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 (10), a brake fluid reservoir (12); a first brake circuit (16) hydraulically connected at least to the master brake cylinder (10); and a second brake circuit (18) hydraulically connected to the master brake cylinder (10) and the brake fluid reservoir (12); characterized by the fact that a first wheel brake cylinder (20) of the brake system assigned to the first brake circuit (16) via at least a first isolating valve (28) and a second wheel brake cylinder (22) of the brake system assigned to the second brake circuit (18) via at least a second isolating valve (30) are connected to the master brake cylinder (10); the first wheel brake cylinder (20) assigned to the first brake circuit (16) is connected to the brake fluid reservoir (12) via at least one first continuously adjustable valve (32) and the second wheel brake cylinder (22) assigned to the second brake circuit (18) is connected to the brake fluid reservoir (12) via at least one second continuously adjustable valve (34); and a third wheel brake cylinder (24) of the brake system assigned to the first brake circuit (16) via at least a first switching valve (36) and a first high-pressure switching valve (38) and a fourth wheel brake cylinder (26) of the brake system assigned to the second brake circuit (18) via at least a second switching valve (40) and a second high-pressure switching valve (42) are connected to the master brake cylinder (10).

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] German patent application DE 10 2009 001 401 A1 describes a braking system for a vehicle, a method for operating a braking system for a vehicle, and a manufacturing method for a braking system for a vehicle. The respective braking system comprises a first brake circuit connected to a master brake cylinder and a second brake circuit connected to the master brake cylinder and a brake fluid reservoir. Both the first and second brake circuits have two wheel brake cylinders. Furthermore, the first brake circuit includes a changeover valve and a high-pressure switching valve, while the second brake circuit is connected to the master brake cylinder via a separating valve and to the brake fluid reservoir via a continuously adjustable valve.

[0003] Disclosures DE 10 2010 030 921 A 1 and DE 10 2011 005 822 A1 both disclose brake systems for a vehicle. Disclosure of the invention

[0004] 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 8. Advantages of the invention

[0005] The present invention provides possibilities for implementing braking systems in which the driver can directly apply the brakes to the third and fourth wheel cylinders by actuating a brake actuator connected to a master cylinder of the respective braking system. The driver thus experiences a standard counterforce while actuating the brake actuator. Simultaneously, due to the ability to isolate the first and second wheel cylinders (by closing the first and second isolating valves), brake fluid displacement from the master cylinder to the first and second wheel cylinders is prevented, even under strong actuation of the brake actuator.As explained in more detail below, the brake pressure present in at least one of the first wheel brake cylinders and / or the second wheel brake cylinders can therefore be adjusted independently of an internal pressure in the master brake cylinder or an actuation of the brake actuation element.

[0006] The present invention also provides braking systems that are advantageously usable for a vehicle with an X-brake circuit layout. This allows the advantages described in the preceding paragraph to also be utilized for this type of vehicle / motor vehicle.

[0007] In an advantageous embodiment of the brake system, a first supply line of the brake system runs from a first pressure chamber of the master cylinder to the first isolating valve, and the first changeover valve and the first high-pressure switching valve are connected in parallel to each other at a first branch point located in the first supply line. Alternatively or additionally, a second supply line of the brake system can also run from a second pressure chamber of the master cylinder to the second isolating valve, and the second changeover valve and the second high-pressure switching valve can be connected in parallel to each other at a second branch point located in the second supply line. In both cases, it is possible to increase the brake pressure present in at least one of the wheel cylinders and / or the second wheel cylinder by operating the first pump and / or the second pump.

[0008] In particular, with this type of brake system design, brake force amplification can be achieved by operating the first and / or second pump without a (conventional) brake booster. This eliminates the need to equip the respective brake system with a brake booster, such as a vacuum brake booster. The elimination of the vacuum brake booster also removes the need to generate a vacuum in at least one pressure chamber of the vacuum brake booster by operating the combustion engine of the vehicle equipped with this brake system. Therefore, the vehicle equipped with this brake system can also use an electric motor instead of the combustion engine and easily do without a mechanical vacuum pump.

[0009] In a further advantageous embodiment of the brake system, a first intake line of the brake system runs from the brake fluid reservoir to the first continuously adjustable valve, and an intake side of a first pump of the brake system is connected to a third branch point located in the first intake line. Likewise, a second intake line of the brake system can also run from the brake fluid reservoir to the second continuously adjustable valve, and an intake side of a second pump of the brake system can be connected to a fourth branch point located in the second intake line.

