Wet-running brush adjuster and externally excited electric motor

Abstract

The invention relates to a wet-running brush adjuster for externally exciting a rotor of an electric motor (EM), said rotor being arranged on a rotor shaft (RW). The brush adjuster (2) has an electric stepping motor with an integrated spindle drive, the spindle of which, which can be moved longitudinally with respect to the stepping motor, acts indirectly via at least one spring and a force distribution element against an associated contact brush (B1) for pressing against an associated slip ring (SR1, SR2) of the rotor shaft (RW). The invention further relates to an externally excited electric motor (EM) having such a brush adjuster.

Description

[0001] Description

[0002] Wet-running brush holder and separately excited electric motor

[0003] The invention relates to a wet-running brush holder for external excitation of a rotor of an electric motor arranged on a rotor shaft, and to an externally excited electric motor with such a brush holder.

[0004] 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.

[0005] This problem is solved by a brush holder having the features of claim 1.

[0006] With this 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.

[0007] The spindle drive enables active control of this contact pressure. Instead of contact pressure, one can also speak of pressure exerted or force applied.

[0008] The spindle drive converts or transmits a rotational movement of a spindle nut – which functions as a rotor with magnets of the stepper motor – into a translational movement of the spindle.

[0009] As a result of this translational movement, at least one spring deforms, thereby exerting a force on the associated grinding brush, either indirectly or indirectly, via this spring. This deformation of the 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] Such quality-based pressure reduces the wear of such grinding brushes to a minimum.

[0014] 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.

[0015] The proposed brush adjuster enables robust, quality-based control of brush force or pressure of the grinding brushes, and does so with the least possible effort from an energy point of view.

[0016] The proposed brush holder also enables reliable current transmission for torque generation. It is proposed that the spindle drive be designed without backlash and 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.

[0017] 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.

[0018] 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.

[0019] For the sake of completeness, reference is made here, for example, to the applicant's German patent application with file number 10 2023 211 551.4, which discloses an active force application or a dynamically adaptive and quality-based control of a brush force. This disclosure is hereby expressly incorporated by reference, and the force control described therein is hereby made the subject of this present disclosure.

[0020] 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.

[0021] It is proposed that the force distribution element be tiltable or inclinable relative to the spindle by forming a joint with the spindle.

[0022] Alternatively, it is proposed that the force distribution element be tiltable or adjustable relative to the spindle by being joined to the spindle with clearance in a joint area. This clearance joint represents a kind of – at least partial – encapsulation of the spindle in this joint area by the force distribution element and can be designed such that the force distribution element can be lifted by the spindle in order to allow for regular adjustment or readjustment of the brush holder, as will be described below.

[0023] 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 applying force evenly to the grinding brushes.

[0024] At least one spring can be provided between the spindle and the force distribution element. Additionally or alternatively, one spring each can be provided between the force distribution element and the associated grinding brush.

[0025] 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 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 spring element in one and the same element or component.

[0026] Claim 10 provides protection for a separately excited electric motor with such a brush holder.

[0027] When using such a stepper motor, it is essential to ensure that no so-called step losses 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 contact pressure of the respective grinding brush against the associated slip ring, these step losses lead to an unintended reduction in this contact pressure.

[0028] However, a shortening of the brush(es) due to wear, which relaxes the spring, also results in an unwanted lowering or reduction of this pressure.

[0029] Therefore, an operating procedure or method for determining a so-called zero-force reference position of such a wet-running brush actuator is proposed, which compensates for these two effects that reduce the contact pressure. This procedure for calibrating, adjusting, or recalibrating the stepper motor can be performed regularly, i.e., at definable or defined time intervals.

[0030] It is proposed that between two driving cycles of an electric vehicle equipped with an electric motor, while the electric vehicle is stationary and the rotor is externally excited, the spindle is moved away from the grinding brushes until the contact between the grinding brushes and the associated slip rings reaches a contact quality limit, whereby the position assumed by the spindle is defined as the zero-force reference position, from which the steps or rotational steps of the stepper motor are counted in order to variably press the grinding brushes against the slip ring as required.

[0031] 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.

[0032] This process can be initiated and carried out by the vehicle system, for example, after a defined mileage – such as mileage – of the electric vehicle, while the electric vehicle is stationary and the rotor is externally excited.

