EP4251481A1

EP4251481A1 - Method for controlling a brake system of a motor vehicle

Info

Publication number: EP4251481A1
Application number: EP21805478.1A
Authority: EP
Inventors: Philip Haug; Markus Kern; Maik Kreller
Original assignee: Mercedes Benz Group AG
Current assignee: Mercedes Benz Group AG
Priority date: 2020-11-27
Filing date: 2021-11-02
Publication date: 2023-10-04
Also published as: US12017654B2; DE102020007248A1; CN116507536A; WO2022111951A1; US20240010202A1

Abstract

The invention relates to a method for controlling a brake system of a motor vehicle, comprising multiple wheels, at least one electric machine as a drive, a service brake and electronic stability control, wherein the wheels can be braked by means of a deceleration torque (MB) applied by the service brake and at least partially by means of a deceleration torque (ME) applied by the electric machine, wherein slip resulting from braking and/or from interventions by the electronic stability control is controlled at least primarily by adapting the deceleration torque (ME) applied by the electric machine.

Description

Method for controlling a brake system of a motor vehicle

The invention relates to a method for controlling a brake system of a motor vehicle according to the preamble of the independent patent claim.

It is known to implement a desired deceleration of a motor vehicle by means of dynamic braking control intervention (ESP/ABS) in the wheel slip range. A mechanical brake control system (BRS) is used for this. The braking torque is generated by braking pressure on the brake lining and the resulting friction on the brake disc.

During the deceleration process, optimal wheel slip is detected and adjusted by adjusting the brake pressure and generating friction torque on the brake discs. An overbraked wheel is driven again by the existing vehicle speed.

When driving, the ESP evaluates the wheel speeds and calculates a vehicle reference speed over ground. Due to existing network architectures, there are different signal propagation times between the affected control units (ESP, CPC - central control of the drive train, INV - inverter for electric machines) in the control loop. When the vehicle is required to decelerate, the ESP control unit implements the dynamic ABS control intervention. If a braked wheel reduces its speed relative to the vehicle speed, this results in increased slippage, as a result of which the power transmission on the axle decreases steadily until it locks. The ESP reduces the braking torque on one side both by reducing the braking pressure in the braking control circuit and by restricting recuperation (permissible slight drag torque (MSR - engine drag torque control)). The maximum deductible recuperation torque of the electric machine (INV) is limited by the minimum deductible wheel torque ("torque balance"). As a result, the locked and now unbraked wheel is pushed again in order to be braked again in the optimal balance of power and to continue to be operated in slip. That Mechanical braking torque is realized in stages through different brake pressure gradients. The opposite wheel, which is not locked but continues to be braked, is forcibly connected via the gearbox/differential and engine. In order to enable the set deceleration and driving stability, the brake circuits are adapted to each other and regulated via the mechanical braking torque. The electric machines only provide a very low engine drag torque via the engine drag control (MSR).

The subsequently published DE 102019004 390 discloses a method for controlling a braking system of a motor vehicle with at least two axles, which comprises an electronic braking system and an anti-lock braking system. In this case, the wheels on the front axle can be braked via a service brake of the electronic brake system and the wheels on the rear axle can be braked via a service brake of the electronic brake system and/or an electric recuperation brake. It is provided that when an upper limit value of the braking torque of the electric recuperation brake on the rear axle is exceeded, an additional braking torque is built up by the service brake on the front axle. The upper limit of the braking torque of the electric regenerative brake on the rear axle can be determined by a maximum slip torque of the motor vehicle in the current driving situation shortly before the anti-lock braking system intervenes or by a maximum braking torque that can be represented by the electric regenerative brake or by the difference between the braking torques on the rear axle and the front axle can be determined. Furthermore, it can be provided in the method that a further additional braking torque is built up by the service brake on the rear axle and the braking torque of the electric recuperation brake is possibly also reduced accordingly.

The invention is based on the object of specifying an improved method for controlling a brake system of a motor vehicle.

The object is achieved according to the invention by a method for controlling a brake system of a motor vehicle according to claim 1.