[0010] Advantageously, a first line can run from the first isolating valve to the first wheel brake cylinder, and a delivery side of the first pump and the first continuously adjustable valve can be connected to this first line. Similarly, it is advantageous if a second line runs from the second isolating valve to the second wheel brake cylinder, and a delivery side of the second pump and the second continuously adjustable valve are connected to this second line.

[0011] Preferably, a first wheel inlet valve and a first wheel outlet valve are connected to the third wheel brake cylinder. Similarly, a second wheel inlet valve and a second wheel outlet valve can be connected to the fourth wheel brake cylinder.

[0012] In a further advantageous embodiment, a first storage chamber of the brake system is connected to the third wheel brake cylinder via the first wheel outlet valve and to the first high-pressure switching valve via a first pressure relief valve. Similarly, it is also advantageous if a second storage chamber of the brake system is connected to the fourth wheel brake cylinder via the second wheel outlet valve and to the second high-pressure switching valve via a second pressure relief valve.

[0013] Furthermore, an intake side of a third pump of the brake system can be connected to the first pressure relief valve and the first high-pressure switching valve, and a delivery side of the third pump can be connected to the first changeover valve and the first wheel inlet valve. In a further advantageous embodiment, an intake side of a fourth pump of the brake system is connected to the second pressure relief valve and the second high-pressure switching valve, and a delivery side of the fourth pump is connected to the second changeover valve and the second wheel inlet valve.

[0014] A corresponding method for operating a vehicle's braking system also provides the advantages described above. This method for operating a vehicle's braking system can be further developed according to the braking system embodiments described above. Brief description of the drawings

[0015] Further features and advantages of the present invention are explained below with reference to the figures. They show: Fig. 1 a schematic representation of an embodiment of the braking system; and Fig. 2. A flowchart to explain one embodiment of the method for operating a vehicle's braking system. Embodiments of the invention

[0016] Fig. Figure 1 shows a schematic representation of one embodiment of the braking system.

[0017] The in Fig. The braking system shown schematically can be used in a vehicle, such as an electric or hybrid vehicle. It should be noted that the application of the braking system is not limited to a specific vehicle type. Although the braking system described below is particularly advantageous in a vehicle with an X-brake circuit layout, the advantages described below are also realized in a vehicle with a parallel brake circuit layout.

[0018] The in Fig. A schematically represented brake system comprises a master brake cylinder 10 and a brake fluid reservoir 12. The brake fluid reservoir 12 is a volume of the brake system in which (generally) atmospheric pressure is present. The brake fluid reservoir 12 can be connected to the master brake cylinder 10, for example, via at least one vent hole. A brake actuation element 14, such as a brake pedal, can also be connected (directly or indirectly) to the master brake cylinder 10. The design of the brake system is not limited to a specific type of brake actuation element.

[0019] The braking system has two brake circuits 16 and 18 and four wheel brake cylinders 20 to 26. A first wheel brake cylinder 20 of the braking system, assigned to a first brake circuit 16, is connected to the master brake cylinder 10 via at least one first isolating valve 28. A second wheel brake cylinder 22 of the braking system, assigned to a second brake circuit 18, is also connected to the master brake cylinder via at least one second isolating valve 30. Furthermore, the first wheel brake cylinder 20 assigned to the first brake circuit 16 is connected to the brake fluid reservoir 12 via at least one first continuously adjustable valve 32, and the second wheel brake cylinder 22 assigned to the second brake circuit 18 is connected to the brake fluid reservoir 12 via at least one second continuously adjustable valve 34. In contrast, a third wheel brake cylinder 24 of the braking system, assigned to the first brake circuit 16, is connected to the master brake cylinder 10 via at least one first switching valve 36 and a first high-pressure switching valve 38.Accordingly, a fourth wheel brake cylinder 26 assigned to the second brake circuit 18 is also connected to the master brake cylinder 10 via at least a second switching valve 40 and a second high-pressure switching valve 42.

[0020] Advantageously, this indicates Fig. The brake system shown in Figure 1 features a parallel arrangement of the first brake circuit 16 and the second brake circuit 18. This facilitates the use of the brake system for a vehicle with an X-shaped brake circuit configuration. For this purpose, the first wheel brake cylinder 20, assigned to the first brake circuit 16, and the second wheel brake cylinder 22, assigned to the second brake circuit 18, can be arranged on a common axle of the vehicle. Preferably, the common axle of the first wheel brake cylinder 20 and the second wheel brake cylinder 22 is a front axle of the vehicle. Alternatively, the first wheel brake cylinder 20 and the second wheel brake cylinder 22 can also be located together on a rear axle of the vehicle.

