Method for determining brush wear of a wet-running brush actuator having a sensorless stepper motor, computer program, computer program product, system and electric vehicle

Abstract

A method for determining brush wear of a wet-running brush controller (2) having a sensorless stepper motor is proposed. In this process, a spindle (10) of a spindle drive integrated into the brush holder (2) interacts with a spindle nut (8) of the spindle drive carrying permanent magnets, the spindle nut (8) being driven by a rotating field generated by a stator (6) of the stepper motor, being moved in a first direction of rotation of the spindle nut (8) against a first stop (18) of the force distribution element (16), the rotating field of the stepper motor then being driven in a second direction of rotation of the spindle nut (8) opposite to the first direction of rotation, until the spindle (10) is moved against a second stop of a housing section (G2) of the stepper motor. Based on the travel distance covered by the spindle (10) from the first to the second stop position and future measurements of this travel distance, which increases with brush wear, a conclusion can be drawn about brush wear by differentiating these travel distances. In addition, a computer program, a computer program product, a system, and an electric vehicle are proposed.

Description

[0001] The invention relates to an operating method or method for adjusting an angle sensorless or sensorless stepper motor of a wet-running brush actuator.

[0002] The invention further relates to a computer program and a computer program product, each of which depicts this method, a system with a brush holder and a control unit for actuating the brush holder, wherein the control unit comprises such a computer program or computer program product, and an electric vehicle with such a computer program or computer program product or such a system.

[0003] One of the problems underlying the invention is to ensure reliable external excitation of an electric motor rotor. A further problem underlying the invention is to ensure this external excitation in an energy-efficient manner.

[0004] This problem is solved by an operating procedure or a procedure with the features of claim 1.

[0005] When using such an angle-sensorless or sensorless stepper motor, it is essential to ensure that so-called step losses do not occur. Alternatively, it must be ensured that such step losses can be compensated for or eliminated. Since, in the proposed brush holder, there is a correlation between the adjustable number of steps or rotations and the corresponding pressure of the respective grinding brush against the associated slip ring, these step losses lead to an unintended reduction in this pressure.

[0006] However, a shortening of the brush(es) due to wear, which relaxes the pressure spring, also results in an unwanted lowering or reduction of this pressure.

[0007] The proposed operating procedure compensates for these two effects that reduce contact pressure. This is because it involves adjusting, re-adjusting, or calibrating the stepper motor. This procedure can be performed regularly, i.e., at definable or defined intervals.

[0008] In the first stop position proposed according to the invention, which represents or describes a first reference position of the stepper motor, the force exerted by the brush holder on the grinding brushes is known, regardless of any wear of the grinding brushes that occurs over a period of use or lifetime of the proposed brush holder.

[0009] In this first stop position, the force exerted by the brush holder on the grinding brushes is at its maximum and undistorted. It is essentially determined by the compressed compression spring, through which the force is indirectly transmitted from the spindle to the grinding brushes.

[0010] In this initial stop position, it is ensured that the force exerted on the grinding brushes by the brush holder cannot be distorted by the aforementioned step losses. And once the spindle drive or stepper motor has come to a standstill, the desired spindle position can be set by appropriately controlling the stepper motor – in steps of the stepper motor – against the influence of the compression spring or the brush force.

[0011] The length of the grinding brushes is irrelevant. This means that brush wear that develops or becomes apparent over time is also irrelevant.

[0012] The proposed method is not about determining or quantifying step losses per se, but rather about regularly eliminating them by approaching this initial stop position. Therefore, the proposed method does not require precise knowledge of any potential or possible step losses.

[0013] Accordingly, the relative first stop position of the spindle relative to a rotor shaft or rotor shaft axis, which develops over time, is irrelevant, as it moves towards the rotor shaft or rotor shaft axis over time. Rather, what is decisive is the first stop position itself – in the sense of an absolute position – in which the spindle rests against the stop of the force distribution element.

[0014] Based on this initial stop position, the force control or control of the brush adjuster can be repeatedly, i.e., regularly, corrected or freed from distortion caused by the aforementioned step losses.

