Method for operating a vehicle's braking system and control device for a vehicle's braking system

Abstract

Method for operating a vehicle's braking system with the step: Limiting a brake pressure build-up in at least one brake circuit (10, 12) of the brake system to a response pressure of a storage volume (46a, 46b) of the at least one brake circuit (10, 12) at least temporarily during an actuation of a brake actuation element (22) connected to a master brake cylinder (18) of the brake system by a driver of the vehicle by controlling at least one wheel outlet valve (40a, 40b) of at least one wheel brake cylinder (14a, 14b) of the at least one brake circuit (10, 12) into an open state; wherein the rear wheel exhaust valves (40a, 40b) of the rear wheel brake cylinders (14a, 14b), each assigned to a rear wheel of the vehicle, are controlled to the open state at least temporarily during the actuation of the brake actuation element (22), and the front wheel inlet valves (34a, 34b) of the front wheel brake cylinders (16a, 16b), each assigned to a front wheel of the vehicle, are controlled to a closed state at least temporarily during the actuation of the rear wheel exhaust valves (40a, 40b) of the rear wheel brake cylinders (14a, 14b) to the open state. characterized by the fact that Before limiting the pressure build-up in the brake circuits (10, 12) to the response pressure, it is determined whether a generator braking torque (Mgen) corresponding to an actuation force of the actuation of the brake actuation element (22) can be exerted by means of at least one electric motor of the vehicle, and the limiting of the pressure build-up in the brake circuits (10, 12) to the response pressure is only carried out if the generator braking torque (Mgen) corresponding to the actuation force can be exerted by means of the at least one electric motor; wherein, if, after limiting the pressure build-up in the brake circuits (10, 12) to the response pressure, it is determined that the generator braking torque (Mgen) corresponding to the actuation force can no longer be exerted by means of the at least one electric motor, the front wheel inlet valves (34a, 34b) of the front wheel brake cylinders (16a, 16b) are controlled from the closed state to an open state, and wherein, if, after controlling the front wheel inlet valves (34a, 34b) from the closed state to the open state, it is determined that the generator braking torque (Mgen) corresponding to the actuation force can be applied again by means of the at least one electric motor, the brake pressure present in the brake circuits (10, 12) is limited to the response pressure by controlling the rear wheel outlet valves (40a, 40b) to the open state.

Description

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

[0002] German patent DE 196 04 134 A1 describes a method and a device for controlling the braking system of a motor vehicle with an electric drive. When the vehicle is decelerating using the electric drive to simultaneously charge a battery, the hydraulic braking torque exerted on at least one wheel by the at least one wheel brake cylinder of the hydraulic braking system is to be reduced / deactivated despite the brake pedal being actuated. This is achieved by counteracting the pressure fluid displaced from the master brake cylinder to the wheel brakes by actuating the brake pedal. Opening the wheel outlet valves of the hydraulic braking system allows the pressure fluid displaced from the master brake cylinder to be transferred via the at least one wheel brake cylinder to at least one storage chamber. In this way, regenerative braking performed by the electric drive is to be masked.

[0003] Furthermore, DE 10 2011 003 346 A1 describes a method for operating a braking system for a motor vehicle, wherein, to prevent brake pressure build-up in the wheel brakes of a brake circuit during brake pedal actuation, only one of the outlet valves assigned to the wheel brakes is controlled open in order to fill a pressure accumulator via the open outlet valve and the assigned wheel brake. In this way, the reduced actuation of the outlet valves is intended to extend the service life of the braking system.

[0004] Furthermore, US 5,951,115 A describes a brake control system for an electric vehicle, designed to check, upon activation of an ignition switch, whether the current state of the electric vehicle's transmission, electric motor (used for braking), and battery allows for regenerative braking. If it is determined that the conditions for regenerative braking are not met, the electric vehicle is braked by building up brake pressure in its wheel brake cylinders. Disclosure of the invention

[0005] The invention provides a method for operating a braking system of a vehicle with the features of claim 1, a control device for a braking system of a vehicle with the features of claim 6 and a braking system for a vehicle with the features of claim 7. Advantages of the invention

[0006] The present invention enables the setting of a brake pressure equal to the response pressure despite the actuation of the brake actuation element connected to the master brake cylinder. Thus, despite the driver directly engaging the master brake cylinder, a build-up of brake pressure above the response pressure can be reliably prevented / prevented in both a first and a second brake circuit.

[0007] The present invention also achieves the transfer of brake fluid from the master cylinder of the brake system into at least one storage volume of the at least one brake circuit solely via the rear wheel cylinders, while the front wheel cylinders remain empty. This is ensured by opening the rear wheel outlet valves (and the rear wheel inlet valves) to transfer the brake fluid from the master cylinder into the at least one storage volume, while the front wheel inlet valves remain closed (at least temporarily). Thus, the present invention ensures a brake pressure of (virtually) zero in the front wheel cylinders, despite the residual brake pressure / response pressure in the brake circuits not being zero. Therefore, when the present invention is applied, no residual friction torque remains at the front wheel cylinders.This means that the present invention can be used to protect the brake pads of the front wheel brake cylinders.