[0021] By closing the first isolating valve 28 and / or the second isolating valve 30, the transfer of brake fluid from the master brake cylinder 10 to the first wheel brake cylinder 20 assigned to the first brake circuit 16 and / or to the second wheel brake cylinder 22 assigned to the second brake circuit 18 can be reliably prevented, even if the brake actuation element 14 is actuated by the driver. This can also be described as the first wheel brake cylinder 20 and / or the second wheel brake cylinder 22 being decoupled from the master brake cylinder 10 by closing the first isolating valve 28 and / or the second isolating valve 30.This ensures that the brake pressure present in the first wheel brake cylinder 20 and / or the second wheel brake cylinder 22 can be determined independently of the internal pressure in the master brake cylinder 10 and / or the actuation of the brake actuating element 14. In particular, the brake pressure present in the first wheel brake cylinder 20 and / or the second wheel brake cylinder 22 can be reduced by at least temporarily opening the first continuously adjustable valve 32 (while simultaneously keeping the first isolating valve 28 closed) and / or by at least temporarily opening the second continuously adjustable valve 34 (while simultaneously keeping the second isolating valve 30 closed).The ability to reduce the brake pressure present in at least one of the first wheel brake cylinders 20 and / or in the second wheel brake cylinder 22 can be used, in particular, to mask a generator braking torque of a generator (not shown). The [missing information] Fig. The braking system shown in Figure 1 can therefore be used particularly advantageously in a vehicle for regenerative braking. Above all, the braking system ensures that, despite at least temporary use of the generator employed for regenerative braking, the driver's braking request, specified by actuating the brake actuation element 14, is not exceeded. The braking system thus increases the driving comfort of its user during regenerative braking and encourages the purchase of an energy-efficient and low-emission vehicle.

[0022] Simultaneously, the braking system ensures that the user can apply the brakes by actuating the brake actuator 14 via at least the valves 36, 38, 40, and 42 into the third wheel brake cylinder 24, which is assigned to the first brake circuit 16, and into the fourth wheel brake cylinder 26, which is assigned to the second brake circuit 18. Thus, even after disconnecting the first wheel brake cylinder 20 and / or the second wheel brake cylinder 22, the driver still experiences a standard brake feel (pedal feel) while actuating the brake actuator 14. Equipping the braking system with a simulator (pedal simulator) is therefore unnecessary. Instead, the third wheel brake cylinder 24 and the fourth wheel brake cylinder 26 simultaneously perform a braking function and a "simulator function."Due to the multifunctionality of the third wheel brake cylinder 24 and the fourth wheel brake cylinder 26, the need to equip the braking system with a simulator is eliminated, thus reducing the weight of the braking system and saving installation space on the equipped vehicle. Additionally, the costs of the simulator are eliminated during the manufacturing process. Fig. 1 brake system shown.

[0023] In the embodiment of the Fig. A first supply line 44 of the brake system runs from a first pressure chamber of the master brake cylinder 10 to the first isolating valve 28. The first changeover valve 36 and the first high-pressure switching valve 38 are connected parallel to each other at a first branch point 46 located in the first supply line 44. For example, a branching intermediate line 48 can extend from the first branch point 46 to the first changeover valve 36 and the first high-pressure switching valve 38. A second supply line 50 of the brake system leads from a second pressure chamber of the master brake cylinder 10 to the second isolating valve 30. The second changeover valve 40 and the second high-pressure switching valve 42 are connected parallel to each other at a second branch point 52 located in the second supply line 50.A branching intermediate line 54 can also extend from the second branch point 52 to the second changeover valve 40 and to the second high-pressure switching valve 42. This reliably ensures that neither the closing of the first isolating valve 28 impairs the transfer of brake fluid from the master brake cylinder 10 to the first changeover valve 36 or the first high-pressure switching valve 38, nor that closing the second isolating valve 30 prevents the transfer of brake fluid from the master brake cylinder 10 to the second changeover valve 40 or the second high-pressure switching valve 42.

[0024] Preferably, the brake system also has a first intake line 56 extending from the brake fluid reservoir 12 to the first continuously adjustable valve 32. Furthermore, the brake system can have a first pump 58 whose intake side is connected to a third branch point 60 located in the first intake line 56. It is also advantageous if a second intake line 62 of the brake system extends from the brake fluid reservoir 12 to the second continuously adjustable valve 34, and an intake side of a second pump 64 of the brake system is connected to a fourth branch point 66 located in the second intake line 62. In this case, the first pump 58 and / or the second pump 64 enable an increase in the brake pressure present in at least one of the first wheel brake cylinders 20 and / or the second wheel brake cylinder 22.The brake pressure increase in the first wheel brake cylinder 20 and / or the second wheel brake cylinder 22, which can be achieved by operating the first pump 58 and / or the second pump 64, can be used, for example, to mask a decreasing generator braking torque over time.

