CN118843568A - Method for controlling a hydraulic brake system and brake system - Google Patents

Abstract

The invention relates to a method for controlling a brake system of a motor vehicle, the brake system having at least one wheel brake (3) and a friction brake actuator for actuating the at least one wheel brake (3), the motor vehicle having an electric power unit (4), calculating a control signal for the friction brake actuator and a control signal for the electric power unit (4) based on a brake demand signal, and transmitting the control signal for the friction brake actuator to the friction brake actuator and the control signal for the electric power unit to the electric power unit. In order to improve the functional performance of the brake system in the event of a partial failure, when a fault is determined, the brake system switches to a backup mode, in which a control signal for the electric power unit (4) is calculated based on the brake demand signal and transmitted to the electric power unit.

Description

Method for controlling a hydraulic brake system and brake system

The present invention relates to a method for controlling a brake device of a motor vehicle, the brake device having at least one wheel brake (3) and a friction brake actuator for operating the at least one wheel brake (3), the motor vehicle having an electric power device (4), calculating a control signal for the friction brake actuator and a control signal for the electric power device (4) based on a brake demand signal, transmitting the control signal for the friction brake actuator to the friction brake actuator, and transmitting the control signal for the electric power device to the electric power device.

Braking systems for motor vehicles exist in many different variants. Due to the safety of these systems, these systems must at least be able to brake the vehicle to a stationary state when some components fail and therefore have different backup modes.

So-called wire-controlled brake systems do not require a mechanical connection between the brake pedal and the wheel brakes for normal braking. This connection can be interrupted (for example in simulator brake systems) or does not exist in principle (for example in electronic pedal systems).

The brake system can be designed as a hydraulic brake system, which correspondingly has hydraulic wheel brakes, which are supplied with pressure by a pressure supply device serving as a friction brake actuator and are thus actuated. Alternatively or in combination, the wheel brakes can be actuated usually directly by an electromechanical friction brake actuator.

The brake control device having an electronic device and a hydraulic device is hydraulically connected to the brake actuator. The brake control device can generate hydraulic pressure by means of a pressure supply device based on an electrical brake demand signal, and the hydraulic pressure decelerates the vehicle via the brake actuator.

The invention relates to a vehicle having at least one power motor, by means of which the vehicle can be braked or decelerated. In fault-free operation, a brake control device (BSG) calculates in particular braking torque signals for at least two different actuator types and processes and/or sends corresponding requests. Thus, a pressure regulation, in particular a pressure supply device, of a hydraulic brake actuator is adjusted and a power control device (ASG) of the vehicle is actuated, which operates an electric power device to generate a corresponding braking torque. In this case, the sum of all braking torque signals corresponds to the braking request.

When the friction brake actuator (hydraulic pressure supply device or alternative friction brake actuator) fails due to a fault, the brake system must ensure that the vehicle can continue to decelerate at least to a standstill. Depending on the system, various methods are known.

In hydraulic brake systems that enable a hydraulic coupling of the brake pedal to the brake actuator, this hydraulic coupling is established in the event of a fault (=hydraulic fallback mode) and the driver can generate hydraulic pressure (without increasing it) by actuating the brake pedal. In addition, an additional braking torque can be generated on the rear axle by the brake control system by actuating the parking brake.

In hydraulic brake systems in which a hydraulic connection between the brake pedal and the wheel brakes is not possible (particularly those with an electronic pedal, i.e. a purely electrically connected brake pedal), in the event of a fault, the hydraulic pressure must be generated by an additional brake control device, such as another brake system with its own hydraulic pump or an additional electric emergency actuator.

In both systems, the brake control device according to the prior art no longer requests a braking torque from the power motor. The vehicle can therefore be braked only by the hydraulic brake actuator and, if necessary, by the parking brake actuator. The resulting braking torque is always less than the total braking torque in the fault-free state.

In hydraulic fallback mode, a greater pedal force is necessary in combination with a longer pedal travel, which not every driver is able to apply. As a result, in certain situations the vehicle is decelerated so little that it could result in a road traffic hazard.