[0008] The present invention additionally utilizes the common practice of equipping conventional braking systems with different wheel brake cylinders for the respective axles of the vehicle. Typically, rear wheel brake cylinders are assigned to the rear axle of the vehicle, and their constant values ​​are significantly smaller than those of the front wheel brake cylinders assigned to the front axle of the vehicle. Typically, the constant values ​​of the front wheel brake cylinders are at least two to three times larger than those of the rear wheel brake cylinders.Since the constants of the wheel brake cylinders represent a quotient of the resulting braking torque and the braking pressure present in the respective wheel brake cylinders, the same pressure in the rear wheel brake cylinders and the front wheel brake cylinders results in a front wheel braking torque generated by the front wheel brake cylinders that is at least two to three times greater than a rear wheel braking torque generated by the rear wheel brake cylinders. Because a braking pressure of (almost) zero can be achieved in the front wheel brake cylinders when applying the present invention, the total braking torque resulting from the addition of the front wheel braking torque and the rear wheel braking torque can be significantly reduced.

[0009] The method according to the invention and the corresponding control device are therefore particularly advantageous for a regenerative braking system. By using the present invention for a regenerative braking system, the recuperation efficiency can be increased during recuperation, and a vehicle battery can thus be charged more quickly. The present invention therefore ensures that a vehicle can be driven with lower energy consumption and reduced pollutant emissions. However, it should be noted that the applicability of the present invention is not limited to regenerative braking systems.

[0010] In an advantageous embodiment, the rear wheel inlet valves of the rear wheel brake cylinders are also controlled to an open state, at least temporarily, while the rear wheel outlet valves of the rear wheel brake cylinders are being controlled to the open state. This allows the brake fluid volume displaced from the master brake cylinder to be reliably transferred via the open rear wheel inlet valves and the also open rear wheel outlet valves into the storage volumes of the brake circuits.

[0011] Preferably, while the rear wheel exhaust valves of the rear wheel brake cylinders are being opened, the front wheel inlet valves of the front wheel brake cylinders are being closed with a delay, so that the front wheel brake cylinders are pre-filled without any brake pressure build-up. In this way, the so-called dead volume of the front wheel brake cylinders can be overcome. This allows for a quick and reliable build-up of the desired brake pressure in the front wheel brake cylinders at a later time.

[0012] Alternatively, to limit the pressure build-up in the brake circuits to the response pressure, the rear wheel exhaust valves can be simultaneously controlled to the open state and the front wheel brake cylinders to the closed state.

[0013] The reduced brake pressure in both brake circuits, compared to the state of the art, can thus be used to exert a comparatively large generator braking torque on the vehicle without exceeding a target total braking torque specified by the driver. This advantageous method therefore enables faster charging of a vehicle battery.

[0014] Furthermore, if, after limiting the pressure build-up in the brake circuits to the response pressure, it is determined that the generator braking torque corresponding to the actuation force can no longer be exerted by means of the at least one electric motor, a brake pressure build-up in the front wheel brake cylinders allows for a quick and reliable response to a reduced usability of the at least one electric motor and / or to a comparatively high driver braking request.

[0015] If necessary, after controlling the front wheel inlet valves from the closed to the open state, a Δp control can be performed using the rear wheel inlet valves of the rear wheel brake cylinders. This allows the brake pressure in the brake circuits to be precisely regulated so that a target deceleration specified by the driver can be reliably achieved.

[0016] Furthermore, if, after controlling the front wheel intake valves from the closed state to the open state, it is determined that the generator braking torque corresponding to the actuation force can be applied again by means of at least one electric motor, the brake pressure present in the brake circuits can be reliably reduced to the response pressure.

[0017] The advantages listed above are also guaranteed with such a control device for a vehicle's braking system. It is expressly noted that the control device can be further developed according to the embodiments of the method for operating a vehicle's braking system.

[0018] Furthermore, the described advantages are guaranteed in a braking system for a vehicle with such a control device. Brief description of the drawings

[0019] 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 control device; and Fig. 2a to 2c three coordinate systems for representing an embodiment of the method for operating a regenerative braking system. Embodiments of the invention

[0020] Fig. Figure 1 shows a schematic representation of an embodiment of the control device.

[0021] The in Fig. The control device 100, shown schematically, and the braking system interacting with it are advantageously usable, for example, in a hybrid or electric vehicle. However, the applicability of the control device 100 and the braking system described below is not limited to use in a hybrid or electric vehicle.

