Method for operating a braking system of a motor vehicle, control device, hydraulic braking system and motor vehicle

Abstract

The invention relates to a method for operating a braking system of a motor vehicle, wherein a hydraulic pressure in the braking system is monitored and, in the event of a pressure loss, an electric pressure generator is always controlled in such a way that the hydraulic pressure is increased. The invention also relates to an associated control device, an associated hydraulic braking system and an associated motor vehicle.

Description

[0001] Method for operating a braking system of a motor vehicle, control device, hydraulic braking system and motor vehicle

[0002] The invention relates to a method for operating a braking system of a motor vehicle, a control device, a hydraulic braking system for a motor vehicle and a motor vehicle with such a braking system.

[0003] Braking systems are typically used to decelerate motor vehicles in a targeted manner. Many braking systems are typically operated in such a way that hydraulic pressure can be built up using a manually operated master cylinder and / or an electrically operated pressure generator, which can then be used to generate braking pressure in the wheel brakes. Modern braking systems typically have a device for measuring pressure in the hydraulic system. However, how to respond to a potentially measured pressure drop can be problematic.

[0004] It is therefore an object of the invention to provide a method for operating a braking system of a motor vehicle, which is alternatively or better designed than known embodiments, for example, exhibiting an improved response to a detected pressure drop. It is also an object of the invention to provide a control device and a hydraulic braking system for implementing such a method. Furthermore, it is an object of the invention to provide a motor vehicle with such a braking system.

[0005] This is achieved according to the invention by a method, a control device, a hydraulic braking system and a motor vehicle according to the respective main claims. Advantageous embodiments can be taken, for example, from the respective subclaims. The content of the claims is made part of the description by express reference. The invention relates to a method for operating a braking system of a motor vehicle. The motor vehicle typically has at least two axles, each with at least one wheel. The braking system has one or more brakes, each of which is assigned to at least one wheel for applying braking torque. The braking system is hydraulic and has at least one electric pressure generator for building up hydraulic pressure. The motor vehicle preferably has, in addition to the braking system, a further braking system which can preferably be actuated independently of the braking system.

[0006] The procedure comprises the following steps:

[0007] Monitoring hydraulic pressure in the brake system and, if a loss of pressure is detected, always controlling the pressure generator to generate or increase the hydraulic pressure.

[0008] Using such a method, it is possible to react advantageously to a detected pressure loss. It was recognized that if there is an additional braking system that can be actuated independently of the braking system, the hydraulic pressure can in principle be generated or increased using the pressure generator. This is because even if the pressure loss has occurred due to a leak and idling of the hydraulic braking system is therefore to be expected, the additional braking system is available and can decelerate the vehicle. A loss of safety is therefore not associated with the basic generation or increase of hydraulic pressure. In particular, measures that ensure the functionality of the braking system even if a leak has occurred in the braking system can be dispensed with.

[0009] In particular, the method can be implemented in a braking system or its control device in such a way that no other reaction to a pressure loss than that specified is possible. In other words, the reaction upon detection of a pressure loss occurs in response to the detection of a pressure loss. The two axles can typically be a front axle and a rear axle. A motor vehicle can in principle also have more than one axle at the front and / or rear; for example, vehicles such as trucks or buses can be provided with two rear axles. In a multi-track motor vehicle, an axle typically has at least two wheels. It can be provided that there is only one wheel on each side of the motor vehicle. However, the provision of several wheels on each side is also possible, for example in the case of dual tires.In a single-track motor vehicle, each axle typically has only one wheel. This corresponds, for example, to the typical design of a motorcycle. However, hybrid designs are also possible, such as a trike, which has only one wheel at the front and two wheels at the rear.

[0010] A brake can be designed as a friction brake, for example, a drum brake or a disc brake. If it is assigned to only one wheel, it can brake that wheel. If it is assigned to multiple wheels, for example, both wheels of a dual-tire system, it can brake these wheels.

[0011] Typically, the hydraulic braking system contains a certain volume of hydraulic fluid, such as brake fluid. This fluid can be pressurized by the pressure generator. This pressure can typically be used in the brakes to build up braking force or braking torque. Valves are typically provided for this purpose, which can control the pressure buildup at the respective brakes. The pressure generator is typically electric, thus generating the pressure without the use of human muscle power.

