Method for cleaning a friction brake of a motor vehicle, cleaning system and vehicle

Abstract

The invention relates to a method for cleaning a friction brake (7) of a motor vehicle (1), comprising the steps of: - monitoring a braking torque request (11) to the brake system (6); - activating the friction brake (7) in order to clean the friction brake (7) if the three following conditions are met simultaneously, a cleaning request (14) is activated by manual input or by automatically determining a need for cleaning; the braking torque request (11) exceeds a minimum braking torque request (12), wherein the minimum braking torque request (12) is greater than zero and lower than the maximum braking torque of the regenerative brake (13); and the braking torque request (11) falls below a maximum braking torque of the regenerative brake (13), - detecting the wheel revolutions with the friction brake (7) activated, and - deactivating the cleaning request (14) if the detected wheel revolutions with the friction brake (7) activated exceed a target number of wheel revolutions with the friction brake (7) activated.

Description

[0001] Method for cleaning a friction brake of a motor vehicle, cleaning system and vehicle

[0002] The present invention relates to a method for cleaning a friction brake of a motor vehicle, wherein the motor vehicle has a braking system comprising a friction brake and a regenerative brake. The invention further relates to a corresponding cleaning system for a motor vehicle for carrying out the method and to a vehicle with such a cleaning system.

[0003] Electrically powered vehicles have a friction brake at each wheel. Due to the continuous improvement of regenerative braking in electric vehicles, these brakes are used less and less. Over time, this leads to some components, especially the brake discs and pads, becoming dirty and corroded. This dirt and corrosion reduce the friction coefficient of the friction brakes, thus decreasing the braking torque they can generate. The simplest way to clean the friction brakes is to use them regularly. However, using the friction brakes reduces the amount of energy recovered and therefore the vehicle's range. Furthermore, braking with high pressure using corroded friction brakes can lead to the formation of magnetite (Fe3O4) on the brakes, particularly on the brake discs.Magnetite also negatively affects braking torque and is difficult to remove. Furthermore, grooves can subsequently form, particularly in the brake pads, which further impair the contact pattern and thus corrosion removal on the brake discs.

[0004] Since the intensity of corrosion depends on many external parameters, it is difficult to predict the optimal time for cleaning. On the one hand, corrosion must not progress to the point where the functionality of the brakes is impaired in a safety-relevant way. On the other hand, premature brake cleaning leads to wasted energy, brake wear, and, depending on when the cleaning is performed, a reduction in driving comfort.

[0005] In the prior art, a method for operating a vehicle is known from DE 10 2016 217 681 A1, wherein, when a cleaning criterion is present, a driver-independent friction braking is carried out for a predetermined period of time with a predetermined pressure if the state of charge of the vehicle battery exceeds a predetermined threshold.

[0006] However, a disadvantage of initiating brake cleaning based on the state of charge is that, depending on vehicle usage, no brake cleaning may be performed for an extended period of time.

[0007] The object of the invention is therefore to provide a method for cleaning a friction brake of a motor vehicle that enables sufficient cleaning of the friction brake as largely as possible independent of usage patterns, but which at the same time does not unduly restrict the vehicle's recuperation capability. Furthermore, the object of the invention is to provide a corresponding cleaning system and a corresponding vehicle with such a cleaning system.

[0008] For the purposes of this patent application, the term friction brake is to be understood as encompassing both a brake for a single wheel of a vehicle and a system of multiple brakes for multiple wheels of a vehicle, wherein each wheel is braked by a separate brake.

[0009] The object of the invention is achieved by the features of the independent claims. Further preferred embodiments of the invention can be found in the dependent claims, the figures, and the accompanying description.

