METHOD FOR GENERATING A TARGET VALUE, METHOD FOR CONTROLLING AN ACTUATOR, AND CONTROLLER

Abstract

A method for generating a target value of a position of an actuator of a brake of a wheel of a motor vehicle is disclosed. Values of another wheel are used and as a result a correction value which corrects a starting value is determined. As a result, a force sensor system on the wheel can be omitted. Further an associated method for controlling an actuator of a brake of a wheel of a motor vehicle and an associated control device are disclosed.

Claims

1. A method for generating a target value of a position of an actuator of a brake of a wheel of a motor vehicle comprising: determining a starting value based on a brake request, determining a correction value based at least on a wheel speed of the wheel, a wheel speed of another wheel and a slip scaling factor, and correcting the starting value using the correction value.

2. The method as claimed in claim 1, wherein the correction value is also determined based on a vehicle speed of the motor vehicle.

3. The method as claimed in e claim 1, further comprising calculating a target wheel speed for the wheel at which the wheel has a slip corresponding to a slip of the other wheel scaled by the slip scaling factor in order to calculate the correction value.

4. The method as claimed in claim 3, wherein the correction value is determined based on a difference between the target wheel speed and an actual wheel speed.

5. The method as claimed in claim 3, wherein the target wheel speed is calculated as follows in the presence of a value for the vehicle speed: (1slip scaling factor)*vehicle speed+slip scaling factor*wheel speed of the other wheel.

6. The method as claimed in claim 3, wherein the target wheel speed is calculated as follows in the absence of a value for the vehicle speed: slip scaling factor*wheel speed of the other wheel+offset.

7. The method as claimed in claim 1, wherein the correction value is reduced to zero based on its current value after it can no longer be determined.

8. The method as claimed in claim 7, wherein the reduction is carried out linearly or in accordance with a predetermined ramp.

9. The method as claimed in claim 1, wherein an actuating force on the other wheel is controlled based on at least one of: a measured value of the actuating force on the other wheel, and a measured value of the actuating force on the wheel is not used.

10. The method as claimed in claim 1, wherein, the correction value is one of added to the starting value and subtracted from the starting value during correction.

11. The method as claimed in claim 1, wherein the starting value is at least one of determined from the brake request using a predefined table or function, and is set to a predefined standby value in the absence of a brake request.

12. The method as claimed in claim 11, wherein, after a correction value or multiple correction values have been determined, a scaling factor is calculated based on at least one correction value and at least one starting value, and the table or function is scaled using the scaling factor.

13. The method as claimed in claim 1, wherein at least one of the wheel and the other wheel are associated with different axles, the wheel is a rear wheel and the other wheel is a front wheel, and wherein the wheel and the other wheel are on the same side.

14. A method for controlling an actuator of a brake of a wheel of a motor vehicle, wherein the method comprising: generating a target value of a position of the actuator by: determining a starting value based on a brake request, determining a correction value based at least on a wheel speed of the wheel, a wheel speed of another wheel and a slip scaling factor, and correcting the starting value using the correction value, determining a difference by subtracting an actual value of the position of the actuator from the target value, and determining a target rotational speed of the actuator based on the difference.

15. A control device for a brake of a wheel of a motor vehicle, wherein the control device is configured for carrying instructions for: determining a starting value based on a brake request, determining a correction value based at least on a wheel speed of the wheel, a wheel speed of another wheel and a slip scaling factor, and correcting the starting value using the correction value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] A person skilled in the art will gather further features from the exemplary embodiment described below with reference to the appended drawing. In the drawings:

[0041] FIG. 1 shows a block diagram,

[0042] FIG. 2 shows a graph of a function, and

[0043] FIG. 3 shows a further block diagram.

DETAILED DESCRIPTION

[0044] FIG. 1 shows a block diagram of a method according to an exemplary embodiment. FIG. 1 shows an overall view, where FIG. 3 shows a corresponding arrangement for the case that the method is activated.

