DE102020125652A1 - Electro-hydraulic braking system and motor vehicle with electro-hydraulic braking system - Google Patents

Abstract

The invention relates to an electrohydraulic brake system (8) having an input device (22) for inputting a braking command by a driver, the input device (22) having an operating element (24) and at least one sensor unit (26) for detecting the braking command, having at least one Wheel brake (10) with a brake cylinder (12), wherein a hydraulic pressure for generating a braking force can be specified in the brake cylinder (12), having an electrically controllable hydraulic system (14) which is connected to the brake cylinder (12) and for specifying the hydraulic Pressure in the brake cylinder (12) and having a control device (18, 20) for controlling the hydraulic system (14) by means of electrical signals, the control device (18, 20) having a primary brake control unit (18) and a secondary brake control unit (20) , and set up in such a way that, in a basic operating mode, the primary brake control unit (18) controls the hydraulic system m (14) regulates in such a way that a primary brake pressure is generated in the brake cylinder (12) as a function of the brake command, and that in an emergency operating mode the secondary brake control unit (20) regulates the hydraulic system (14) in such a way that a secondary brake pressure is generated in the brake cylinder (12).

Description

The invention relates to an electro-hydraulic brake system. The invention also relates to a motor vehicle with an electrohydraulic brake system.

Most of the passenger cars currently available have a brake system in which a hydraulically controlled wheel brake is assigned to each wheel. In these brake systems, during a braking process, a brake pressure is specified for the wheel brakes via a hydraulic system of the brake system, which brake pressure is then converted into a braking force dependent on the brake pressure in the respective wheel brake.

In some cases, such a brake system is designed as a so-called electrohydraulic brake system. In an electrohydraulic brake system, the brake pressure is regulated electrically, typically with the help of electrically controllable valves and with the help of electric hydraulic pumps in the hydraulic system. The regulation takes place here as a function of sensor signals from a sensor with which braking commands from a driver are recorded, which the driver specifies by actuating a brake pedal.

In the event that the electrical regulation in an electrohydraulic brake system fails, a so-called hydraulic fallback level is typically implemented in electrohydraulic brake systems. For this purpose, the brake pedal is coupled to the hydraulic system, so that hydraulic pressure can be exerted by actuating the brake pedal and converted into brake pressure via the hydraulic system. In the hydraulic fallback level, the brake pressure is then regulated without electrical signals, in that the actuation of the brake pedal is converted into brake pressure via a purely mechanical-hydraulic coupling.

The object of the present invention is to create an advantageously designed electrohydraulic brake system and an advantageously designed motor vehicle.

This object is achieved by an electrohydraulic brake system with the features of claim 1 and by a motor vehicle with the features of claim 9. The advantages and preferred refinements cited with regard to the electrohydraulic brake system can also be applied to the motor vehicle and vice versa. Advantageous configurations with expedient developments of the invention are specified in the dependent claims.

An electrohydraulic brake system according to the invention, hereinafter also referred to as brake system for short, is usually designed for a motor vehicle. In this case, the brake system is then part of a motor vehicle in the installed state.

Independently of this, the brake system has an input device for inputting a braking command by a driver. The input device in turn has an operating element and at least one sensor unit for detecting the braking command, which can be entered by the driver by means of the operating element. The operating element is typically designed as a so-called brake pedal, which is usually arranged in a footwell of a motor vehicle when the brake system is installed and can be operated with one foot. Alternatively, the operating element is designed for one-handed operation and, when the brake system is installed, is positioned, for example, on or in the area of a steering wheel.

Regardless of the precise configuration of the control element, the input device is set up in such a way that actuation of the control element, for example the brake pedal, is detected by means of the at least one sensor unit, at least if the brake system is in operation. Depending on the actuation detected by sensors by means of the at least one sensor unit, that is to say the brake command entered or specified by the driver, an electrical brake signal is then generated which reproduces the brake command and thus the driver's brake request.

Furthermore, the brake system has at least one wheel brake with a brake cylinder, a hydraulic pressure for generating a braking force being able to be specified in the brake cylinder. The wheel brake is thus designed as a hydraulically controllable wheel brake. If the electrohydraulic brake system is part of a motor vehicle and in particular a passenger car, the brake system preferably has one hydraulically controllable wheel brake per wheel, for example four wheel brakes in a passenger car with four wheels. For the sake of simplicity, however, only the at least one wheel brake is assumed below, since the number is not of particular importance for the inventive concept described here. The transfer of the concept to a brake system with several corresponding wheel brakes is no hurdle for the expert.

