Pressure supply device for a hydraulic braking system, and hydraulic braking system for a vehicle

Abstract

Pressure supply device (10) for a hydraulic braking system of a vehicle with: a first pressure chamber (12a) and a second pressure chamber (12b), wherein the first pressure chamber (12a) is bounded by at least a first surface (16a) and the second pressure chamber (12b) by at least a second surface (16b) of at least one piston (18) of the pressure supply device (10); a motor (20); and a transmission via which the at least one piston (18) is connected to the motor (20) in such a way that the at least one piston (18) can be adjusted at least in a first direction (22) by means of operation of the motor (20); wherein the pressure supply device (10) comprises a reservoir shut-off valve (26, 50) hydraulically connected to the first pressure chamber (12a), which can be connected to a brake fluid reservoir (24) of the brake system and which is mechanically designed or electrically switchable in such a way that an exceedance of a predetermined maximum pressure difference between a chamber pressure present in the first pressure chamber (12a) and a reservoir pressure present in the brake fluid reservoir (24) can be prevented by opening the reservoir shut-off valve (26, 50), and wherein a first brake circuit (28a) with at least one first wheel brake cylinder is connected to the first pressure chamber (12a) and a second brake circuit (28b) with at least one second wheel brake cylinder is connected to the second pressure chamber (12b) in such a way that by adjusting the at least one piston (18) in the first direction (22) an increase in brake pressure can be effected in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder, characterized by a circuit isolation valve (32) via which the first brake circuit (28a) is connected to the second brake circuit (28b).

Description

[0001] The invention relates to a pressure supply device for a hydraulic braking system of a vehicle. The invention also relates to a hydraulic braking system for a vehicle. State of the art

[0002] German patent application DE 10 2013 205 627 A1 describes braking systems for a vehicle. All described braking systems include an externally applied braking device, which is exemplified as a plunger. The at least one pressure chamber of the externally applied braking device can be connected to a first brake circuit and a second brake circuit of the braking system via a separating valve. By operating the externally applied braking device, the brake pressure in at least one wheel brake cylinder of the first brake circuit and the second brake circuit can be increased.

[0003] Furthermore, DE 10 2011 077 693 A1 discloses a braking system for a vehicle with a master brake cylinder having two pressure chambers. A fluid storage device is connected to one of the two pressure chambers via a continuously adjustable / regulated / controllable valve such that brake fluid from the respective pressure chamber can be transferred into the fluid storage device via the at least partially open valve. Disclosure of the invention

[0004] The invention provides a pressure supply device for a hydraulic brake system of a vehicle with the features of claim 1 and a hydraulic brake system for a vehicle with the features of claim 5. Advantages of the invention

[0005] The present invention provides a means for generating externally applied brake pressure in at least one wheel brake cylinder, whereby a comparatively large volume of brake fluid can be transferred from the pressure supply device to the at least one wheel brake cylinder in a short time. This ensures advantageously high dynamics during the required phases of brake pressure generation in the at least one wheel brake cylinder. At the same time, the present invention enables the use of a comparatively inexpensive motor for generating externally applied brake pressure in the at least one wheel brake cylinder.

[0006] This can also be described as the present invention resolving a conventional conflict between the volume of brake fluid required to generate the external braking pressure in the at least one wheel brake cylinder and the resulting pressure in the brake system with regard to engine power. Specifically, this allows the use of a compact, lightweight, and cost-effective engine for generating the external braking pressure in the at least one wheel brake cylinder without compromising the braking performance of the vehicle.

[0007] Furthermore, a first brake circuit with at least one first wheel brake cylinder on the first pressure chamber and a second brake circuit with at least one second wheel brake cylinder on the second pressure chamber can be connected in such a way that, by adjusting the at least one piston in the first direction, an increase in brake pressure can be achieved in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder. The pressure supply device can thus be used to effect an externally applied brake pressure build-up in both the at least one first wheel brake cylinder of the first brake circuit and the at least one second wheel brake cylinder of the second brake circuit.

