Reduction of electrolytic corrosion in a brushless direct-current motor

Abstract

The invention relates to a control device (1) for reducing electrolytic corrosion in a brushless direct-current motor (3). The control device (1) is designed to control phases (9, 11, 13) of the brushless direct-current motor (3). The control device (1) has a potential equalization connection (5) and a potential equalization line (7). The potential equalization line (7) is designed to connect the brushless direct-current motor (3) to the potential equalization connection (5). An anti-corrosion resistor (R.sub.K) is provided on the potential equalization line (7), which anti-corrosion resistor is designed to reduce a current flow between the phases (9, 11, 13) of the brushless direct-current motor (3) and the potential equalization line (7).

Claims

1. A control device (1) for reducing electrolytic corrosion in a brushless direct-current motor (3), the control device (1) having a potential equalization connection (5); a potential equalization line (7) which is configured to connect a brushless direct-current motor (3) to the potential equalization connection (5); wherein the control device (1) is designed to actuate phases (9, 11, 13) of the brushless direct-current motor (3); characterized in that an anticorrosion resistance (R.sub.K) is provided on the potential equalization line (7), which anti-corrosion resistance (R.sub.K) is designed to reduce a flow of current between the phases (9, 11, 13) of the brushless direct-current motor (3) and the potential equalization line.

2. The control device (1) as claimed in claim 1, wherein the potential equalization line (7) has a line resistance (R.sub.L); wherein the anti-corrosion resistance (R.sub.K) is larger than the line resistance (R.sub.L).

3. The control device (1) as claimed in claim 1, wherein the anti-corrosion resistance (R.sub.K) is in a range between 100 kilo-ohms and one mega-ohm.

4. The control device (1) as claimed in claim 1, also having a capacitor (C) which is connected in parallel with the anti-corrosion resistance (R.sub.K) in such a way that a high-frequency interference signal is extracted from the potential equalization line (7).

5. A system (25) for reducing electrolytic corrosion in a brushless direct-current motor (3), the system (25) having a control device (1) as claimed in claim 1, further comprising an electric feed pump (15) into which the brushless direct-current motor (3) is integrated; wherein a potential equalization line (7) connects the electric feed pump (15) to the potential equalization connection (5).

6. A method for manufacturing a control device (1) as claimed in claim 1, the method comprising: provision of a control device (1) which is designed to actuate phases (9, 11, 13) of a brushless direct-current motor (3); provision of a potential equalization connection (5) on the control device (1); provision of a potential equalization line (7) which is configured to connect the brushless direct-current motor (3) to the potential equalization connection (5); characterized in that the method also has provision of an anti-corrosion resistance (R.sub.K) on the potential equalization line (7); wherein the anti-corrosion resistance (R.sub.K) is designed to reduce a flow of current between the phases (9, 11, 13) of the brushless direct-current motor (3) and the potential equalization line (7).

7. The system (25) as claimed in claim 5, wherein an electrically conductive feeding medium (17) of the electric feed pump (15) has a feeding medium resistance (R.sub.F) between the phases (9, 11, 13) and the potential equalization line (7); wherein the anti-corrosion resistance (R.sub.K) is connected in series with the feeding medium resistance (R.sub.F).

8. The system (25) as claimed in claim 5, wherein the anti-corrosion resistance (R.sub.K) is arranged in the control device (1).

9. The system (25) as claimed in claim 5, wherein the electric feed pump (15) is an electric fuel pump.

10. The system (25) as claimed in claim 5, wherein the anti-corrosion resistance (R.sub.K) is arranged on a flange (23) between the electric feed pump (R.sub.F) and the control device (1).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the present invention are apparent to a person skilled in the art from the following description of exemplary embodiments, which are, however, not to be interpreted as restricting the invention, and with reference to the appended drawings.

(2) In said drawings:

(3) FIG. 1 shows an electrolysis effect which takes place in the electrically conductive medium,

(4) FIG. 2 shows control signals for actuating phases of a brushless direct-current motor,

(5) FIG. 3 shows a potential profile between a potential equalization line and a phase of a brushless direct-current motor in the 120° block mode, and

(6) FIG. 4 shows a system with a control device and brushless direct-current motor according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION

(7) All the figures are merely schematic illustrations of inventive devices or components thereof according to exemplary embodiments of the invention. In particular, distances and size relations are not represented true to scale in the figures. In the various figures, corresponding elements are provided with the same reference numbers.

(8) In the figures, the control device 1 and the system 25 are illustrated using the example of an electric fuel pump with BLDC operation. The electric fuel pump and therefore the brushless direct-current motor 3 are located in the fuel in this case. The service life of the electric fuel pump can depend on the fuel quality. In corrosive and conductive fuels, an electrolysis effect can occur between components which are at different potentials, i.e. at different voltages. These components can be parts of the electric motor. FIG. 1 is a schematic view of the occurrence of an electrolysis effect or of erosion of material and corrosion 31 in an electrically conductive medium 25. In this context, a voltage of a voltage source 33 is present between an anode 29 and a cathode 27. As is apparent in FIG. 4, in this context a first phase 9 of the brushless direct-current motor can function as an anode 29, and a potential line 7 as a cathode 27. In this context, material can erode from the anode 29 and be deposited on the cathode 27.