[0045] It is generally assumed that electromechanical wheel brakes of a first axle, in this case the front wheel axle, are operated in a known manner, that is to say are controlled, for example, by means of a force sensor or a similar device. In this case, the corresponding brake application force, spreading force or braking torque is determined and adjusted or controlled by means of specific force or torque sensors according to the required deceleration request. The block diagram illustrated in FIG. 1 shows the overall arrangement for an electric brake actuator of a second axle, in this case the rear wheel axle, in which, for example, a motor speed control system which is not illustrated in FIG. 1 and which produces a motor speed target value or a target rotational speed of the actuator .sub.Mot,Soll as the target value and a motor target torque M.sub.Akt,Soll as manipulated variable for the actuator is subordinate to an actuator control system. It is essential in the arrangement shown that a controller structure in which the use of clamping force sensors or brake torque sensors is dispensed with is used.

[0046] In FIG. 2, for example for a better understanding of further consideration, the definition of the coordinate system under consideration here and the relationship between the brake application force or actuating force F.sub.SP and brake application travel X.sub.SP of the actuator is illustrated in the form of a characteristic curve, wherein, as an alternative to the brake application travel X.sub.SP (translational movement), a motor angle .sub.Akt or .sub.SP (rotational view) can also be considered. Both variables are clearly linked to one another, for example by a transmission gear of the electromechanical drive train. A contact position X.sub.SP=0 is determined, for example, during an initialization routine and is continuously corrected, even when the brake is actuated. Since no clamping force sensors are available, the determination of the contact detection is based, for example, on the consideration of the motor torque and takes into account the fact that the motor torque M.sub.Akt also increases as a result of the increase in force during the transition from free movement (driving in release clearance) to non-positive movement (application of the brake).

[0047] The basic idea of the arrangement illustrated in FIG. 1 is that the electromechanical brake is operated in a clamping force or spreading force control process and that the target value for the actuator position, determined from the force or braking torque target value and the relationship between the requested force and the corresponding position, is corrected by means of a wheel speed control process. In the further embodiments, the case of electromechanically actuated disk brakes, in which a deceleration request is converted into a brake application force to be applied, is considered here as an example. Transfer to electrically operated drum brakes is easily possible. It is also assumed that the first axle is the front axle and the second axle is the rear axle.

[0048] If there a deceleration request, that is to say a request for applying a defined brake application force or a defined braking torque in the form of a brake request F.sub.SP,Soll, the actuator is moved in the brake application direction from its rest position (idle position/standby position; see FIG. 2) in the direction of brake application. If there is no request or if an existing brake application request is reset again (target value=0), the actuator is transferred or held in an unactuated state in which a defined distance from brake pad to brake disk (release clearance) is set and maintained by the actuator so that there is no residual braking torque. In this case, in accordance with the arrangement according to FIG. 1, a selection parameter ModeSelect_1 is defined so that the actuator position sets the target position X.sub.Akt,Soll,Idle (ModeSelect_1=0). In this case, X.sub.Akt,Soll=X.sub.Akt,Soll,Ilde=X.sub.Standby thus holds true. In the event of a deceleration request, ModeSelect_1 is defined in such a way that the starting value X.sub.Akt,Soll=X.sub.Akt,Soll,FCtrl is determined for the actuator position controller (ModeSelect_1=1).

[0049] It is now proposed, according to this exemplary embodiment, during braking, to relate the braking forces of the first force-controlled or braking-torque-controlled axle to the braking forces of the second axle. This is done by means of rotational wheel speeds or wheel speeds. During braking, the wheel speed controller is activated as a correction controller for correcting X.sub.Akt,Soll by appropriately setting a selection parameter ModeSelect_2 (ModeSelect_2=1), for example when the function described herein is activated.

