill the pressure accumulator 10 after each pressure increase in the at least one partial area 16. Furthermore, a pressure increase up to a target pressure initially above the first pressure p1 up to a switching pressure below the first pressure p1 can also be partially achieved by draining brake fluid from the first partial volume 26 into the at least one partial area 16. This also reduces the volume of brake fluid that must later be refilled into the pressure accumulator 10.

[0024] Pumping brake fluid into the pressure accumulator 10 by means of at least one pump 18 is counteracted by the accumulator pressure p H In contrast, the pumping of brake fluid into the first partial volume 26 by means of the at least one pump 18 is counteracted by the first pressure p1, for which the following applies: p1=p2∗A2A1=pH∗A2A1

[0025] Thus, significantly less energy is required to replace a (previously drained) amount of brake fluid in the first partial volume 26 than to replace the same amount of brake fluid in the pressure accumulator 10. In the pressure supply device of the Fig. 1a and Fig. 1b, the energy / work required to recharge the pressure accumulator 10 by means of the at least one pump 18 is therefore significantly reduced by the stepped piston 22. The pressure supply device of the Fig. 1a and Fig. 1b therefore has a reduced energy consumption compared to the prior art. In addition, during operation of the pressure supply device, the at least one pump 18 can usually be used gently (only for "recharging" the first partial volume 26). Furthermore, during operation of the pressure supply device, the first valve device 12 and 14 are generally also protected. When brake fluid is drained from the pressure accumulator 10 into the at least one partial area 16, the accumulator pressure p is present on an inflow side of the first valve device 12 and 14. Hwhile on the downstream side of the first valve device 12 or 14 the (usually) significantly lower pressure prevails in the at least one partial area 16. Due to the high pressure difference between the inflow side and the downstream side, brake fluid is pressed at high speed through the at least one valve opening of the first valve device 12 and 14. However, since in the pressure supply device of the Fig. 1a and Fig. 1b Since draining brake fluid from the pressure accumulator 10 is only necessary for strong and / or rapid pressure increases in the at least one partial area 16, the frequency of a high pressure difference occurring at the first valve device 12 or 14 is reduced compared to the prior art. By pre-filling the at least one partial area 16 by draining brake fluid from the first partial volume 26, the resulting pressure difference can additionally be reduced. The first valve devices 12 and 14 are therefore (mostly) protected during operation of the pressure supply device. In this way, the service life of the first valve devices 12 and 14 can be increased compared to the prior art. Costs and labor required to replace / repair the first valve devices 12 and 14 can thus be saved.

[0026] The stepped piston 22 can be compact. The additional design of the stepped piston 22 and the stepped volume on the pressure supply device therefore only slightly increases its installation space and weight.

[0027] The stepped volume can, for example, be a stepped bore. The stepped piston 22 is arranged to be freely movable within the stepped volume, with the first pressure p1 applied to the first piston surface 24 and the second pressure p2 applied to the second piston surface 28.

[0028] Preferably, the stepped piston 22 has a first seal 25 adjacent to its first piston surface 24 and / or a second seal 29 adjacent to its second piston surface 28 ( Fig. 1b). In particular, low-friction seal types can be used for the first seal 25 and / or the second seal 29. The first seal 25 and the second seal 29 can be, for example, sleeve seals, mechanical seals, and / or quad rings. Thus, low-friction seal types are available for the first seal 25 and / or the second seal 29. A space between the first seal 25 and the second seal 29 is preferably kept pressureless by means of a connection to the brake fluid reservoir 20. For example, a suction line 31 can extend from the space between the seals 25 and 29 to the brake fluid reservoir 20 or can be connected to a pump suction line (or valve / valve group line).

[0029] Preferably, the first partial volume 26 is hydraulically connected to the at least one delivery side of the at least one pump 18 via at least one first check valve 32. By means of a suitable orientation of the at least one first check valve 32, an undesired flow of brake fluid from the first partial volume 26 to the at least one delivery side of the at least one pump 18 can be reliably prevented. In addition, the first partial volume 26 can also be connected to the first valve device 12 and 14 and / or the second valve device via at least one second check valve 34. In this case, the at least one second check valve 34 is preferably aligned such that an undesired flow of brake fluid from the first valve device 12 and 14 and / or the second valve device into the first partial volume 26 is prevented by means of the at least one second check valve 34.Furthermore, the at least one discharge side of the at least one pump 18 can be connected to the pressure accumulator 10 via at least one third check valve 36. In this case, the at least one third check valve 36 decouples the at least one pump 18 from the accumulator pressure p present in the pressure accumulator 10. H such that after switching off at least one motor M of the at least one pump 18, an undesired backflow of brake fluid into / through the at least one pump 18 is reliably prevented by means of the orientation of the at least one third check valve 36.

