Optimized wheel brake slip regulation for motor vehicle wheel brakes and such motor vehicle brakes

Abstract

The invention generally relates to a method for optimized wheel brake slip regulation for a motor vehicle brake and to a motor vehicle brake of this type.

Description

Technical Field

[0001] The present invention generally relates to a method for optimizing wheel brake slip adjustment for motor vehicle wheel brakes and a such motor vehicle brake. Background Technology

[0002] In addition to known hydraulically operated wheel brakes, electrically operated wheel brakes are increasingly being used in motor vehicle braking systems; these are also known as electromechanical wheel brakes (“EMB”). These EMBs typically have an electrical or electronic drive unit that cooperates with a mechanism or transmission mechanism. Thus, a braking unit, which may include friction pads, can be arranged on the output side, pressing against a brake disc or brake drum by means of translational movement. This allows for deceleration during wheel brake operation. For example, an EMB is described in patent document DE 10 2017 206 798 A1.

[0003] Here, the electric drive unit may include an electrically driven motor, also referred to below as an actuator. The relevant functions for controlling or regulating the actuator are typically stored in an electronic control unit or brake controller.

[0004] The actuator or force actuator can apply force to the friction pair—a spreading force in the case of a drum brake and a clamping force in the case of a disc brake—so that the wheel, which is anti-rotatingly connected to the friction pair, is subjected to a braking torque for reducing the wheel's rotation.

[0005] To operate such wheel brakes, control information corresponding to the requested braking force is typically acquired via a control device, such as an electronic brake pedal. The corresponding braking signal may also be provided, for example, by a higher-level central controller. The requested braking force can be interpreted by the brake control unit and converted into a control command, which can then be transmitted to the individual wheel brakes and converted accordingly.

[0006] If the requested braking force exceeds a certain limit, the corresponding wheels may tend to lock up. Locked wheels can cause vehicle instability or loss of steering ability, and therefore should be avoided whenever possible. In the prior art, this problem is typically addressed holistically through a central controller or central control unit, which has a corresponding ABS adjustment module for all wheels of the vehicle. For example, an ABS adjustment method is disclosed in the applicant's patent document DE 10 2008 036546 A1.

[0007] A disadvantage here is the time delay in data exchange between the central controller or higher-level vehicle computer and the local regulator / regional regulator. Regulation runtime or cycle time can reach 10 ms or longer, thus limiting the regulation accuracy. Summary of the Invention

[0008] Therefore, it is desirable to provide a method for adjusting the braking force of motor vehicle wheels that does not have the aforementioned disadvantages or at least mitigates them. Therefore, it is also desirable to provide a motor vehicle braking system suitable for performing this method.

[0009] The inventor has begun to address this problem.

[0010] Surprisingly, this problem is simply solved by a method for operating wheel brakes (particularly for motor vehicles) and a braking system according to any independent claim. Preferred embodiments and improvements of the invention can be derived from the dependent claims.

[0011] Therefore, in a first aspect, the present invention relates to a method for operating a wheel brake, particularly for a wheel brake of a motor vehicle. Here, the wheel brake may be assigned to a wheel of the motor vehicle that is to be operated according to the invention. It should be understood that the method for operating the wheel brake described below is shown exemplarily for only one wheel, but the method can be performed on all relevant wheels of the motor vehicle.

[0012] Here, the wheel brakes of the motor vehicle wheels are preferably operated by a local brake control unit (“WCU” = “Wheel Control Unit”), which is locally assigned to the wheel brakes.

[0013] Here, the method may include the following steps: - Provide a central braking force request F to the observed local brake control unit. DriverReq , - Provide vehicle reference speed V to the local braking control unit Ref Or the wheel speed V of another wheel x , - Provide the local brake control unit with the observed wheel speed V of the wheel. Rad , - Provides the current wheel braking force F of the observed wheel. Rad ,as well as - Provide wheel speed limits V to the local brake control unit. min , - The local braking control unit generates a local braking force request F based on the information provided above.CMD and / or local regulator status information Zustand RBV , - By applying the local braking force component F CMD The force actuator that operates the local wheel brake of the observed wheel.

[0014] This method offers the possibility of executing specific functions of the vehicle's service brakes locally or directly at the respective wheel brakes via a correspondingly configured local brake control unit. Several advantages are provided by transferring the relevant functions of the service brakes from a higher-level central brake controller or central controller to brake control units locally assigned to each wheel brake. In the context of this invention, "local" means that the associated component or function can be individually assigned to the wheels of the vehicle and / or can be kept near the wheels. In other words, specific functions of the service brakes can be executed directly at the wheel brakes or on brake control units directly assigned to the wheel brakes.

[0015] In this way, when particularly time-critical functions or adjustments are performed directly locally on the wheel brakes, the time delay of data exchange between the central brake controller and the local regulator can be minimized. Therefore, for example, the adjustment run time or cycle time for data exchange, which might be 10 ms or longer in a braking system with a central brake controller, can be reduced to less than 10 ms, preferably less than 5 ms, and particularly preferably to 1 ms or even less, especially for functions transferred locally to the wheel brakes. Furthermore, a pre-defined limit V for wheel speed can be used... min To improve wheel slippage.

[0016] The inventors have discovered that, particularly advantageously, safety-critical functions such as ABS adjustment can also be performed locally within the local brake control unit. This significantly improves the accuracy of brake adjustment, as shorter cycle times result in greater precision and responsiveness for individual wheel brakes. Particularly advantageously, the method according to the invention can be used for wheel slip adjustment and the necessary adjustment techniques or routines. By transferring wheel slip adjustment to the local brake control unit, wheel slip adjustment can be performed faster, more precisely, and wheel-specifically, thereby reducing overall braking time and / or further shortening braking distance.