[0022] The brake system shown here as an example has a first brake circuit 10 and a second brake circuit 12, each with two wheel brake cylinders 14a, 14b, 16a, and 16b. Optionally, each of the two brake circuits 10 and 12 has a rear wheel brake cylinder 14a or 14b and a front wheel brake cylinder 16a and 16b. However, the brake system described below is not limited to such a brake circuit distribution (X-brake circuit distribution). The wheels assigned to brake circuits 10 and 12 can, for example, also be located on a common axle of the vehicle or on one side of the vehicle.

[0023] The braking system includes a master brake cylinder 18, which can, for example, be configured as a tandem master brake cylinder. The master brake cylinder 18 can be connected to a brake fluid reservoir 20 via at least one brake fluid exchange port, such as a vent hole. However, the applicability of the control device 100 is not limited to the use of a tandem master brake cylinder or to a specific configuration of the master brake cylinder 18.

[0024] The braking system preferably comprises a brake actuation element 22, such as a brake pedal, arranged on the master brake cylinder 18. Advantageously, the brake actuation element 22 is arranged directly or indirectly on the master brake cylinder 18 such that, when the brake actuation element 22 is actuated with at least a minimum braking force, the driver's braking force applied to the brake actuation element 22 can be transmitted to the at least one adjustable piston of the master brake cylinder 18, such as a rod piston and a floating piston, in such a way that the at least one piston can be adjusted by means of the driver's braking force. Preferably, this adjustment of the at least one piston increases the internal pressure in at least one pressure chamber of the master brake cylinder 18.

[0025] Preferably, the braking system also includes at least one brake actuation element sensor 24, by means of which the actuation force of the brake actuation element 22 by the driver can be determined. The brake actuation element sensor 24 can, for example, be a pedal travel sensor, a differential travel sensor, and / or a rod travel sensor. However, to detect the actuation force corresponding to the driver's braking request, a different type of sensor can also be used instead of or in addition to the sensor types listed here.

[0026] The depicted braking system also includes a brake booster 26. The brake booster 26 applies a booster force to at least one piston of the master brake cylinder 18, thus facilitating the operation of the brake actuator 22 for the driver. The brake booster 26 can, in particular, be a continuously variable / controllable brake booster.

[0027] The in Fig. The braking system shown in Figure 1 has an electromechanical brake booster 26. An electromechanical brake booster 26 is characterized by a variable boosting force. This makes it possible to easily influence the braking force perceived by the driver during braking by means of the electromechanical brake booster 26. However, instead of an electromechanical brake booster 26, the braking system interacting with the control device 100 can also have a brake booster 26 of a different type.

[0028] The following will be discussed with reference to Fig. One further component of the embodiment of the brake system is described. It is expressly pointed out that the components of the brake system described below represent only an example of a possible embodiment of the advantageous brake system. One advantage of the control device 100, described in more detail below, is that the brake circuits 10 and 12 interacting with it are not limited to a specific design or the use of specific components. Instead, the brake circuits 10 and 12 can be modified with a high degree of flexibility without impairing the applicability and advantages of the control device 100. Each of the brake circuits 10 and 12 is designed so that the driver can brake directly into the wheel brake cylinders 14a, 14b, 16a and 16b via the master brake cylinder 18. Each of the brake circuits 10 and 12 has a high-pressure switching valve 28a or 28b and a changeover valve 30a or 30b (each with a parallel bypass line 29a and 29b and a check valve 31a and 31b arranged in each bypass line 29a and 29b).

[0029] In the first brake circuit 10, a rear wheel inlet valve 32a is assigned to the rear wheel brake cylinder 14a, and a front wheel inlet valve 34a is assigned to the front wheel brake cylinder 16a, each with a parallel bypass line 36a and a check valve 38a located in each bypass line 36a. Additionally, a rear wheel outlet valve 40a is assigned to the rear wheel brake cylinder 14a, and a front wheel outlet valve 42a is assigned to the front wheel brake cylinder 16a. Similarly, in the second brake circuit 12, a rear wheel inlet valve 32b is assigned to the rear wheel brake cylinder 14b, and a front wheel inlet valve 34b is assigned to the front wheel brake cylinder 16b. Parallel to each of the two wheel inlet valves 32b and 34b of the second brake circuit 12, a bypass line 36b runs with a check valve 38b arranged therein.Furthermore, in the second brake circuit 12, a rear wheel exhaust valve 40b is assigned to the rear wheel brake cylinder 14b and a front wheel exhaust valve 42b is assigned to the front wheel brake cylinder 16b.

[0030] Furthermore, each of the brake circuits 10 and 12 comprises a pump 44a and 44b, the intake side of which is connected to the wheel outlet valves 40a and 42a or 40b and 42b, and the delivery side of which is directed to the wheel inlet valves 32a and 34a or 32b and 34b. Each of the brake circuits 10 and 12 also has an accumulator chamber 46a or 46b arranged between the wheel outlet valves 40a and 42a or 40b and 42b and the associated pump 44a or 44b, with an accumulator volume of 46a or 46b, and a pressure relief valve 48a or 48b located between the respective pump 44a or 44b and the accumulator chamber 46a or 46b. Each of the accumulator chambers 46a and 46b can, in particular, be a low-pressure accumulator chamber. It should be noted that the storage chambers 46a and 46b can be used as ESP storage chambers in both brake circuits 10 and 12.