[0025] The achievable increase in brake pressure can also be used to amplify the braking force. While the driver applies the brakes without amplification to the third wheel cylinder 24 and the fourth wheel cylinder 26 by actuating the brake actuating element 14, the braking pressure present in the first wheel cylinder 20 and / or the second wheel cylinder 22 can be significantly increased (after closing the first isolating valve 28 and / or the second isolating valve 30) by operating the first pump 58 and / or the second pump 64, building up the brake pressure present in the first wheel cylinder 20 and / or the second wheel cylinder 22 to a level significantly higher than the pressure build-up in the third wheel cylinder 24 and / or the fourth wheel cylinder 26. Therefore, equipping the braking system with a brake booster, such as a vacuum brake booster, is unnecessary. Instead, the first pump 58 and / or the second pump 64 can fully perform the function of the omitted brake booster.In particular, despite the comparatively large increase in brake pressure in the first wheel brake cylinder 20 and / or in the second wheel brake cylinder 22, the driver only has to apply a comparatively small driver braking force to the brake actuation element 14.

[0026] Eliminating the need for a brake booster, particularly a vacuum brake booster, from the braking system not only reduces installation space, weight, and manufacturing costs. More importantly, the brake booster-free system ensures a pleasant brake feel (pedal feel) for the driver even when the vehicle equipped with this system does not have an internal combustion engine or when the engine is not in use for extended periods. Since the braking system does not require a vacuum brake booster to guarantee good brake feel, the need for a vacuum supply is also eliminated. Furthermore, the advantageous design of the braking system allows for the elimination of a mechanical vacuum pump, which is still commonly required in vehicles and whose emissions are negatively impacted.

[0027] The braking system of Fig. 1. A first line 68 runs from the first isolating valve 28 to the first wheel brake cylinder 20. A delivery side of the first pump 58 and the first continuously adjustable valve 32 are connected to the first line 68. For example, an intermediate line 70 branches off to the delivery side of the first pump 58 and the first continuously adjustable valve 32, with the intermediate line 70 opening into the first line 68. Similarly, the brake system also has a second line 72, which runs from the second isolating valve 30 to the second wheel brake cylinder 22. A delivery side of the second pump 64 and the second continuously adjustable valve 34 are connected to the second line 72. This is also possible via an intermediate line 74 that branches off to the second pump 64 and the second continuously adjustable valve 34 and opens into the second line 72.

[0028] The braking system can also have a first wheel inlet valve 76 and a first wheel outlet valve 78, which are connected to the third wheel brake cylinder 24 (for example, via a branching intermediate line 80). Similarly, a second wheel inlet valve 82 and a second wheel outlet valve 84 can be connected to the fourth wheel brake cylinder 26 (e.g., via a branching intermediate line 86). For a vehicle axle equipped with the third wheel brake cylinder 24 and the fourth wheel brake cylinder 26, a conventional brake pressure control system is thus possible using the wheel inlet valves 76 and 82 and the wheel outlet valves 78 and 84. In particular, ABS control is easily implemented on the respective axle. (A conventional ESP function is also possible due to the respective vehicle axle being equipped with the changeover valves 36 and 40 and the high-pressure switching valves 38 and 42.)

[0029] In the embodiment of the Fig. 1. A first storage chamber 88 of the brake system is also connected via the first wheel outlet valve 78 to the third wheel brake cylinder 24 and via a first pressure relief valve 90 to the first high-pressure switching valve 38. For example, an intermediate line 92, in which the first pressure relief valve 90 is installed, extends from the first high-pressure switching valve 38 to the first wheel outlet valve 78. The first storage chamber 88 can be connected to a branch point 94 located in the intermediate line 92. Accordingly, the brake system of Fig. 1. A second storage chamber 96 is also provided, which is connected to the fourth wheel brake cylinder 26 via the second wheel outlet valve 84 and to the second high-pressure switching valve 42 via a second pressure relief valve 98. An intermediate line 100 with the inserted second pressure relief valve 98 can also extend from the second high-pressure switching valve 42 to the second wheel outlet valve 84, with the second storage chamber 96 being connected to a branch point 101 located in the intermediate line 100.