[0012] The additional braking system can be actuated independently of the braking system. This ensures, in particular, independent braking capability of the vehicle, so that, preferably, even in the event of a complete failure of the braking system, the motor vehicle can be braked by means of the additional braking system. In particular, it can be provided that the braking system and the additional braking system can implement a braking request from a driver and / or a vehicle control system independently of one another. In particular, the braking system and the additional braking system can be controlled simultaneously and / or in combination in order to implement a driver braking request. Advantageously, the additional braking system, if it is a hydraulic braking system, has a hydraulic circuit that is completely decoupled from the braking system.In particular, it can also be provided that the braking system and the additional braking system are or can be fed from different on-board electrical systems, so that in particular an independent power supply is ensured. Further measures can also be implemented to ensure independent actuation. In particular, it can be provided that the additional braking system can be actuated independently of the braking system in that the additional braking system has no components in common with the braking system and / or is connected to a different on-board electrical system and / or is supplied electrically by a different on-board electrical system than the braking system. As an alternative to supply from different on-board electrical systems, it can also be provided that the braking system and the additional braking system are supplied via the same two on-board electrical systems, so that in the event of a failure of one on-board electrical system, it can be assumed that both braking systems will continue to function.

[0013] The hydraulic pressure in the braking system can be monitored, for example, by means of one or more pressure sensors. This can, in particular, be done continuously. It can, for example, be done at certain time intervals. A pressure loss can, for example, be detected if the measured hydraulic pressure falls below a threshold value and / or remains below a predetermined threshold value for a predetermined minimum period of time. In this case, it may be necessary to react to the detected pressure loss. According to the invention, the reaction is always by controlling the pressure generator to generate or increase the hydraulic pressure. By "generating" is meant, in particular, that before the pressure generator is controlled to generate the hydraulic pressure, the pressure generator does not generate any hydraulic pressure.Increasing the hydraulic pressure means, in particular, that the pressure generator already generates hydraulic pressure prior to the activation described here, but that this pressure is increased by the activation. A generated hydraulic pressure can then be increased.

[0014] In particular, it can be provided that the braking system, in addition to the electric pressure generator, has a brake cylinder that can be operated manually and / or by muscle power and can also generate hydraulic pressure. This can be a master brake cylinder, for example a tandem master brake cylinder. The braking system can also have a simulator. Typically, the brake cylinder that can be operated manually and / or by muscle power and the simulator can be separated from the rest of the braking system by means of an isolating valve. During normal braking operation, a force generated in the master brake cylinder typically acts on the simulator, with the isolating valve being closed. The braking request is then implemented by means of the electric pressure generator and / or by means of the further braking system.

[0015] By generating or increasing the hydraulic pressure using the electric pressure generator as described herein, it is possible to advantageously respond to a situation in which the pressure drop is caused by an air bubble or other bubble having formed in the hydraulic system, which must be compressed before pressure can build up, thus hindering the pressure buildup. Such a condition can often not be distinguished, at least not directly, from a condition in which the pressure loss is caused by a leak. In the embodiment described herein, the basic reaction is to increase the pressure, thus addressing the former cause, in particular without carrying out leak tests.However, if the second cause, i.e. a leak, actually occurs, this does not pose a safety risk in the implementation described here, since the additional braking system is available for braking tasks. In particular, it can be provided that the pressure generator is activated to generate or increase the hydraulic pressure immediately after a pressure loss is detected or a predetermined time after a pressure loss is detected. This can ensure that the same reaction always occurs when a pressure loss is detected. In particular, whether and when the pressure generator is activated does not depend on other parameters such as the outcome of tests. The predetermined time can, in particular, be specified in such a way that it is permanently stored in the braking system or a control system of the braking system. In particular, the pressure generator is activated after a pressure loss is detected for the first time.It is therefore preferable not to wait until several pressure losses are detected.

[0016] In particular, it can be provided that the control of the pressure generator to generate or increase the hydraulic pressure occurs independently of a leak test. This ensures that the same reaction is always provided as soon as a pressure loss is detected. In particular, no leak tests or similar tests are performed before the pressure generator is activated. It has been shown that this is not necessary in the design described here.

[0017] In particular, it can be provided that when a pressure loss is detected, between the detection of a pressure loss and the activation of the pressure generator to generate or increase the hydraulic pressure, and / or during the activation of the pressure generator to generate or increase the hydraulic pressure, no valves are closed that are fluidly connected between the pressure generator and the brakes. This prevents brakes from being disconnected, which would then no longer be available for braking.

[0018] In particular, if a pressure loss is detected, the pressure generator can always remain connected or be connected to at least one brake, or to some or all of the brakes. This ensures immediate braking action. Disconnecting brakes and / or the pressure generator to prevent the braking system from shutting down due to a leak can advantageously be omitted. If the pressure generator is already connected to the respective brake before a pressure loss is detected, it can remain connected. Otherwise, it can be connected. This can be achieved, in particular, by appropriately switching existing valves.

[0019] According to one embodiment, it can be provided that, after a pressure loss has been detected, the pressure generator remains connected to all brakes for at least as long as the pressure generator is controlled to generate or increase the hydraulic pressure, or until the braking system is taken out of operation. According to one embodiment, it can be provided that, after a pressure loss has been detected, the pressure generator remains connected to at least one brake, or to some, but not all, brakes, for at least as long as the pressure generator is controlled to generate or increase the hydraulic pressure, or until the braking system is taken out of operation. In particular, valves can be switched such that the pressure generator remains connected to the brakes as specified. This results in the pressure generator acting on the brakes.Measures that would require fluid separation between the pressure generator and the brakes, such as leak tests, can be advantageously omitted. The braking system can be deactivated, for example, when parking or otherwise shutting down the vehicle.