Braking torque assistance via the parking brake in hydraulic backup mode is not possible in all fault situations and for all systems. Braking torque assistance via the parking brake in hydraulic backup mode is only possible if the parking brake system can be electrically actuated and has the capability of dynamic deceleration via vehicle stability maintenance measures (so-called "dynamic braking functions", such as ADBF or FSI). This is not always the case. Another possibility known from the prior art for implementing braking torque assistance in hydraulic backup mode is to use an additional control device which is able to actuate the hydraulic brake actuator. This leads to increased costs due to the manufacturing costs of the control device itself, its installation in the vehicle and its commissioning.

The object of the present invention is therefore to avoid the above-mentioned disadvantages and to enable safe and redundant operation of the brake system.

The object is achieved by a method for controlling a brake system of a motor vehicle, the brake system having at least one wheel brake and a friction brake actuator for actuating the at least one wheel brake, wherein the motor vehicle has an electric power unit. Furthermore, based on a brake demand signal, a control signal for the friction brake actuator is calculated and transmitted to the friction brake actuator. Here, the control signal can be a requested braking torque, a hydraulic pressure or a deceleration request. Furthermore, a control signal for the electric power unit is calculated and transmitted to the electric power unit, in particular to an associated power control unit. Here, the control signal can also be a requested braking torque, a hydraulic pressure, a deceleration request or another equivalent signal.

According to the invention, when a fault is detected, the brake system, in particular the brake control device, switches to a backup mode. In the backup mode, a control signal for the electric power device is calculated by the brake control device based on the brake demand signal and transmitted to the electric power device, in particular to an associated control device.

The present invention makes it possible to ensure safe braking to a parking state when the friction brake actuator fails or at least partially fails, in particular with respect to generating hydraulic pressure, for example due to a leak or an electrical fault in a control/regulation circuit or in the power supply of a pressure supply device within the brake system (e.g. a linear actuator).

In order to ensure braking by means of the electric power unit, it may be checked in advance whether communication between the brake control unit (BSG) and a control unit of the electric powertrain (ASG) of the vehicle is available.

According to the invention, the brake control device also continues to calculate a brake request signal in the fallback mode, if necessary depending on the regenerative capacity, and sends it to the power control device, which controls the electric drive train in such a way that a corresponding braking torque is generated.

In a preferred embodiment of the invention, the brake system is a hydraulic brake system having a pressure supply device, such as in particular a linear actuator, serving as a friction brake actuator for supplying pressure to the hydraulic friction brake.

In a preferred embodiment of the invention, the control signal for the electric drive unit predetermines the braking torque of the electric drive unit. For this purpose, the requested braking torque or a similar variable can be directly transmitted.

In a preferred embodiment of the invention, the brake system implements anti-slip regulation in the backup mode. For this purpose, the braking torque requested by means of the control signal from the electric power unit is reduced based on the wheel speed signal. Therefore, the corresponding braking torque for the electric power unit is determined based on the braking demand, but based on the wheel speed signal, in the case of a determined lock or a tendency to lock, a smaller braking torque is requested and/or limited by means of the control signal from the electric power unit. Therefore, during the assistance of the braking torque by the electric powertrain, the driver is also assisted by functions and measures for vehicle stability. Therefore, even in the above-mentioned fault situation, wheel slip is prevented, wherein the braking demand for the electric powertrain is sufficiently reduced so that the wheels do not lock.

In another preferred embodiment of the invention, the brake system uses a transverse acceleration signal, in particular from an acceleration sensor, in a fallback mode. Based on the transverse acceleration, a smaller braking torque is requested for the electric drive unit and/or limited by means of a control signal. This prevents overbraking during fast cornering and thus prevents the occurrence of instabilities.

In another preferred embodiment of the present invention, in the backup mode, the brake device limits the requested braking torque to a maximum value that is lower than the maximum regeneration capacity of the electric power device. Therefore, the requested braking torque is no longer directly dependent on the current regeneration capacity, but is limited to be slightly lower than the current regeneration capacity, so that the braking torque can be kept constant at least within a certain range. This improves the comfort of the driver.

In another preferred embodiment of the invention, the load state of the motor vehicle is taken into account when calculating the control signal. Thus, the driving behavior and stability behavior of the motor vehicle can be taken into account in relation to the load state.