[0031] Pumps 44a and 44b can be arranged on a common shaft 50 of a motor 52. Each of the pumps 44a and 44b can be designed as a three-piston pump. However, instead of a three-piston pump, a different pump type can also be used for at least one of the pumps 44a and 44b. Differently designed modulation systems, such as pumps with multiple or fewer pistons, asymmetric pumps, or gear pumps, can also be used. The braking system interacting with the control device 100 can thus be implemented as a modified standard modulation system, in particular as a six-piston ESP system.

[0032] Furthermore, each of the two brake circuits 10 and 12 can include at least one pressure sensor 54, in particular for determining a pre-pressure and / or a circuit pressure.

[0033] The braking system described above can be controlled by means of the control device 100 described below. However, it should be noted again that the applicability of the control device 100 described below is not limited to its use in conjunction with a braking system designed in this way.

[0034] The control device 100 described below can, in particular, be integrated into the control electronics of the brake system. However, it should be noted that the configuration of the control device 100 is not limited to such integration. For example, the control device 100 can also be used together with separately designed and arranged control electronics of the brake system.

[0035] The control device 100 comprises a control unit 102, by means of which at least the rear wheel exhaust valves 40a and 40b and the front wheel inlet valves 34a and 34b of the two brake circuits 10 and 12 can be controlled. The control of the rear wheel exhaust valves 40a and 40b and the front wheel inlet valves 34a and 34b of the two brake circuits 10 and 12 by the control unit 102 takes into account at least one provided sensor signal 104 regarding the actuation force of an actuation of the brake actuation element 22 connected to the master brake cylinder 18 by a driver of the vehicle. The sensor signal 104 can, in particular, be provided by the brake actuation element sensor 24 already mentioned above.The actuation force taken into account during control is, for example, a determined driver braking force, a driver braking pressure, and / or an actuation / adjustment travel of the brake actuation element 22, such as, in particular, a rod travel. However, the possibilities for actuation force listed here are only examples.

[0036] The rear wheel exhaust valves 40a and 40b of the rear wheel brake cylinders 14a and 14b, each assigned to a rear wheel of the vehicle, can be controlled to an open state by means of at least one first control signal 106 from the control device 102. At least temporarily during the provision of the at least one first control signal 106 to the rear wheel exhaust valves 40a and 40b, the front wheel inlet valves 34a and 34b of the front wheel brake cylinders 16a and 16b, each assigned to a front wheel of the vehicle, can be controlled to a closed state by means of at least one second control signal 108 from the control device 102.Brake fluid can be transferred into the storage volumes / chambers 46a and 46b via the rear wheel outlet valves 40a and 40b of the rear wheel brake cylinders 14a and 14b, which are controlled to the open position by means of the first control signal 106 of the control device 102 (and via the at least partially open rear wheel inlet valves 32a and 32b of the rear wheel brake cylinders 14a and 14b). In this way, the brake pressure build-up in the brake circuits 10 and 12 can be limited to a response pressure of the storage chambers / volumes 46a and 46b of the brake circuits 10 and 12, despite the brake fluid being transferred from the master brake cylinder 18 into the brake circuits 10 and 12 (due to actuation of the brake actuating element 22).At the same time, by controlling the front wheel inlet valves 34a and 34b of the front wheel brake cylinders 16a and 16b into the closed state at least temporarily by means of at least one second control signal 108 of the control device 102, a brake pressure of (almost) zero in the front wheel brake cylinders 16a and 16b can be ensured.

[0037] During the transfer of brake fluid into the storage volumes / chambers 46a and 46b, the brake pressure in the rear wheel brake cylinders 14a and 14b is (approximately) equal to the response pressure, while the brake pressure in the front wheel brake cylinders 16a and 16b is (almost) zero. Similarly, during the interim period between the transfer of brake fluid into the storage volumes / chambers 46a and 46b and a subsequent (desired) pressure build-up in the brake circuits 10 and 12, the brake pressure in the rear wheel brake cylinders 14a and 14b is (approximately) equal to the response pressure, while the brake pressure in the front wheel brake cylinders 16a and 16b is (almost) zero.

[0038] During the transfer of brake fluid into storage volumes 46a and 46b, and in the interim, only a rear brake torque corresponding to the response pressure acts on the rear wheels, while at the same time a front brake torque of (almost) zero is present at the front wheels. The resulting "hydraulic" brake torque from the rear brake torque and the front brake torque is therefore comparatively low.