[0010] The object of the invention is accordingly achieved by a method for cleaning a friction brake of a motor vehicle comprising the following steps, wherein the motor vehicle has a braking system with a friction brake and a regenerative brake: a) monitoring a braking torque request to the braking system; b) activating the friction brake for cleaning the friction brake when the following three conditions are met simultaneously: c1) a cleaning request is activated by manual input or by automatic detection of a cleaning need; c2) the braking torque request exceeds a minimum braking torque request, wherein the minimum braking torque request is greater than zero and less than the maximum braking torque of the regenerative brake;and c3) the braking torque request falls below a maximum braking torque of the recuperation brake, d) detection of wheel revolutions with activated friction brake, and e) deactivation of the cleaning request if the detected wheel revolutions with activated friction brake exceed a target number of wheel revolutions with activated friction brake.;

[0011] The cleaning of the friction brake thus takes place during defined deceleration phases with comparatively low braking torques, which are within the capabilities of the regenerative braking system. The braking system remains capable of providing full braking torque at any time, i.e., when the braking torque requirement exceeds the maximum braking torque of the regenerative braking system.

[0012] The friction brake is preferably deactivated again as soon as the requested braking torque drops to a value below the minimum braking torque requirement, or the number of detected wheel revolutions with the friction brake activated has reached the target number.

[0013] The advantage of monitoring the braking torque requirement for the braking system and activating the friction brake accordingly is that in driving situations favorable for recuperation, such as coasting or gentle braking, no energy is converted into heat through the use of the friction brake. The friction brake is therefore only activated for cleaning when the vehicle is going to be slowed down anyway. The minimum braking torque requirement allows for setting an optimal balance between cleaning performance and the impact on recuperation.

[0014] Overall, a greater range can be achieved with the cleaning method, as the energy loss through the use of the friction brake for cleaning purposes is minimized, in particular by defining the necessary wheel revolutions as required, i.e., the target number of wheel revolutions.

[0015] Determining the wheel revolutions with the friction brake activated can be done, for example, by counting the revolutions via a sensor signal, such as from a rotation sensor, or by measuring the distance traveled with the friction brake activated and calculating the wheel revolutions via the wheel circumference.

[0016] The cleaning request can be activated manually, for example. This can be used, for instance, if dirt is detected on the brake discs.

[0017] Preferably, activation according to step b) is carried out with a predetermined brake pressure in the range of 1 bar to 3 bar. More preferably, activation according to step b) is carried out with a predetermined brake pressure of 2 bar. These comparatively low brake pressures are particularly advantageous for cleaning the friction brake because, during cleaning in this pressure range, especially at 2 bar, the conversion of rust to magnetite can be prevented. Furthermore, the formation of grooves on the brake disc and brake pad can also be avoided. Driving comfort is only minimally affected.

[0018] In an advantageous embodiment, the minimum braking torque is greater than or equal to 550 Nm, and the maximum braking torque of the recuperation brake is greater than or equal to 2000 Nm.

[0019] The corresponding minimum braking torque requirement ensures that the friction brake only withholds energy from recuperation when a cleaning effect is expected. Furthermore, any noise generated during cleaning is more likely to be tolerated or even ignored with such a braking torque requirement. The proposed minimum braking torque requirement allows for an optimal balance between cleaning performance and minimal disruption to recuperation.

[0020] Furthermore, according to a further development, it is proposed that the time span since the last deactivation of the cleaning request be recorded in order to automatically determine a cleaning requirement.

[0021] This allows for the automatic detection of cleaning requirements, taking into account the vehicle's idle time and the associated lack of use of the friction brakes. The time period can be recorded, for example, using a clock or stopwatch in an electronic control unit.

[0022] In an advantageous embodiment, the cleaning request is activated when the time interval since the last deactivation of the cleaning request is longer than 24 hours. This allows the determination of a cleaning requirement for the cleaning brake and a corresponding activation of the cleaning request.

[0023] This proposed minimum time period ensures that the next cleaning cycle does not immediately follow a completed cleaning cycle.

[0024] According to a preferred embodiment, it is proposed that the target number of wheel revolutions with the friction brake activated is determined by multiplying the detected time span since the last deactivation of the cleaning request by a cleaning factor of wheel revolutions per time interval with the friction brake activated.