(9) This electrolysis effect occurs, for example, if a potential gradient exists between the components over relatively long time periods. This gives rise to a current in the electrically conductive medium and therefore causes erosion of material. In the brushless direct-current motor 3, there are generally pure alternating potentials between the individual phases or phase connections U, V, W. Averaged over time, the electrolysis effect and the associated corrosion between the phase connections is very low. FIG. 2 shows, for example, control signals of a control device 1 for the actuation of phases 9, 11, 13 of a brushless direct-current motor 3 in the 120° block mode. In this context, signals of the output stage transistors T1, T2, T3, T4, T5 and T6 of a 120° B6 inverter 39 are illustrated in FIG. 2A. In FIG. 2B, envelope curves of the phase currents of the 120° B6 inverter 39 are shown. An electrical angle α is plotted on the x axis, and a voltage or a current is plotted on the y axis respectively. In FIG. 2B, the dashed curve represents a current, and the continuous curve represents a pole wheel voltage. From FIG. 2 it is apparent that the currents or the potential differences between the individual phases 9, 11, 13 or U, V, W are approximately zero or very low when averaged over time.

(10) However, a potential difference between a potential equalization line 7 and the individual phases 9, 11, 13 may also be present when considered averaged over time. This is illustrated, for example, in FIG. 3. FIG. 3 shows an envelope curve of a voltage 43 which is present between the first phase 9 or U and a potential equalization line 7. The same voltage differences with respect to the potential equalization line 7 occur with phase shifts for a second phase 11 or V and a third phase 13 or W. Possible effects of clocking are ignored here. The electrical angle α is plotted on the x axis of FIG. 3, and a voltage 43 is plotted in volts on the y axis. When averaged over time, a voltage of 6 volts occurs between the first phase 9 and a potential equalization line 7 in the example in FIG. 3.

(11) In order to avoid the electrolysis effect resulting from this voltage, a high-impedance anti-corrosion resistance R.sub.K is provided in the potential equalization line 7, as is shown in FIG. 4. Said anti-corrosion resistance R.sub.K is connected in series with the feeding media resistances R.sub.F occurring in the electrically conductive medium 17, and it considerably reduces electrical currents between the phases 9, 11, 13 and the potential equalization line 7.

(12) The feeding media resistances R.sub.F which occur between the phases 9, 11, 13 and the potential equalization line 7 can be, for example, between 5 and 15 kilo-ohms. In order to reduce the electrolysis effect significantly, the anti-corrosion resistance R.sub.K may be higher than the feeding medium resistance R.sub.F by a factor of 30 to 50. For example, the anti-corrosion resistance R.sub.K can be between 100 and 500 kilo-ohms. The anti-corrosion resistance R.sub.K is inserted directly into the otherwise non-current-conducting potential equalization line 7 in the control unit 1 in the example in FIG. 4. The potential equalization line 7 retains its ESD functionality despite high impedance wiring here since the anti-corrosion resistance R.sub.K is lower than 1 mega-ohm. In addition, in order to ensure an EMC functionality, a possible high-frequency interference signal is extracted with low inductance upstream of the anti-corrosion resistance R.sub.K in the potential equalization line 7. For this purpose, a low-inductance capacitor C is inserted in the control device 1. In the exemplary embodiment in FIG. 4, the base point of the capacitor C is connected by way of example to the potential equalization line 7. Alternatively, the potential equalization line 7 can be connected at high frequency to further suitable points or components in the control device 1.

(13) In detail, the system 25 shown in FIG. 4 has a control device 1 and an electric feed pump 15 which is driven by a brushless direct-current motor 3. The electric feed pump 15 is an EFP and is located in a fuel tank 21 in a fuel feeding module 19. The electrically conductive feeding medium 17, specifically fuel, rinses the brushless direct-current motor 3 here. The housing of the electric feed pump 15 and therefore also the brushless direct-current motor 3 are connected electrically to a potential equalization connection 5 on the control device 1 via a potential equalization line 7.

(14) The brushless direct-current motor 3 has three phases 9, 11, 13 which are connected to the control device 1 via phase connections U, V, W. The control device 1 is arranged outside the fuel tank 21 here. The phase connections U, V, W and the potential equalization line 7 are led to the control device 1 from the fuel tank 21 via a flange 23. The control device 1 has here a B6 inverter 39 with six main transistors T1, T2, T3, T4, T5 and T6. In addition, the control device has a connection to an energy source which is, for example, a battery (+, −). Furthermore a pulse width modulator 41 is provided in the control device 1. The potential equalization line 7 has a line resistance R.sub.L, which is significantly smaller than the anti-corrosion resistance R.sub.K. The potential equalization line 7 within the control device 1 can also be referred to as a ground rail.

(15) A circuit which is possible as a result of electrolysis in the conductive feeding medium 17 could have the following form: an electric current runs from the positive pole or (+) terminal of the control device 1 to the phase connection U, V or W via the B6 bridge inverter 39. In addition, the electric current flows through the feeding medium resistance R.sub.F formed in the conductive feeding medium 17, to the potential equalization line 7 and ground rail of the control device 1 and from there to the negative pole or to the (−) terminal of the control device 1 via the anti-corrosion resistance R.sub.K.

(16) In conclusion it is to be noted that expressions such as “having” or similar are not intended to rule out the possibility of further elements or steps being provided. Furthermore, it is to be noted that “a” does not rule out a plurality. Furthermore, features which are described in conjunction with the various embodiments can be combined with one another in any desired way. It is also to be noted that the reference signs in the claims are not to be interpreted as restricting the scope of the claims.