[0039] The control device 100 additionally takes advantage of the fact that different types of wheel brake cylinders 14a, 14b, 16a and 16b are typically used on the different axles of a vehicle. Generally, the following applies to the rear wheel braking torque M exerted on the rear wheels. HR : MHR=2∗p∗cHR, where p is the brake pressure present in the rear wheel brake cylinders 14a and 14b and c HR The constant of the rear wheel brake cylinders 14a and 14b is.

[0040] Accordingly, the following often applies to the front wheel braking torque M exerted on the front wheels: VR : MVR=2∗p∗cVR, where p is the brake pressure present in the front wheel brake cylinders 16a and 16b and c vR The constant of the front wheel brake cylinders 16a and 16b is.

[0041] In general: cVR≥2∗cHR

[0042] The actuation of the rear wheel exhaust valves 40a and 40b of the rear wheel brake cylinders 14a and 14b with the at least one first control signal 106 and the actuation of the front wheel inlet valves 34a and 34b of the front wheel brake cylinders 16a and 16b with the at least one second control signal 108, which is carried out at least temporarily during this time, thus produces a “hydraulic” braking torque M h : Mh=2∗p∗cHR,

[0043] If the front wheel exhaust valves 42a and 42b were used to move the brake fluid instead of the rear wheel exhaust valves 40a and 40b, the following would apply: Mh≥4∗p∗cHR

[0044] The low “hydraulic” braking torque M specified in equation (Eq. 4) despite the actuation of the brake actuation element h This can be used to increase the generator braking torque produced by at least one (not shown) electric motor. This allows the battery of the vehicle equipped with the braking system to be charged more quickly without exceeding a vehicle deceleration set by the driver via the brake actuation element 22 during the charging process.

[0045] The braking system equipped with the control device 100 thus combines the advantages of high recuperation efficiency with the feasibility of a masking function. Furthermore, by using the control device 100, it is possible to implement the masking function without any perceptible feedback to the driver at the brake actuation element 22.

[0046] It is expressly pointed out that when using the control device 100, the level of the response pressure of the storage chambers 46a and 46b, which are used as storage volumes 46a and 46b of the brake circuits 10 and 12, becomes less significant. The response pressure of the storage volumes 46a and 46b of the brake circuits 10 and 12 can therefore also be comparatively high without the resulting residual pressure "hydraulic" braking torque M being affected. h becomes significantly large. Therefore, cost-effective storage volumes 46a and 46b can also be used together with the control device 100.

[0047] Furthermore, by controlling the front wheel inlet valves 34a and 34b of the front wheel brake cylinders 16a and 16b into the closed state by means of at least one second control signal 108 from the control device 102, wear of their brake linings can be prevented / delayed. Thus, the control device 100 can also be used to protect the brake linings.

[0048] Furthermore, the control device 100 can additionally be configured to perform the process steps described below. In particular, the control signals Ie-HR, Ie-VR, Ia-Hr, and Ia-VR described below can be output by the control device 100, with the control signal Ie-HR being output to the rear wheel intake valves 32a and 32b, the control signal Ie-VR (as the second control signal 108) to the front wheel intake valves 34a and 34b, the control signal Ia-HR (as the first control signal 106) to the rear wheel exhaust valves 40a and 40b, and the control signal Ia-VR to the front wheel exhaust valves 42a and 42b. A more detailed description of other possible functions of the control device 100 is therefore omitted here.

[0049] The advantages described above are also realized in a braking system for a vehicle with control device 100, or with a corresponding further development of control device 100. It is expressly pointed out that in the braking system, control device 100 is not only designed to output at least the control signals. Instead, control device 100 is connected to at least valves 34a, 34b, 40a, and 40b in such a way that (during operation of the braking system) at least the first control signal 106 can be output to the rear wheel exhaust valves 40a and 40b, and the second control signal 108 can be output to the front wheel intake valves 34a and 34b.In an advantageous further development, the brake system has a circuit which ensures that the control signal Ie-HR can be output to the rear wheel inlet valves 32a and 32b, the control signal Ie-VR (as second control signal 108) to the front wheel inlet valves 34a and 34b, the control signal Ia-HR (as first control signal 106) to the rear wheel outlet valves 40a and 40b and the control signal Ia-VR to the front wheel outlet valves 42a and 42b.

[0050] Fig. Figures 2a to 2c show three coordinate systems for representing an embodiment of the method for operating a vehicle's braking system.

[0051] For the sake of clarity, the procedure is described using the regenerative braking system explained above. However, the procedure is not limited to the use of this braking system.

[0052] In the coordinate systems of Fig. In 2a to 2c, the abscissa is the time axis t. The ordinate of the coordinate system is... Fig. 2a represents a braking torque M. The ordinate of the coordinate system of Fig. 2b is a storage volume V, which is temporarily stored in the storage chambers / volumes of the brake circuits. A (normalized) current I is determined using the ordinate of the coordinate system of the Fig. 2c is displayed.

