Braking system for a vehicle and method for operating a vehicle's braking system

Abstract

Braking system for a vehicle with: a master brake cylinder (70); a motorized piston-cylinder device (106); and at least two wheel brake cylinders (88a, 88b, 92a, 92b), to which a first valve (94a, 94b, 96a, 96b) and a second valve (98a, 98b, 100a, 100b) are connected via a branching valve-free line path (102a, 102b, 104a, 104b) per wheel brake cylinder (88a, 88b, 92a, 92b), wherein the at least two wheel brake cylinders (88a, 88b, 92a, 92b) are hydraulically connected to the master brake cylinder (70) via at least their first valves (94a, 94b, 96a, 96b) in such a way that brake fluid from the master brake cylinder (70) flows through at least the at least partially open first valves (94a, 94b, 96a, 96b) into the at least two wheel brake cylinders (88a, 88b, 92a, 92b), and wherein the at least two wheel brake cylinders (88a, 88b, 92a, 92b) are hydraulically connected to the motorized piston-cylinder device (106) in such a way,that brake fluid can be displaced between the motorized piston-cylinder device (106) and the at least two wheel brake cylinders (88a, 88b, 92a, 92b) by means of the operation of a motor (112) of the motorized piston-cylinder device (106); characterized by the fact that Each of the at least two wheel brake cylinders (88a, 88b, 92a, 92b) is hydraulically connected to the motorized piston-cylinder device (106) via the respective second valve (98a, 98b, 100a, 100b).

Description

[0001] The invention relates to a braking system for a vehicle. Furthermore, the invention relates to a method for operating a braking system of a vehicle. State of the art

[0002] Fig. Figure 1 shows a schematic representation of a conventional braking system, which is known to the applicant as prior art.

[0003] The in Fig. A schematically depicted brake system for a vehicle has a master brake cylinder 10 with a first pressure chamber, which comprises a first sub-volume 12a and a second sub-volume 12b as a brake-in volume. The sub-volumes 12a and 12b can be reduced by means of the associated piston walls of an adjustable rod piston 14. The master brake cylinder 10 also has a second pressure chamber 16 and an adjustable floating piston 18. The first sub-volume 12a, the second sub-volume 12b, and the second pressure chamber 16 are each connected to a brake fluid reservoir 20 via a vent hole.

[0004] The braking system of the Fig. 1 also has a first brake circuit 24 with first wheel brake cylinders 26 connected to the first partial volume 12a via a first separating valve 22a and a second brake circuit 28 with second wheel brake cylinders 30 connected to the second pressure chamber 16 via a second separating valve 22b. Each wheel brake cylinder 26 and 30 is assigned a wheel inlet valve 32 and a wheel outlet valve 34.

[0005] Furthermore, the second sub-volume 12b is connected to the first brake circuit 24 via a check valve 36. Additionally, the second sub-volume 12b is connected to the brake fluid reservoir 20 via both an electrically controlled valve 38 and a regulated check valve 40.

[0006] The conventional brake system also includes a piston-cylinder device 42, the pressure chamber 44 of which is limited by a piston 48 adjustable by the operation of a motor 46. The pressure chamber 44 of the piston-cylinder device 42 is connected to the first brake circuit 24 via a third isolating valve 50a and to the second brake circuit 28 via a fourth isolating valve 50b. Furthermore, the pressure chamber 44 of the piston-cylinder device 42 is hydraulically connected to the brake fluid reservoir 20.

[0007] Furthermore, the conventional braking system includes a simulator unit 52, which is hydraulically connected to the first partial volume 12a via a simulator valve 54. A pre-pressure sensor 56a is also connected to the first brake circuit 24 such that the pre-pressure sensor 56a is positioned upstream of the simulator valve 54. A brake pressure sensor 56b is additionally connected to each brake circuit 24 and 26. To determine the actuation force of a brake actuation element 58 of the braking system by a driver, the braking system also includes brake actuation sensors 60.

[0008] Document DE 196 20 228 A1 discloses a master brake cylinder for a hydraulic external power brake system, with a device for increasing a pressure ratio, which optionally brings the pressure chamber and the after-chamber of the master cylinder into fluid contact. Disclosure of the invention

[0009] The invention provides a braking system for a vehicle with the features of claim 1 and a method for operating a braking system of a vehicle with the features of claim 9. Advantages of the invention

[0010] By utilizing the present invention, a volume of brake fluid can be moved with high dynamics between the motorized piston-cylinder device and the at least one wheel brake cylinder with a comparatively lower force. Compared to conventionally moving the brake fluid volume via at least one wheel inlet valve, the hydraulic resistance to be overcome is reduced in the brake fluid movement realized according to the invention via the second valves. The present invention thus provides, in particular, a connection of the motorized piston-cylinder device to the wheel brake cylinder via at least one pressure build-up path with reduced hydraulic resistance compared to the prior art.

