Method for operating brake system in motor vehicle and brake system for motor vehicle

Abstract

To provide a method for operating a brake system inside a motor vehicle.SOLUTION: One step of the method includes detecting (S1) a value of the supply voltage of a brake force device of a brake system. Another step includes detecting (S3) a brake request that a user of the motor vehicle inputs (S2) to a brake pedal of the brake system. When the supply voltage is equal to a first threshold voltage or greater than the first threshold voltage (S4), output by the brake force device is generated (S5) in accordance with the brake request and in accordance with a first characteristic line. In contrast, when the supply voltage is smaller than the first threshold voltage (S4), output by the brake force device is generated (S6) in accordance with the brake request and in accordance with a second characteristic line.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method of operating a brake system in a motor vehicle and to a brake system for a motor vehicle. [Background technology]

[0002] Electromechanical brake force boosters for motor vehicles are known that allow the pedal feel to be adjusted in relation to the force required by the driver when operating the brake pedal ("pedal force adjustment" = PFA). Brake systems with simulators that generate the pedal feel are also known. Brake systems with simulators typically have a fixed force-stroke characteristic (characteristic line), and the corresponding deceleration or braking force is adjustable.

[0003] Furthermore, it is known that a brake booster monitors the required supply voltage and turns off the brake booster when the voltage falls below a certain minimum voltage. In this case, the driver must brake the vehicle using only his own force, without brake force assistance. This case is also called "mechanical backup." In this case, the force that the driver must apply is significantly higher than when the brake booster is active. Therefore, a considerable number of drivers may find it difficult to apply the force required to brake the vehicle in mechanical backup mode. This may result in a correspondingly high safety risk.

[0004] Patent Document 1 discloses a method for operating a vehicle brake system for a motor vehicle having hydraulically operated wheel brakes on the front axle and electromechanically operated wheel brakes on the rear axle. The wheels on the rear axle can be driven at least temporarily by an electric motor, which operates as a generator to recover braking energy and thereby generate braking force on the rear axle. A pedal stroke sensor detects the driver's braking request and supplies it to an open-loop and closed-loop control unit. The open-loop and closed-loop control unit distributes the brake force between the hydraulically operated wheel brakes, the electromechanically operated wheel brakes, and the electric motor, which can operate in generator mode. To improve energy recovery, this brake force distribution is implemented so that, in the range of slight vehicle deceleration, the proportion of brake force on the rear axle is greater than the proportion of brake force on the front axle. At the rear axle, power is generated exclusively or almost exclusively by the generator.

[0005] Patent Document 2 describes a method for operating a brake system of a motor vehicle, which includes a user-operable brake pedal that is mechanically coupled to a main brake cylinder of the brake system for pumping hydraulic fluid. A brake force generator pumps hydraulic fluid through the brake system, thereby generating hydraulic brake pressure in the brake system and supplying it to wheel brake devices of the brake system. The brake pressure generated by the brake force generator and the actuation stroke of the brake pedal are detected. Depending on the detected brake pressure and the actuation stroke, a first partial volume of hydraulic fluid is supplied to a storage chamber of the brake system through a valve.

[0006] Patent Document 3 describes a method for controlling a hydraulic brake system having a hydraulic main brake cylinder operable by a brake pedal and a simulator unit hydraulically connected to the main brake cylinder via a simulator valve. A pressure supply device supplies hydraulic pressure to one or more wheel brakes based on brake pedal actuation and a pedal characteristic line. When the simulator valve is closed, a switchover is made from a first pedal characteristic line to a second pedal characteristic line. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2008 / 003614 [Patent Document 2] German Patent Application Publication No. 102022200558 [Patent Document 3] German Patent Application Publication No. 102022202019 Summary of the Invention

[0008] The inventors recognized the problems in the prior art and set themselves the task of providing an improved brake system and a corresponding method for operating a brake system in a motor vehicle that allows the driver to prepare for a mechanical backup in the event of a supply voltage drop. In particular, it is desirable to indicate to the driver that only reduced brake force assistance can be provided by adapting the pedal feel. This can improve safety because the driver can adapt to having to exert a higher pedal force. Furthermore, it is advantageous to achieve a low current required for brake force assistance.

[0009] The problem of the present invention is solved by a method for operating a brake system in a motor vehicle according to claim 1. Furthermore, according to a second aspect of the present invention, there is provided a brake system for a motor vehicle according to claim 8. Preferred configurations of the invention are the subject of the dependent claims, the drawings and the description of the examples.

