Redundant brake system for a vehicle and method for controlling a braking system

Abstract

The invention relates to a redundant brake system (1) for a vehicle, comprising an actuation control unit (2) which can receive one or more raw actuation signals from a brake actuation unit (3). The actuation control unit (2) is connected to each friction brake of the vehicle via signal lines (8, 9, 10, 11, 12) and can calculate a braking request from the raw actuation signals and a corresponding actuation signal for each of the friction brakes. The brake system (1) should be easier to modify without affecting the hardware of a central control unit (19, 20) of the vehicle. For this purpose, the brake system (1) comprises a wheel control unit (4, 5, 6, 7) for each wheel, in order to convert the actuation signal received from the actuation control unit (2). A wheel control unit (4) is designed as an intelligent wheel control unit (4) that receives the raw actuation signals from the actuation control unit (2) and can independently calculate a braking request therefrom. The invention also relates to an associated control method and a vehicle

Description

[0001] Description

[0002] Redundant braking system for a vehicle and method for controlling a braking system

[0003] The present invention relates to a redundant braking system for a vehicle, comprising an actuation control unit which is configured to be connected to at least one actuation sensor of a brake actuation unit in order to receive one or more raw actuation signals which indicate an actuation of the brake actuation unit, wherein the braking system further comprises at least two friction brakes, each assigned to a wheel of the vehicle, wherein the actuation control unit is connected to each of the friction brakes via a signal line and is configured to independently calculate a braking request from the raw actuation signals and to calculate and send a corresponding control signal for each of the friction brakes.

[0004] Such a braking system is known, for example, from EP 0961 724 B2, in which a pedal unit is connected to a central control unit. Both redundantly calculate a braking torque request from the pedal unit's sensor signals and transmit them to the friction brake actuators. Transmission occurs via a data bus connected to all of the aforementioned components, as well as via additional signal lines from the pedal unit to the actuators.

[0005] DE 101 04 194 A1 discloses another braking system in which the brake pedal is connected to the brake control units of the individual brakes via a bus line and can actuate the brakes directly using electrical signals without going through one or more central control units. A main control unit is electrically connected to the brakes via a main communication bus and a safety bus, among other things. The main control unit actuates the brakes, if necessary, via the main communication bus or, in the event of its failure, via the safety bus. Additionally or alternatively, the brake pedal signals can also be transmitted to the central control unit via the brake control units.

[0006] The central control unit of such braking systems must generally be adapted to the brake actuation unit (e.g., the brake pedal) to enable redundant braking command calculation and control of the friction brakes by the central control unit. For safety reasons, redundant braking command calculation is almost indispensable in by-wire braking systems, although this can also be achieved in two redundant central control units. At the same time, this complicates the use of different brake pedals or the replacement or adaptation of a brake pedal in an existing braking system architecture during vehicle development, as the central control unit must then also be adapted to the new brake pedal (e.g., to changed actuation sensor signals).At the same time, the central control unit is becoming increasingly complex due to the expansion of autonomous driving functions, and in more and more situations it is taking over braking control independently of the brake pedal. Therefore, any structural modification of the central control unit is associated with increasing effort and cost. The braking system and the central control unit are often manufactured by different manufacturers, which further complicates adaptation.

[0007] Furthermore, the expansion of autonomous driving functions means that in the event of a vehicle accident, the question is increasingly being asked whether the cause of the accident was the control commands from the central control unit or the driver's control commands. This can also contribute to the decision as to whether the driver's personal liability or the manufacturer's product liability is more likely to be considered. If all braking functions (driver-controlled and autonomous) are converged via a central control unit, this makes assignment more difficult, especially when both the driver and the central control unit initiate braking simultaneously (e.g., in an emergency stop). The invention is therefore based on the object of providing a redundant braking system that at least partially overcomes the aforementioned problems.

[0008] According to the invention, this object is achieved by a braking system according to claim 1, a vehicle according to claim 11 and by a method according to claim 12.

[0009] Accordingly, a redundant braking system of the type mentioned at the outset is provided, characterized in that the braking system comprises a separate wheel control unit for each wheel, which is designed to convert the actuation signal received from the actuation control unit into an actuation of the respectively assigned friction brake, wherein at least one wheel control unit is designed as an intelligent wheel control unit, which is designed to receive the raw actuation signals from the actuation control unit and to independently calculate a braking request from the raw actuation signals and to calculate and send a corresponding actuation signal for each of the friction brakes.