[0050] The target value for the wheel speed V.sub.Rad,H_s,Soll (with s=L for left or R for right) or rotational wheel speed .sub.Rad,H_s,Soll results from the wheel speed V.sub.Rad,V_s or the rotational wheel speed .sub.Rad,V_s of the wheel of the front wheel axle on the same side (v.sub.Rad=R.sub.dyn.sub.Rad; the wheel speed is considered as an example in the following text). It is proposed that this target value V.sub.Rad,H_s,Soll be determined for the wheel speed in such a way that a defined ratio between the wheel slip S.sub.V_s of the (force-controlled) electromechanical brake of the front wheel axle and the (force-controlled) electromechanical brake of the rear wheel axle on the same side is established. The following therefore applies:

[00001]$S_{H\_s,\mathrm{Soll}}={}_{S,\mathrm{Scale}}{S}_{V\_s}$$\mathrm{or}$$S_{H\_s,\mathrm{Soll}}={}_{S,\mathrm{Scale}}\left(\left(V_{\mathrm{Ref}}-V_{\mathrm{Rad},V\_s}\right)/V_{Ref}\right).$

[0051] S in this case basically refers to a slip. V denotes the wheel speed, index V indicates the front, H indicates the rear.

[0052] The parameter .sub.S,Scale where 0<.sub.S,Scale<1 represents, in particular, the required ratio between the slip of the front wheel and the slip of the rear wheel on the same side and can be specified from the point of view of driving dynamics and from the point of view of driving stability and, if necessary, adapted to the respective driving situation. This involves, for example, the slip scaling factor already mentioned above. The resulting target value for the wheel speed then results in:

[00002]$V_{\mathrm{Rad},H\_s,\mathrm{Soll}}=\left(1-{}_{S,\mathrm{Scale}}\right)V_{Ref}+{}_{S,\mathrm{Scale}}{V}_{\mathrm{Rad},V\_s}.$

[0053] Alternatively, or in the event that no or no valid vehicle reference speed or vehicle speed V.sub.Ref is available, the target value can also be calculated as follows:

[00003]$V_{\mathrm{Rad},H\_s,\mathrm{Soll}}={}_{S,\mathrm{Scale}}{V}_{\mathrm{Rad},V\_s}+v_{\mathrm{Rad},\mathrm{Offset}}.$

[0054] Here, too, a defined ratio between the rotational wheel speed of the front wheel and the rotational wheel speed of the rear wheel on the same side can be set through appropriate definition of the parameters. For example, an offset V.sub.Rad,Offset can be specified for this purpose.

[0055] The parameters described here for forming the target value for the wheel speed can also be changed dynamically during control of the wheel brake. This then takes place, for example, depending on the requirement of the function requiring braking.

[0056] The correction controller illustrated in FIG. 1 and FIG. 3 produces a correction value X.sub.Akt,Korr for the actuator position target value and starting value X.sub.Akt,Soll,FCtrl, respectively, based on the deviation between the target value and the actual value of the wheel speed. For example, this value is additively superimposed by the target value X.sub.Akt,Soll,FCtrl and thus brings about a correction of inaccuracies or changes in the model for the relationship X.sub.Akt=f(F.sub.SP). The result is a target value X.sub.Akt,Soll2 which represents an input variable for an actuator position controller. A linear controller with proportional-integral (PI) behavior is used as the structure for the correction controller. In principle however, other controllers can also be used. A differentiating component in the controller (PID) can also be added to increase the actuating dynamics in the event of rapid changes in the target value or actual value. In another embodiment (not shown here), the manipulated variable of the correction controller X.sub.Akt,Korr can still be limited to minimum and maximum permissible values.

[0057] If there is a request for wheel-specific brake interventions which are not able or only with difficulty are able to be represented by means of the function f(X) shown in FIG. 1 and described here, or if the wheel speed signal is in the range of low speeds or close to standstill, where the signal quality is not sufficient for finely meterable brake actuation due to the limited resolution, the correction controller is deactivated by setting ModeSelect_2=0, so that only the force control remains active. The correction actuator position X.sub.Akt,Korr requested at the time of deactivation is ensured (X.sub.Akt,Korr,null) and reduced to a value of zero during further actuation of the wheel brake depending on the actuator position X.sub.Akt. For this purpose, when the correction controller is deactivated, the actuator position present at this point in time is typically also stored (X.sub.Akt,null). The correction reduction function illustrated in FIG. 1 is activated and reduces the correction position X.sub.Akt,Korr so far when values for X.sub.Akt become smaller that the correction position or the correction value X.sub.Akt,Korr is also reduced to the value zero until the actuator position X.sub.Akt=0 is reached. This is illustrated in FIG. 1 by a reduced correction value X.sub.Akt,Korr,Reduce.

