Method for determining contact quality, computer program, computer program product, system and electric vehicle

Abstract

The invention relates to a method for determining a contact quality between at least one grinding brush (4, 6) of a brush actuator (2) and an associated slip ring (8, 10) of a rotor shaft, against which the grinding brush (4, 6) is pressed in a quality-based manner for the external excitation of a rotor of an electric motor arranged on the rotor shaft in such a way that, for a given excitation current and when the smallest possible contact pressure is applied, sufficient contact is brought about by the grinding brushes (4, 6) with the slip ring (8, 10). In this case, electromagnetic radiation emitted by this arrangement of the at least one grinding brush (4, 6) and the associated slip ring (8, 10), which radiation arises as a result of the grinding brush (4, 6) being lifted off the slip ring (8, 10) during operation of the electric motor, is detected by means of an electrical component with sufficient inductance in a region of this arrangement and used to determine the contact quality. The invention also relates to a computer program, a computer program product, a system and an electric vehicle.

Description

[0001] The invention relates to a method for determining a contact quality between at least one grinding brush of a brush actuator and an associated slip ring of a rotor shaft, against which the grinding brush is pressed in a quality-based manner for the external excitation of a rotor of an electric motor arranged on the rotor shaft.

[0002] The invention also relates to a computer program and a computer program product, each of which depicts this method, to a system with 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 an electric vehicle with such a computer program or computer program product or such a system.

[0003] From the prior art, the applicant's publication DE 10 2023 206708 A1 is known, which is directed to a method for operating an electric motor for driving a vehicle.

[0004] 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.

[0005] The present invention also aims to enable dynamically adaptive and quality-based control of a brush force, with which an arrangement of brushes is pressed against assigned slip rings of a rotor shaft in a quality-based manner. Such a control is implemented in a control unit of an electric vehicle, which maps this control.

[0006] At this point, reference is made to the applicant's German patent application with the file number 10 2023 211 551.4, which discloses such a dynamically adaptive and quality-based control of a brush force.

[0007] These objects are achieved by a proposed method having the features of claim 1. The subclaims relate to advantageous developments.

[0008] Quality-based - or a quality-based contact pressure or pressing of the at least one grinding brush against the associated slip ring - means that in order to ensure sufficient contact of the slip ring by the grinding brush via the brush actuator - actively - no more pressure is applied to the grinding brush than is necessary.

[0009] From an energy perspective, such contact pressure can be described as the best possible or optimal contact, which, for a given load-dependent excitation current, results in minimal wear on the grinding brushes. This wear is composed of a superposition of mechanically abrasive and electrically erosive wear and is a function of the contact pressure on the grinding brushes.

[0010] Such quality-based contact pressure reduces the wear of grinding brushes to a minimum.

[0011] This advantageously also minimizes friction of an electric motor and thus also friction of a drive train of an electric vehicle, against which the electric motor works as the drive unit of the electric vehicle.

[0012] The proposed method enables a robust, quality-based control of a brush force of the type described above.

[0013] The proposed method also enables safe power transmission for torque generation.

[0014] Adequate contact between slip rings and associated brushes can be detected and monitored using various physical parameters, such as: - via a course of an excitation current in the form of a ripple current, also called hum current, which occurs as such shortly before an interruption of the contact, - via a transition resistance arising from a voltage drop and a flowing or monitorable excitation current and / or - via a broadband electromagnetic radiation emitted by the arrangement comprising the at least one grinding brush and the associated slip ring, the frequency and amplitude of which can be detected or monitored.

[0015] The present invention is concerned with utilizing or exploiting this latter electromagnetic radiation to determine a contact quality between at least one brush of a brush actuator and an associated slip ring of a rotor shaft in order to enable a quality-based control of a brush force of the type described above.

[0016] This broadband emitted electromagnetic radiation is generated during transient operation of an electric motor - with such a brush actuator - due to the lifting of at least one grinding brush from the associated slip ring by reducing the contact pressure or pressure of the grinding brush and / or increasing the shaft speed.

[0017] In one embodiment, it is proposed that an electrical component in the form of a coil - with a sufficient inductance - is used to detect the electromagnetic radiation emitted by the arrangement comprising the at least one grinding brush and the associated slip ring.