[0010] Instead of the central control unit, one of the wheel control units now acts as an intelligent wheel control unit, redundantly calculating the braking request from the raw actuation signals. This means that in the event of a partial failure of the actuation control unit (i.e., if it can no longer perform the braking request calculation or if the control of the wheel control units by the actuation control unit is disrupted), the intelligent wheel control unit can perform an independent braking request calculation and send a corresponding control signal to each of the friction brakes. This provides a high level of reliability, while at the same time eliminating the need to adapt a central control unit to the brake actuation unit in use.If the brake actuation unit is modified, only the significantly less complex actuation control unit and the intelligent wheel control unit need to be adapted, which are usually also from the same manufacturer in a braking system (unlike the central control unit). Furthermore, the reaction time of the braking system to actuation of the brake actuation unit can be significantly improved because, unlike the state of the art, the detour of the raw actuation signals (or preprocessed actuation signals) via the central control unit for calculating the braking request is avoided, and the actuation control unit can control the wheel control units directly (e.g., via independent signal lines).

[0011] Furthermore, in the event of an accident, the control unit that sent an accident-relevant braking command can be used to more clearly determine whether the driver or the central control unit (in an autonomous driving mode) was primarily responsible for the accident.

[0012] When this description refers to a brake pedal, it also generally refers to a brake actuation unit, and vice versa. The brake actuation unit is preferably an electromechanical brake pedal without a connection to any hydraulic components of the braking system. However, with the exception of the brake actuation unit, the braking system can be fully hydraulic, semi-dry, or completely dry. The brake actuation unit can be part of the claimed braking system, but it does not have to be.

[0013] The brake actuation unit preferably comprises the actuation control unit, e.g., in a common housing. The brake actuation unit preferably has a plurality of actuation sensors, which are preferably arranged with the actuation control unit in a common housing / module. This provides increased reliability. Preferably, at least two actuation sensors of a different sensor type are provided, for example, a displacement sensor and / or a force sensor and / or an angle sensor and / or an optical sensor. Particularly preferably, one pair, two pairs, or three pairs of redundant actuation sensors are provided, for example, two displacement sensors and / or two force sensors and / or two angle sensors. This enables a high level of reliability of the brake actuation unit to be achieved.

[0014] It is also possible to configure more than one wheel control unit as an intelligent wheel control unit, in accordance with the features disclosed for an intelligent wheel control unit, for example, an intelligent wheel control unit for each vehicle axle. This further increases reliability, but also significantly increases the cost of the braking system.

[0015] Preferred embodiments and further developments of the invention can be found in the respective subclaims.

[0016] In one embodiment, the actuation control unit is connected to each of the wheel control units via at least one direct signal line that is independent of other components. This has the advantage that a system bus that may be shared by other system components does not need to be used, thus reducing signal propagation times and thus the reaction time of the braking system. At the same time, reliability can be increased, since a failure of one of the independent signal lines only affects the connection from the actuation control unit to one of the wheel control units, and communication with the remaining wheel control units continues to function.

[0017] The term "independent of" with regard to a signal line / signal network is to be understood in this document to mean that the corresponding component is not directly connected to the signal line or signal network. This does not preclude an indirect connection of the component "independent" of the signal line or signal network via another component connected to the signal line or signal network.

[0018] When this document refers to a failure of a component or a signal line, this refers to temporary disruptions in the functionality of the component or signal line and not necessarily a total failure.

[0019] Preferably, the actuation control unit is connected to the intelligent wheel control unit via two direct signal lines that are independent of other components. This direct signal connection, which is crucial for the braking system and is important for calculating and controlling the braking command, is duplicated to further increase reliability. The two signal lines can be used simultaneously (for dual transmission of the raw actuation signals and / or dual transmission of the friction brake-specific control signal) or alternately, or one of the signal lines can be used only if the other fails.

[0020] Preferably, the intelligent wheel control unit is connected to each other wheel control unit via at least one signal network independent of the actuation control unit, preferably via two signal networks independent of the actuation control unit. This embodiment has the advantage that in the event of a failure of the actuation control unit (in particular of an intelligent section of the actuation control unit) or of one of the signal lines from the actuation control unit to the wheel control units, the intelligent wheel control unit can communicate with all wheel control units and completely take over the braking request calculation and the control of the wheel control units. The signal networks can be used simultaneously or alternately, or one of the signal networks can only be used in the event of a failure of the other signal network. Preferably, the signal network or the signal networks are independent of a signal network used for other vehicle communication (e.g.CAN bus) different and independent.

