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

Abstract

Method for operating a braking system of a motor vehicle, comprising a friction braking device and a recuperative braking device, in which the cleaning requirement of the respective wheel brakes of the friction braking device of the motor vehicle is determined (V1) and a braking force required for a given deceleration of the motor vehicle is determined (V2), wherein a first, predetermined part of this braking force is distributed to the recuperative braking device and the remainder of the required braking force is distributed to the friction braking device (V3), wherein the braking force provided by the friction braking device is distributed to the wheel brakes depending on the determined cleaning requirement of the respective wheel brakes, wherein the first predetermined part of the braking force is selected to be the maximum possible recuperation power of the recuperative braking device.where, if the braking force required for the specified deceleration of the motor vehicle is less than or equal to the maximum possible recuperation power of the recuperation braking system and the cleaning requirement has been determined, the first specified part of the braking force is selected as a lower recuperation power than the maximum possible recuperation power of the recuperation braking system and the remainder of the required braking force is distributed to the friction braking system.

Description

[0001] The present invention relates to a method for operating a braking system of a motor vehicle, a control device for a braking system of a motor vehicle, and a motor vehicle with a braking system and a control device.

[0002] German patent application DE 10 2016 222 504 A1 discloses a method for removing contaminants from at least one brake disc of a motor vehicle. The motor vehicle comprises at least one mechanical brake with at least one brake disc and a regenerative braking system. The method determines the degree of contamination of the brake disc and detects an activation signal from the regenerative braking system. Furthermore, the mechanical brake with the at least one brake disc is automatically actuated to remove contaminants from the brake disc, taking into account the determined degree of contamination, when the activation signal from the regenerative braking system is detected.When the mechanical brake is automatically applied, taking into account the determined degree of contamination of the brake disc, the deceleration of the recuperation braking device is reduced accordingly once the activation signal of the recuperation braking device has been detected.

[0003] A method for operating a vehicle braking system is also known from DE 10 2020 204 345 A1, wherein the braking system comprises at least one friction brake and at least one regenerative brake. A defined switching pattern for switching between a self-cleaning operating mode for cleaning the friction brake and a normal operating mode of the braking system is specified. The method involves determining information describing the state of the at least one friction brake and determining the state of the at least one friction brake from this information. Furthermore, it is determined whether the state meets a specific switching criterion. If the self-cleaning operating mode is to be activated according to the switching pattern and the state of the friction brake does not meet the switching criterion, the activation of the self-cleaning operating mode is suppressed and the normal operating mode is maintained.

[0004] Furthermore, a method for cleaning a vehicle's friction brake system is known from DE 10 2017 205 810 A1. In this method, a corrosion characteristic value is determined for each friction brake of the system. If the corrosion characteristic value of at least one friction brake exceeds a predetermined threshold, the vehicle's brake force distribution system is configured to use the at least one friction brake for which the corrosion characteristic value exceeding the predetermined threshold was determined more frequently during future braking maneuvers compared to a standard configuration of the brake force distribution system.

[0005] Furthermore, EP 2 159 117 A1 discloses a method for repairing a friction brake in a vehicle which, in addition to the friction brake, has a recuperation brake.

[0006] The object of the present invention is to provide a solution which enables particularly good cleaning of the respective wheel brakes of a motor vehicle with particularly high energy recuperation of braking energy.

[0007] This problem is solved by the subject matter of the independent claims. Further possible embodiments of the invention are disclosed in the dependent claims, the description, and the figures.

[0008] The invention relates to a method for operating a motor vehicle's braking system. This motor vehicle's braking system comprises a friction braking device and a regenerative braking device. The friction braking device includes a wheel brake designed as a friction brake for each wheel of the motor vehicle. Particularly in vehicles with regenerative braking, the respective friction brakes are used for deceleration to a significantly lesser extent than in vehicles that are decelerated exclusively via friction brakes. This can quickly and frequently lead to suboptimal friction coefficients at the wheel brakes, especially due to corrosion, which can negatively affect braking performance, including the vehicle's acoustics. Consequently, the friction brakes may need to be replaced more frequently. If the regenerative braking component is reduced in favor of an increased hydraulic braking component, this leads to an increase in the motor vehicle's fuel consumption.

