Pressure build-up delay during service functions

Abstract

The invention relates to a hydraulic motor vehicle braking system comprising at least one wheel brake which can be supplied with pressurized brake fluid via at least one pressure supply device, an electronic brake pedal unit which does not have a hydraulic coupling to the at least one wheel brake and the pressure supply device or whose hydraulic coupling is separated by a closed valve, and is connected to a control device via a signal line in order to transmit a brake pedal actuation value, wherein the control device controls the pressure supply device based on the brake pedal actuation value.To improve the availability of the braking system, the implementation of a pressure build-up via the pressure supply device based on the brake pedal actuation magnitude is delayed when a hydraulic service function is active or necessary and at least one additional condition is met.

Description

[0001] The invention relates to a hydraulic motor vehicle brake system comprising at least one wheel brake which can be supplied via at least one pressure supply device by means of a pressurized brake fluid, an electronic brake pedal unit which has no hydraulic coupling to the at least one wheel brake and the pressure supply device, but is connected via a signal line to a control device in order to transmit a brake pedal actuation variable, wherein the control device is configured to control the pressure supply device based on the brake pedal actuation variable.

[0002] Traditionally, braking systems are equipped with a hydraulic pedal that has a hydraulic connection to hydraulic wheel brakes. Some variants exist in which the pedal always has direct contact with the wheel brakes, with brake force boosted by vacuum brake boosters or e-boosters. Other variants exist in which the brake pedal is isolated from the wheel brakes by valves and only has direct contact with the wheels in a hydraulic fallback mode. When operating correctly, such a braking system operates in by-wire mode, in which the brake pedal is decoupled from the wheels and instead feeds pressure into a simulator. The pressure buildup in the wheels is then not via the pedal, but via an electric pressure supply device.

[0003] A driver's request (pedal activation) is always implemented with the highest priority on the wheels and other hydraulic activities are interrupted if necessary.

[0004] DE 10 2015 106 089 A1 discloses a braking system with multiple wheel brakes and an adjustable pressure source. A control device is configured to initiate a diagnostic procedure after the end of a braking operation, which utilizes the hydraulic pressure still present in a brake circuit.

[0005] A method for performing service routines in a hydraulic brake system is known from DE 10 2020 207 390 A1. An electromechanical parking brake is applied with the assistance of the hydraulic brake system, and then a pressure in a first partial circuit is maintained at a first value, while the pressure in a second partial circuit is modulated according to a test profile.

[0006] Another method for performing service routines in a hydraulic brake system is known from DE 10 2020 211 431 A1, which also involves two partial circuits. At the end of a braking application, the pressure used for braking is maintained in one part by locking it in place with a valve. In the other part, the pressure is modulated according to a test profile. The standard concept of always and immediately implementing pedal activation as a deceleration request is state of the art in all classic and by-wire braking systems, including e-pedal variants that have a purely electronic connection of the brake pedal.

[0007] It is an object of the present invention to provide an improved brake control for e-pedal braking systems.

[0008] The problem is solved by a braking system according to claim 1, wherein the implementation of a pressure buildup by means of the pressure supply device is delayed based on the brake pedal actuation magnitude when a hydraulic service function is active or required and at least one additional requirement is met. This makes it possible to optimally arbitrate the external pressure buildup request into the hydraulic services and the safety concept. Hydraulic self-tests of the braking system can also be considered a service function for testing mechanical components, such as valves, the linear actuator, or the pump, and hydraulic properties, such as leaks or the pressure control capability.

[0009] In a preferred embodiment of the invention, the additional requirement includes at least the vehicle being stationary. Thus, a delay in a driver's braking request is only permitted if the vehicle is stationary. A speed below a certain threshold can also be considered stationary. However, if the vehicle is traveling at a significant speed, the driver's braking request is immediately detected to prevent dangerous situations from occurring.

[0010] In a further preferred embodiment of the invention, the additional requirement includes at least one activated parking brake unit. In such situations, an alternative braking force already exists, so that a delay in the buildup of hydraulic brake pressure can be implemented without danger.