[0021] Preferably, the signal network(s) is / are connectable or connected to one or more central control units of the vehicle. This allows the central control unit to control brake activations, for example, in a (semi-)autonomous driving mode, to the wheel control units via the signal network(s).

[0022] In one embodiment, the actuation control unit comprises a non-intelligent section and an intelligent section, wherein the non-intelligent section is configured to receive the raw actuation signals and forward them to the intelligent section and the intelligent wheel control unit, and wherein the intelligent section is configured to calculate braking commands. This division can increase reliability, since in the event of a failure of the intelligent section, the non-intelligent section can continue to forward raw actuation signals to the intelligent wheel control unit.

[0023] Preferably, the unintelligent section comprises means for duplicating the raw actuation signals so that the raw actuation signals can be forwarded to the intelligent section and the intelligent wheel control unit. Alternatively, the unintelligent section can also split the raw actuation signals between the intelligent section and the intelligent wheel control unit, for example, if the brake actuation unit already provides each raw actuation signal twice or if the brake actuation unit has at least redundant actuation sensors and therefore provides the same types of raw actuation signals twice (e.g., 2 x displacement signals, 2 x angle signals, 2 x force signals, 2 x optical signals).

[0024] Particularly preferably, the unintelligent section and the intelligent section are either arranged on separate circuit boards or galvanically isolated on the same circuit board. Alternatively or additionally, the unintelligent section and the intelligent section have a separate power supply. These embodiments each increase the chance that, in the event of a failure of the intelligent section, the unintelligent section will not also fail and the braking system will thus remain functional, since the intelligent wheel control unit can take over the braking request calculation and control of the friction brakes. The braking system preferably comprises at least one drive control unit, preferably one drive control unit for each driven vehicle axle, preferably one drive control unit for each driven wheel, which is configured to control an electric motor of the vehicle for regenerative braking.Preferably, the drive control unit(s) is / are connected to the signal network or networks independent of the actuation control unit. Preferably, the drive control unit is not directly connected to the actuation control unit. Preferably, the wheel control units are configured to control the drive control unit (or to forward a received first control component for regenerative braking to the drive control unit(s)) after receiving (or calculating) the control signal and if the calculated braking command is not above a threshold value, in order to execute the braking command solely by means of regenerative braking. Preferably, the wheel control units are further configured to control the drive control unit (or to forward a received first control component for regenerative braking to the drive control unit(s)) after receiving (or calculating) the control signal and if the braking command is above a threshold value.to forward a received first control component for the recuperative braking to the drive control unit(s) in order to execute the braking request both via the drive control unit by means of recuperative braking and via the wheel control units (to the extent of a second control component) by means of friction brakes.

[0025] In a preferred embodiment, the braking system comprises at least one central control unit, preferably two central control units, wherein the central control unit is configured to determine the need for braking depending on a control mode of the vehicle and to send control signals to the wheel control units and / or the drive control unit and / or the electric motor. Such a control mode can, for example, be a (semi-)autonomous driving mode of the vehicle. In this embodiment, the central control unit can still have access to all wheel control units, but without being directly involved in the driver-determined braking application.

[0026] Preferably, the actuation control unit and the central control unit do not have a direct signal connection for calculating the braking request and for brake control. This makes the braking system easier to adapt to existing vehicles or vehicles under development and requires fewer adjustments to the vehicle and the central control unit when changing the rest of the braking system. It should be clarified that this particularly includes signal connections for the raw actuation signals, processed actuation signals, and the control signals. However, other signal connections may exist, for example, for the central control unit to check the functionality of the actuation control unit. It is also possible, however, for the actuation control unit and the central control unit to have no direct signal connection at all and to communicate exclusively indirectly via other components of the braking system or vehicle.

[0027] In one embodiment, the central control unit or the two central control units are connected to the signal network independent of the actuation control unit, preferably to both signal networks independent of the actuation control unit. This configuration allows for a simple connection of the central control unit to the wheel control units for control depending on the driving mode, without the central control unit having to be connected to the signal connections between the actuation control unit and the wheel control units. This also avoids signal delays, for example, if a driver has already initiated (insufficient) braking and the central control unit has detected the need for emergency braking through sensors (radar, lidar, cameras, etc.) and must initiate it.

