Predicted brush regulation in a separately excited motor

Abstract

The invention relates to a device and a method for predictive brush regulation in a separately excited electric machine. The separately excited electric machine (10) comprises a brush unit (20) with sub-brushes (21) which are movable by means of a regulating mechanism (22) driven by a regulating motor (23) either towards the commutator (13) to establish electrical contact between the sub-brushes (21) and the commutator (13) in a reversible manner or away from the commutator (13) to disconnect the electrical contact between the sub-brushes (21) and the commutator (13) in a reversible manner. The brush unit (20) is connected to a control unit which is designed to control the regulating motor (23) in such a way that only the minimum contact area between the entire sub-brush (10) and the commutator (13) required for reaching a predicted, i.e. future, electric machine (10) operating point is provided.

Description

TECHNICAL FIELD

[0001] The present invention relates to a device and a method for predictive brush regulation in a separately excited electric machine. BACKGROUND

[0002] In a separately excited electric machine, the excitation current is transmitted via a brush to a commutator or a slip ring located on the rotor (mover). The brush is pressed against the commutator via a pressure spring. This establishes an electrically conductive connection between the two subcomponents, so that current can flow into the rotor, which in turn excites the rotor to rotational movement. The function of the sliding contact achieved by the brush is the same in direct current and alternating current machines, except that alternating current machines do not require a commutator, since the excitation power is transmitted to the mover via a slip ring.

[0003] The pressure spring continuously presses the brush against the commutator or slip ring. As a result, friction losses also occur when the electric machine is not working in motor or generator operating mode. This operating point exists in the case of electrically powered vehicles when the vehicle is coasting, i.e. for example when idling. The sliding contact (transition from brush to commutator / slip ring) leads to permanent wear. In addition, in many operating points, the entire contact surface of the brush with the commutator or slip ring is not needed at all, since maximum power is not always required to be transmitted (for example when driving continuously in partial load range). In addition, the sliding contact always produces noise due to the sliding movement. Depending on the construction, the components used and the power required, these noise emissions can be disturbing (in the vehicle and outside the vehicle). The continuous contact of the brush also leads to continuous wear, which in turn leads to contamination of the electric machine, which over time has a negative effect on the function and efficiency of the electric machine.

[0004] US 2008 / 131 099 A1 discloses a method, computer readable medium and system for automatically determining a prescribed operating current of an electric machine. In the method, a test signal is sent to an input of the electric machine and a response to the test signal is measured at an output of the electric machine. Based on the measured response, a position of a brush is determined, which can conduct current through a commutator of the electric machine. A first input current is supplied to the electric machine when the brush is in a first position and a second input current is supplied to the electric machine when the brush is in a second position.

[0005] GB 2 059 686 A relates to a brush for an electric machine, wherein the brush is split, i.e. comprises a number of electrically conductive layers which are not joined. The electrically conductive layers of the split brush are spaced apart from each other by an insulating layer.

[0006] A brush holder device for an electric motor generator is known from WO 2010 / 093 617 A2. It comprises a brush holder which is fixed in a snap-in manner on a shielding device. A brush element is movably mounted in the brush device and comprises a recessed area and a shunt element. A spring with constant force is operatively connected between a second end section of the brush and a brush fixing. SUMMARY

[0007] Against this background, it is an object of the present application to provide a device and a method by which the efficiency of an electric machine of a vehicle power device can be increased and wear of the electric machine can be reduced.

[0008] According to the application, this object is achieved by a device having the features of claim 1 and by a method having the features of claim 8. Variants and refinements of the application result from the dependent claims, the description and the drawings.

[0009] The subject of the present application is a separately excited electric machine comprising a brush unit with sub-brushes, which are moved by means of an adjusting mechanism driven by an adjusting motor, respectively, towards a commutator to establish an electrical contact between the sub-brushes and the commutator in a reversible manner, or away from the commutator to disconnect the electrical contact between the sub-brushes and the commutator in a reversible manner. According to the application, the brush unit comprises the sub-brushes and the associated adjusting mechanism and adjusting motor. According to the application, the brush unit is connected with a control unit, which is set up to control the adjusting motor in such a way that only the minimum contact area required for reaching a predicted imminent operating point of the electric machine is provided between the totality of the sub-brushes and the commutator. In one embodiment, the control unit is integrated in the electric machine. In another embodiment, the control unit is located outside the electric machine.

[0010] The separately excited electric machine is configured in such a way that instead of one large brush a plurality of smaller brushes with reduced width are provided according to the contact. Each of these sub-brushes can be actively adjusted by the adjusting motor, respectively, away from the commutator / collector or pressed onto it. If the brush is moved away from the commutator / collector, respectively, an air gap is formed between the sub-components, then no current flows. With the aid of prediction data of the imminent operating point, the sub-brushes are correspondingly applied or moved away in a variable manner in a preparation phase, so that only the minimum required contact area is provided between the totality of the sub-brushes and the commutator / collector. The aim is to implement an ideal brush configuration on the commutator or collector at the time of power output or consumption.