[0011] In a particularly preferred embodiment of the invention, the parking brake unit comprises an integrated parking brake, a transmission lock, and / or a mechanical locking mechanism for a dry brake actuator. Such systems provide reliable options for a parking brake unit and can be selected and combined as appropriate depending on the vehicle type.

[0012] In a further preferred embodiment of the invention, a service function is required when a low brake fluid level is detected. Such a situation triggers the execution of special service functions. By delaying the implementation of the driver's braking request, the necessary service functions can be implemented particularly quickly, thus improving the readiness of the braking system.

[0013] In a preferred embodiment of the invention, the service function comprises a brake fluid shift. This can, in particular, be a shift to secure brake fluid in the event of leaks. With a flush / deflush concept, for example, the brake fluid is pumped into an area where the brake fluid is not lost before the brake system goes to sleep. When the brake system is reactivated, the brake fluid is then shifted back to the areas where the brake fluid is required for the brake system to function. By delaying the buildup of brake pressure and thus prioritizing the flush / deflush service function, the functionality of the brake system is ensured.

[0014] In a preferred embodiment of the invention, the service function comprises heating the brake system. In braking systems for highly autonomous driving, there is a need for block heating of the hydraulic functional units to ensure the functionality of the brake system even at temperatures below -25°C. The hydraulic block is to be heated by energizing the coils of the hydraulic valves in order to warm up the brake fluid and thus achieve the desired vehicle deceleration. Since target vehicles are often battery-electric vehicles, the vehicle's battery is heated in parallel to prevent any additional delay when starting off. For such a block heating system to work, a pressure request must not be implemented; otherwise, the volume flow with active valves would simply cause a disturbance.Delaying pressure requests is therefore particularly possible when the outside temperature is < 25°C and the hydraulic block needs to be heated. To ensure safety, additional conditions (parking brake applied, vehicle stationary, pressure request less than the threshold) can also be checked.

[0015] In a preferred embodiment of the invention, the service function includes leak detection. In a situation where leak detection is necessary or already active, direct pressure transfer can lead to unnecessary loss of brake fluid. This is avoided by the delay according to the invention.

[0016] In a preferred embodiment of the invention, the additional requirement includes that the brake pedal actuation magnitude does not exceed a predetermined actuation threshold and / or is not applied for a period of time greater than a time threshold. A pressure threshold, for example, can be set to 20 bar as the actuation threshold. This would allow the driver to always cancel the deceleration requested by the driver in an emergency by building up a higher hydraulic pressure via the brake pedal. Alternatively or additionally, a time period can be specified. If the driver actuates the brake pedal for a period of time greater than this threshold, the requested brake pressure is implemented. The time threshold can advantageously be set to 250 ms.

[0017] The object is further achieved by a method for controlling a hydraulic motor vehicle brake system having at least one wheel brake, a pressure supply device, and an electronic brake pedal unit which does not have a hydraulic coupling to the at least one wheel brake and the pressure supply device, but is connected to a control device via a signal line in order to transmit a brake pedal actuation variable, wherein the control device controls the pressure supply device based on the brake pedal actuation variable, wherein the implementation of a pressure build-up by means of the pressure supply device is delayed based on the brake pedal actuation variable when a hydraulic service function is active or necessary and at least one additional requirement is met.

[0018] Further features, advantages, and possible applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features, both individually and in any combination, are part of the subject matter of the invention, regardless of their summary in the claims or their references.

[0019] Fig. 1 shows schematically a braking system according to the invention;

[0020] In Fig. Figure 1 shows a redundant hydraulic braking system for motor vehicles. For example, the braking system is designed to actuate four hydraulically actuated wheel brakes 8; expansion to more wheel brakes is easily possible. For example, the wheel brakes (HL, HR) are assigned to the rear axle, and the wheel brakes (VL, VR) to the front axle of the vehicle.

[0021] The brake system comprises a first structural unit, which is designed, for example, as a first electro-hydraulic brake control unit with a valve block and a first electronic control device ECU1, and a second structural unit, which is designed, for example, as a second electro-hydraulic brake control unit with a valve block and a second electronic control device ECU2.

[0022] A pressure fluid reservoir 4 with two chambers is arranged on the first structural unit, with a first reservoir connection being assigned to the first chamber and a second reservoir connection being assigned to the second chamber. Reservoirs with three or more chambers are also possible.