[0028] The object of the invention is also achieved by a method for controlling a braking system according to one of the preceding embodiments, wherein after a braking request calculation by the actuation control unit or by the intelligent wheel control unit, the braking system carries out the following steps:

[0029] If the calculated braking request is not above a threshold value: controlling the drive control unit via the wheel control units in order to execute the braking request solely by means of regenerative braking; and If the calculated braking request is above a threshold value: controlling the drive control unit and the friction brakes via the wheel control units in order to execute the braking request both via the drive control unit by means of regenerative braking and via the wheel control units by means of friction brakes.

[0030] This approach places the final execution of the brake control under the responsibility of the wheel control units, so that in the event of a deceleration, for example when starting regenerative braking, neither the actuation control unit, the intelligent control unit, nor the central control unit needs to be further involved or decide which control units need to be addressed in this case for the further execution of the braking request. This approach reduces the overall time from the actuation of the brake actuation unit to the start of braking. The phrase "control ... via the wheel control units" is to be understood in particular to mean that the control signals (for the friction brakes and the electric motor) are calculated by the actuation control unit or the intelligent wheel control unit according to the calculated braking request and then sent "via the wheel control units" to the friction brakes and the drive control unit(s).The wheel control units therefore assume a forwarding function for the control signals, in particular to the drive control unit(s).

[0031] Preferably, the threshold value differs for the various wheel control units, in particular between wheel control units assigned to the front wheels of the vehicle and wheel control units assigned to the rear wheels of the vehicle. The threshold values ​​can also differ depending on the brake type of the assigned friction brake (drum brake, disc brake). It is therefore possible that, when a braking request is calculated on the front axle, the friction brakes are also activated, but the threshold value for the friction brakes on the rear axle is not exceeded and they remain inactive, or vice versa.

[0032] Preferably, the method comprises the step:

[0033] - Waiting after the drive control unit has been activated by the wheel control units for a predefined period of time to see whether at least one electric motor starts the regenerative braking, and

[0034] - if this does not happen, the braking request is fully executed via the wheel control units using the friction brakes in a substitute braking mode.

[0035] This backup braking mode improves the reaction time of the braking system if at least one electric motor reacts late. Since vehicles with an electric motor in their drivetrain generally react more quickly than vehicles with a pure combustion engine, the driver is accustomed to fast reaction times during both acceleration and braking. If the onset of braking is noticeably delayed due to a lack of reaction or a delayed reaction from the electric motor, this can lead to unnecessary (and potentially dangerous) over-braking by the driver and reduced driving comfort as a reaction to the perceived "non-response" of the brake. Therefore, the above-mentioned procedure ensures that the braking system always becomes active after a predefined period of time at the latest, even if the electric motor delays or does not perform its intended portion of the braking.The above procedure can be carried out both for an initially determined sole braking application through regenerative braking and for an initially determined mixed braking application through regenerative braking and friction braking. In the first case, the inactive friction brakes are activated to initially implement the braking request on their own. In the second case, the already active control signals to the friction brakes are changed or exchanged in order to increase the braking force or braking torque of the friction brakes so that the braking request is fully implemented by the friction brakes for as long as necessary. The predefined time period is preferably between 35 and 60 milliseconds, in particular approximately 50 milliseconds. Such a time period is long enough that the electric motor should have reacted under normal circumstances and regenerative braking should have started, and short enough not to be perceived by the driver as a significant deceleration.

[0036] In a further embodiment, the method comprises the step:

[0037] - if regenerative braking by the electric motor is delayed after the friction brakes have already taken over the execution of the braking request in backup braking mode, the wheel control units reduce the control of the friction brakes in accordance with the increase in the proportion of regenerative braking until a braking request distribution between regenerative braking and friction braking calculated for a normal braking mode is achieved. This results in a "phase-out" of the excess friction braking portion of the braking request implemented at the respective time compared to the normal braking mode. During the "phase-out", the sum of the total braking force (or the total braking torque) applied from regenerative braking and friction braking corresponds at all times to the calculated braking request, in particular with a deviation of less than ±10%, preferably with a deviation of less than ±5%.This procedure has the advantage that the friction brakes are only loaded for as long as necessary and there is no excessive wear of the friction brakes and excessive loss of otherwise recovered recuperation energy.