[0033] 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 – with regard to the contact pressure, at which there is insufficient contact between the respective slip ring and the associated grinding brush. At or along this contact quality limit, the spindle of the spindle drive assumes the so-called zero-force reference position, from which – as already mentioned – the steps or rotational steps of the stepper motor are counted in order to variably apply the required contact pressure of the grinding brushes against the slip ring.

[0034] The condition at which the contact quality limit is reached and at which the contact pressure of the respective grinding brush is essentially reduced to zero, causing the grinding brush to lift 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.

[0035] This advantageously avoids the need for large currents or rotor currents and power levels, which would otherwise cause high wear on the grinding brushes. The stepper motor position – or rather the position of the stepper motor spindle – at the moment the grinding brushes lift off is stored as the new zero-force reference position in a control unit, such as the inverter control unit. All further requirements for corresponding force control, etc.

[0036] The brush positioner settings can then be recalculated on this basis.

[0037] Furthermore, by evaluating such zero-force reference positions determined over the lifetime of a vehicle, conclusions can be drawn about brush wear and also about the wear rate of the grinding brush(es).

[0038] The contact quality between the respective grinding brushes and the associated slip rings can be detected or monitored using various physical quantities, such as: the 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, a developing or established contact resistance resulting from a voltage drop and a flowing or monitorable excitation current, and / or 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.

[0039] 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.

[0040] Furthermore, the use of a wet-running brush actuator of the type described above for force control of the brush force according to the type described above is proposed, in which the brush force is controlled dynamically, adaptively, and based on quality. Further advantages and features will become apparent from the dependent claims and the exemplary embodiments. These are shown in:

[0041] Fig. 1 shows a proposed first brush holder in a perspective view,

[0042] Fig. 2a) the brush holder shown in Fig. 1 in a first sectional view,

[0043] Fig. 2b) the brush holder shown in Fig. 1 in a second sectional view,

[0044] Fig. 3 shows the brush holder shown in Fig. 1 in a perspective view arrangement on an electric motor,

[0045] Fig. 4 shows a proposed second brush holder in a sectional view and

[0046] Fig. 5 shows a proposed third brush holder in a perspective view.

[0047] The bidirectional brush holders 2 – or brush modules 2 – illustrated in Figures 1 to 5, serve to externally excite a rotor of an electric motor EM arranged on a rotor shaft RW. This motor is a synchronous machine used to drive a vehicle or electric vehicle. The electric motor EM is combined with a reduction gearbox, which is oil-lubricated and oil-cooled. Gear oil lubricates and cools the electric motor EM and is circulated within an oil cooling circuit that includes the gearbox and the electric motor EM.

[0048] These brush holders 2 are each wet-running in the area of ​​an oil-lubricated bearing point of the rotor shaft RW and are radially aligned to the rotor shaft RW, and are fixedly mounted to a housing of the electric motor EM. An oil seal is omitted at this bearing point, allowing the gear oil from inside the housing of the electric motor EM to escape through the bearing point and reach the brush holder 2. This arrangement of the brush holder 2 is sealed off from the environment by a housing cover (not shown).

[0049] Such a brush holder 2 is attached or fastened to the housing of the electric motor EM via mounting points APi, AP2, AP3 (see e.g. Fig. 2a)).

[0050] The proposed brush holders 2 each have an electric stepper motor 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.

[0051] The spindle 10, which is longitudinally movable relative to the stepper motor 4, acts indirectly via at least one spring 14, 14a, 14b and an electrically non-conductive or insulating force distribution element 16 – made, for example, of plastic – against an associated first and second grinding brush Bi, B2 to press against an associated slip ring SR1, SR2 of the rotor shaft RW. Depending on the direction and travel of the spindle 10, the pressure of the grinding brushes Bi, 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.

[0052] This brush holder 2 or its stepper motor 4 can be electrically contacted via a trunk-shaped socket BU, which can be - at least partially - molded onto a housing of the stepper motor 4.

[0053] The two grinding brushes Bi and B2 are each movably arranged within an associated brush holder and brush guide element 26 and radially to the rotor shaft RW. Grinding brush Bi is, for example, negatively polarized and grinding brush B2 is therefore positively polarized (see the electrical connections 28 and 30 in Fig. 1). In the embodiment according to Figs. 1, 2a), 2b), and 3, a 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 force distribution element 16. The free end of the spindle 10, facing the force distribution element 16, extends through this spring 14 to or into the force distribution element 16. This force distribution element 16 is joined in the region of its associated end of the spindle 10 to at least one shell-shaped or shell-like element 18, e.g. clipped or clamped. However, other methods are also possible, e.g.at least two such shell-shaped or shell-like elements 18 are joined together and with the force distribution element 16 and are clipped or clamped together with the force distribution element 16.