In another preferred embodiment of the invention, a brake demand signal is generated by the assistance function or the virtual driver based on the actuation of the brake pedal. The brake pedal can be an electronic pedal or a mechanical brake pedal. An electronic pedal is a brake pedal that has no mechanical connection, in particular a hydraulic connection, to the wheel brake. Instead, there is only an electrical connection, by means of which the actuation data are transmitted to the brake control device. Although the mechanical pedal has such a connection, the connection may be disconnected during normal braking operation, in particular in the absence of a fault, so that the brake device still works according to the brake-by-wire principle. Depending on the system design, the electric brake demand signal in the brake control device is determined based on measured variables derived from the actuation of the brake pedal (for example, pressure and/or actuation travel and/or actuation angle). Alternatively, the brake demand signal is determined by an external system and transmitted to the brake control device via an interface. In the brake system, there is at least one sensor for detecting the brake demand (for example, a pressure sensor, a pedal travel sensor, a pedal angle sensor, a force sensor, a radar, a camera). It can be an internal sensor in the brake control device or an external sensor that transmits a signal to an interface of the brake control device. The sensor reproduces the driver's braking request or forms the basis for a braking request generated by an assistance function or a virtual driver. Based on the available measurement signals, the brake control device can calculate a braking request signal.

In another preferred embodiment of the present invention, the sum of the braking torques corresponding to the control signal for the friction brake actuator, in particular the pressure supply device, and the control signal for the electric power device corresponds to the brake demand signal. In other words, the brake demand signal corresponds to the total braking torque distributed to the pressure supply device and the electric power device.

In another preferred embodiment of the present invention, the determined fault includes a failure or partial failure in the generation of hydraulic pressure. This may involve the pressure providing device itself or other hydraulic units required for generating hydraulic braking force.

In another preferred embodiment of the invention, the braking device, in particular the corresponding control device (i.e. the braking control device), receives information about the instantaneous regeneration capability from the electric power device, in particular from the power control device. Then, the control signal for the electric power device is determined based on the braking demand signal and the received regeneration capability. Thus, the braking device can take into account the actual possibilities when requesting a braking torque. Alternatively, the braking control device calculates a braking request for the electric powertrain without using the regeneration capability signal. In this case, when the request exceeds the instantaneous (regeneration) possibility, the power control device may generate a braking torque that is less than the braking torque already requested by the braking control device.

In another preferred embodiment of the invention, the electric power device comprises an independent unit for each axle, and the hydraulic brake device calculates and transmits the control signal for each axle separately. Therefore, the brake force distribution in the backup mode can also be adjusted as needed and optimally.

In another preferred embodiment of the invention, in the backup mode, the control signal for the electric power unit is limited to a certain maximum braking torque. Thus, in the backup mode, overbraking is avoided and thus the risk of instability is avoided.

In another preferred embodiment of the present invention, in the backup mode, the braking assistance provided by the electric power device is gradually weakened. To this end, for example, the maximum braking torque provided by the electric power device can be gradually reduced. Alternatively or additionally, the conversion parameter between the braking demand and the braking torque can be reduced. This ensures that the driver does not get used to the good performance of the braking torque assistance in the hydraulic backup mode. This avoids the driver not going to the repair station despite the fact that a fault occurs in the brake control device and the warning light is on. Therefore, the preferred weakening strategy for the braking torque assistance achieved by the electric powertrain slightly reduces the request to the power control device for each new braking demand, so as to reduce the braking torque assistance accordingly, with the aim of making the driver adapt to the system state of the hydraulic backup mode caused by the fault and go to the repair station.

In another preferred embodiment of the invention, in the fallback mode, hydraulic intervention/hydraulic control is established between the brake pedal and the wheel brakes, and/or the emergency actuator provides electrically generated hydraulic pressure in the wheel brakes. Thus, further redundancy is added, thereby improving the safety of the hydraulic brake system.

In another preferred embodiment of the invention, in the backup mode, hydraulic intervention is formed on the wheel brakes whose wheels are not braked by the electric power device. Therefore, some wheels are braked by the driver's muscle force and other wheels are braked by the electric power device. Since the brake pedal with the master brake cylinder only needs two wheel brakes, the required pedal travel is shorter.

In another preferred embodiment of the invention, in the fallback mode, the brake system calculates an actuation signal for the electromechanical parking brake based on the braking demand and transmits it to the electromechanical parking brake. Accordingly, in the fallback mode, the braking demand is distributed to the actuators that are still available.