[0030] Optionally, a bypass line 38 with a pressure relief valve 40 installed therein can run parallel to the at least one pump 18 (and the at least one third check valve 36 associated with it). In this case, the bypass line 38 and the pressure relief valve 40 protect the pressure supply device from damage caused by an imprecise shutdown of the at least one pump 18 or by temperature influences.

[0031] Furthermore, at least one pressure sensor 42 can be connected to the pressure accumulator 10. By means of the pressure sensor 42, the accumulator pressure p present in the pressure accumulator 10 can be measured. Hdetermined and used to control the at least one pump 18 and / or the pressure supply device. Optionally, the first pressure p1 in the first partial volume 26 can also be determined by means of a further pressure sensor and used to control the at least one pump 18 and / or the pressure supply device. Options for controlling the at least one pump 18 and / or the pressure supply device will be discussed below.

[0032] In the embodiment of the Fig. 1a, the first valve device 12 and 14 comprises an electrically switchable valve 12, which is designed as a directional valve with two switching positions (and two connections), and a pressure control valve 14, which is designed as a directional valve with three switching positions (and three connections). A line 44 extends from the pressure accumulator 10 to the electrically switchable valve 12, while the electrically switchable valve 12 is connected to the pressure control valve 14 via a line section 48. The pressure control valve 14 is also connected to the brake fluid reservoir 20 via a suction line 46, to which the at least one suction side of the at least one pump 18 and / or the bypass line 38 are preferably also connected. A further line 50 (with the at least one second check valve 34) opens into the line section 48, via which the first partial volume 26 is connected to the pressure control valve 14.A further line section 52 runs from the second partial volume 30 to the line 44 and thus connects the second partial volume 30 to the pressure accumulator 10. At least one line section 54 (with the at least one third check valve 36) also opens into the line 44, which connects the at least one discharge side of the at least one pump 18 to the pressure accumulator 10. At least one further line section 56 (with the at least one first check valve 32) runs from the at least one discharge side of the at least one pump 18 to the line 50.

[0033] The pressure supply device preferably has at least one sensor 58, by means of which information regarding a position of the stepped piston 22 within the stepped volume can be determined. The at least one sensor 58 can, for example, comprise at least one Hall sensor and / or at least one reed switch. Likewise, another type of contactless magnetic sensor can also be used for the at least one sensor 58. Furthermore, the at least one sensor 58 can have at least one (mechanical) switch element, which is closed whenever the stepped piston 22 is in at least one specific position within the stepped volume. Direct switch elements or switch elements actuated via intermediate elements can equally be used as the at least one sensor 58. Reliable monitoring of a piston stroke of the stepped piston 22 is ensured using all of the sensor types listed here.By means of the at least one sensor 58, it can thus be reliably determined whether the first partial volume 26 is sufficiently "charged", i.e., whether a sufficient quantity of brake fluid is available by means of the first partial volume 26 to increase the brake fluid pressure in the at least one partial region 16. Preferably, by means of the at least one sensor 58, it can be determined when the first partial volume 26 is sufficiently "discharged", i.e., no more brake fluid can currently be drawn from the first partial volume 26 to increase the brake fluid pressure in the at least one partial region 16. The at least one sensor 58 can be designed such that it can be checked (automatically) each time the vehicle is started.

[0034] Fig. 2 shows a schematic overall view of a second embodiment of the pressure supply device.

[0035] The Fig. The pressure supply device schematically illustrated in Figure 2 has, as the first valve device 60, an electrically switchable valve 60, which is designed as a directional valve with two switching positions (and two connections). A further electrically switchable valve 62, which is also a directional valve with two switching positions (and two connections), serves as the second valve device 62. The further electrically switchable valve 62 is inserted into the line 50 between the at least one second check valve 34 and its opening (in the line section 48). Preferably, the electrically switchable valves 60 and 62 are designed as continuously adjustable / continuously controllable valves. The valves 60 and 62, which can be designed as seat valves, improve the tightness of the embodiment of the Fig. 2. Furthermore, the pressure supply device of the Fig. 2 may also have an electrically switchable valve 64, via which brake fluid can be drained from the at least one partial area 16 into the brake fluid reservoir 20. For this purpose, a line 66 with the electrically switchable valve 64 can open into the bypass line 38 / suction line 46.