[0015] For the sake of completeness, reference is made here to the applicant's German patent application under file number 10 2023 211 551.4, which discloses an active force application in the form of a dynamically adaptive and quality-based control of brush force. This disclosure is hereby expressly incorporated by reference.

[0016] The proposed method enables the precise implementation of such quality-based force control, or control of such a brush actuator, along a so-called contact quality limit. Such a brush actuator will be described in detail below.

[0017] A contact quality limit is understood to be a critical state - in the sense of a threshold value in the form of a fixed value or a characteristic curve or a characteristic map - with regard to the contact pressure, in which there is no sufficient contact of the respective slip ring by the associated grinding brush.

[0018] The condition at which the contact quality limit is reached, and at which either the contact pressure of the respective grinding brush is no longer sufficient for a sufficient current flow, or at which such a current flow is completely prevented by the grinding brush(es) lifting off, can be detected by a controller or rotor current controller, e.g. in a so-called inverter control unit or such a control unit.

[0019] The contact quality between the respective grinding brushes and the associated slip rings can be measured or monitored using various physical quantities, such as: - via a course of an excitation current in the form of a ripple current, also called hum current, which arises as such shortly before an interruption of the contact, - via a developing or established contact resistance resulting from a voltage drop and a flowing or monitorable excitation current and / or - via broadband electromagnetic radiation emitted by the arrangement of the respective grinding brushes and the associated slip rings, the frequency and amplitude of which can be detected or monitored.

[0020] From an energy perspective – and in line with what has been said above – it is proposed to ensure sufficient contact between the respective slip rings and the associated grinding brushes.

[0021] It is proposed that the method according to the invention be initiated and carried out regularly over the lifetime of an electric vehicle whose electric motor is externally excited by means of the brush controller, i.e., at defined time intervals, which can be expressed or determined, for example, in a defined mileage – such as kilometers driven – and / or in driving cycles of the electric vehicle.

[0022] Alternatively, the vehicle system could issue a prompt to the driver, suggesting that the stepper motor or brush adjuster be set, recalibrated, or the method according to the invention be performed. The driver could then initiate, arrange, start, or have the method according to the invention carried out at a later time.

[0023] It is proposed that the inventive method is initiated or carried out between two driving cycles of such an electric vehicle, while the electric vehicle is stationary and the rotor is externally excited.

[0024] In the simplest case, a driving cycle is understood to be a period of time to which a speed profile of the electric vehicle with speed values ​​greater than zero is assigned.

[0025] And when such an electric vehicle is idling or stationary, it is advantageous that no large currents or rotor currents and power are required, which as such would cause high wear on the grinding brushes.

[0026] It is proposed that a wear rate be determined based on brush wear determined in this way, relating to the mileage of an electric vehicle whose electric motor is externally excited by means of the brush actuator.

[0027] This allows for an estimation of when worn grinding brushes need to be replaced based on a driver-specific wear rate.

[0028] With the proposed brush holder - also called brush module - the pressure of the respective grinding brush against the associated grinding ring can be variably adjusted as required, depending on the direction of travel and the travel distance of the spindle.

[0029] The spindle drive enables active control of this contact pressure. Instead of contact pressure, one could also speak of compression or force application.

[0030] The spindle drive converts or transmits a rotational movement of a spindle nut – which functions as a rotor with magnets of the (angle) sensorless stepper motor – into a translational movement of the spindle.

[0031] As a result of this translational movement, at least one compression spring deforms, thereby exerting a force on the associated grinding brush, either indirectly or indirectly, via this compression spring. This deformation of the compression spring can be adjusted stepwise, in the form of steps, rotational steps, or microsteps of the rotating field generated by the electric stepper motor; that is, it can be either increased or decreased.

[0032] It is proposed that the brush holder be operated in such a way that the respective grinding brush is pressed or pushed against the assigned grinding ring based on quality.

[0033] Quality-based contact pressure of the associated grinding brush(es) means that, in order to achieve sufficient contact, no more pressure is actively applied to the grinding brush(es) than is necessary.

[0034] With such a contact pressure, one can therefore speak – from an energy perspective – of the best possible or optimal contact, in which – for a given load-dependent excitation current – ​​a minimum of wear on the grinding brushes is achieved. 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.

[0035] Such quality-based pressure reduces the wear of such grinding brushes to a minimum.

