Coordination of a vehicle dynamics control system with other vehicles stability systems

The present invention relates to a vehicle dynamics control system.

Vehicle dynamics control systems, such as the ESP (electronic stability program), are used to improve the controllability of motor vehicles in critical driving situations, e.g., during oversteering when cornering, and to stabilize the vehicle. Known vehicle dynamics control systems include a control unit which includes a control algorithm for executing a float angle regulation and/or a yaw speed regulation, as well as a series of sensors which provide measured values about the vehicle's current driving state. Different setpoint variables are calculated from the driver inputs, in particular the steering wheel position, the accelerator pedal position, and the brake operation. If the deviation of the vehicle's actual behavior from its setpoint behavior is too great, the vehicle dynamics control system intervenes in the driving operation and creates a compensating yaw moment which counters the vehicle's yaw motion. For this purpose, the vehicle dynamics control system normally uses the vehicle brakes and/or the engine management as actuators.

In addition to a vehicle dynamics control system, modern vehicles oftentimes also include other systems which may also intervene in the driving operation for the purpose of vehicle stabilization, such as an active steering system AFS (active front steering), an active chassis ARC (active roll compensation), or a system for actively influencing the tire properties. Such systems are referred to in the following as “vehicle stability systems.” They normally include their own control electronics (control unit) and their own actuators, such as a steering actuator, via which the steering angle may be adjusted, an active spring-and-shock-absorber unit for influencing the tire contact forces, or other actuators via which the vehicle's handling properties may be influenced.

The mentioned vehicle stability systems also determine different setpoint values of driving state variables, such as a setpoint yaw rate or a setpoint float angle, and calculate from the deviation a necessary stabilizing intervention, such as a change in the steering angle or a change in the wheel contact force on predefined wheels. The calculated values are implemented via the appropriate actuators and influence the vehicle's handling properties. Since the vehicle dynamics control system ESP as well as the other vehicle stability systems (e.g., AFS, ARC) execute stabilizing interventions, it is possible for the systems to constrain or block one another.

FIG. 1 shows a controller structure for a stability system known from the related art which has an active steering system AFS and an active chassis ARC in addition to a vehicle dynamics control system ESP. Systems ESP, AFS, and ARC each include a separate control unit 1 , 2 , 3 which each include a control algorithm 4 , 5 , 6 . Algorithms 4 - 6 each include in a known manner an “observer” B in which different state variables, such as the float angle or the wheel slip angle, are estimated, a unit So for calculating setpoint values of the regulation, a setpoint yaw rate for example, and a state controller ZR which generates a controller output variable y which is converted into an actuating request for different actuators 8 . Controller output variables ya-yc are transferred to appropriate actuators 8 or associated electronics 1 , 3 via interfaces 7 . Vehicle 10 forms the control path of the control system.

The driving state is recorded by different sensors which are combined here in a block 11 . The corresponding sensor signals are supplied as actual values to algorithms 4 - 6 of control systems AFS, ESP, ARC.

Such a parallel controller structure has the disadvantage that multiple control algorithms 4 - 6 are present, at least partially. This is an expensive proposition since, in addition to the control algorithms, the necessary security software must also be implemented several times. Moreover, individual control systems AFS, ESP, ARC may pursue different control targets, thereby constraining or blocking one another.

Therefore, it is the object of the present invention to create a method and a device for stabilizing a vehicle in critical driving situations which have a particularly simple design and operate reliably.

The object of the present invention is achieved by the features specified in Claim 1 and Claim 8 . Further embodiments of the present invention are the object of the subclaims.

A fundamental aspect of the present invention is to create an advanced vehicle dynamics control system (VDM) which, in addition to the brake system and the engine management, is able to also address other actuators, and to provide this system with only one single control algorithm which generates one controller output variable (e.g., a yaw moment) from which an actuating request for an actuator (i.e., the brake system or the engine management) of the vehicle dynamics control system as well as for an actuator (e.g., a steering actuator or an active spring-and-shock-absorber unit) of at least one additional vehicle stability system is derived. This has the substantial advantage that only one central control algorithm is present, and its controller output variable is implemented by one or multiple actuators. Such a central control is particularly easily implementable and particularly safe and reliable.

The appropriate control algorithm may be implemented, for example, in the control unit of the vehicle dynamics control system (e.g., ESP). The previously present vehicle dynamics control algorithm (ESP) needs to be only marginally retrofitted and adjusted for this purpose. No separate stability control is to be carried out in the additional vehicle stability systems, such as AFS or ARC.