Advantageous configurations of the invention are the subject matter of the dependent claims.

In the present patent application, both single-wheel electric drives and those electric drives that are connected to one another via a differential are intended as electric machines are connected to be understood. With single-wheel electric drives, there are no mutual dependencies, which increases the dynamics and removable power transmission.

The term slip initiation should be understood to mean that a wheel speed of a wheel under consideration deviates from the vehicle speed, so that slip occurs.

In a method according to the invention for controlling a brake system of a motor vehicle, comprising a plurality of wheels, at least one electric machine as a drive, a service brake and a vehicle dynamics control system, the wheels being decelerated by means of a deceleration torque (MB) applied by the service brake and at least partially by a deceleration torque (MB) applied by the electric If the deceleration torque (M _E ) applied by the machine can be braked, slip that occurs as a result of braking and/or interventions by the driving dynamics control system is controlled at least primarily or exclusively by adapting the deceleration torque applied by the electric machine, since this has better and shorter control times as the service brake.

As a result, the re-engagement of the wheels can be supported and vibrations in the drive train can be reduced through the slower control of the conventional components.

In one embodiment, if required, a drive torque is applied by means of the electric machine for slip control or for turning a locked wheel.

In one embodiment, at least one axle of the motor vehicle is driven by the electric machine via a differential, with the electric machine generating an increased wheel slip run-in by means of evaluated wheel speeds in relation to a limiting minimum shaft speed, which is specified by a control unit of the vehicle dynamics control system, when deceleration is requested. detects and regulates, the wheel speed and the wheel torque being detected by the electric machine and the wheel torque being controlled in such a way that the braked wheel is operated in a slip range specified by a control unit of the vehicle dynamics control system.

In one embodiment, the wheel slip is detected and controlled. preventively through the deceleration torque of the electric motor and the wheel speed, in such a way that a locking of the wheel and an increase in the wheel slip is detected and the wheel slip is controlled before the braked wheel comes to a standstill.

In one embodiment, the electric machine indicates to the control unit of the driving dynamics control a maximum drag torque that can be deducted via the axle, and the control unit of the driving dynamics control counteracts a reduction in the electric deceleration torque by increasing the deceleration torque of the service brake if the vehicle deceleration remains the same or the deceleration request remains the same.

In one embodiment, wheel slip is detected by the permissible minimum shaft speed and thus increased wheel slip running-in by the electric machine and/or by applying a mechanical deceleration torque on both sides.

In one embodiment, each wheel of the motor vehicle is driven by a respective electric machine, with the electric machine detecting and regulating an increased wheel slip run-in by means of evaluated wheel speeds in relation to a limiting minimum shaft speed, which is specified by a control unit of the vehicle dynamics control system , wherein the wheel speed is detected by the electric machine and the wheel torque is controlled by the electric machine in such a way that the braked wheel is operated in a slip range specified by a control unit of the driving dynamics control system.

In one embodiment, the electric machine indicates to the control unit of the vehicle dynamics control a maximum drag torque that can be deducted, and the control unit of the vehicle dynamics control counteracts a reduction in the electrical deceleration torque by increasing the deceleration torque of the service brake if the vehicle's deceleration remains the same or the deceleration request remains the same.

In one embodiment, the wheel slip is detected by the permissible minimum shaft speed and thus increased wheel slip running-in by the electric machine and/or by impressing a wheel-specific mechanical deceleration torque.

According to one aspect of the present invention, a motor vehicle is provided, comprising a plurality of wheels, at least one electric machine as a drive, a Service brake and vehicle dynamics control, the wheels being able to be braked by means of a deceleration torque applied by the service brake and at least partially by a deceleration torque applied by the electric machine. According to the invention, the motor vehicle is configured to carry out the method described above.

Using the electric machine, higher control dynamics are possible than with conventional solutions.

Exemplary embodiments of the invention are explained in more detail below with reference to a drawing.

It shows:

1 is a schematic diagram showing a deceleration request and deceleration moments of a service brake and an electric machine.