The object is also achieved by a brake system for a motor vehicle, the brake system having a friction brake actuator for actuating at least one wheel brake and a brake control device for regulating the friction brake actuator, wherein the brake control device is configured to switch to a backup mode when a fault is detected, in which a control signal for an electric power unit of the motor vehicle is generated and sent based on received data to achieve a braking torque. The brake control device is particularly configured to implement one of the above methods.

In a preferred embodiment of the brake system according to the invention, the brake control device is at least partially part of an intelligent electronic brake pedal, wherein the part generates and sends actuation signals for the electric drive unit in the fallback mode.

Further features, advantages and application possibilities of the invention are also apparent from the following description of the exemplary embodiments and the accompanying drawings. All described and/or illustrated features are subject matter of the invention, either alone or in any combination, and are independent of their generalization in the claims or their references.

FIG. 1 schematically shows a first embodiment of a brake system according to the invention,

FIG. 2 schematically shows a second embodiment of a brake system according to the invention,

FIG. 3 schematically shows a third embodiment of a brake system according to the invention,

FIG. 4 schematically shows a fourth specific embodiment of a brake system according to the invention.

In the hydraulic brake system of FIG. 1 , driver braking is performed using a hydraulic pedal. The vehicle has four hydraulic wheel brakes 3 and an electric power unit 4 on at least one axle, which allows electric (e.g. regenerative) braking. Wheels 5 together with corresponding wheel brakes 3 and power units 4 are assigned to the left front axle 6, the right front axle 7, the left rear axle 8 and the right rear axle 9. The electric power unit is controlled by a power control unit 10. The brake pedal is hydraulically connected to the brake control unit (BSG) 1. The power control unit (ASG) 10 continuously transmits the maximum possible regenerative capacity of the electric power unit to the brake control unit.

The driver's braking demand is calculated in the brake control device and split into two parts (hydraulic part and part for the electric powertrain) so that the largest possible part is generated as a braking demand for the powertrain in order to maximize energy regeneration.

One part (hydraulic brake demand) is converted by the hydraulic actuator of the brake control device into hydraulic pressure, by which the wheel brake actuator is actuated. The other part (brake demand of the electric powertrain) is transmitted as a brake demand to the power control device via signal transmission. The power control device controls the electric powertrain so that a corresponding braking torque is generated on at least one axle.

Due to a fault in the hydraulic brake system, the brake control device switches to a hydraulic fallback mode in which the driver is directly connected to the wheel brakes via the brake pedal by means of a corresponding valve position. Accordingly, the hydraulic pressure is not increased but is generated directly by the force of the driver 1 operating the pedal. Analogously to the fault-free situation, the brake control device receives the maximum possible regenerative capacity of the electric power device 4 from the power control device and calculates the braking demand of the electric power train and sends it to the power control device 10. As in the fault-free situation, the power control device 10 controls the electric power device 4 so that a corresponding braking torque is generated on at least one axle.

The embodiment of FIG. 2 shows the case of autonomous braking. The vehicle also has four hydraulic wheel brakes 3 and an electric power unit 4 on at least one axle, which allows electric (e.g. regenerative) braking. The power control device 10 continuously transmits the maximum possible regenerative capacity of the electric power unit to the brake control device 2. In addition, the vehicle has an automatic driving control device 11, which transmits a braking request to the brake control device 2.

This external brake demand is further divided into a hydraulic part and an electric power device part in the brake control device 2. The hydraulic brake demand is converted into hydraulic pressure by a hydraulic actuator, in particular a pressure supply device of the brake control device 2, by which the wheel brakes are actuated. The brake demand part of the electric powertrain is transmitted as a brake demand via signal transmission to the power control device 10. The power control device 10 controls the electric power device 4 so that a corresponding braking torque is generated on at least one axle.

If a fault occurs in the hydraulic brake system, the brake control device 2 switches to a fallback mode in which the hydraulic brake pressure on at least one axle is generated by an emergency actuator. The emergency actuator can be contained in the brake control device 2 or in a separate control device. The brake control device 2 (or the emergency actuator) also receives the maximum possible regeneration capacity of the electric power device from the power control device 10 and calculates the braking demand of the electric powertrain 4 and sends it to the power control device 10. The power control device 10 controls the electric power device so that a corresponding braking torque is generated on at least one axle.