[0018] In a further embodiment, it is proposed, in addition or alternatively, that an electrical component in the form of an SMD component - with sufficient inductance - of a printed circuit board is used to detect this electromagnetic radiation.

[0019] In a further embodiment, it is proposed that an electrical component in the form of a coil of an inductive signal generator and / or an SMD component of a printed circuit board of a speed sensor of the electric motor be advantageously used to detect this electromagnetic radiation in order to save additional electrical components and thus costs.

[0020] In another version, this circuit board is also used to control the brush actuator, which also saves on components and costs.

[0021] A computer program for carrying out the method of the type described above is also proposed.

[0022] Furthermore, a computer program product comprising program code means stored on a computer-readable data carrier is proposed for carrying out the method of the type described above when the program code means are executed on a computer.

[0023] Furthermore, a system comprising a brush actuator and a control unit for actuating the brush actuator is proposed, wherein the control unit comprises a computer program product of the type described above.

[0024] In addition, an electric vehicle with a computer program product of the type described above and / or a system of the type described above is proposed.

[0025] Further advantages and features emerge from the subclaims and the exemplary embodiments. These are shown in: Fig. 1 a proposed brush actuator in a sectional view, Fig. 2 the in Fig. 1 shown brush actuator in a perspective view, Fig. 3 a first embodiment of a printed circuit board and Fig. 4 a second version of a printed circuit board.

[0026] The one in the Fig. 1 and Fig. The bidirectional brush actuator 2 illustrated in Figure 2, also called an active brush module 2, is used for the external excitation of a rotor (not shown here) of an electric motor in the form of a synchronous machine for driving an electric 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.

[0027] This brush actuator 2 is provided or arranged wet-running in the area of an oil-lubricated bearing point (not shown here) of the rotor shaft RW and is radial to the rotor shaft RW and fixed to a housing of the electric motor. An oil seal is not required at this bearing point in order to avoid friction associated with the oil seal. As a result, during operation of the electric vehicle, gear oil escapes from the interior of the housing of the electric motor through the bearing point and reaches or penetrates to the brush actuator 2. The Fig. 1 and Fig. The arrangement of the brush actuator 2 illustrated in Figure 2 is closed off from the surroundings of the electric motor by means of a housing cover (not shown here).

[0028] 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 RW. These two grinding brushes 4, 6 are arranged within a brush receiving and guide element 7 and are movable radially relative to the rotor shaft RW. For example, the grinding brush 4 has a negative polarity, and the grinding brush 6 has a positive polarity.

[0029] The two slip rings 8, 10 are inserted into a so-called rotor shaft attachment RWA made of a plastic, whereby this rotor shaft attachment RWA is pushed or plugged onto one end of the rotor shaft RW.

[0030] The grinding brushes 4, 6 are at least passively spring-loaded against the slip rings 8, 10 via a spring in the form of a helical spring inside the electromagnet EM – also called a solenoid. When the brush actuator 2 is de-energized, these grinding brushes 4, 6 thus experience only a passive spring preload against the associated slip rings 8, 10.

[0031] By applying appropriate current to the electromagnet EM, this spring preload can be increased or decreased as needed by applying an electromagnetic force to the armature of the electromagnet EM, acting in the direction of the spring preload or in the opposite direction. In this context, this is referred to as active pressure of the grinding brushes 4, 6 against the slip rings 8, 10.

[0032] The brush force with which the two grinding brushes 4, 6 are pressed against the associated slip rings 8, 10 of the rotor shaft RW - actively - in a quality-based manner is the subject of a so-called quality-based control of the brush force, which is implemented as such in a control unit of the electric vehicle.

[0033] The brush actuator 2 and this control unit belong to a system of the electric vehicle or the system has these two components.

[0034] Such a quality-based control of the brush force is described, for example, in the applicant's German patent application with the file number 10 2023 211 551.4, already mentioned at the beginning, to which reference is hereby expressly made.

[0035] In the Fig. 1 and Fig. 2, a circuit board L is shown to the left of this grinding brush arrangement, via which the brush actuator 2 is contacted and controlled.