[0020] In particular, if a pressure loss is detected, the braking system can always remain in a mode in which the hydraulic pressure is applied entirely or partially by the electric pressure generator. Disconnecting the pressure generator to prevent the braking system from shutting down due to a possible leak can be advantageously omitted. In particular, existing valves can be switched accordingly.

[0021] In particular, the additional braking system can be an electromechanical braking system. This allows the advantages of a hydraulic braking system and an electromechanical braking system to be advantageously combined. In an electromechanical braking system, electromechanical brake actuators typically act directly on the respective brake, i.e., without the need for an intermediate hydraulic system. This allows braking force to be generated directly by means of an electromechanical brake actuator.

[0022] According to one embodiment, the braking system has only brakes on one front axle or multiple front axles of the motor vehicle. According to one embodiment, the braking system has only brakes on one rear axle or multiple rear axles of the motor vehicle. This allows the effect of the braking system to be concentrated on one axle. Instabilities of a motor vehicle due to different failure events in the braking systems can thus be avoided.

[0023] In particular, the braking system may not have brakes on at least one axle of the motor vehicle. This can reduce the complexity. In such a design, the braking system can be used selectively to brake one or more axles, but not all axles.

[0024] In particular, the further braking system may have one or more brakes on an axle of the motor vehicle on which the braking system has no brake.

[0025] In particular, the additional braking system can exclusively have brakes on one or more axles of the motor vehicle, on which the braking system does not have brakes. This allows, in particular, the two braking systems to be divided such that each axle is braked either by the braking system or by the additional braking system.

[0026] According to one embodiment, each axle of the motor vehicle has at least or exactly two wheels. This corresponds to the typical design of a multi-track motor vehicle. In principle, however, the design described here can also be used for single-track motor vehicles. A design with multiple wheels per side and axle is also possible. This can be understood as dual tires.

[0027] In particular, a pressure loss can be detected based on the hydraulic pressure falling below a predefined or dynamic threshold. A predefined threshold can, for example, be permanently programmed. It can, for example, be designed so that it can only be changed with special effort, such as during a visit to the workshop using a special programming device. A dynamic threshold can, for example, be changed depending on a driving situation, environmental influences, or other parameters.

[0028] In particular, it may be provided that a pressure loss is detected based on the hydraulic pressure remaining below a predetermined or dynamic threshold for at least a predetermined period of time. This can prevent a random, short-term undershoot of the threshold from triggering measures, even if it is unlikely to be due to a malfunction.

[0029] The following describes a possible embodiment that can be implemented within the framework of the method described so far, but can also be implemented independently and thus represents a separate aspect of the invention. This embodiment and the specific embodiments mentioned can therefore also be claimed independently of the method features and other features described so far.

[0030] It may be provided that, in response to the braking system and / or the motor vehicle being switched off, the following steps are carried out:

[0031] Determining at least one value of an operating parameter of the braking system,

[0032] Determining whether the value of the operating parameter is in a critical range and, in response to the value of the operating parameter being in a critical range, controlling the pressure generator to increase the hydraulic pressure.

[0033] This procedure can be used, in particular, to prevent bubbles from forming within the hydraulic system. This procedure can be applied in particular when the braking system is not in use, for example when the motor vehicle is parked. This can be manifested, for example, by an activated parking brake or a switched-off ignition. The operating parameter can, in particular, be selected such that it indicates an increased risk of bubbles forming within a certain value range. Such bubbles can make it more difficult to build up pressure and thus result in a pressure loss. By deliberately increasing the hydraulic pressure using the pressure generator, particularly when the motor vehicle is stationary, bubble formation is prevented and the braking system continues to function normally.

[0034] In particular, the operating parameter can be the temperature of a component of the braking system. Such a temperature can be measured, for example, using a temperature sensor. It can also be determined using a temperature model, whereby such a temperature model typically estimates a temperature based on one or more other parameters. For example, energy flows can be considered for this purpose. The temperatures of several components can also be considered and / or other operating parameters can be used. These can, for example, be evaluated summarily, or each operating parameter can be evaluated individually. In the latter case, it can be provided, in particular, that each operating parameter can separately trigger control of the pressure generator.The method may in particular further comprise the following step before, during or after controlling the pressure generator to increase the hydraulic pressure:.

[0035] Controlling one or more valves of the braking system in such a way that the hydraulic pressure is confined in a section of the braking system.

[0036] Such a section can, in particular, be a subsection of the braking system, i.e., not the entire hydraulic system. This section can be separated from the rest of the hydraulic system, for example, by switching valves. This allows the pressure to be maintained within this section and prevents the pressure from possibly dissipating at points outside this section. This can also prevent the formation of bubbles.

