METHOD FOR DETERMINING AN OPERATING VARIABLE OF A DRUM BRAKE, DRUM BRAKE ASSEMBLY

Abstract

A method for determining an operating variable of a drum brake comprises actuating the brake in at least one of: a first wheel speed range and a second wheel speed range. The operating variable is calculated based on bearing force of a leading brake shoe and the further bearing force of a trailing brake shoe when in the first wheel speed range. The operating variable is calculated when in the second wheel speed range based on a current actuator position and an actuator contact position, in which brake shoes of the drum brake come into engagement with a drum of the drum brake.

Claims

1-15. (canceled)

16. A method for determining an operating variable of a drum brake comprising: actuating the brake with an electromechanical actuator in at least one of: a first wheel speed range and a second wheel speed range, wherein wheel speeds of the first wheel speed range are higher than wheel speeds of the second wheel speed range; determining at least one bearing force of a leading brake shoe and a further bearing force of a trailing brake shoe of the drum brake when in the first wheel speed range; calculating the operating variable when in the first wheel speed range based on the bearing force and the further bearing force; determining at least one current actuator position when in the second wheel speed range; and calculating the operating variable when in the second wheel speed range based on the actuator position and an actuator contact position, in which brake shoes of the drum brake come into engagement with a drum of the drum brake.

17. The method as claimed in claim 16, wherein the operating variable in the case of a rotating drum of the drum brake is a braking torque.

18. The method as claimed in claim 16, wherein calculating the operating variable further comprises calculating the difference between the bearing force and the further bearing force in the first wheel speed range.

19. The method as claimed in claim 18, wherein when the direction of rotation is unknown, wherein calculating the operating variable further comprises calculating the difference between the higher of the bearing force and the further bearing force minus the lower of the bearing force and the further bearing force.

20. The method as claimed in claim 16, wherein, wherein calculating the operating variable further comprises calculating a product of a first multiplier and a function in the second wheel speed range, and wherein a difference between the actuator position and the actuator contact position is an input variable of the function.

21. The method as claimed in claim 20, further comprising: calculating the first multiplier as a quotient with a dividend and a divisor; calculating the dividend as the average of a difference between a bearing force and a further bearing force over a predetermined period of time; and calculating the divisor as the average of the function over a predetermined value range.

22. The method as claimed in claim 20, wherein the function rises exponentially.

23. The method as claimed in claim 16, wherein a transition from the first wheel speed range to the second wheel speed range takes place below a predetermined wheel speed threshold.

24. The method as claimed in claim 16, wherein calculating the operating variable at a standstill is the same as calculating in the second wheel speed range when braking to a standstill with the drum brake in the applied state.

25. The method as claimed in claim 24, wherein the operating parameter at a standstill is a clamping force.

26. The method as claimed in claim 16, wherein calculating the operating variable further comprises calculating a product of a second multiplier and the higher of the bearing force and the further bearing force when actuating the drum brake out of the released state at a standstill.

27. The method as claimed in claim 26, wherein calculating the second multiplier further comprises calculating quotient of a maximum achievable torque-free clamping force divided by a maximum bearing force difference.

28. The method as claimed in claim 16, wherein a transition from one of the second wheel speed range and a standstill to the first wheel speed range takes place when a predetermined wheel speed threshold plus a hysteresis is exceeded.

29. The method as claimed in claim 16, further comprising measuring at least one of the bearing force at a supporting bearing for the brake shoe, and the further bearing force at a further supporting bearing for a further brake shoe.