[0036] In the Fig. 2, an arrangement comprising a coil S and a sensor wheel GR is also schematically shown to the right of the brush actuator 2, which interact inductively and thereby form a speed sensor or a sensor arrangement SA, which serves to commutation of the said electric motor for driving the electric vehicle.

[0037] This coil S is integrated into the circuit board L or is part of this circuit board L. The encoder wheel GR, however, is integrated into the rotor shaft RW or the rotor shaft attachment RWA, in the form of the Fig. 1 shown slip ring 8, and thus part of the rotor shaft attachment RWA.

[0038] It is proposed to advantageously use this coil S of the speed sensor of the electric motor to detect the broadband electromagnetic radiation emitted by the arrangement of the grinding brushes 4, 6 and the associated slip rings 8, 10, which radiation arises as a result of the grinding brushes 4, 6 being lifted off the associated slip rings 8, 10 during operation of the electric motor.

[0039] The Fig. 3 illustrates another possible embodiment of a printed circuit board L with such an integrated coil S as part of a speed sensor of an electric motor, wherein this coil S is also used on the one hand for commutating the electric motor and on the other hand for detecting such - broadband - electromagnetic radiation.

[0040] Investigations show that such shared use of the speed sensor's coil S is possible, because the voltage signals inductively generated by this coil S in conjunction with the sensor wheel GR are in the MHz range, whereas the broadband electromagnetic radiation emitted by the arrangement of the brushes 4, 6 and the associated slip rings 8, 10 induces or generates voltage signals in this coil S that are in a range below 1 kHz. In this respect, these signals can be very well separated and differentiated from one another across the frequency range.

[0041] The arcs created when the grinding brushes 4, 6 are lifted off the associated slip rings 8, 10 represent the spectrum of the emitted electromagnetic radiation visible to the human eye.

[0042] The Fig.4, however, illustrates a possible design of a printed circuit board L with an SMD component arranged thereon - in the sense of an alternative - with sufficient inductance to detect such broadband emitted electromagnetic radiation.

[0043] In a further embodiment - not shown here - both a coil and an SMD component of such a circuit board can be provided or used in the sense of a redundant arrangement of electrical components, each with a sufficient inductance for detecting such broadband emitted electromagnetic radiation.

[0044] 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 device. The CPU is configured 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 electric vehicle and the proposed brush actuator.

[0045] Suitable for carrying out the proposed method is a computer program (product) 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.

[0046] The computer program or computer program product can be easily read into an existing control electronics system and used to control and / or regulate both the electric vehicle and the proposed brush actuator.

[0047] 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.

[0048] 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 changes, particularly with regard to the function and arrangement of the described components, can be made without departing from the scope of protection as it results from the claims and equivalent combinations of features.

Claims

[1] Method for determining a contact quality between at least one grinding brush (4, 6) of a brush actuator (2) and an associated slip ring (8, 10) of a rotor shaft, against which the grinding brush (4, 6) is pressed in a quality-based manner for the external excitation of a rotor of an electric motor arranged on the rotor shaft, such that, for a given excitation current and when applying the smallest possible contact pressure, sufficient contact of the slip ring (8, 10) is effected by the grinding brushes (4, 6), characterized bythat an electromagnetic radiation emitted by this arrangement of the at least one grinding brush (4, 6) and the associated slip ring (8, 10), which arises as a result of the grinding brush (4, 6) being lifted off the slip ring (8, 10) during operation of the electric motor, is detected by means of an electrical component with sufficient inductance in a region of this arrangement and is used to determine the contact quality. [2] Method according to claim 1, wherein an electrical component in the form of a coil (S) is used to detect said electromagnetic radiation. [3] Method according to claim 1 or 2, wherein an electrical component in the form of an SMD component (SMD) of a printed circuit board is used to detect said electromagnetic radiation. [4] Method according to one of the preceding claims, wherein an electrical component in the form of a coil of an inductive signal transmitter (S) and / or an SMD component (SMD) of a printed circuit board (L) of a speed sensor of the electric motor are used to detect this electromagnetic radiation. [5] Method according to claim 3 or 4, wherein the circuit board (L) is also used to control the brush actuator (2). [6] Computer program for carrying out a method according to one of the preceding claims. [7] 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 5 when the program code means are executed on a computer. [8] 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 7. [9] Electric vehicle with a computer program product according to claim 7.

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