[0010] According to the present invention, the supply voltage of a braking force device of a braking system can be monitored, thereby determining the value of the supply voltage. This monitoring can preferably be performed continuously or periodically, for example, several times per minute or several times per second. For this purpose, for example, a control unit or the like can be connected to the braking force device via a bus system or the like within the vehicle, and can thereby determine the supply voltage and compare it with a preset threshold voltage.

[0011] A preferred braking system may include one or more brake force devices. A typical brake force device may include, for example, a master brake cylinder connected to the brake pedal and a brake force booster.

[0012] A preferred braking force device may comprise an ABS (anti-lock system) and / or an ESP ("electronic stability program") and / or a BWA ("by-wire actuator").

[0013] In a preferred embodiment, a sensor for detecting the pressure on the brake pedal or detecting the pedal stroke can be arranged on the brake pedal, which generates a corresponding sensor signal that can be transmitted to one or more brake force devices.

[0014] A vehicle user or driver can provide an input or generate a braking request by exerting pressure or force on or displacing the brake pedal. In response to the input or braking request, the brake force device generates an output that acts on mechanical brakes on the vehicle's wheels. In this way, the brake force device is used as a brake force booster in a known manner, so that the driver does not have to apply all of the brake force required to brake the vehicle.

[0015] To function properly, a brake force device requires a supply voltage, which is provided, for example, via the vehicle's onboard electrical grid. If the supply voltage drops or fails completely, the brake force device can no longer provide much or even no brake force boost. In this case, the driver must apply most of the brake force himself via the brake pedal. The possibility of generating braking action by applying pressure to the brake pedal when there is no or only little brake force boost from the brake force device is also called a "mechanical backup."

[0016] The present invention is particularly concerned with cases where there is not yet a complete failure of the supply voltage, but rather a continuous transfer to a mechanical backup is performed in the event of a drop in the supply voltage, in order to prepare the driver for a reduced or even complete failure of brake force boost.

[0017] When the supply voltage is equal to or greater than the first threshold voltage, the brake force device generates an output in response to the input and in response to the first characteristic line, which corresponds to normal operation of the brake system. The first characteristic line is thus the normal characteristic line. The first threshold voltage may also be referred to as the rated voltage of the brake force device.

[0018] The first characteristic line may preferably have a jump-in, a slope, and a run-out. The jump-in causes the output to be generated only after a minimum input force is applied. The slope determines how strongly the input force is boosted, and thus corresponds to the boost factor. The run-out may have a reduced slope or boost. By adjusting the three parameters (jump-in, slope, and run-out), the pedal feel can be adjusted.

[0019] When the detected supply voltage is less than the first threshold voltage, the output by the braking force device is generated according to the input and according to a second characteristic line. The second characteristic line is flatter than the first characteristic line, so that the braking force device generally generates a smaller braking force boost. In the event of a complete failure (the supply voltage is equal to zero), the braking force device generally no longer generates a braking force boost. This obvious case, however, should not be interpreted as a "second characteristic line" according to the present invention. In other words, it is obvious that a detected supply voltage less than the first threshold voltage is greater than zero.

[0020] The second characteristic line may preferably have a jump-in and / or slope and / or runout similar to the first characteristic line. The jump-in of the second characteristic line may preferably be smaller than the jump-in of the first characteristic line. The slope of the second characteristic line may preferably be smaller than the slope of the first characteristic line. The runout of the second characteristic line may preferably be smaller than the runout of the first characteristic line. In other words, the second characteristic line is generally flatter than the first characteristic line. As a result, the brake force boost provided by the second characteristic line is smaller than that provided by the first characteristic line, and operation with mechanical backup is not yet necessary.

[0021] When the supply voltage is less than the second threshold voltage, the output by the brake force device may be generated according to the input and according to the third characteristic line. The second threshold voltage is less than the first threshold voltage. At this time, it should be noted that the second threshold voltage is greater than zero. This prevents a complete failure of the brake force device. By presetting the second threshold voltage, a continuous transition to a mechanical backup can be achieved, and the driver continues to be provided with minimal assistance. Further reducing the brake force assistance additionally reduces the energy consumption of the brake force device, so that emergency driving can be maintained for a longer period of time, thereby improving safety.

[0022] The jump-in of the third characteristic line may preferably be smaller than the jump-in of the second characteristic line. The slope of the third characteristic line may preferably be smaller than the slope of the second characteristic line. The runout of the third characteristic line may preferably be smaller than the runout of the second characteristic line. In other words, the third characteristic line may be flatter than the second characteristic line.

