Electronically commutatable motor comprising an electronic control unit

The present invention relates to an electronically commutatable motor, whose field windings are controllable by an electronic control unit via semiconductor output stages using PWM control signals, a nominal setpoint speed being selectable for the control unit and the actual speed being comparable with the setpoint, and when the actual speed deviates from the setpoint by a selected or selectable speed difference, the control unit and/or the semiconductor output stages are capable of being switched off.

An electronically commutatable motor is discussed in U.S. Pat. No. 5,744,921. This motor is operable at different nominal operating speeds, the setpoint applied determining the PWM control signals and the associated nominal operating speed. Each operating state may be monitored by comparison and deviation between the actual speed and an associated setpoint speed. The motor may be switched off when the speeds differ by a selected speed deviation. In this motor, the control unit may be capable of modifying the PWM control signals so that the motor runs in the correct direction of rotation for the operating state as a function of the rest position of the rotor.

The motor may be switched off in the event of a speed deviation from the setpoint by a selected value, as discussed in Japanese Patent No. 10 322 894, where the motor may be switched off by switching off the supply voltage, as discussed in German Published Patent Application No. 43 30 823.

These types of electronically commutatable motors may be used for various applications. In this regard, it may happen that even the acceleration of the motor to a desired nominal operating speed, which is selectable or selected via a setpoint, does not occur in the correct way. The motor may be capable of stalling in the rest position or prevented from accelerating correctly by an excessive load or other impediments. Mechanical defects may also cause such a phenomenon. The motor may also block in any phase of the acceleration. The motor and/or its electronic components may be overloaded and even damaged.

It is the object of the present invention to monitor and switch off an electronically commutatable motor of the type initially described, during each phase of the acceleration in such a way that an overload or damage to the motor is prevented as early as in this acceleration phase, rather than in the desired operating state.

In an exemplary embodiment of the present invention, with the selection of the setpoint and/or switching on the control unit and/or the semiconductor output stages as a function of the selected setpoint, the control unit determines a corresponding acceleration time in which the PWM control signals, which gradually increase the speed, increase to a final value associated with the selected setpoint. In the control unit a setpoint speed is associated with each control value of the PWM control signals. In each control phase of the acceleration time, the actual speed is measured and compared with the setpoint speed associated with the corresponding PWM control signal. Switch-off occurs as early as during acceleration if in a control phase the measured actual speed deviates by the selected speed difference from the setpoint speed associated with the corresponding PWM control signal.

The acceleration phase is divided into time segments by the gradually increasing PWM control signals; in each case the coincidence of the actual speed with the setpoint (i.e., the PWM control signal being applied) also corresponds to the motor characteristic and indicates undistrubed acceleration of the motor. If a deviation from a permissible speed deviation occurs in a time segment of the acceleration phase, a mechanical or electric malfunction may be present, which may justify the motor being switched off in order to protect the motor or its components from overload and damage.

In this manner, the entire acceleration phase may be monitored for correct start and acceleration from the time the motor is switched on.

The PWM control signals which gradually increase the speed may continuously increase in pulse amplitude, pulse width, and/or commutating frequency.

The actual speed may be compared to the setpoint speed continuously or repeatedly at time intervals during the acceleration.

The simple protective circuit may be obtained by switching the control unit and/or the semiconductor output stages on and off by switching the supply voltage on and off.

For different operating modes, the design may advantageously be such that the acceleration time depends on the magnitude of the selectable setpoint and/or on the magnitude of the supply voltage.

The variation of the permissible speed deviation may be designed so that the selected speed deviation depends on the selected setpoint and/or on the magnitude of the supply voltage.

If necessary, the deviation from the selected speed deviation may be visually displayed and/or acoustically indicated.

The comparison device required to compare actual speed and setpoint speed may be integrated into the control unit.

For the duration of the operation of the motor with the operating speed defined by the selected setpoint, the comparison between actual and setpoint speed may be continued to obtain overload protection also in this phase of the steady-state operation and be capable of switching off if necessary.

The FIGURE illustrates schematically an exemplary embodiment of the present invention.

The motor unit may include the following functional units: control unit STE, semiconductor output stages EST, and actual motor M having the field windings of the stator and the permanent magnet rotor, which may be designed as an external or internal rotor.

If motor M is to be put into operation, a setpoint N setpointv which characterizes a desired motor speed N is selected for control unit STE. The selection may, for example, be performed manually via a potentiometer. In this control unit STE, a function is stored which reflects the dependence of PWM control signals PWM actual for semiconductor output stages EST on the associated setpoint speed N setpoint .

If a setpoint N setpointv is selected and control unit STE and semiconductor output stages EST are connected to supply voltage U batt (i.e., switched on), then a selected acceleration of motor M to the intended setpoint speed N setpointr is forced. For this purpose, a ramp-type PWM control which effects an increase in speed using PWM control signals PWM endr is performed and this is done in a selected or selectable acceleration time. In each phase of the acceleration, the setpoint speed N setpointr associated with the corresponding PWM control signal is compared with a detected actual speed N actualr by a comparison device VE in the control unit. Comparison device VE, which may be integrated into control unit STE, outputs a switch-off signal AB in the event a selected or selectable speed deviation ΔN is exceeded, in order to switch off control unit STE and/or semiconductor output stages EST, as contacts ab show, and to protect motor M and the electronic components from overload. The comparison between the two values—setpoint speed N setpointr and actual speed N actualr —may be performed continuously or at intervals during the acceleration phase, with the possibility always existing of switching off if permissible speed deviation ΔN is exceeded.

The acceleration time may additionally be tailored to the magnitude of selected setpoint N setpointv and to the magnitude of supply voltage U batt , with, for example, the acceleration time of the ramp also increasing with increasing setpoint N setpointv . Permissible speed deviation ΔN may also be varied. Thus, permissible speed deviation ΔN may also increase and be selected larger with increasing magnitude of setpoint N setpointv . The same also applies for supply voltage U batt .

For specific applications it may be advisable to evaluate the exceeding of permissible speed deviation ΔN in control unit STE, display it optically and/or acoustically, and switch off control unit STE and/or semiconductor output stages EST with a delay, which may still avoid an overload of motor M and the electronic components.

The comparison between setpoint speed N setpointr and actual speed N actualr performed in the acceleration phase may also be performed in the subsequent steady-state operation of motor M using the setpoint speed determined by selected setpoint N setpointv and used for overload protection.