Method, device for operating a friction-based brake system of a vehicle having an electric drive unit, and corresponding computer program and machine-readable storage medium

Abstract

A method for operating a friction-based brake system of a vehicle having an electric drive unit is described, comprising the steps of: actuating the friction-based brake system such that a friction-based braking torque is generated; ascertaining whether a predefined braking criterion is met by the friction-based brake system; storing the result of the ascertainment in a data memory. Furthermore, a corresponding device, a corresponding computer program, and a corresponding machine-readable storage medium are disclosed.

Description

[0001] R. 412361

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[0003] title

[0004] Method, device for operating a friction-based braking system of a vehicle with an electric drive unit, as well as corresponding computer program and machine-readable storage medium

[0005] The present invention relates to a method for operating a friction-based braking system of a vehicle with an electric drive unit according to the independent claim.

[0006] State of the art

[0007] In modern electric cars, the electric drive unit(s) are also used to decelerate the vehicle. Deceleration using the electric drive unit reduces the particulate matter emitted by brake pad wear and increases the vehicle's overall efficiency / range, for example, through recuperation, i.e., charging the battery using the energy generated during deceleration. The usable deceleration power of electric drives is already up to -0.3g, which can cover up to 99% of all deceleration processes during normal driving. Even higher deceleration power can potentially be expected in next-generation vehicles.

[0008] The primary use of the electric drive unit results in significantly reduced use of the friction brakes. This significantly reduced use can lead to premature aging of the friction brake system and / or a loss of braking performance. This fact is not currently being specifically addressed. The brake system is located in a very exposed position close to the road surface and is therefore unprotected against environmental influences (e.g., splash water, de-icing salt, dirt, dust). These environmental influences lead to severe aging or corrosion of the brake system, such as oxidation of the brake discs. Similarly, R. 412361

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[0010] Friction linings become damp (hydrophilic material mix) or brake pistons become stiff. If regular conditioning through the use of friction brakes is subsequently neglected, the braking system will very likely be impaired in its function.

[0011] The publication DE 10 2013 224 783 A1 relates to a braking system for a motor vehicle with at least two axles, wherein the wheels of a drive axle are connected to an electric drive which has at least one electric machine that can be operated as a motor or generator, which comprises a first hydraulic brake circuit with at least one wheel brake, in particular two wheel brakes, a master brake cylinder which can be actuated by the driver via a brake pedal and which is connected to the wheel brakes of the first brake circuit, a brake actuation sensor, and a second hydraulic brake circuit with at least one wheel brake, in particular two wheel brakes.

[0012] The publication DE 10 2016 221 939 A1 relates to a method for operating a braking system of a motor vehicle, which has a drive device designed for recuperative deceleration of the motor vehicle and a service brake device assigned to at least one wheel of the motor vehicle.

[0013] Document WO 2021 160 287 A1 concerns a method for braking a vehicle for transporting passengers.

[0014] The publication DE 10 2021 127 908 A1 relates to a method for controlling a recuperation system of a motor vehicle, wherein the recuperation system is designed to effect a contribution to a braking torque to reduce the speed of the motor vehicle by means of at least one electric machine switched to generator operation, wherein a recuperation contribution results from a ratio of the contribution of the recuperation system on the one hand and a contribution of friction brakes of the motor vehicle to the braking torque on the other hand.

[0015] Disclosure of the invention R. 412361

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[0017] Advantages of the invention

[0018] A method for operating a friction-based braking system of a vehicle with an electric drive unit, comprising the features of the independent patent claim, is disclosed.

[0019] The friction-based braking system is activated, generating a friction-based braking torque.

[0020] The system then determines whether the friction-based braking system meets a predefined braking criterion and stores the result in a data storage device.

[0021] This is advantageous because it prevents premature aging of the braking system, especially the brake pads, through monitoring and conditioning. Furthermore, it also determines the current condition of the braking system, thus eliminating the need for separate testing of the braking system, e.g., on a roller dynamometer.

[0022] Further advantageous embodiments of the present invention are the subject of the dependent claims.