[0011] Therefore, when using the present invention, comparatively little power is required from the motor of the motorized piston-cylinder device to move / draw in / out of the brake fluid volume to / from the at least one connected wheel brake cylinder. The present invention thus enables the use of a comparatively low-powered, small, lightweight, cost-effective, and / or energy-saving motor for the motorized piston-cylinder device, while still allowing for the build-up / reduction of brake pressure in at least one wheel brake cylinder with the same dynamics as conventionally available, using the motor of the motorized piston-cylinder device. The present invention therefore also allows the use of a more cost-effective and energy-saving motorized piston-cylinder device in a braking system.

[0012] In an advantageous embodiment of the brake system, the at least two wheel brake cylinders are hydraulically connected to a brake fluid reservoir of the brake system via at least their first valves, such that brake fluid can be drained from the at least two wheel brake cylinders into the brake fluid reservoir via the at least partially open first valves. A locking of at least one wheel can thus be easily and quickly resolved. For example, the first valves can be hydraulically connected to the brake fluid reservoir via at least one first isolating valve.

[0013] Furthermore, the first valves can be hydraulically connected to the master brake cylinder via at least one second isolating valve. In this case, the wheel brake cylinders can be disconnected from the master brake cylinder by closing at least one second isolating valve.

[0014] Preferably, each of the first valves is a check-valve-less two-way valve. Similarly, each of the second valves can also be a check-valve-less two-way valve. This allows for the use of cost-effective valves in the brake system.

[0015] Preferably, the second valves are hydraulically connected to the motorized piston-cylinder assembly via a valveless line path that begins at the motorized piston-cylinder assembly and ends at the respective second valve. The total hydraulic resistance that must be overcome to move brake fluid between the motorized piston-cylinder assembly and the connected wheel brake cylinders is therefore relatively low.

[0016] In a further advantageous embodiment, each wheel brake cylinder of the braking system has its first and second valves connected via a single branching, valve-free line path per wheel brake cylinder. In this case, the brake pressure in each wheel brake cylinder of the braking system can be individually increased or decreased by operating the motor of the motorized piston-cylinder device.

[0017] The advantages described above can also be realized by implementing a corresponding method for operating a vehicle's braking system. This method can be further developed according to the braking system embodiments described above. Brief description of the drawings

[0018] Further features and advantages of the present invention are explained below with reference to the figures. They show: Fig. 1 a schematic representation of a conventional braking system; Fig. 2 a schematic representation of an embodiment of the braking system according to the invention for a vehicle; and Fig. 3 A flowchart to explain one embodiment of the method for operating a vehicle's braking system. Embodiments of the invention

[0019] Fig. Figure 2 shows a schematic representation of an embodiment of the braking system according to the invention for a vehicle.

[0020] The in Fig. The braking system shown schematically can be used in a vehicle / motor vehicle, such as an electric or hybrid vehicle. However, the applicability of the braking system is not limited to a specific vehicle type.

[0021] The braking system has a master brake cylinder 70 with at least one first pressure chamber 72, which comprises at least one first partial volume 72a that is variable by means of an adjustable piston 74. In the embodiment of the Fig. 2. The first pressure chamber 72 comprises, in addition to the first partial volume 72a, a second partial volume 72b, wherein the first pressure chamber 72 is structurally subdivided into partial volumes 72a and 72b. Alternatively, the first pressure chamber 72 can also be subdivided into partial volumes 72a and 72b by means of at least one controllable partition. If the first pressure chamber 72 comprises the two partial volumes 72a and 72b, the partial volumes 72a and 72b can optionally be designed as two (structurally) separate chambers or as hydraulically separable chambers by means of a valve component. However, the design of the first pressure chamber 72 with the second partial volume 72b in addition to the first partial volume 72b described here is merely an example.