30. A drum brake assembly, comprising: at least one brake shoe and one further brake shoe; at least one supporting bearing for the brake shoe and one further supporting bearing for the further brake shoe; at least one force sensor at the supporting bearing which measures a bearing force produced in the supporting bearing by the brake shoe; at least one further force sensor at the further supporting bearing which measures a further bearing force produced in the further supporting bearing by the further brake shoe, and an evaluation device which executes a method for determining an operating variable of a drum brake comprising: actuating the brake with an electromechanical actuator in at least one of: a first wheel speed range and a second wheel speed range, wherein wheel speeds of the first wheel speed range are higher than wheel speeds of the second wheel speed range; determining at least one bearing force of a leading brake shoe and a further bearing force of a trailing brake shoe of the drum brake when in the first wheel speed range; calculating the operating variable when in the first wheel speed range based on the bearing force and the further bearing force; determining at least one current actuator position when in the second wheel speed range; and calculating the operating variable when in the second wheel speed range based on the actuator position and an actuator contact position, in which brake shoes of the drum brake come into engagement with a drum of the drum brake.

31. The brake assembly as claimed in claim 30, wherein the operating variable in the case of a rotating drum is a braking torque.

32. The brake assembly as claimed in claim 30, wherein the operating variable is the difference between the bearing force and the further bearing force in the first wheel speed range.

33. The brake assembly as claimed in claim 30, wherein the operating variable is a product of a first multiplier and a function in the second wheel speed range, and wherein a difference between the actuator position and the actuator contact position is an input variable of the function.

34. The brake assembly as claimed in claim 33, wherein the first multiplier as a quotient with a dividend and a divisor, the dividend is an average of a difference between a bearing force and a further bearing force over a predetermined period of time, and the divisor is an average of the function over a predetermined value range.

35. The brake assembly as claimed in claim 30, wherein the operating parameter at a standstill is a clamping force.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0028] FIG. 1 shows a detail of a drum brake assembly;

[0029] FIG. 2 shows a state diagram;

[0030] FIG. 3 shows processing of input variables to give output variables; and

[0031] FIG. 4 shows function curves.

DETAILED DESCRIPTION

[0032] FIG. 1 schematically shows a part of a drum brake assembly 10 having a drum brake 15. The drum brake assembly 10 has a brake shoe 20 and a further brake shoe 25. It has a brake drum 30, wherein the two brake shoes 20, 25 can be pressed against the brake drum 30 to actuate the drum brake assembly 10. An actuator 40 is used for this purpose. This is actuated electrically.

[0033] The drum brake assembly 10 has a supporting bearing 50 and a further supporting bearing 55. Here, the brake shoe 20 is supported on the supporting bearing 50. The further brake shoe 25 is supported on the further supporting bearing 55. Arranged in the supporting bearing 50 is a force sensor 51 for measuring a bearing force with which the brake shoe 20 is supported in the supporting bearing 50. Arranged in the further supporting bearing 55 is a further force sensor 56 for measuring a further bearing force with which the further brake shoe 25 is supported in the further supporting bearing 55.

[0034] The drum brake assembly 10 furthermore has an evaluation device 60, which is here illustrated only schematically. This is designed to execute a method according to the invention. One possible embodiment will be described below.

[0035] The forces measured in the supporting bearings 50, 55, which are supporting forces, are designated as F.sub.Ab,Aufl for the leading shoe and F.sub.Ab,Abl for the trailing shoe. These can assume widely differing values for the same actuator position. This can make it necessary to implement rescaling of the output values for force feedback, and therefore an operating state of the drum brake assembly 10 is taken into account only in an actual value calculation and not in a setpoint value calculation and a parameter adjustment of a force controller that is used. Here, a braking torque M.sub.Br can be calculated as follows, for example:

M.sub.Br=m.sub.l*(F.sub.Ab,Aufl−F.sub.Ab,Abl)=m.sub.l*ΔF

[0036] In this context, m.sub.l designates a predeterminable parameter and ΔF designates a force difference.

[0037] The force difference ΔF can be used, for example, as a controlled variable for the closed-loop or open-loop control of the drum brake 15.