[0009] To address these disadvantages, the procedure involves determining the cleaning requirements of each wheel brake within the vehicle's friction braking system. This cleaning requirement can arise, for example, from corrosion of the respective wheel brakes. This means that the wheel brakes must be cleaned if they exhibit a certain degree of corrosion. Furthermore, the procedure involves determining the braking force required for a given deceleration of the vehicle. This means determining how much the vehicle needs to decelerate at a given moment, as well as the braking force required for this deceleration. A first, predetermined portion of this braking force is distributed to the regenerative braking system, and the remainder is distributed to the friction braking system.The vehicle is thus decelerated by both the regenerative braking system and the friction braking system. The braking force provided by the friction braking system is distributed to the wheel brakes according to the determined cleaning requirements of each wheel brake. The friction braking system can, for example, include individual hydraulic brakes, with each wheel of the vehicle having its own hydraulic brake. The brake pressure at each wheel brake can be adjusted via hydraulic fluid to distribute the braking force. The greater the cleaning requirement of a particular wheel brake, the greater the proportion of the remaining required braking force applied to that wheel brake to clean it, particularly to remove corrosion.In particular, the braking system can be operated in a cleaning mode in which the cleaning requirements of each wheel brake are determined, and the remaining required braking force is distributed among the wheel brakes of the braking system according to these determined cleaning needs. This method thus enables a particularly large proportion of braking energy to be recovered via the regenerative braking system, allowing the vehicle to be operated with exceptional efficiency and low energy consumption. Furthermore, it allows for targeted cleaning of individual wheel brakes within the braking system by distributing the braking force.

[0010] The invention provides that the first predetermined part of the braking force is selected to be the maximum possible recuperation power of the regenerative braking system. This allows a particularly large amount of energy to be recovered through recuperation during deceleration of the vehicle, enabling particularly efficient and fuel-efficient operation. Thus, the recuperation capacity of the regenerative braking system is fully utilized to achieve the maximum possible recuperation power.

[0011] Furthermore, it is provided that if the braking force required for the specified deceleration of the vehicle is less than or equal to the maximum possible recuperation power of the regenerative braking system, and the cleaning requirement has been determined, then the first specified part of the braking force will be a lower recuperation power than the maximum possible recuperation power of the regenerative braking system, and the remainder of the required braking force will be distributed to the friction braking system. If the braking force required for the specified deceleration of the vehicle is less than or equal to the maximum possible recuperation power of the regenerative braking system, and the first specified part of the braking force were the maximum possible recuperation power of the regenerative braking system, then the braking force available for the friction braking system would be zero.Therefore, cleaning of the wheel brakes of the friction braking system would not be possible. For this reason, once the cleaning requirement has been determined, the first predetermined component of the braking force is selected as the recuperation power, which is lower than the maximum possible recuperation power of the recuperation braking system, provided that the braking force required for the specified deceleration of the vehicle is less than or equal to the maximum possible recuperation power. If the braking force required for the specified deceleration of the vehicle is greater than the maximum possible recuperation power of the recuperation braking system, then the maximum possible recuperation power of the recuperation braking system can be selected as the first predetermined component of the braking force. In other words, a case distinction is made.If it is determined that regenerative braking alone is sufficient for the required deceleration of the vehicle, but at least one of the wheel brakes is dirty and therefore requires cleaning, then less deceleration is applied via the regenerative braking system than would be possible with its maximum possible regenerative braking power. In this case, the vehicle is additionally decelerated via hydraulic braking using the friction brake system. In a second case, the regenerative braking is insufficient to decelerate the vehicle by the required amount. In this case, the remaining required braking force is provided by the friction brake system, with this braking force being distributed between the wheel brakes depending on their respective cleaning requirements.One goal of the recuperation process is to recover a particularly large proportion of braking force through recuperation. To achieve this, the braking force is distributed between the friction braking system and the recuperative braking system, whereby, in addition to cleaning at least one wheel brake, as much braking force as possible is recovered via the recuperative braking system. This allows the vehicle to be operated with particularly high energy efficiency.