[0008] Advantageously, during the increase in brake pressure in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder, the engine torque to be applied by the engine increases with a first slope when the pressure difference between the chamber pressure and the reservoir pressure is below the specified maximum pressure difference, and, from a pressure difference between the chamber pressure and the reservoir pressure equal to the specified maximum pressure difference, increases with a second slope that is at most smaller than the first slope.Alternatively or additionally, during the brake pressure increase, a first volume flow from the pressure supply device can be transferred into the two brake circuits in at least one first wheel brake cylinder and at least one second wheel brake cylinder when the pressure difference between the chamber pressure and the reservoir pressure is below the specified maximum pressure difference. Once the specified maximum pressure difference between the chamber pressure and the reservoir pressure is reached, a second volume flow from the pressure supply device can be transferred into the two brake circuits, with the first volume flow being greater than the second. The requirements for the motor of the pressure supply device are therefore comparatively low. This allows the use of a motor with a small installation space requirement, light weight, and comparatively low manufacturing costs for the pressure supply device.The gearbox that interacts with the engine can also be designed cost-effectively due to the comparatively low requirements that need to be met.

[0009] For example, the pressure supply device may have only a single piston, designed as a stepped piston, instead of the at least one piston. However, the design possibilities of the pressure supply device are not limited to this example.

[0010] The advantages described above are also guaranteed with a corresponding hydraulic braking system for a vehicle.

[0011] In the hydraulic brake system, a first brake circuit with at least one wheel brake cylinder connected to the first pressure chamber and a second brake circuit with at least one wheel brake cylinder connected to the second pressure chamber are connected in such a way that, by moving the at least one piston in the first direction, an increase in brake pressure can be achieved in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder. Thus, power-assisted braking or brake force boosting can also be performed with the hydraulic brake system. Furthermore, the hydraulic brake system includes a circuit isolator valve through which the first brake circuit is connected to the second brake circuit. Therefore, opening the circuit isolator valve allows pressure equality to be achieved in the first and second brake circuits.Specifically, opening the circuit isolating valve after closing it ensures that the brake pressure present in at least one of the first wheel brake cylinders of the first brake circuit can still be increased via brake fluid transfer from the second pressure chamber through the second brake circuit into the first brake circuit. Furthermore, closing the circuit isolating valve at a predetermined minimum pressure improves the pressure build-up dynamics in both the first and second brake circuits.

[0012] In a further advantageous embodiment, the hydraulic brake system comprises a hydraulically connected isolation valve to the first pressure chamber, through which the first brake circuit is connected to the first pressure chamber. Closing the isolation valve prevents an undesired pressure drop in the first brake circuit, even if the reservoir isolation valve opens.

[0013] For example, the reservoir shut-off valve can be a pressure-switched valve that can be controlled by the pressure difference between the chamber pressure in the first pressure chamber and the reservoir pressure in the brake fluid reservoir. Therefore, controlling the reservoir shut-off valve with an electrical signal is not necessary for its desired operation. This also eliminates the need to equip a control system interacting with the hydraulic brake system with an additional signal output to provide the electrical signal for the reservoir shut-off valve.

[0014] However, the reservoir shut-off valve can also be an electrically switchable valve, which can be switched by means of at least one control signal from a control device. Optionally, the hydraulic brake system can include the control device, which is preferably designed to detect whether the pressure difference between the chamber pressure present in the first pressure chamber and the reservoir pressure present in the brake fluid reservoir reaches or exceeds the predetermined maximum pressure difference, and, if applicable, to switch the reservoir shut-off valve to an at least partially open state by means of the at least one control signal.The use of an electrically switchable valve allows, in particular, the setting / resetting of the maximum pressure differential or the threshold value, taking into account at least one physical parameter, such as the temperature and / or viscosity of the brake fluid in the hydraulic brake system. Thus, the operation of the reservoir shut-off valve can be adapted to ambient conditions in such a way that, especially at low temperatures and / or with high brake fluid viscosity, the motor of the pressure supply device is operated gently. Brief description of the drawings

[0015] Further features and advantages of the present invention are explained below with reference to the figures.