[0037] When one or more valves are activated, at least one valve can be closed, which separates a master brake cylinder and / or a simulator from the rest of the braking system. A master brake cylinder is typically a hydraulic pressure generator that can be operated manually and / or using muscle power. A simulator is typically a device that absorbs the pressure generated in the master brake cylinder during normal braking operation and thus gives the driver a realistic braking feel, whereas the hydraulic pressure actually used in the brakes is applied by the electric pressure generator. By separating the master brake cylinder and / or simulator, pressure is prevented from being reduced in these components, which can occur, for example, if a brake pedal is pushed outwards or a spring in the simulator is compressed.

[0038] In particular, depending on whether the value of the operating parameter is within the critical range, the pressure generator can be controlled to increase the hydraulic pressure by at least 5 bar and / or by a maximum of 15 bar. Such increased pressure values ​​have proven advantageous for typical applications, as they effectively prevent unwanted bubble formation while simultaneously avoiding component overload. In principle, however, other values ​​can also be used. The pressure increase can be determined, in particular, with reference to a pressure existing immediately before the pressure generator is controlled to increase the pressure.

[0039] In particular, in response to the fact that the value of the operating parameter is in the critical range, the pressure generator can be controlled to increase the hydraulic pressure within a predetermined pressure range. This allows a specific pressure range, or alternatively just a single pressure value, to be set independently of the previously existing pressure, which advantageously prevents bubble formation.

[0040] In particular, in response to the fact that the value of the operating parameter is in a critical range, the pressure generator can be controlled to increase the hydraulic pressure above ambient pressure. By increasing the pressure above ambient pressure, bubble formation can be prevented. In particular, the ambient pressure can be the ambient air pressure. This can be measured or it can be implemented as an assumption in a control system using a predetermined value. For example, this can be an assumed average pressure of one atmosphere or 1,013 mbar.

[0041] In particular, after it has been determined that the value of the operating parameter is in the critical range while the braking system and / or the motor vehicle are switched off, the pressure generator can be controlled again to increase the hydraulic pressure. This can occur in particular in addition to the already mentioned control to increase the hydraulic pressure and / or in particular after the previous control has ended and a certain time has passed thereafter. In particular, the pressure generator can be controlled again at predetermined time intervals and / or in response to the hydraulic pressure falling below a predetermined activation threshold. As a result, the previously described functionality of preventing bubble formation by increasing the pressure after the braking system or the motor vehicle has been switched off can occur not just once, but multiple times.

[0042] According to one embodiment, it can be provided that only when an operating hour counter of the braking system has reached at least a predetermined value is it determined whether the operating parameter is in a critical range. According to one embodiment, it can be provided that only when an operating hour counter of the braking system has reached at least a predetermined value, in response to the value of the operating parameter being in a critical range, is the pressure generator activated to increase the hydraulic pressure. Such embodiments can prevent a pressure increase from occurring to prevent bubble formation, even though such bubble formation is not yet to be expected even at elevated temperatures due to the operating time of the braking system.The hour meter may be zero, particularly during vehicle production, and / or reset to zero after a brake fluid change. The hour meter typically indicates how long the braking system has been operating since the hour meter was last reset. It does not necessarily display the number of operating hours per se; it may alternatively display a value that can be converted to the number of operating hours or otherwise indicate this number.

[0043] Preferably, any pressure generated is released before the vehicle starts moving again.

[0044] In particular, it can be provided that it is determined that the value of the operating parameter is in the critical range if the value of the operating parameter is above or below a predetermined critical threshold value. The critical range can then extend, for example, from this critical threshold value to the respective end of a value range. Alternatively, a narrower definition of a value range is also possible. For example, the critical threshold value can be a boiling point of a hydraulic fluid. This can prevent evaporation of hydraulic fluid by increasing the pressure, for example if the temperature, which can be used as an operating parameter, rises above the boiling point.

[0045] In particular, once the value of the operating parameter has returned outside the critical range, the hydraulic pressure can be reduced and / or one or more valves of the brake system can be opened. This allows the previously described measures to prevent blistering to be reversed once there is no longer any risk of blistering. This can prevent unnecessary stress on components.

[0046] The invention further relates to a control device for a braking system, in particular for a hydraulic braking system, which is configured to carry out a method as described herein. With regard to the method, all embodiments and variants described herein can be used. In particular, the control device can be configured such that the aforementioned reaction to a pressure loss always occurs. In particular, it can be provided that no reaction other than the aforementioned reaction to a pressure loss occurs. In particular, it can be provided that no leak test is implemented for the braking system.

[0047] The invention further relates to a non-volatile computer-readable storage medium on which program code is stored, the execution of which causes a processor to perform a method as described herein. With regard to the method, all embodiments and variants described herein can be used.