[0017] According to a preferred embodiment of the invention, a motor vehicle may include local braking control units on all wheels 1…x (x = the number of wheels of the motor vehicle), for example, at wheels 1, 2, 3, and 4 in the case of four wheels. These local braking control units can operate independently and can independently perform assigned functions or adjustment routines. This significantly improves the reliability of the braking system because redundancy exists on all wheels in this way. For example, if one local braking control unit fails, the remaining three local braking control units remain operational. However, the method according to the invention may also be applied only to the wheels of, for example, one axle of the motor vehicle. The above method constitutes an adjustment operation or cycle / loop.

[0018] According to another equally preferred embodiment of the invention, the local braking control unit of the wheel brakes of the axle can be functionally integrated with a local, axle-dependent braking control unit. For simplicity, only the local braking control unit will be referred to below within the scope of the invention, but it should be understood that the local, axle-dependent braking control unit should also be included therein. Therefore, the method according to the invention can also operate on the local, axle-dependent braking control unit of the wheel brakes of a wheel of an axle of a motor vehicle.

[0019] The method for operating a wheel brake, examined within the scope of this invention, can be responsible for setting the requested braking torque or the braking force of the wheel. The centrally pre-defined braking request is also referred to below as F. DriverReq (“DriverRequest” = driver braking request), but in the sense of this invention, it refers not only to a driver's braking request, but also, for example, to a braking request from a higher-level vehicle system or onboard system. According to the invention, a braking request F can be pre-given centrally. DriverReq Determine the local braking force component F CMD (“CMD” = “Command”, braking command), this local braking force component can be applied to the corresponding wheel brake. Depending on the type of wheel brake, this braking force component can then be provided as braking pressure for hydraulically operated brake cylinders, or as clamping or releasing force for electromechanically operated wheel brakes. Simplified, this is also referred to as applying the local braking force component F. CMD The force actuator used to operate the local wheel brakes.

[0020] Preferably, the wheel brake used in this invention can be configured as an electromechanically operable wheel brake (EMB), such as an electromechanical disc brake or an electromechanical drum brake. The advantages of this invention, such as its short response time, are particularly evident here. Specifically, the wheel brake can be configured as a service brake, in which a parking brake function can also be integrated.

[0021] This method proposes to use appropriate sensors to detect important state information of the brakes of the corresponding wheels, such as the current wheel speed V. Rad Or the current wheel braking force F Rad Alternatively, the critical state information can be determined based on a model empirically determined and stored in non-volatile memory, preferably within the local brake control unit. Additionally, with respect to the method according to the invention, the local brake control unit can continuously exchange critical information or signals with a higher-level central controller (VCU = "Vehicle Control Unit") during operation. This central controller may, for example, include a central brake modulator or other higher-level control systems of the vehicle. The central controller can also be connected to or integrated into a higher-level vehicle computer. Therefore, the central controller can provide functions and / or information for multiple wheels of the vehicle.

[0022] For data exchange, at least one data link can be established between the local brake control unit and the central controller. This can be implemented redundantly to improve fail-safety. According to embodiments of the invention, a data link may also exist between at least two, preferably multiple, local brake control units.

[0023] According to a preferred embodiment of the invention, the central controller may, for example, provide a central braking request F to the local braking control unit. Driver Request Here, braking request F is made. Driver Request The braking request can be detected by means of a control device, such as an electronically operable brake pedal. However, the braking request can also be provided by a higher-level vehicle computer, for example.

[0024] Furthermore, according to a preferred embodiment of the present invention, the central controller can determine the vehicle speed, hereinafter referred to as the reference speed V. Ref Alternatively, the wheel speeds of the other wheels of the vehicle can be periodically provided to the local braking control unit. Therefore, in the case of the observed first wheel (x = 1) and a total of four wheels of the vehicle, the wheel speeds V of the other wheels (x = 2, 3, 4) can be provided when observing wheel 1. 2、 V 3、 And V4.

[0025] Therefore, according to another preferred embodiment of the invention, the local braking control unit may propose that wheel state variables (such as the current wheel speed V of the corresponding wheel) be... rad Or the current wheel braking force F Rad The information is transmitted to the central controller. Based on this wheel speed information, the central controller can determine the vehicle's reference speed V. Ref Reference driving speed V Ref The determination can be made by means of known methods of adjusting ABS.

[0026] The method can also specify that the current wheel speed V of the observed wheel is provided to the local braking control unit. Rad The current wheel speed can be provided, for example, via a corresponding wheel speed sensor, which can be directly connected to the local brake control unit.

[0027] The method can also specify that the current wheel braking force F of the observed wheel is provided to the local brake control unit. Rad The current wheel braking force can be provided, for example, by a corresponding force sensor at the wheel brake, which can be directly connected to the local brake control unit.

[0028] According to a particularly preferred embodiment of the present invention, the central controller can also limit the wheel speed V. min This is provided to the local brake control unit as another requirement for wheel brake slip adjustment. The limit V... min This can represent a threshold, preferably a lower limit, and thus an additional condition for adjusting wheel speed. By adding a lower limit to the current wheel speed, which thus sets the speed that should not be lowered during braking, excessive brake slip can be very advantageously avoided.