[0036] This also advantageously minimizes the friction of an electric motor and thus also the friction of a drivetrain of an electric vehicle, against which the electric motor works as the drive unit of the electric vehicle.

[0037] The proposed brush adjuster enables robust, quality-based control of brush force or pressure of the grinding brushes, and does so with minimal energy consumption.

[0038] The proposed brush holder also enables safe current transmission for torque generation.

[0039] It is proposed that the spindle drive be designed to be backlash-free. It is also proposed that the spindle drive be self-locking. This ensures that power consumption is minimized and limited to the time required for adjusting the brush holder. Furthermore, if the stepper motor fails during operation or a driving cycle, the basic functionality of the external excitation of the electric motor or vehicle drive is maintained. Thus, this spindle drive guarantees the operational reliability of the electric motor or vehicle drive, preventing the vehicle from stalling due to a lack of external excitation of the rotor.

[0040] Furthermore, translation of the spindle towards the stepper motor is prevented as a result of an external force, which is transmitted as such from the respective slip ring or rotor shaft to the associated grinding brush during a dynamic driving operation or driving cycle.

[0041] Limiting the power consumption of the proposed brush adjuster to the time period of its adjustment means that active control of the force application is only provided for or carried out during this period of energization of the stepper motor. Beyond this, i.e., when the brush adjuster remains unenergized, the force application by the brush adjuster is purely passive.

[0042] It is further proposed that the force distribution element be fork-shaped and interact with a first grinding brush via a first fork section and with a second grinding brush via a second fork section. Instead of fork sections, one could also refer to arms of the force distribution element.

[0043] It is proposed that the force distribution element be tiltable or inclinable relative to the spindle by forming a joint with the spindle.

[0044] By allowing the force distribution element to tilt relative to the spindle, it is possible to counteract different wear of the grinding brushes or different brush wear when force is applied evenly to the grinding brushes.

[0045] At least one compression spring can be provided between the spindle and the force distribution element. Additionally or alternatively, a compression spring can be provided between the force distribution element and the associated grinding brush.

[0046] Additionally or alternatively, the force distribution element itself can be designed or shaped to be elastic in such a way that it also forms a compression spring. Through appropriate material selection in conjunction with a suitable geometric design of the force distribution element, a defined stiffness of the fork sections or arms can be achieved, thus combining the function of uniform force application or distribution with the function of a compression spring element in one and the same element or component.

[0047] Furthermore, a separately excited electric motor with such a brush holder is proposed.

[0048] Further advantages and features will become apparent from the dependent claims and the exemplary embodiments. These are shown, partly schematically: Fig. 1 a proposed brush holder in a sectional view, Fig. 2 an excerpt of the in Fig. 1 shown brush holder in a first state, Fig. 3 an excerpt of the in Fig. 1 shown brush holder in a second state, Fig. 4 an excerpt of the in Fig. 1 shown brush holder in a third state, Fig. 5 an excerpt of the in Fig. 1 shown brush holder in a fourth state, Fig. 6a) an overview of different states of such a brush holder according to the invention, Fig. 6b) an overview of different states of such a brush holder according to the invention in an alternative representation, Fig. 7 den in Fig. 1 brush holder shown in another sectional view and Fig. 8 a sectional view along section line A - A in Fig. 7.

[0049] The Fig. Figures 1 to 8 each illustrate a bidirectionally acting brush actuator 2 – also called brush module 2 – which serves to externally excite a rotor of an electric motor in the form of a synchronous machine, mounted on a rotor shaft, for driving a vehicle or electric vehicle. The electric motor is combined with a reduction gearbox, which is oil-lubricated and oil-cooled. Gear oil lubricates and cools the electric motor and is circulated within an oil cooling circuit that includes the gearbox and the electric motor.

[0050] The proposed brush holder 2 is wet-running in the area of ​​an oil-lubricated bearing point of the rotor shaft and is radially aligned to the rotor shaft. It is fixed to, or arranged on, the housing of the electric motor. An oil seal is omitted at this bearing point, allowing the gear oil from inside the electric motor housing to escape through the bearing point and reach the brush holder 2. This arrangement of the brush holder 2 is sealed off from the surrounding environment by a housing cover.