[0036] Otherwise, the pressure supply device of the Fig. 2 all features and advantages of the previously described embodiment. The pressure supply device of the Fig. 2 not only has improved energy efficiency, but also offers improved protection of the at least one pump 18 and the first valve device 60. With both pressure supply devices, an increased air gap of at least one wheel brake cylinder can also be closed by draining brake fluid from the first partial volume 26. Thus, the wheel brake cylinders interacting with the pressure supply device can also be efficiently designed with an increased air gap, which reduces / avoids residual braking torques (due to dragging pads). With an increased air gap, the additional fuel consumption of up to 7% that typically occurs in urban traffic due to residual braking torques can be saved. This also means a significant reduction in CO2 emissions from the vehicle equipped with an increased air gap.

[0037] In both pressure supply devices described above, the first surface area A1 of the first piston surface 24 is larger than the second surface area A2 of the second piston surface 28. Preferably, the first surface area A1 of the first piston surface 24 is larger than the second surface area A2 of the second piston surface 28 by a factor between 2 and 7, for example by a factor between 3.5 and 6, preferably by a factor between 4 and 5. Such an area ratio takes into account that a high factor increases the first pressure p1 relative to the accumulator pressure p Hreduced, and thus also reduces the energy / work required to "charge" the first partial volume 26. However, a high factor also reduces the switching pressure above which brake fluid must be drained from the pressure accumulator 10 to further increase the pressure in the at least one partial area 16. The higher the factor, the slower the brake fluid is shifted from the first partial volume 26 into the at least one partial area 16. These effects show that the optimal area ratio A1 / A2 is between 3 and 7, in particular between 4 and 6.

[0038] When determining the area ratio A1 / A2, the following braking profile can be used as a simplified basis: - Approximately 0.1% of emergency braking operations require a brake pressure of approximately 100 bar in at least one section 16 / wheel brake cylinder, 100% of which are emergency braking operations (emergency braking operations require the opening of valves 12 and 60 from the start of braking so that the accumulator pressure p H for the rapid build-up of brake pressure in which at least one section 16 / wheel brake cylinder is available.) - About 20% of heavy braking operations require a brake pressure of approximately 60 bar, of which about 10% are emergency braking operations. - About 60% of medium-strength braking operations require a brake pressure of approximately 40 bar, of which about 1% are emergency braking operations. - About 20% of light braking operations require a brake pressure of approximately 20 bar, of which about 0% are emergency braking operations.

[0039] With such a braking profile, an area ratio A1 / A2 of 4, and a switching pressure of approximately half the maximum first pressure p1, an energy saving of approximately 60% can be derived for each of the pressure supply devices. (The exact values ​​depend on the design and degree of wear of at least one pump 18.)

[0040] The above-described embodiments of the pressure supply device can all be implemented in a hydraulic unit for a vehicle's braking system. A braking system for a vehicle with such a pressure supply device also provides the advantages described above. It should be noted that the applicability of each of the above-described embodiments is neither limited to a specific braking system type nor to a particular vehicle type.

[0041] Each of the pressure supply devices can be designed as a compact component / device. Likewise, each pressure supply device can also be understood as a pressure supply system consisting of several components designed as separate components that are connected to one another only via lines / line sections.

[0042] Each of the pressure supply devices can also be used as a brake booster with a corresponding design of the brake control valve 14 or with corresponding control of the valves 60 and 64. In particular, such a pressure supply device eliminates the need for a vacuum brake booster. In contrast to a conventional vacuum brake booster, the respective pressure supply device does not require a vacuum source, has a higher energy density, can be manufactured in a smaller size, and is lighter.

[0043] It should also be noted that the individual components of each pressure supply device can also be used for other braking functions, such as ABS control, traction control, and / or vehicle dynamics control. Practically all functions of a modern vehicle control system can be integrated, in particular, into a hydraulic unit equipped with the respective pressure supply device.

[0044] Each of the pressure supply devices described above can in particular comprise a control device by means of which it can be controlled to carry out the method steps described below.

[0045] Fig. 3 shows a block diagram for explaining an embodiment of the method for increasing a brake fluid pressure in at least one subregion of a brake system of a vehicle.

[0046] The method described below can be implemented, for example, using one of the pressure supply devices explained above. However, it should be noted that the implementation of the method is not limited to these pressure supply devices.

[0047] In a method step S1, at least one pump is operated such that brake fluid is pumped from a brake fluid reservoir hydraulically connected to at least one intake side of the at least one pump into at least one pressure accumulator hydraulically connected to at least one discharge side of the at least one pump. In this way, a "recharging" of the pressure accumulator for later execution of a method step S2 can be ensured. In method step S2, by at least partially opening at least one first valve device hydraulically connected to the pressure accumulator, brake fluid is drained from the pressure accumulator via the first valve device into the at least one partial area.