[0016] They show: Fig. 1a to 1c a schematic partial representation of a first embodiment of the hydraulic brake system and coordinate systems to explain its operation; Fig. 2 a schematic partial representation of a second embodiment of the hydraulic braking system; and Fig. 3 a flowchart to explain a method for operating a hydraulic braking system of a vehicle, which is not part of the present invention. Embodiments of the invention

[0017] Fig. Figures 1a to 1c show a schematic partial representation of a first embodiment of the hydraulic brake system and coordinate systems to explain its operation.

[0018] The in Fig. Figure 1a, a partially schematic representation of a hydraulic braking system, is applicable in a vehicle / motor vehicle. For example, the hydraulic braking system can be used in an electric or hybrid vehicle. It should be noted that the applicability of the hydraulic braking system is not limited to a specific vehicle type.

[0019] The hydraulic brake system comprises a pressure supply device 10 with a first pressure chamber 12a and a second pressure chamber 12b. (The pressure supply device 10 can be described, in particular, as a plunger.) Preferably, the first pressure chamber 12a and the second pressure chamber 12b are formed in a common housing 14 of the pressure supply device 10. The first pressure chamber 12a is bounded by at least one first surface 16a of at least one piston 18 of the pressure supply device 10. Similarly, the second pressure chamber 12b is also bounded by at least one second surface 16b of the at least one piston 18 of the pressure supply device 10.The at least one piston 18 is connected to a motor 20 of the pressure supply device 10 via a (not shown) transmission such that the at least one piston 18 can be adjusted in at least a first direction 22 (preferably also in a second direction opposite to the first direction 22) by operating the motor 20. As explained in more detail below, adjusting the at least one piston 18 in the first direction 22 preferably means adjusting the at least one piston 18 into the first pressure chamber 12a and into the second pressure chamber 12b. This can also be described as reducing the volume of the first pressure chamber 12a and the second pressure chamber 12b, both of which can be filled with brake fluid, by adjusting the at least one piston 18 of the pressure supply device 10 in the first direction 22.The first direction 22 can therefore also be described as a braking direction.

[0020] The hydraulic brake system also includes a brake fluid reservoir 24. Furthermore, the hydraulic brake system has a reservoir shut-off valve 26, through which the first pressure chamber 12a of the pressure supply device 10 is connected to the brake fluid reservoir 24. The reservoir shut-off valve 26 is mechanically designed or electrically switchable such that an exceedance of a predetermined maximum pressure differential between the first chamber pressure in the first pressure chamber 12a and the reservoir pressure in the brake fluid reservoir 24 can be prevented by opening the reservoir shut-off valve 26. Opening the reservoir shut-off valve 26 includes, for example, the (automatic) opening of the reservoir shut-off valve 26 due to its mechanical design.Likewise, the electrical switching capability of the reservoir shut-off valve 26 can also be interpreted as meaning that a (not shown) control device is designed to switch the reservoir shut-off valve 26 in such a way that, before / when the specified maximum pressure difference between the first chamber pressure present in the first pressure chamber 12a and the reservoir pressure present in the brake fluid reservoir 24 is exceeded, the reservoir shut-off valve 26 can be controlled by the control device to an at least partially open state.

[0021] The reservoir pressure can be understood to be atmospheric pressure. Preferably, the reservoir shut-off valve 26 is operable such that, at the beginning of a pressure build-up in the first pressure chamber 12a, the reservoir shut-off valve 26 is closed. Preferably, the reservoir shut-off valve 26 is also mechanically designed or electrically switchable such that, as long as the pressure difference between the first chamber pressure (present in the first pressure chamber 12a) and the reservoir pressure (present in the brake fluid reservoir 24) remains smaller than the predetermined maximum pressure difference during the adjustment of the first surface 16a in the first direction 22 / braking direction, the reservoir shut-off valve 26 is / remains in its closed state.As soon as the pressure difference (between the first chamber pressure and the reservoir pressure) equals the specified maximum pressure difference, the reservoir shut-off valve 26 is advantageously (due to its mechanical design or its electrical switching capability) moved into its at least partially open state. Even during further adjustment of the first surface 16a in the first direction 22 / braking direction, the reservoir shut-off valve 26 can remain in its at least partially open state until the first surface 16a is moved back in a direction opposite to the first direction 22 / braking direction.