[0023] The investigation should ideally include at least one of the steps described below:

[0024] The vehicle's recuperation strategy is adjusted, modulating the ratio between electric and friction-based braking torque. Alternatively or additionally, the friction-based braking system and the electric drive unit are controlled in such a way that a braking torque is balanced by a corresponding drive torque. Alternatively or additionally, the braking system is controlled until a desired coefficient of friction is achieved. This is advantageous because it can be carried out imperceptibly by the vehicle user, thus resulting in no loss of comfort or other impairments. R. 412361

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[0026] It is advisable to continue determining the current degree of corrosion of the friction-based braking system and to carry out further steps depending on the result. This is advantageous because the friction-based braking system is then only activated as needed, and not according to predefined times or events.

[0027] The corrosion assessment conveniently comprises the following steps. The friction-based braking system and the electric drive unit are controlled in such a way that a drive torque and a friction-based braking torque of equal magnitude are applied, and the efficiency and / or effectiveness of the friction-based braking system are determined. This is advantageous because it allows for an accurate assessment of the condition and functionality of the braking system without restricting vehicle use, and based on this, a decision can be made as to whether brake system conditioning is necessary.

[0028] Corrosion is expediently determined based on at least one of the following predefined criteria. These criteria include the passage of a predefined time period, predefined calendar, weather, or temperature data, topology information from map data, the vehicle's load status, and rain status information from a rain sensor (i.e., whether or not it is measuring rain). This is advantageous for determining the optimal time for measurement, for example, on level ground and not during uphill or downhill driving, as this yields the best results with the fewest uncertainties.

[0029] Advantageously, the friction-based braking system and the electric drive unit are controlled in such a way that a braking torque is balanced by a corresponding drive torque, and in this context, a control-based compensation of the friction-based braking torque takes place, whereby the efficiency of the friction-based braking system is also determined. This is advantageous to ensure that the compensation is not noticeable to the driver. The compensation can be symmetrical in the case of axle-wise aging, or it can be asymmetrical in the case of differences in braking performance on one axle. R. 412361

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[0031] Furthermore, the invention relates to a device for operating a friction-based braking system of a vehicle with an electric drive unit, comprising at least one means, in particular an electronic control unit, wherein the means is configured to perform the steps of a method according to the invention. Thus, the aforementioned advantages can be achieved.

[0032] Furthermore, the invention relates to a computer program which is configured to execute all steps of a method according to the invention. Thus, the aforementioned advantages can be achieved.

[0033] Furthermore, the invention relates to a machine-readable storage medium on which the computer program according to the invention is stored. Thus, the aforementioned advantages can be achieved.

[0034] Brief description of the drawings

[0035] Advantageous embodiments of the invention are shown in the figures and explained in more detail in the following description.

[0036] They show:

[0037] Figure 1 shows a flowchart of a method according to the invention in a first embodiment; and

[0038] Figure 2 shows a flowchart of a method according to the invention in a second embodiment.

[0039] Embodiments of the invention

[0040] The same reference numerals denote identical device components or identical process steps in all figures. R. 412361

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[0042] Figure 1 shows a flowchart of a method according to the invention for operating a friction-based braking system of a vehicle with an electric drive unit according to a first embodiment.

[0043] In a first step, S11 activates the vehicle's friction-based braking system, generating a friction-based braking torque. This can be achieved, for example, by controlling the existing drive actuator to a specific target wheel speed.

[0044] In a second step, S12, it is determined whether the friction-based braking system fulfills a predefined braking criterion. This can be done, for example, by selectively activating the friction braking system until a desired coefficient of friction is reached.

[0045] In a third step (S13), the result of the investigation, i.e., whether the braking criterion is met or not, is stored in a data storage device. For traceability reasons, this can be stored, for example, in non-volatile memory (e.g., EEPROM) of a control unit in the vehicle. This could be, besides the brake control unit, also a vehicle central computer, for example.

[0046] Figure 2 shows a flowchart of a method according to the invention for operating a friction-based braking system of a vehicle with an electric drive unit according to a second embodiment.

