Method for operating a braking system in a motor vehicle and braking system for a motor vehicle

Abstract

The present invention relates to a method for operating a braking system in a motor vehicle. One step of the method serves to detect (S1) a value of a supply voltage to a braking force device of the braking system. A further step serves to detect (S3) a braking request that a user of the motor vehicle inputs into a brake pedal of the braking system (S2). If (S4) the supply voltage is equal to or greater than a first threshold voltage, an output force is generated by the braking force device depending on the braking request and according to a first characteristic curve (S5). If, on the other hand, (S4) the supply voltage is less than the first threshold voltage, the output force is generated by the braking force device depending on the braking request and according to a second characteristic curve (S6).

Description

State of the art

[0001] The present invention relates to methods for operating a braking system in a motor vehicle and to a braking system for a motor vehicle.

[0002] Electromechanical brake boosters for motor vehicles are known that allow the adjustment of the pedal feel with respect to the force required by the driver when depressing a brake pedal ("Pedal Force Adjustment" = PFA). Brake systems that incorporate a simulator to generate pedal feel are also known. Such brake systems with a simulator typically have a fixed force-displacement characteristic (curve), whereby the corresponding deceleration or braking force is adjustable.

[0003] Furthermore, it is known to monitor the required supply voltage in brake boosters and to deactivate the brake booster if a certain minimum voltage is undershot. In this case, the driver must brake the vehicle without power assistance, relying solely on their own strength. This is also referred to as "mechanical backup." The force required by the driver in this situation is significantly higher than with an active brake booster. Therefore, some drivers may find it difficult to exert the necessary force to brake the vehicle in mechanical backup mode. Consequently, a high safety risk can arise.

[0004] WO 2008 / 003 614 A1 discloses a method for operating a vehicle braking system for motor vehicles with hydraulically actuated wheel brakes on a front axle and electromechanically actuated wheel brakes on a rear axle. The rear axle wheels can be driven, at least temporarily, by an electric motor that operates as a generator to recuperate braking energy and thereby generates a braking force at the rear axle. A pedal position sensor detects a braking request from the driver and transmits this information to a control unit, which distributes the braking force between the hydraulically actuated wheel brakes, the electromechanically actuated wheel brakes, and the electric motor operating in generator mode. To increase energy recuperation, the braking force distribution is adjusted during low vehicle deceleration such that the proportion of braking force at the rear axle is greater than the proportion of braking force at the front axle.Power is generated exclusively or almost exclusively by the generator at the rear axle.

[0005] DE 10 2022 200 558 A1 describes a method for operating a motor vehicle's braking system, comprising a user-operated brake pedal mechanically coupled to a master brake cylinder of the braking system to circulate hydraulic fluid. A brake force generator circulates hydraulic fluid within the braking system to generate hydraulic brake pressure and supply it to a wheel brake assembly. The brake pressure generated by the brake force generator and the travel of the brake pedal are detected. Depending on the detected brake pressure and the travel of the pedal, an initial volume of hydraulic fluid is supplied through a valve to a storage chamber of the braking system.

[0006] DE 10 2022 202 019 A1 relates to a method for controlling a hydraulic brake system with a hydraulic master brake cylinder actuated by a brake pedal and a simulator unit hydraulically connected to the master brake cylinder via a simulator valve. A pressure supply device provides hydraulic pressure to one or more wheel brakes based on brake pedal actuation and a pedal characteristic curve. If a simulator valve fails to open, the system switches from a first pedal characteristic curve to a second pedal characteristic curve. Disclosure of the invention

[0007] The inventors recognized the problem in the prior art and set themselves the task of providing an improved braking system and a corresponding method for operating a braking system in a motor vehicle that prepares the driver for the mechanical backup in the event of a drop in supply voltage. Specifically, the system is designed to indicate to the driver, by adjusting the pedal feel, that only reduced brake force assistance can be provided. This increases safety, as the driver can prepare to apply more pedal force. Furthermore, it advantageously reduces the amount of current required for brake force assistance.

[0008] The problem addressed by the invention is solved by a method for operating a braking system in a motor vehicle according to claim 1. Furthermore, according to a second aspect of the invention, a braking system for a motor vehicle is provided according to claim 7. Preferred embodiments of the invention are the subject of the dependent claims, the drawings, and the description of exemplary embodiments.

[0009] According to the invention, the supply voltage of a braking force device of the braking system is monitored in order to detect a value of the supply voltage. The monitoring can preferably be continuous or periodic, for example several times per minute or several times per second. For this purpose, a control unit or the like can be connected to the braking force device via an internal bus system or the like of the vehicle in order to detect the supply voltage and compare it with a predetermined threshold voltage.