[0038] Preferably, the intelligent wheel control unit and / or the actuation control unit calculates both control signals for the normal braking mode and the backup braking mode for each calculated braking request and sends both to the wheel control units in parallel. This has the advantage that the control signals for the backup braking mode are available immediately and do not have to be calculated and resent after the predefined time period has elapsed. Instead, the wheel control units can respond immediately with a modified control of the respective assigned friction brake in backup braking mode once the predefined time period has elapsed.

[0039] This further optimizes the reaction time of the braking system.

[0040] Further details of the invention emerge from the description of the illustrated embodiments and the appended claims.

[0041] The

[0042] Fig. 1 shows an embodiment of a braking system according to the invention, and

[0043] Fig. 2 is a flow chart of a method according to the invention.

[0044] In the following detailed description of preferred embodiments, like reference numerals designate substantially the same or identical parts in or on these embodiments. However, to better illustrate the invention, the preferred embodiments illustrated in the figures are not always drawn to scale.

[0045] Figure 1 shows a redundant braking system 1 for a vehicle, comprising an actuation control unit 2, which is configured to be connected to at least one actuation sensor of a brake actuation unit 3 (e.g., an electromechanical brake pedal) in order to receive one or more raw actuation signals (generated, for example, by one or more actuation sensors in the brake actuation unit 3) that indicate an actuation of the brake actuation unit 3. Although the brake actuation unit 3 and the actuation control unit 2 are shown here as separate units, they are preferably arranged in a common housing with the actuation sensor(s). Alternatively, the actuation control unit 2 and the brake actuation unit 3 can also be designed as spatially separate units that are connected via signal lines.The braking system 1 comprises at least two (here four) friction brakes (not shown), each assigned to a wheel of the vehicle. The actuation control unit 2 is configured to independently calculate a braking request from the raw actuation signals and to calculate and transmit a corresponding actuation signal for each of the friction brakes. The braking system 1 comprises a separate wheel control unit 4, 5, 6, 7 for each wheel, which is configured to convert the actuation signal received from the actuation control unit 2 into an actuation of the respectively assigned friction brake.

[0046] The actuation control unit 2 is connected to each of the wheel control units 4, 5, 6, 7 via at least one direct signal line 8, 9, 10, 11, 12 that is independent of other components. One of the wheel control units 4 is designed as an intelligent wheel control unit 4, which is configured to receive the raw actuation signals from the actuation control unit 2 and to independently calculate a braking request from the raw actuation signals and to calculate and send a corresponding control signal for each of the friction brakes or wheel control units 4, 5, 6, 7. The actuation control unit 2 is connected to the intelligent wheel control unit 4 via two direct signal lines 8, 12 that are independent of other components.

[0047] The actuation control unit 2 comprises a non-intelligent section 13 and an intelligent section 14. The non-intelligent section 13 is configured to receive the raw actuation signals and forward them to the intelligent section 14 and the intelligent wheel control unit 4. The intelligent section 14 is configured to calculate the braking request. The non-intelligent section 13 and the intelligent section 14 can be arranged on separate circuit boards or galvanically isolated on the same circuit board, in particular to increase reliability. Alternatively or additionally, the non-intelligent section 13 and the intelligent section 14 can have separate power supplies. The actuation control unit 2 and brake actuation unit 3 can be designed as an integrated unit, e.g., with a common housing.Alternatively, the unintelligent section 13 of the actuation control unit 2 and the brake actuation unit 3 can be designed as an integrated unit, e.g., with a common housing, wherein the intelligent section can be designed as a separate unit, e.g., spatially separated from the brake actuation unit 3. The independent signal line 8 connects the intelligent section 14 and the intelligent wheel control unit 4. It is preferably used to communicate the control signals (in particular for the normal braking mode and the backup braking mode) during normal operation, when the actuation control unit 2 calculates the braking request and also sends the wheel control unit 4 the control signals assigned to it. The signal line 8 thus corresponds in use to the signal lines 9, 10, 11 to the other wheel control units 5, 6, 7.