[0029] The background is that the braked wheel rotates more slowly than the unbraken wheel. The difference in wheel rotation between the braked and unbraken wheels can also be called slip speed. In terms of adjustment technology, to improve braking efficiency, it may be desirable to obtain an optimal value between maximum braking force or maximum braking torque and sufficient driving stability. By transferring the corresponding adjustment technology function to the local brake control unit and combining it with the short cycle time during data exchange at the wheel level, local wheel brake slip adjustment can be achieved particularly well. If brake slip is reduced according to the present invention, this can improve driving stability during braking.

[0030] According to one embodiment of the present invention, this limit value V min It can be fixed and preset, for example, by the central controller. This limit can be set according to the vehicle type and stored in the memory of the central controller.

[0031] According to another embodiment of the present invention, the limit value V can be specified. min It can be set variably. This could mean that the limit value V min For example, it can be changed during vehicle operation or even during braking. This allows the limit V to be adjusted, for example, based on the current vehicle speed and / or estimated lane conditions. min This improves braking stability. In this way, for example, a larger limit value V can be set at higher speeds. min Set a smaller limit V at lower speeds. min In other words, the method of the present invention may further include the following method steps: - Based on the current vehicle speed V Ref And / or adjust the limit V according to lane conditions min .

[0032] Therefore, for example, the limit value V can be set during braking while taking speed limits into account. min Adapted to the current vehicle speed V Ref .

[0033] According to a particularly preferred embodiment of the invention, the limit value V min This can include an absolute value for wheel speed, which sets a minimum wheel speed that should not be exceeded. The regulating system can then take this value into account as a lower limit for the observed wheel speed. These values ​​define the maximum wheel slip that will not be exceeded during operation or braking. If lane conditions worsen, this value can be reduced, for example, at the same travel speed, thereby resulting in a smaller maximum wheel slip.

[0034] According to an improved embodiment of the present invention, the maximum wheel slippage can also be specified as a limit value V. min The parameters are pre-defined. The adjustment can then be formulated in such a way that a lower limit for the wheel speed to be considered can be determined and used for further calculations.

[0035] As an output, the local braking control unit can generate a local braking force request F based on the information provided above. CMD and / or local regulator status information Zustand RBV Therefore, the local brake control unit may have one or more correspondingly configured adjustment technology modules to determine these quantities. The local braking force component F can then be applied to the corresponding one or more force actuators of the local wheel brake. CMD .

[0036] During braking, the above-mentioned method steps that can form corresponding adjustment operations can be executed at least multiple times. - Provide central braking force request F DriverReq , - Provides vehicle reference speed V Ref The wheel speed V of other wheels x , - Provides the current wheel speed V Rad , - Provides current wheel braking force F Rad , and / or - Provides a limit value V for the slip velocity. min ,as well as - The local braking force request F is generated by the local braking control unit. CMD and / or local controller status information Zustand RBV .

[0037] Herein lies the provision that the time or cycle time for this adjustment operation is less than 10 ms, preferably less than 5 ms, and particularly preferably 1 ms or even less. This allows for particularly precise and fine adjustments to the wheel brakes. Here, the adjustment operation time or cycle time refers to the time period required for one operation (one run) of the aforementioned method steps.

[0038] The local braking control unit can be understood, in particular, as a functional unit for implementing the aforementioned functions. To this end, the local braking control unit may include corresponding adjustment algorithms and be constructed, for example, modularly. The adjustment algorithms may be implemented, for example, in hardware or software. The local braking control unit may be constructed, for example, as a microcontroller, microprocessor, application-specific integrated circuit (ASIC), programmable logic controller, or other programmable or fixed-wired unit. In particular, the local braking control unit may have a processor device and a memory device, wherein program code is stored in the memory device, and when the program code is executed, the processor device performs the functions as described herein.

[0039] According to a preferred embodiment of the present invention, the wheel brake slip adjustment system according to the present invention within the local brake control unit may include four sub-modules. These sub-modules may be assigned functions such as signal processing, wheel anti-lock braking, target wheel speed formation, and / or wheel speed adjustment.

[0040] The signal processing submodule can, for example, be configured to, if not provided by the central controller, process the signals based on the wheel speeds V1...V of the vehicle's wheels. x Calculate the vehicle's reference speed V Ref In addition, the vehicle's deceleration Acc Ref and wheel deceleration Acc Rad It can be determined by the corresponding wheel speed V RadExport or wheel speed V Rad It is derived from the changes from one adjustment operation to the next.

[0041] The target wheel speed forming submodule can be constructed, for example, to determine the optimal target wheel speed V for wheel speed regulation. Soll Here, the optimal wheel braking slip should be achieved, considering both braking efficiency and wheel stability. This is within a predefined limit V. min In such cases, it is advantageous to set the target wheel speed slightly higher than the limit, so that the additional condition is also satisfied by the wheel speed adjustment.

[0042] The state regulator submodule can be configured, for example, for wheel anti-lock braking (RBV) functionality. To this end, the module can perform, for example, the following regulation tasks: - Identify the braking status of the wheels. - Perform calculations for the braking force request in the corresponding state, and / or - Initiate transitions between different states.

[0043] For the state regulator, different braking states of the wheels can be defined so that the corresponding adjustment strategy can be adapted more efficiently and quickly to the corresponding operating states of the vehicle and wheel brakes. According to a preferred embodiment of the invention, for example, the following four braking states or state information (Zustand) can be defined. RBV "Inactive", "Unstable", "Maintained", and "Stable".