[0054] This creates an encapsulation – possibly in multiple parts – of the end of the spindle 10 facing the force distribution element 16, so that the grinding brushes Bi , B2 can be briefly lifted for the purpose of calibrating or adjusting or readjusting the stepper motor 4 to compensate for or eliminate so-called step errors of the stepper motor 4 – also called step losses.

[0055] Alternatively, this element 18, with which the spindle 10 is joined with play, can also be formed in one piece or as a single unit with the force distribution element 16, by injection-molding or injection-casting a correspondingly pivotable functional element 18 onto the force distribution element 16, which is made of a plastic, for example (functional integration), which can be opened accordingly in order to be joined with the spindle 10.

[0056] This joint or encapsulation is designed with sufficient play to allow the force distribution element 16 to tilt or incline relative to the spindle 10 in the joint area. This compensates for uneven wear of the grinding brushes Bi, B2, with the tilt or inclination adjusting accordingly. The two free ends of the force distribution element 16, or rather its forked sections, each have a gripping section 20 with, for example, two gripping fingers or lugs, which engage the respective grinding brush Bi, B2 in a form-fitting and force-fitting or friction-fit manner.

[0057] These gripping fingers or gripping noses and the associated grinding brushes Bi , B2 can also be shaped in such a way that these gripping fingers or gripping noses of the gripping sections 20 also snap or lock behind or enclose the associated grinding brushes Bi , B2.

[0058] For example, Figures 1 and 2a) show an oil connection 22 which leads into a forking or branching oil line 24, through which the oil is supplied to the two grinding brushes Bi, B2. This ensures that the grinding brushes Bi, B2 are always sufficiently supplied with oil during operation of the electric motor EM and during forward movement of the electric vehicle. Figure 1 shows one of two such branching or forking sections 24a, 24b of the oil line 24.

[0059] Fig. 3 illustrates an arrangement consisting of the previously described brush holder 2 and an electric motor EM, whose rotor shaft RW has two metallic slip rings SR1, SR2, which interact with the associated grinding brushes Bi , B2 - approximately in the form of silver graphite brushes.

[0060] A helical spring provided in Figs. 2a) and 2b) above the stop section 12 and 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 backlash.

[0061] According to Fig. 4, the brush holder 2 has a helical spring 14a, 14b located between the power transmission element 16 and the associated grinding brush Bi, B2. Both fork sections extend into their respective helical springs 14a, 14b. A head-like section 11, which can be screwed or attached to the spindle 10, or alternatively formed integrally with the spindle 10, is articulated relative to the power transmission element 16. This section 11 has a concave recess – in the sense of a ball socket – into which a correspondingly shaped projection section of the power transmission element 16 – in the sense of a ball head – engages, so that the power transmission element 16 forms a ball joint with the section 11.The arrangement of the force transmission element 16 and the two coil springs 14a, 14b is essentially or largely received, encompassed, or enclosed by a housing section G of the brush holder 2.

[0062] This ball joint allows the force distribution element 16 to be tilted relative to the spindle 10, thus preventing uneven wear of the grinding brushes Bi, B2.

[0063] In this version as well, a helical spring provided above section 11 and acting from above against this section 11 ensures that the spindle drive is free of play by clamping the spindle 10 against the spindle nut 8.

[0064] Figures 1 to 4 describe a transverse force-free design of a brush holder 2. This means that the spindle 10 does not experience any operational transverse force.

[0065] In contrast to Figures 1 to 4, Figure 5 illustrates an embodiment with a spring 14 in the form of a leaf spring (or in the sense of a bending beam). This spring 14 is supported at a support point SP or support section, which is fixed to the housing of the stepper motor 4. At one of its two ends, it interacts with the spindle 10, and at the other end with the power transmission element 16. The leaf spring 14 transmits a movement of the spindle 10 in the opposite direction.

[0066] When the spindle 10 moves upwards or out of the housing of the stepper motor 4, the two grinding brushes Bi , B2 experience an increasing pressure or compression by the power transmission element 16 against the associated slip rings SR1, SR2 of the rotor shaft RW.

