Method for pressing at least one first and / or one second contact brush against, in each case, an associated slip ring arranged on a rotor shaft of an electric motor for externally exciting a rotor of the electric motor arranged on the rotor shaft, computer program, computer program product, system and vehicle

Abstract

The invention relates to a method for pressing at least one first and / or one second contact brush (4, 6) against, in each case, an associated slip ring (8, 10) arranged on a rotor shaft of an electric motor for externally exciting a rotor of the electric motor arranged on the rotor shaft. The at least one first and / or second contact brush (4, 6) are / is contact-pressed in a quality-based manner, wherein a non-linear, saw-tooth-like progression of a contact pressing (F, FI, FII) of the contact brush(es) (4, 6) over an operating time of the electric motor is provided, which is brought about in that the contact pressing (F, FI, FII), as a control variable, repeatedly and continuously approaches a critical state (KQG, FI) and, as soon as said critical state is reached, moves back rapidly from said critical state so as to correct the contact pressing (FII). The invention also relates to a computer program, a computer program product, a system and a vehicle.

Description

[0001] Description

[0002] Method for pressing at least one first and / or one second grinding brush against an associated slip ring arranged on a rotor shaft of an electric motor for external excitation of a rotor of the electric motor arranged on the rotor shaft, computer program, computer program product, system and vehicle

[0003] The invention relates to a method for pressing at least one first and / or one second grinding brush against an associated slip ring arranged on a rotor shaft of an electric motor for externally exciting a rotor of the electric motor arranged on the rotor shaft, in particular 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 or such a system.

[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 proposed method having the features of claim 1. The subclaims relate to advantageous developments.

[0007] A method is proposed for pressing at least a first and / or a second grinding brush against an associated slip ring arranged on a rotor shaft of an electric motor - in particular for driving a vehicle - for externally exciting a rotor of the electric motor arranged on the rotor shaft.

[0008] In this case, at least the first and / or second grinding brush is / are pressed on in a quality-based manner and a non-linear, sawtooth-shaped course of pressure of the grinding brush(es) is provided over an operating time of the electric motor.

[0009] This non-linear, sawtooth-shaped course of the contact pressure is caused by the fact that the contact pressure as a controlled variable is repeatedly and continuously approached towards a critical state and, as soon as this critical state is reached, it is abruptly retreated from this critical state in the sense of a correction of the contact pressure.

[0010] This interplay between an approach to the critical state in the form of a contact quality limit and a retreat from the critical state in the sense of correction is carried out over the operating time of the electric motor.

[0011] Quality-based or quality-based contact pressure or pressure of the grinding brushes means that no more pressure is actively applied to the grinding brushes than necessary to achieve sufficient contact.

[0012] From an energy perspective, such a contact pressure can be considered the best possible or optimal contact, which – for a given load-dependent excitation current – ​​results in minimal 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. This proposed quality-based contact pressure therefore reduces wear on the grinding brushes to a minimum.

[0013] And the proposed sawtooth-shaped contact pressure helps to further reduce this contact pressure and thus the resulting wear of the grinding brushes.

[0014] 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.

[0015] Adequate contact between the slip rings and the grinding brushes can be measured and monitored using various physical parameters, such as:

[0016] - 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,

[0017] - via a transition resistance arising from a voltage drop and a flowing or monitorable excitation current and / or

[0018] - arcs appearing or occurring as a result of a local loss of contact, whereby these arcs emit electromagnetic waves whose frequency and amplitude can be detected or monitored (- plasma formation as a result of electrons passing through the air).

[0019] It is proposed that the grinding brushes be pressed primarily based on the excitation current or based on the load. This is because the lower the rotor's excitation current, the lower the quality-based contact pressure of the grinding brushes can be selected or adjusted, and the more the friction of the drive train can be reduced. In addition, it is proposed that the grinding brushes be pressed in a quality-based manner, taking into account various phenomena or influences that need to be compensated, such as

[0020] • a rotor (shaft) speed or 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),

[0021] • a rotor (shaft) non-uniformity or a non-uniformity of the slip rings arranged on the rotor or the rotor shaft and / or

[0022] • a vehicle acceleration in the direction of the grinding brushes, whereby the vehicle acceleration can be caused by a rough road and / or by a vibration source within the vehicle.

[0023] To approach the critical pressure, it is proposed that a rate of change for the pressure be set such that the stepwise pressure is reduced in a linear or nonlinear manner. In the latter case, the stepwise pressure can be reduced in a nonlinear progressive or degressive manner.

[0024] The correction can be set variable depending on an operating point of the electric motor or alternatively constant.

[0025] A computer program for carrying out the method of the type described above is also proposed (claim 5).