[0022] The advantageous connection of the first pressure chamber 12a to the brake fluid reservoir 24 via the advantageously mechanically designed or electrically switchable reservoir shut-off valve 26 limits the counterforce acting against the movement of the at least one piston 18 of the pressure supply device 10 in the first direction 22 / braking direction. The counterforce is generally defined as the sum of a first product of the first area 16a and the first chamber pressure present in the first pressure chamber 12a, and a second product of the second area 16b and the second chamber pressure present in the second pressure chamber 12b. Thus, by limiting the pressure difference between the first chamber pressure and the reservoir pressure, the maximum counterforce occurring during the movement of the at least one piston 18 in the first direction 22 / braking direction can also be limited.

[0023] By limiting the counterforce that the motor 20 of the pressure supply device 10 has to overcome, the power required by the motor 20 can also be reduced (by opening the reservoir shut-off valve 26). Therefore, compared to a standard externally driven braking device (without the reservoir shut-off valve 26), the motor 20 of the pressure supply device 10 can have a smaller installation space requirement, a lower weight, and / or a reduced maximum motor power. Consequently, the pressure supply device 10 can also be equipped with a more cost-effective motor type for the motor 20.

[0024] In the embodiment of the Fig. 1a The reservoir shut-off valve 26 is arranged outside the housing 14 of the pressure supply device 10. However, it should be noted that the described advantages are also guaranteed with a pressure supply device 10 with a reservoir shut-off valve 26 arranged on and / or in the housing 14.

[0025] Furthermore, in the embodiment described here, the reservoir shut-off valve 26 is a pressure-switched valve 26, which can be switched by means of the pressure difference between the first chamber pressure (present in the first pressure chamber 12a) and the reservoir pressure (present in the brake fluid reservoir 24). Due to the mechanical design of the reservoir shut-off valve 26, it is in its closed state when the pressure difference between the first chamber pressure and the reservoir pressure is below the predetermined (mechanically / structurally defined) maximum pressure difference.In contrast, a pressure difference (between the first chamber pressure and the reservoir pressure) equal to the maximum pressure difference causes the reservoir shut-off valve 26 to be (automatically) opened at least partially, so that a further pressure increase in the first pressure chamber 12a can be prevented by means of a brake fluid transfer from the first pressure chamber 12 via the reservoir shut-off valve 26 into the brake fluid reservoir 24.

[0026] The hydraulic braking system of the Fig. 1a also has a first brake circuit 28a (with at least one first wheel brake cylinder not shown) and a second brake circuit 28b (with at least one second wheel brake cylinder not shown). The first brake circuit 28a is connected to the first pressure chamber 12a, in particular to a first bore 29a formed therein. Similarly, the second brake circuit 28b is connected to the second pressure chamber 12b, preferably to a second bore 29b formed therein.The connection of the first brake circuit 28a to the first pressure chamber 12a and the second brake circuit 28b to the second pressure chamber 12b is such that, by adjusting the at least one piston 18 in the first direction 22, brake fluid from the pressure supply device 10 can be transferred / pressed into the connected brake circuits 28a and 28b in such a way that the brake pressures in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder can be increased. This can also be described as follows: by adjusting the at least one piston 18 in the first direction 22, an increase in brake pressure can be effected in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder.

[0027] The hydraulic braking system of the Fig. 1a also includes a hydraulically connected isolating valve 30 to the first pressure chamber 12a / the first bore 29a, via which the first brake circuit 28a is connected to the first pressure chamber 12a. Furthermore, the hydraulic brake system has a circuit isolating valve 32, via which the first brake circuit 28a can be connected to the second brake circuit 28b.

[0028] Valves 30 and 32 are preferably designed as electrically switchable valves 30 and 32. A control device (not shown) can be used to switch valves 30 and 32, which outputs at least a first switching signal 34 to the isolation valve 30 and at least a second switching signal 36 to the circuit isolation valve 32.

[0029] Fig. Figure 1b shows a coordinate system whose abscissa indicates the second chamber pressure p present in the second pressure chamber 12b. An ordinate of the coordinate system of Fig. 1b represents the total volume V filled from the pressure supply device 10 into the first brake circuit 28a and the second brake circuit 28b during the adjustment of the at least one piston 18 in the first direction 22.

