PROTECTION CIRCUIT FOR AN ELECTRIC MOTOR WITH A SINGLE-PHASE WINDING, AN ELECTRIC CENTRIFUGAL PUMP AND AN OIL MIST SEPARATOR WITH SUCH A PROTECTION CIRCUIT

Abstract

A protection circuit for an electric motor with a single phase winding, consisting of two coil sections with central tapping, wherein the two coil ends of the coil sections are each connected to ground via a switching element. The task of the invention is for an electric motor of this type to ensure a thermal relief for the switching elements, improved and smoother running, reduced warming of the printed circuit board, improved EMC characteristics, a more robust design of the overall switching, a focused conduction of the losses and an extra protection against any surge impulses from a mains network.

Claims

1. A protection circuit for an electric motor powered by a voltage source, the motor having a single-phase winding which consists of two coil sections each having first and second ends, and a center tapping connected to the voltage source and to the first ends of the two coil sections, the protection circuit comprising: the second winding ends of the coil sections being connected to ground via a respective switching element, wherein a cut-off current of a coil section is dispersed via an electrical power component that is connected to the switching element in parallel.

2. The protection circuit according to claim 1, further comprising means for controlling the cut-off current of a coil section.

3. The protection circuit according to claim 1, wherein the electrical power component comprises a power Z-diode, so that each coil section is assigned a power Z-diode.

4. The protection circuit according to claim 1, the electrical power component comprising a bipolar power transistor, so that each coil section is assigned a bipolar power transistor.

5. The protection circuit according to claim 4, wherein the bipolar power transistor can be switched through by a control transistor whose emitter is connected to the base of the power transistor.

6. The protection circuit according to claim 5, wherein the base of the control transistor is connected to a reverse-biased control Z-diode.

7. The protection circuit according to claim 6, wherein the switching behavior of the control transistor is positively influenced with regard to EMC behavior by an additional circuit.

8. The protection circuit according to claim 7, wherein the base of the control transistor is connected via Schottky diodes to the second end of a coil section on the one hand and to the base of the power transistor on the other hand.

9. The protection circuit according to claim 1, further comprising an RC attenuator connected between the second end of one of the coil sections and the ground (10).

10. The protection circuit according to claim 1, wherein the switching element and the bipolar power transistor are thermally decoupled.

11. An electric centrifugal pump comprising incorporating the protection circuitry of claim 1.

12. The electric centrifugal pump according to claim 11, further comprising an electric motor wherein the electric motor is a brushless DC motor with a stator winding.

13. The electric centrifugal pump according to claim 11, wherein the centrifugal pump is an auxiliary cooling water pump.

14. An electric oil mist separator comprising incorporating the protection circuitry of claim 1.

15. The protection circuit according to claim 1, wherein each respective switching element is a field-effect transistor.

16. The protection circuit according to claim 1, wherein each respective switching element is a bipolar transistor.

17. The protection circuit according to claim 1, wherein the RC attenuator comprises a snubber network.

18. The protection circuit according to claim 11, wherein the centrifugal pump is a vehicle cooling water pump.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0017] The invention is described below using a plurality of exemplary embodiments which are explained in more detail with reference to Figures.

[0018] FIG. 1 shows a wiring diagram of a first embodiment of the invention,

[0019] FIG. 2 shows partial circuitry of a second embodiment of the invention,

[0020] FIG. 3 shows a first variant of the second embodiment and

[0021] FIG. 4 shows a second variant of the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0022] In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.

[0023] FIG. 1 shows a wiring diagram 1 of a first embodiment of the invention in order to provide an explanation of the basic function of the invention. A first coil section 5, a second coil section 6, a center tapping 7 off coils 5 and 6 that is connected to a voltage source 4 (supply voltage) are shown. The two other ends of the coil sections 5, 6 are connected to a field effect transistor (FET) 8 and/or 9, respectively. The two field-effect transistors (MOSFETs) switch the coil sections 5, 6 alternately, so that a current passes through the coil sections 5 and/or 6, respectively. An equivalent resistor 16 represents the DC resistance of the coil windings. When the first field effect transistor 8 is switched off, the inductance of the first coil section 5 drives the current further in the same direction. As a result, the voltage at the FET 8 increases until an avalanche voltage of a power-Z diode 11 connected in parallel with the FET is reached. The power Z-diode 11 becomes conductive, which is why the current no longer acts via the field-effect transistor 8 but via the power Z-diode 11. The energy of the first coil section 5 is thus no longer converted into heat at the field-effect transistor 8 but in the power Z-diode 11. The same applies to the connection of the second coil section 6 whose current is dispersed via the second field-effect transistor 9 or the second power Z-diode. If the current is dispersed from the motor winding 3 (coil section 5 or 6), the voltage at the respective power Z-diodes 11 and/or 12 decreases again and no more current is applied.