[0038] In the case of a relatively high wheel speed ω.sub.Rad which is in a first wheel speed range including all the wheel speeds ω.sub.Rad above a threshold ε, a controlled variable F.sub.Ctrl can be calculated as follows as an operating parameter by means of the force difference and the forces measured in the supporting bearings 50, 55:

F.sub.Ctrl=ΔF=F.sub.Ab,Aufl−F.sub.Ab,Abl

[0039] If there is no information on the direction of rotation for the wheel speed ω.sub.Rad, the allocation of the two forces F.sub.Ab,S1 and F.sub.Ab,S2 measured in the supporting bearings 50, 55, which are generalized forms of the forces for the case where the leading and the trailing brake shoe have not yet been identified, can be performed by means of a maximum value and minimum value determination. The following then applies:

F.sub.Ctrl=ΔF=Max{F.sub.Ab,S1,F.sub.Ab,S2}−Min{F.sub.Ab,S1,F.sub.Ab,S2}

[0040] In the transitional range to particularly low wheel speeds ω.sub.Rad which are below the abovementioned threshold value ε, the curve of the forces is not clearly defined since dynamic compensating processes are taking place here. Depending on how powerful the braking is, there may be a brief reversal of the torques. On completion of this compensating process, F.sub.Ab,Aufl≈F.sub.Ab,Abl is approximately the case. As regards the calculation of the operating parameter, a force signal calculated from a characteristic curve is therefore determined as follows in this transitional range:

F.sub.Ctrl=K.sub.1*f(X.sub.Sp−X.sub.0)

[0041] Here, K.sub.1 designates a first multiplier, f designates a function, X.sub.Sp designates a current actuator position, and X.sub.0 designates an actuator contact position, in which the brake shoes 20, 25 just rest by means of their respective linings against the brake drum 30.

[0042] To enable a changeover between the wheel speed ranges to take place without jumps, given a constant specified force, the force/displacement characteristic curve or function f used is preferably updated before the changeover by determining the first multiplier K.sub.1 as a scaling parameter. A basis for this relationship is, for example, a characteristic curve which has been measured at a standstill in the torque-free state. In the present case, the following applies for the scaling factor or first multiplier K.sub.1, which is preferably to be determined at low wheel speeds:

K.sub.1=Average{ΔF}/Average{f(X.sub.Sp−X.sub.0)}

[0043] This allows virtually or completely jump-free calculation of the operating parameter. In this case, the force difference obtained in this process is typically calculated over a predetermined period of time, e.g. before the respective calculation. The function f is typically calculated over a predetermined value range of X.sub.Sp.

[0044] For the case of standstill, i.e. ω.sub.Rad=0, a distinction is drawn as to whether actuation of the drum brake assembly 10 takes place after braking by the drum brake assembly 10 or whether the vehicle has come to a standstill independently thereof.

[0045] In the first case, in which the vehicle has been braked by means of the drum brake assembly 10, the calculation continues to be formed under force control to avoid dealing with special cases, and therefore the signal calculated from a characteristic curve or function continues to be determined as the operating parameter or controlled variable:

F.sub.Ctrl=K.sub.1*f(X.sub.Sp−X.sub.0)

[0046] If, when at a standstill, the actuation of the drum brake assembly 10 takes place from a previously released state, then, as the feedback signal, the higher of the two force values is determined because F.sub.Ab,Aufl≈F.sub.Ab,Abl:

F.sub.Ctrl=K.sub.2*Max{F.sub.Ab,S1,F.sub.Ab,S2}

[0047] In this case, a second multiplier K.sub.2 is defined in such a way that, for the case of a standstill and torque-free actuation, an achievable maximum supporting force at the design point corresponds approximately to the maximum differential force at the design point.

[0048] FIG. 2 shows a state diagram in which the four states already mentioned are illustrated.

[0049] State 1 is the case in which the wheel speed ω.sub.Rad is in a typical normal operating range during driving, and the wheel speed ω.sub.Rad is therefore in the first wheel speed range. In this case, calculation of the operating parameter can be performed based on a difference between the leading force and the trailing force.