The control algorithm of the advanced vehicle dynamics control system (VDM) preferably includes a distribution unit which generates from a controller output variable an actuating request for an actuator (i.e., the brake system or the engine management) of the vehicle dynamics control system as well as an actuating request for an actuator of an additional vehicle stability system.

The vehicle stability system may include, for example, an active steering system (AFS), an active chassis system (ARC), and/or another system which, for vehicle stabilization purposes, may actively intervene in the driving operation.

The control algorithm preferably includes a yaw rate controller; in this case, the controller output variable would be a yaw moment or a variable proportional thereto.

According to a preferred embodiment of the present invention, the distribution unit is implemented in such a way that an actuating request for a first actuator (e.g., an active spring-and-shock-absorber unit) is derived from the controller output variable, and that a residual value of the controller output variable is determined from the controller output variable and the actuating request actually implementable by the actuator, and that an actuating request for a second actuator (e.g., a steering actuator) is generated from the residual value. This means that the part of the control intervention which cannot be implemented by the first actuator (e.g., an active spring-and-shock-absorber unit) is implemented by a second actuator (e.g., an active steering system or an active brake system) or by additional actuators if needed.

FIG. 1 shows a vehicle dynamics control system known from the related art having control algorithms which operate in parallel.

FIG. 2 shows an advanced vehicle dynamics control system having additional actuators.

FIG. 3 shows a detailed view of the vehicle dynamics control system of FIG. 2 .

FIG. 4 shows an exemplary embodiment of a unit for distributing the controller output variable.

FIG. 5 shows the calculation of a superimposed steering angle from the controller output variable.

FIG. 6 shows an example of a hardware architecture for an advanced vehicle dynamics control system.

Regarding the explanation of FIG. 1 , reference is made to the preamble of the description.

FIG. 2 shows an advanced vehicle dynamics control system VDM which has the ability, for vehicle stabilization purposes, to control additional actuators—steering actuator 8 a of an active steering system and spring-and-shock-absorber unit 8 c of an active chassis in this case—in addition to the vehicle's engine management and brake systems. The vehicle dynamics control system includes a control algorithm which is schematically depicted by blocks 4 d - 6 d.

Reference numeral 4 d indicates an “observer,” reference numeral 5 d indicates a unit for the setpoint value calculation which determines a setpoint yaw rate in particular, and reference numeral 6 d indicates a state controller whose controller output variable ΔM GiSo is a yaw moment or a variable proportional thereto.

The control algorithm also includes a distribution unit 9 which converts controller output variable ΔM GiSo into different actuating requests ΔF Nstab , δ stab , M stab , where ΔF Nstab is a change in the wheel contact force, δ stab is a superimposed steering angle, and P wheelsetpoint is a brake force. The individual actuating requests are transferred to control units 1 , 3 of active steering system AFS, active chassis ARC, and the electronics of an active brake system 8 b via interfaces 7 a - 7 c . Control units 1 , 2 subsequently control corresponding actuators 8 a , 8 c . The modified actual state of vehicle 10 is recorded via a sensor 11 .

Unlike known vehicle dynamics control algorithms (e.g., ESP), this advanced system VDM may address one or multiple different actuators 8 without coming into conflict with other systems. The vehicle's handling properties may be influenced by controlling steering actuator 8 a or an active spring-and-shock-absorber unit 8 c.

Since the additional stability systems (AFS, ARC, etc.) influence the vehicle's handling properties, information about the state of these actuators 8 , such as information about the actual steering angle or information about the calibration of spring-and-shock-absorber unit 8 c , must be supplied to control algorithm 4 d - 6 d . Vehicle dynamics control algorithm 4 d - 6 d would otherwise carry out the control on the basis of wrong parameters (e.g., only based on the steering wheel angle, but not based on the steering angle at the wheel), which may result in erroneous brake and engine interventions.

FIG. 3 shows an advanced vehicle dynamics control system VDM in detail. The overall system includes vehicle 10 as the control path, sensors 12 for determining the controller input variables, actuators 18 a - 18 e for influencing the handling properties, as well as a hierarchically structured controller 4 , 5 , 6 , 9 a , 13 , 14 including a superimposed vehicle dynamics controller 6 (state controller) and a subordinate brake and drive slip controller 14 . The controller functions are implemented in control unit 2 of vehicle dynamics control system ESP in the form of software.