[0023] A first electrically actuated pressure source 5 is arranged in the first structural unit.

[0024] In the second structural unit, a second electrically actuated pressure source 2 and wheel-individual brake pressure modulation valves are arranged, which are designed as an electrically actuated inlet valve 6 and an electrically actuated outlet valve 7 for each wheel brake 8.

[0025] The first pressure source 5 and the second pressure source 2 are connected on the pressure side to a brake supply line to which the four inlet valves 6 are connected. Thus, all four wheel brakes 8 can be actuated by means of the first pressure source 5 and / or the second pressure source 2.

[0026] An electrically actuated circuit isolation valve 40 is arranged in the brake supply line, so that when the circuit isolation valve 40 is closed, the brake supply line is separated into a first line section, to which the inlet valves 6 or the wheel brakes 8 of the rear axle are connected, and a second line section, to which the inlet valves 6 or the wheel brakes 8 of the front axle are connected. The second pressure source 2 is hydraulically connected to the first line section, and the first pressure source 5 is hydraulically connected to the second line section. When the circuit isolation valve 40 is closed, the brake system is thus separated or divided into two hydraulic brake circuits I and II.In the first brake circuit I, pressure source 2 (via the first line section) is connected only to the wheel brakes 8 of the rear axle, and in the second brake circuit II, the first pressure source 5 (via the second line section) is connected only to the wheel brakes 8 of the front axle. The circuit isolation valve 40 is advantageously designed to be open when de-energized.

[0027] As already mentioned, the braking system comprises an inlet valve 6 and an outlet valve 7 for each hydraulically actuated wheel brake 8, which are hydraulically interconnected in pairs via central connections and each connected to a hydraulic wheel connection of the second structural unit to which the corresponding wheel brake 8 is connected. A check valve opening towards the brake supply line is connected in parallel to each of the inlet valves 6. The output connections of the outlet valves 7 are connected to the pressure fluid reservoir 4 or its second chamber via a common return line. The input connections of all inlet valves 6 can be supplied with a pressure provided by the first pressure source 5 or, for example, if the first pressure source 5 fails, by the second pressure source 2.

[0028] The first electrically controllable pressure source 5 of the valve block is designed as a hydraulic cylinder-piston arrangement (or a single-circuit electro-hydraulic actuator (linear actuator)), the piston of which can be actuated by a schematically indicated electric motor with the interposition of a rotation-translation gear, also shown schematically, in particular can be moved forwards and backwards in order to build up and reduce pressure in a pressure chamber. The piston delimits the pressure chamber of the pressure source 5. To control the electric motor, a rotor position sensor (only schematically indicated) is provided that detects the rotor position of the electric motor. By means of this sensor, the piston position and speed, and thus the released or absorbed brake fluid volume, can be determined.

[0029] A system pressure line section is connected to the pressure chamber of the first electrically controllable pressure source 5. By means of the line section, the pressure source 5 or its pressure chamber is connected to a hydraulic connection of the first structural unit, which is connected to a hydraulic connection of the second structural unit via a hydraulic connecting element. This connection represents the only hydraulic pressure connection, in particular the only hydraulic connection, between the first and second structural units. It is a hydraulic connection for transmitting brake pressure for actuating the wheel brakes 8.

[0030] The pressure chamber is connected to the pressure fluid reservoir 4 via a (suction) line, regardless of the actuation state of the piston. A check valve 53, closing in the direction of the pressure fluid reservoir 4, is arranged in the line in connection with the second chamber. An electrically switchable valve 23 forms a further connection to this line, which is connected to the output port of the linear actuator 5. This isolating valve 23 is designed to be open when de-energized, so that when de-energized, the wheel brakes 8 are connected to the brake fluid reservoir 4. The cylinder-piston arrangement 5, for example, has no sniffing holes.

[0031] The second electrically controllable pressure source 2 of the second assembly is designed, for example, as a two-piston pump whose two pressure sides are interconnected. The suction sides are connected to the return line and thus to the pressure fluid reservoir 4. The pressure sides are connected to the first line section of the brake supply line.