[0030] Furthermore, the braking system... Fig. 1. A suction side of a third pump 102 of the brake system is connected to the first pressure relief valve 90 and to the first high-pressure switching valve 38. A delivery side of the third pump 102 is connected to the first changeover valve 36 and to the first wheel inlet valve 76. The third pump 102 can be inserted into an intermediate line 104, which opens into the intermediate line 92 on one side and whose other side is connected at a branch point 106 to an intermediate line 108 from the first changeover valve 36 to the first wheel inlet valve 76. A suction side of a fourth pump 110 of the brake system is connected to the brake system of the Fig. 1 is connected to the second pressure relief valve 98 and the second high-pressure switching valve 42. One delivery side of the fourth pump 110 is hydraulically connected to the second changeover valve 40 and the second wheel inlet valve 82, or to an intermediate line 112 extending from the second changeover valve 40 to the second wheel inlet valve 82. For example, the fourth pump 110 is inserted into an intermediate line 114, which opens into the intermediate line 100 on one side and into the intermediate line 112 on the other.

[0031] In the embodiment of the Fig. The four pumps 58, 64, 102, and 110 of the brake system are connected to a common shaft 116 of a pump motor 118. Therefore, equipping the brake system with multiple pump motors is not necessary. The four pumps 58, 64, 102, and 110 are each designed as a single-piston pump by way of example. The brake system of Fig. 1 can therefore be described as a four-piston ESP system. However, it should be noted that the configuration of the brake system is not limited to a specific pump type. For pumps 58, 64, 108, and 110, at least one pump with a different number of pistons, at least one asymmetric pump, and / or at least one gear pump can therefore be used.

[0032] For example, the braking system of the Fig. 1. A pre-pressure sensor 120 connected to the first brake circuit 16 and a pressure sensor 122 each connected to the first wheel brake cylinder 20 and the second wheel brake cylinder 22. However, the configuration of the brake system is not limited to a specific set of pre-pressure sensors 120 or pressure sensors 122. To detect a driver's braking request, or the force with which the driver actuates the brake actuator 14, at least one additional brake actuator sensor 124 can be used in the brake system. This at least one brake actuator sensor 124 can be, for example, a pedal travel sensor, a differential travel sensor, and / or a rod travel sensor. Detection of the driver's braking request via a different type of sensor is also possible.

[0033] During operation of the braking system, a target braking torque can be set by means of the brake actuation element sensor 124 based on the actuation force of the brake actuation element 14. To achieve the target braking torque desired by the driver, the first isolating valve 28 and / or the second isolating valve 30 can be closed, so that, by operating the first pump 58 and / or the second pump 64, brake pressure can be built up in the first wheel brake cylinder 20 and / or in the second wheel brake cylinder 22 until the specified target braking torque is applied to the assigned wheels by means of the four wheel brake cylinders 20, 22, 24 and 26 as a sum. Since the driver moves brake fluid into the third wheel brake cylinder 24 and the fourth wheel brake cylinder 26 by actuating the brake actuation element 14 during the process described here, he continues to have a standard brake actuation feel (pedal feel).At the same time, a brake force increase can be achieved by making the brake pressure build-up in the first wheel brake cylinder 20 and / or the second wheel brake cylinder 22 significantly higher than the pressure caused by the driver's braking force in the third wheel brake cylinder 24 and in the fourth wheel brake cylinder 26.

[0034] During deceleration, the driver can transfer a volume of brake fluid from the third wheel cylinder 24 and the fourth wheel cylinder 26 back into the master cylinder 10. Similarly, the first continuously adjustable valve 28 and / or the second continuously adjustable valve 30 can also reduce brake pressure in the first wheel cylinder 20 and / or the second wheel cylinder 22. The driver therefore does not perceive that, in addition to the brake fluid transfer directly caused by the driver's braking force between the master cylinder 10, the third wheel cylinder 24, and the fourth wheel cylinder 26, further brake fluid transfers occur within the braking system.

[0035] In an emergency braking situation, e.g., in the event of panic braking and the associated very rapid actuation of the brake actuator 14 by the driver, the isolating valves 28 and 30 can be kept open. This allows the driver to quickly apply the brakes by displacing the fluid volume from the master brake cylinder 10 to the first wheel brake cylinder 20 and the second wheel brake cylinder 22. Therefore, it is not necessary to design the first pump 58 and the second pump 64 for rapid fluid delivery in an emergency braking situation. Instead, cost-effective models can be used for pumps 58 and 64.

[0036] For example, the at least one brake actuation element sensor 124 can be used to investigate whether actuation of the brake actuation element 14 indicates an emergency braking situation / panic braking. In particular, an entry gradient executed during actuation of the brake actuation element 14 can be examined. At least one environmental sensor can also be used to detect an emergency braking situation. In the event of an emergency braking situation / panic braking, the isolating valves 28 and 30 can remain in their open state. This allows the braking system to optimally utilize the driver's dynamics under high-speed braking demands. Despite limited pump dynamics due to cost-effective pump models, high braking dynamics can still be achieved.After a certain time or when a predetermined braking torque is reached, the isolating valves 28 and 30 can be closed, so that a further pressure increase can be achieved by means of the first pump 58 and the second pump 64.