[0048] The invention further relates to a hydraulic braking system for a motor vehicle. The braking system has one or more brakes. The braking system has at least one electric pressure generator for generating a hydraulic pressure to actuate the brakes. The braking system has a control device configured to carry out a method as described herein. With regard to the method, all embodiments and variants described herein can be used. The advantages already mentioned can thus be achieved. In particular, all implementations described with reference to the method, even insofar as they relate to device features, can be applied to the described braking system.

[0049] The invention further relates to a motor vehicle with a braking system as described herein. With regard to the braking system, all embodiments and variants described herein can be used. The advantages already described can thus be achieved.

[0050] In particular, the motor vehicle may have an additional braking system, which can preferably be actuated independently of the braking system. This makes it possible to achieve the advantages already described, namely that a fundamentally identical reaction to a detected pressure loss can occur without compromising the safety of the motor vehicle.

[0051] In particular, the additional braking system can be an electromechanical braking system. However, the use of a hydraulic braking system as an additional braking system is also possible in principle.

[0052] In other words, it was found that when a vehicle braking system with hydraulic brakes or wheel brakes is subjected to a worst-case temperature scenario, for example during long downhill driving, the brake fluid can heat up significantly locally in the area of ​​the wheel brakes. If the boiling point of the brake fluid is exceeded, vapor bubbles form, which must be compressed as additional volume by the brake pressure generators before pressure can be built up and the brake can then generate clamping force and ultimately braking torque in accordance with the pressure. This increases the pressure build-up time. In extreme cases, it can also happen that a pressure generator reaches its volume limit, thus impairing the braking effect. This is known as pedal diarrhea when the brake is hot. As the water content in the brake fluid increases, the boiling point drops and the failure described becomes more likely.For this reason, brake fluid changes are required every two years in most vehicles to prevent excessive water content.

[0053] In a braking system with a hydraulic simulator, also known as brake-by-wire with hydraulic fallback mode, the pressure generator can draw in new volume from a brake fluid reservoir in by-wire operation and compress the vapor bubbles. One problem here is the conflicting system monitoring. If there is no system pressure, a system pressure monitor can leave the by-wire state and switch to the hydraulic fallback mode, which can particularly result in direct driver intervention. This can be done, for example, to prevent a hydraulic leak in the pressure generator from preventing it from being shut down in time. Volume monitoring, on the other hand, prefers to remain in by-wire operation and compensate for any volume deficit, which is the correct strategy in the case of vapor bubbles.In the case of large additional volumes, however, leaks and vapor locks are often indistinguishable, which can lead to shutdown and, in the case of vapor locks, pedal failure. For example, in a mixed system that operates electrohydraulically on the front axle and electromechanically on the rear axle, or vice versa, a different strategy can be chosen: the system generally remains in by-wire mode, both when absorbing additional volume in the event of a leak and in the event of a possible vapor lock formation. If the system is mistaken, only the braking force on one axle is lost; the other axle remains capable of braking, since there are no vapor locks there either to endanger the system. This achieves effective vapor lock compensation and, at least from a safety perspective, the system can forgo changing the brake fluid or extend the change interval, for example from two years to six years.However, boiling brake fluid can not only generate water vapor bubbles, but also air bubbles due to this outgassing, which do not completely disappear after the fluid cools down. Thus, while the immediate danger can be averted after a temperature limit load case in which the fluid boils, the brake system should be bled afterward, for example, in a service center, and the residual air should be reduced to a level below a monitoring threshold.

[0054] Since this superheating of the liquid usually occurs in the shut-down state after the temperature limit load case, in particular in the so-called "heat soak", the following procedure is proposed, which can be carried out separately or in combination with the other procedures described herein.

[0055] If such a borderline maneuver takes place, during which the formation of vapor locks is to be feared when the vehicle is switched off, the system can remain active in the switched off state and supply the wheel brakes with a low pressure via the by-wire pressure generator, for example 10 bar, and then volumetrically lock this condition by closing the MCV (Master Cut Valve) or the isolation valve. Since the pressure can change due to cooling or reheating, the system can remain active and keep the pressure within specified limits, in particular between an upper threshold and a lower threshold, for example 10 bar ± 5 bar. The distance between the thresholds can be specified, in particular through the accuracy of the pressure setting. In particular, it can be ensured that a pressure greater than ambient pressure is present at all times. It may also be necessary to compensate for small valve leaks.This volume limitation prevents unwanted expansion of the vapor bubbles or prevents their formation. As soon as the temperature has fallen below a boiling point or another point, the system can reduce the brake pressure or restore the connection to the atmosphere by opening the MCV. The MCV can, in particular, be a valve that separates a master brake cylinder and / or a simulator from the rest of the hydraulic system. It can also be referred to as an isolation valve. In particular, a temperature can be controlled using a temperature model that can determine the cooling accurately enough. This can be supported by input data on the ambient temperature, the applied braking energy, and a measured temperature, for example from a load cell sensor and, if applicable, in electromechanical brakes.As a result, for example, it is no longer necessary to vent a motor vehicle after such a scenario, since the formation of vapor bubbles when parked can be prevented by the measures described here.