[0022] The specific feature is the embodiment of the Fig. 2. The first partial volume 72a is limited by a first piston wall 74a of at least one adjustable piston / rod piston 74 such that a first volume of the first partial volume 72a, which can be filled with brake fluid, is variable by means of a displacement of the first piston wall 74a, in particular, it can be reduced by displacement of the first piston wall 74a in a braking direction. Furthermore, the second partial volume 72b is limited by a second piston wall 74b of the at least one adjustable piston / rod piston 74 such that a second volume of the second partial volume 72b, which can be filled with brake fluid, is variable by means of displacement of the second piston wall 74b. In particular, the second volume of the second partial volume 74b can be reduced by displacement of the second piston wall 74b in the (same) braking direction. However, the Fig. The common boundary of the partial volumes 72a and 72b shown in Figure 1a by means of the piston walls 74a and 74b of the same piston / rod piston 74 is to be understood as merely an example. The design of the piston 74 as a rod piston 74 shown here should also only be interpreted in this way.

[0023] In the embodiment described here, the master brake cylinder 70 comprises a second pressure chamber 76 and a floating piston 78 adjustable between the first partial volume 72a of the first pressure chamber 72 and the second pressure chamber 76. The master brake cylinder 70 can thus also be used as a "modified" tandem master brake cylinder. However, it should be noted that a configuration of the master brake cylinder 70 with two pressure chambers 72 and 76 is optional.

[0024] In the embodiment of the Fig. 2. The master brake cylinder 70 specifically has a stepped bore within which at least the first pressure chamber 72 is formed. For example, the stepped bore can have a first (inner) internal diameter oriented perpendicular to the braking direction of the at least one adjustable rod piston 74 and / or the floating piston 78, which is smaller than a second (outer) internal diameter of the stepped bore oriented perpendicular to the braking direction. The first partial volume 72a and / or the second pressure chamber 76 can have the first / inner diameter perpendicular to the braking direction, while the second partial volume 72b has the second / outer internal diameter perpendicular to the braking direction.The master brake cylinder 70 can also have a stepped piston 74 as the at least one adjustable piston / rod piston 74, which, with the first piston wall 74a, delimits the first partial volume 72a and, with the second piston wall 74b, the second partial volume 72b. The second partial volume 72b can therefore also be designed as an annular volume. However, it is pointed out that the in . Fig. The representation of the master brake cylinder 70 shown in section 2 is to be interpreted merely as an example. Even a version that differs from the illustration in Fig. 2. A different design of the master brake cylinder 70 can be used to implement the brake system described below.

[0025] The braking system preferably also includes a brake fluid reservoir 80 (with atmospheric pressure present therein). At least the first partial volume 72a may have a vent hole 82, via which the first partial volume 72a is hydraulically connected to the brake fluid reservoir 80. The second partial volume 72b and / or the second pressure chamber 76 may also each be hydraulically connected to the brake fluid reservoir 80 via a further vent hole 82.

[0026] The braking system also has at least one first brake circuit 86 with at least one first wheel brake cylinder 88a and 88b, wherein the first brake circuit 86 is hydraulically connected to the first partial volume 72a only by way of example. Preferably, a second brake circuit 90 with at least one second wheel brake cylinder 92a and 92b is also hydraulically connected to the second pressure chamber 76. However, the braking system described here is not limited to a design with two brake circuits 86 and 90. Likewise, the number of wheel brake cylinders 88a, 88b, 92a, and 92b used / possible in a brake circuit 86 and 90 is relatively freely selectable. Overall, however, the braking system has at least two of the wheel brake cylinders 88a, 88b, 92a, and 92b.

[0027] Furthermore, at least two of the wheel brake cylinders 88a, 88b, 92a and 92b of the brake system are connected to a first valve 94a, 94b, 96a and 96b and a second valve 98a, 98b, 100a and 100b via a branching valve-free line path 102a, 102b, 104a and 104b per wheel brake cylinder 88a, 88b, 92a and 92b. The respective valve-free line path 102a, 102b, 104a and 104b thus contacts at least two of the wheel brake cylinders 88a, 88b, 92a and 92b of the brake system and branches off from the contacted wheel brake cylinder 88a, 88b, 92a or 92b to the associated first valve 94a, 94b, 96a and 96b and second valve 98a, 98b, 100a and 100b.It is expressly pointed out that no further electrically controlled and / or pressure-switched hydraulic valve is used between the first valve 94a, 94b, 96a and 96b of a wheel brake cylinder 88a, 88b, 92a and 92b, the second valve 98a, 98b, 100a and 100b of the same wheel brake cylinder 88a, 88b, 92a and 92b and the respective wheel brake cylinder 88a, 88b, 92a and 92b in the associated valve-free line path 102a, 102b, 104a and 104b.

[0028] The at least two wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b) are hydraulically connected to the master brake cylinder 70 via at least their first valves 94a, 94b, 96a and 96b. This connection to the master brake cylinder 70 ensures that brake fluid can be transferred from the master brake cylinder 70 to the at least two wheel brake cylinders 88a, 88b, 92a and 92b via at least the at least partially open first valves 94a, 94b, 96a and 96b.

