Method for operating an electric motor, computer program, computer program product, system, and vehicle

Abstract

The invention relates to a method for operating an electric motor for driving a vehicle, wherein in order to separately excite a rotor of the electric motor, said rotor being arranged on a rotor shaft, at least one first and second contact brush (4, 6) are pressed against paired contact rings (8, 10) of the rotor shaft in a quality-based manner such that a sufficient contact of the contact rings (8, 10) is produced by the contact brushes (4, 6) for a given excitation current while applying as little pressure as possible. The invention additionally relates to a computer program, to a computer program product, to a system, and to a vehicle.

Description

[0001] Description

[0002] Method for operating an electric motor, computer program, computer program product, system and vehicle

[0003] The invention relates to a method for operating an electric motor for driving a vehicle.

[0004] The invention also relates to a computer program and a computer program product, each of which depicts this method, to a system having a brush actuator and a control unit for actuating the brush actuator, wherein the control unit has such a computer program or computer program product, and to a vehicle having such a computer program or computer program product.

[0005] One object underlying the invention is to ensure reliable external excitation of a rotor of an electric motor. Another object underlying the invention is to ensure this external excitation in an energy-saving manner.

[0006] This object is achieved by a method for operating an electric motor having the features of claim 1. The subclaims relate to advantageous developments.

[0007] A method for operating an electric motor for driving a vehicle is proposed, in which method for separately exciting a rotor of the electric motor arranged on a rotor shaft, at least a first and a second grinding brush are pressed or pressed against assigned slip rings of the rotor shaft in a quality-based manner such that, for a given load-dependent excitation current, sufficient contact between the slip rings is achieved by the grinding brushes by applying the smallest possible contact pressure. Quality-based or quality-based contact pressure of the grinding brushes means that in order to achieve sufficient contact, no more pressure is actively applied to the grinding brushes than is necessary. With this type of contact pressure, therefore, the best possible quality or, respectively, the best possible contact pressure can be achieved from an energy perspective.This is referred to as optimal contact, which – for a given load-dependent excitation current – ​​results in a minimum of wear on the grinding brushes. This wear consists of a superposition of mechanically abrasive and electrically erosive wear and is a function of the contact pressure on the grinding brushes.

[0008] Accordingly, the quality of the contact pressure of the grinding brushes is better, or can be better understood and interpreted, the lower the energy expenditure required to achieve sufficient contact between the slip rings by the grinding brushes.

[0009] This quality-based contact pressure reduces the wear of the grinding brushes to a minimum.

[0010] This advantageously also minimizes friction in the electric motor and thus also in the vehicle's drive train, against which the electric motor works as the vehicle's drive unit.

[0011] Adequate contact between the slip rings and the brushes can be detected or monitored using various physical variables, such as: via the course of an excitation current in the form of a ripple current, also called hum current, which occurs shortly before the contact is interrupted, via a transition resistance that occurs or is established from a voltage drop and a flowing or monitorable excitation current and / or

[0012] - about electromagnetic waves that appear or appear and are emitted in the form of arcs, the frequency and amplitude of which can be detected or monitored.

[0013] It is proposed that the grinding brushes be pressed primarily based on excitation current or load-dependently based on excitation current. This is because the lower the rotor's excitation current, the lower the quality-based contact pressure of the grinding brushes can be selected, and the more the aforementioned friction in the drive train can be reduced.

[0014] Alternatively or additionally, it is proposed that the grinding brushes are also pressed in a quality-based manner, taking into account various phenomena or influences that need to be compensated for, for example taking into account a rotor (shaft) speed, which as such in connection with a so-called wet-running brush actuator can cause the grinding brushes to float (hydrodynamic effect), a rotor (shaft) position, which as such is related to a non-uniformity of the slip rings, and / or a vehicle acceleration in the direction of the grinding brushes, whereby the vehicle acceleration can be caused by a rough road section and / or by a vehicle-specific vibration source.

[0015] In one embodiment, it is proposed that the grinding brushes are spring-biased against the slip rings via an armature of an electromagnet and a support section of the electromagnet that interacts with the armature via a spring, wherein an electromagnetic force acting in or against a pretensioning direction of the spring, which can be variably adjusted as required, is impressed on the armature via a coil body of the electromagnet in order to increase or decrease the pressure on the grinding brushes via the spring and to prevent the grinding brushes from lifting off during operation of the electric motor.