[0044] The state is "inactive" (Zustand) RBV =“Inactive” can mean that the braking force request F DirverReq Relatively small, and when the braking force is requested by F DirverReq When the wheel brakes are fully adjusted, the magnitude of the braking force request will not compromise wheel stability. Therefore, there is no need to adjust the braking force request F. DirverReq Appropriate restrictions should be imposed. For adjustment strategies, this could mean that the central braking force request F can be made. DirverReq The braking force is directly transmitted to the wheel brakes. In this case, the braking force request F from the condition regulator or the anti-lock braking system... RBV Can request braking force F DirverReq same.

[0045] The state is "unstable" (Zustand) RBV = "unstable") can mean that the wheel dynamics state indicates: due to strong wheel deceleration Acc RadAnd / or a tendency for wheels to lock up due to significant wheel slippage. For adjustment strategies, this could mean: if an "unstable" state is first identified, the current wheel braking force F can be increased. Rad Assuming the locking limit is F Lock To prevent wheel lock-up, the braking force can be immediately reduced, i.e., the current braking force can be decreased.

[0046] F RBV = F Lock - F Offset .

[0047] Here, the offset F Offset It can depend on the wheel dynamics and represent the force reduction component of the first reduction step used for braking force. Offset F Offset It can be used in a single adjustment run to reduce the braking force share F from the state regulator during the initial adjustment run when a tendency for wheel lock-up is identified. RBV This is to quickly reduce braking force and thus prevent the wheels from locking up.

[0048] Afterwards, as long as the "unstable" state remains in effect, the braking force reduction can continue to be implemented step by step according to the following formula.

[0049] F RVB = F RVB,Old - F ab

[0050] F RVB,Old This represents the previously requested braking force share from the state regulator in the previous adjustment run. During further reduction of braking force, the reduction share F can be recalculated for each adjustment run based on the wheel dynamics state. ab That is, the current force decreases by a certain amount.

[0051] The state is "stable" (Zustand) RBV = "Stable" can mean the wheel dynamics state, especially the wheel deceleration Acc. Rad And / or wheel slip is within a relatively stable range. Here, a tendency for wheel lock-up cannot be identified. If a "stable" state is identified, braking force request F can be applied according to the following rules. RVB Increase in force: F RVB = F RVB,Old + F auf .

[0052] Here, the increase in braking force F for each adjustment operation is... auf It depends on the wheel dynamics. Therefore, F aufThis represents the force increase component during the force increase step used for braking force.

[0053] "State maintained" (Zustand) RBV = "Holding") can mean that the braking state is between "unstable" and "stable". Here, neither the conditions for "unstable" nor the conditions for "stable" are met. If a "holding" state exists, the braking force requested is F. RVB It can remain unchanged.

[0054] The transition from one state to another can be performed according to the following rules: 1) The "Inactive" state is the initial state. This state is set at the start of the braking process and remains in this state until wheel instability is detected. When wheel instability is detected, the wheel braking state changes from "Inactive" to "Unstable".

[0055] 2) It can switch from the "inactive" state and the "stable" state to the "unstable" state. It can also switch from the "held" state to the "unstable" state. By actively reducing the braking force, the state can be switched from "unstable" to "held" or "stable".

[0056] 3) The transition to the "Stay" state can only be made from the "Unstable" state.

[0057] 4) You can switch from the state "Stable" or "Unstable".

[0058] 5) The state regulator always returns to the "inactive" state when the following occurs.

[0059] a. The driving speed is below a certain threshold, or

[0060] b. RBV braking force request F RVB Greater than the braking force request F DirverReq ,or

[0061] c. There is no braking force request F DirverReq .

[0062] A wheel speed regulation submodule can be constructed, for example, for speed regulation to determine the wheel speed relative to the optimal target wheel speed V. Soll The deviation between them. For this purpose, a PID controller can be set up, for example. In this way, the desired wheel slippage can be achieved very well through continuous and precise adjustment.

[0063] The state regulator used to prevent wheel lock-up ensures that the V-regulator is reset and reinitialized via the speed regulator during "inactive" and "unstable" braking states. Here, wheel speed regulation can continue to operate continuously during "hold" and "stable" braking states. The additional braking force request F is calculated accordingly. VRegler This can then help eliminate the discrepancy between wheel speed and the optimal target wheel speed V. Soll The speed deviation between them.

[0064] By superimposing two braking force requests F from the state regulator for preventing wheel lock-up and the speed regulator for regulating wheel speed. RVB and F VRegler This allows us to determine the final local braking force request F for wheel brake slip adjustment. CMD .

[0065] Here, the final braking force request F for wheel brake slip adjustment is... CMD F can be requested through braking force DirverReq As an upper limit, it is restricted. Meanwhile, the final braking force request F CMD It should not be negative.

[0066] According to another aspect, the present invention also relates to a braking system, particularly a braking system for a motor vehicle, which is configured to perform the method described above for operating wheel brakes.

[0067] Further details of the invention can be derived from the description of the described embodiments and the appended claims. Attached Figure Description

[0068] In the attached diagram: Figure 1 This shows the standard interface for wheel brake slip adjustment. Figure 2 The main input and output quantities of wheel brake slip adjustment according to the present invention are shown. Figure 3 The four main modules for wheel brake slip adjustment are shown. Figure 4 This shows the input and output quantities used for signal processing. Figure 5 The input and output quantities used to generate the target wheel speed are shown. Figure 6 The input and output quantities for the state regulator are shown. Figure 7 The four braking states for the state regulator and their possible transitions are shown. Figure 8 The input and output quantities for wheel speed regulation are shown. Figure 9 The relationship between the two sub-regulators and the final output of the wheel brake slip adjustment are shown. Detailed Implementation

[0069] In the following detailed description of preferred embodiments, for clarity, the same reference numerals denote substantially the same components in or on the embodiments. To better illustrate the invention, the preferred embodiments shown in the drawings are not necessarily drawn to scale.