[0012] In a further development of the invention, it is provided that the motor vehicle is operated at least partially automatically, and in particular fully automatically, and is longitudinally controlled. This can mean, among other things, that the brake pedal position of the motor vehicle is independent of the respective deceleration of the motor vehicle, in particular of the proportion of the braking force distributed to the friction braking system, and in particular independent of the distribution of the braking force to the individual wheel brakes of the wheel braking system. A disadvantage in pedal feel, in particular due to differing distributions of the braking force to the individual wheel brakes depending on the respective cleaning requirements of the wheel brakes, can thus be avoided.This allows for a particularly high level of driving comfort for vehicle occupants, regardless of the distribution of braking force between the recuperation braking system and the friction braking system, or between the respective wheel brakes of the friction braking system.

[0013] In a further possible embodiment of the invention, a larger proportion of the braking force of the friction brake system is distributed to the wheel brakes of all rear wheels of the motor vehicle compared to the wheel brakes of all front wheels. If the motor vehicle is a motorcycle, then the larger proportion of the braking force of the friction brake system is distributed to the wheel brake of the rear wheel of the motorcycle compared to the wheel brake of the front wheel of the motorcycle. However, if the motor vehicle is a car, then the larger proportion of the braking force of the friction brake system is distributed to the wheel brakes of both rear wheels of the motor vehicle compared to the wheel brakes of the front wheels.Disc brakes, especially those on the rear axle of a vehicle, require particularly intensive cleaning because they experience less energy input during normal operation than front brakes. Distributing a larger proportion of the braking force from the friction brake system across the rear wheel brakes compared to the front wheel brakes allows for reliable cleaning of the rear wheel brakes.

[0014] In a further possible embodiment of the invention, the cleaning requirement of the respective wheel brakes is determined by a model based on the braking pressure and frequency applied to each wheel brake, and in particular, the braking pressure and frequency applied to each wheel brake over its service life. This model can thus be a type of energy calculator that, over the operating time of each wheel brake, can calculate when and for how long braking occurred at each wheel brake due to a given braking force, and how corrosion develops accordingly. The model can therefore be used to accurately estimate how the cleaning requirement of each wheel brake develops over its service life.This advantageously eliminates the need for additional sensors to determine the cleaning requirements of each wheel brake. The model allows for the precise recording of each braking event at the wheel brakes in terms of duration and / or brake pressure, enabling the model to determine the cleaning requirements for each wheel brake with exceptional accuracy.

[0015] In a further possible embodiment of the invention, the braking force applied to a particular wheel brake by means of the wheel brake device is set higher the greater the determined cleaning requirement for that wheel brake. The braking force applied to the respective wheel brake can cause it to wear down, with the grinding effect being greater the higher the braking force applied. This means that for particularly effective grinding off of, for example, corrosion, a particularly high braking force is applied to the wheel brake being cleaned. Thus, a particularly effective cleaning effect can be achieved by applying the braking force to the respective wheel brake.

[0016] In a further possible embodiment of the invention, the remaining braking force is distributed between the wheel brakes depending on at least one predetermined stability criterion. Here, the predetermined stability criterion can define specific ranges for the ratios of braking forces applied to the respective wheel brakes in comparison to one another. Adherence to the predetermined stability criterion ensures that the vehicle does not skid during deceleration. This results in minimal, and in particular, exceptionally high, negative impacts on the vehicle's stability during deceleration.