Part of the electrohydraulic brake system is also an electrically adjustable or controllable hydraulic system which is connected to the brake cylinder of the at least one wheel brake and is set up to specify the hydraulic pressure in the brake cylinder. That The hydraulic system usually has a number of controllable hydraulic pumps and a number of controllable valves, the valves being expediently controllable via electrical signals and the hydraulic pumps usually being designed as electrical hydraulic pumps that are operated by means of electrical power.

In addition, the brake system has a control device for controlling the hydraulic system by means of electrical signals. Here, the control device is designed in particular to process the electrical brake signal and to control the hydraulic system based on the electrical brake signal or as a function of the electrical brake signal. Furthermore, the control device has a primary brake control unit and a secondary brake control unit, each of the two brake control units expediently being designed as data processing units or the two brake control units each having at least one data processing unit.

Here, the two brake control units are preferably designed to operate independently of one another. For this purpose in particular, each of the two brake control units is preferably assigned its own energy supply unit. This means that, for example, two accumulators are provided, one of the two accumulators supplying the primary brake control unit with electrical power during operation and the other of the two accumulators supplying the secondary brake control unit with electrical power during operation.

Furthermore, the control device and the hydraulic system are typically set up in such a way that the hydraulic system can be controlled by each of the two brake control units, in particular independently of one another, and also takes place depending on the operating mode. This means that the primary brake control unit preferably controls the hydraulic system in a basic operating mode and that the secondary brake control unit controls the hydraulic system in an emergency operating mode. For this purpose, the aforementioned controllable hydraulic pumps and the aforementioned controllable valves of the hydraulic system, which enable the control, can be controlled by both brake control units, in particular independently of one another, and / or each of the two brake control units is assigned a corresponding number of controllable hydraulic pumps and a corresponding number of controllable valves . In this case, each of the two brake control units is preferably assigned at least a corresponding number of electrical hydraulic pumps, so that redundancy is created at least with regard to the hydraulic pumps of the hydraulic system.

Independently of this, the two brake control units are preferably connected to one another for signal and / or data exchange, for example via a field bus or data bus. Means of the connection and a corresponding signal and / or data exchange during operation, it is preferably ensured that in the event of an error or defect in the primary brake control unit, the secondary brake control unit takes over the tasks of the primary brake control unit. The data exchange thus enables the secondary brake control unit to recognize when there is an error or defect in the primary brake control unit and in this case the secondary brake control unit then takes over the tasks of the primary brake control unit.

The electrohydraulic brake system now has the input device, the at least one wheel brake, the electrically controllable hydraulic system and the control device. In addition, the brake system is set up in such a way that, in the basic operating mode, the primary brake control unit regulates the hydraulic system in such a way that a primary brake pressure is generated in the brake cylinder based on the brake command or as a function of the brake command. In addition, the brake system is set up in such a way that, in the emergency operating mode, the secondary brake control unit regulates the hydraulic system in such a way that a secondary brake pressure is generated in the brake cylinder based on the brake command or as a function of the brake command.

When the brake system is in operation, the basic operating mode is then preferably active as standard, so that the regulation of the hydraulic system and consequently the control of the braking force is carried out as standard by the primary brake regulating unit. The emergency operating mode, on the other hand, is typically only activated if a fault occurs or is present in the primary brake control unit, so that the primary brake control unit no longer functions properly. The secondary brake control unit then takes over the control of the hydraulic system and consequently the control of the braking force. A corresponding error is present, for example, if the primary brake control unit is no longer supplied with sufficient electrical power and / or if there is a defect in the primary brake control unit.

The primary brake control unit and the secondary brake control unit thus preferably create a redundancy at least for the control of the hydraulic system, the secondary brake control unit typically being part of what is known as a fall-back level. Regardless of this, both the primary brake control unit and the secondary brake control unit regulate the hydraulic system and thus control the Braking force based on the braking command. When the brake system is in operation, this is typically present in both brake control units after input by the driver and is expediently also processed in both. Thus, both brake control units, as it were, preferably recognize the driver brake request and control the braking force in accordance with the driver brake request.

The hydraulic system is preferably also controlled both by the primary brake control unit and by the secondary brake control unit in each case in such a way that an increased brake pressure is generated. This means that the force and / or the pressure that the driver exerts when the operating element is actuated is, as it were, increased for a braking process by using electrical power. In this case, the electrical power is converted by means of at least one previously mentioned electrical hydraulic pump and is thereby used to boost pressure in the hydraulic system. An unregulated, mechanical-hydraulic emergency operation without amplification by electrical power, as is known from the prior art, is then preferably dispensed with. This means that the emergency operating mode described here replaces such a purely mechanical-hydraulic emergency operation in this case, so that in this case in particular the hydraulic fall-back level described at the beginning is not provided and also not implemented.