[0070] Figure 1 The standard interface of a braking system 10 is shown schematically. The braking system includes a local braking control unit 11 adapted to operate wheel brakes 40, particularly wheel brakes for motor vehicles. The local braking control unit 11 can be configured to perform wheel brake slip adjustment 11. In the illustrated embodiment, the braking system 10 also includes a central controller 30.

[0071] Figure 2 The main input and output quantities of wheel brake slip adjustment according to the invention are shown schematically, and the wheel brake slip adjustment is implemented in the local brake control unit 21 of the braking system 20. The braking system 20 is also designed to operate wheel brakes 40, which are not shown for clarity. The braking system 20 also includes a central controller 30, which is also not shown for clarity.

[0072] Therefore, the method for controlling the wheel brake 40, particularly for a wheel brake of a motor vehicle, according to the present invention is performed by a local brake control unit 21, which is locally configured with the wheel brake 40. For each wheel to be controlled, the method includes the following steps: - Provide a central braking force request F to the local braking control unit DriverReq , - Provide vehicle reference speed V to local brake control unit 21 Ref Or the wheel speed V of the other wheels of the motor vehicle x , - Provide the local brake control unit 21 with the current wheel speed V of the observed wheel. Rad , - Provides the current wheel braking force F of the observed wheel. Rad ,as well as - Provides the local brake control unit 21 with a limit value V for wheel speed. min .

[0073] In the case of four wheels as described in the embodiment, the motor vehicle includes four wheels and four wheel brakes, wherein each wheel brake includes a local brake control unit 21, so that when the wheel under consideration is the first wheel x = 1, the alternative vehicle reference speed V is used. Ref Alternatively, the wheel speed V of the remaining wheels can be used. 2、 V 3、 V4 is provided to the local brake control unit 21.

[0074] Based on this input information, the local braking control unit 21 generates a local braking force request F. CMD and / or local regulator status information Zustand RBV .

[0075] Then, a local braking force component F can be applied to the force actuator of the local wheel brake 40. CMD .

[0076] Braking force request F is provided by the higher-level central controller 30. DriverReq This central controller can form the central brake regulator or other higher-level regulation system of a motor vehicle, or it can form the on-board computer of a motor vehicle.

[0077] Here, at least one data link is provided between the local brake control unit 21 and the central controller 30 to enable the transmission of data, signals or information.

[0078] According to another embodiment of the invention, a data link can also be provided between local brake control units. This allows for faster exchange of information, such as information about the corresponding wheel brakes or the corresponding wheel speeds, between the local brake control units.

[0079] Here, wheel brake 40 is configured as a service brake. Unaffected by this, other functions, such as the function of a parking brake, can be additionally integrated into the wheel brake.

[0080] The wheel brake 40 is configured as an electromechanical wheel brake (EMB). This can be, for example, in the form of an electromechanical disc brake or an electromechanical drum brake.

[0081] The method according to the invention provides the possibility of transferring the relevant functions of the service brake from the higher-level central controller 30 to the brake control unit 21 locally assigned to each wheel brake.

[0082] In the context of this invention, "local" means that the local brake control unit 21 is individually assigned to and / or held in direct proximity to a wheel of the motor vehicle. This could be, for example, directly on or within the wheel brake, or on or within the peripheral housing of the wheel brake. However, this may mean that the local brake control unit 21 is also unsprung mass and may be exposed to adverse environmental effects. Therefore, within the scope of this invention, the local brake control unit 21 can also refer to a local brake control unit 21 that is, for example, arranged on or within the wheel arch, preferably in direct proximity to the wheel brake, and thus advantageously belongs to sprung mass.

[0083] According to the present invention, safety-critical functions such as ABS adjustment or wheel slip adjustment are particularly executed locally in the local brake control unit 20. This significantly improves the accuracy of brake adjustment because shorter adjustment execution times or cycle times result in greater precision and responsiveness for each wheel brake.

[0084] According to another equally preferred embodiment of the invention, the local brake control units 21 of the wheel brakes 40 of the same axle can be combined into a single local brake control unit. This reduces the number of local brake control units 21, resulting in a cost advantage. Even in this embodiment, the cycle time can be kept very short. This combined local axle brake control unit also provides the advantage that the component belongs to the sprung mass.

[0085] The local braking force component F determined by the method according to the invention CMD During operation, it provides braking pressure for hydraulically operated brake cylinders, or clamping or releasing force for electromechanically operated wheel brakes.

[0086] Current wheel speed V Rad and the current wheel braking force F Rad It is detected by means of appropriate sensors, such as force sensors, strain gauge-based force sensors, or wheel speed sensors.

[0087] During operation, relevant information is exchanged between the vehicle's local braking control unit 21 and a higher-level central controller 30, which provides functions and / or information for all wheels of the vehicle. The central controller may also be connected to a higher-level vehicle computer.

[0088] The central controller 30 provides a central braking request F to the local braking control unit. Driver Request Here, braking request F is made. Driver RequestThe braking request can be detected by means of a control device, such as an electronically operable brake pedal. However, the braking request can also be provided by a higher-level vehicle computer, for example.