[0053] Up to time t0, the driver exerts no force on the brake actuator. Therefore, the brake actuator of the braking system operated by this method remains in its initial / non-actuated position until time t0.

[0054] From time t0, the driver exerts an increasing force on the brake actuator, thereby adjusting it. Between times t0 and t1, however, the total target braking torque Mges requested by the driver is below the maximum generator braking torque Mkann that can be achieved by at least one electric motor. Therefore, between times t0 and t1, the (executed) generator braking torque Mgen can be adjusted according to the total target braking torque Mges, and the driver's entire braking request can be fulfilled purely through regenerative braking.

[0055] To execute purely regenerative braking, during times t0 and t1, the build-up of brake pressure in the brake circuits of the braking system is limited to a response pressure of the accumulator chambers / storage volume of the brake circuits, despite the driver's actuation of the brake actuator located on the master brake cylinder. This is achieved by controlling the rear wheel outlet valves of the rear wheel brake cylinders, each assigned to a rear wheel of the vehicle, to the open position. Conversely, at least temporarily while the rear wheel outlet valves are being controlled to the open position, the front wheel inlet valves of the front wheel brake cylinders, each assigned to a front wheel of the vehicle, are controlled to a closed position.In this way, despite brake fluid being shifted from the master cylinder of the brake system into the brake circuits, a build-up of brake pressure can be successfully counteracted via the response pressure of the storage chambers / storage volume.

[0056] During times t0 and t1, the driver transfers a volume of brake fluid from the master cylinder into the reservoirs, thereby increasing the reservoir volume V. Thus, between times t0 and t1, the brake pressure in the rear wheel cylinders equals the response pressure of the reservoirs / reservoir, while the brake pressure in the front wheel cylinders is (almost) zero. The rear wheel cylinders therefore produce a rear brake torque M-HR equal to the response pressure brake torque between times t0 and t1. The front brake torque M-VR of the front wheel cylinders is (almost) zero between times t0 and t1. Due to the resulting limitation of pressure build-up in the brake circuits, a comparatively high generator brake torque Mgen can be applied to the vehicle by means of at least one electric motor during times t0 and t1.Despite the application of the high generator braking torque Mgen, the previously described procedure steps reliably ensure that the target total braking torque Mges specified by the driver via the brake actuation is not exceeded.

[0057] When the rear wheel exhaust valves of the rear wheel brake cylinders of the brake circuits are configured as normally closed valves, a non-zero control signal Ia-HR is output to the rear wheel exhaust valves between times t0 and t1 (as the first control signal). Advantageously, at least temporarily during the opening of the rear wheel exhaust valves, the rear wheel inlet valves of the rear wheel brake cylinders are also opened. To open the rear wheel inlet valves of the rear wheel brake cylinders, a zero control signal Ie-HR can be output to them if they are configured as normally open valves.

[0058] If the front wheel inlet valves of the front wheel brake cylinders are designed as normally open valves, a non-zero control signal Ie-VR is provided to the front wheel inlet valves between times t0 and t1 (as a second control signal). Preferably, the front wheel outlet valves of the front wheel brake cylinders of both brake circuits are also closed between times t0 and t1. If the front wheel outlet valves of the front wheel brake cylinders are normally closed valves, this can be achieved using a zero control signal Ia-VR.

[0059] In an advantageous embodiment of the method, the front wheel inlet valves of the front wheel brake cylinders are closed with a delay (simultaneously / while the rear wheel outlet valves are being controlled to the open position) to limit the pressure build-up in the brake circuits to the response pressure. This allows the front wheel brake cylinders to be pre-filled without any brake pressure build-up. In this way, a dead volume can be overcome before the front wheel inlet valves of the front wheel brake cylinders close. Pre-filling the front wheel brake cylinders prevents a sudden collapse of brake pressure / residual pressure in the brake circuits when the front wheel inlet valves are subsequently opened. Such a sudden collapse of brake pressure / residual pressure is often noticeable to a driver during actuation of the brake actuator and is perceived as disadvantageous.However, this reduction in comfort can be reliably prevented by pre-filling the front wheel brake cylinders. Furthermore, the delayed closing of the front wheel inlet valves ensures that an unnecessarily large amount of fluid is not stored in the reservoirs. This also reduces the load on the reservoirs and increases their service life.

[0060] The delayed closing of the front wheel brake cylinders means that the front wheel brake cylinders are held in the open position for a short delay period Δt. Immediately after this delay, the front wheel brake cylinders are closed. With the exception of this delay period Δt, this ensures that the front wheel brake cylinders remain closed while the rear wheel exhaust valves are being opened. Alternatively, the rear wheel exhaust valves can be opened and the front wheel brake cylinders closed simultaneously.