[0048] However, the method also includes method steps S1a and S2a: Therefore, during operation of the at least one pump, additional brake fluid is pumped into a first partial volume of a stepped volume, which is hydraulically connected to the at least one intake side of the at least one pump and is delimited by a first piston surface of a stepped piston adjustably arranged in the stepped volume (method step S1a). Pumping brake fluid into the first partial volume causes an enlargement of the first partial volume by correspondingly adjusting the stepped piston within the stepped volume, wherein a second partial volume of the stepped volume, which is delimited by a second piston surface of the stepped piston smaller than the first piston surface and hydraulically connected to the pressure accumulator, is reduced.

[0049] In method step S2a, brake fluid can therefore be drained from the first partial volume into the at least one partial area via at least the part of the first valve device and / or the second valve device by at least partially opening at least a part of the first valve device and / or a second valve device.

[0050] A slow increase in the brake fluid pressure in the at least one sub-area or an (initial) increase in the brake fluid pressure in the at least one sub-area up to a target pressure / switching pressure below a first pressure p1 present in the first sub-volume can therefore be carried out by means of method step S2a. Method step S2 is only to be carried out for a rapid increase in the brake fluid pressure in the at least one sub-area and / or an (additional) increase in the brake fluid pressure in the at least one sub-area up to a target pressure above the switching pressure, which is to be set below the first pressure p1 present in the first sub-volume. Thus, the method described here also provides the advantages listed above.

[0051] For example, a brake pressure can be increased as brake fluid pressure in at least one wheel brake cylinder, which forms at least one sub-area of ​​the brake system. Alternatively or in addition, a pre-chamber pressure in a pre-chamber located upstream of a master brake cylinder of the brake system (e.g., a hydraulic brake booster device) can also be increased as brake fluid pressure. In both cases, the brake fluid pressure can be increased to at least 80 bar, preferably up to 150 bar, in particular up to 180 bar.

[0052] The process steps S1 and S1a can be started as soon as a storage pressure p Hin the pressure accumulator falls below a minimum pressure threshold (e.g. 140 bar). If the first partial volume does not have its maximum brake fluid volume when the at least one pump is switched on, the at least one pump delivers into the first partial volume until the stepped piston reaches the stop and the second partial volume is at its minimum. This process is not / hardly affected by a simultaneous flow of brake fluid from the at least one pump and / or from the first partial volume to the at least one partial area. Only when the first partial volume has its maximum volume does the pump delivery pressure increase to the accumulator pressure p prevailing in the pressure accumulator. H and increases the storage pressure p H. At each start of driving and / or each start of braking, at least one pump can be activated to execute process steps S1 and S1a. Furthermore, process steps S1 and S1a can be terminated when the accumulator pressure p H in the pressure accumulator exceeds a maximum pressure threshold (e.g., at 160 bar). As an alternative or in addition to a pressure sensor connected to the pressure accumulator, a sensor signal from a pressure sensor connected to the first partial volume can also be evaluated accordingly. Furthermore, activation of the at least one pump can also be dependent on a current position of the stepped piston within the stepped volume. In this case, the at least one pump starts as soon as the volume of the first partial volume is partially discharged. Preferably, the at least one pump is also operated in this case until the volume of the first partial volume is maximum and a storage pressure pH above the maximum pressure threshold.

[0053] In an optional method step S3, a decision can be made as to whether only method step S2a, only method step S2, or first method step S2a and then method step S2 is to be carried out to increase the brake fluid pressure in the at least one partial area. For example, as soon as a pedal travel sensor indicates rapid actuation of a brake actuating element (brake pedal) by a driver and / or when braking control (ABS, ASR, ESP) is initiated, only method step S2 can be carried out or the system can immediately switch from method step S2a to method step S2. Also in certain driving conditions / traffic situations, such as upon detection of a high risk of overturning (based on a signal from at least one environmental detection sensor) and / or in the presence of a fault in the braking system / vehicle (e.g.damage to a wheel brake), only method step S2 can be carried out or an immediate switch can be made from method step S2a to method step S2. Accordingly, if the target pressure requested by the driver or a cruise control system is above the first pressure p1, only method step S2 can be carried out or, after a switchover pressure has been reached, a switch can be made from method step S2a to method step S2. In all of the cases listed here, a sufficiently high brake fluid pressure and / or a rapid pressure build-up in at least one partial area is achieved by draining brake fluid from the pressure accumulator.However, if a braking instruction from the driver or the cruise control system indicates that only a slow increase in the brake fluid pressure in the at least one partial area and / or an increase in the brake fluid pressure in the at least one partial area up to a target pressure below the first pressure p1 is required, then preferably only method step S2a is carried out.

