WO2010112389A1

WO2010112389A1 - Circuit for a brushless motor and method for operating same

Info

Publication number: WO2010112389A1
Application number: PCT/EP2010/053886
Authority: WO
Inventors: Mario Engelmann; Bernhard Giers
Original assignee: Continental Automotive Gmbh
Priority date: 2009-04-01
Filing date: 2010-03-25
Publication date: 2010-10-07
Also published as: DE102010003241A1

Abstract

The present invention relates to a circuit for a brushless electric motor (1) of an electromechanical steering apparatus, the windings (U, V, W) of said electric motor being driven by an inverter (12) with the aid of six switches (11, 12, 13, 14, 15, 16), wherein an identification unit (A) for identifying defective switches, a unit for voltage measurement (B) at the outputs (17, 18, 19) of the inverter (2) and a microcontroller (G) for controlling the switches are provided. In addition, the present invention relates to a method for operating such a circuit. It is important, particularly in safety-relevant applications, for the voltage supplied to the electric motor to be interrupted in the event of a fault in order to exclude risk of a fire. In electromechanical steering apparatuses, an increased steering torque is required by the vehicle driver in addition in the event of a fault. According to the invention, therefore, at least one safety switch (3, 4) is provided, which is opened in order to prevent overload.

Description

Brushless motor circuit and method of operation.

The present invention relates to a circuit for a brushless electric motor of an electromechanical steering apparatus, the windings of which are driven by an inverter by means of six switches, wherein a detection unit for detecting defective switches, a unit for measuring voltage at the outputs of the inverter and a microcontroller for controlling the switch is provided. Moreover, the present invention relates to a method for operating such a circuit.

Inverters for controlling brushless motors usually consist of six switches. Each switch can in principle have two different properties after a defect: non-conductive, that is blocked in the open switch position, or conductive, that is blocked in the closed switch position. A conductive defective switch is colloquially known as a short circuit. Especially in safety-relevant applications, it is important that the power supply to the electric motor is interrupted in the event of a fault in order to prevent the risk of fire. In electromechanical steering devices also an increased steering torque by the driver is necessary in case of failure. From DE 10 2007 011 548 Al a method and a device for thermal overload contactor of a drive system of a motor vehicle is known. In the prior art device is a window lift drive with an electronic anti-trap. When a first temperature limit value is reached, the drive system is deactivated, and when a second temperature limit value is reached, the power supply to the drive system is interrupted. A disadvantage of the previously known device and the previously known method is that temperature changes are relatively slow, so that exceeding certain temperature limits is also recognized relatively late.

DE 10 2005 014 601 A1 discloses an electronic subassembly in which the connections between conductor tracks, components and / or components are each manufactured via a spring-loaded contact clip.

The present invention is therefore based on the object to represent a fast, inexpensive and reliable method to interrupt the power supply of the electric motor of an electromechanical steering device.

This object is solved by the features of claim 1. In this case, at least one safety switch is provided, which is opened in the event of a fault and interrupts the power supply to the electric motor to prevent overloading. By this measure, the power supply for the electric motor is separated particularly easily and efficiently. Advantageous developments are the dependent claims.

Thus, in a preferred embodiment of the safety switch is designed as a fuse, which is opened when supplied with thermal energy. The safety switch is formed in a preferred embodiment by a metal clip whose first portion generates a bias on a second portion, wherein the second portion is held by means of a thermally deformable portion in the closed position of the safety switch.

In a particularly advantageous embodiment of the subject invention, the second portion has a foot area, which cooperates with the thermally deformable area, and a lever which biases the foot area in the direction of opening the safety switch.

The first section is plugged into a circuit board while the thermally deformable section is applied to the circuit board.

There is provided a heat source for generating thermal energy for opening the safety switch. The heat source is a transistor, an ohmic resistor or a PTC element in question. In this case, the ohmic resistance is designed so that sufficient thermal energy is generated to open the safety switch when both switches of a switch pair are closed. The inventive method provides to operate such a circuit with the following steps:

Detecting a defective switch by the detection unit;

-Ansteuern the heat source and

-Open one or both safety switches.

The invention will be explained in more detail with reference to an embodiment in conjunction with the accompanying drawings. In the drawing show:

1 shows a schematic representation of an electromechanical steering system;

Fig. 2 is a circuit diagram of a circuit for a brushless electric motor of an electromechanical steering apparatus;

3 shows a simplified representation of the safety switch according to the invention in the closed switch position;

Fig. 4 is a Fig. 2 corresponding representation in the open switch position and

Fig. 5a, b is a further illustration of the safety switch according to the invention in the open and closed positions.