[0051] Such a brush holder 2 is connected via mounting points AP1, AP2, AP3 (see e.g. Fig. 7) attached or fastened to the housing of the electric motor.

[0052] The proposed brush holder 2 has an electric stepper motor or stepper motor unit 4 with a stator 6 and a rotor 8 arranged internally to the stator 6, which is designed in the form of a spindle nut carrying magnets and which, in conjunction with a spindle 10 with which it interacts, forms a spindle drive integrated into the stepper motor 4.

[0053] The spindle 10, which is longitudinally movable relative to the stepper motor unit 4 or along the X-axis shown, acts indirectly via at least one compression spring 14 and an electrically non-conductive or insulating force distribution element 16 – made of, for example, plastic – against an associated first and second grinding brush B1, B2 to press against an associated slip ring SR1, SR2 of the rotor shaft (not shown here). Depending on the direction and travel of the spindle 10, the pressure of the grinding brushes B1, B2 against the associated slip rings SR1, SR2 can be variably adjusted as required. The spindle drive is designed to be backlash-free and self-locking.

[0054] This brush holder 2 or its stepper motor can be electrically contacted via a socket BU on the housing of the stepper motor or the stepper motor unit 4.

[0055] The two grinding brushes B1 and B2 are each movably arranged within an associated brush holder and brush guide element, and radially to the rotor shaft. Grinding brush B1 is, for example, negatively polarized, and grinding brush B2 is therefore positively polarized.

[0056] In the explanations following the Fig. In sections 1 to 5, 7 and 8, a compression spring 14 in the form of a helical spring is provided or arranged between a stop section 12 of the spindle 10 and a fork-shaped or fork-like force distribution element 16. This compression spring 14 normally keeps the spindle 10 or the stop section 12 apart from the force distribution element 16. The force distribution element 16 is connected to the compression spring 14 with some play.

[0057] The connection between the compression spring 14 and the force distribution element 16 is designed such that the force distribution element 16 can be tilted relative to the spindle 10. This allows uneven wear of the grinding brushes B1 and B2 to be compensated for, with the tilting or inclination adjusting according to the wear pattern.

[0058] The two free, brush-side ends of the force distribution element 16 are each rounded and lie against the force distribution element 16, forming a point contact and / or line contact and / or surface contact.

[0059] The Fig. 7. An oil connection is located at point 7, which leads into a forking or branching oil line through which the oil is supplied to the two grinding brushes B1 and B2. This ensures that the grinding brushes B1 and B2 are always sufficiently supplied with oil during operation of the electric motor and during forward movement of the electric vehicle.

[0060] For example, in the Fig. 1 and Fig. The helical spring or compression spring shown above the stop section 12, acting from above against this stop section 12, clamps the spindle 10 against the spindle nut 8 and thereby ensures that the spindle drive is free of play.

[0061] The in the Fig. Figures 1 to 8 of the brush holders 2 each describe a transverse force-free design of a brush holder 2. This means that the spindle 10 does not experience any operational transverse force.

[0062] In another embodiment – ​​not shown here – the force distribution element 16 can be designed or shaped to be elastic in such a way that it itself forms a compression spring or compression spring element – ​​with a defined stiffness, in particular of the individual fork sections or arms – and forms or represents a series compression spring connection with the previously described helical spring or compression spring 14. Alternatively, such a force distribution element 16 can also replace or render such a helical spring or compression spring 14 superfluous. In the latter case, this would save installation space.

[0063] It is intended to regularly adjust, readjust or calibrate the stepper motor 4 of this brush holder 2 in order to eliminate step errors, also called step losses, that occur in the meantime and / or to counteract wear of the grinding brushes B1, B2.

[0064] Such step errors or step losses occur when the stepper motor 4 is briefly overloaded by an external load torque and the rotor - in the form of the spindle nut 8 - can no longer follow the rotating field of the stator 6, so that steps are skipped as a result and the information about the actual or current position or orientation of the rotor 8 is lost.

[0065] In the Fig. 2 The spindle 10 is spaced apart from a stop 18 of the force distribution element 16. This Fig. Figure 2 shows a state in which the spindle 10 is normally located, or in a normal case, or in normal operation of the brush holder 2.