[0029] The braking system also includes a motorized piston-cylinder device 106. The motorized piston-cylinder device 106 comprises, for example, at least one piston 110 that delimits an associated pressure chamber 108. This piston 110 is linearly adjustable by means of a motor 112 of the motorized piston-cylinder device 106, such that the volume of the associated pressure chamber 108 that can be filled with brake fluid can be selectively increased or decreased. For this purpose, the at least one piston 110 can be connected to the motor 112 of the motorized piston-cylinder device 106, for example, via a thread 114. Such a motorized piston-cylinder device 106 is also frequently referred to as a (motorized) plunger or a (motorized) plunger device.

[0030] Each of the at least two wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b) is hydraulically connected to the motorized piston-cylinder device 106 via the respective second valve 98a, 98b, 100a and 100b in such a way that brake fluid can be moved between the motorized piston-cylinder device 106 and the at least two wheel brake cylinders 88a, 88b, 92a and 92b by means of operation of the motor 112 of the motorized piston-cylinder device 106. This allows brake pressure to build up in the at least two wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b) by feeding a volume of brake fluid from the motorized piston-cylinder device 106 into the associated wheel brake cylinder 88a, 88b, 92a and 92b via the at least partially open second valve 98a, 98b, 100a and 100b arranged between them.Accordingly, a reduction in brake pressure in the at least two wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b) can also be achieved by drawing brake fluid from the respective wheel brake cylinder 88a, 88b, 92a and 92b into the motorized piston-cylinder device 106 via the associated at least partially open second valve 98a, 98b, 100a and 100b. A brake pressure present in the wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b) can therefore be adjusted by means of the operation of the motor 112 of the motorized piston-cylinder device 106 independently of an actuation of a brake actuation element connected to the master brake cylinder 70 by a driver.

[0031] Furthermore, the second valves 98a, 98b, 100a, and 100b replace the conventional wheel outlet valves in the brake system. Filling / emptying the at least two wheel brake cylinders 88a, 88b, 92a, and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a, and 100b) can therefore be carried out by bypassing the first valves 94a, 94b, 96a, and 96b / wheel inlet valves of the brake system. Conventionally, moving a volume of brake fluid between a cylinder and a wheel brake cylinder via a wheel inlet valve requires a comparatively large amount of force / energy, as the wheel outlet valve offers relatively high hydraulic resistance to the desired brake fluid movement.In contrast, when filling / emptying the at least two wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b) via the second valves 98a, 98b, 100a and 100b as implemented here, the hydraulic resistance to be overcome is reduced. Therefore, the desired brake fluid volume between the at least two wheel brake cylinders 88a, 88b, 92a and 92b and the motorized piston-cylinder device 106 can be moved with a comparatively lower force / energy via the associated second valves 98a, 98b, 100a and 100b.

[0032] Due to the advantageous connection of the motorized piston-cylinder device 106 via the second valves 98a, 98b, 100a and 100b, the hydraulic efficiency occurring during the filling / emptying of the at least two wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b) is (essentially) determined by the hydraulic resistances of the second valves 98a, 98b, 100a and 100b. However, the second valves 98a, 98b, 100a and 100b (unlike conventional wheel inlet valves) can be designed with a great deal of freedom. Accordingly, the hydraulic resistance occurring during the filling / emptying of the at least two wheel brake cylinders 88a, 88b, 92a and 92b can also be set to a low level.

[0033] In the braking system described here, the need to use a motor type for the motorized piston-cylinder assembly 106 whose dynamics / power are sufficient to overcome a pressure build-up path extending via at least one wheel inlet valve is eliminated. The advantageous connection of the motorized piston-cylinder assembly 106 via the second valves 98a, 98b, 100a, and 100b thus enables the use of a comparatively low-powered, small, lightweight, cost-effective, and / or energy-efficient motor 112 for the motorized piston-cylinder assembly 106. Consequently, a cost-effective, small, lightweight, and energy-efficient motorized piston-cylinder assembly 106 can also be used in the braking system.

[0034] Furthermore, the second valves 98a, 98b, 100a, and 100b can each be hydraulically connected to the motorized piston-cylinder device 106 via a valveless line path 116, which begins at the motorized piston-cylinder device 106 and ends at the respective second valve 98a, 98b, 100a, and 100b. For example, each of the second valves 98a, 98b, 100a, and 100b can be connected to the motorized piston-cylinder device 106 via its own (separate) valveless line section, which begins at the motorized piston-cylinder device 106 and ends at the respective second valve 98a, 98b, 100a, and 100b. Likewise, a valveless line section 118 contacting the motorized piston-cylinder device 106 can branch off to the second valves 98a, 98b, 100a and 100b.