As already explained above, the regulation of the hydraulic system and thus the control of the braking force takes place both in the basic operating mode and in the emergency operating mode, that is to say in an emergency, based on the braking command. The value of the brake pressure is then typically dependent on the brake command, in particular on the force or pressure with which the driver operates the control element and / or the distance over which the control element is moved by the driver. The amplification described above is also preferably dependent on the braking command in the manner described above. Depending on the variant, a braking characteristic is also stored in the control device, through which different force values for the force with which the driver operates the control element, or different pressure values for the pressure that the driver exerts on the control element, or different distances over which When the driver moves the control element away, values for the amplification described above or values for the brake pressure are assigned in each case. In an advantageous development, two brake characteristics are stored in the control device, in particular a primary brake characteristic in the primary brake control unit and a secondary brake characteristic in the secondary brake control unit. In this case, the primary braking characteristic and the secondary braking characteristic then preferably differ from one another.

Independently of this, the brake system is designed in such a way that the brake command is present at least in the basic operating mode in the primary brake control unit and at least in the emergency operating mode in the secondary brake control unit. This is ensured in different ways depending on the application and variant of the brake system. In any case, however, the brake system has the at least one sensor unit.

The at least one sensor unit is designed, for example, as a type of position sensor or has a position sensor with which the position of the operating element, for example the brake pedal, can be detected and with which the corresponding position is then detected during operation of the brake system. As an alternative or in addition to this, the distance over which the control element is moved when the driver is actuated is recorded with the at least one sensor unit during operation. In some cases, the at least one sensor unit is also designed as an optical sensor unit, that is to say, for example, as a camera. An embodiment variant is also advantageous in which the at least one sensor unit has a pressure sensor or is designed as a pressure sensor.

This variant is particularly useful when the control element, for example the brake pedal, is coupled to the hydraulic system and has, for example, a master brake cylinder or control cylinder in which a pre-pressure is built up by actuating the control element, which is generated by a hydraulic connection between the master brake cylinder and is transferred from the hydraulic system to the hydraulic system. In such a case, the form reproduces the braking command specified by the driver and, according to at least one embodiment variant, the form is then detected by means of the at least one sensor unit. The at least one sensor unit or the pressure sensor is then arranged, for example, in the master brake cylinder or in an adjoining part of the hydraulic system.

If the brake command and thus the driver's brake request are detected by a pressure sensor to detect the pre-pressure, a pressure boost is then typically built up by the hydraulic system, depending on the pressure value determined, in order to generate and specify the brake pressure. As a result, depending on the design of the hydraulic system, the form pressure drops in some cases. The brake control unit regulating this will then preferably briefly stop boosting or increasing it in the meantime in order to test whether the admission pressure builds up again because the driver wants to continue to brake, or whether he has interrupted the braking and therefore no more pre-pressure builds up. If the pre-pressure builds up again, the amplification is expediently continued in accordance with the predetermined amplification characteristic. If the driver has canceled the braking, the reinforcement is also canceled.

Regardless of the precise configuration of the at least one sensor unit, according to one embodiment variant, it is connected to the primary brake control unit in terms of signal technology and, in addition, the at least one sensor unit is connected to the secondary brake control unit in terms of signal technology. For this purpose, for example, two independent signal lines are implemented, one of the two signal lines connecting the at least one sensor unit to the primary brake control unit and the second of the two signal lines connecting the at least one sensor unit to the secondary brake control unit. Alternatively, a signaling connection is implemented in such a way that, during operation, the signals of the at least one sensor unit are passed on from the at least one sensor unit to the primary brake control unit and then at least in the emergency operating mode further from the primary brake control unit to the secondary brake control unit. In this case, at least in the emergency operating mode, the signals are passed through the primary brake control unit to the secondary brake control unit, that is to say, for example, looped through the primary brake control unit to the secondary brake control unit.

It is also advantageous if the brake system has at least two sensor units, in particular two sensor units for detecting the brake command. Depending on the embodiment variant, the at least two sensor units are designed, for example, as sensor units of the same type, in particular in order to create redundancy with regard to the sensor system. In addition, in an advantageous development, one of the at least two sensor units is signal-connected to the primary brake control unit and the other of the two sensor units is signal-connected to the secondary brake control unit. Depending on the application, these two sensor units of the same type are, for example, both designed as a previously described position sensor, as a previously described distance sensor or as a previously described pressure sensor.