[0010] A preferred braking system may include one or more braking force devices. A typical braking force device includes, for example, a master brake cylinder coupled to a brake pedal and a brake booster.

[0011] A preferred braking force device may include an ABS (Anti-lock Braking System) and / or an ESP (Electronic Stability Program) and / or a BWA (by-wire actuator).

[0012] In preferred embodiments, sensors can be arranged on the brake pedal to detect pressure on the brake pedal or to detect pedal travel. The sensors can generate corresponding sensor signals and transmit them to one or more brake force devices.

[0013] A user or driver of the vehicle can input a force or request braking by applying pressure or force to the brake pedal or by deflecting the brake pedal. Depending on the input force or braking request, the braking system generates an output force that acts on the mechanical brakes at the vehicle's wheels. In this way, the braking system functions as a brake booster, so that the driver does not have to apply the entire braking force required to slow the vehicle.

[0014] To function properly, the braking system requires a supply voltage, which is provided, for example, by the vehicle's electrical system. If the supply voltage drops or fails completely, the braking system can only provide minimal or no brake force amplification. The driver must then apply most of the braking force manually via the brake pedal. The ability to generate braking by applying pressure to the brake pedal when there is no or only minimal brake force amplification from the braking system is also known as "mechanical backup."

[0015] The present invention relates in particular to a case in which there is not yet a total failure of the supply voltage. Rather, when the supply voltage drops, a continuous transition to the mechanical backup is to be carried out in order to prepare the driver for the fact that the brake force amplification will decrease or may fail completely.

[0016] When the supply voltage is equal to or greater than a first threshold voltage, the output force is generated by the braking system depending on the input force and according to a first characteristic curve. This corresponds to the normal operation of the braking system. The first characteristic curve is therefore the normal characteristic curve. The first threshold voltage can also be referred to as the nominal voltage of the braking system.

[0017] The first characteristic curve preferably features a jump, a slope, and a run-out. The jump ensures that an output force is only generated when a minimum input force is applied. The slope determines how much the input force is amplified and thus corresponds to an amplification factor. The slope, or amplification, can be reduced at the run-out. By adjusting the three parameters—jump, slope, and run-out—the pedal feel can be customized.

[0018] If the detected supply voltage is lower than the first threshold voltage, the output force is generated by the braking force device depending on the input force and a second characteristic curve. The second characteristic curve is flatter than the first, so the braking force device generally generates a lower braking force amplification. In the event of a total failure (supply voltage equal to zero), the braking force device typically no longer generates any braking force amplification. However, this trivial case is not to be understood as a "second characteristic curve" according to the invention. In other words, it is understood that the detected supply voltage, which is lower than the first threshold voltage, is greater than zero.

[0019] The second characteristic curve, like the first, may preferably have a jump and / or a slope and / or a run-off. The jump of the second characteristic curve may preferably be smaller than the jump of the first characteristic curve. The slope of the second characteristic curve may preferably be smaller than the slope of the first characteristic curve. The run-off of the second characteristic curve may preferably be smaller than the run-off of the first characteristic curve. In other words, the second characteristic curve is generally flatter than the first characteristic curve. Thus, the braking force amplification with the second characteristic curve is lower than with the first characteristic curve, without yet requiring operation in mechanical backup mode.

[0020] If the supply voltage is lower than a second threshold voltage, the output force can be generated by the braking system depending on the input force and a third characteristic curve. The second threshold voltage is lower than the first threshold voltage. It is important to note that the second threshold voltage is greater than zero. Therefore, a complete failure of the braking system does not yet occur. By setting the second threshold voltage, a continuous transition to the mechanical backup can be achieved, while still providing the driver with minimal assistance. Further reducing the braking assistance also lowers the energy consumption of the braking system, allowing emergency operation to be maintained for longer periods, thus improving safety.

[0021] The step in the third characteristic curve can preferably be smaller than the step in the second characteristic curve. The slope of the third characteristic curve can preferably be smaller than the slope of the second characteristic curve. The roll-off of the third characteristic curve can preferably be smaller than the roll-off of the second characteristic curve. In other words, the third characteristic curve can be flatter than the second characteristic curve.