[0026] 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 (claim 6). Furthermore, a system with 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 (claim 7).

[0027] In addition, a vehicle with a computer program product of the type described above and / or a system of the type described above is proposed (claim 8).

[0028] 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.

[0029] Further advantages and features emerge from the subclaims and the exemplary embodiments. These are shown in:

[0030] Fig. 1 a proposed brush actuator in a perspective view,

[0031] Fig. 2 shows the brush actuator shown in Fig. 1 in a sectional view,

[0032] Fig. 3 a qualitative illustration of wear of grinding brushes.

[0033] Fig. 4 a proposed force control principle for an active brush actuator and

[0034] Fig. 5 shows a time course of a proposed force setting and a corresponding contact quality.

[0035] The bidirectional brush actuator 2, also called an active brush module 2, illustrated in Figs. 1 and 2, is used 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.

[0036] This brush actuator 2 is provided or arranged in a wet-running manner in the area of ​​an oil-lubricated bearing point of the rotor shaft and radially to the rotor shaft, as well as stationary to a housing of the electric motor. An oil seal is omitted at this bearing point in order to avoid friction associated with the oil seal. As a result, during vehicle operation, transmission 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 arrangement of the brush actuator 2 illustrated in Figs. 1 and 2 is sealed off from the surroundings of the electric motor by means of a housing cover (not shown here).

[0037] 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 socket, for example, shaped like a trunk, which is integrally formed on the housing of an electromagnet 12.

[0038] 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 arranged within a brush receiving and guide element 7 and are movable radially relative to the rotor shaft. For example, the grinding brush 4 has a negative polarity, and the grinding brush 6 has a positive polarity.

[0039] 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 as part of a support section of the electromagnet 12. This support section is arranged stationary relative to the housing of the electromagnet 12. 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 stationary relative to it.

[0040] 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.

[0041] 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 made purely metallic, for example, from a ferromagnetic metal or a stainless, magnetized steel.

[0042] The gear oil reaching the brush actuator 2 also cools or heats the grinding brushes 4, 6 and the electromagnet 12. This favors smaller-sized grinding brushes 4, 6 on the one hand and a smaller-sized electromagnet 12 on the other.

[0043] The spring 20 therefore exerts a nominal or static force of approximately 30 N on the grinding brushes 4, 6. When the electromagnet 12 is de-energized, this is the force with which the grinding brushes 4, 6 are pressed or pressed against the slip rings 8, 10.

[0044] Below a definable limit speed of the rotor shaft of, for example, approximately 800 rpm, the electromagnet 12 can remain de-energized in order to minimize the total power loss of the brush actuator 2.

[0045] 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, the electrical power loss of the electromagnet 12 at a reduced contact pressure or contact force, and the ohmic losses associated with the contact resistance from the respective grinding brush 4, 6 to the associated slip ring 8, 10. Below this limiting speed of approximately 800 rpm, the electrical power loss when actuating the brush actuator 2 is greater than the friction power savings at the grinding brushes 4, 6, which, as such - in comparison to passive operation of the brush actuator 2 - are achieved through a reduced contact force 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 orplay a subordinate role.

[0046] Below this limit speed, the grinding brushes 4, 6 are therefore advantageously pressed passively against the slip rings 8, 10.

[0047] Above this limit speed, however, an active pressing 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) irregularity or out-of-roundness, a vehicle acceleration in the direction of the grinding brushes 4, 6 and the like, so that a rotor (shaft) out-of-roundness, a floating of the grinding brushes 4, 6 on the transmission oil that wets the slip rings 8, 10 and / or vibrations and / or impacts that act on the brush actuator 2 can be counteracted as required.

[0048] By appropriately energizing the electromagnet 12, a required electromagnetic force of, for example, up to approximately 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 to up to approximately 80N in order to prevent the grinding brushes 4, 6 from lifting off during vehicle operation.

[0049] The armature 18 is joined to a force distribution element 22, namely under

[0050] Formation of a so-called ball joint. The anchor 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.

[0051] 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.

[0052] 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).

[0053] It is proposed that the grinding brushes 4, 6 be designed as silver graphite brushes, which improve the durability of the gear oil.

[0054] Figure 3 qualitatively illustrates wear A (A = wear) of the grinding brushes 4, 6 as a function of contact pressure P on the grinding brushes. The wear consists of mechanically abrasive wear M and electrically erosive wear E. This qualitative progression of wear M+E refers to a given excitation current. If this excitation current decreases, the minimum contact pressure required or to be applied to effect contact also decreases.