[0032] In addition to the pressure source 2 and the brake pressure modulation valves 6, 7, an electrically actuated, preferably normally open, isolation valve 26 is arranged in the second structural unit, for example. Isolation valve 26 is hydraulically arranged between the connection and the second line section of the brake supply line. Thus, the first pressure source 5 is detachably connected to the second line section or the brake supply line via the isolation valve 26.

[0033] For example, the braking system includes a pressure sensor in brake circuit I, which is thus assigned to the second pressure source 2. This is advantageous for burst protection during active circuit separation, i.e., when the circuit separation valve 40 is closed. However, the pressure sensor can also be located in brake circuit II.

[0034] For example, the brake system for leakage monitoring comprises a level measuring device for determining a pressure medium level in the pressure medium reservoir 4.

[0035] Each valve block is assigned an electronic control unit (ECU1 and ECU2). Each electronic control unit comprises electrical and / or electronic elements (e.g., microcontrollers, power units, valve drivers, other electronic components, etc.) for controlling the electrically actuated components of the associated valve block and, if applicable, the associated sensors. The valve block and electronic control unit are advantageously designed as an electrohydraulic unit, as is known in the art.

[0036] The first electronic control device controls the first pressure source 5. For example, the first pressure source 5 is supplied with energy (from a first electrical energy source) via the first electronic control device.

[0037] The second electronic control device controls the second pressure source 2. For example, the second pressure source 2 is supplied with energy (from a second electrical energy source) via the second electronic control device.

[0038] For example, the first pressure source 5 can be or is controlled exclusively by the first electronic control device and the second pressure source 2 can be or is controlled exclusively by the second electronic control device.

[0039] The brake system has a primary pressure source 5 and a secondary pressure source 2, each electrically operated by an ECU and having a suction port and a pressure port. No brake fluid can flow into the pressure port of the secondary pressure source 2, even when de-energized. For example, the primary pressure source 5 is a linear actuator with a suction check valve 53, and the secondary pressure source 2 is a piston pump. Preferably, the secondary pressure source 2 can generate a higher pressure than the primary pressure source 5.

[0040] The suction sides of the two pressure sources 2, 5 are connected to a pressure medium reservoir 4, preferably each to at least one of two separate chambers.

[0041] The pressure side of the primary pressure source 5 is connected to a primary circuit node via an electromagnetic valve 26, also called a pressure connection valve or isolation valve.

[0042] The pressure side of secondary pressure source 2 is connected directly (without the interposition of a valve) to a secondary circuit node. The two circuit nodes are connected via an electromagnetic valve 40, also called a circuit dividing valve.

[0043] During normal operation, the pressure in the wheel brakes is built up by primary pressure source 5. The pressure in primary pressure source 5 is released by retracting its piston. The pressure is modulated for each wheel as needed by the inlet and outlet valves. If necessary, isolation valve 26 is closed so that primary pressure source 5 can draw in additional volume.

[0044] If a particularly high flow rate is required, both pressure sources 5 and 2 operate in parallel. If a particularly high pressure is required, the isolation valve 26 is closed, and the secondary pressure source 2 increases the pressure above the pressure of the primary pressure source 5. Outside of braking situations, atmospheric pressure equalization can be permanently ensured via the isolation valve 23 and the isolation valve 26.

[0045] In the event of a leak in the brake system, the circuit isolation valve 40 is closed and the system is divided into two independent brake circuits I and II.

[0046] Isolation valve 26 is preferably controlled by the secondary ECU. The following description of operation in the event of a fault refers to this valve assignment.

[0047] If the primary system fails electrically, particularly the primary or its power supply, the secondary ECU closes the isolation valve 26 to build up pressure via the secondary pressure source 2. Pressure is released via the exhaust valves 7. Preferably, the intake and exhaust valves are controlled by the secondary ECU so that the pressure can be modulated for each individual wheel.

[0048] If the secondary system fails electrically, specifically the secondary ECU or its voltage source, the pressure is increased and decreased via the primary pressure source 5, as in normal operation. Individual wheel pressure control is not required, but joint modulation of the wheel pressures remains possible to prevent the vehicle from being destabilized by locking wheels.