The present invention proposes primarily to use the electric machine for controlling slip when braking (ABS) and/or when a driving dynamics control system ESC or ESP intervenes in a vehicle that includes an electric machine as a drive, since this has better and shorter control times than the hydraulic brake.

According to the present invention, the braking torques of the (hydraulic) service brake (ABS) and/or an ESP control are superimposed with the torques of the electric machine in such a way that an optimized braking force is achieved while avoiding wheel slip. In this case, the electric machine can apply not only a braking torque but also a drive torque to the wheels in order to avoid slipping, slipping or locking of the wheels.

The very fast regulation/control of the electric machine is an advantage here, since even with small changes, a corresponding counter-torque can be set by the electric machine and thus the appropriate measures against slip, Slipping or locking of the wheels can be taken. This is not possible with the long control times of the service brake and/or with conventional (hydraulic) braking and control systems (ABS, ESP, etc.).

In this way, vibrations in the drive train can also be suppressed, which could otherwise occur due to the delayed control times of conventional braking and control systems if repeated interventions occur.

In one embodiment, the moments of the electric machine can be distributed directly to the individual wheels, so that such a wheel-specific control is made possible. This is possible in particular when each wheel is either directly assigned an electric machine or at least each axle has a type of torque vectoring.

However, the principle of the present invention also works when the electric machine is arranged by axis. With an electric four-wheel drive or one electric machine per axle, this is also possible on both or all axles and thus on all wheels.

FIG. 1 shows a schematic diagram for representing a deceleration request W, a deceleration torque M _B of an in particular hydraulic service brake of the vehicle and a deceleration torque M _E of an electric machine over time t.

In the event that an electric machine drives an axle of a vehicle via a differential, the following applies:

When the vehicle decelerates or when a deceleration request W is made, the axle-driven electric motor detects and regulates the increased wheel slip by means of evaluated wheel speeds in relation to a limiting minimum shaft speed that is specified by an ESP control unit.

Through direct speed detection and immediate torque detection and torque control of the electric motor, the braked wheel can be operated independently in the optimal slip range (especially without locking) that is specified by the ESP control unit. The wheel slip is detected and controlled preventively by the deceleration torque M _E of the electric motor and the wheel speed, so that locking of the wheel and an increase in wheel slip are detected and controlled before the wheel comes to a standstill.

The electric machine indicates to the ESP control unit a maximum drag torque (shaft torque) that can be deducted via the axle in order to counteract the reduction in the electrical deceleration torque M _E by increasing the _deceleration torque MB of the mechanical service brake while the vehicle decelerates the same (driver braking specification). .

Before the wheel-specific mechanical deceleration torque M _B is applied, the electric machine detects the wheel slip. This can be done both by the permissible minimum shaft speed and thus increased wheel slip run-in by the electric machine and by impressing a mechanical deceleration torque M _B on both sides (drag torque superimposed).

In general, wheel slip can also be detected from the comparison or ratio of an actual wheel speed to a target wheel speed, in which case the actual wheel speed can be determined from the shaft speed, in particular a side drive shaft, and the Wheel target speed can be derived from a specification of the ESP control unit, which can determine the speed that this wheel should have from the specifications of an actual speed of the vehicle and yaw rates or steering angle.

The electric motor allows wheel slip to be controlled more sensitively in order to transfer frictional forces more dynamically to the ground. Compared to conventional ESP control, the deceleration time is used more effectively, with the braking distance being shortened by providing both an electrical deceleration torque M _E and a superimposed mechanical deceleration torque M _B .

The classic mechanical ABS control by the ESP control unit serves as a fallback level (functional safety).

In the case of an individual wheel drive by a respective electric machine without a differential, the following applies:

If the vehicle decelerates or if you want to decelerate W, the single-wheel drive electric motor detects and regulates the increased wheel slip by means of evaluated wheel speeds in relation to a limiting minimum wheel speed that is specified by the ESP control unit.