[0025] The cleaning of the friction brake is therefore carried out as needed, so that losses during recuperation through the use of the friction brake can be further minimized.

[0026] Preferably, the cleaning factor of wheel revolutions per time interval is in the range of 75 wheel revolutions per 24 hours to 200 wheel revolutions per 24 hours. A cleaning factor of 100 wheel revolutions per 24 hours, for example, is advantageous to achieve sufficient cleaning while minimizing energy loss through reduced recuperation of the regenerative braking system. Therefore, for example, 100 wheel revolutions with the friction brake activated can be used as the cleaning factor for each day of downtime within the cleaning brake procedure.

[0027] In advantageous embodiments, the cleaning factor can be adjusted by taking into account environmental conditions, e.g. rain sensor, car wash sensor, weather data, with which the corrosion intensity can be roughly estimated.

[0028] The target number of wheel revolutions with the friction brake activated is preferably limited to a range of 400 to 600, for example to 500. A higher target number does not result in any further increase in the cleaning effect.

[0029] Furthermore, the object of the invention is proposed by a cleaning system for a motor vehicle for carrying out the method of the type described above or according to one of claims 1 to 8. The cleaning system comprises a braking system with a friction brake and a recuperative brake, an electronic control unit for monitoring the brake torque request and controlling the braking system, and at least one rotation sensor on at least one wheel.

[0030] Furthermore, in advantageous embodiments, the cleaning system includes a timer for measuring the time interval since the last deactivation of the cleaning request.

[0031] Therefore, for example, a coating on the brake disc to prevent corrosion can be omitted.

[0032] Furthermore, the object of the invention is solved by a vehicle comprising a cleaning system of the type described above, in particular according to claim 9.

[0033] A suitable vehicle can be operated efficiently while simultaneously maintaining the friction brake at high, achievable friction values.

[0034] The invention is explained below with reference to preferred embodiments and the accompanying figures.

[0035] Fig. 1 shows a schematic representation of the method for cleaning a friction brake with a cleaning system; and

[0036] Fig. 2 shows a schematic representation of a vehicle with a cleaning system. Figure 1 shows an exemplary sequence of the process for cleaning a friction brake 7 of a motor vehicle 1 using a schematic representation of a cleaning system 2. A brake torque request 11 to a brake system 6 is issued, for example, by a brake pedal and / or a driver assistance system. The brake system 6 has a friction brake 7 and a regenerative brake 8, which can act on the wheels 9 of a vehicle 1.

[0037] The braking torque requirement 11 is monitored by an electronic control unit 5. The electronic control unit 5 compares the current braking torque requirement 11 with a minimum braking torque requirement 12 for activating the cleaning of the friction brake 7. If the minimum braking torque requirement 12 is not reached by the braking torque requirement 11, the cleaning is not carried out. In this case, the braking torque requirement 11 is processed in the usual way, so that, for example, the regenerative brake 8 is actuated with the braking torque requirement 11. In this embodiment, the minimum braking torque requirement 12 is 550 Nm.

[0038] Furthermore, the electronic control unit 5 compares the current braking torque request 11 with the maximum braking torque of the recuperation brake 13. If the braking torque request 11 exceeds the maximum braking torque of the recuperation brake 13, the friction brake 7 is activated in the usual manner, for example, alone or in addition to the recuperation brake 8. Such activation serves to fulfill the braking torque request 11 and is not an activation for the purpose of cleaning the friction brake 7. A condition for carrying out cleaning according to the cleaning procedure is that the braking torque request 11 is less than the maximum braking torque of the recuperation brake 13. The maximum braking torque of the recuperation brake 13 is, for example, 2000 Nm. The electronic control unit 5 also checks whether a cleaning request 14 is activated.Cleaning request 14 can be activated, for example, by manual entry or by an automatic detection of a cleaning need.

[0039] The electronic control unit 5 activates the friction brake 7 for cleaning the friction brake 7 when the three previously specified conditions are met simultaneously.