[0089] Furthermore, according to a preferred embodiment of the present invention, the central controller 30 provides a reference speed V to the local braking control unit 21. Ref And / or the wheel speed of the remaining wheels of the motor vehicle.

[0090] Therefore, the local braking control unit 21 transmits wheel state quantities, such as the current wheel speed V of the corresponding wheel. Rad Or the current wheel braking force F Rad The data is transmitted to the central controller 30. Based on this wheel speed information, the central controller 30 can determine the vehicle reference speed V. Ref Reference driving speed V Ref The determination can be made by means of known methods of adjusting ABS.

[0091] Current wheel speed V Rad Determined by a local wheel speed sensor connected to the local brake control unit 21.

[0092] The corresponding force sensor on the wheel brake provides the current wheel braking force F to the local brake control unit 21. Rad The force sensor is directly connected to the local braking control unit.

[0093] This invention proposes that the central controller 30 additionally set a limit V for wheel speed. min This is provided to the local brake control unit 21 as another requirement for wheel brake slip adjustment. The limit V min This is an additional threshold for wheel speed regulation, and thus constitutes an additional condition for wheel speed regulation. By adding another boundary to the current wheel speed, excessive braking slip can be avoided extremely advantageously; this other boundary thus sets the speed that should not be lowered during braking.

[0094] According to one embodiment of the present invention, the limit value V min It is fixedly given in advance by the central controller 30.

[0095] According to the embodiments described herein, the limit value V min It can be variably adjusted. This means, as in this example, that the limit V can be adapted during vehicle operation, and especially during braking. min Therefore, the limit V can be adapted based on the current vehicle speed and / or estimated lane conditions during braking. minIn this way, it is also possible to respond to changes during braking, such as changes in road surface or speed limits, and the method according to the invention can be adapted accordingly.

[0096] In this embodiment, the limit value V min This is the absolute value of the wheel speed, which sets the minimum wheel speed that should not be exceeded at the observed wheel. At the assumed travel speed V... Ref = At a speed of 100 km / h, for example, the limit value V can be... min = 90 km / h is set as the lower limit. Therefore, the adjustment can take this value into account as the lower boundary for wheel speed. These example values ​​produce a maximum wheel slip of 10%, which can be a feasible amount for good lane conditions, for example, at the stated driving speed. If the lane conditions deteriorate or are already not very good, then, for example, at a driving speed V... Ref Under the same conditions of 100 km / h, this value can be set to V. min = 95 km / h, which can produce a maximum wheel slip of 5%.

[0097] According to an improved embodiment of the present invention, the maximum wheel slippage can also be specified as a limit value V. min The parameters are pre-defined. The adjustment can then be formulated in such a way that a lower limit for the wheel speed to be considered can be determined and used for further calculations.

[0098] As an output, the local braking control unit 21 generates a local braking force request F based on the input information. CMD In this embodiment, local regulator state information Zustand is generated. RBV .

[0099] To this end, the local brake control unit 21 has a correspondingly constructed adjustment technology module to determine these quantities. According to the illustrated embodiment of the invention, four adjustment technology modules are provided for this purpose, which will be discussed below. Figure 3 These adjustment technology modules will be explained in further detail.

[0100] Wheel slip adjustment is performed at least at the level of the local brake control unit 21, providing a significant speed advantage in completing the required adjustment technical steps.

[0101] Therefore, the method according to the invention offers the significant advantage that at least the steps described below can be fully completed in less than 10 ms, preferably 5 ms or less, particularly preferably 1 ms or even less. This very short adjustment run or cycle time enables particularly precise and fine coordination of the wheel brakes. The method steps include: - Provide central braking force request F DriverReq , - Provides vehicle reference speed V Ref The wheel speed V of other wheels x , - Provides the current wheel speed V Rad , - Provides current wheel braking force F Rad , - Provides a limit value V for the slip velocity. min , - The local braking force request F is generated by the local braking control unit. CMD and / or local controller status information Zustand RBV , and / or - Output control information to the force actuator of the local wheel brake 40, or apply a local braking force component F. CMD To operate the force actuator of the local wheel brake 40.

[0102] It may also include the following method steps: - In generating local braking force request F CMD and / or local regulator status information Zustand RBV Previously, based on the current vehicle speed V Ref And / or the limit V based on lane conditions min Adaptation is required.

[0103] Therefore, the local brake control unit 21 includes a corresponding adjustment algorithm, or is configured to perform these method steps. Here, the adjustment algorithm is preferably implemented in corresponding hardware and / or software. According to the invention, the wheel brake slip adjustment within the local brake control unit 21 is divided into four adjustment technology sub-modules or modules 22, 23, 24, and 25, as follows: Figure 3 As shown in the embodiments.

[0104] Signal processing submodule 22 is configured to, if the central controller 30 does not provide the vehicle's reference speed V Ref Then, based on the wheel speeds V1...V of the motor vehicle wheels... x Calculate the reference velocity V Ref In addition, the vehicle's deceleration Acc Ref and wheel deceleration Acc Rad It can be determined by the corresponding wheel speed V Rad Or wheel speed V Rad This is derived from the changes from one adjustment cycle to the next. Therefore, Figure 4 The input and output quantities used for signal processing 22 are schematically shown.