[0048] The independent signal line 12 connects the unintelligent section 13 and the intelligent wheel control unit 4. It is preferably used to communicate the raw actuation signals so that the intelligent wheel control unit 4 can also calculate the braking request. Preferably, the raw actuation signals are always transmitted to the intelligent wheel control unit 4 when the vehicle is active so that in the event of a failure of the actuation control unit 2 (in particular the intelligent section 14), the intelligent wheel control unit 4 can directly start calculating the braking request. Alternatively, the intelligent wheel control unit 4 can always perform the redundant braking request calculation, including calculation of the control signals for all wheel brakes (and optionally for the drive control unit(s)), in parallel with the actuation control unit 2, so that the intelligent wheel control unit 4 can react more quickly in the event of a failure of the actuation control unit 2.However, this reduces the service life and increases the power consumption of the intelligent wheel control unit 4.

[0049] The intelligent wheel control unit 4 is connected to each other wheel control unit 5, 6, 7 via at least one, here two, signal networks 15, 16, which are independent of the actuation control unit. The signal network(s) 15, 16 are preferably designed as a common network to which the wheel control units 4, 5, 6, 7 are connected, and not, for example, as a point-to-point connection of the wheel control units 4, 5, 6, 7. A failure of a component connected to the signal network(s) 15, 16 then does not lead to an interruption in signal transmission between the remaining connected components. Alternatively, the signal network(s) 15, 16 can also be designed as a point-to-point connection, e.g., with the intelligent wheel control unit 4 as a common endpoint, or as a U-shaped or O-shaped chain connection.The braking system 1 comprises a drive control unit 17, 18 for each driven vehicle axle, which is configured to control one or more electric motors of the vehicle for regenerative braking. The drive control unit(s) 17, 18 are connected to the signal network(s) 15, 16, which are independent of the actuation control unit 2.

[0050] The braking system comprises (at least one, but here) two central control units 19, 20. At least one central control unit 19, 20 is configured to determine the need for braking depending on a control mode of the vehicle and to send control signals to the wheel control units 4, 5, 6, 7 and / or the drive control unit(s) 17, 18 and / or an electric motor(s). The actuation control unit 2 and the central control unit(s) 19, 20 have no direct signal connection for transmitting brake control-related data or signals. The central control unit(s) 19, 20 is / are connected to the signal network(s) 15, 16, which are independent of the actuation control unit 2.

[0051] Figure 2 shows a method according to the invention for controlling a braking system 1 according to one of the embodiments described above. After calculating 100 the braking command by the actuation control unit 2 or by the intelligent wheel control unit 4, the braking system 1 executes the following further steps. Then, the calculation 110 determines whether the calculated braking command is above a threshold value or not. This calculation preferably takes place in the actuation control unit 2 or in the intelligent wheel control unit 4 (the latter if the intelligent wheel control unit 4 performs the braking command determination). Alternatively, this step can also take place in the individual wheel control units 4, 5, 6, 7. The threshold value can be specific for each friction brake or specific for the front friction brakes and the rear friction brakes.

[0052] After calculating 110 whether the calculated braking request is above a threshold value or not, the currently responsible control unit (actuation control unit 2 or the intelligent wheel control unit 4) sends the control signals to the wheel control units 4, 5, 6, 7 (or the wheel control units 5, 6, 7 if the intelligent wheel control unit 4 calculates the braking request). Each control signal can include a first control component for regenerative braking and a second control component for friction braking. Optionally, second control signals for a backup braking mode are also calculated in parallel and sent to the wheel control units 4, 5, 6, 7 (or the wheel control units 5, 6, 7 if the intelligent wheel control unit 4 calculates the braking request), which are calculated so that the friction brakes would execute the entire braking request (more on this later).

[0053] If the calculated braking request is not above the threshold value, the drive control unit 17, 18 is controlled 120 by the actuation control unit 2 or the intelligent wheel control unit 4 to execute the braking request solely by means of regenerative braking. The control signal to the drive control unit 17, 18 is preferably sent from the actuation control unit 2 or the intelligent wheel control unit 4 via the wheel control units 4, 5, 6, 7 to the drive control unit 17, 18.

[0054] If the calculated braking request is above the threshold value, the drive control unit 17, 18 and the wheel control units 4, 5, 6, 7 are controlled 130 by the actuation control unit 2 or the intelligent wheel control unit 4 in order to execute the braking request both via the drive control unit using regenerative braking and via the wheel control units 4, 5, 6, 7 using friction brakes. Here, too, the control signal to the drive control unit 17, 18 is preferably sent from the actuation control unit 2 or the intelligent wheel control unit 4 to the drive control unit 17, 18 via the wheel control units 4, 5, 6, 7.