[0056] In particular, the measures described herein can be used within the framework of a brake-by-wire braking system, in particular a brake-by-wire simulator braking system. In particular, a hydraulic version can be provided on the front axle and an electromechanical version on the rear axle. However, the reverse is also possible. Other configurations are also possible.

[0057] Individual brake temperatures and the brake fluid temperature can be modeled, particularly by balancing the applied braking energy, vehicle-specific cooling conditions, and measured temperatures (e.g., via a sensor, force sensor, or engine temperature). Detection and warning can be implemented when increased volume absorption occurs due to the brake fluid beginning to boil. In particular, by-wire operation can be continued in all cases, even if large vapor bubbles may form.

[0058] When the vehicle is switched off, volume limitation can be implemented, in particular, by closing the MCV and / or by actively replenishing lost volume, in particular monitored by system pressure and to prevent the formation of vapor bubbles when stationary. The applied system pressure can be regulated, in particular, between two thresholds; the lower threshold is preferably greater than the ambient pressure. Controlling and terminating the volume limitation when stationary can be achieved, in particular, by a temperature model. A particular advantage of this is that the time interval for changing the brake fluid can be extended. Vapor bubbles that form in the braking system as a result of heating typically no longer pose a hazard.

[0059] Further features and advantages will become apparent to those skilled in the art from the exemplary embodiment described below with reference to the accompanying drawings. These show:

[0060] Fig. 1 : a braking system, and

[0061] Fig. 2: a motor vehicle.

[0062] Fig. 1 shows purely schematically a braking system BS according to an embodiment of the invention.

[0063] The braking system BS has a master brake cylinder HBZ, which can be operated manually using a brake pedal BP. It has a simulator S, which is connected to the master brake cylinder HBZ via a simulator valve SIV. Both the master brake cylinder HBZ and the simulator valve SIV are connected to an isolating valve MCV, as shown. In contrast to the two components mentioned, master brake cylinder HBZ and simulator S, an on-off valve ZV is connected to the isolating valve MCV, which is connected to a pressure generator DE in the opposite direction to the isolating valve MCV. The pressure generator DE is designed here as a linear actuator and is driven by an electric motor M. This enables discontinuous pressure generation. Alternatively, the use of a piston pump, which can deliver pressure continuously in particular, would also be possible.

[0064] The braking system BS has a brake fluid reservoir BFB. This allows the braking system BS to be supplied with brake fluid without pressure. As shown, it is connected to the pressure generator DE via a check valve and is also connected to the master brake cylinder HBZ for sucking in brake fluid. The braking system BS has a first brake B1 and a second brake B2. These act on a first wheel R1 and a second wheel R2. The brakes B1, B2 are connected to the pressure-generating components via a first inlet valve E1 and a second inlet valve E2. Furthermore, the brakes B1, B2 are connected to the brake fluid reservoir BFB via a first outlet valve A1 and a second outlet valve A2. This allows the brakes B1, B2 to be selectively pressurized and the pressure can also be released again via the outlet valves A1, A2.

[0065] To measure the hydraulic pressure, two pressure sensors are shown, labeled U / p. One pressure sensor U / p is connected to the master brake cylinder HBZ, and another is connected on the opposite side of the isolation valve MCV, so that it can measure the pressure present between the isolation valve MCV, the activation valve ZV, and the input valves E1 and E2.

[0066] The braking system BS has a control device SV. This is designed, among other things, to detect when the braking system BS or the motor vehicle containing the braking system BS is switched off and parked. In this case, it calculates a temperature of the components of the braking system BS using a temperature model. If this temperature is above a critical threshold value, which is in particular a boiling point of the brake fluid used, the pressure generator DE or its electric motor M is controlled such that the pressure in the braking system is increased to a value above atmospheric pressure, in particular a value approximately 10 bar above the previously existing pressure. This is maintained in particular until the temperature model indicates that the temperature has dropped below the critical threshold value. After the pressure has been generated, the isolation valve MCV is closed and the generated pressure is thus locked in.This prevents pressure loss due to the flexibility of components of the master brake cylinder (HBZ) or the simulator S. This measure can prevent the brake fluid from evaporating and forming bubbles due to excessive temperatures, which can occur, for example, during long downhill rides followed by immediate parking of the vehicle. These bubbles could potentially impair the functionality of the brake system (BS).