[0030] A graph g1 of the coordinate system of Fig. 1b gives the hydraulic braking system of the Fig. 1a shows the values ​​obtained for the total volume V again. In contrast, graph g10 shows the corresponding values ​​of a standard external power braking device (without a pressure chamber connection to the brake fluid reservoir 24 via the reservoir shut-off valve 26).

[0031] By adjusting the second surface 16b of the at least one piston 18 in the first direction 22 / braking direction, the second chamber pressure p can be increased. Since the reservoir shut-off valve 26 of the pressure supply device 10 is closed at the start of operation of the motor 20, the first chamber pressure in the first pressure chamber 12a can also be increased accordingly during this phase. (The shut-off valve 30 is also open during this phase.)

[0032] From a second chamber pressure p above a predetermined response pressure p0, brake fluid is forced from the first pressure chamber 12a into the first brake circuit 28a and from the second pressure chamber 12b into the second brake circuit 28b via the open isolating valve 30. Therefore, the total volume V filled from the two pressure chambers 12a and 12b into the first brake circuit 28a and the second brake circuit 28b increases continuously from a second chamber pressure p above the predetermined response pressure p0. Preferably, the control device is designed such that, from a predetermined minimum pressure just above the response pressure p0, it switches the circuit isolating valve 32 from its closed state to its open state. This ensures pressure equality in the two brake circuits 28a and 28b at the beginning of the pressure build-up.Additionally, closing the circuit separation valve 32 can at least temporarily improve the pressure build-up dynamics in the two brake circuits 28a and 28b and ensure circuit separation.

[0033] As long as the pressure difference between the first chamber pressure (present in the first pressure chamber 12a) and the reservoir pressure (present in the brake fluid reservoir 24) remains smaller than the specified maximum pressure difference during the adjustment of the first surface 16a in the first direction 22 / braking direction, brake fluid transfer from the first pressure chamber 12a to the brake fluid reservoir 24 is prevented. Instead, the brake fluid volume forced out of the first pressure chamber 12a is transferred to the first brake circuit 28a and the second brake circuit 28b. Therefore, graph g1 exhibits a comparatively high initial slope for a second chamber pressure p between the response pressure p0 and a specified threshold value ps.

[0034] When the second chamber pressure p equals the predetermined threshold ps, the pressure difference between the first chamber pressure and the reservoir pressure reaches the predetermined maximum pressure difference. Thus, when the second chamber pressure p equals the predetermined threshold ps, a switching point of the reservoir isolation valve 26 is reached, and the reservoir isolation valve 26 is moved to an at least partially open state. Preferably, the control device is additionally designed to close the isolation valve 30 shortly before the switching point of the reservoir isolation valve 26 is reached. This ensures that the first brake circuit 28a is already decoupled from the first pressure chamber 12a when the reservoir isolation valve 26 is subsequently opened, and that opening the reservoir isolation valve 26 does not cause a pressure drop in the first brake circuit 28a.Thus, from a second chamber pressure p equal to the specified threshold ps, the brake fluid forced out of the first pressure chamber 12a is transferred exclusively into the brake fluid reservoir. (Preferably, the circuit separator valve 32a is also opened after the reservoir separator valve 26 opens, so that brake fluid from the second pressure chamber 12b can be filled into the first brake circuit 28a via the second brake circuit 28b through the open circuit separator valve 32.)

[0035] For a second chamber pressure p above the threshold ps, the graph g1 therefore exhibits a second slope, which is smaller than the first slope. This can also be described as follows: during the brake pressure increase in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder, when the pressure difference between the first chamber pressure and the reservoir pressure is below the specified maximum pressure difference (or, for a second chamber pressure p, between the response pressure p0 and the threshold ps), a first volume flow q1 from the pressure supply device 10 can be transferred into the two brake circuits 28a and 28b, and once the specified maximum pressure difference between the first chamber pressure and the reservoir pressure (or, for a second chamber pressure p, between the response pressure p0 and the threshold ps) is reached, the flow ceases.From a second chamber pressure p above the threshold ps, a second volume flow q2 from the pressure supply device 10 can be transferred into the two brake circuits 28a and 28b, wherein the first volume flow q1 is greater than the second volume flow q2. (The first volume flow q1 and the second volume flow q2 can each be understood as a time derivative of the total volume V.) In contrast, the graph g10 shows the same slope and the same volume flow for all second chamber pressures p above the response pressure p0.