[0023] The invention will be explained in more detail below on the basis of examples shown in schematic drawings. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 2 is a schematic diagram illustrating an exemplary first characteristic line of a braking force device. [Figure 2] 3 is a schematic diagram illustrating an exemplary transition from a first characteristic line to a second characteristic line of a braking force device. FIG. [Figure 3] FIG. 10 is a diagram comparing a first characteristic line of a braking force device with a third characteristic line, and showing a characteristic line of a mechanical backup. [Figure 4] FIG. 10 compares a first characteristic line of a braking force device with an alternative configuration of a third characteristic line and with the characteristic line of a mechanical backup. [Figure 5] 1 is a flow diagram of an exemplary method according to the present invention for operating a brake system. DETAILED DESCRIPTION OF THE INVENTION

[0025] The accompanying drawings are intended to provide a further understanding of embodiments of the present invention. The drawings illustrate embodiments and, together with the description, serve to explain the principles and concepts of the present invention. Other embodiments and many of the stated advantages will become apparent from a consideration of the drawings. Elements of the drawings are not necessarily to scale relative to each other.

[0026] In the figures of the drawings, elements, features and components that are the same, functionally identical or have the same effect are respectively designated by the same reference numerals unless otherwise configured differently.

[0027] 1, 2, 3, and 4 each show a characteristic line of a brake force device. Each of these characteristic lines represents the relationship between the input applied by the user to the brake pedal and the output generated by the brake force device. The output acts, in particular, on the mechanical friction brakes on the vehicle wheels.

[0028] FIG. 1 shows an exemplary first characteristic line K1, which has a jump-in, a slope in the middle section of the characteristic line K1, and a run-out with a smaller slope than the middle section. The jump-in causes the power output to be generated at its initial value only when a minimum force is applied. In particular, the jump-in facilitates simple adjustment of braking action in low deceleration ranges. The run-out indicates the range beyond which no additional brake force boost is implemented. The increase in power output is now only caused by additional input force applied by the driver. By adapting the jump-in, slope, and run-out, the pedal feel can be adjusted.

[0029] 2 compares the first characteristic line K1 from FIG. 1 with an exemplary second characteristic line K2 for a state in which the supply voltage of the brake force device is less than the first threshold voltage. The illustrated second characteristic line K2 no longer has a jump-in. Furthermore, the slope in the mid-section and the runout are flatter, resulting in a flatter overall second characteristic line K2.

[0030] The present invention thereby provides for a gradual or continuous reduction in the capacity of the braking force device when the supply voltage is reduced, for example, in a first reduced voltage region where the supply voltage is less than a first threshold voltage and greater than a second threshold voltage, the capacity of the braking force device can be reduced according to the second characteristic line K2 shown in FIG.

[0031] Figure 3 shows the case where the supply voltage is lowered below the second threshold voltage but still greater than zero. The third characteristic line K3 provides minimal assistance to the driver. The runout is lowered so strongly that the driver is only assisted when overcoming the initial force, but not when boosting. This is significantly easier for the driver than the mechanical backup M (see characteristic line M in Figure 3), which requires a high initial force.

[0032] A high input voltage is required at the third characteristic line K3 to boost the vehicle's braking, so that the driver is already prepared for a possible subsequent downgrade to the mechanical backup M. The advantage of a strong downgrade when the supply voltage is low is that in addition to allowing the driver to get used to the reduced performance of the brake power system, it also limits the current consumption by the brake power system, thereby preserving, for example, a battery that may already be damaged in any case, and thus delaying a complete failure in time.

[0033] A second example of a third characteristic line K3' for minimal brake force assistance is shown in FIG. 4. The third characteristic line K3' has a negative jump-in, as shown diagrammatically by the dotted line. That is, in the jump-in region without an increase in input power, an increase in input power without an increase in output power is required, instead of achieving higher power output with minimal brake force assistance. Compared to the mechanical backup M, the input power after which the power output begins to increase is, however, lower, since the brake force system still assists the driver from this point onward. Additionally, the boost can also be reduced compared to the first characteristic line K1.

[0034] All these adaptations of the pedal feel can be achieved via a conventional Pedal Feel Adjustment (PFA) and therefore will not be described in detail here, where the target control amount of the brake force booster is adapted (to reduce the assist, increase the target differential stroke).

[0035] Brake systems with simulators usually have a fixed force-stroke characteristic, but the corresponding deceleration can be adjusted. According to the explanation in the paragraph above, the achieved deceleration can also be reduced for simulator systems. As a result, the driver experiences a higher pedal stroke and a higher pedal force (in the case of the system described in the paragraph above, the stroke is the same, only an increase in force occurs).

[0036] Because motor braking force is not additive to the driver in the simulator system, performance reduction is only meaningful up to the point where mechanical backup performance has been achieved. Nevertheless, the driver can prepare for mechanical backup performance with a preventative reduction.