[0066] To correct such step errors or step losses, i.e., to (re)adjust or calibrate the electric stepper motor 4, it is proposed that – between two driving cycles of the electric vehicle – while the electric vehicle is stationary and the rotor is externally excited, the spindle 10 – acting indirectly via the compression spring 14 and the force distribution element 16 against the two associated grinding brushes B1, B2 – is moved in a first direction of rotation of the spindle nut 8 against this stop 18 of the force distribution element 16 (see Fig. 3).

[0067] The spindle drive, and thus the stepper motor 4, comes to a standstill. This standstill is detected by a control unit or control device controlling the stepper motor 4 – for example, an inverter control unit. This stop position of the spindle 10, or the stepper motor 4, acts as a reference position from which the rotating field of the stepper motor is operated in a second direction of rotation of the spindle nut 8, opposite to the first direction of rotation, until the spindle 10 assumes a desired position. In this position, the grinding brushes B1, B2 experience the desired, demand-dependent pressure against their respective slip rings SR1, SR2 on the rotor shaft.

[0068] In this stop position of the spindle 10, in which the spindle 10 rests against the stop 18 of the force distribution element 16, the force exerted by the brush holder 2 on the two grinding brushes B1, B2 is defined and at its maximum. This force is essentially determined by the compression of the compression spring 14.

[0069] And this defined maximum force is unambiguous and unaltered in this stop position of spindle 10, i.e., free from the aforementioned step losses. This force is also unambiguous and unaltered regardless of the wear condition of the two grinding brushes B1 and B2. Therefore, in this stop position, stepper motor 4 is free from the aforementioned step losses, regardless of the wear condition of the two grinding brushes B1 and B2. Stepper motor 4 is thus considered adjusted, (re)adjusted, or calibrated in this stop position.

[0070] And as the spindle 10 is moved away from this stop position in steps of the stepper motor 4, the compression spring 14 relaxes and the force exerted by the brush holder 2 on the two grinding brushes B1, B2 is reduced to a desired, demand-dependent force, depending on the travel distance of the spindle 10. And the resulting force is unaltered – due to the adjustment or (re-)adjustment or calibration of the stepper motor.

[0071] From this stop position, the steps of the stepper motor are counted correctly again, so that the grinding brushes B1, B2 against the slip rings SR1, SR2 can be adjusted accurately and variably as required.

[0072] This proposed operating method thus eliminates the need for a position encoder - a so-called incremental encoder or absolute encoder - which detects the exact rotational position or orientation of the spindle nut 8 in order to control the stepper motor accordingly - and to correct the resulting step losses.

[0073] To determine brush wear, it is suggested to start from this first stop position ( Fig. 3) to operate the rotating field of the stepper motor 4 in a second direction of rotation of the spindle nut 8, opposite to the first direction of rotation, until the spindle 10 moves against a stop of a housing section G2 of the stepper motor 4 ( Fig. 5) And in this case, too, the spindle drive or the stepper motor 4 comes to a standstill, whereby this standstill is also detected by the control unit or the control device controlling the stepper motor 4.

[0074] In the Fig. In contrast, spindle 10 is spaced away from this stop of housing section G2. Also the Fig. Figure 4 shows a state in which the spindle 10 is normally located, or in a normal case, or in normal operation of the brush holder 2.

[0075] This second stop position of the spindle 10 or the stepper motor 4 ( Fig. 5) functions as a reference position, in which the spindle 10 exerts either no force or at least a reduced force on the grinding brushes B1, B2. This depends on the selected length of the compression spring 14.

[0076] In the Fig. Figure 1 shows the spindle 10 also resting against the upper or second stop, or illustrated in the second stop position, so that with regard to the Fig. 1 - depending on the selected length of the compression spring 14 and / or the upper or second stop of the spindle 10 - the compression spring 14 can be unpressurized or uncompressed, or it can undergo a minimum compression.

[0077] In the latter case as well – analogous to the first stop position – the force exerted by the spindle 10 on the grinding brushes B1, B2 is undistorted and free of step losses. It is minimal.