[0037] ABS control can be achieved conventionally via the wheel inlet valves 76 and 82 and via the wheel outlet valves 78 and 84. ABS control for an axle with the first wheel brake cylinder 20 and the second wheel brake cylinder 22 can also be achieved via the continuously adjustable valves 32 and 34 by releasing brake fluid into the brake fluid reservoir 12. Thus, advantageous ABS control performance (comparable to a conventional braking system) is also possible with the braking system of the Fig. 1 created.

[0038] Vehicle stabilization via individual wheel braking interventions is possible at wheel brake cylinders 24 and 26 using the standard ESP modulation system. Stabilization interventions at wheel brake cylinders 20 and 22 are possible with separating valves 28 and 30 closed, using continuously adjustable valves 32 and 34 and pumps 58 and 64 (as in a conventional braking system).

[0039] Active pressure build-up capability is possible via the changeover valves 36 and 40 and the high-pressure switching valves 38 and 42. Likewise, the continuously adjustable valves 32 and 34 can be used for drive slip control (for both axles). The braking system of the Fig. The system is therefore suitable for front-, rear-, and all-wheel-drive vehicles without any functional disadvantages. Semi-active functions, combining driver input with support from the modulation unit, are also possible thanks to the classic valve arrangements. All known semi-active functions can thus be implemented without any functional limitations.

[0040] If regenerative braking can be performed using the generator, brake fluid can be drained into the brake fluid reservoir 12 via the continuously adjustable valves 32 and 34 (with the separating valves 28 and 30 closed), and a corresponding braking torque can be requested from the generator. During regenerative braking, the driver retains a standard brake feel (pedal feel) due to the connection to the third wheel brake cylinder 24 and the fourth wheel brake cylinder 26. Because of the significant over-braking of the wheel brake cylinders 20 and 22, a comparatively large, dissipable hydraulic braking torque is available for recuperative braking. High regenerative efficiency is thus ensured.

[0041] Preferably, valves 28, 30, 36, 40, 76 and / or 82 are normally open valves. Valves 38, 42, 78 and / or 84 are preferably normally closed. This allows the driver to apply the brakes without amplification to all wheel brake cylinders 20 to 26 as a mechanical fallback (when the valves are de-energized), thus achieving a sufficient minimum deceleration.

[0042] The braking system of the Fig. 1 thus combines the advantages of a pleasant brake feel (pedal feel), low manufacturing costs, low weight, small installation space requirement, high safety, and suitability for X-brake circuit distribution. The brake system can also be designed as a compact component.

[0043] Fig. Figure 2 shows a flowchart to explain one embodiment of the method for operating a vehicle's braking system.

[0044] The procedure described below can be carried out, for example, using the braking system described above. However, the feasibility of the procedure is not limited to precisely this type of braking system.

[0045] In process step S1, the displacement of brake fluid from a master brake cylinder of the brake system to a first wheel brake cylinder of the brake system, which is assigned to a first brake circuit of the brake system, and to a second wheel brake cylinder of the brake system, which is assigned to a second brake circuit of the brake system, is prevented during the actuation of a brake actuation element connected to the master brake cylinder. This is achieved by closing a first isolating valve, through which the first wheel brake cylinder is connected to the master brake cylinder, and closing a second isolating valve, through which the second wheel brake cylinder is connected to the master brake cylinder.The brake pressure present in at least one of the first and / or second wheel cylinders can therefore be adjusted independently of the master cylinder's internal pressure and the driver's actuation of the brake actuator. The procedure steps for adjusting the brake pressure present in at least one of the first and / or second wheel cylinders are described below.

[0046] Simultaneously with process step S1, a process step S2 is executed. In process step S2, a first switching valve and a first high-pressure switching valve, via which a third wheel brake cylinder of the brake system assigned to the first brake circuit is connected to the master brake cylinder, and a second switching valve and a second high-pressure switching valve, via which a fourth wheel brake cylinder of the brake system assigned to the second brake circuit is connected to the master brake cylinder, are controlled in such a way that a volume of brake fluid forced out of the master brake cylinder by means of actuation of the brake actuation element is at least partially shifted into the third wheel brake cylinder and into the fourth wheel brake cylinder.Despite the decoupling of the first and second wheel cylinders from the master cylinder (achieved by process step S1), the driver still experiences a standard brake feel (pedal feel) while operating the brake actuator. In particular, the driver does not notice the adjustment of the brake pressure present in at least one of the first and / or second wheel cylinders, independent of the master cylinder's internal pressure and the actuation of the brake actuator.