[0067] Fig. 2 shows a purely schematic view of a motor vehicle KF in which the braking system BS is installed, although not all components of the braking system BS are shown. The braking system BS acts on the front axle, with the first wheel R1 being a left front wheel and the second wheel R2 being a right front wheel. Furthermore, the motor vehicle KF also has a further braking system WBS. This is controlled by a further control device WSV and is designed as a purely electromechanical braking system. It therefore has no hydraulic components. The motor vehicle KF has a rear axle with a left rear wheel, which is a third wheel R3, and a right rear wheel, which is a fourth wheel R4. The third wheel R3 is braked by a third brake B3 of the further braking system WBS. The fourth wheel R4 is braked by a fourth brake B4 of the further braking system WBS.The braking system BS and the additional braking system WBS can be controlled completely independently of each other and are designed completely independently of each other.

[0068] This ensures that if one of the two braking systems BS, WBS fails, the other is still functional.

[0069] The control device SV is implemented to detect a pressure loss in the brake system BS by means of at least one of the two pressure sensors U / p. This can occur in particular when the measured pressure falls below a threshold value. In this case, the control device SV generally controls the pressure generator DE in such a way that the pressure is increased. The inlet valves E1, E2 (not shown in Fig. 2) are opened in the process. This ensures that, if the pressure loss is due to bubble formation, the bubbles are compressed and the pressure for braking can be built up. It is also possible that the pressure loss is due to a leak, in which case increasing the pressure and opening the valves can lead to brake fluid leaking out.However, this is not safety-critical in this case, since the additional braking system WBS is designed to be completely independent and redundant to the braking system BS and thus the motor vehicle KF can still be braked via the additional braking system WBS.

[0070] The steps mentioned in the method according to the invention can be carried out in the specified order. However, they can also be carried out in a different order, as long as this is technically reasonable. The method according to the invention can be carried out in one of its embodiments, for example, with a specific combination of steps, in such a way that no further steps are carried out. However, in principle, further steps can also be carried out, even those not mentioned.

[0071] It should be noted that features may be described in combination in the claims and the description, for example, to facilitate understanding, although they may also be used separately. Those skilled in the art will recognize that such features may also be combined independently with other features or combinations of features.

[0072] References in subclaims may indicate preferred combinations of the respective features, but do not exclude other combinations of features.

[0073] List of reference symbols

[0074] BS braking system

[0075] DE pressure generator

[0076] M electric motor

[0077] BP brake pedal

[0078] HBZ master brake cylinder

[0079] BFB brake fluid reservoir

[0080] SV control device

[0081] R wheel

[0082] B Brake

[0083] A exhaust valve

[0084] E Inlet valve

[0085] U / p pressure sensor

[0086] Central locking valve

[0087] MCV isolation valve

[0088] SIV simulator valve

[0089] S Simulator

[0090] WBS additional braking system

[0091] WSV additional control device

[0092] KF motor vehicle

Claims

Patent claims 1 . Method for operating a braking system (BS) of a motor vehicle (KF), wherein the motor vehicle (KF) has at least two axles, each with at least one wheel (R), wherein the braking system (BS) has one or more brakes (B), each of which is assigned to at least one wheel (R) for applying braking torque, wherein the braking system (BS) is hydraulic and has at least one electric pressure generator (DE) for building up hydraulic pressure, wherein the motor vehicle (KF) has, in addition to the braking system (BS), a further braking system (WBS) that can be actuated independently thereof, wherein the method comprises the following steps: Monitoring a hydraulic pressure in the brake system (BS), and if a pressure loss is detected, always controlling the pressure generator (DE) to generate or increase the hydraulic pressure.

2. Method according to claim 1, wherein the control of the pressure generator (DE) to generate or increase the hydraulic pressure takes place immediately after the detection of a pressure loss or a predetermined time after the detection of a pressure loss.

3. Method according to one of the preceding claims, wherein the control of the pressure generator (DE) for generating or increasing the hydraulic pressure takes place independently of a leak test.

4. Method according to one of the preceding claims, wherein upon detection of a pressure loss, between the detection of a pressure loss and the activation of the pressure generator to generate or increase the hydraulic pressure, and / or during the activation of the pressure generator to generate or increase the hydraulic pressure no valves are closed which are fluidically connected between the pressure generator (DE) and the brakes (BE).

5. Method according to one of the preceding claims, wherein when a pressure loss is detected, the pressure generator (DE) always remains or is connected to at least one brake (B), or to some or all of the brakes (B).

6. Method according to one of the preceding claims, wherein the pressure generator (DE) remains connected to all brakes (B) after a pressure loss has been detected at least as long as the pressure generator (DE) is controlled to generate or increase the hydraulic pressure, or remains connected until the braking system (BS) is taken out of operation.

7. Method according to one of claims 1 to 5, wherein the pressure generator (DE) remains connected to at least one brake (B), or to some but not all brakes (B), after a pressure loss has been detected, at least as long as the pressure generator (DE) is controlled to generate or increase the hydraulic pressure, or until the braking system (BS) is taken out of operation.