[0067] If, however, the spindle 10 moves downwards or into the housing of the stepper motor 4, the two grinding brushes Bi, B2 experience a decreasing contact pressure from the power transmission element 16 against the associated slip rings SR1, SR2 of the rotor shaft RW. This design represents a particularly compact arrangement in the vertical direction.

[0068] 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 spring or spring element – ​​with a defined stiffness, in particular of the individual fork sections or arms – and forms a series spring connection with the previously described helical spring 14. Alternatively, such a force distribution element 16 can also replace or render unnecessary the previously described helical spring 14. In the latter case, space could be saved.

[0069] It is intended to regularly calibrate or readjust the stepper motor 4 of this brush holder 2 in order to eliminate step errors, so-called step losses, that occur in the meantime and / or to counteract wear of the grinding brushes Bi, B2.

[0070] 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.

[0071] To correct such step errors or step losses, 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 is moved away from the grinding brushes Bi , B2 until the contact between the grinding brushes Bi , B2 and the associated slip rings SR1, SR2 reaches a contact quality limit.

[0072] The position assumed by the spindle 10 is recorded as the zero-force reference position and is defined, stored, or saved as such in a control unit, from which the steps of the stepper motor 4 are correctly counted in order to be able to press the grinding brushes Bi , B2 against the slip rings SR1, SR2 variably as required.

[0073] In the embodiment according to Figs. 1 to 3, the force distribution element 16, which encompasses or surrounds the two grinding brushes Bi , B2 via the respective associated gripping sections 20, is lifted by the spindle 10, specifically via the element 18 forming the aforementioned encapsulation, against which the spindle 10 abuts when it is moved away from the grinding brushes Bi , B2.

[0074] This proposed operating method thus eliminates the need for a position encoder - a so-called incremental encoder or absolute encoder - which measures or detects the exact rotational position or orientation of the spindle nut 8 in order to correct the control of the stepper motor 4 accordingly.

[0075] Furthermore, a computer program for carrying out the procedure of the type described above is proposed.

[0076] 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. A system comprising a brush actuator and a control unit for actuating the brush actuator is also proposed, the control unit comprising a computer program product of the type described above.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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 actuator. For this purpose, a computer program product is provided with program code stored on a computer-readable data carrier to execute the method according to any one of the claims when the computer program product is run in the CPU. The computer program product can also be integrated into the control electronics as a retrofit option.

[0081] 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

Patent claims 1. Wet-running brush holder (2) for external excitation of a rotor of an electric motor (EM) arranged on a rotor shaft (RW), wherein the brush holder (2) has an electric stepper motor (4) with an integrated spindle drive, the spindle (10) of which is longitudinally movable relative to the stepper motor (4) acts indirectly via at least one spring (14, 14a, 14b) and a force distribution element (16) against an associated grinding brush (Bi , B2) to press against an associated slip ring (SR1, SR2) of the rotor shaft (RW).

2. Wet running brush holder (2) according to claim 1, wherein the spindle drive is self-locking.

3. Wet running brush holder (2) according to claim 1 or 2, wherein the force distribution element (16) is fork-shaped and interacts with a first grinding brush (Bi) via a first fork section and with a second grinding brush (B2) via a second fork section.

4. Wet running brush holder (2) according to claim 3, wherein the force distribution element (16) is tiltable relative to the spindle (10) by forming a joint with the spindle (10).

5. Wet running brush holder (2) according to claim 3, wherein the force distribution element (16) is tiltable relative to the spindle (10) by being joined with the spindle (10) in a joining area with clearance.

6. Wet running brush holder (2) according to claim 5, wherein the assembly is shaped such that the force distribution element (16) can be lifted by the spindle (10).

7. Wet running brush holder (2) according to any one of the preceding claims 1 to 6, wherein the spring (14) is provided between the spindle (10) and the force distribution element (16).

8. Wet running brush holder (2) according to one of the preceding claims 1 to 7, wherein a spring (14a, 14b) is provided between the force distribution element (16) and the associated grinding brush (Bi, B2).

9. Wet running brush holder (2) according to any one of the preceding claims 1 to 8, wherein the force distribution element (16) is designed to be elastic such that it forms a spring.

10. Externally excited electric motor (EM) with a brush controller according to one of claims 1 to 9.

11. Use of a wet-running brush holder according to one of the preceding claims 1 to 9 for a force control of the brush holder in which the brush force is controlled dynamically adaptively and based on quality.

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