The configuration and the function of such a vehicle dynamics controller are widely known from the related art so that only the essential functions and in particular the differences with respect to known controllers are discussed in the following. The actual values of the regulated state variables (yaw speed, float angle) are determined in “observer” 4 . The setpoint values of the state variables are calculated in a unit 5 for the setpoint value calculation.

Superimposed controller 6 carries out a yaw speed and/or float angle regulation in a known manner and generates a controller output variable ΔM GiSo in the form of a yaw moment or a variable proportional thereto. Part of controller output variable ΔM GiSo is converted into a setpoint slip λ So and supplied to subordinate brake and drive slip controller 14 . Setpoint slip λ So , calculated for the individual wheels, is converted into corresponding instructions P wheelsetpoint , M SoMot for the actuators “brake hydraulics” 18 a and “engine management” 18 b which adjust the required brake and drive forces on the individual wheels. Another part of controller output variable ΔM GiSo , is converted into moments ΔM zx which are implemented by actuators 18 c - 18 e of additional subsystems (AFS, SRC, etc.). The distribution of controller output variable ΔM GiSo to individual subsystems 1 , 3 , 15 - 18 e may basically be adjusted in any way, depending on how forceful the intervention of the individual subsystems should be. The vehicle dynamics control system is designed in such a way that the control intervention may be implemented by one or multiple subsystems 18 a - 18 e.

In this case, the subsystems include an active steering system AFS having a control unit 1 and a steering actuator 18 e , an active chassis having a control unit 3 and an actuator 18 d , a further optional subsystem having a control unit 17 and an associated actuator 18 c , an engine management having a control unit (Motronic) 16 and an actuator 18 b , and a brake system having electronics 15 and brake hydraulics 18 a as actuators.

Unlike known vehicle dynamics control systems, the vehicle dynamics controller includes a function block 9 a - 9 e which is used to distribute controller output variable ΔM GiSo to subsystems 1 , 3 , 15 - 18 e . For this purpose, block 9 a initially generates partial variables ΔM zx from controller output variable ΔM GiSo , partial variables ΔM zx being implemented by actuators 18 a - 18 c of subsystems AFS, ESP, ARC, etc. Partial variables ΔM zx are calculated by units 9 b - 9 e into corresponding actuating requests, such as a change in wheel contact force ΔF Nstab for a wheel, a superimposed steering angle δ stab , a steering torque M stab , or another control value ΔX for another optional subsystem 17 , 18 c.

Individual actuating requests P wheelsetpoint , M SoMot , ΔX, ΔF Nstab , δ stab , M stab are supplied to control units 1 , 3 , 17 and control electronics 15 , 16 via predefined interfaces (not shown). Actuating requests P wheelsetpoint , M SoMot , ΔX, ΔFN stab , δ stab , M stab are subsequently converted into corresponding electrical control signals for individual actuators 18 a - 18 e.

Necessary control intervention ΔM GiSo may basically be distributed in any way to the different subsystems 1 , 3 , 15 - 18 e . However, a larger part of the overall control intervention is preferably assigned to individual systems, such as an active suspension ARC, than to other systems.

FIG. 4 shows a preferred embodiment of a distribution unit 9 which converts controller output variable ΔM GiSo into multiple actuating requests ΔFN stab , δ stab , Δλ for different subsystems 1 , 3 , 15 . Controller output variable ΔM GiSo is initially converted into wheel contact forces F for the individual wheels of vehicle 10 using a unit 31 . Downstream unit 32 limits calculated values F if the values are not able to be implemented directly for reasons of the efficiency of active suspension ARC 3 . For this purpose, values F and/or their gradient are/is reduced when predefined limits are exceeded. Resulting actuating request ΔFN stab may thus accept only values which are able to be implemented by actuator 18 d of the active suspension.

Value ΔFN stab is conveyed to active suspension 3 where a corresponding control intervention is effected. The part of controller output variable ΔM GiSo which is not able to be implemented by active chassis 3 is determined as a residual value ΔM GiSo — AFS . A unit 33 is provided for this purpose which converts the implementable actuating request ΔFN stab back into a variable ΔM GiSo — ARCO of the unit of controller output variable ΔM GiSo . At node 39 , the difference between controller output variable ΔM GiSo and estimated variable ΔM GiSo — ARCO is calculated and residual value ΔM GiSo — AFS is formed.