[0050] If the wheel speed ω.sub.Rad undershoots the threshold value ε, state 2 occurs. A return to state 1 is envisaged only if the wheel speed exceeds the threshold value ε plus a hysteresis ε.sub.Hysterese. Continuous switching backward and forward between states and calculation methods stored in the states is thereby avoided in a transitional range.

[0051] In state 2, which corresponds to the second wheel speed range, calculation is performed as described above based on the function f and the actuator position X.sub.Sp as well as the actuator contact position X.sub.0.

[0052] If the braking forces F.sub.Ab,Aufl and F.sub.Ab,Abl are approximately equal or if, in the present implementation, a predetermined transition time has expired, the procedure switches to state 3. In this case, it is assumed that the wheel speed ω.sub.Rad is equal to zero, that is to say the vehicle is stationary. In this case, in which the vehicle has been braked by means of the drum brake assembly 10, the calculation is not modified, however.

[0053] In a development, the provision of state 3 opens up the possibility in this state of once again using the forces to determine the operating variable. Here too, a further adaptable scaling factor, which ensures switching over without signal jumps, can preferably be provided for this purpose. Otherwise, as described here, the calculation can be carried out in accordance with state 2.

[0054] State 4 corresponds to a case in which the vehicle comes to a standstill independently of the drum brake assembly 10, that is to say, for example, merely coasts to a halt, and the drum brake assembly 10 is only then actuated. In this case, different force conditions apply since the self locking of the drum brake 15 is not active. In this case, calculation of the operating parameter takes place based on the higher of the two measured forces, as already described above.

[0055] Moreover, state 4 can also be reached directly from state 2 if the vehicle comes to a standstill in a corresponding manner.

[0056] As shown, state 1 is fundamentally adopted when the wheel speed ω.sub.Rad exceeds the threshold value ε plus a predeterminable hysteresis ε.sub.Hysterese.

[0057] By means of the sequence shown or states shown, it is possible to ensure that an operating parameter of the drum brake assembly 10 is always calculated with the best possible available calculation method.

[0058] FIG. 3 shows schematically one possible calculation of output variables from input variables. Here, the already explained forces F.sub.Ab,Aufl and F.sub.Ab,Abl, which, in the case of an unknown direction of rotation, may also be designated as F.sub.Ab,S1 and F.sub.Ab,S2, serve as input variables. Also serving as input variables are the wheel speed ω.sub.Rad, the direction (Dir_ω.sub.Rad), the actuator position X.sub.Aktuator or X.sub.Sp, the actuator contact position X.sub.Aktuator, Kontakt or X.sub.0 and the information eDB_Betätigt, which indicates whether the drum brake assembly 10 is currently being actuated. In particular, the calculation produces the already mentioned operating parameter F.sub.Ctrl and an associated status.

[0059] FIG. 4 shows a typical curve of the function f, which has already been described above. Here, the available movement range or working range of the actuator 40 is shown on the horizontal axis. Here, the entire working range available is denoted by the double arrow VAB. The actually usable movement range from the origin illustrated is denoted as VB.

[0060] On the one hand, the diagram shows the function f(X) in its original form, which becomes the function f(X−X.sub.0) when shifted to the right by the amount of the actuator contact position X.sub.0. Starting from this function curve, the function can be scaled up or down, namely by means of the first multiplier K.sub.1, two function curves with different values of K.sub.1 being shown in FIG. 4. It is thereby possible to adapt the function f accordingly. As shown, the function f rises more sharply than a linear function, this having proven feasible and appropriate for typical applications.

[0061] The mentioned steps of the method may be carried out in the order indicated. However, they may also be carried out in a different order, if this is technically appropriate. In one of its embodiments, for example with a specific combination of steps, the method according to the invention may be carried out in such a way that no further steps are carried out. However, in principle, further steps can also be carried out, even steps that have not been mentioned.

[0062] It is pointed out that features may be described in combination in the claims and in the description, for example to facilitate understanding, although these may also be used separately from each other. A person skilled in the art will gather that such features may also be combined with other features or feature combinations independently of each other.

[0063] The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.