[0016] In one embodiment, it is proposed that the grinding brushes are passively spring-loaded up to a definable limit speed of the rotor shaft and, above this limit speed, are actively spring-loaded by energizing the electromagnet, pressed against the assigned slip rings in a demand-dependent or variable manner and in a quality-based manner.

[0017] In a further embodiment, it is proposed that the grinding brushes are pressed against the associated slip rings actively in a spring-loaded manner up to a definable first limit speed and above a definable second limit speed of the rotor shaft, which is higher than the first speed, depending on requirements or variably depending on requirements and in a quality-based manner, wherein the two limit speeds define a speed range lying between them, in which the grinding brushes are pressed against the associated slip rings passively in a spring-loaded manner.

[0018] Passive means that the electromagnet is not energized, so that only a static spring force acts on the grinding brushes. Active, on the other hand, means that this static spring force or this static contact pressure is electromagnetically amplified or weakened via the spring by energizing the electromagnet accordingly, so that an electromagnetically adjustable force acting in or against the preload direction of the spring is impressed on the armature via the coil body of the electromagnet, and this force is required or variable depending on requirements or variable according to requirements or variable according to requirements, for example taking into account at least one of the previously mentioned influencing parameters, such as a rotor (shaft) speed, a rotor (shaft) position and / or vehicle acceleration in the direction of the grinding brushes and the like.

[0019] In a further embodiment, it is proposed that the first and second limit speeds be set, and thus the speed range between them, such that the most frequently occurring speeds during a driving cycle are covered by this speed range, in which the electromagnet is not energized. A WLTC driving cycle (WLTC = Worldwide Harmonized Light Vehicles Test Cycle) can be used as the driving cycle, for example.

[0020] The previously described quality-based contact pressure of the grinding brushes can be carried out in a controlled or regulated manner.

[0021] Furthermore, a computer program for carrying out a method of the type described above is proposed, as well as a computer program product comprising program code means stored on a computer-readable data carrier for carrying out the method described above when the program code means are executed on a computer.

[0022] Furthermore, a system with a brush actuator and a control unit for actuating the brush actuator are proposed, wherein the control unit has a computer program or a computer program product of the type described above, as well as a vehicle with a computer program or a computer program product of the type described above.

[0023] A vehicle is defined as any type of vehicle or motor vehicle powered by an electric motor, but in particular includes passenger cars and / or commercial vehicles in the form of electric or hybrid vehicles. These can be semi-autonomous or fully autonomous vehicles.

[0024] Further advantages and features emerge from the subclaims and the exemplary embodiments. These are shown in:

[0025] Fig. 1 shows a proposed brush actuator in a perspective view, Fig. 2 shows the brush actuator shown in Fig. 1 in a sectional view,

[0026] Fig. 3 shows another proposed brush actuator in a perspective view,

[0027] Fig. 4 shows the brush actuator shown in Fig. 3 in a sectional view and

[0028] Fig. 5 a qualitative illustration of wear of grinding brushes.

[0029] The bidirectional brush actuator 2 or the bidirectional brush module 2 illustrated in Fig. 1 serves to separately excite a rotor of an electric motor arranged on a rotor shaft in the form of a synchronous machine for driving a vehicle. The electric motor is combined with a reduction gear that is oil-lubricated and oil-cooled. The gear oil also lubricates and cools the electric motor and is pumped within an oil cooling circuit that encompasses the gear box and the electric motor.

[0030] This brush actuator 2 is provided or arranged in a wet-running manner in the area of ​​an oil-lubricated bearing LS of the rotor shaft, radially to the rotor shaft, and fixed to a housing of the electric motor. An oil seal is not required at this bearing LS, allowing transmission oil to escape from the housing interior through the bearing LS and reach the brush actuator 2. This arrangement of the brush actuator 2 is sealed off from the environment by a housing cover (not shown here).

[0031] The brush actuator 2 is attached or fastened to the housing of the electric motor via a first and second mounting point AP1, AP2. This brush actuator 2 or the electromagnet 12 of the brush actuator 2 can be electrically contacted via a bushing, for example in the shape of a trunk, which is formed on a housing of an electromagnet 12. The brush actuator 2 has a first and a second grinding brush 4, 6, each of which can be variably pressed against an associated slip ring 8, 10 of the rotor shaft. These two grinding brushes 4, 6 are each arranged within an associated brush receiving and brush guide element 7 and are movable radially to the rotor shaft. The grinding brush 4 is, for example, negatively polarized and the grinding brush 6 is therefore positively polarized.