Alternatively or in addition to this, the brake system has at least two different sensor units for redundant detection of the brake command, one of these at least two sensor units being signal-connected to the primary brake control unit and the other of these at least two sensor units being signal-connected to the secondary brake control unit. Here, too, electrical signals are typically generated with the at least two sensor units, each reflecting the braking command, but different sensor units or sensors are used so that the braking commands are recorded in different ways. In this case, for example, one of the at least two sensor units is designed as a previously described pressure sensor for detecting the pre-pressure and the other of the at least two sensor units is designed, for example, as a previously described position sensor or distance sensor.

If at least two sensor units for redundant detection of the brake command are part of the brake system, this is designed in an advantageous development such that the sensor signals of these at least two sensor units are fed to both brake control units during operation and are thus made available. For this purpose, for example, both sensor units are then connected to both brake control units or, alternatively, sensor signals are exchanged between the brake control units via a previously indicated connection between the two brake control units, which is designed as a data bus, for example.

Regardless of this, it is advantageous if the brake system has a pressure sensor unit for detecting a brake pressure, i.e. the primary brake pressure or the secondary brake pressure, in the hydraulic system or in the brake cylinder of the at least one wheel brake, in particular an actual value of the brake pressure.

It should be noted that the brake pressure is regulated during operation via the hydraulic system and is specified by the hydraulic system. In this case, a setpoint dependent on the braking command is then typically specified for the brake pressure, which setpoint is specified by activating the aforementioned number of valves and the aforementioned number of hydraulic pumps. By detecting an actual value of the brake pressure by the pressure sensor unit for detecting the brake pressure, a control loop can then be implemented, and such a control loop is also preferably implemented.

Apart from that, it can be ensured with such a pressure sensor unit for detecting the brake pressure that an undesired parallel operation of the brake control units, in which both brake control units intervene in the control of the hydraulic system at the same time, is excluded. In particular, a double brake force boost is thereby preferably excluded.

In some cases, the braking system is still set up in such a way that the primary Brake pressure is essentially identical to the secondary brake pressure. No difference is noticeable to the driver when the emergency operating mode is active instead of the basic operating mode. In this case in particular, the brake system is then further preferably designed in such a way that a warning message is output in acoustic and / or optical form, with which it is indicated that the emergency operating mode has been activated.

However, the brake system is preferably set up in such a way that the driver can feel a significant difference when the emergency operating mode is active instead of the basic operating mode. Here, the emergency operating mode should, for example, be perceived as less efficient. It should be noted that the emergency operating mode is typically only activated if there is an error or defect. Such a fault or defect usually necessitates maintenance or repair of the brake system, the maintenance or repair should be carried out as promptly as possible. If the driver can then feel a significant difference when the emergency operating mode is active instead of the basic operating mode, it is more likely that the driver will actually have the maintenance or repair carried out promptly.

According to one embodiment variant, the brake system is then set up in such a way that the secondary brake pressure is lower than the primary brake pressure or that at least the maximum value of the secondary brake pressure is lower than the maximum value of the primary brake pressure.

The brake system is further preferably set up in such a way that the maximum value of the secondary brake pressure is used to achieve a deceleration that is less than or equal to 5.50 m / s ² , more preferably less than or equal to 4.50 m / s ² and in particular less than or equal to 3, 50 m / s ² is. In addition, the brake system is preferably set up in such a way that the maximum value of the primary brake pressure is used to achieve a deceleration that is greater than 6.43 m / s ² and more preferably greater than or equal to 7.5 m / s ² and in particular greater than or equal to 9.5 m / s ² or greater than or equal to 11 m / s ² .

Independently of this, the brake system is preferably set up in such a way that the maximum value of the secondary brake pressure is used to achieve a deceleration that is greater than or equal to 2.44 m / s ² .

An embodiment of the brake system is also preferred in which, in the emergency operating mode, a value of 2.44 m / s ² for the deceleration and / or the maximum value of the secondary brake pressure is reached or exceeded if the control element covers a distance of less than or equal to 10 cm, more preferably less than or equal to 8 cm and in particular less than or equal to 6 cm is moved, for example over a distance of 5 cm. This means that, for example, a brake pedal travel of less than 10 cm, more preferably less than 8 cm and in particular less than 6 cm, a deceleration greater than or equal to 2.44 m / s ^{2 is} achieved.

The aforementioned deceleration relates to a motor vehicle in which the brake system is installed. In addition, the aforementioned deceleration values usually relate to deceleration on a dry asphalt roadway.