[0055] Regardless of whether purely regenerative braking or mixed braking is performed, the next step is to wait 140 after the wheel control units have activated the drive control unit(s) 17, 18 for a predefined period of time (preferably 35-60 ms) to see whether the at least one electric motor starts regenerative braking. If this occurs within the predefined period of time, the braking request is executed 150 in a normal braking mode with the calculated distribution between regenerative braking and friction braking.

[0056] If the electric motor does not initiate regenerative braking within the predefined time period, the calculated braking request is executed 160 entirely via the wheel control units 4, 5, 6, 7 using the friction brakes in a backup braking mode. Preferably, the second control signal is used for the backup braking mode, which is provided to the wheel control units 4, 5, 6, 7 by the currently responsible control unit (actuation control unit 2 or the intelligent wheel control unit 4) in parallel with the first control signal for this case. This avoids the otherwise necessary request for such a second control signal from the responsible control unit (actuation control unit 2 or intelligent wheel control unit 4), its calculation, and its re-transmission to the wheel control units 4, 5, 6, 7 before a reaction of the friction brakes would be possible.

[0057] If the backup braking mode has already started and the electric motor begins regenerative braking after the friction brakes have already taken over the execution of the braking request in backup braking mode, a shutdown 170 (phase-out) of the control of the friction brakes by the wheel control units 4, 5, 6, 7 preferably takes place in accordance with the increase in the proportion of regenerative braking, so that the calculated braking request is implemented as accurately as possible at all times (e.g., with less than ± 10% deviation), until a braking request distribution calculated for a normal braking mode between regenerative braking and friction braking is achieved. The intelligent wheel control unit 4 and / or the actuation control unit 2 can calculate control signals for both the normal braking mode and the backup braking mode in parallel for each calculated braking request and send them to the wheel control units 4, 5, 6, 7.The wheel control units 4, 5, 6, 7 can be used by the wheel control units 4, 5, 6, 7 as required to control the friction brakes and / or the drive control unit(s) 17, 18.

[0058] List of reference symbols

[0059] 1 braking system

[0060] 2 Actuation control unit

[0061] 3 Brake actuation unit

[0062] 4 Wheel control unit / intelligent wheel control unit

[0063] 5 Wheel control unit

[0064] 6 Wheel control unit

[0065] 7 Wheel control unit

[0066] 8 independent signal lines

[0067] 9 independent signal lines

[0068] 10 independent signal lines

[0069] 11 independent signal lines

[0070] 12 independent signal lines

[0071] 13 unintelligent section

[0072] 14 intelligent section

[0073] 15 independent signal network

[0074] 16 independent signal network

[0075] 17 Drive control unit

[0076] 18 Drive control unit

[0077] 19 central control unit

[0078] 20 central control unit

[0079] 100 Calculate

[0080] 110 Calculate

[0081] 120 Control

[0082] 130 Control

[0083] 140 Wait and see

[0084] 150 Execute

[0085] 160 Execute

[0086] 170 Shutdown

Claims

Patent claims 1. Redundant braking system (1) for a vehicle, comprising an actuation control unit (2) which is configured to be connected to at least one actuation sensor of a brake actuation unit (3) in order to receive one or more raw actuation signals indicating an actuation of the brake actuation unit (3), wherein the braking system (1) further comprises at least two friction brakes, each assigned to a wheel of the vehicle, wherein the actuation control unit (2) is connected to each of the friction brakes via a signal line (8, 9, 10, 11, 12) and is configured to independently calculate a braking request from the raw actuation signals and to calculate and send a corresponding control signal for each of the friction brakes, characterized in that the braking system (1) comprises a separate wheel control unit (4, 5, 6, 7) for each wheel, which is configured toconverting the actuation signal received from the actuation control unit (2) into an actuation of the respectively assigned friction brake, wherein at least one wheel control unit (4, 5, 6, 7) is designed as an intelligent wheel control unit (4) which is configured to receive the raw actuation signals from the actuation control unit (2) and to independently calculate a braking request from the raw actuation signals and to calculate and send a corresponding actuation signal for each of the friction brakes.