[0078] The travel distance of spindle 10 from the first to the second stop position is recorded, defined as a reference distance, and stored in the control unit. Based on this reference distance, and in conjunction with future measurements of this travel distance, which increases with brush wear over time, conclusions can be drawn about brush wear or the actual wear of the grinding brushes B1 and B2. This is done by calculating the difference between such a future travel distance, after the two grinding brushes B1 and B2 have experienced a certain amount of wear, and this reference distance.

[0079] It is proposed to determine this reference distance in an unworn or new condition of the two grinding brushes B1, B2.

[0080] Both the first and second stop positions can be approached by time-based or step-based pre-control of the rotating field generated by the stator 6.

[0081] A time-based pre-control of the rotating field is understood to mean an applicable or definable time specification or time span within which the spindle 10, driven by the spindle nut 8, will have reached the respective stop position.

[0082] In contrast, step-based pre-control of the rotating field refers to an applicable or definable step specification with which the spindle 10 - driven by the spindle nut 8 - is moved against the respective stop position.

[0083] Once the spindle 10 has reached its respective stop or stop position, it remains at that stop or in that stop position. This means that the spindle nut 8 can no longer follow the pre-controlled rotating field, causing the stepper motor 4 to stop. This, in turn, leads to the aforementioned step losses.

[0084] By implementing a so-called sensorless or angle-sensorless step loss detection system, for example in the aforementioned inverter control unit, these first and second end positions can be detected. Upon detection of step losses in one of these end positions, it can be concluded that the stepper motor 4 has stopped. Consequently, the feedforward control of the rotating field against the respective end position can be immediately interrupted or switched off.

[0085] To detect or identify these end positions, the stepper motor 4 can be operated in so-called partial steps. Unlike a full step, in partial steps not all phases of the stepper motor 4 are energized, allowing the voltage induced by the spindle nut 8 in the unenergized phases of the stepper motor 4 – a so-called back EMF – to be monitored and measured. When the stepper motor 4 is at rest, i.e., in one of these end positions, this back EMF is absent, thus confirming that the motor is stationary.

[0086] Such stall detection of a stepper motor is known to experts and will therefore not be described further here.

[0087] The Fig. 6a) schematically illustrates different states A, B1, B2, A*, A**, C, D1 and D2 of such a brush holder 2. These individual states A, B1, B2, A*, A**, C, D1 and D2 describe a developing compression spring force F, which is the relevant factor in the individual considerations.

[0088] In the Fig. 6a) The compression spring has the same length with respect to all the states shown: A, B1, B2, A*, A**, C, D1, and D2. However, with respect to the two states A* and A**, the upper end point of the spindle moves slightly downwards. As a result, the difference analyses shown remain unchanged and valid. The two states A* and A** each show a compression spring which, compared to states A, B1, B2, C, D1, and D2, remains under pressure, albeit reduced, even at the upper end point of the spindle.

[0089] In the Fig. 6b) However, the compression spring is designed to be comparatively longer with respect to the states A* and A** shown, so that in these states A* and A**, the compression spring remains under pressure – albeit reduced – even at the upper end of the spindle, compared to the other states A, B1, B2, C, D1, and D2. Such a longer compression spring experiences a correspondingly higher compression in the two states D1 and D2.

[0090] The state D1 illustrates the brush holder 2 described in this disclosure in a so-called new condition - i.e., with unworn grinding brushes B1, B2 - and in the first stop position, in which the spindle 10 rests against the stop 18 of the force distribution element 16.

[0091] State D2, on the other hand, illustrates this brush holder 2 with a certain amount of brush wear. Therefore, the stop position in state D2 is closer to the illustrated rotor shaft or rotor shaft axis.

[0092] In these two states D1, D2, the force applied or exerted by the brush holder 2, with which the grinding brushes B1, B2 are pressed or pushed against the associated grinding rings SR1, SR2, is at its maximum and unaltered (F = Fmax in each case). "Unaltered" here means that the force exerted by the spindle 10 in this first stop position is uniquely determined or determinable and has two components.