Residual value ΔM GiSo — AFS in turn is subsequently converted into an actuating request δ stab for steering actuator 18 e of an active steering system AFS 1 via a unit 34 . If needed, this value δ stab is limited via a unit 35 . Actuating request δ stab (in this case a superimposed steering angle) is supplied to active steering system 1 and to a unit 36 which determines the part which is able to be implemented by active steering system AFS 1 .

A residual value ΔM GiSo — AB , which is supplied to active brake system 15 , is in turn calculated from setpoint request ΔM GiSo — AFS and the actually implementable request ΔM GiSo — AFSO . This residual moment ΔM GiSo — AB is converted into a wheel slip λ via a unit 37 and limited via unit 38 . Resulting setpoint slip λ stab is finally converted by active brake system 15 into a corresponding brake intervention.

The distribution of controller output variable ΔM GiSo is illustrated here as an example for only three different subsystems 1 , 3 , 15 . The control intervention may basically be distributed to any number of subsystems in any sequence.

Another embodiment of a distribution unit 9 may be implemented, for example, in such a way that controller output variable ΔM GiSo is supplied to multiple subsystems 1 , 3 , 15 - 18 e and implemented in a weighted manner. Depending on the preference, subsystems 1 , 3 , 15 - 18 e may take on different portions, e.g., 60% by the active suspension ARC, 30% by the active steering system AFS, and 10% by brake system 15 .

FIG. 5 shows the calculation of superimposed steering angle δ stab from controller output variable ΔM GiSo as it may be carried out in control unit 2 , for example. Controller output variable ΔM GiSo is initially supplied to a low-pass filter 21 and a filtered variable ΔM GiSof is generated. This variable ΔM GiSof is converted into a steering angle δ Raw via a unit 22 . This raw value δ Raw is again bandwidth-limited in downstream unit 23 and a value δ ToZo is generated. The bandwidth of filter 23 is dependent on friction factor μ which is incorporated in filter function F via a characteristic curve 25 . Block 25 generates a parameter P ToZo which changes filter function F as a function of friction factor μ.

Filtered steering angle δ ToZo is finally scaled using a unit 24 , whereby the superimposed steering angle, i.e., steering angle change δ stab to be set, is maintained. The scaling is in turn dependent on friction factor μ which is incorporated in scaling function 24 via a characteristic curve 26 .

FIG. 6 shows a possible hardware architecture for the advanced vehicle dynamics control system VDM. The system includes two data buses 19 , 20 , multiple sensors 27 - 30 as well as different control units 1 , 2 , 3 being connected to first bus 19 , also known as the chassis CAN. Indicated control units 1 , 2 , 3 are also connected to the other data bus 20 , also known as the power train CAN. An engine management (Motronic) 16 and a control unit 31 for a speed controller ACC are additionally connected to data bus 20 .

The sensors include redundantly embodied yaw speed and transverse acceleration sensors 27 , a steering wheel angle sensor 28 , and a steering angle sensor 29 , as well as additional optional sensors 30 . Actuating requests ΔF Nstab , δ stab , Δλ for active steering system AFS 1 , active chassis ARC 3 , and possibly additional subsystems 17 generated by VDM control unit 2 are preferably conveyed via bus 19 , since this bus is typically less overloaded and carries fewer interference signals than power train CAN 20 .

1 AFS control unit

2 VDM control unit

3 ARC control unit

4 observer

5 setpoint value calculation

6 state controller

7 interfaces

8 subsystems

9 distribution unit

10 vehicle

11 sensor signals

12 sensors

13 setpoint slip and blocking moment calculation

14 brake and drive slip controller

15 hydraulic control

16 motronic

17 control unit

18 actuators

19 chassis CAN

20 power train CAN

21 low-pass filter

22 conversion unit

23 filter

24 scaling unit

25 characteristic curve

26 characteristic curve

27 yaw speed and transverse acceleration sensors

28 steering wheel angle sensor

29 steering angle sensor

30 optional sensor

31 conversion unit

32 limiting unit

33 estimator

34 conversion unit

35 limiting unit

36 estimator

37 conversion unit

38 limiting unit

Y controller output variable

M GiSo yaw setpoint moment

ΔF Nstab change in the wheel contact force

δ stab steering angle change

M stab steering moment

ΔX actuating request