[0024] FIG. 2 shows partial circuitry 2a of a second embodiment of the invention, wherein only one of two coil sections 5a is shown with its circuitry with the understanding that the discussion also applies to the other coil section 6. In this case, the energy of the coil section 5a, which becomes free as it is switched off, is not conducted via a power Z-diode but via a bipolar power transistor 13a. The base of the bipolar power transistor 13a is connected to the emitter of a control transistor 14a. The base of the control transistor 14a is electrically connected to a control Z-diode 15a.

[0025] After reaching the avalanche voltage of the control Z-diode 15a, a control current flows through via the base-emitter extensor of the control transistor 14a, whereby the bipolar power transistor 13a correspondingly switches on and receives the cut-off energy of the coil section, converts it into heat and emits it to the environment. Overall, the circuitry acts like a Z-diode, but the power loss limits and controllability are significantly improved. Due to the magnitude of the base current of the transistors 14a, 13a and due to the current gain of the transistors 14a, 13a, the circuitry can be adapted in such a way that the steepness of the signal flanks can be set. Furthermore, an equivalent resistor 16a for the resistance of the coil section 5a is shown.

[0026] FIG. 3. Shows a variant of the second embodiment according to FIG. 2 with additional circuit elements. A coil section 5b, a bipolar power transistor 13b, a control transistor 14b, a control Z-diode 15b, an equivalent resistor 16b for the coil section 5b and a field effect transistor 8b for switching the coil section 5b are shown. In addition, a snubber resistor 17b and a snubber capacitor 18b are shown, which form a snubber network. This results in a clean switching slope and thus has a positive effect on the losses in the transistors and the EMC characteristics.

[0027] FIG. 4 shows a second variant of a second embodiment of the invention. In this case, the energy of the coil section 5c, which becomes free as it is switched off, is likewise conducted via a bipolar power transistor 13c. The base of the bipolar power transistor 13c is connected to the emitter of the control transistor 14c. The base of the control transistor 14c is connected to the control Z-diode 15c. After reaching the avalanche voltage of the control Z-diode 15c, a control current flows through via the base-emitter extensor of the control transistor 14c, whereby the bipolar power transistor 13c correspondingly switches on and receives the cut-off energy of the coil section 5c, converts it into heat and emits it to the environment. Overall, the circuitry acts like a Z-diode, but the power loss limits and controllability are significantly improved.

[0028] Due to the magnitude of the base current of the transistors 14c, 13c and due to the current gain of the transistors 14c, 13c, the circuitry can be adapted in such a way that the steepness of the signal flanks can be set. Furthermore, an equivalent resistor 16c for the resistance of the coil section 5c is shown. In addition, a snubber resistor 17c and a snubber capacitor 18b are shown, which form a snubber network. This results in a clean switching slope and thus has a positive effect on the losses in the transistors and the EMC characteristics. Schottky diodes 19c are also shown, which ensure that the base emitter voltage at the transistors does not become excessive, and thus quick switching can be ensured. To this end, the base of the control transistor 14c is connected via the Schottky diodes 19c to the coil end of a coil section 5c on the one hand and to the base of the power transistor 13c on the other.

[0029] Other variants are conceivable, but these will not be further described here. Furthermore, not each coil section needs to have its own wiring, but rather a single circuit block can be used for both coil sections.

[0030] The person skilled in the art concedes that the above-described exemplary embodiments merely have exemplary character, and that the individual aspects of the exemplary embodiments may be combined with one another without departing from the inventive concept.

[0031] Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.

LIST OF REFERENCE NUMBERS

[0032] 1 Principle wiring diagram [0033] 2 Partial circuitry [0034] 3 Winding [0035] 4 Voltage source [0036] 5 First coil section [0037] 6 Second coil section [0038] 7 Center tapping [0039] 8 First switching element [0040] 9 Second switching element [0041] 10 Ground contact [0042] 11 First power Z diode [0043] 12 Second power Z diode [0044] 13 Bipolar power transistor [0045] 14 Control transistor [0046] 15 Control Z diode [0047] 16 Equivalent resistor [0048] 17 Snubber resistor [0049] 18 Snubber capacitor [0050] 19 Schottky diode