[0049] The control units ECU1 and ECU2 are configured to implement a pressure buildup using the linear actuator 5 and / or the piston pump 2 based on pressure requests. These requests can originate from automatic functions of the assistance program and, in particular, from the driver, who transmits the driver's request via the brake pedal. This is transmitted to the control units as a brake pedal actuation variable. The brake pedal actuation variable can be a brake pedal travel, a brake pedal force, and / or similar variables.

[0050] If a brake pedal actuation value other than zero is present, this is no longer implemented directly by controlling the pressure supply devices 2, 5 and the valves in all cases. Instead, a check is carried out to determine whether conditions exist for a delay in this implementation.

[0051] For example, if the driver presses the brake pedal during a flush / deflush routine—a process that secures the brake fluid due to leaks—the system also checks whether the parking brake is engaged. In this case, a current pedal input is not immediately applied if the vehicle is demonstrably still stationary. Advantageously, the service, i.e., the flush / deflush routine, can be shortened and interrupted at a stable point to transfer to the pressure control system.

[0052] Another scenario is when the system wakes up with the parking brake engaged and a low fluid level is detected in the reservoir. Without the inventive delay, pedaling would lead to direct pressure regulation and unnecessary loss of brake fluid volume. The inventive concept makes it possible to first perform a rapid, controlled leak location and then pressure regulation when the parking brake is released.

[0053] Important service functions can therefore still be implemented despite a driver braking request if the additional requirements guarantee the safety of the vehicle and therefore passengers.

Claims

[1] Hydraulic motor vehicle brake system comprising at least one wheel brake which can be supplied via at least one pressure supply device by means of a pressurised brake fluid, an electronic brake pedal unit which has no hydraulic coupling to the at least one wheel brake and the pressure supply device or whose hydraulic coupling is separated by a closed valve, and is connected via a signal line to a control device in order to transmit a brake pedal actuation variable, wherein the control device controls the pressure supply device based on the brake pedal actuation variable, characterized by that the implementation of a pressure build-up by means of the pressure supply device based on the brake pedal actuation value is delayed if a hydraulic service function is active or necessary and at least one additional requirement is met. [2] Hydraulic motor vehicle brake system according to claim 1, characterized by that the additional requirement includes at least the vehicle being stationary. [3] Hydraulic motor vehicle brake system according to one of the preceding claims, characterized by that the additional requirement includes at least an activated parking brake unit. [4] Hydraulic motor vehicle brake system according to claim 3, characterized by that the parking brake unit comprises an integrated parking brake, a transmission lock and / or a mechanical lock of a dry brake actuator. [5] Hydraulic motor vehicle brake system according to claim 3, characterized by that a service function is necessary if a low brake fluid level is detected. [6] Hydraulic motor vehicle brake system according to one of the preceding claims, characterized by that the service function includes a brake fluid shift. [7] Hydraulic motor vehicle brake system according to one of the preceding claims, characterized by that the service function includes heating the brake system. [8] Hydraulic motor vehicle brake system according to one of the preceding claims, characterized by that the service function includes leak localization. [9] Hydraulic motor vehicle brake system according to claim 1, characterized by that the delay is only carried out if the service function has at least a specified priority. [10] Hydraulic motor vehicle brake system according to one of the preceding claims, characterized by that the additional requirement includes that the brake pedal actuation value does not exceed a predetermined actuation threshold and / or is not applied for a period of time greater than a time threshold. [11] Hydraulic motor vehicle brake system according to one of the preceding claims, characterized bythat the delay in pressure build-up is implemented when the control device starts and an initial fault is known from the previous ignition run. [12] Method for controlling a hydraulic motor vehicle brake system comprising at least one wheel brake, a pressure supply device, an electronic brake pedal unit, which has no hydraulic coupling to the at least one wheel brake and the pressure supply device, the hydraulic coupling of which is separated by a closed valve, and is connected via a signal line to a control device in order to transmit a brake pedal actuation variable, wherein the control device controls the pressure supply device based on the brake pedal actuation variable, characterized bythat the implementation of a pressure build-up by means of the pressure supply device based on the brake pedal actuation value is delayed if a hydraulic service function is active or necessary and at least one additional requirement is met.

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