[0047] For example, in process step S3, which is executed during process steps S1 and S2, the brake pressure in the first wheel brake cylinder and / or in the second wheel brake cylinder can be reduced during actuation of the brake actuation element. This is possible by at least temporarily opening a first continuously adjustable valve, through which the first wheel brake cylinder is connected to a brake fluid reservoir of the brake system (while the first isolating valve is kept closed), and / or by at least temporarily opening a second continuously adjustable valve, through which the second wheel brake cylinder is connected to the brake fluid reservoir (while the second isolating valve is kept closed).By reducing the brake pressure in the first wheel brake cylinder and / or in the second wheel brake cylinder, for example, a generator braking torque that increases over time can be masked for the recuperative braking of the vehicle equipped with the braking system.

[0048] As an alternative or supplement to process step S3, process step S4 can also be executed during process steps S1 and S2. In process step S4, the brake pressure in the first wheel brake cylinder and / or the second wheel brake cylinder is increased during actuation of the brake actuator. This is achieved by operating a first pump of the brake system, whose suction side is connected to the brake fluid reservoir (while the first isolating valve is kept closed), and / or by operating a second pump of the brake system, whose suction side is connected to the brake fluid reservoir (while the second isolating valve is kept closed). By increasing the brake pressure in the first wheel brake cylinder and / or the second wheel brake cylinder, a decreasing generator braking torque can, for example, be masked.Furthermore, process step S4 can also be used for brake force amplification. While the driver (due to process step S2) applies the brakes without amplification to the third and fourth wheel cylinders, process step S4 in this case builds up a significantly increased brake pressure in the first and / or second wheel cylinders. Process step S4 thus makes brake force amplification possible in a braking system without a brake booster.

[0049] Optionally, a process step S0 can be executed before process steps S1 and S2. In process step S0, it can be determined whether an emergency braking situation exists (during the driver's actuation of the brake actuator). If an emergency braking situation is detected, the first and second isolating valves can be controlled to their open state in process step S5. The driver's rapid braking dynamics in the emergency braking situation can thus also be used to build up brake pressure in the first and second wheel cylinders. This means that only if no emergency braking situation is detected is the transfer of brake fluid from the master cylinder to the first and second wheel cylinders prevented during actuation of the brake actuator by means of process step S1.