[0011] During idling, i.e., when no current flow is required, all brushes can be raised to achieve maximum efficiency without frictional losses at that operating point. Once more power must be transferred to the motor, the control unit controls the individual regulating motors to generate feed, which brings one or more sub-brushes into contact with the commutator or slip rings. The required brush placement area is calculated throughout the entire driving process.

[0012] The brush unit includes two sets of sub-brushes, one set for each contact portion. Each contact portion includes multiple sub-brushes, such as two, three, or four sub-brushes. In one embodiment, the brush unit includes sub-brushes of different widths. In another embodiment, all sub-brushes in a set have different widths. In a particular embodiment, the widths of the sub-brushes are progressive, for example, in a ratio of 1:2:3:...n, or 1:2:4:...2n, or 1:3:9:...3 n , or 1:4:8:...2 n Because the widths of the sub-brushes are different, the overall brush surface that fits against the commutator / sliding contact can be adjusted more flexibly.

[0013] In one embodiment, the brush unit includes means for detecting the length of the sub-brush. In another embodiment, the means for detecting the length of the sub-brush is configured to transmit the length of the sub-brush to a control unit. The control unit can use this data to control the sub-brush, thereby ensuring reliable contact with the commutator / slip ring even when the sub-brush has shortened due to wear. The length of the sub-brush can also be used to identify when replacement is necessary.

[0014] Typically, the regulating motor is an electric motor. In one embodiment, the regulating motor is a linear electric motor.

[0015] In one embodiment, the control unit is connected to a computing unit configured to predict upcoming operating points of the separately excited motor. In another embodiment, the computing unit is configured to receive and process real-time information about vehicle environment, route, and traffic data.

[0016] The present invention also relates to a method for operating a separately excited motor according to the invention for a vehicle power unit, wherein the control unit controls the regulating motor of the brush unit as follows: providing only the minimum contact surface required to achieve the predicted upcoming operating point of the motor between the entire sub-brush and the commutator.

[0017] In one embodiment of the method, the length of each sub-brush of the brush unit is determined, and the length of each sub-brush of the brush unit is taken into account when controlling the associated regulating motor.

[0018] In an embodiment of the method, the upcoming operating point of the electric machine is predicted by the computing unit on the basis of real-time information relating to the vehicle environment, route, traffic data, and data relating to the current driving behavior of the vehicle driver.

[0019] The computing unit calculates on the basis of the current driving behavior, route, traffic data, and data from the communication with other vehicles and traffic infrastructure, how much power the electric machine will probably call for next.

[0020] In an embodiment, the vehicle can use various real-time information relating to the vehicle environment, route, online traffic data, and data obtained by exchange with other traffic participants (car-to-car) and other objects (car-to-X). These data are evaluated by means of a central computing unit (ECU: electronic control unit) in the vehicle or by means of a data processing unit (server) located on the Internet. On the basis of these and other information (for example, the current driving behavior of the driver), it is possible to predict what power will be required in the subsequent driving situation. The computing unit determines how much brush bearing area is required at the respective immediately following operating point and the control unit controls the individual sub- brushes of the brush unit accordingly.

[0021] In an embodiment of the method, in the case of a self-learning algorithm in the ECU or server, it is possible to predict more and more accurately how the driving behavior of the driver will be and how this, in combination with the prediction data, influences the power output and consumption of the vehicle or, respectively, of the electric machine. As a result, the brush bearing area can be selected more and more accurately and precisely to the situation.

[0022] The advantage of the solution according to the invention is that, because all sub- brushes can be driven and moved vertically predictively, the most energy- efficient configuration of the brush bearing area can be selected individually and according to the upcoming power output and consumption. This contributes to an increase in the efficiency of the power device. Furthermore, the computing unit in the vehicle can determine accurately whether and when a (sub-) brush must be replaced. In addition, the method contributes to a considerable reduction or complete avoidance of noise emissions, which often have a disruptive effect in vehicles, in particular. Another positive effect is that the brush material is saved, because wear is reduced. This can increase the durability and avoid high-cost repairs. At the same time, unnecessary power device pollution and associated efficiency losses are avoided. The reduction in the heating of the sliding surfaces and, in turn, the suppression of the overall heating of the electric machine contribute to the fact that the electric machine does not have to be cooled very intensively and, in turn, the vehicle can be driven for longer without having to reduce the power (due to excessive temperatures). The predicted brush application management also avoids unexpected acceleration delays that occur in the case of brushes that are applied only at the exact point in time at which the load is called, for example, when the driver steps on the accelerator pedal. Further advantages and design solutions of the invention result from the description and the drawings.