[0017] The invention further relates to a control device for a braking system of a motor vehicle, wherein the control device is configured to execute the method according to the invention or a further development thereof. The invention further relates to a motor vehicle with a braking system and with a control device as already described in connection with the control device according to the invention. The braking system comprises, in particular, a friction braking device and a recuperation braking device. Advantages and advantageous further developments of the method according to the invention are to be regarded as advantages and advantageous further developments of the control device according to the invention and of the motor vehicle according to the invention, and vice versa.

[0018] Further features of the invention may become apparent from the following description of the figures and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures themselves, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0019] The drawing shows in the single figure a process diagram for a method for operating a braking system of a motor vehicle.

[0020] The drawing shows in Fig.1. A process diagram for a method for operating a braking system of a motor vehicle, wherein the braking system comprises a friction braking device and a regenerative braking device. The friction braking device is configured to decelerate the motor vehicle by means of individual friction brakes assigned to the respective wheels of the motor vehicle, hereinafter referred to as wheel brakes. The regenerative braking device is configured to decelerate the motor vehicle, whereby the kinetic energy of the motor vehicle during deceleration is converted into electrical energy via the regenerative braking device, which in turn can be stored in a battery of the motor vehicle. This allows the motor vehicle to be driven particularly energy-efficiently using the energy stored in the motor vehicle's battery by means of the regenerative braking device.

[0021] In the first step of the process, V1, the cleaning requirement of each wheel brake of the vehicle's friction braking system is determined. This cleaning requirement can be calculated using a model that considers the brake pressure applied to each wheel brake, the frequency of braking during specific braking events, and, in particular, the service life of the wheel brakes. In the second step, V2, the braking force required for a given deceleration of the vehicle is determined. This step determines the required deceleration of the vehicle and the braking force necessary to achieve this deceleration.In a third process step V3 of the procedure, a first, predetermined portion of the braking force required for the specified deceleration of the vehicle is distributed to the recuperative braking system, and the remainder of the required braking force is distributed to the friction braking system. Here, the portion of the braking force provided by the friction braking system is distributed to the wheel brakes depending on the determined cleaning requirements of the respective wheel brakes.

[0022] The first predetermined component of the braking force is selected to achieve the maximum possible recuperation power of the regenerative braking system, in order to recover as much braking energy as possible and thus operate the vehicle with maximum energy efficiency. If the braking force required for the specified deceleration of the vehicle is less than or equal to the maximum possible recuperation power of the regenerative braking system, and if the cleaning requirement for at least one wheel brake of the friction braking system has also been determined, then a lower recuperation power than the maximum possible recuperation power of the regenerative braking system is selected as the first predetermined component of the braking force, and the remainder of the required braking force is distributed between the respective wheel brakes of the friction braking system.The higher the determined cleaning requirement of a particular wheel brake, the more braking force can be applied to that wheel brake to remove the contamination. To ensure vehicle stability during braking, the remaining braking force to be distributed among the wheel brakes can be allocated according to a predefined stability criterion. A larger proportion of the friction brake force can be distributed to the wheel brakes of all rear wheels of the vehicle compared to the wheel brakes of the individual front wheels. This procedure is carried out, in particular, while the vehicle is being driven with driver assistance, especially with assisted longitudinal control. For this purpose, the vehicle can be driven longitudinally in a semi-automated, and in particular fully automated, manner.