[0105] The submodule "Target Wheel Speed ​​Formation 24" is configured to determine the optimal target wheel speed V for wheel speed regulation. Soll Here, optimal wheel braking slip should be achieved for both braking efficiency and wheel stability. This is based on a predetermined limit V according to the present invention. min In this case, it is advantageous to set the target wheel speed slightly higher than the limit, so that the additional condition is also satisfied by the wheel speed adjustment. Figure 5 The input and output quantities for the target wheel speed formation 24 are shown.

[0106] The submodule “State Regulator 23” is configured to prevent wheel lock-up (RBV). Figure 6 The input and output quantities for the state regulator 23 are shown. The module 23 is configured to perform at least the following regulation tasks: - Identify the braking status of the wheels. - Perform calculations for the braking force request in the corresponding state, and / or - Initiate transitions between different states.

[0107] For the state regulator 23, different braking states of the wheels are defined according to the embodiments described above, so that the corresponding adjustment strategies can be adapted more efficiently and quickly to the corresponding operating states of the vehicle and wheel brakes. According to a preferred embodiment of the invention, the following four braking states or state information are distinguished by Zustand. RBV "Inactive", "Unstable", "Maintained", and "Stable".

[0108] The state is "inactive" (Zustand) RBV = "Inactive") means that the braking force request F DirverReq Relatively small, and when the braking force is requested by F DirverReq When the wheel brakes are fully adjusted, the magnitude of the braking force request will not, or substantially will not, jeopardize wheel stability. Therefore, there is no need to adjust the braking force request F. DirverReq Appropriate restrictions should be imposed. For the adjustment strategy, this means that the central braking force requests F... DirverReq It is directly transmitted to the wheel brakes. Therefore, in this case, the braking force request F from the state regulator... RBV With braking force request F DirverReq same.

[0109] The state is "unstable" (Zustand) RBV = "Unstable") means that the wheel dynamics state is indicated by a strong wheel deceleration Acc. RadAnd / or a tendency for wheels to lock up due to significant wheel slippage. For the adjustment strategy, this means: if an "unstable" state is first identified, the current wheel braking force F... Rad Assuming the locking limit is F Lock To prevent wheel lock-up, the force should be reduced immediately by pressing the following formula. F RBV = F Lock - F Offset .

[0110] In this way, a safe operating state can be re-established as quickly as possible. Here, according to this embodiment, the offset F... Offset Depends on the wheel dynamics. Offset F Offset In the first adjustment operation that identifies the tendency for wheels to lock up, it is used once to reduce the braking force share F from the condition regulator. RBV This is to quickly reduce braking force and thus prevent the wheels from locking up.

[0111] Subsequently, during the subsequent adjustment and operation, as long as the "unstable" state remains effective, the reduction in braking force will continue to be executed step by step according to the following formula.

[0112] F RVB = F RVB,Old - F ab , In the process of further reducing braking force, the reduction fraction F can be recalculated based on the wheel dynamics for each adjustment operation. ab That is, the current force decreases by a certain amount.

[0113] The state is "stable" (Zustand) RBV = "Stable") means that the wheel dynamics, especially the wheel deceleration Acc, is stable. Rad And / or wheel slip is within a relatively stable range. Here, a tendency for wheel lock-up cannot be detected. If a "stable" state is detected, the braking force request F is implemented according to the following rules. RVB Increase in force: F RVB = F RVB,Old + F auf .

[0114] Here, the increase in braking force F for each adjustment operation is... auf It depends on the wheel dynamics.

[0115] "State maintained" (Zustand) RBV= "Holding") means that the braking state is between "unstable" and "stable". Here, neither the conditions for "unstable" nor the conditions for "stable" are met. If the state is "Holding", then the RBV braking force requests F RBV It remains unchanged.

[0116] Figure 7 Zustand shows four braking states or state information for the state regulator 23. RBV And its possible transitions. Transitions from one state to another follow these rules: 1) The "Inactive" state is the initial state ("Start"). This state is set at the start of the braking process and remains in this state until wheel instability is detected. When wheel instability is detected, the wheel braking state changes from "Inactive" to "Unstable".

[0117] 2) It can switch from the "inactive" state and the "stable" state to the "unstable" state. It can also switch from the "held" state to the "unstable" state. By actively reducing the braking force, the state can be switched from "unstable" to "held" or "stable".

[0118] 3) You can only switch to the "maintained" state from the "unstable" state.

[0119] 4) You can switch from the "Stable" or "Unstable" state to the "Stable" state.

[0120] 5) The state regulator always returns to the "inactive" state when the following occurs.

[0121] a. The driving speed is below a certain threshold, or

[0122] b. RBV braking force request F RVB Greater than the braking force request F DirverReq ,or

[0123] c. There is no braking force request F DirverReq .

[0124] Wheel speed regulation submodule 25 is configured for speed regulation to determine the wheel speed relative to the optimal target wheel speed V. Soll The deviation between them. Therefore, a PID controller is provided in this embodiment. Figure 8 The input and output values ​​for wheel speed regulation 25 are shown.

[0125] The state regulator 23, used to prevent wheel lock-up, ensures that the speed regulator 25 is reset and reinitialized via the speed regulator during the "inactive" and "unstable" braking states. Here, wheel speed regulation continues to operate continuously during the "hold" and "stable" braking states. The additional braking force request F is thus calculated. VRegler Used to eliminate the difference between wheel speed and the optimal target wheel speed V Soll The speed deviation between them.

[0126] By superimposing two braking force requests F from the state regulator for preventing wheel lock-up and the speed regulator for regulating wheel speed. RBV and F VRegler Determine the final local braking force request F for wheel brake slip adjustment. CMD Using this braking force, request F CMD Force actuator for loading wheel brake 40.