[0022] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures. These figures show: Fig. Figure 1 shows a schematic representation of an exemplary first characteristic curve of a braking force device; Fig. Figure 2 shows a schematic representation of an exemplary transition from the first characteristic curve to a second characteristic curve of the braking force device; Fig. 3 compares the first characteristic curve with a third characteristic curve of the braking force device and shows a characteristic curve of a mechanical backup; Fig. 4 compares the first characteristic curve with an alternative implementation of the third characteristic curve of the braking force device and the characteristic curve of the mechanical backup; and Fig. Figure 5 illustrates a process of an exemplary method according to the invention for operating the braking system.

[0023] The accompanying figures are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain the principles and concepts of the invention. Other embodiments and many of the advantages mentioned will become apparent with reference to the drawings. The elements of the drawings are not necessarily shown to scale.

[0024] In the figures of the drawing, identical, functionally equivalent and similarly acting elements, features and components - unless otherwise stated - are each provided with the same reference symbols.

[0025] In Fig. 1, Fig. 2, Fig. 3 and Fig. Figure 4 shows the characteristic curves of a braking system. These curves describe the relationship between the input force applied by a user to the brake pedal and the output force generated by the braking system. The output force acts primarily on the mechanical friction brakes at the vehicle's wheels.

[0026] Fig. Figure 1 illustrates an exemplary first characteristic curve K1 with a jump, a slope in a central section of the curve, and a run-off area with a gentler slope than the central section. The jump ensures that an output force with an initial value is only generated when a minimum force is applied. In particular, the jump can simplify the modulation of the braking effect in the low deceleration range. The run-off area denotes the range beyond which no additional braking force amplification occurs. An increase in the output force is only achieved here by an additional input force applied by the driver. By adjusting the jump, slope, and run-off area, the pedal feel can be fine-tuned.

[0027] Fig. 2 compares the first characteristic curve K1 from Fig. Figure 1 shows an exemplary second characteristic curve K2 for a state where the supply voltage of the braking force device is lower than a first threshold voltage. The second characteristic curve K2 shown no longer exhibits a step. Furthermore, the slope in the middle section and the run-off are flatter, so that the second characteristic curve K2 is flatter overall.

[0028] The invention thus effects a stepwise or continuous reduction in the power of the braking system as the supply voltage decreases. For example, in a first reduced voltage range, where the supply voltage is less than a first threshold voltage and greater than a second threshold voltage, the power of the braking system can be reduced according to the invention described in the invention. Fig. The second characteristic curve K2 shown in 2 will be lowered.

[0029] Fig. Figure 3 illustrates a case where the supply voltage has dropped below the second threshold voltage but is greater than zero. The third characteristic curve, K3, provides minimal support to the driver. The coast-down is so significantly reduced that the driver is only assisted in overcoming the initial force, not in building up pressure. This is advantageous for the driver compared to the mechanical backup M, which requires high initial forces (see characteristic curve M in Figure 3). Fig. 3) a significant simplification.

[0030] For pressure build-up to brake the vehicle, the third characteristic curve, K3, requires a high input force, thus preparing the driver for the potential subsequent degradation to the mechanical backup system, M. Besides allowing the driver to become accustomed to the reduced performance of the braking system, an advantage of significant degradation at low supply voltages is the limitation of current consumption by the braking system, thereby protecting, for example, an already damaged battery. This can delay total failure.

[0031] A second example of the third characteristic curve K3' for minimal brake force support is in Fig. Figure 4 illustrates this. The third characteristic curve, K3', includes a negative step, as indicated by the dotted line. This means that instead of achieving a higher output force without increasing the input force in the area of ​​the step, with minimal brake force assistance, an increase in the input force is necessary without increasing the output force. Compared to the mechanical backup M, the input force at which the output force increases is lower, as the brake force assists the driver from this point onward. Additionally, the gain can also be reduced compared to the first characteristic curve, K1.

[0032] All these pedal feel adjustments can be implemented via the established Pedal Feel Adjustment (PFA) and are therefore not explained in detail here. This involves adjusting the target control variable of the brake booster (to reduce assistance, the target differential travel is increased).

[0033] Braking systems with a simulator typically have a fixed force-displacement characteristic, but the corresponding deceleration can be adjusted. As explained in the section above, the deceleration achieved can also be reduced for simulator systems. This results in a greater pedal travel and higher pedal force for the driver (in the systems described in the section above, there is only an increase in force while maintaining the same travel distance).

[0034] Since the engine's braking force in simulator systems does not act additively to the driver, reducing performance is only useful until the performance of the mechanical backup is reached. Nevertheless, the driver can be prepared for the performance of the mechanical backup by preemptively reducing the engine's power.