[0023] In this process, during autonomous braking, where the driver does not brake manually but a system such as adaptive cruise control does, a hydraulic component of the braking torque—specifically, the braking force required for the specified deceleration—is distributed selectively and within the vehicle's stability limits to axles or, more specifically, to individual wheels, particularly the wheel brakes assigned to those wheels. This is intended to increase the energy input at the wheel brakes and thus enhance the braking effect. This makes it possible to apply even a small hydraulic braking torque component, especially during regenerative braking, to a specific axle or defined wheels of the vehicle, independent of the vehicle's inherent brake force distribution.Negative effects on pedal feel can be avoided, particularly in coupled systems, because the braking system is only operated during autonomous braking maneuvers. The available hydraulic braking torque is distributed to the respective wheel brakes, especially during autonomous braking, resulting in less wheel slippage than during braking without recuperation. However, the advantages of this method are long-term. By selectively distributing the hydraulic braking torque, particularly during braking with a recuperative component, to individual axles or wheels—specifically the wheel brakes assigned to those axles or wheels—fuel consumption can be avoided. Furthermore, using this function during autonomous braking maneuvers prevents any negative impact on pedal feel.An algorithm can be used to determine and distribute the hydraulic braking torque.

[0024] The method can be applied to a coupled braking system, in particular a so-called dual-box braking system, or a decoupled braking system, in particular a so-called single-box system. In a brake control system control unit, and thus a control device for the vehicle's braking system, a driver's requested braking torque can be divided into a regenerative and a hydraulic component, depending on the available hydraulic regenerative torque. The hydraulic component can then be distributed to the wheel brakes assigned to the axles or wheels, which potentially have the highest cleaning requirements and therefore the highest need for grinding. In particular, the distribution of the remaining required braking force to the wheel brakes of the friction braking system is imperceptible to the driver, with minimal, if any, impact on the vehicle's stability.The cleaning requirements of each wheel brake can be determined using an algorithm that sums up the energy input per wheel brake. Generally, rear disc brakes require more frequent cleaning to remove contaminants, especially corrosion, as they experience less energy input during normal operation than front axle brakes.

[0025] Overall, the invention demonstrates how a function for improving the friction properties of respective wheel brakes in customer operation can be achieved through a situational brake torque distribution. Reference symbol list V1 to V3 respective process steps

Claims

[1] Method for operating a braking system of a motor vehicle, comprising a friction braking device and a recuperative braking device, in which the cleaning requirement of the respective wheel brakes of the friction braking device of the motor vehicle is determined (V1) and a braking force required for a given deceleration of the motor vehicle is determined (V2), wherein a first, predetermined part of this braking force is distributed to the recuperative braking device and the remainder of the required braking force is distributed to the friction braking device (V3), wherein the braking force provided by the friction braking device is distributed to the wheel brakes depending on the determined cleaning requirement of the respective wheel brakes, wherein the first predetermined part of the braking force is selected to be the maximum possible recuperation power of the recuperative braking device,where, if the braking force required for the specified deceleration of the motor vehicle is less than or equal to the maximum possible recuperation power of the recuperation braking system and the cleaning requirement has been determined, the first specified part of the braking force is selected as a lower recuperation power than the maximum possible recuperation power of the recuperation braking system and the remainder of the required braking force is distributed to the friction braking system. [2] Method according to claim 1, wherein the motor vehicle is operated at least partially automatically, in particular fully automatically, and in particular longitudinally controlled. [3] Method according to one of the preceding claims, wherein a larger proportion of the braking force of the friction brake device is distributed to wheel brakes of all rear wheels of the motor vehicle compared to wheel brakes of all front wheels. [4] Method according to one of the preceding claims, wherein the cleaning requirement of the respective wheel brakes is determined via a model as a function of the brake pressure and braking frequency applied to the respective wheel brakes, in particular the brake pressure and braking frequency applied to the respective wheel brakes over their service life. [5] Method according to one of the preceding claims, wherein the braking force to be applied to a respective wheel brake by means of the wheel brake device is set higher the higher the respective cleaning requirement determined for that wheel brake is. [6] Method according to one of the preceding claims, wherein the remainder of the braking force is distributed between the wheel brakes depending on a predetermined stability criterion. [7] Control device for a braking system of a motor vehicle, which is configured to perform a method according to any of the preceding claims. [8] Motor vehicle, comprising a braking system and a control device according to claim 7.

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