The embodiment of FIG. 3 now shows driver braking with an electronic pedal 12. The electronic or electric brake pedal 12 is not hydraulically connected to the brake control device 2. Instead, the vehicle has an electronic pedal 12 which independently calculates the driver's braking demand and transmits it to the brake control device 2 as an external braking demand. Alternatively, the electronic pedal does not calculate the driver's braking demand, but transmits one or more sensor signals to the brake control device 2, which calculates the driver's braking demand based on these sensor signals. In other respects, the mode of operation corresponds to the embodiment of FIG. 2.

In FIG. 4 , an embodiment with an intelligent electronic pedal 12 is now shown. This electronic pedal has a control device function and can therefore be regarded as part of the brake control device 2. This part of the brake control device 2 calculates the driver's braking demand and transmits it to the main brake control device 2 and the power control device 10 via a bus connection (e.g. CAN/Flexray/LIN). In the event of a fault in which the main brake control device 2 is, for example, physically separated from the electronic pedal 12, or in which the main brake control device 2 is unavailable for other reasons (e.g. power failure, CPU failure, etc.), the power control device 10 can still implement the braking demand part for the electric powertrain 4. As a result, the vehicle can still be brought to a stop with the help of the powertrain 4 (without hydraulic means).

If the vehicle has a parking brake system that can be decelerated dynamically with stability-maintaining measures (so-called "dynamic braking functions", such as ADBF or FSI), in the above-mentioned fault situation, an electromechanical braking request component for the parking brake is calculated in addition to the braking request for the electric drive train and transmitted to the power control device 10. In this case, the electric drive train can be used preferentially and the parking brake is only actuated if the regenerative capacity is too low.

The brake control device 2 calculates corresponding control signals for the parking brake actuator based on the braking request, so that the parking brake actuator generates corresponding braking torques on the wheels. By intelligently distributing the braking request to the available brake actuators according to the axle, the braking behavior of the vehicle can be further optimized.

For example, brake assistance is performed on the front axle by a power motor and brake assistance is performed on the rear axle by a parking brake actuator. Alternatively, there is no brake assistance on the front axle, but brake assistance is performed on the rear axle by a power motor and a parking brake actuator. In a third variant, brake assistance is performed on the front axle by a power motor and brake assistance is performed on the rear axle by a power motor and a parking brake actuator.

In another variant with a mechanical brake pedal, by closing the inlet valve of the hydraulic brake actuator of one axle (front or rear axle), the actuator of this axle can be hydraulically decoupled from the brake pedal, so that less hydraulic volume is displaced when the brake pedal is actuated. As a result, the pedal travel for achieving the required pedal force that the driver must apply in the hydraulic backup mode in the event of a fault can be shortened. The hydraulic braking force lost due to the closing of the inlet valve on one axle is compensated by the braking torque assistance of the electric drive train on this axle.

Depending on the specific embodiment, the following information is taken into account when calculating the braking torque request:

a) A braking request by the driver or an automatic control system (which is calculated based on available sensor signals or received via signal transmission at an input of the brake control system).

b) The regenerative capability of the electric powertrain (this signal is transmitted from the power control device to the brake control device).

c) Specific limitation of the braking request level for the electric powertrain for the backup mode, for example to prevent overbraking or to limit the impact on vehicle deceleration in the event of fluctuations in regenerative capacity.

Although the sum of all generated braking torques may be lower than in the error-free case, a significant braking torque assistance can nevertheless be achieved by the electric drive train in comparison with the prior art.

In this case, the braking torque assistance in the event of a fault is particularly independent of the properties and design of the parking brake system. In general, the braking torque assistance in the event of a fault is higher than the assistance provided by the parking brake system and has a shorter response time. The braking torque assistance in the event of a fault can also be regulated and metered more precisely than the assistance provided by the parking brake system, in which the actuator can only switch between two states (on/off = digital). The brake control device has functions or measures for stabilizing the vehicle that other control devices (such as the power control device) do not have or have only limited access due to signal transmission times, so that the braking torque assistance can be maximized.