[0036] The hydraulic braking system of the Fig. 1 thus exhibits advantageous dynamics for brake pressure build-up in the wheel brake cylinders of its brake circuits 28a and 28b. In a comparatively short time (i.e., at a second chamber pressure p between the response pressure p0 and the threshold ps), a comparatively large total volume V can be transferred into the brake circuits 28a and 28b, while from a second chamber pressure p equal to the threshold ps, the desired pressure increase is achieved with the reduced second volume flow q2.

[0037] Fig. Figure 1c shows a coordinate system whose abscissa represents the second chamber pressure p and whose ordinate represents a motor torque M required to build up pressure.

[0038] A graph g2 of the coordinate system of Fig. 1c gives the output of motor 20 of the hydraulic braking system of the Fig. 1a the motor torque M to be applied. In contrast, graph g20 shows a motor torque M of a motor of a standard external power braking device (without a pressure chamber connection to the brake fluid reservoir 24 via the reservoir shut-off valve 26).

[0039] From the response pressure p0, the motor torque M required to transfer the brake fluid from the pressure supply device 10 into the two brake circuits 28a and 28b by the motor 20 of the pressure supply device 10 increases with a first slope ΔM1. Immediately before the threshold value ps, the graph g2 has a maximum M0. However, the graph g2 shows a sharp drop Δ of the motor torque M at a second chamber pressure p equal to the threshold value ps. For a second chamber pressure p greater than the threshold value ps, the motor torque M increases only with a second slope ΔM2, which is smaller than the first slope ΔM1.During the increase in brake pressure in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder, the motor torque M to be supplied by the motor 20 increases with the first slope ΔM1 at a pressure difference between the first chamber pressure and the reservoir pressure below the specified maximum pressure difference and, after the drop Δ of the motor torque M, with a pressure difference (between the first chamber pressure and the reservoir pressure) (almost) equal to the specified maximum pressure difference, with the second slope ΔM2 smaller than the first slope ΔM1.

[0040] Preferably, the difference between the first slope ΔM1 and the second slope ΔM2 is such that the motor torque M of graph g2 no longer reaches the maximum M0 immediately before the threshold ps after the drop Δ. During the brake pressure increase in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder, the motor torque M to be applied by the motor 20 of the pressure supply device 10 can thus be limited to the maximum M0 as a predetermined limiting motor torque M0 by switching the reservoir shut-off valve 26 to its open state. This creates a degree of freedom for cost optimization of the motor 20 without altering the system dynamics.

[0041] The hydraulic braking system of the Fig. The pressure supply device 10, as implemented in Figure 1a, can be described as a two-stage pressure supply device 10. By way of example only, the housing 14 of the pressure supply device 10 is designed with an annular volume 12a as the first pressure chamber 12a. The pressure supply device 10 has only a single piston 18, which is designed as a stepped piston 18. The stepped piston 18 has a first subsection with a first outer diameter d1, which is adjustable at least partially into the first pressure chamber 12a, wherein a first inner diameter di1 of the first pressure chamber 12a correlates with the first outer diameter d1 of the stepped piston 18. Furthermore, the stepped piston 18 has a second subsection with a second outer diameter d2 smaller than the first outer diameter d1, which is adjustable at least partially into the second pressure chamber 12b with a corresponding / adapted second inner diameter di2.It should be noted that considerable design freedom is ensured when defining the ratio between the first outer diameter d1 (or the first surface 16a) and the second outer diameter d2 (or the second surface 16b). In particular, the desired dynamics of the pressure supply device 10 can be ensured by appropriately defining the ratio between the first outer diameter d1 (or the first surface 16a) and the second outer diameter d2 (or the second surface 16b).

[0042] Fig. Figure 2 shows a schematic partial representation of a second embodiment of the hydraulic brake system.