[0055] Fig. 4 illustrates, schematically or in the form of a block diagram, a proposed dynamic adaptive control of a brush force, with which the two sliding brushes 4, 6 are pressed against the associated slip rings 8, 10 of the rotor shaft in a quality-based manner. This control is implemented in a control unit of the vehicle, which maps this control. A controller 30 is shown, into which an excitation current le provided by an inverter Inv and, if applicable, information about a predictable or foreseeable, impending event are input. The controller 30 - or a model on which it is based - determines from this a desired force specification Fsoii, which is implemented as such in the brush module 40 by appropriately energizing the electromagnet 12 and then exerted on the sliding brushes 4, 6.This results in a force Ftat actually exerted on the grinding brushes 4, 6, which may deviate slightly from the target force Fsoii.

[0056] This force Ftat is changed or distorted during the operation of the vehicle by various disturbances or influencing factors, because these disturbances or influencing factors act on the brush module 40 and change or distort a contact 50 caused by the force Ftat between the brushes 4, 6 and the associated slip rings 8, 10. The disturbances or influencing factors are illustrated here:

[0057] • a hydrodynamic effect of the gear oil, which acts on the brush module 40 and thereby forms an oil film between the grinding brushes 4, 6 and the associated slip rings 8, 10,

[0058] • an out-of-roundness of the slip rings 8, 10 and

[0059] • Vibrations or oscillations which as such act on the brush module 40.

[0060] The oil film between the grinding brushes 4, 6 and the associated slip rings 8, 10 builds up with increasing rotor (shaft) (rotational) speed and thereby reduces the contact quality KQ between the grinding brushes 4, 6 and the slip rings 8, 10.

[0061] The out-of-roundness of a slip ring 4, 6 interacting with the associated

[0062] The outer surface of the respective slip ring 8, 10 causes a decrease in the contact quality KQ between the grinding brushes 4, 6 and the slip rings 8, 10 with increasing rotor (shaft) (rotational) speed.

[0063] Vibrations or oscillations, which as such act on the brush module 40 and thereby influence the contact 50 between the brushes 4, 6 and the associated slip rings 8, 10, counteract the contact quality KQ between the brushes 4, 6 and the slip rings 8, 10 with increasing rotor (shaft) (rotational) speed. These can be vibrations generated by a rough road and / or vibrations generated by a drive train, which can be detected as such by sensors, for example in the area of ​​an electric front- and / or rear-wheel drive by means of appropriate sensors.

[0064] These previously listed disturbance variables can be compensated either completely by controller 30 or, alternatively, only partially by controller 30. In the latter case, these disturbance variables are detected or pre-controlled as pilot control variables. This simplifies the proposed control and makes it more dynamically agile.

[0065] A rough road section, for example in the area of ​​a construction site, could also be predicted or predicted based on at least one camera of the vehicle and / or map data of a vehicle navigation system (see the input variable KQext in the controller 30, which illustrates such an external influence on the contact quality KQ).

[0066] As a result, a resulting brush force or actual force Fist is established on the brush module 40, which causes a corresponding contact 50 between the grinding brushes 4, 6 and the associated slip rings 8, 10.

[0067] This actual force Factual causes a contact quality KQactual between the brushes 4, 6 and the associated slip rings 8, 10. This contact quality KQactual is fed back to the controller 30. This contact quality KQactual can be expressed as an excitation current or a corresponding voltage and can be recorded or measured.

[0068] This proposed quality-based contact 50 ensures the provision of a torque requirement DA. It minimizes friction losses RV and also reduces electrically erosive wear eeV (eeV = electrically erosive wear) of the grinding brushes 4, 6 or between the grinding brushes 4, 6 and the associated slip rings 8, 10.

[0069] The graph to the left of controller 30 qualitatively illustrates the relationship between a brush force F (or contact pressure) set on the brush module 40 and a contact quality KQ between the brushes 4, 6 and the associated slip rings 8, 10. As the brush force F (or contact pressure) increases, the contact quality KQ generally increases. In addition, a contact quality range KQB is also qualitatively shown, within which this control takes place.

[0070] Fig. 5 qualitatively illustrates, on the one hand, a temporal course of a brush force F and, on the other hand, a measured or measurable contact quality KQg (g = measured) caused or caused by this brush force F.

[0071] The set brush force F, with which the brushes 4, 6 are pressed against the associated slip rings 8, 10 in a quality-based manner, has a first component Fl corresponding to a contact quality limit KQG and a second component FH in the sense of a specified safety distance or a specified correction to this contact quality limit KQG.

[0072] Starting from a setting of the brush force F at a time at which the second component FH is abruptly impressed on the first component Fl in the sense of the safety distance or the correction, the set brush force F is continuously reduced by a rate of change until the measured contact quality KQg between the brushes 4, 6 and the slip rings 8, 10 caused by the brush force F reaches or falls below the contact quality limit KQG. And after this contact quality limit KQG has been reached or fallen below, the brush force Fl is again abruptly increased in a corrective manner, only to be reduced again afterwards, whereby this interplay between correction and reduction of the brush force F is carried out or is to be understood as occurring over an operating time of the electric motor.