The braked wheel can be operated independently in the optimum slip range, which is specified by the ESP control unit, thanks to the direct speed measurement of the electric motor. A wheel that tends to lock is detected at an early stage and the wheel-specific drag torque can be dynamically adjusted.

The electric machine indicates to the ESP control unit a maximum drag torque that can be delivered (actual wheel braking torque) in order to counteract the reduction in the electrical deceleration torque M _E by increasing the deceleration torque MB of the mechanical service brake while the vehicle decelerates the same (delay request _W ). .

Wheel slip is detected before the mechanical deceleration torque M _B is applied to the individual wheels. This can be done both by the permissible minimum wheel speed and thus increased wheel slip running-in by the electric machine and by impressing a wheel-specific mechanical deceleration torque M _B (drag torque superimposed).

In general, the wheel slip can be detected from the comparison or ratio of an actual wheel speed to a target wheel speed, in which case the actual wheel speed can be determined from the speed of the electric machine and the wheel target Speed can be derived from a specification of the ESP control unit, which can determine the speed that this wheel should have from the specifications of an actual speed of the vehicle and yaw rates or steering angle.

A torque above a vertical axis (yaw moment) of the vehicle is detected by the ESP control unit and regulated taking into account the driving dynamics specifications. This also means that a locked wheel can be turned on again via a predetermined torque using the electric machine in order to be actively accelerated.

The electric motor allows wheel slip to be controlled more sensitively in order to transfer frictional forces more dynamically to the ground. Compared to conventional ESP control, the deceleration time is used more effectively, with the braking distance being shortened by both an electrical Deceleration torque M _E and a superimposed mechanical deceleration torque M _B is provided.

To reduce vibrations in the drive train, the described sensitive and dynamic brake control intervention by the at least one electric machine can take place outside the natural frequencies of the drive train (side shafts, electric machine, engine mounts, etc.) when decelerating the vehicle.

The electrical component of the deceleration torque M _E during the deceleration process can reduce electrical friction losses and wear on the brake control system (brake lining, brake disc, brake caliper).

The design of the thermal requirements can be optimized by saving material and thus weight.

The solution according to the invention allows the braking distance to be shortened by the quickly controllable deceleration torques ME, i.e. recuperation torques, of the _electric machine, in that the deceleration torque ME is controlled before the wheels come to a standstill (in the case of ABS braking, the locked wheels must be pushed/accelerated again). According to the invention, the wheel slip is detected and the optimum wheel slip is adjusted during the deceleration process. Dynamic torque adjustments for individual wheel deceleration and acceleration are possible.

A wheel that is tending to lock can thus be detected at an early stage and the wheel-specific drag torque can be dynamically adjusted within the specified ESP torque limits without the wheel having to come to a standstill.

In addition, the electric machine constantly reports to the ESP control unit a current drag torque that can be transmitted to the electric machine (actual wheel braking torque), which can then be taken into account when determining the braking and within the framework of the overall deceleration. The decelerating braking torque of the motor vehicle, or more precisely at the individual wheels of the motor vehicle, can also be made up of an electrical deceleration torque and, if necessary, an additional deceleration torque of the mechanical service brake, in order to decelerate the vehicle if the deceleration request or the deceleration specification exceeds the maximum over the axle or the wheel deductible drag torque by the electric machine exceeds. Starting from a base contribution of the deceleration torque of the mechanical service brake far below an expected slip torque of the wheel to a total deceleration torque, dynamic control by the electric machine can be carried out more efficiently and sensitively, since the remaining electrical deceleration torque to the total deceleration torque also has the advantages of the present invention having.

The invention can therefore also be used when the specified deceleration torque exceeds the maximum deceleration torque that can be applied by the electric machine, ie the maximum electric deceleration torque. In this case, only part of the specified deceleration torque is applied by the mechanical service brake, which is far enough away from an expected slip torque of the wheel and also small enough not to unnecessarily reduce the remaining electrical deceleration torque, so that efficient regenerative braking and slip detection can continue of the present invention is possible. The distribution of the proportions of the deceleration torques can depend on various parameters, such as a total deceleration torque and/or a driving mode of the motor vehicle and/or a specified deceleration torque and/or a maximum electrical deceleration torque and/or a state of charge of the battery and/or a temperature the battery and/or environmental conditions and/or a slip torque of the wheel.