[0043] The hydraulic braking system of the Fig. 2. The reservoir shut-off valve 50 is an electrically switchable valve 50, which can be switched by means of at least one control signal 52 from a control device 54. Preferably, in this case, the control device 54 is designed to detect whether a pressure difference between the first chamber pressure present in the first pressure chamber 12a and the reservoir pressure present in the brake fluid reservoir reaches / exceeds the predetermined maximum pressure difference. (The detection that a pressure difference between the first chamber pressure present in the first pressure chamber 12a and the reservoir pressure present in the brake fluid reservoir reaches / exceeds the predetermined maximum pressure difference can be carried out directly by evaluating a pressure sensor signal or indirectly, e.g., by evaluating an engine sensor signal.)If this is the case, the control device 54 is designed to switch the reservoir shut-off valve 50 into an at least partially open state by means of the at least one control signal 52. The advantages described above can also be achieved by designing the reservoir shut-off valve 50 as an electrically switchable valve 50.

[0044] Fig. Figure 3 shows a flowchart to explain a method for operating a hydraulic braking system of a vehicle, which is not part of the present invention.

[0045] The procedure described below can be carried out, for example, using the hydraulic brake systems explained above. However, it should be noted that the feasibility of the procedure is not limited to the use of such a hydraulic brake system.

[0046] In process step S1, the brake pressure is increased in at least one first wheel brake cylinder of a first brake circuit of the hydraulic brake system and in at least one second wheel brake cylinder of a second brake circuit of the hydraulic brake system. For this purpose, a motor of a pressure supply device of the hydraulic brake system is controlled such that, by operating the motor, at least one piston of the pressure supply device is moved in a first direction, thereby transferring brake fluid, at least temporarily, from a first pressure chamber bounded by at least one first surface of the at least one piston into the connected first brake circuit, and from a second pressure chamber bounded by at least one second surface of the at least one piston into the connected second brake circuit.During the execution of process step S1, the first pressure chamber is connected to a brake fluid reservoir of the hydraulic brake system via a reservoir isolation valve. The reservoir isolation valve is mechanically designed or electrically switched in such a way that an exceedance of a predetermined maximum pressure difference between the chamber pressure present in the first pressure chamber and the reservoir pressure present in the brake fluid reservoir can be prevented by opening the reservoir isolation valve. For example, the reservoir isolation valve can be closed at the beginning of the pressure build-up in the wheel brake cylinders of the brake circuits.When the pressure difference between the pressure in the first pressure chamber and the pressure in the brake fluid reservoir equals the specified maximum pressure difference, the reservoir shut-off valve can be electrically switched from its closed to its open state. However, a pressure-switched valve can also be used as the reservoir shut-off valve to carry out the procedure described here.

[0047] In an optional process step S0, a separating valve, through which the first brake circuit is connected to the first pressure chamber, can be switched from its open to its closed state when the pressure difference between the chamber pressure in the first pressure chamber and the reservoir pressure in the brake fluid reservoir is just below the specified maximum pressure difference. This prevents an undesirable pressure drop in the first brake circuit.