[0032] The grinding brushes 4, 6 are spring-loaded against the slip rings 8, 10 by a spring 20 in the form of a helical spring inside the electromagnet 12 - or a solenoid 12. The spring 20 is arranged between an armature 18 and a bolt or pin 14 of a support section of the electromagnet 12. This support section is fixed to the housing of the electromagnet. The armature 18 is arranged largely within a coil body 16 of the electromagnet 12 and is longitudinally movable relative to the coil body 16. The armature 18 is also joined in sections to the bolt or pin 14, which is also arranged largely within the coil body 16 and is fixed to it.

[0033] The said support section of the electromagnet 12 comprises a cylindrical metallic return element made of, for example, iron or steel, into which the pin 14 is pressed. The pin 14 itself can also be made of metal.

[0034] The armature 18 is designed as a permanent magnet and can be formed or injection-molded from a plastic with magnetic particles, such as ferromagnetic magnetic particles. Alternatively to such a magnetic plastic design, the armature 18 can be metallic, for example, from a ferromagnetic metal or a stainless, magnetized steel.

[0035] The spring 20 therefore exerts a nominal or static force of, for example, approximately 30 N on the brushes 4, 6. When the electromagnet 12 is de-energized, this is the force with which the brushes 4, 6 are pressed or pushed against the slip rings 8, 10. Below a definable limit speed of the rotor shaft, for example, approximately 800 rpm, the electromagnet 12 can remain de-energized in order to minimize the overall power loss of the brush actuator 2.

[0036] This total power loss of the brush actuator 2 results essentially from the friction of the grinding brushes 4, 6 on the rotating rotor shaft and the electrical power loss of the electromagnet 12 when the contact pressure is reduced. Below this limiting speed of approximately 800 rpm, the electrical power loss when the brush actuator 2 is actuated is greater than the friction power savings on the grinding brushes 4, 6, which, as such—compared to passive operation of the brush actuator 2—results from a reduced contact pressure as a result of the actuation of the brush actuator 2. For the sake of completeness, the friction in the electromagnet 12 and the spring 20 should also be mentioned at this point, although these power loss components are negligible or play a subordinate role.

[0037] Below this limit speed, the grinding brushes 4, 6 are therefore advantageously pressed passively against the slip rings 8, 10.

[0038] Above this limit speed, however, an active pressure of the grinding brushes 4, 6 against the slip rings 8, 10 can be provided via the armature 18 and the coil body 16 acting on the armature 18, depending on various definable influencing parameters, such as a rotor (shaft) speed, a rotor (shaft) position, vehicle acceleration in the direction of the grinding brushes 4, 6 and the like, so that a rotor (shaft) out-of-roundness, floating of the grinding brushes 4, 6 on the transmission oil which wets the slip rings 8, 10 and / or vibrations and / or impacts which act on the brush actuator 2 can be counteracted as required. By appropriately supplying current to the electromagnet 12, an electromagnetic force as required of, for example, up to approx.50N can be impressed on the armature 18, which additionally acts on the armature 18, so that the force exerted on the grinding brushes 4, 6 can be variably increased up to approx. 80N in order to prevent the grinding brushes 4, 6 from lifting off during vehicle operation.

[0039] The armature 18 is joined to a force distribution element 22, forming a so-called ball joint. The armature 18 comprises a joint head with a spherical shape, which is enclosed by a complementarily shaped section of the force distribution element 22 or a joint socket or ball socket of the force distribution element 22. The force distribution element 22 can be designed as an injection-molded plastic element.

[0040] Thus, the armature 18 is articulated relative to the force distribution element 22, which is divided into two arms and supported against the slip rings 8, 10.

[0041] On the rotor shaft and between the slip rings 8, 10, a plastic insulating section 24 is provided, projecting circumferentially in the radial direction of the rotor shaft, to protect against short circuits. This insulating section 24 provides sufficient insulation in the form of a creepage and clearance path between the slip rings 8, 10. This insulating section 24 forms part of the rotor shaft (not shown in Figs. 1 and 2).

[0042] It is proposed that the grinding brushes 4, 6 be designed as silver graphite brushes, which improves the durability of the gear oil.