[0061] Preferably, the increase of the control signal Ie-VR from 0 to 1 to close the front wheel inlet valves is therefore carried out taking into account a sensor signal from a brake actuator sensor, such as a pedal travel sensor. Based on this sensor signal, the volume of brake fluid already transferred from the master cylinder into the brake circuits, and in particular into the front wheel cylinders, can be determined / estimated. Only when a volume of brake fluid corresponding to the typical initial dead volume has been transferred into the front wheel cylinders can the front wheel inlet valves of the front wheel cylinders be closed. In this way, it can be reliably ensured that no brake pressure is built up in the front wheel cylinders despite the (slight) filling.At the same time, it can be ensured that the brake pressure / residual pressure present in the brake circuits does not collapse when the front wheel inlet valves are opened later.

[0062] Preferably, before limiting the pressure build-up in the brake circuits to the response pressure, it is determined whether a generator braking torque Mgen corresponding to the actuation force of the brake actuation element can be exerted by means of the vehicle's at least one electric motor. Limiting the pressure build-up in the brake circuits to the response pressure is only carried out if the generator braking torque Mgen corresponding to the actuation force can actually be exerted by means of the at least one electric motor.

[0063] It is also noted that in a braking system with an X-brake circuit split, a comparatively large maximum achievable Kann-generator braking torque Mkann is generally present. Therefore, the advantages described during times t0 and t1 can often be utilized for the entire duration of the braking process.

[0064] If, after limiting the pressure build-up in the brake circuits to the response pressure, it is determined that the generator braking torque Mgen corresponding to the actuation force can no longer be exerted by means of the at least one electric motor, the following procedure can be carried out to reliably brake the vehicle nonetheless: From time t2 onwards, the increasing target total braking torque Mges specified by the driver approaches the maximum achievable generator braking torque Mkann. To maintain a standard brake feel / pedal feel for the driver, brake pressure is built up in the front wheel cylinders from time t2 onwards. For this purpose, the front wheel inlet valves of the front wheel cylinders are opened from the closed state to an open state. In this way, further actuation of the brake pedal by the driver can cause brake pressure to build up in the front wheel cylinders. Thus, from time t1 onwards, the front wheel cylinders produce a non-zero front wheel braking torque MVR. Provided the actuation force of the brake actuator remains constant from time t2 onwards, the front wheel braking torque M-VR, produced by the front wheel brake cylinders, also does not increase. A decrease in actuation force from time t3 onwards also results in a corresponding decrease in the front wheel braking torque M-VR.

[0065] By using the front wheel brake cylinders to apply the front wheel braking torque M-VR in addition to the generator braking torque Mgen, it is ensured that the comparatively large constant of the front wheel brake cylinders can be used to maintain the target vehicle deceleration Mges specified by the driver.

[0066] Preferably, after controlling the front wheel inlet valves from the closed to the open state between times t1 and t4, a Δp control is performed using the rear wheel inlet valves of the rear wheel brake cylinders. In this way, the front wheel braking torque M-VR can be precisely adjusted to a preferred value.

[0067] If, after controlling the front wheel inlet valves from the closed to the open state, it is determined that the generator braking torque Mgen corresponding to the actuation force can again be applied by means of the at least one electric motor, the brake pressure present in the brake circuits can be limited back to the response pressure. This is carried out, for example, after time t4, once the total target braking torque Mges requested by the driver falls below the maximum achievable generator braking torque Mkann. To limit the brake pressure present in the brake circuits to the response pressure, only the rear wheel outlet valves are controlled to the open state. The front wheel inlet valves can remain in the open state even after time t4.Up to a time t5, from which the driver ends the actuation of the brake actuation element, only the response pressure of the storage volumes is present in all wheel brake cylinders.