[0040] In this case, the friction brake 7 of the brake system 6 is activated with a predefined brake pressure of 2 bar. Additionally, the recuperative brake 8 can be activated to meet the brake torque requirement 11 during the cleaning of the friction brake 7. The recuperative brake 8 is activated when the friction brake, operating at the predefined brake pressure, generates a brake torque that is below the brake torque requirement.

[0041] The wheel rotations of a wheel 9 with activated friction brake 7 are detected by a rotation sensor 4. The electronic control unit 5 compares the detected wheel rotations with a target number of wheel rotations and deactivates the cleaning request 14 when the target number of wheel rotations is reached.

[0042] After the cleaning request 14 is deactivated, the electronic control unit 5 records the elapsed time since the deactivation. After a period of 24 hours, as specified in this advantageous embodiment, a cleaning requirement is automatically detected and the cleaning request 14 is activated. The target number of wheel revolutions is multiplied by this time period by a cleaning factor of, for example, 100 wheel revolutions per 24 hours, so that the target number of wheel revolutions with the friction brake 7 activated is 200 after 48 hours.

[0043] Figure 2 schematically shows a vehicle 1 with a cleaning system 2.

[0044] Cleaning request 14 can also be triggered manually, for example by means of an operating terminal in a vehicle 1 with a cleaning system 2.

Claims

Patent claims 1. Method for cleaning a friction brake (7) of a motor vehicle (1), wherein the motor vehicle (1) has a braking system (6) with a friction brake (7) and a regenerative brake (8), comprising the following steps: a) monitoring a braking torque request (11) to the braking system (6); b) Activating the friction brake (7) to clean the friction brake (7) if the following three conditions are met simultaneously: c1) a cleaning request (14) is activated by manual input or by automatic detection of a cleaning need; c2) the braking torque request (11) exceeds a minimum braking torque request (12), where the minimum braking torque request (12) is greater than zero and less than the maximum braking torque of the regenerative brake (13); and c3) the braking torque request (11) is less than a maximum braking torque of the regenerative brake (13); d) wheel rotations with the friction brake (7) activated are detected; and e) the cleaning request (14) is deactivated if the detected wheel rotations with the friction brake (7) activated exceed a target number of wheel rotations with the friction brake (7) activated.

2. Method according to claim 1, characterized in that the activation according to step b) is carried out with a predetermined brake pressure in a range of 1 bar to 3 bar.

3. Method according to one of claims 1 to 3, characterized in that the minimum braking torque (12) is greater than or equal to 550 Nm, and the maximum braking torque of the recuperation brake (13) is greater than or equal to 2000 Nm.

4. Method according to one of claims 1 to 4, characterized in that the time span since the last deactivation of the cleaning request (14) is recorded for the automatic determination of a cleaning requirement.

5. Method according to claim 5, characterized in that the cleaning request (14) is activated when the time interval since the last deactivation of the cleaning request (14) is longer than 24 hours.

6. Method according to claim 5 or 6, characterized in that the target number of wheel revolutions with activated friction brake (7) is determined by multiplying the detected time span since the last deactivation of the cleaning request (14) by a cleaning factor of wheel revolutions per time interval with activated friction brake (7).

7. Method according to claim 7, characterized in that the cleaning factor of wheel revolutions per time interval is in the range of 75 wheel revolutions per 24 hours to 200 wheel revolutions per 24 hours.

8. Cleaning system (2) for a motor vehicle (1) for carrying out the method according to one of the preceding claims, characterized in that the cleaning system (2) comprises a brake system (6) with a friction brake (7) and a recuperation brake (8), an electronic control unit (5) for monitoring the brake torque request (11) and control of the brake system (6), and has at least one rotation sensor (4) on at least one wheel (9).

9. Cleaning system (2) for a motor vehicle (1) according to claim 9 characterized in that the friction brake 10. Vehicle (1), characterized in that the vehicle (1) comprises a cleaning system (2) according to claim 9.

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