[0093] On the one hand, the spindle 10 acts indirectly on the grinding brushes B1 and B2 via the compressed compression spring 14 in conjunction with the force distribution element 16. On the other hand, the spindle 10 also acts indirectly on the grinding brushes B1 and B2 via the stop 10, against which it is electrically driven. These two force components superimpose. However, until shortly before reaching this first stop position, only the force component exerted via the compression spring 14 acts on the grinding brushes B1 and B2.

[0094] For the adjustment, readjustment, or calibration of the brush holder 2 – with regard to the force it exerts – it is therefore sufficient to focus only on the resulting maximum compression spring force 14 in this first stop position, which is clearly defined or determinable. Thus, the force or force component exerted via the stop 10 is neglected when considering this adjustment, readjustment, or calibration of the brush holder 2.

[0095] In this first stop position, there are no step losses that could reduce or distort the contact pressure.

[0096] The two states B1 and B2, however, illustrate an embodiment of a brush adjuster not described within the scope of this disclosure, in which the force distribution element is raised by the spindle in such a way that a so-called contact quality limit is reached and thus a so-called zero-force reference position of the brush adjuster.

[0097] For the sake of completeness, reference is made here to the applicant's German patent application under file number 10 2024 206 925.6, which discloses such a brush holder and a proposed method for determining such a zero-force reference position. This disclosure is hereby expressly incorporated by reference.

[0098] State B1 illustrates such a brush holder in a so-called new condition, i.e., with unworn grinding brushes and in this zero-force reference position of the brush holder.

[0099] State B2, on the other hand, illustrates this brush holder with a certain amount of brush wear. Therefore, in state B2, this zero-force reference position is closer to the illustrated rotor shaft or rotor shaft axis.

[0100] In these two states B1 and B2, the brush holder exerts no force on the grinding brushes B1 and B2. The applied or exerted force is zero or at least nearly zero (F = 0).

[0101] State A also illustrates the brush holder 2 described in this disclosure, but in the second stop position, in which the spindle 10 rests against the stop of the housing section G2.

[0102] The two states A* and A**, however, each describe a state in which the compression spring 14 is not depressurized or uncompressed in the second stop position, but rather experiences a minimum compression. State A* refers to an unworn pair of grinding brushes B1, B2, whereas state A** refers to a worn pair of grinding brushes B1, B2.

[0103] State C illustrates a normal state in which the brush holder 2, or such a brush holder, is in normal operation. In this state, the spindle 10 is spaced away from both the stop 18 of the force distribution element 16 and the stop of the housing section G2 of the stepper motor 4. In this state C, the force applied or exerted by the brush holder 2, with which the grinding brushes B1, B2 are pressed against the associated slip rings SR1, SR2, lies between zero and the maximum possible force (0 < F < Fmax).

[0104] The image on the far right illustrates the distance of each spindle 10 from the housing section G2 of the stepper motor 4 (lengths or length segments L1, L2, L3, L4, L5, L4*, L5*). These are also the respective measurable travel distances from which brush wear can be determined.

[0105] With reference to the brush holders 2 described in this disclosure, brush wear results from the difference between L5 - L4 or L5* - L4* with reference to the two states D1 and D2.

[0106] And with reference to the aforementioned German patent application of the applicant with file number 10 2024 206 925.6 and the embodiments of the brush holders described therein, brush wear results from the difference between L2 and L1 with reference to states B1 and B2.

[0107] These individual difference lengths result from a determinable or determined difference in rotary steps or angular steps of the stepper motor 4 multiplied by a translation of the spindle drive (translation = axial stroke along the X - X - axis related to a partial revolution or an angular step of the stepper motor 4).

[0108] The Fig. 7 shows the one in Fig. Figure 1 illustrated brush holder 2 in a further sectional view.

[0109] In the sectional view according to Fig. Figure 8 shows that a housing section G1 of the stepper motor is designed or shaped as a guide section for the spindle 10, to which the spindle 10 is positively connected and relative to which the spindle 10 can be moved longitudinally along the depicted X-A axis. This housing section G1, or guide section, ensures that the spindle 10 cannot rotate over its entire stroke. As a result, the spindle drive, or stepper motor 4, comes to an immediate standstill in the first and second end positions, which is detected as such by the control unit (so-called stall detection).

[0110] Furthermore, a computer program for carrying out the procedure of the type described above is proposed.