Claims

[1] Pressure supply device (10) for a hydraulic braking system of a vehicle with: a first pressure chamber (12a) and a second pressure chamber (12b), wherein the first pressure chamber (12a) is bounded by at least a first surface (16a) and the second pressure chamber (12b) by at least a second surface (16b) of at least one piston (18) of the pressure supply device (10); a motor (20); and a transmission via which the at least one piston (18) is connected to the motor (20) in such a way that the at least one piston (18) can be adjusted at least in a first direction (22) by means of operation of the motor (20); wherein the pressure supply device (10) comprises a reservoir shut-off valve (26, 50) hydraulically connected to the first pressure chamber (12a), which can be connected to a brake fluid reservoir (24) of the brake system and which is mechanically designed or electrically switchable in such a way that an exceedance of a predetermined maximum pressure difference between a chamber pressure present in the first pressure chamber (12a) and a reservoir pressure present in the brake fluid reservoir (24) can be prevented by opening the reservoir shut-off valve (26, 50), and wherein a first brake circuit (28a) with at least one first wheel brake cylinder is connected to the first pressure chamber (12a) and a second brake circuit (28b) with at least one second wheel brake cylinder is connected to the second pressure chamber (12b) in such a way that by adjusting the at least one piston (18) in the first direction (22) an increase in brake pressure can be effected in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder, characterized by a circuit isolation valve (32) via which the first brake circuit (28a) is connected to the second brake circuit (28b). [2] Pressure supply device (10) according to claim 1, wherein during the increase in brake pressure in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder, a motor torque (M) to be applied by the motor (20) increases with a first slope (ΔM1) when the pressure difference between the chamber pressure and the reservoir pressure is below the specified maximum pressure difference, and, from a pressure difference between the chamber pressure and the reservoir pressure equal to the specified maximum pressure difference, increases with a second slope (ΔM2) that is smaller than the first slope (ΔM1). [3] Pressure supply device (10) according to claim 1 or 2, wherein during the increase in brake pressure in the at least one first wheel brake cylinder and in the at least one second wheel brake cylinder, a first volume flow (q1) from the pressure supply device (10) can be transferred into the two brake circuits (28a, 28b) when the pressure difference between the chamber pressure and the reservoir pressure is below the predetermined maximum pressure difference, and from the point at which the predetermined maximum pressure difference between the chamber pressure and the reservoir pressure is reached, a second volume flow (q2) from the pressure supply device (10) can be transferred into the two brake circuits (28a, 28b), wherein the first volume flow (q1) is greater than the second volume flow (q2). [4] Pressure supply device (10) according to one of the preceding claims, wherein the pressure supply device (10) has only one piston (18) which is designed as a stepped piston (18) than the at least one piston (18). [5] Hydraulic braking system for a vehicle with: a brake fluid reservoir (24); a pressure supply device (10) with a first pressure chamber (12a) and a second pressure chamber (12b), wherein the first pressure chamber (12a) is bounded by at least a first surface (16a) and the second pressure chamber (12b) by at least a second surface (16b) of at least one piston (18) of the pressure supply device (10), and wherein the at least one piston (18) is connected to a motor (20) of the pressure supply device (10) via a transmission such that the at least one piston (18) is adjustable at least in a first direction (22) by means of operation of the motor (20); and a reservoir isolation valve (26, 50) via which the first pressure chamber (12a) of the pressure supply device (10) is connected to the brake fluid reservoir (24), wherein the reservoir isolation valve (26, 50) is mechanically designed or electrically switchable in such a way that an exceedance of a predetermined maximum pressure difference between a chamber pressure present in the first pressure chamber (12a) and a reservoir pressure present in the brake fluid reservoir (24) can be prevented by opening the reservoir isolation valve (26, 50); wherein a first brake circuit (28a) with at least one first wheel brake cylinder on the first pressure chamber (12a) and a second brake circuit (28b) with at least one second wheel brake cylinder on the second pressure chamber (12b) are connected in such a way that by adjusting the at least one piston (18) in the first direction (22) a brake pressure increase in the at least one first wheel brake cylinder and in which at least one second wheel brake cylinder can be activated, characterized by a circuit isolation valve (32) via which the first brake circuit (28a) is connected to the second brake circuit (28b). [6] Hydraulic brake system according to claim 5, wherein the hydraulic brake system comprises a separating valve (30) hydraulically connected to the first pressure chamber (12a), via which the first brake circuit (12a) is connected to the first pressure chamber (12a). [7] Hydraulic brake system according to claim 5 or 6, wherein the reservoir shut-off valve (26) is a pressure-switched valve (26) which can be switched by means of the pressure difference between the chamber pressure present in the first pressure chamber (12a) and the reservoir pressure present in the brake fluid reservoir (24). [8] Hydraulic brake system according to claim 5 or 6, wherein the reservoir shut-off valve (50) is an electrically switchable valve (50) which can be switched by means of at least one control signal (52) of a control device (54). [9] Hydraulic brake system according to claim 8, wherein the hydraulic brake system comprises the control device (54), and wherein the control device (54) is designed to detect whether the pressure difference between the chamber pressure present in the first pressure chamber (12a) and the reservoir pressure present in the brake fluid reservoir (24) reaches or exceeds the predetermined maximum pressure difference, and, if necessary, to switch the reservoir shut-off valve (50) to an at least partially open state by means of the at least one control signal (52).

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