In Fig. 1, an electromechanical steering device is shown, which comprises a steering wheel 22 and a steering housing 24. The electromechanical steering device is connected via a steering rod 29 connected to wheels 31. Preferably, the e- lektromechanische steering device is arranged in a motor vehicle.

In the steering housing 24, a steering column is arranged, which couples the steering wheel 22 with the steering linkage 29. The electromechanical steering device further comprises a steering gear 26, an electronic control unit 28 and a steering torque sensor 35. Furthermore, the electromechanical steering device, in particular the steering gear 26, is coupled to an electric motor 1, not shown in FIG. 1, which controls the steering movement in dependence on a steering angle the steering wheel 22 supports or performs and / or the steering wheel 22 is acted upon by a manual torque through which a driver of the motor vehicle receives feedback from the electromechanical steering device. In this case, the electronic control unit 28 determines, for example, depending on a measured value of the steering torque sensor 35 at least one control signal for the electric motor 1. Driven by the determined control signal, the electric motor 1 then generates a torque to support a steering movement of the driver, so that the wheels 31 are made easier so can that the motor vehicle moves in the direction predetermined by the steering wheel 22 direction. Alternatively or additionally, the electric motor 1 can generate the manual torque depending on the actuating signal. Furthermore, in order to support the steering and to generate the manual torque, in each case a separate control signal can be generated and / or a separate electric motor can be provided. The direction in which the wheels 31 are set, for example, via a mechanical coupling of the steering wheel 22 with the wheels 31 predetermined by the position of the steering wheel 22. FIG. 2 schematically shows a brushless electric motor 1 of an electromechanical steering device whose windings U, V, W are driven by an inverter 2. For this purpose, the inverter 2 has six switches 11, 12, 13, 14, 15, 16, wherein the switches 11, 12, 13 of the positive supply voltage shown in FIG. 2 and the lower switches 14 in FIG. 2, 15, 16 are associated with the negative supply voltage. For example, the switches 11 and 14 supply the winding V with a suitable supply voltage. As further shown in FIG. 2, there are taps 17, 18, 19 between the switches 11, 12, 13 associated with the positive supply voltage and the switches 14, 15, 16 associated with the negative supply voltage where the voltage applied to the windings U, V, W voltage is tapped and a unit B is supplied to the voltage measurement. The measurement results of the unit B for voltage measurement are supplied to a microcontroller C which controls the switches 11, 12, 13, 14, 15, 16 on the one hand and evaluates the information generated by the voltage measurement unit B on the other hand. In addition, a detection unit A for detecting defective switches 11, 12, 13, 14, 15, 16 is provided. The information generated by the recognition unit A is also supplied to the microcontroller C for evaluation.

In one embodiment, in practice, the switches 11, 12, 13, 14, 15, 16 are formed by semiconductor switches or transistors or MOSFETs. The detection unit A is formed in practice as a bridge driver and applies to the transistors formed as switches 11, 12, 13, 14, 15, 16, a voltage and controls whether the switch position of the transistor changes. Unit B for voltage Measurement at the tapping points 17, 18, 19 is formed in practice as a voltage divider and determines the duty cycle of a pulse width modulated voltage, the duty cycle corresponds to the quotient of pulse duration and period.

Each switch 11, 12, 13, 14, 15, 16 may in principle have two different types of defect or is located after a defect basically in one of the two states described below: non-conductive defect, that is blocked in the open switch position, or conductive defective, that is blocked in the closed switch position. A conductive defective switch 11, 12, 13, 14, 15, 16 is colloquially known as a short circuit. Since a conductive defective switch 11, 12, 13, 14, 15, 16 for the operation of the electromechanical steering device is much more critical, it is assumed in the following of this error case.

Especially in safety-relevant applications, it is important to react very quickly in order to switch off the electric motor 1 immediately. In the event that the switch 11, 12, 13, 14, 15, 16 is in the state "conductively defective", a safety switch 3, 4 is opened in order to release the short circuit by a switch blocked in the conductive state In addition, this error case also means an increased steering torque, since the driver moves the electric motor 1 in generator operation in the event of a fault and thereby induces a current that just counteracts the steering movement on the steering wheel 22. By opening a Safety switch 3, 4 is the increased steering reduced expenses for the driver. In the embodiment shown in Fig. 2, two safety switches 3, 4 are provided, which separate the point negative power supply and the point positive power supply. The safety switches 3, 4 must be closed during normal operation of the electric motor 1 and are opened only in the described error case. It must be ensured that the safety switches 3, 4 open safely. Therefore, the safety switches 3, 4 realized by a prestressed metal clip 5, 6, 7, which can be opened electrically initiated.