[0043] In the embodiment according to Figs. 3 and 4, the brush actuator 2 also has a printed circuit board 28 (also called PCB; PCB = Printed Circuit Board), via which the brush actuator 2 or the electromagnet 12 of the brush actuator 2 can be electrically contacted via a socket illustrated in Fig. 3.

[0044] This circuit board 28 has a rotor shaft position sensor and / or an acceleration sensor. The circuit board 28 is housed in a plastic housing section 26, which is molded onto a plastic housing section of the electromagnet 12 and extends transversely, preferably orthogonally, to the rotor shaft RW and into an area around an end face of one end of the rotor shaft RW, so that the circuit board 28 is arranged transversely, preferably orthogonally, to the rotor shaft RW and opposite the end of the rotor shaft RW in such a way that the circuit board 28 covers an area around the end face of the end of the rotor shaft RW in order to be able to interact with this end face, for example, inductively.

[0045] Even in this version of the brush actuator 2, the arrangement proposed here must be imagined as being closed off from the environment by a housing cover (not shown here).

[0046] Fig. 4 illustrates a metallic end of the rotor shaft RW with a rotor shaft section RWA arranged thereon, made of a plastic material that can be pushed or molded onto the end of the rotor shaft RW. Embedded in this plastic material are metallic contact means in the form of two slip rings 8, 10 and a conductor track associated with the respective slip ring 8, 10. The conductor track extends from the associated slip ring 8, 10 through the plastic section toward the separately excited rotor (not shown here) arranged on the rotor shaft RW.

[0047] The slip ring 8 is pot-shaped and is formed, for example, as a so-called deep-drawn part, wherein the bottom of the pot forms a front-side metallic section 30 - which is only partially illustrated in Fig. 4 - of the end of the rotor shaft RW in order to be able to interact with, for example, an inductive signal generator of the printed circuit board 28.

[0048] This base of the pot, or rather this frontal metallic section 30 of the slip ring 8, must be imagined with interruptions in the circumferential direction of the slip ring 8, which as such can be filled with plastic. Between two adjacent interruptions or recesses in this pot base there is a metallic web-shaped section which is formed onto the outer, closed-circuit section of the slip ring 8, which interacts with the grinding brush 4. The rotor shaft section RWA according to Fig. 4 thus performs two functions. On the one hand, it serves to separately excite the rotor of the rotor shaft RW and, on the other hand, to detect the position of the separately excited rotor. The slip ring 8 combines two functions in one component. On the one hand, it acts as a contacting element with the grinding brush 4 and, on the other hand, as a sensor wheel with the inductive signal generator of the circuit board 28.When used in conjunction with the signal generator, periodic or sine-cosine voltage signals are generated, from which an absolute angular position of the rotor relative to a stator of the synchronous machine can be determined in a control unit, allowing the synchronous machine to be commutated efficiently. The control unit can be, for example, a control unit of an inverter.

[0049] An acceleration sensor can also be provided on the circuit board 28, with which vehicle accelerations in the direction of the grinding brushes 4, 6 – as a result of impacts and / or vibrations – can be determined. These vehicle accelerations can be used – along with other vehicle parameters – to adjust the contact pressure of the grinding brushes 4, 6. Additionally or alternatively, vehicle acceleration information can also be tapped, for example, from a drive axle or front and / or rear axle of the vehicle and provided via a CAN bus, to which the brush actuator 2 proposed here is connected via the circuit board 28, in order to be able to counteract such vehicle accelerations with the brush actuator 2.

[0050] And since vehicle accelerations in the direction of the grinding brushes 4, 6 - as a result of impacts and / or vibrations - can be compensated by a correspondingly active contact pressure of the grinding brushes 4, 6, the number of grinding brushes 4, 6 required for external excitation can be reduced to a pair.

[0051] The brush actuator 2 illustrated in Figs. 1 to 4 requires very little installation space in the axial direction of the rotor shaft RW. It is also easy to mount on the housing of the electric motor and radially to the rotor shaft. The design of the brush actuator 2 according to Figs. 3 and 4 differs from the design of the brush actuator 2 according to Figs. 1 and 2 only in the added circuit board 28 and the plastic housing section 26 receiving it, as well as the plastic receiving section also molded onto the plastic housing section of the electromagnet 12, with receiving points via which the brush actuator 2 is or can be attached to the housing of the electric motor - lying radially to the rotor shaft RW.