Claims

[1] Braking system for a vehicle, with a master brake cylinder (10), a brake fluid reservoir (12); a first brake circuit (16) hydraulically connected at least to the master brake cylinder (10); and a second brake circuit (18) hydraulically connected to the master brake cylinder (10) and the brake fluid reservoir (12); characterized by , that a first wheel brake cylinder (20) of the brake system assigned to the first brake circuit (16) via at least a first isolating valve (28) and a second wheel brake cylinder (22) of the brake system assigned to the second brake circuit (18) via at least a second isolating valve (30) are connected to the master brake cylinder (10); the first wheel brake cylinder (20) assigned to the first brake circuit (16) is connected to the brake fluid reservoir (12) via at least one first continuously adjustable valve (32) and the second wheel brake cylinder (22) assigned to the second brake circuit (18) is connected to the brake fluid reservoir (12) via at least one second continuously adjustable valve (34); and a third wheel brake cylinder (24) of the brake system assigned to the first brake circuit (16) via at least a first switching valve (36) and a first high-pressure switching valve (38) and a fourth wheel brake cylinder (26) of the brake system assigned to the second brake circuit (18) via at least a second switching valve (40) and a second high-pressure switching valve (42) are connected to the master brake cylinder (10). [2] Brake system according to claim 1, wherein a first supply line (44) of the brake system runs from a first pressure chamber of the master brake cylinder (10) to the first isolating valve (28) and the first switching valve (36) and the first high-pressure switching valve (38) are connected parallel to each other at a first branching point (46) located in the first supply line (44), and / or a second supply line (50) of the brake system runs from a second pressure chamber of the master brake cylinder (10) to the second isolating valve (30) and the second switching valve (40) and the second high-pressure switching valve (42) are connected parallel to each other at a second branching point (52) located in the second supply line (50). [3] Brake system according to claim 1 or 2, wherein a first suction line (56) of the brake system extends from the brake fluid reservoir (12) to the first continuously adjustable valve (32) and a suction side of a first pump (58) of the brake system is connected to a third branch point (60) located in the first suction line (56), and / or a second suction line (62) of the brake system extends from the brake fluid reservoir (12) to the second continuously adjustable valve (34) and a suction side of a second pump (64) of the brake system is connected to a fourth branch point (66) located in the second suction line (62). [4] Brake system according to claim 3, wherein a first line (68) runs from the first isolating valve (28) to the first wheel brake cylinder (20) and a delivery side of the first pump (58) and the first continuously adjustable valve (32) are connected to the first line (68), and / or a second line (72) runs from the second isolating valve (30) to the second wheel brake cylinder (22) and a delivery side of the second pump (64) and the second continuously adjustable valve (34) are connected to the second line (72). [5] Brake system according to one of the preceding claims, wherein a first wheel inlet valve (76) and a first wheel outlet valve (78) are connected to the third wheel brake cylinder (24), and / or a second wheel inlet valve (82) and a second wheel outlet valve (84) are connected to the fourth wheel brake cylinder (26). [6] Brake system according to claim 5, wherein a first storage chamber (88) of the brake system is connected via the first wheel outlet valve (78) to the third wheel brake cylinder (24) and via a first pressure relief valve (90) to the first high-pressure switching valve (38), and / or a second storage chamber (96) of the brake system is connected via the second wheel outlet valve (84) to the fourth wheel brake cylinder (26) and via a second pressure relief valve (98) to the second high-pressure switching valve (42). [7] Brake system according to claim 6, wherein an intake side of a third pump (102) of the brake system is connected to the first pressure relief valve (90) and to the first high-pressure switching valve (38) and a delivery side of the third pump (102) is connected to the first changeover valve (36) and to the first wheel inlet valve (76), and / or an intake side of a fourth pump (110) of the brake system is connected to the second pressure relief valve (98) and to the second high-pressure switching valve (42) and a delivery side of the fourth pump (110) is connected to the second changeover valve (40) and to the second wheel inlet valve (82). [8] Method for operating a vehicle braking system comprising the steps: Preventing brake fluid displacement from a master brake cylinder (10) of the brake system into a first wheel brake cylinder (20) of the brake system and into a second wheel brake cylinder (22) of the brake system, wherein the first wheel brake cylinder (20) is assigned to a first brake circuit (16) of the brake system and the second wheel brake cylinder (22) is assigned to a second brake circuit (18) of the brake system, during actuation of a brake actuating element (14) connected to the master brake cylinder (10) by closing a first isolating valve (28) through which the first wheel brake cylinder (20) is connected to the master brake cylinder (10) and closing a second isolating valve (30) through which the second wheel brake cylinder (22) is connected to the master brake cylinder (10) (S1); and Controlling a first switching valve (36) and a first high-pressure switching valve (38), via which a third wheel brake cylinder (24) of the brake system assigned to the first brake circuit (16) is connected to the master brake cylinder (10), and a second switching valve (40) and a second high-pressure switching valve (42), via which a fourth wheel brake cylinder (26) of the brake system assigned to the second brake circuit (18) is connected to the master brake cylinder (10), such that a volume of brake fluid forced out of the master brake cylinder (10) by means of actuation of the brake actuation element (14) is at least partially shifted into the third wheel brake cylinder (24) and into the fourth wheel brake cylinder (26) (S2). [9] Method according to claim 8, wherein a brake pressure in the first wheel brake cylinder (20) and / or in the second wheel brake cylinder (22) is reduced during actuation of the brake actuation element (14) by the steps: At least temporary opening of a first continuously adjustable valve (32) through which the first wheel brake cylinder (20) is connected to a brake fluid reservoir (12) of the brake system, while the first isolating valve (28) is kept closed; and / or At least temporarily opening a second continuously adjustable valve (34) via which the second wheel brake cylinder (22) is connected to the brake fluid reservoir (12), while the second separating valve (30) is kept closed (S3). [10] Method according to claim 8 or 9, wherein the brake pressure in the first wheel brake cylinder (20) and / or in the second wheel brake cylinder (22) is increased during actuation of the brake actuation element (14) by the steps: Operating a first pump (58) of the brake system, the suction side of which is connected to the brake fluid reservoir (12), while the first separating valve (28) is kept closed; and / or Operating a second pump (64) of the brake system, the suction side of which is connected to the brake fluid reservoir (12), while the second separating valve (30) is kept closed (S4). [11] Method according to one of claims 8 to 10, wherein it is determined whether an emergency braking situation exists (S0), and, if an emergency braking situation is detected, the first isolating valve (28) and the second isolating valve (30) are controlled to their open state (S5), and only otherwise is the brake fluid displacement from the master brake cylinder (10) to the first wheel brake cylinder (20) and to the second wheel brake cylinder (22) prevented during the actuation of the brake actuating element (14).

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