Patent Application
20120200245
The present application claims priority under 35 U.S.C. ยง119, to German Patent Application No. 10 2011 010 567.0 (filed on Feb. 7, 2011), which is hereby incorporated by reference in its entirety.
The invention relates to a brushless DC motor, and in particular, a brushless DC motor with a control circuit.
A conventional brushless DC motor with a control circuit is disclosed in document EP 0 088 277 A2. The document discloses in particular the detection of the current consumption of a three-phase bridge driver by shunts. The detected value is used for controlling the motor.
A conventional protective circuit for a bridge driver in a polyphase synchronous motor is disclosed in document DE 10 2005 014 167 A1 This protective circuit is aimed at identifying a state of damage in a switching means and in particular in a MOSFET in order to be able to take measures to counteract subsequent damage, if appropriate.
Furthermore, document DE 10 2005 058 221 B3 discloses an overcurrent fuse for various purposes. A fuseable electrically conductive material, which heats up as an electrical current flows owing to the electrical resistance of said material, is arranged between two holders. The cross section of the current flow is dimensioned such that, when a fixed value is exceeded, the fusing temperature is exceeded. The fused material then flows out of the conduction path, as a result of which the current flow is interrupted.
Yet further, alternative embodiments for overcurrent fuses are disclosed in documents DE 10 2009 036 578 B3 and DE 10 2005 040 308 A1.
In accordance with embodiments, a brushless DC motor is provided with a control circuit which integrates an overcurrent protection means in a particularly expedient manner.
In accordance with embodiments, a brushless DC motor is provided having a plurality of electrical windings and a control circuit operatively connected thereto, and includes a device for time-dependent application of an electrical voltage from an external voltage supply (UB) to the windings, a measuring device configured to generate an electrical signal depending on the current flow (IB) from the external voltage supply (UB) through the control circuit, and an overcurrent fuse configured to protect the control circuit and the windings, whereby a voltage drop across the overcurrent fuse can be supplied to the measuring device as an input value.
Advantageous configurations and developments of the present invention are defined in the dependent claims.
The invention is described in more detail in the enclosed figures and drawings, which present an implementation example. The drawings demonstrate:
As illustrated in
A control circuit 3 is provided for connecting the voltage from an external voltage source UB to the windings 3 in a time-dependent fashion and with alternating polarity. For this purpose, the control circuit 3 includes a plurality of switches 4, which, in a manner known per se, are in the form of MOSFETs and are connected to one another as a three-phase bridge driver. The three-phase bridge driver for its part is driven by control logic 7. Reference is made to the relevant technical literature as regards the details of the MOSFETs and driving thereof by the control logic 7.
In addition, the control circuit 3 also includes an overcurrent fuse 6 which is arranged in the feedline of the supply voltage. The overcurrent fuse 6, in the event of a predetermined current value being exceeded, is configured to interrupt the supply of supply voltage, and therefore, the current flow through the control circuit 3. The overcurrent fuse 6 can be in the form of an irreversible fusable link, a bimetallic-strip or magnet fuse or have another known design. The overcurrent fuse 6 is configured to prevent the windings 2 from overheating and catching tire, and also to prevent subsequent destruction of the switches 4 in the event of a short circuit in one of the switches 4 of the three-phase bridge driver.
Furthermore, the control circuit 3 includes a measuring device 5 configured to generate an electrical signal depending on the current flow IB from the external voltage supply UB through the control circuit 3. A value for the instantaneous power consumption of the brushless DC motor 1 is derived in a manner known per se from this electrical signal and possibly from a comparable signal depending on the applied supply voltage UB. The value for the instantaneous power consumption, in turn, influences the time-dependent driving of the windings 2. This measure has particularly considerable significance when the rotor position of the motor is not available for driving the windings 7.
A voltage drop along the overcurrent fuse 6 can be supplied to the measuring device 5 by virtue of suitable circuitry. Correspondingly, the schematic illustration shows the overcurrent fuse 6 in terms of its equivalent circuit diagram including an ideal fuse component and a real internal impedance. Since the real internal impedance of the overcurrent fuse 6 is a virtually resistive impedance, the voltage drop across said internal impedance is approximately proportional to the current IB to be detected apart from the effects of temperature. Therefore, the power consumption of the control circuit 3 from the voltage source can be determined approximately from the measured current and the value for the supplied voltage.
Conventional embodiments of overcurrent fuses with tolerances for their impedance value are not available on the market, however. Therefore, in practice additional measures are required for managing the influences of variations in production as regards the overcurrent fuses 6 on the quality of the motor operation. In principle, although it is possible to measure the impedance value of the overcurrent fuse 6 individually in series production and to adjust this by way of processing the overcurrent fuse or to compensate for this by changing the rest of the control circuit 2, for example, by providing a compensating resistor, a significant advantage of the proposed integration would thus be lost.
It is, therefore, preferred to determine the impedance of the overcurrent fuse 6 which is to be installed in each case and to provide data corresponding to the specific impedance value in a data storage 8 such as, e.g., a non-volatile program memory) in the control logic 7 (such as, e.g., a computation device) of the control circuit 2 in the case of series production. Accordingly, it is possible for the data to be read electrically during operation of the brushless DC motor 1 and supplied to a computation device 7. This computation device 7 then provides the desired correction. Such a computation device 7 does not require any additional components in the embodiments which are typical at present because the control logic 7 typically includes a microprocessor and a non-volatile program memory 8 for sequential control of the microprocessor. In addition, in the majority of cases the program code required for operation is written individually to the non-volatile program memory 8. To this extent, there is the possibility of the data relating to the measured impedance of the overcurrent fuse 6 likewise being stored as a parameter for the program to be implemented when the non-volatile program memory 8 is written to in this way, an electrical signal can be generated within the control circuit 3 depending on the current flow IB, with this electrical signal still only deviating from the theoretical precise value within predetermined limits.
Although embodiments have been described herein, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 010 567.0 | Feb 2011 | DE | national |