With regard to the aforementioned braking characteristics, that is to say the primary braking characteristic and the secondary braking characteristic, an embodiment is also advantageous in which the secondary braking characteristic is flatter compared to the primary braking characteristic. Alternatively, the secondary braking characteristic has a steeper first section compared to the primary braking characteristic and is then flatter in a second section with higher values for the distance of the operating element or the pedal path of the brake pedal. This means that, for example, the deceleration value of a motor vehicle in which the brake system is installed in the emergency operating mode initially increases faster with increasing pedal travel than in the basic operating mode, but then in the emergency operating mode remains essentially constant as the pedal travel increases, whereas the deceleration value in the basic operating mode continues to increase as the pedal travel continues increases. As a result, the brake system then has a rougher effect in the emergency operating mode, which typically causes the driver to have maintenance or repairs carried out.

As already explained above, the electrohydraulic brake system according to the invention is typically designed for a motor vehicle and, when installed, is usually part of a corresponding motor vehicle. Conversely, a motor vehicle according to the invention has an electrohydraulic brake system described above. The motor vehicle is preferably set up for manual vehicle guidance in one driving mode and for automated vehicle guidance in a second driving mode. In the context of this application, automated vehicle guidance is understood to mean, in particular, vehicle guidance using an automated driving function from level 3. In the case of a level 3 driving function, the motor vehicle takes over the vehicle control completely under certain conditions, but the driver is expected to take over the vehicle control again within a short time in the event of a fault in the system.

If the driver is now expected to take over driving the vehicle again within a short period of time in the event of an error in the system, then this results this sometimes leads to contradicting objectives. On the one hand, the driver should be offered a high level of comfort while driving. This can be achieved, for example, if the seat is moved back during the automated vehicle guidance and / or the backrest is in a kind of reclining position. Nevertheless, sometimes for legal reasons, the driver must always be able to brake, in particular to carry out emergency braking, even while the vehicle is being driven automatically.

However, if the driver is driven into a comfort position during automated vehicle guidance, in which he has more leg / foot room, for example, then the distance to the operating elements is inevitably increased, for example to the brake pedal. Here, too, it must still be ensured that the driver can still achieve a minimum deceleration from the comfort position when a maximum actuation force on the brake pedal that can be achieved from the comfort position is specified.

This can be ensured with an electrohydraulic brake system according to the invention, even if the electrohydraulic brake system is in the emergency operating mode when the vehicle control is handed over to the driver. The motor vehicle according to the invention is preferably set up in such a way that the two operating modes of the electrohydraulic brake system, namely the basic operating mode and the emergency operating mode, are two operating modes for manual vehicle guidance in the first driving operating mode. In addition, both operating modes of the electrohydraulic brake system are preferably also available in the second driving operating mode.

In addition, the brake system in such a motor vehicle is preferably set up in such a way that the maximum deceleration value that can be achieved with the secondary brake pressure is greater than ^{or equal to 2.44 m / s 2} and that this deceleration value and / or the maximum value of the secondary brake pressure is even more preferred over a distance or when the brake pedal travel is less than or equal to 6 cm. This means that in comparison to a hydraulic fallback level mentioned at the beginning, the driver typically has to actuate the operating element, i.e. in particular the brake pedal, with less force or less pressure in the emergency operating mode and / or must move it over a shorter distance by a deceleration value greater than or equal to 2.44 m / s ² and / or to achieve the maximum value of the secondary brake pressure. This is then typically also possible for the driver from a comfort position.

It was also explained above that the basic operating mode is preferably active as standard when the brake system is in operation, so that the regulation of the hydraulic system and consequently the control of the braking force is carried out as standard by the primary brake regulating unit. The emergency operating mode, on the other hand, is typically activated when a fault occurs or is present in the primary brake control unit, so that the primary brake control unit no longer functions properly. As an alternative or in addition to this, the emergency operating mode is activated if the driver and / or the driver's seat is in a comfort position during automated vehicle guidance, which in particular deviates from a standard position of the driver or the driver's seat during manual vehicle guidance, and if a handover of vehicle guidance to the driver is not initiated by the driver but by the motor vehicle. Depending on the application, the motor vehicle according to the invention and in particular the brake system according to the invention are set up to implement one of these alternation variants between basic operating mode and emergency operating mode. To implement the second variant, the motor vehicle then typically also has at least one sensor unit for detecting the seat position and / or for detecting the driver's position, for example a camera. The change between the basic operating mode and the emergency operating mode then preferably takes place as a function of a sensor signal from the at least one sensor unit for detecting the seat position and / or for detecting the driver's position.

• 1 schematisch ein Kraftfahrzeug mit einer ersten Ausführung einer Bremsanlage;
• 2 eine zweite Ausführung der Bremsanlage;
• 3 eine dritte Ausführung der Bremsanlage; und
• 4 eine vierte Ausführung der Bremsanlage.