8. Method according to one of the preceding claims, wherein when a pressure loss is detected, the braking system (BS) always remains in a mode in which the hydraulic pressure is applied wholly or partly by means of the electrical pressure generator (DE).

9. Method according to one of the preceding claims, wherein the further braking system (WBS) is an electromechanical braking system.

10. Method according to one of the preceding claims, wherein the braking system (BS) has only brakes (B) on one front axle or several front axles of the motor vehicle (KF).

11. Method according to one of claims 1 to 9, wherein the braking system (BS) has only brakes (B) on one rear axle or several rear axles of the motor vehicle (KF).

12. Method according to one of the preceding claims, wherein the braking system (BS) has no brakes (B) on at least one axle of the motor vehicle (KF).

13. Method according to one of the preceding claims, wherein the further braking system (WBS) has one or more brakes (B) on an axle of the motor vehicle (KF) on which the braking system (BS) has no brake (B).

14. Method according to one of the preceding claims, wherein the further braking system (WBS) exclusively has brakes (B) on one or more axles of the motor vehicle (KF) on which or on which the braking system (BS) has no brakes (B).

15. Method according to one of the preceding claims, wherein each axle of the motor vehicle (KF) has at least two wheels (R).

16. A method according to any one of the preceding claims, wherein a pressure loss is detected in response to the hydraulic pressure falling below a predetermined or dynamic threshold.

17. A method according to any one of the preceding claims, wherein a pressure loss is determined in response to the hydraulic pressure remaining below a predetermined or dynamic threshold for at least a predetermined period of time.

18. Method according to one of the preceding claims, which further comprises the following steps in response to the braking system (BS) and / or the motor vehicle (KF) being switched off: determining at least one value of an operating parameter of the braking system (BS), determining whether the value of the operating parameter is in a critical range, and in response to the value of the operating parameter being in a critical range, controlling the pressure generator (DE) to increase the hydraulic pressure.

19. The method according to claim 18, wherein the operating parameter is a temperature of a component of the braking system (BS).

20. The method according to claim 18 or 19, further comprising the following step before, during or after controlling the pressure generator (DE) to increase the hydraulic pressure: controlling one or more valves of the brake system (BS) such that the hydraulic pressure is confined in a portion of the brake system (BS).

21. Method according to claim 20, wherein when one or more valves are activated, at least one valve (MCV) is closed, which valve separates a master brake cylinder (HBZ) and / or a simulator (S) from the rest of the brake system (BS).

22. Method according to one of claims 18 to 21, wherein, in response to the value of the operating parameter being in the critical range, the pressure generator (DE) is controlled to increase the hydraulic pressure by at least 5 bar and / or by at most 15 bar.

23. Method according to one of claims 18 to 22, wherein in response to the value of the operating parameter being in the critical range, the pressure generator (DE) is controlled to increase the hydraulic pressure into a predetermined pressure range.

24. Method according to one of claims 18 to 23, wherein in response to the value of the operating parameter being in the critical range, the pressure generator (DE) is controlled to increase the hydraulic pressure to more than ambient pressure.

25. Method according to one of claims 18 to 24, wherein, after it has been determined that the value of the operating parameter is in the critical range while the braking system (BS) and / or the motor vehicle (KF) are switched off, the pressure generator (DE) is again controlled to increase the hydraulic pressure.

26. The method according to claim 25, wherein the pressure generator (DE) is reactivated at predetermined time intervals and / or in response to the hydraulic pressure falling below a predetermined activation threshold.

27. The method according to any one of claims 18 to 26, wherein it is determined that the value of the operating parameter is in the critical range if the value of the operating parameter is above or below a predetermined critical threshold value.

28. Method according to one of claims 18 to 27, wherein, after the value of the operating parameter is again outside the critical range, the hydraulic pressure is reduced again and / or one or more valves of the brake system (BS) are opened.

29. The method according to any one of claims 18 to 28, wherein only when an operating hour counter of the braking system (BS) has reached at least a predetermined value is it determined whether the operating parameter is in a critical range; and / or wherein only when an operating hour counter of the braking system (BS) has reached at least a predetermined value, in response to the value of the operating parameter being in a critical range, is the pressure generator (DE) activated to increase the hydraulic pressure.

30. Control device (SV) for a braking system (BS), which is configured to carry out a method according to one of the preceding claims.

31. Hydraulic braking system (BS) for a motor vehicle (KF), comprising one or more brakes (B), at least one electric pressure generator (DE) for generating a hydraulic pressure for actuating the brakes (B), and a control device (SV) configured to carry out a method according to one of claims 1 to 29.

32. Motor vehicle (KF), comprising a braking system (BS) according to claim 31.

33. Motor vehicle (KF) according to claim 32, further comprising an additional braking system (WBS) that can be actuated independently of the braking system (BS).

34. Motor vehicle (KF) according to claim 33, wherein the additional braking system (BS) is an electromechanical braking system.

Images