[0035] To fill / empty the at least two wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b), only the one second valve 98a, 98b, 100a and 100b needs to be opened for each filled / emptied wheel brake cylinder 88a, 88b, 92a and 92b. This further reduces the requirements for the motor 112 of the motorized piston-cylinder device 106.

[0036] Preferably, the second valves 98a, 98b, 100a and 100b are individually controllable. In this case, brake pressure build-up or reduction can be carried out individually for each wheel in the at least two wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b) without the need for an additional isolating valve between the motorized piston-cylinder device 106 and the at least two wheel brake cylinders 88a, 88b, 92a and 92b.

[0037] In particular, each of the wheel brake cylinders 88a, 88b, 92a and 92b of the brake system can have its first valve 94a, 94b, 96a and 96b and its second valve 98a, 98b, 100a and 100b connected via the single branching valve-free line path 102a, 102b, 104a and 104b per wheel brake cylinder 88a, 88b, 92a and 92b. In this case, each brake pressure in each wheel brake cylinder 88a, 88b, 92a and 92b of the brake system can be individually increased or decreased by operating the motor 112 of the motorized piston-cylinder device 106.

[0038] Advantageously, the braking system of Fig. 2 the at least two wheel brake cylinders 88a, 88b, 92a and 92b (with the first and second valves 94a, 94b, 96a, 96b, 98a, 98b, 100a and 100b) are hydraulically connected to the brake fluid reservoir 80 of the brake system via at least their first valves 94a, 94b, 96a and 96b in such a way that brake fluid from the at least two wheel brake cylinders 88a, 88b, 92a and 92b can be drained into the brake fluid reservoir 80 via the at least partially open first valves 94a, 94b, 96a and 96b. The first valves 94a, 94b, 96a and 96b can therefore fulfill the function of conventional wheel exhaust valves in addition to the function of conventional wheel intake valves.This multifunctionality of the first valves 94a, 94b, 96a and 96b (despite the equally implemented adjustability of the brake pressure in the wheel brake cylinders 88a, 88b, 92a and 92b, independent of the actuation of the brake actuator) allows for a reduction in the number of electrically controlled valves required in the brake system. Consequently, a control electronics unit suitable for controlling all electrically controlled valves of the brake system can be designed to be smaller, lighter and more cost-effective.

[0039] In the embodiment of the Fig. 2. The first valves 94a, 94b, 96a, and 96b are hydraulically connected to the brake fluid reservoir 80 via at least one first isolating valve 120a and 120b. For example, each brake circuit 86 and 90 has one first isolating valve 120a or 120b, which is connected via a branching, valveless line section 122a or 122b to the two first valves 94a, 94b, 96a, and 96b of the respective brake circuit 86 and 90. The at least one first isolating valve 120a and 120b offers virtually no hydraulic resistance to the movement of brake fluid into the brake fluid reservoir 80. Since a wheel blockage can usually be quickly and reliably remedied by operating the motor 112 of the motorized piston-cylinder device 106, the at least one first separating valve 120a and 120b is also relatively rarely activated.

[0040] As an alternative or supplement to the at least one first isolating valve 120a and 120b, the first valves 94a, 94b, 96a, and 96b can also be hydraulically connected to the master brake cylinder 70 via at least one second isolating valve 124a and 124b. In particular, each brake circuit 86 and 90 can be connected to the master brake cylinder 70 via a second isolating valve 124a and 124b. In this case, brake circuits 86 and 90 can be individually disconnected from the master brake cylinder 70 by closing their respective second isolating valves 124a and 124b. Subsequently, the brake pressure in the wheel brake cylinders 88a, 88b, 92a and 92b, which are decoupled from the master brake cylinder 70, can be adjusted individually for each wheel by means of the motor 112 of the motorized piston-cylinder device 106.If desired, a simultaneously applied generator braking torque of at least one electric motor used as a generator for recuperative braking can also be taken into account when adjusting the brake pressure (wheel-individual) in the wheel brake cylinders 88a, 88b, 92a and 92b which are decoupled from the master brake cylinder 70.