[0023] It is apparent that the features mentioned above and to be explained below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the application. BRIEF DESCRIPTION OF DRAWINGS

[0024] The application is schematically presented on the basis of the embodiments in the drawings and is further described with reference to the drawings. In which:

[0025] Figure 1 A schematic diagram showing an embodiment of a brush unit according to the application. DETAILED DESCRIPTION

[0026] Figure 1 A separately excited electric machine 10 is shown, which has a brush unit 20 according to an embodiment of the application. The separately excited electric machine 10 has a rotor 11 and a stator 12, wherein the rotor 11 rotates when an electric current I flows through it. The rotor 11 is supplied with current by means of a commutator 13. The electric current I is fed to the commutator 13 via the brush unit 20.

[0027] The brush unit 20 comprises a plurality of (sub) brushes 21 (1...n), which can be moved individually via an adjustment mechanism 22 and an adjustment motor 23, respectively, towards the commutator 13 and into electrically conductive contact with the commutator or away from the commutator 13, whereby the electric contact between the (sub) brushes 21 and the commutator is broken and an air gap is formed. The (sub) brushes 21 have a vertical variability / variable stroke 24, which is indicated by the arrows in the drawing, i.e. they can be moved individually away from the surface of the commutator 13 to a maximum distance or, on the other hand, towards the surface of the commutator 13 to compensate for the wear of the (sub) brushes 21 due to wear. The individual (sub) brushes 21 are electrically isolated from one another. In the embodiment shown in the drawing, the (sub) brushes 21 have different brush widths (x, y) 25. The brush unit 20 has a device 26 for detecting the length of the (sub) brushes 21. The measurement of the length of the (sub) brushes 21 enables, on the one hand, an exact adjustment of the positioning of the (sub) brushes 21 even in the case of a change in length of the (sub) brushes 21 due to wear and, on the other hand, the determination of the point in time at which the (sub) brushes 21 need to be replaced.

[0028] A control unit, not shown in the drawing, controls the adjustment motors 23 of the individual (sub) brushes 21 in order to adjust the electric current flowing through the commutator 13 required for the respective immediately following operating point. The control unit (or a central computing unit connected thereto) determines how many brush bearing surfaces are required at the respective operating point at the very least and controls the individual (sub) brushes 21 accordingly.

[0029] In the freewheeling mode, all (sub) brushes 21 can also be raised when no current is flowing, in order to achieve maximum efficiency at this operating point without friction losses. As soon as more power is required again, the respective adjustment motor 23 is actuated, i.e. a corresponding advance is generated, as a result of which the respective (sub) brush 21 contacts the commutator 13. The required brush landing area is calculated throughout the journey.

[0030] List of reference signs:

[0031] 10 separately excited electric machine

[0032] 11 rotor

[0033] 12 stator

[0034] 13 commutator

[0035] 20 brush unit

[0036] 21 brush

[0037] 22 adjustment mechanism

[0038] 23 adjustment motor

[0039] 24 vertical variability

[0040] 25 different brush widths

[0041] 26 detection of brush length

Claims

1. A separately excited electric machine (10) comprising a brush unit (20) with a sub- brush (21), which sub-brush (21) can be moved by means of an adjustment mechanism (22) driven by an adjustment motor (23) towards a commutator (13) to establish electrical contact between the sub-brush (21) and the commutator (13) in a reversible manner or away from the commutator (13) to disconnect the electrical contact between the sub-brush (21) and the commutator (13) in a reversible manner, respectively, characterized in that, The brush unit (20) is connected to a control unit, which is arranged to control the regulating motor (23) such that only the minimum contact area between the entirety of the sub brushes (21) and the commutator (13) is provided which is required to reach a predicted, imminent operating point of the electric machine (10), the control unit being connected to a calculation unit arranged to predict an imminent operating point of the separately excited electric machine (10), the calculation unit being arranged to receive and process real-time information relating to the vehicle environment, route, traffic data and data relating to the current driving behaviour of the driver of the vehicle, the imminent operating point of the electric machine being predicted by the calculation unit on the basis of the real-time information.

2. The separately excited electric machine (10) of claim 1, characterized in that The brush unit (20) comprises sub brushes (21) of different widths.

3. The separately excited electric machine (10) according to claim 1 or 2, characterized in that The separately excited electric machine comprises means (26) for detecting the length of the sub brushes (21).

4. The separately excited electric machine (10) of claim 3, characterized in that The means (26) for detecting the length of the sub brushes (21) are arranged to communicate the length of the sub brushes (21) to the control unit.

5. The separately excited electric machine (10) according to claim 1 or 2, characterized in that The regulating motor (23) is a linear motor.

6. A method for operating a separately excited electric machine (10) according to any one of claims 1-5 for operating a vehicle power plant, the control unit controlling the regulating motor (23) of the brush unit (20) such that only the minimum contact area between the entirety of the sub brushes (21) and the commutator (13) is provided which is required to reach a predicted, imminent operating point of the electric machine (10).

7. The method of claim 6, wherein, The length of each sub brush (21) is determined, the length of the respective sub brush being taken into account when controlling the associated regulating motor (23).

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