[0127] Here, the final braking force request F for wheel brake slip adjustment is... CMD Braking force request F, which is used as the upper limit DirverReq Limitations. Meanwhile, the final braking force request F CMD It should not be negative.

[0128] at last, Figure 9 This illustrates the relationship between the two adjustment modules 25 and 26 and the determination of the final output amount of the wheel brake slip adjustment according to the invention. The outputs of the two adjustment modules 25 and 26 are operated via a limiter 26, which limits the determined braking force F of the two adjustment modules 25 and 26. Sum Limit to central braking force request F DriverReq .

[0129] According to another aspect, the present invention also relates to a braking system 20, particularly a braking system for a motor vehicle, which is configured to perform the method described above for operating the wheel brake 40.

[0130] List of reference numerals in the attached diagram: 10. Braking System 11 Local Braking Control Unit 20 Braking System 21 Local Braking Control Unit 22 Modules for signal processing 23 Modules for preventing wheel lock-up 24 Modules for Target Wheel Speed ​​Formation 25 Modules for wheel speed regulation 26 Limiters 30 Central Controller 40 Wheel brakes Acc Ref Vehicle deceleration Acc Rad Wheel deceleration F DriverReq Central braking force request F Rad Current wheel braking force F CMD Local braking force component F RBV Braking force share requested by the state regulator F RVB,Old The braking force share previously requested by the state regulator F Lock Lock-up limit F Offset Force reduction component used in the first reduction step F ab Force reduction component used in additional force reduction steps F auf Force increase component used in the force increase step F VRegler Requested share from speed regulator V Rad Current wheel speed V Ref Vehicle reference speed V min Limits for slip velocity V Soll Optimal target wheel speed V x Wheel speed x The wheels of a motor vehicle VCU “Vehicle Control Unit” = Central Control Unit WCU “Wheel Control Unit” = Local Brake Control Unit Zustand RBV Regulator status information

Claims

1. A method for operating a wheel brake (40), particularly for a motor vehicle, said method being performed by a local brake control unit (21) locally associated with the wheel brake (40), said method comprising at least the following steps: - Provide a central braking force request (F) to the local braking control unit (21). DriverReq ), - Provide vehicle reference speed (V) to the local braking control unit (21) Ref ) or the wheel speed of other wheels of the motor vehicle (V) x ), - Provide the local braking control unit (21) with the current wheel speed (V) of the observed wheel. Rad ), - Provides the current wheel braking force (F) of the observed wheel. Rad ),as well as - Provide the local braking control unit (21) with a limit value (V) for wheel speed. min ), - The local braking control unit (21) generates a local braking force request (F) based on the information provided above. CMD ) and / or local regulator status information (Zustand RBV ), - By applying the local braking force component (F) CMD ) to manipulate the force actuator of the wheel brake (40) of the observed wheel.

2. The method according to the preceding claim, characterized in that, Braking force request (F) DriverReq The provision of the control is performed by the higher-level central controller (30), especially by the central brake regulator of the motor vehicle or other higher-level control systems.

3. The method according to any one of the preceding claims, characterized in that, There is at least one data link between the local brake control unit (21) and the central controller (30).

4. The method according to any one of the preceding claims, characterized in that, There are data links between the various local braking control units (21).

5. The method according to any one of the preceding claims, characterized in that, The wheel brake (40) is configured as a service brake.

6. The method according to any one of the preceding claims, characterized in that, The wheel brake (40) is configured as a wheel brake that can be operated electromechanically, preferably an electromechanical disc brake or an electromechanical drum brake.

7. The method according to any one of the preceding claims, characterized in that, The limit (V) min This includes the minimum wheel speed.

8. The method according to any one of the preceding claims, characterized in that, The limit (V) min The settings are fixed in advance by the central controller (30).

9. The method according to any one of claims 1 to 7, characterized in that, The method includes the following steps: - Based on the current vehicle speed (V) Ref ) and / or the limit (V) based on lane conditions min Adaptation is performed, preferably during the generation of local braking force requests (F). CMD ) and / or local regulator status information (Zustand RBV Adaptation should be performed beforehand.

10. The method according to any one of the preceding claims, characterized in that, At least the following methods and steps constitute a single adjustment operation and can be repeated during braking: - Provide braking force request (F DriverReq ), - Provides vehicle reference speed (V) Ref ) or the wheel speed of other wheels (V) x ), - Provides wheel speed (V) Rad ), - Provides wheel braking force (F Rad ), - Provides a limit value for wheel speed (V) min ), and / or - The local braking force request (F) is generated by the local braking control unit. CMD ) and / or local regulator status information (Zustand RBV ), Among them, the time for a single adjustment operation is less than 10 ms, preferably less than 5 ms, and especially preferably less than 1 ms.

11. The method according to any one of the preceding claims, characterized in that, The local braking control unit (21) includes at least one of the following adjustment technology modules: a module (22) for signal processing, a module (23) for preventing wheel lock-up, a module (24) for target wheel speed formation, or a module (25) for wheel speed adjustment.

12. The method according to the preceding claim, characterized in that, Different braking states of the wheels are defined by a module (23) for preventing wheel lock-up, specifically four different braking states: "inactive," "unstable," "holding," and "stable," wherein the module is used to determine the local braking force request (F). RBV The control strategy is selected based on the braking state.

13. A braking system (20), particularly for motor vehicles, said braking system being designed to perform a method for operating wheel brakes (40) according to any one of the preceding claims.

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