[0041] Optionally, a simulator 126 can be connected to the first pressure chamber 72 or the second pressure chamber 76 in such a way that, after closing at least one second isolating valve 124a and 124b, the driver operating the brake actuator transfers brake fluid to the simulator 126. Thus, even after both brake circuits 86 and 90 are disconnected from the master brake cylinder 70, the driver operating the brake actuator still has a standard brake actuation feel (pedal feel). Furthermore, the simulator 126 can be connected to the first pressure chamber 72 or the second pressure chamber 76 via an additional isolating valve 127.

[0042] The braking system of the Fig. Section 2 additionally features an electrically controlled valve 128, through which the second subvolume 72b is connected to the brake fluid reservoir 80. In this case, the electrically controlled valve 128 is positioned between the second subvolume 72b and the brake fluid reservoir 80 in such a way that, when the electrically controlled valve 128 is open, the second subvolume 72b remains depressurized despite the displacement of the second piston wall 74b. However, the inclusion of the electrically controlled valve 128 in the brake system is optional.

[0043] Likewise, this has in Fig. The brake system shown in Figure 2 includes at least one check valve 130, through which the second partial volume 72b is connected to at least the first brake circuit 86. The at least one check valve 130 is mechanically designed such that (if the electrically controlled valve 128 is in its closed state) pressure can be built up in the second partial volume 72b by moving the second piston wall 74b, whereby, once a pressure threshold (pressure difference) mechanically predetermined at the respective check valve 130 is exceeded between the brake circuit pressure present in the at least one brake circuit 86 and 90 and the partial volume pressure present in the second partial volume 72b, brake fluid can be transferred via the at least one check valve 130 at least into the first brake circuit 86.

[0044] In the embodiment of the Fig. In the second sub-volume 72b, the second sub-volume is connected to the first brake circuit 86 via exactly one check valve 130. In a further development, however, the brake system can also have another (unregulated) check valve, via which the second sub-volume 72b is hydraulically connected to the second brake circuit 90.

[0045] The brake system also features a controlled check valve 132, through which the second sub-volume 72b is connected to the brake fluid reservoir 80. The controlled check valve 132 defines a limit pressure as the maximum permissible pressure in the second sub-volume 72b. The mechanical design of the controlled check valve 132 prevents the limit pressure in the second sub-volume 72b from being exceeded.

[0046] Due to its advantageous design, the braking system can be operated in a normal operating mode in which the driver only applies braking force to the first pressure chamber 72 by means of a first surface of the first piston wall 74a, which delimits the first partial volume 72a. Therefore, in the normal operating mode of the braking device / brake system, the driver experiences a pleasant braking feel (pedal feel) due to the comparatively small contact area for braking, at least in the first pressure chamber 72. This is ensured by controlling the electrically controlled valve 128 in its open state. The timing of this control can be delayed in the event of detected rapid braking, such as during emergency braking, in order to improve the pressure build-up dynamics in this operating condition.

[0047] The braking system can also be operated in a fallback mode in which the braking area (for braking, at least into the first pressure chamber 72) is increased compared to the normal operating mode. By (automatically) controlling the electrically controlled valve 128 to its closed state, an additional pressure build-up in the second partial volume 72b can be achieved. The (total) braking area effective in the fallback mode (for braking, at least into the first pressure chamber 72) thus corresponds to the sum of the first area and a second area of ​​the second piston wall 74b, which delimits the second partial volume 72b.By increasing the braking surface (for braking at least into the first pressure chamber 72) to the sum of the first surface and the second surface, the ratio of the master brake cylinder 70 is increased, so that the driver can effect even greater brake pressures in the wheel brake cylinders 88a, 88b, 92a and 92b of the brake system with a certain driver braking force.

[0048] At the same time, the advantageous mechanical design of the controlled check valve 132 ensures that the partial volume pressure present in the second partial volume 72b (barely) exceeds a mechanically predetermined limit pressure. Thus, even in the fallback mode, it is guaranteed that the driver perceives the actuation of the brake actuator as pleasant.

[0049] The braking system can operate in fallback mode, particularly in the event of a partial or complete failure of at least one electrical component of the braking system or a failure of the vehicle's electrical system. This ensures that even in such a fault situation, the driver can still comfortably bring the vehicle equipped with the braking system to a standstill. In fallback mode / mechanical fallback mode, the electrically controlled valve 128 is kept in its closed state. If the electrically controlled valve 128 is designed as a normally closed valve, this is achieved automatically by interrupting the power supply to the electrically controlled valve 128.