[0037] A brake system with a simulator is characterized in that the driver pushes brake fluid into the simulator during normal driving. The simulator generates a force-stroke characteristic curve, which the driver perceives as pedal feel, via a spring set or similar. Pressure and / or brake pedal displacement can be measured. The target deceleration can then be determined via the characteristic curve. The target deceleration is generated in the wheel brakes by pressure generators. In this state, the wheel brakes are hydraulically decoupled from the driver. The level of the generated pressure can therefore be freely selected (technically). This allows the deceleration to be set lower for undervoltage cases than for normal cases. The driver must then brake more firmly to achieve the desired deceleration. In the event of a complete supply voltage failure, the driver is decoupled from the simulator and recoupled to the wheels by switching the valves (or by returning the valves to their de-energized state). This means that, in a mechanical backup, the driver brakes the wheels directly. This places a lower limit on the braking performance of such a system.

[0038] FIG. 5 shows a flow chart illustrating a method according to the invention for operating a braking system in a motor vehicle.

[0039] In a first step S1, the value of the supply voltage of the braking force device of the braking system is detected, preferably the supply voltage may be monitored continuously.

[0040] In step S2, a user or driver of the vehicle generates a braking command by exerting an input on the vehicle's brake pedal, which is then detected in step S3.

[0041] In step S4, the detected supply voltage is compared with a first threshold voltage.

[0042] If the supply voltage is equal to or greater than the first threshold voltage, in step S5, an output by the brake force device is generated according to the input and according to the first characteristic line, which corresponds to normal operation of the brake system.

[0043] If the supply voltage is, however, less than the first threshold voltage, then in step S6, an output by the braking force device is generated in response to the input and in response to a second characteristic line, which, as described above, is flatter than the first characteristic line.

[0044] In the present invention, features are designated as "first" and "second." These designations are used solely to clearly distinguish between individual features. In particular, no spatial or functional priority is to be derived from these designations.

[0045] Whenever the term "or" appears in this application in connection with a list of alternatives, it should be understood that this refers to each listed alternative alone or, where meaningful, to a combination of more than one or all of the listed alternatives. [Explanation of symbols]

[0046] K1 First characteristic line K2 Second characteristic line K3, K3' Third characteristic line M characteristic line, mechanical backup S1 Step S2 Step S3 Step S4 Step S5 Step S6 Step

Claims

1. 1. A method of operating a brake system in a motor vehicle, comprising: A step (S1) of detecting a value of a supply voltage of a braking force device of the braking system; detecting (S3) a braking request input (S2) by a user of the vehicle on a brake pedal of the braking system; comparing the supply voltage with a first threshold voltage (S4); (S5) generating an output by the braking force device in response to the braking request and in response to a first characteristic line when the supply voltage is equal to or greater than a first threshold voltage; or (S6) generating the output by the braking force device in accordance with the braking request and in accordance with a second characteristic line when the supply voltage is less than the first threshold voltage; Including, A method for operating a braking system in a motor vehicle.

2. The method of claim 1 , wherein the brake request represents an input force on the brake pedal and / or a displacement of the brake pedal.

3. The method according to claim 1 or 2, wherein the first characteristic line has a jump-in, a slope, and a run-out.

4. The method according to claim 1 , wherein the second characteristic line has a jump-in, a slope and a run-out.

5. the jump-in of the second characteristic line is smaller than the jump-in of the first characteristic line, and / or the slope of the second characteristic line is less than the slope of the first characteristic line; and / or The runout of the second characteristic line is smaller than the runout of the first characteristic line. The method according to claims 3 and 4.

6. generating the output by the braking force device in response to the input and in response to a third characteristic line when the supply voltage is less than a second threshold voltage; At this time, the second threshold voltage is lower than the first threshold voltage.

6. The method according to any one of claims 1 to 5.

7. the jump-in of the third characteristic line is smaller than the jump-in of the second characteristic line, and / or the slope of the third characteristic line is smaller than the slope of the second characteristic line; and / or the runout of the third characteristic line is smaller than the runout of the second characteristic line; The method of claim 6.

8. A braking system for a motor vehicle, comprising: a brake force device that generates an output to operate one or more wheel brakes; a brake pedal through which a user inputs a braking request; Equipped with The braking force device is generating said output in response to said braking request and in response to a first characteristic line when the supply voltage is equal to or greater than a first threshold voltage; or generating the output in response to the braking request and in response to a second characteristic line when the supply voltage is less than the first threshold voltage; It is composed of Brake systems for automobiles.

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