[0052] By actively pressing or pushing the grinding brushes 4, 6 against the associated slip rings 8, 10, as proposed in this disclosure, sliding contact friction or sliding contact friction power can be advantageously reduced to a necessary minimum as needed, compared to a purely passive system in which a spring force for pressing or pushing the grinding brushes is determined based on a maximum rotor shaft speed. This also advantageously results in reduced or lower brush wear. This also advantageously minimizes friction in a vehicle's drive train, against which an electric motor operated with the brush actuator of the type described above works as the vehicle's drive unit. This also reduces the power consumption of the electric motor, thus increasing the range of a battery supplying the electric motor.

[0053] The grinding brushes 4, 6 are pressed against the associated slip rings 8, 10 of the rotor shaft in such a quality-based manner that, for a given excitation current, sufficient contact between the slip rings 8, 10 is achieved by the grinding brushes 4, 6 while applying the smallest possible contact pressure.

[0054] In addition, the grinding brushes 4, 6 are pressed based on the excitation current and based on the smallest possible excitation current of the rotor.

[0055] Figure 5 qualitatively illustrates wear A (A = wear) of the grinding brushes 4, 6 as a function of contact pressure P on the grinding brushes. Wear is comprised of mechanically abrasive wear M and electrically erosive wear E. This qualitative progression of wear M+E relates to a given excitation current. If this excitation current decreases, the minimum contact pressure required or to be applied to achieve sufficient contact also decreases.

[0056] It is proposed that the grinding brushes 4, 6 be pressed primarily based on excitation current or load-dependent excitation current, and thus quality-based, for example in the form of or within the framework of so-called excitation current-based control of the contact pressure (or contact pressure). This is because the electrical wear E depends significantly on the excitation current used or provided. The lower the excitation current, the lower the contact pressure of the grinding brushes 4, 6 can be. If the current is zero, the grinding brushes 4, 6 can also be lifted off, so that the friction caused by the grinding brushes 4, 6 is zeroed, for example if the vehicle is to be moved with a de-energized electric motor.

[0057] Various phenomena or influences to be compensated for can be incorporated into this control system in the form of pilot control variables, thereby making it more robust and faster. For the pilot control of this control system, it is proposed to use a rotor (shaft) speed, which in conjunction with a so-called wet-running brush actuator can cause the brushes to float (hydrodynamic effect), a rotor (shaft) position, which in itself is associated with non-uniformity of the slip rings, and / or a vehicle acceleration in the direction of the brushes. The vehicle acceleration can be caused by a rough road surface and / or by a vibration source within the vehicle.

[0058] The excitation current for regulating the contact pressure within a control unit, which is connected to the aforementioned CAN bus, can be provided by the inverter's control unit via a communication interface. This communication interface can also be used to provide the aforementioned pilot control variables to temporarily increase the contact pressure and prevent damaging lifting of the grinding brushes 4, 6.

[0059] The contact pressure via spring 20 can be reduced up to a definable first limit speed of the rotor shaft and increased above a definable second limit speed of the rotor shaft, which is higher than the first speed. However, above the first limit speed and up to the second limit speed, which define a speed range between them, the electromagnet 12 can remain de-energized.

[0060] It is proposed to define or specify the first and second limit speeds, and thus to specify the speed range defined by them or lying between them, in such a way that the most frequently occurring speeds in a driving cycle—for example, in the form of a so-called WLTC (Worldwide Harmonized Light Vehicle Test Cycle)—are covered by this speed range, in which the electromagnet can remain de-energized. This results in a minimal power requirement for actively pressing the brushes 4, 6 over the lifetime of the aforementioned vehicle.

[0061] As an alternative to the electromagnet 12 shown in Figs. 1 to 4, in which the coil body 16 is designed as a stator which acts on the armature 18 located inside it or on the armature 18 which is designed as a permanent magnet and which is enclosed by it, the electromagnet can also be designed in the form of a plunger coil - not shown here - whose armature is designed as a coil body which, as such, plunges into a stator designed as a permanent magnet and is designed to be longitudinally movable relative to it.