[0073] The measured contact quality KQg is shown as a thick line. This is intended to illustrate signal noise around an average value of the measured contact quality KQg.

[0074] The contact quality limit (KQG) is set at a sufficient distance from a so-called forbidden contact quality range (vKQB), which must be avoided at all costs. This distance between the contact quality limit (KQG) and the forbidden contact quality range (vKQB) is to be understood as ensuring that signal noise in the form of detectable or measurable current or voltage ripples is avoided.

[0075] This interplay between correction and reduction of the brush force F is also to be understood, interpreted and read within the contact quality range KQB illustrated in Fig. 4 (see the graphic there to the left of the controller 30).

[0076] As a result, the illustrated method of adjusting the brush force F, Fl, FH creates a nonlinear, sawtooth-shaped or sawtooth-like force curve, which results in a measured sawtooth-shaped or sawtooth-like contact quality KQg close to the quality limit KQG. Such a sawtooth-shaped force curve or such a sawtooth-shaped contact quality KQg advantageously minimizes the computational effort of the previously described control system.

[0077] The said rate of change of the brush force F can be selected such that the brush force F is reduced in a linear or nonlinear manner. A nonlinear reduction of the brush force F can be represented in a nonlinear progressive or degressive manner. The said safety margin or correction FH can be set variably depending on an operating point of the electric motor or, alternatively, simply be set constant.

[0078] The quality-based contact pressure of the grinding brushes 4, 6 described here describes a dynamically adaptive control of a brush force to ensure a required contact quality (corresponding to a torque requirement DA). This required contact quality is met or counteracted by the second component of the contact pressure (or the brush force component) FH.

[0079] The basic idea behind this proposed control is based on a repeated, continuous approach of the controlled variable (= contact pressure or brush force or the contact quality caused by it) to a critical state (= contact quality limit) and the immediate retreat from the critical state as soon as the first signs of reaching or falling below this critical state are detected.

[0080] This proposed control is mapped or implemented in a control unit for actuating the brush actuator or brush module. This control unit is connected to a CAN bus of the vehicle. The excitation current, which serves as the input variable for this contact pressure control within the control unit, can be provided by a control unit of the inverter via a communication interface. The aforementioned pilot control variables can also be provided via this communication interface to temporarily increase the contact pressure and prevent damaging lifting of the grinding brushes 4, 6.

[0081] 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 vehicle and the proposed brush actuator.

[0082] 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.

[0083] The computer program or computer program product can be read into an existing control electronics system using simple means and used to control and / or regulate both the vehicle and the proposed brush actuator 2.

[0084] 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.

[0085] 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 it results from the claims and equivalent combinations of features.

Claims

Patent claims 1. A method for pressing at least one first and / or one second grinding brush (4, 6) against a respective slip ring (8, 10) arranged on a rotor shaft of an electric motor for externally exciting a rotor of the electric motor arranged on the rotor shaft, wherein the at least one first and / or second grinding brush (4, 6) is / are pressed in a quality-based manner, wherein a non-linear, sawtooth-shaped profile of a contact pressure (F, Fl, FH) of the grinding brush(es) (4, 6) is provided over an operating time of the electric motor, which is achieved by repeatedly and continuously approximating the contact pressure (F, Fl, FH) as a controlled variable to a critical state (KQG, Fl) and, as soon as this critical state is reached, abruptly retreating from this critical state in the sense of a correction of the contact pressure (FH).This interplay between an approach to the critical state in the form of a contact quality limit (KQG, Fl) and a retreat from the critical state in the sense of the correction (FH) is carried out over an operating time of the electric motor.

2. Method according to claim 1, wherein for approaching the contact pressure to the critical state, a rate of change for the contact pressure is provided such that the abruptly adjusted contact pressure (F, Fl, FH) is reduced in a linear or non-linear form.

3. Method according to claim 2, wherein the abruptly adjusted contact pressure (F, Fl, FH) is reduced in a non-linear progressive or degressive manner.

4. Method according to one of the preceding claims, wherein the correction (FH) is set variable or, alternatively, constant depending on an operating point of the electric motor.

5. A computer program for performing a method according to one of the preceding claims.

6. A computer program product comprising program code stored on a computer-readable data carrier for performing the method according to one of the preceding claims 1 to 4 when the program code is executed on a computer.

7. 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 6.

8. Vehicle with a computer program product according to claim 6 and / or a system according to claim 7.

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