Traffic safety is significantly increased for the above-mentioned fault situations. In addition, the method according to the invention does not require additional hardware and therefore offers a clear cost advantage over alternative methods. For the braking torque assistance according to the invention, a redundant design of multiple control devices can be implemented by purely software functions and is therefore particularly cost-effective.

Claims (19)

1. Method for controlling a brake system of a motor vehicle, which brake system has at least one wheel brake (3) and a friction brake actuator for actuating the at least one wheel brake (3), wherein the motor vehicle has an electric power system (4), wherein a control signal for the friction brake actuator and a control signal for the electric power system (4) are calculated on the basis of a brake demand signal, and wherein the control signal for the friction brake actuator is transmitted to the friction brake actuator and the control signal for the electric power system is transmitted to the electric power system, characterized in that, upon determining that a fault is present, the brake system is switched to a backup mode, wherein the control signal for the electric power system (4) is calculated on the basis of the brake demand signal and is transmitted to the electric power system.

2. A method according to claim 1, characterized in that the brake device is a hydraulic brake device having pressure providing means acting as a friction brake actuator for pressurizing a hydraulic friction brake.

3. Method according to claim 1 or 2, characterized in that the control signal for the electric power plant (4) predefines the braking torque of the electric power plant (4).

4. Method according to one of the preceding claims, characterized in that the braking device effects anti-slip adjustment in a backup mode in that: based on the wheel speed signal, the control signal predefines a smaller braking torque to the electric drive (4).

5. Method according to one of the preceding claims, characterized in that in the backup mode the braking device requests a smaller braking torque and/or limits a braking torque based on the lateral acceleration signal.

6. Method according to one of the preceding claims, characterized in that in the backup mode the braking device limits the requested braking torque to a maximum value, which is lower than the maximum regeneration capacity of the electric power device.

7. Method according to one of the preceding claims, characterized in that the load state of the motor vehicle is taken into account when calculating the control signal.

8. Method according to one of the preceding claims, characterized in that a brake demand signal is generated by an auxiliary function and/or a virtual driver (12) on the basis of the actuation of the brake pedal (11).

9. Method according to one of the preceding claims, characterized in that the sum of the respective braking torques of the actuation signal for the friction brake actuator and the actuation signal for the electric power plant (4) corresponds to a braking demand signal.

10. The method according to one of claims 2 to 9, characterized in that the determined malfunction comprises a failure or partial failure in the production of hydraulic pressure.

11. Method according to one of the preceding claims, characterized in that the brake device obtains information about the instantaneous regeneration capacity of the electric power device (4), and that the control signal for the electric power device (4) is determined on the basis of the brake demand signal and the received regeneration capacity.

12. Method according to one of the preceding claims, characterized in that the electric power plant (4) comprises a separate unit for each axle, and that the braking device calculates and transmits the control signal separately for the respective axle.

13. Method according to one of the preceding claims, characterized in that in the backup mode the control signal for the electric power plant (4) is limited to a specific maximum braking torque.

14. Method according to one of the preceding claims, characterized in that in the backup mode the braking assistance provided by the electric power plant (4) is gradually weakened.

15. Method according to one of claims 2 to 14, characterized in that in the backup mode a hydraulic intervention is established between the brake pedal and the wheel brakes (3) and/or the emergency actuator provides an electrically generated hydraulic pressure in the wheel brakes (3).

16. Method according to claim 15, characterized in that in the backup mode hydraulic intervention is made on the wheel brakes (3) whose wheels (5) are not braked by the electric power unit (4).

17. Method according to one of the preceding claims, characterized in that in the backup mode the braking device calculates a steering signal for the electromechanical parking brake based on the braking demand and transmits the steering signal for the electromechanical parking brake to the electromechanical parking brake.

18. Brake device for a motor vehicle, having a friction brake actuator for actuating at least one wheel brake (3) and a brake control device (2) for adjusting the friction brake actuator, characterized in that the brake control device (2) is configured for switching to a backup mode, in which a control signal for an electric power device (4) of the motor vehicle is generated and transmitted on the basis of received data for realizing a braking torque, when a fault is determined to be present.

19. The brake apparatus of claim 16, wherein the brake control apparatus is at least partially a portion of an intelligent electronic brake pedal, wherein the portion generates and transmits a steering signal for an electric power apparatus in a backup mode.