[0050] The first valves 94a, 94b, 96a, and 96b are preferably normally open valves 94a, 94b, 96a, and 96b. This allows the driver to apply the brakes to the wheel brake cylinders 88a, 88b, 90a, and 90b even in the event of a failure of the vehicle's electrical system. In particular, each of the first valves 94a, 94b, 96a, and 96b can be a check-valve-less two-way valve 94a, 94b, 96a, and 96b. Therefore, each of the first valves 94a, 94b, 96a, and 96b can also be described as a switching valve (allowing flow in two opposite directions). Therefore, when equipping the brake system, the check valve conventionally required for each wheel inlet valve can be omitted for the first valves 94a, 94b, 96a and 96b. The costs for the omitted check valves can be saved.

[0051] Preferably, the second valves 98a, 98b, 100a and 100b are normally closed valves 98a, 98b, 100a and 100b. Each of the second valves 98a, 98b, 100a and 100b can, for example, be a check-free 2-way valve 98a, 98b, 100a and 100b.

[0052] The second valves 98a, 98b, 100a and 100b can also be opened for ABS pressure relief to draw brake fluid from at least one wheel brake cylinder 88a, 88b, 90a and 90b into the motorized piston-cylinder device 106. Likewise, the first valves 94a, 94b, 96a and 96b and the at least one first separating valve 120a and 120b can also be used to transfer a volume of brake fluid from at least one of the wheel brake cylinders 88a, 88b, 90a and 90b (of a locked wheel) into the brake fluid reservoir 80.

[0053] It is also noted that brake fluid forced out of the master brake cylinder 70 can also be moved via the at least one second valve 124a and 124b into the connected brake circuit 86 and 90, and subsequently (bypassing the at least one wheel brake cylinder 88a, 88b, 90a and 90b of the respective brake circuit 86 and 90) via the at least one first valve 120a and 120b into the brake fluid reservoir 80.

[0054] Fig. Figure 3 shows a flowchart to explain one embodiment of the method for operating a vehicle's braking system.

[0055] The method described below can be carried out, for example, with the braking system explained above. However, it should be noted that the feasibility of the method is not limited to the use of such a braking system. Instead, the method can be carried out with any braking system of a vehicle / motor vehicle that has at least two wheel brake cylinders, to which a first valve and a second valve are connected via a branching, valve-free line path per wheel brake cylinder, wherein the at least two wheel brake cylinders are hydraulically connected via at least their first valves to a master brake cylinder of the braking system and via their second valves to a motorized piston-cylinder device of the braking system.

[0056] In process step S1, at least one brake pressure in at least one of the at least two wheel brake cylinders (with the first and second valves) is varied by controlling the at least one associated second valve (of the wheel brake cylinder with the brake pressure to be varied) into an at least partially open state and by actuating a motor of the motorized piston-cylinder device to move brake fluid between the motorized piston-cylinder device and the at least one wheel brake cylinder (with the brake pressure to be varied). In particular, each brake pressure in each wheel brake cylinder of the brake system, all of which are connected to the one first valve and the one second valve via the one branching valve-free line path per wheel brake cylinder, can be individually increased or decreased by operating the motor of the motorized piston-cylinder device.

[0057] Optionally, a process step S2 is also performed in the procedure. In process step S2, brake fluid from at least one of the at least two wheel brake cylinders (with the first and second valves) is drained via at least one associated second valve into a hydraulically connected brake fluid reservoir of the brake system. In this way, a lockup of at least one associated wheel can be quickly cleared. Alternatively, to clear the lockup, brake fluid can also be drawn from the respective at least one wheel brake cylinder into the motorized piston-cylinder device. Thus, the procedure described here also offers all the advantages already mentioned above.