[0035] A braking system with a simulator is characterized by the fact that, during normal operation, the driver transfers brake fluid into the simulator. This simulator, using a spring assembly or similar mechanism, generates a force-displacement characteristic that the driver perceives as pedal feel. Pressure and / or deflection of the brake pedal can be measured. This allows a target deceleration to be determined via a characteristic curve. This deceleration is generated by a pressure generator at the wheel brakes. In this state, the wheel brakes are hydraulically decoupled from the driver. The level of pressure generated can therefore (technically speaking) be freely selected. This allows the deceleration to be set lower than under normal conditions in the event of a power failure. The driver then has to brake harder to achieve the desired deceleration. In the event of a complete power failure, valve switching (or...)(The return of the valves to their de-energized state) decouples the driver from the simulator and couples them to the wheels. This means that in the mechanical backup, the driver brakes directly into the wheels. This represents the lower limit of braking performance for such a system.

[0036] Fig. Figure 5 shows a flowchart illustrating a method according to the invention for operating a braking system in a motor vehicle.

[0037] In the first step S1, a value of the supply voltage of the braking force device of the braking system is recorded. Preferably, the supply voltage can be continuously monitored.

[0038] In step S2, a user or driver of the vehicle generates a braking command by applying an input force to a brake pedal of the vehicle. Consequently, in step S3, the generated input force is recorded.

[0039] In step S4, the measured supply voltage is compared with a first threshold voltage.

[0040] If the supply voltage is equal to or greater than a first threshold voltage, an output force is generated in step S5 by the braking force device, depending on the input force and according to a first characteristic curve. This corresponds to the normal operation of the braking system.

[0041] However, if the supply voltage is lower than the first threshold voltage, the output force in step S6 is generated by the braking force device depending on the input force and according to a second characteristic curve. As described above, the second characteristic curve is flatter than the first.

[0042] In the present invention, several features are designated as "first" and "second". These designations serve only to clearly distinguish the individual features. In particular, no spatial or functional arrangement or prioritization should be derived from them.

[0043] If the present application contains a list of alternatives marked with the term “or”, it should be understood that the listed alternatives should be understood to be taken individually, but also, where appropriate, as a combination of several or all of the listed alternatives. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2008 / 003 614 A1

[0004] DE 10 2022 200 558 A1

[0005] DE 10 2022 202 019 A1

[0006]

Claims

[1] Method for operating a braking system in a motor vehicle; Detection (S1) of a value of a supply voltage of a braking force device of the braking system; Detection (S3) of a braking request that a user of the motor vehicle inputs to a brake pedal of the braking system (S2); Comparing (S4) the supply voltage with a first threshold voltage; and if the supply voltage is equal to or greater than a first threshold voltage, generating (S5) an output force by the braking force device depending on the braking request and depending on a first characteristic curve; or If the supply voltage is less than the first threshold voltage, the output force is generated (S6) by the braking force device depending on the braking request and depending on a second characteristic curve. [2] Method according to claim 1, wherein the braking request describes an input force at the brake pedal and / or a deflection of the brake pedal. [3] Method according to claim 1 or 2, wherein the first characteristic curve has a jump, a slope and a run-off. [4] Method according to one of the preceding claims, wherein the second characteristic curve has a jump, a slope and a run-off. [5] Method according to claims 3 and 4, wherein the step in the second characteristic curve is smaller than the step in the first characteristic curve; and / or the slope of the second characteristic curve is smaller than the slope of the first characteristic curve; and / or The slope of the second characteristic curve is smaller than the slope of the first characteristic curve. [6] Method according to one of the preceding claims, wherein if the supply voltage is less than a second threshold voltage, the output force is generated by the braking force device depending on the input force and depending on a third characteristic curve, wherein the second threshold voltage is less than the first threshold voltage. [7] Method according to claim 6, wherein the step in the third characteristic curve is smaller than the step in the second characteristic curve; and / or the slope of the third characteristic curve is smaller than the slope of the second characteristic curve; and / or The slope of the third characteristic curve is smaller than the slope of the second characteristic curve. [8] Braking system for a motor vehicle, comprising: a braking force device for generating an output force for actuating one or more wheel brakes; and a brake pedal for a user to input a braking request, wherein the braking force device is configured: to generate the output force depending on the braking request and depending on a first characteristic curve, when the supply voltage is equal to or greater than a first threshold voltage; or to generate the output force depending on the braking request and depending on a second characteristic curve, when the supply voltage is smaller than the first threshold voltage.

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