[0047] In a first step, S21 activates the vehicle's friction-based braking system, generating a friction-based braking torque. For example, parallel to each deceleration request, whether initiated by an automation function or by the driver, the current degree of corrosion in the friction braking system can be determined using corrosion detection. If the defined corrosion limit is exceeded, a brake conditioning process can be triggered. R. 412361

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[0049] In a second step, S22 determines whether the friction-based braking system fulfills a predefined braking criterion. For this purpose, the vehicle's recuperation strategy is adjusted, modulating the ratio between electric and friction-based braking torque. The predefined braking criterion could, for example, include braking efficiency. Another criterion could be, for instance, vibration / flutter during mechanical braking caused by corrosion.

[0050] Alternatively or additionally, the friction-based braking system and the electric drive unit can be controlled in such a way that a braking torque is balanced by a corresponding drive torque. To ensure that there is no negatively perceptible impact on the driving situation during an active conditioning process of the braking system, a compensation controller can be used. This controller compensates for any disturbances that may occur. In addition to the measured variables of the vehicle structure, this compensation is also based on a central setpoint calculation for the vehicle's longitudinal movement. This setpoint calculation can also take into account external influencing factors such as the current topology.

[0051] In a third step, S23, the current degree of corrosion of the friction-based braking system is determined, for which the predefined braking criterion can be used. For example, a high braking efficiency indicates relatively low corrosion. A braking system always has a nominal coefficient of friction, called the cp value. This is defined as the proportionality factor between braking torque and braking pressure. Conversely, the actual cp value can be derived from the test control, including compensation. For example, an applied braking pressure is transferred via the brake pad / disc, resulting in a braking torque. This braking torque can be compensated with an equal drive torque. Thus, the actual cp value can be determined. By comparing the actual cp value with the nominal cp value, the braking efficiency can be determined.This determination is preferably carried out at a constant vehicle speed in order to eliminate the influence of driving resistance. R. 412361.

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[0053] In a fourth step (S24), the result of the investigation, i.e., whether the braking criterion is met or not, is stored in a data storage device. For reasons of traceability, this can be stored, for example, in a non-volatile memory (e.g., EEPROM) of a control unit in the vehicle. Besides the brake control unit, this could also be, for example, a vehicle central computer.

Claims

R. 412361 - 9 - Claims 1. Method for operating a friction-based braking system of a vehicle with an electric drive unit, comprising the steps: - Activating the friction-based braking system so that a friction-based braking torque is generated; - Determine whether a predefined braking criterion is met by the friction-based braking system; - Saving the investigation results in a data storage device.

2. A method according to the preceding claim, wherein the determination comprises at least one of the following steps: - Adapting the vehicle's recuperation strategy by modulating the ratio between electric and friction-based braking torque; - Controlling the friction-based braking system and the electric drive unit in such a way that a braking torque is balanced by a corresponding drive torque; - Controlling the braking system until a desired coefficient of friction is achieved.

3. Method according to one of the preceding claims, wherein the current degree of corrosion of the friction-based brake system is further determined and the subsequent steps are carried out depending on the determination result.

4. Method according to the preceding claim, wherein determining the corrosion comprises: - Controlling the friction-based braking system and the electric drive unit in such a way that a drive torque and a friction-based braking torque of the same magnitude are applied; - Determining the efficiency and / or effect of the friction-based braking system; R. 412361 - 10 - 5. A method according to claim 3 or 4, wherein the determination of corrosion is carried out depending on at least one of the following predefined criteria: - Expiration of a predefined time period; - Predefined calendar, weather, or temperature data; - Topology information from map data; - Vehicle load condition; - Rain condition information from a rain sensor; 6. Method according to any one of claims 3 to 5, further comprising: - Controlling the friction-based braking system and the electric drive unit in such a way that a braking torque is balanced by a corresponding drive torque; - Control-based compensation of the friction-based braking torque; - Determine at least one efficiency of the friction-based braking system.

7. Device for operating a friction-based braking system of a vehicle with an electric drive unit, wherein the device comprises at least one means, in particular an electronic control unit, wherein the means is configured to perform the steps of the method according to any one of claims 1 to 6.

8. Computer program configured to perform all steps of the method according to any one of claims 1 to 6.

9. Machine-readable storage medium on which the computer program according to the preceding claim is stored.

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