Claims

[1] Braking system for a vehicle with: a master brake cylinder (70); a motorized piston-cylinder device (106); and at least two wheel brake cylinders (88a, 88b, 92a, 92b), to which a first valve (94a, 94b, 96a, 96b) and a second valve (98a, 98b, 100a, 100b) are connected via a branching valve-free line path (102a, 102b, 104a, 104b) per wheel brake cylinder (88a, 88b, 92a, 92b), wherein the at least two wheel brake cylinders (88a, 88b, 92a, 92b) are hydraulically connected to the master brake cylinder (70) via at least their first valves (94a, 94b, 96a, 96b) in such a way that brake fluid from the master brake cylinder (70) flows through at least the at least partially open first valves (94a, 94b, 96a, 96b) into the at least two wheel brake cylinders (88a, 88b, 92a, 92b), and wherein the at least two wheel brake cylinders (88a, 88b, 92a, 92b) are hydraulically connected to the motorized piston-cylinder device (106) in such a way,that brake fluid can be displaced between the motorized piston-cylinder device (106) and the at least two wheel brake cylinders (88a, 88b, 92a, 92b) by means of the operation of a motor (112) of the motorized piston-cylinder device (106); characterized by , that Each of the at least two wheel brake cylinders (88a, 88b, 92a, 92b) is hydraulically connected to the motorized piston-cylinder device (106) via the respective second valve (98a, 98b, 100a, 100b). [2] Brake system according to claim 1, wherein the at least two wheel brake cylinders (88a, 88b, 92a, 92b) are hydraulically connected to a brake fluid reservoir (80) of the brake system via at least their first valves (94a, 94b, 96a, 96b) in such a way that brake fluid from the at least two wheel brake cylinders (88a, 88b, 92a, 92b) can be drained into the brake fluid reservoir (80) via the at least partially open first valves (94a, 94b, 96a, 96b). [3] Brake system according to claim 2, wherein the first valves (94a, 94b, 96a, 96b) are hydraulically connected to the brake fluid reservoir (80) via at least one first separating valve (120a, 120b). [4] Brake system according to one of the preceding claims, wherein the first valves (94a, 94b, 96a, 96b) are hydraulically connected to the master brake cylinder (70) via at least one second isolating valve (124a, 124b). [5] Brake system according to one of the preceding claims, wherein each of the first valves (94a, 94b, 96a, 96b) is a check valve-less 2-way valve (94a, 94b, 96a, 96b). [6] Brake system according to one of the preceding claims, wherein each of the second valves (98a, 98b, 100a, 100b) is a check valve-less 2-way valve (98a, 98b, 100a, 100b). [7] Brake system according to one of the preceding claims, wherein the second valves (98a, 98b, 100a, 100b) are hydraulically connected to the motorized piston-cylinder device (106) via a valveless line path (116) which begins at the motorized piston-cylinder device (106) and ends at the respective second valve (98a, 98b, 100a, 100b). [8] Brake system according to one of the preceding claims, wherein each of the wheel brake cylinders (88a, 88b, 92a, 92b) of the brake system has a first valve (94a, 94b, 96a, 96b) and a second valve (98a, 98b, 100a, 100b) connected via the branching valve-free line path (102a, 102b, 104a, 104b) per wheel brake cylinder (88a, 88b, 92a, 92b), whereby each brake pressure in each wheel brake cylinder (88a, 88b, 92a, 92b) of the brake system can be selectively increased or decreased by means of operation of the motor (112) of the motorized piston-cylinder device (106). [9] Method for operating a braking system of a vehicle according to any one of the preceding claims 1 to 8, comprising at least two wheel brake cylinders (88a, 88b, 92a, 92b), to which a first valve (94a, 94b, 96a, 96b) and a second valve (98a, 98b, 100a, 100b) are connected via a branching valve-free line path (102a, 102b, 104a, 104b) per wheel brake cylinder (88a, 88b, 92a, 92b), wherein the at least two wheel brake cylinders (88a, 88b, 92a, 92b) are connected via at least their first valves (94a, 94b, 96a, 96b) to a master brake cylinder (70) of the braking system and via their second valves (98a, 98b, 100a, 100b) are hydraulically connected to a motorized piston-cylinder device (106) of the brake system, with the step: Varying at least one brake pressure in at least one wheel brake cylinder (88a, 88b, 92a, 92b) of the at least two wheel brake cylinders (88a, 88b, 92a, 92b) by controlling the at least one associated second valve (98a, 98b, 100a, 100b) into an at least partially open state and controlling a motor (112) of the motorized piston-cylinder device (106) for moving brake fluid between the motorized piston-cylinder device (106) and the at least one wheel brake cylinder (88a, 88b, 92a, 92b) (S1). [10] Method according to claim 9, wherein brake fluid from at least one wheel brake cylinder (88a, 88b, 92a, 92b) of the at least two wheel brake cylinders (88a, 88b, 92a, 92b) is drained via at least one associated first valve (94a, 94b, 96a, 96b) into a hydraulically connected brake fluid reservoir (80) of the brake system (S2). [11] Method according to claim 9 or 10, wherein each brake pressure in each wheel brake cylinder (88a, 88b, 92a, 92b) of the brake system, each of which is connected to the one first valve (94a, 94b, 96a, 96b) and the one second valve (98a, 98b, 100a, 100b) via the one branching valve-free line path (102a, 102b, 104a, 104b) per wheel brake cylinder (88a, 88b, 92a, 92b), is selectively increased or decreased by means of an operation of the motor (112) of the motorized piston-cylinder device (106).

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