Claims

[1] Method for operating a vehicle braking system by the step: Limiting a brake pressure build-up in at least one brake circuit (10, 12) of the brake system to a response pressure of a storage volume (46a, 46b) of the at least one brake circuit (10, 12) at least temporarily during an actuation of a brake actuation element (22) connected to a master brake cylinder (18) of the brake system by a driver of the vehicle by controlling at least one wheel outlet valve (40a, 40b) of at least one wheel brake cylinder (14a, 14b) of the at least one brake circuit (10, 12) into an open state; wherein the rear wheel exhaust valves (40a, 40b) of the rear wheel brake cylinders (14a, 14b), each assigned to a rear wheel of the vehicle, are controlled to the open state at least temporarily during the actuation of the brake actuation element (22), and the front wheel inlet valves (34a, 34b) of the front wheel brake cylinders (16a, 16b), each assigned to a front wheel of the vehicle, are controlled to a closed state at least temporarily during the actuation of the rear wheel exhaust valves (40a, 40b) of the rear wheel brake cylinders (14a, 14b) to the open state. characterized by , that Before limiting the pressure build-up in the brake circuits (10, 12) to the response pressure, it is determined whether a generator braking torque (Mgen) corresponding to an actuation force of the actuation of the brake actuation element (22) can be exerted by means of at least one electric motor of the vehicle, and the limiting of the pressure build-up in the brake circuits (10, 12) to the response pressure is only carried out if the generator braking torque (Mgen) corresponding to the actuation force can be exerted by means of the at least one electric motor; wherein, if, after limiting the pressure build-up in the brake circuits (10, 12) to the response pressure, it is determined that the generator braking torque (Mgen) corresponding to the actuation force can no longer be exerted by means of the at least one electric motor, the front wheel inlet valves (34a, 34b) of the front wheel brake cylinders (16a, 16b) are controlled from the closed state to an open state, and wherein, if, after controlling the front wheel inlet valves (34a, 34b) from the closed state to the open state, it is determined that the generator braking torque (Mgen) corresponding to the actuation force can be applied again by means of the at least one electric motor, the brake pressure present in the brake circuits (10, 12) is limited to the response pressure by controlling the rear wheel outlet valves (40a, 40b) to the open state. [2] Method according to claim 1, wherein at least temporarily during the control of the rear wheel exhaust valves (40a, 40b) of the rear wheel brake cylinders (14a, 14b) into the open state the rear wheel inlet valves (32a, 32b) of the rear wheel brake cylinders (14a, 14b) are controlled into an open state. [3] Method according to claim 1 or 2, wherein while controlling the rear wheel exhaust valves (40a, 40b) of the rear wheel brake cylinders (14a, 14b) into the open state, the front wheel inlet valves (34a, 34b) of the front wheel brake cylinders (16a, 16b) are controlled into the closed state with such a delay that the front wheel brake cylinders (16a, 16b) are prefilled without a brake pressure build-up. [4] Method according to claim 1 or 2, wherein to limit the pressure build-up in the brake circuits (10, 12) to the response pressure, the rear wheel exhaust valves (40a, 40b) are simultaneously controlled to the open state and the front wheel brake cylinders (34a, 34b) to the closed state. [5] Method according to claim 1, wherein after controlling the front wheel inlet valves (34a, 34b) from the closed state to the open state, a Δp control is carried out by means of the rear wheel inlet valves (40a, 40b) of the rear wheel brake cylinders (14a, 14b). [6] Control device (100) for a braking system of a vehicle with: a control device (102) by means of which at least one wheel outlet valve (40a, 40b) of a wheel brake cylinder (14a, 14b) of at least one brake circuit (10, 12) of the brake system can be controlled to an open state by a driver of the vehicle, taking into account at least one provided sensor signal (104) with regard to the actuation force of an actuation of a brake actuation element (22) connected to a master brake cylinder (18) of the brake system, so that a brake pressure build-up at least in the at least one brake circuit (10, 12) can be limited at least temporarily during an actuation of the brake actuation element (22) to a response pressure of a storage volume (46a, 46b) of the at least one brake circuit (10, 12); wherein the control device (102) is additionally designed to control the rear wheel exhaust valves (40a, 40b) of the rear wheel brake cylinders (14a, 14b), each assigned to a rear wheel of the vehicle, into the open state at least temporarily during the actuation of the brake actuation element (22) by means of at least one first control signal (106, Ia-HR), and to control the front wheel inlet valves (34a, 34b) of the front wheel brake cylinders (16a, 16b), each assigned to a front wheel of the vehicle, into a closed state at least temporarily during the provision of the at least one first control signal (106, Ia-HR) to the rear wheel exhaust valves (40a, 40b) by means of at least one second control signal (108, Ie-VR). characterized by , that the control device (102) is additionally designed to determine, before limiting the pressure build-up in the brake circuits (10, 12) to the response pressure, whether a generator braking torque (Mgen) corresponding to an actuation force of the actuation of the brake actuation element (22) can be exerted by means of at least one electric motor of the vehicle, and to only carry out the limitation of the pressure build-up in the brake circuits (10, 12) to the response pressure if the generator braking torque (Mgen) corresponding to the actuation force can be exerted by means of the at least one electric motor; wherein, if, after limiting the pressure build-up in the brake circuits (10, 12) to the response pressure, it is determined that the generator braking torque (Mgen) corresponding to the actuation force can no longer be exerted by means of the at least one electric motor, the front wheel inlet valves (34a, 34b) of the front wheel brake cylinders (16a, 16b) can be controlled from the closed state to an open state by means of the control device (102), and wherein, after controlling the front wheel inlet valves (34a, 34b) from the closed state to the open state, that the generator braking torque (Mgen) corresponding to the actuation force can be applied again by means of the at least one electric motor, the brake pressure present in the brake circuits (10, 12) can be limited to the response pressure by means of the control device (102) by means of the rear wheel exhaust valves (40a, 40b) being controllable to the open state by means of the control device (102). [7] Braking system for a vehicle with a control device (100) according to claim 6.

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