Further advantages, features and details of the invention emerge from the claims, the following description of preferred embodiments and on the basis of the schematic drawings. Show:

• 1 schematically a motor vehicle with a first embodiment of a brake system;
• 2 a second version of the braking system;
• 3 a third embodiment of the braking system; and
• 4th a fourth version of the braking system.

A motor vehicle described below as an example 2 is set up for manual vehicle guidance in a first driving mode and for automated vehicle guidance in a second driving mode. The motor vehicle then becomes accordingly 2 Manually guided in the first driving mode by a driver not shown in detail and in the second driving mode without the driver by an automation device of the motor vehicle that is not completely shown 2 .

The automation device is essential here in the exemplary embodiment Components two control units 4th , 6th for controlling the motor vehicle 2 on, namely a primary control unit 4th and a secondary control unit 6th . With the two control units 4th , 6th a redundancy is created through which the automatic vehicle guidance is secured. The primary control unit is then the default 4th active during automatic vehicle guidance. However, if an error or defect occurs in the primary control unit 4th on, the secondary control unit takes over 6th automatic vehicle guidance.

To ensure that in the event of a fault or defect, the secondary control unit 6th the tasks of the primary control unit 4th takes over, is typically a signaling connection, not shown, between the primary control unit 4th and the secondary control unit 6th trained, via which a data exchange takes place in the company. The data exchange then enables the secondary control unit 6th to detect when in the primary control unit 4th there is an error or defect and in this case the secondary control unit takes over 4th the tasks of the primary control unit 6th as long as the motor vehicle 2 is in the second driving mode.

The primary control unit is used to implement the second driving mode and automatic vehicle guidance 4th one hand and the secondary control unit 6th on the other hand, signaling with an electro-hydraulic brake system 8th of the motor vehicle 2 tied together. In the second driving mode, a braking command is sent from the primary control unit via the signaling connection 4th or the secondary control unit 6th to the electrohydraulic braking system 8th transmitted and in the electro-hydraulic brake system 2 , hereinafter referred to as the brake system 8th called, converted into braking force with which the motor vehicle 2 can be slowed down.

The brake system 2 four wheel brakes, for example, to generate braking force 10 on, with each wheel of the motor vehicle 2 a wheel brake 10 assigned. That is, the motor vehicle 2 in the exemplary embodiment has four wheels, not explicitly shown, and is designed, for example, as a passenger car. Part of every wheel brake 10 is a brake cylinder 12th , in which a brake pressure can be specified. Part of the braking system 2 is also an electrically controllable hydraulic system 14th , which with the brake cylinders 12th is hydraulically connected, so via the hydraulic system 14th a brake pressure in the brake cylinders 12th is predeterminable.

For the sake of simplicity, an embodiment of the brake system is shown here 8th described in the case of all brake cylinders 12th the same brake pressure is specified. However, it is advantageous if the brake pressure is for each brake cylinder 12th is additionally individualized, in particular as a function of sensor signals that reflect the rotation of the wheels and / or of sensor signals from acceleration sensors in the motor vehicle 2 . In this way, for example, an anti-lock braking system (ABS) is implemented or a vehicle stabilization system (ESP) in which each wheel is braked individually if necessary. A necessary individualization of the brake pressure for each brake cylinder 12th however, it is already known from the prior art and it is easily possible for a person skilled in the art to use the brake system described here 8th to be modified in such a way that instead of a uniform brake pressure for all brake cylinders 12th a correspondingly individualized brake pressure for each brake cylinder 12th is specified.

In any case, the electrically controllable hydraulic system 14th a number of electrically controllable valves and a number of electrical hydraulic pumps, which are part of an electrical control device 16 and over which the brake pressure in the brake cylinders 12th is predeterminable. The electric valves and the electric hydraulic pumps are controlled by a control device using electric signals. The control device here has a primary brake control unit 18th and a secondary brake control unit 20th on, whereby a kind of redundancy is created for the control device.

The braking system is set up 8th continue to be such that the primary brake control unit 18th in a basic operating mode the hydraulic system 14th regulates and that in an emergency operating mode, the secondary brake control unit 20th the hydraulic system regulates. The hydraulic system is regulated in both operating modes 14th as a function of a braking command that is specified by the driver in the first driving mode and by one of the control units, that is to say by the primary control unit, in the second driving mode 4th or from the secondary control unit 6th , depending on which of the two is currently active.

The two brake control units are preferred 18th , 20th also designed to operate independently of one another. In the exemplary embodiment, each of the two brake control units is used in particular for this purpose 18th , 20th its own accumulator 21 assigned, with one of the two accumulators 21 the primary brake control unit 18th supplied with electrical power during operation and the other of the two accumulators 21 the secondary brake control unit 20th supplied with electrical power during operation.