[0062] The control unit described above comprises a digital microprocessor unit (CPU) data-connected to a memory system and a bus system, a random access memory (RAM), and a storage medium. The CPU is designed to process commands embodied as a program stored in a memory system, to detect input signals from the data bus, and to output output signals to the data bus. The memory system can have various storage media in the form of magnetic, solid-state, and other non-volatile media, on which a corresponding computer program for implementing the method and the advantageous embodiments is stored. The program can be designed in such a way that it embodies or is capable of executing the method aspects described here, so that the CPU can execute the steps of such methods and thus control both the vehicle and the brush actuator.

[0063] Suitable for carrying out the proposed method is a computer program which has program code means for carrying out all the steps of any of the claims or method claims when the program is executed in the CPU.

[0064] The computer program can be easily read into an existing control electronics and used to control both the vehicle and the proposed brush actuator 2.

[0065] For this purpose, a computer program product is provided with program code means stored on a computer-readable data carrier for carrying out the method according to any of the claims when the computer program product is executed in the CPU. The computer program product can also be integrated into the control electronics as a retrofit option.

[0066] Although exemplary embodiments are explained in the foregoing description, it should be noted that numerous modifications are possible. Furthermore, it should be noted that the exemplary embodiments are merely examples and are not intended to limit the scope of protection, applications, or structure in any way. Rather, the foregoing description provides the skilled person with a guide for implementing at least one exemplary embodiment, whereby various modifications, particularly with regard to the function and arrangement of the described components, can be made without departing from the scope of protection as defined by the claims and equivalent combinations of features.

Claims

Patent claims 1 . A method for operating an electric motor for driving a vehicle, in which, for the external excitation of a rotor of the electric motor arranged on a rotor shaft, at least a first and a second grinding brush (4, 6) are pressed against associated slip rings (8, 10) of the rotor shaft in a quality-based manner such that, for a given excitation current, sufficient contact of the slip rings (8, 10) by the grinding brushes (4, 6) is effected by applying the smallest possible contact pressure.

2. Method according to claim 1, wherein the grinding brushes (4, 6) are also pressed on the basis of excitation current.

3. Method according to claim 1 or 2, wherein the grinding brushes (4, 6) are also pressed in a quality-based manner taking into account a rotor (shaft) speed, a rotor (shaft) position and / or a vehicle acceleration in the direction of the grinding brushes.

4. Method according to one of claims 1 to 3, wherein the grinding brushes (4, 6) are spring-biased against the slip rings (8, 10) via an armature (18) of an electromagnet (12) and a support section of the electromagnet (12) which cooperates with the armature (18) via a spring (20), wherein an electromagnetic force acting in or against a prestressing direction of the spring (20) and variably adjustable as required is impressed on the armature (18) via a coil body (16) of the electromagnet (12) in order to increase or decrease the pressure on the grinding brushes (4, 6) via the spring (20) and to prevent the grinding brushes (4, 6) from lifting off during operation of the electric motor.

5. Method according to claim 4, wherein the grinding brushes (4, 6) are passively spring-biased up to a definable limit speed of the rotor shaft and above this limit speed by energising the electromagnet actively spring-loaded, variable as required and quality-based, pressed against the assigned slip rings (8, 10).

6. Method according to claim 4, wherein the grinding brushes (4, 6) are pressed against the associated slip rings (8, 10) in an actively spring-preloaded manner up to a definable first limit speed and above a definable second limit speed of the rotor shaft which is higher than the first speed, in a variable manner as required and in a quality-based manner, wherein the two limit speeds define an intermediate speed range in which the grinding brushes (4, 6) are pressed against the associated slip rings (8, 10) in a passive spring-preloaded manner.

7. The method according to claim 6, wherein the first and second limit speeds are determined and thus the speed range lying between them is determined such that the speeds occurring most frequently in a driving cycle are covered by this speed range in which the electromagnet is not energized.

8. The method according to claim 7, wherein a WLTC driving cycle (WLTC = Worldwide Harmonized Light Vehicles Test Cycle) is used as the driving cycle.

9. Method according to one of the preceding claims, wherein the grinding brushes (4, 6) are pressed in a controlled or regulated manner.

10. Computer program for carrying out a method according to one of the preceding claims 1 to 9.

11. A computer program product comprising program code means stored on a computer-readable data carrier for carrying out the method according to any one of the preceding claims 1 to 9 when the program code means are executed on a computer.

12. A system comprising a brush actuator (2) and a control unit for actuating the brush actuator (2), wherein the control unit comprises a computer program product according to claim 11.

13. A vehicle comprising a computer program product according to claim 11.

Images