FIGS. 3 and 4 show an embodiment of the safety switch 2, 3. The prestressed metal clip 5, 6, 7 is arranged on a printed circuit board 10 and is functionally divided into two sections, as shown by the dashed line in Fig. 3. The first section is provided with the reference numeral 5 and serves to create a bias on the second section 6, 7 in the direction of opening. The second section 6, 7 in turn consists of a lever 7 and a foot portion 6. The foot portion 6 is held by a thermally deformable portion 9 in the closed switch position, which is shown in Fig. 3. The thermally deformable region 9 is applied to the printed circuit board 10 and at the same time electrically conductive, so that an electrically non-conductive region 20 is bridged by means of the foot region 6. In practice, the thermally deformable region 9 will be formed as a solder joint and the non-conductive region 20 as a gap. If the solder joint 9 is heated, the following happens: The first portion 5 is inserted into the printed circuit board 10 and is supported there. The bias of the first portion 5 acts on the lever 7. The lever 7 in turn rests on the circuit board 10 and thereby unfolds a lever effect on the foot region 6, which is pulled from the molten solder 9. The foot region 6 is spatially removed from the thermally deformable region 9 and the electrical connection is separated due to the gap 20. The safety switch 2, 3 is open. This condition is shown in FIG.

The thermally deformable region 9 is supplied with thermal energy in the form of heat, which causes the thermally deformable region 9 to melt. For this purpose, a heat source 8 is necessary, as shown in Fig. 5a. The safety switch 3, 4 is initially closed, as shown in Fig. 5a. A supply of heat (heat) opens the safety switch 3, 4 as shown in Fig. 5b.

As a heat source 8 is a transistor, an ohmic resistance or a PTC element in question. An ohmic resistance is designed so that during normal operation of the electric motor 1, the heat generated by the resistor is insufficient to melt the thermally deformable region. On the other hand, are both switches of a switch pair 11, 14; 12, 15; 13, 16 of a winding U, V, W closed simultaneously, a maximum current flows, which generates the necessary thermal energy for melting the solder joint 9 and thus to open the safety switch 3, 4 in ohmic resistance. The case that both switches of a switch pair 11, 14; 12, 15; 13, 16 of a winding U, V, W closed simultaneously occurs when one of the switches 11, 12, 13, 14, 15, 16 defective in the closed switch position - that is conductive defective - is and the other switch a pair of switches 11, 14; 12, 15; 13, 16 is also closed.

It should be noted that with the present invention, the power supply for the electric motor 1 of an electromechanical steering device is separated particularly easily and efficiently.

Claims

Claims:

A circuit for a brushless electric motor (1) of an electromechanical steering apparatus whose windings (U, V, W) are driven by an inverter (2) by means of six switches (11, 12, 13, 14, 15, 16), a detection unit (A) for detecting defective switches (11, 12, 13, 14, 15, 16), a unit (B) for measuring voltage at the outputs (17, 18, 19) of the inverter (2) and a microcontroller (C) for controlling the switches (11, 12, 13, 14, 15, 16) is provided, characterized in that at least one safety switch (3, 4) is provided, which is opened in the event of a fault and the power supply to the electric motor (1 ) interrupts to prevent overloading.

2. A circuit according to claim 1, characterized in that the safety switch (3, 4) is designed as a fuse, which is opened upon supply of thermal energy.

3. A circuit according to claim 1 or 2, characterized in that the safety switch (3, 4) by a metal clip (5, 6, 7) is formed, the first portion (5) a bias on a second portion (6, 7) wherein the second portion (6, 7) is held in the closed position of the safety switch (3, 4) by means of a thermally deformable portion (9).

4. A circuit according to claim 3, characterized in that the second section (6, 7) has a foot region (6) with the thermally deformable region (9) cooperates, and a lever (7) which biases the foot region (6) in the direction of opening the safety switch (3, 4).

5. A circuit according to claim 3 or 4, characterized in that the first portion (5) is inserted into a printed circuit board (10), while the thermally deformable region (9) on the printed circuit board (10) is applied.

6. A circuit according to any one of claims 2 to 5, characterized in that a heat source (8) for generating thermal energy for opening the safety switch (3, 4) is provided.

7. A circuit according to claim 6, characterized in that the heat source (8) is designed as a transistor, ohmic resistor or PTC element.

8. A circuit according to claim 7, characterized in that the ohmic resistance is designed so that sufficient thermal energy for opening the safety switch (3, 4) is generated when both switches of a switch pair (11, 14; 12, 15; 16) are closed.

9. A method for operating a circuit according to one of claims 1 to 8, characterized by the following steps:

Recognition of a defective switch (11, 12, 13, 14, 15,

16) by the recognition unit (A); -Ansteuern the heat source (8) and -Open one or both safety switches (3, 4).