In operation of the braking system 8th the basic operating mode is then preferably active as standard, so that the control of the hydraulic system 14th by default by the primary brake control unit 18th he follows. The emergency operating mode, on the other hand, is typically only activated if there is a fault in the primary brake control unit 18th occurs or is present, so that the primary brake control unit 18th no longer works properly. Then the secondary brake control unit takes over 20th the regulation of the hydraulic system 14th and consequently the control of the braking force. A corresponding error is present, for example, when the primary brake control unit 18th is no longer supplied with sufficient electrical power and / or if in the primary brake control unit 18th there is a defect.

To ensure that in the event of a fault or defect, the secondary brake control unit 20th the tasks of the primary brake control unit 18th takes over, are the two brake control units 18th , 20th in the exemplary embodiment connected to one another for signal and / or data exchange, for example via a field bus or data bus. The exchange of data then enables the secondary brake control unit 20th to recognize when in the primary brake control unit 18th there is an error or defect and in this case the secondary brake control unit takes over 20th the tasks of the primary brake control unit 18th .

The primary control unit is also in the exemplary embodiment 4th signaling with the primary brake control unit 18th connected and the secondary control unit 6th is with the secondary brake control unit 20th tied together. Alternatively, both are control units 4th , 6th with both brake control units 18th , 20th connected so that both control units 4th , 6th Brake commands to both brake control units 18th , 20th can transmit.

As already mentioned above, in the first driving mode, that is, during manual vehicle guidance, the braking command is given by the driver. To do this, the brake system 8th an input device 22nd on. That input device 22nd again has in the embodiment according to 1 a brake pedal 24 as well as two sensor units 26th , 28 on. There are two sensor units 26th , 28 designed for redundant detection of the brake command from the driver and both are designed, for example, as position sensors with which the position or position of the brake pedal 24 is detectable. The two sensor units generate when the brake system is in operation 26th , 28 an electrical signal in each case, which reflects the driver's braking command.

One of the two sensor units 26th then transmits the electrical signal to the primary brake control unit 18th and for that purpose this sensor unit is 26th signaling with the primary brake control unit 18th tied together. The other of the two sensor units 28 transmits its signal to the secondary brake control unit 20th and is accordingly connected to it in terms of signaling. As a result, there are then both brake control units 18th , 20th electrical signals are available that reflect the driver's braking command. This then makes it possible to use the hydraulic system both in the basic operating mode and in the emergency operating mode 14th to regulate depending on the brake command, the primary brake control unit 18th in the basic operating mode, a primary brake pressure is generated as a function of the brake command, and the secondary brake control unit 20th Generates a secondary brake pressure in the emergency operating mode as a function of the brake command.

In 2 and 3 are two alternative design variants of the brake system 8th shown schematically. These differ from the variant according to 1 in the way of the two brake control units 18th , 20th , i.e. the primary brake control unit 18th and the secondary brake control unit 20th , electrical signals are made available that reflect the driver's braking command. In the exemplary embodiment according to 2 just a sensor unit 26th used, which is designed in particular as a position sensor of the type described above. However, here the electrical signal of this sensor unit is used both by the primary brake control unit 18th as well as the secondary brake control unit 20th fed. For this purpose, this sensor unit is on the one hand with the primary brake control unit 18th connected for signaling purposes and on the other hand with the secondary brake control unit 20th .

In the embodiment according to 3 are again two sensor units 26th , 30th intended to detect the driver's braking command, but here the two sensor units are used 26th , 30th designed differently. So is the one with the primary brake control unit 18th connected sensor unit 26th for example designed as a position sensor of the aforementioned type, whereas that with the secondary brake control unit 20th connected sensor unit 30th is designed for example as a pressure sensor. The sensor unit, which is designed as a pressure sensor, detects 30th in the exemplary embodiment, a form in the hydraulic system 14th . This form is generated by pressing the brake pedal 24 , which is on a master cylinder 32 the input device 22nd acts and generates the form here. Through a hydraulic connection between the master brake cylinder 32 and the hydraulic system 14th becomes the pre-pressure to the hydraulic system 14th passed, in which the pressure sensor is arranged. The pressure sensor for detecting the pre-pressure is only an example in the hydraulic system 14th arranged in part of the hydraulic system 14th in which the form predominates. Alternatively, the pressure sensor is in the master brake cylinder 32 arranged. In principle, the pressure sensor can be positioned at any point when the brake pedal is pressed 24 the form prevails. The corresponding area in which the pre-pressure predominates, the pre-pressure area 34 , is in the representations 1 until 4th symbolized by a dashed frame.