2. Braking system (1) according to claim 1, characterized in that the actuation control unit (2) is connected to each of the wheel control units (4, 5, 6, 7) via at least one direct signal line (8, 9, 10, 11, 12) which is independent of other components.

3. Braking system (1) according to claim 1 or 2, characterized in that the actuation control unit (2) is connected to the intelligent wheel control unit (4) via two direct signal lines (8, 12) which are independent of other components.

4. Braking system (1) according to one of the preceding claims, characterized in that the intelligent wheel control unit (4) is connected to each other wheel control unit (5, 6, 7) via at least one signal network (15, 16) independent of the actuation control unit (2), preferably via two signal networks (15, 16) independent of the actuation control unit.

5. Braking system (1) according to one of the preceding claims, characterized in that the actuation control unit (2) comprises a non-intelligent section (13) and an intelligent section (14), wherein the non-intelligent section (13) is configured to receive the raw actuation signals and to forward them to the intelligent section (14) and the intelligent wheel control unit (4), and wherein the intelligent section (14) is configured to calculate the braking request.

6. Braking system (1) according to claim 5, characterized in that the unintelligent section (13) and the intelligent section (14) are either arranged on separate circuit boards or are arranged galvanically isolated on the same circuit board, and / or the unintelligent section (13) and the intelligent section (14) have a separate power supply.

7. Braking system (1) according to one of the preceding claims, characterized in that the braking system (1) comprises at least one drive control unit (17, 18), preferably one drive control unit (17, 18) for each driven vehicle axle, preferably one drive control unit for each driven wheel, which is designed to control an electric motor of the vehicle for regenerative braking.

8. Braking system (1) according to one of the preceding claims, characterized in that the braking system (1) comprises at least one central control unit (19, 20), preferably two central control units (19, 20), wherein the central control unit (19, 20) is configured to determine the need for braking as a function of a control mode of the vehicle and to send control signals to the wheel control units (4, 5, 6, 7) and / or the drive control unit (17, 18) and / or an electric motor.

9. Braking system (1) according to claim 8, characterized in that the actuation control unit (2) and the central control unit (19, 20) have no direct signal connection for calculating the braking request and for controlling the braking.

10. Braking system (1) according to claim 8 or 9, characterized in that the central control unit (19, 20) or the two central control units (19, 20) are connected to the signal network (15, 16) independent of the actuation control unit (2), preferably to both signal networks (15, 16) independent of the actuation control unit (2).

11. Vehicle comprising a braking system (1) according to one of claims 1 to 10.

12. Method for controlling a braking system (1) according to one of claims 7 to 10, wherein after a braking request calculation by the actuation control unit (2) or by the intelligent wheel control unit (4), the braking system (1) carries out the following steps: - If the calculated braking request is not above a threshold value: controlling (120) the drive control unit (17, 18) via the wheel control units (4, 5, 6, 7) in order to execute the braking request solely by means of regenerative braking; and - If the calculated braking request is above a threshold value: controlling (130) the drive control unit (17, 18) and the friction brakes via the wheel control units (4, 5, 6, 7) in order to both via the drive control unit (17, 18) by means of recuperative Brakes and via the wheel control units (4, 5, 6, 7) by means of friction brakes.

13. The method according to claim 12, comprising the step: - waiting (140) after the activation (120, 130) of the drive control unit (17, 18) for a predefined period of time by the wheel control units (4, 5, 6, 7) to see whether the at least one electric motor starts the regenerative braking, and - if this does not happen, complete execution (160) of the braking request via the wheel control units (4, 5, 6, 7) by means of the friction brakes in a substitute braking mode.

14. The method according to claim 13, characterized in that the predefined time period is between 35 and 60 milliseconds.

15. The method according to claim 13 or 14, comprising the step: - in the event of a delayed start of recuperative braking by the electric motor after the friction brakes have already taken over the execution of the braking request in the backup braking mode, reducing (170) the control of the friction brakes by the wheel control units (4, 5, 6, 7) in accordance with the increase in the proportion of recuperative braking until a braking request distribution between recuperative braking and friction braking calculated for a normal braking mode is achieved.

16. Method according to one of claims 13 to 15, characterized in that the intelligent wheel control unit (4) and / or the actuation control unit (2) calculates, for each calculated braking request, both control signals for the normal braking mode and the substitute braking mode in parallel and uses these as required to control the wheel control units (4, 5, 6, 7) and / or the drive control unit (17, 18).

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