Claims

[1] Pressure supply device for a braking system of a vehicle comprising: a pressure accumulator (10); a first valve device (12, 14, 60) hydraulically connected to the pressure accumulator (10), wherein a draining of brake fluid from the pressure accumulator (10) can be controlled by means of the first valve device (12, 14, 60); and at least one pump (18), the intake side of which is or can be hydraulically connected to a brake fluid reservoir (20) which is part of the pressure supply device or is external to the pressure supply device, and the delivery side of which is hydraulically connected to the pressure accumulator (10); characterized by a stepped piston (22) which is adjustably arranged in a stepped volume and which, with a first piston surface (24), delimits a first partial volume (26) of the stepped volume, which is hydraulically connected to the at least one delivery side of the at least one pump (18), and which, with a second piston surface (28) smaller than the first piston surface (24), delimits a second partial volume (30) of the stepped volume, which is hydraulically connected to the pressure accumulator (10), wherein the first partial volume (26) is additionally hydraulically connected to the first valve device (12, 14, 60) and / or to a second valve device (62) in such a way that a draining of brake fluid from the first partial volume (26) can be controlled by means of at least a part of the first valve device (12, 14, 60) and / or the second valve device (62). [2] Pressure supply device according to claim 1, wherein the first partial volume (26) is hydraulically connected to the at least one delivery side of the at least one pump (18) via at least one first check valve (32) and / or the first partial volume (26) is hydraulically connected to the first valve device (12, 14, 60) and / or the second valve device (62) via at least one second check valve (34). [3] Pressure supply device according to claim 1 or 2, wherein a first surface area (A1) of the first piston surface (24) is larger by a factor between 2 and 7 than a second surface area (A2) of the second piston surface (28). [4] Pressure supply device according to one of the preceding claims, wherein the pressure supply device comprises at least one sensor (58) by means of which information regarding a position of the stepped piston (22) within the stepped volume can be determined. [5] Pressure supply device according to claim 4, wherein the at least one sensor (58) comprises at least one Hall sensor and / or at least one reed switch. [6] Pressure supply device according to claim 4 or 5, wherein the at least one sensor (58) comprises at least one switch element which is closed when the stepped piston (22) is in at least one specific position within the stepped volume. [7] Pressure supply device according to one of claims 4 to 6, wherein it can be determined by means of the at least one sensor (58) when brake fluid can currently no longer be removed from the first partial volume (26) for increasing a brake fluid pressure in at least one partial region (16) of the brake system. [8] Hydraulic unit for a braking system of a vehicle with a pressure supply device according to one of the preceding claims. [9] Braking system for a vehicle with a pressure supply device according to one of claims 1 to 7 and / or a hydraulic unit according to claim 8. [10] Method for increasing a brake fluid pressure in at least one partial area (16) of a braking system of a vehicle, comprising the steps: Operating at least one pump (18) in such a way that brake fluid is pumped (S1) from a brake fluid reservoir (20) hydraulically connected to at least one intake side of the at least one pump (18) into at least one pressure accumulator (10) hydraulically connected to at least one discharge side of the at least one pump (18); and At least partially opening at least one first valve device (12, 14, 60) hydraulically connected to the pressure accumulator (10), whereby brake fluid is drained from the pressure accumulator (10) via the first valve device (12, 14, 60) into the at least one partial region (16) (S2); characterized bythe steps that During operation of the at least one pump (18), additional brake fluid is pumped into a first partial volume (26) of a stepped volume, which is hydraulically connected to the at least one intake side of the at least one pump (18), and which is delimited by a first piston surface (24) of a stepped piston (22) adjustably arranged in the stepped volume, whereby a second partial volume (30) of the stepped volume, which is delimited by a second piston surface (28) of the stepped piston (22) smaller than the first piston surface (24) and hydraulically connected to the pressure accumulator (10), is reduced (S1a); and by at least partially opening at least a part of the first valve device (12, 14, 60) and / or a second valve device (62), brake fluid is drained from the first partial volume (26) via at least the part of the first valve device (12, 14, 60) and / or the second valve device (62) into the at least one partial region (16) (S2a). [11] Method according to claim 10, wherein a brake pressure is increased as brake fluid pressure in at least one wheel brake cylinder as the at least one partial region (16) of the brake system.

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