In 4th is also a variant of the braking system 8th reproduced, with the addition of a pressure sensor 36 for recording the brake pressure part of the brake system 8th and which is arranged in an area in which the brake pressure prevails during operation, namely in the brake pressure area 38 . This brake pressure range 38 is in the representations 1 until 4th also symbolized by a dashed frame. The brake pressure range 38 also extends into the brake cylinder 12th and accordingly the pressure sensor 36 to detect the brake pressure, as an alternative to displaying it in one of the brake cylinders 12th arrange.

With the pressure sensor 36 To record the brake pressure, an actual value of the brake pressure is then recorded during operation and the control of the hydraulic system 14th based on. It should be noted that the brake pressure during operation via the hydraulic system 14th is regulated and by the hydraulic system 14th is specified. In this case, a setpoint dependent on the braking command is then typically specified for the brake pressure, which setpoint is specified by activating the aforementioned number of valves and the aforementioned number of hydraulic pumps. By detecting an actual value of the brake pressure by the pressure sensor 36 a control loop can then be implemented, and such a control loop is also preferably implemented.

List of reference symbols

2

Motor vehicle

4th

primary control unit

6th

secondary control unit

8th

electro-hydraulic braking system

10

Wheel brake

12th

Brake cylinder

14th

Hydraulic system

16

Control device

18th

primary brake control unit

20th

secondary brake control unit

21

accumulator

22nd

Input device

24

Brake pedal

26th

Sensor unit

28

Sensor unit

30th

Sensor unit

32

Master cylinder

34

Form area

36

Pressure sensor

38

Brake pressure range

Claims (10)

Having an electro-hydraulic brake system (8) - an input device (22) for inputting a braking command by a driver, the input device (22) having an operating element (24) and at least one sensor unit (26) for detecting the braking command, - At least one wheel brake (10) with a brake cylinder (12), wherein a hydraulic pressure for generating a braking force can be specified in the brake cylinder (12), - An electrically controllable hydraulic system (14) which is connected to the brake cylinder (12) and is set up to specify the hydraulic pressure in the brake cylinder (12) and - A control device (18, 20) for controlling the hydraulic system (14) by means of electrical signals, the control device (18, 20) having a primary brake control unit (18) and a secondary brake control unit (20), and set up such that - In a basic operating mode, the primary brake control unit (18) controls the hydraulic system (14) in such a way that a primary brake pressure is generated in the brake cylinder (12) as a function of the brake command, and - In an emergency operating mode, the secondary brake control unit (20) regulates the hydraulic system (14) in such a way that a secondary brake pressure is generated in the brake cylinder (12) as a function of the brake command. Brake system (8) Claim 1 , whereby the emergency operating mode replaces an unregulated mechanical-hydraulic emergency operating mode. Brake system (8) Claim 1 or 2 wherein the at least one sensor unit (26) is signal-connected to the primary brake control unit (18) and the at least one sensor unit (26) is signal-connected to the secondary brake control unit (26). Brake system (8) according to one of the Claims 1 until 3 , wherein the input device (22) has two sensor units (26, 28) of the same type for redundant detection of the brake command, one of the two sensor units (26) being signal-connected to the primary brake control unit (18) and the other of the two sensor units (28) is signal-connected to the secondary brake control unit (20). Brake system (8) according to one of the Claims 1 until 4th , this having two different sensor units (26, 30) for redundant detection of the brake command, one of the two sensor units (26) being signal-connected to the primary brake control unit (18) and the other of the two sensor units (30) being signal-connected to the secondary Brake control unit (20) is connected. Brake system (8) Claim 5 , wherein one of the two sensor units (26) is designed to detect a position of the operating element (24) and the other of the two sensor units (30) is designed to detect a pre-pressure in the hydraulic system (14) or in one with the hydraulic system (14) connected master cylinder (32) of the input device (22). Brake system (8) according to one of the Claims 1 until 6th , this having a pressure sensor unit (36) for detecting a brake pressure in the hydraulic system (14) or in the brake cylinder (12) of the at least one wheel brake (10). Brake system (8) according to one of the Claims 1 until 7th , where the primary brake pressure is higher than the secondary brake pressure. Motor vehicle (2) having an electrohydraulic brake system (8) according to one of the preceding claims. Motor vehicle (2) according to Claim 9 This is set up for manual vehicle guidance in a first driving mode and for automated vehicle guidance in a second driving mode and the two operating modes of the electrohydraulic brake system (8), namely the basic operating mode and the emergency operating mode, two operating modes for manual vehicle driving in the first Are driving mode.

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