Dynamic torque adjustment outside of the inherent natural frequencies is possible to reduce drive train vibrations.

A reduction/avoidance of the classic ESP/ABS control intervention can be achieved by the solution according to the invention. In addition, energetic friction losses and wear on the brake control system (BRS) are reduced and the mass of the brake components and thus of the motor vehicle can be reduced. Reference List t Time

W Delay request M _B Delay moment M _E Delay moment

Claims

patent claims

1. A method for controlling a brake system of a motor vehicle, comprising a plurality of wheels, at least one electric machine as a drive, a service brake and a driving dynamics control system, the wheels being decelerated by means of a deceleration torque (MB) applied by the service brake and at least partially by a The deceleration torque (M _E ) applied by the machine can be braked, with the slip that occurs as a result of braking and/or interventions by the driving dynamics control system being controlled at least primarily by adapting the deceleration torque (M _E ) applied by the electric machine, characterized in that If necessary, a drive torque is applied for slip control or for turning a locked wheel by means of the electric machine.

2. The method according to claim 1, characterized in that at least one axle of the motor vehicle is driven by the electric machine via a differential, wherein the electric machine when there is a deceleration request (W) increases wheel slip by means of evaluated wheel speeds in relation to a limiting minimum Shaft speed, which is specified by a control unit of the vehicle dynamics control, is recorded and regulated, with the wheel speed and the wheel torque being recorded by the electric machine and the wheel torque being controlled in such a way that the braked wheel is in one by a control unit of the vehicle dynamics control predetermined slip range is operated.

3. The method according to claim 2, characterized in that the detection and control of the wheel slip. preventively by the deceleration torque (M _E ) of the electric machine and the wheel speed, such that a locking of the wheel and an increase in wheel slip is detected and the wheel slip is regulated before the braked wheel comes to a standstill.

4. The method according to claim 2 or 3, characterized in that the electric machine indicates to the control unit of the driving dynamics control a maximum drag torque that can be deducted via the axle, and the control unit of the driving dynamics control indicates a reduction if the deceleration of the vehicle remains the same or the deceleration request (W) remains the same of the electrical deceleration torque (M _E ) counteracts by increasing the deceleration torque (MB) of the service brake.

5. The method according to any one of claims 2 to 4, characterized in that the wheel slip is detected by the permissible minimum shaft speed and thus increased wheel slip run-in by the electric machine and/or by impressing a mechanical deceleration torque (MB) on both sides.

6. The method according to claim 1, characterized in that each wheel of the motor vehicle is driven by a respective electric machine, wherein the electric machine when deceleration is requested (W) an increased wheel slip run-in by means of evaluated wheel speeds in relation to a limiting minimum shaft speed, the is specified by a control unit of the vehicle dynamics control, recorded and regulated, with the wheel speed being recorded by the electric machine and the wheel torque being controlled by the electric machine in such a way that the braked wheel is operated in a slip range specified by a control unit of the driving dynamics control becomes.

7. The method according to claim 6, characterized in that the electric machine indicates to the control unit of the vehicle dynamics control a maximum drag torque that can be deducted, and the control unit of the vehicle dynamics control indicates a reduction in the electrical deceleration torque (M _E ) counteracts this by increasing the deceleration torque (MB) of the service brake.

8. The method according to claim 7, characterized in that the wheel slip is detected by the permissible minimum shaft speed and thus increased wheel slip running-in by the electric machine and/or by impressing a wheel-specific mechanical deceleration torque (MB).

9. Motor vehicle comprising a plurality of wheels, at least one electric machine as a drive, a service brake and a vehicle dynamics control system, the wheels being decelerated by means of a deceleration torque (MB) applied by the service brake and at least partially by a deceleration torque (M _E ) can be braked, characterized in that the motor vehicle is configured for carrying out the method according to one of the preceding claims.