[0111] Furthermore, a computer program product comprising program code means stored on a computer-readable data carrier is proposed to carry out the procedure of the type described above when the program code means are executed on a computer.

[0112] Furthermore, a system comprising a brush holder and a control unit for actuating the brush holder is proposed, wherein the control unit comprises a computer program product of the type described above.

[0113] Furthermore, an electric vehicle is proposed that incorporates a computer program product of the type described above and / or a system of the type described above.

[0114] The control unit described above comprises a digital microprocessor unit (CPU) connected to a memory system and a bus system, a working memory (RAM), and a storage medium. The CPU is configured to execute instructions stored as a program in the memory system, to acquire input signals from the data bus, and to output signals to the data bus. The memory system can utilize various storage media, including magnetic, solid-state, and other non-volatile media, on which a corresponding computer program for carrying out the method and its advantageous embodiments is stored. The program can be designed to embody or execute the process aspects described herein, enabling the CPU to perform the steps of such processes and thus control both the electric vehicle and the proposed brush actuator.

[0115] A computer program (product) suitable for carrying out the proposed method is one which has program code means to perform all steps of any one of the claims or method claims when the program is executed in the CPU.

[0116] The computer program or computer program product can be easily integrated into existing control electronics and used to control and / or regulate both the electric vehicle and the proposed brush controller.

[0117] This includes a computer program product with program code stored on a computer-readable data carrier to perform the method according to any one 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.

[0118] Although the preceding description explains exemplary embodiments, it should be noted that a multitude of variations are possible. Furthermore, it should be emphasized that the exemplary embodiments are merely examples and are not intended to restrict the scope of protection, applications, or structure in any way. Rather, the preceding description provides the skilled person with a guideline 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 these equivalent combinations of features.

Claims

[1] Method for determining brush wear of a wet-running brush actuator (2) having a sensorless stepper motor, in which a spindle (10) of a spindle drive integrated into the brush holder (2) - interacting with a spindle nut (8) of the spindle drive carrying permanent magnets, wherein the spindle nut (8) is driven by a rotating field generated by a stator (6) of the stepper motor, - in a first direction of rotation of the spindle nut (8) - and thereby indirectly via at least one compression spring (14) and a force distribution element (16) acting against two associated grinding brushes (B1, B2) - is moved against a first stop (18) of the force distribution element (16) and thereby the spindle drive comes to a standstill, wherein, in this first stop position, an unadulterated, defined maximum pressure spring force is applied by the brush holder (2) to the grinding brushes (B1, B2), where this standstill is detected and whereupon the rotating field of the stepper motor is operated in a second direction of rotation of the spindle nut (8) opposite to the first direction of rotation, until the spindle (10) is moved against a second stop of a housing section (G2) of the stepper motor and the spindle drive also comes to a standstill, wherein in this second stop position either no pressure spring force or at least a reduced pressure spring force is applied by the brush holder (2) to the grinding brushes (B1, B2), wherein this standstill is also detected and wherein the travel distance covered by the spindle (10) from the first to the second stop position is recorded as a reference distance, wherein based on this reference distance and future recordings of this travel distance, which increases with the appearance of brush wear, a conclusion is drawn about brush wear by calculating a difference with the reference distance. [2] Method according to claim 1, wherein the method is initiated on the vehicle system side after a defined mileage of an electric vehicle whose electric motor is externally excited by means of the brush holder (2). [3] Method according to one of the preceding claims, wherein the method is initiated while an electric vehicle is stationary, the electric motor of which is externally excited by means of the brush holder (2). [4] Method according to one of the preceding claims, wherein a wear rate is determined on the basis of a determined brush wear in relation to a mileage of an electric vehicle whose electric motor is externally excited by means of the brush holder (2). [5] Method according to claim 4, wherein a time of replacement of worn grinding brushes (B1, B2) is estimated on the basis of a driver-specific wear rate. [6] Computer program which implements a method according to any of the preceding claims. [7] 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 5 when the program code means are executed on a computer. [8] System comprising a brush holder (2) and a control unit for actuating the brush holder (2), wherein the control unit comprises a computer program product according to claim 7. [9] Electric vehicle with a computer program product according to claim 7.

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