[0058] The basic characteristic curve illustrated in FIG. 2 can be adjusted using the correction values X.sub.Akt,Korr that were determined by the correction controller during braking. A characteristic curve correction parameter K.sub.k which can also be referred to as a scaling factor and which can be determined based on the correction values is used for this purpose. The following then applies:

[00004]$X_{\mathrm{Akt},\mathrm{Soll},\mathrm{FCtrl}}+X_{\mathrm{Akt},\mathrm{Korr}}=K_k{X}_{\mathrm{Akt},\mathrm{Soll},\mathrm{FCtrl}}.$

[0059] If a defined minimum value for the target position of the actuator X.sub.Akt,Soll,FCtrl,min>0 is considered, then the following applies:

[00005]$K_k=\left(X_{\mathrm{Akt},\mathrm{Soll},\mathrm{FCtrl}}+X_{\mathrm{Akt},\mathrm{Korr}}\right)/X_{\mathrm{Akt},\mathrm{Soll},\mathrm{FCtrl}}.$

[0060] According to this equation, the characteristic curve correction parameter K.sub.k can be determined as described above in each controller loop during actuation of an electromechanical brake and with the correction controller activated (ModeSelect_1=1). The value determined in this way is for example filtered again to smooth out fluctuations and interference excitation. Filters which may be used are those which have a diminishing memory or only a limited memory. The simplest form of such a filter with a limited memory represents the determination of a sliding mean value from the last n previous values. The value K.sub.k,Filt is then obtained. The calculation of the new characteristic curve correction value is carried out after braking has been completed if there is no deceleration request and the actuator position is in the release clearance. In this case, Mode Select_1=0, and X.sub.Akt,Soll=X.sub.Akt,Soll,Idle=X.sub.Standby then applies to the requested actuator position.

[0061] The model or characteristic curve F.sub.SP=f(X.sub.Akt) is then adapted, for example, if the determined correction value K.sub.k,Filt deviates by a specific value of 1.0, for example if Abs(1.0K.sub.k,Filt)> applies, where represents a threshold value. If this is the case, the supporting points X.sub.Akt,i of the characteristic curve F.sub.SP=f(X.sub.Akt) or the model parameters which depend on the position are updated for example. If the characteristic curve is mapped using a number of interfaces, the following applies:

[00006]$X_{\mathrm{Akt},i}=K_{k,\mathrm{Korrektur}}{X}_{\mathrm{Akt},i}.$

[0062] The index i here means the i-th interface of the characteristic curve i=1 . . . n).

[0063] In the embodiment shown, it is proposed to determine the correction parameter K.sub.k,Korrektur from K.sub.k,Filt via the relationship illustrated below:

[00007]$K_{k,\mathrm{Korrektur}}=K_{k,\mathrm{Filt}}+\left(1-\right)1..$

[0064] The parameter (0<<1) in this case determines the extent to which correction values determined during braking are taken into account, where it holds true that for =0 there is no correction and for =1 the specified value for K.sub.k,Filt is adopted at 100%. When defining , a compromise can be found here, for example, between great adaptation dynamics and sufficiently good filtering and stability of the model.

[0065] Mentioned steps of the method can be executed in the specified order. However, they can also be executed in a different order, if technically feasible. The method can be executed in one of its embodiments, for example with a specific set of steps, in such a way that no further steps are executed. However, further steps can also be executed in principle, even those that are not mentioned.

[0066] It is pointed out that features may be described in combination in the claims and in the description, for example in order to facilitate understanding, even though these can also be used separately from one another. A person skilled in the art will recognize that such features may also, independently of one another, be combined with other features or combinations of features.

[0067] Dependency references in dependent claims may characterize combinations of the respective features but do not exclude other combinations of features.