WO2011035611A1

WO2011035611A1 - Thermal protection device for motor

Info

Publication number: WO2011035611A1
Application number: PCT/CN2010/073747
Authority: WO
Inventors: Ke JIANG; Yongbao Zhang
Original assignee: Emerson (China) Motor Co., Ltd.
Priority date: 2009-09-27
Filing date: 2010-06-10
Publication date: 2011-03-31
Also published as: CN201515214U

Abstract

A thermal protection device for a motor driven by a PWM signal outputted from a controller comprises an overheating detecting module which includes a temperature sensor attached to a temperature measuring point and outputs an overheating detection result signal on the basis of the temperature measured by the temperature sensor. The controller has a first terminal for receiving a controlling signal and a second terminal for outputting the PWM signal. The controller stops outputting the PWM signal at the second terminal, when the controlling signal is uncoupled from the first terminal. The thermal protection device further comprises a switching element (SW41, SW51, SW61, SW71, SW81) which is coupled to the first terminal of the controller and receives the overheating detection result signal from the overheating detecting module to selectively couple or uncouple the controlling signal to or from the first terminal.

Description

Thermal Protection Device for Motor

Field of the Invention

The present invention pertains generally to a thermal protection device for a motor. More particularly, the invention relates to a thermal protection device for a motor with a controller.

Background of the Invention

In a brushless DC motor or a permanent magnet synchronous motor, an electronic controller is normally utilized to drive a base driving circuit of a power device, to further drive the motor. Faults such as a short circuit, overloading, locked-rotor, over-long starting time, etc, sometimes occur during the operation of the motor, resulting in temperature rise in stator windings. If the temperature rises above some limit value, the lifetime of the motor will be shortened. In an even more critical case, there is a risk that the motor will be burnt out. On the other hand, overheating or even damages of the electronic controller or power devices may be caused by continually operating in certain rigorous running conditions such as insufficient ventilating, high ambient temperature, etc,. Many low cost electronic controllers for the motor do not posses a corresponding pin for receiving a thermal protection action signal, or a corresponding protective function. Thus, when the motor, the controller or the power devices have overheated, it is impossible to shut down the controller itself or the respective signals to drive the power devices. In this situation, even though overheating has occurred, the motor continues operating instead of being be shut down automatically, until the motor, controller or power devices damage ultimately.

To resolve the above-mentioned problem, an electronic controller is proposed in the art in the form of a motor driving dedicated IC or a MPU/MCU (Micro Processor Unit/Micro Controller Unit). The motor driving dedicated IC is provided with a dedicated thermal protection function and a dedicated pin for inputting a thermal protection signal. Similarly, the MPU/MCU is provided with a dedicated pin for inputting the thermal protection signal or interrupt pin for receiving the thermal protection signal. In addition, an overheating detection circuit, which is integrated for the controller, the power devices and/or the motor windings, generates a controlling signal and inputs the same into the dedicated or interrupt pin for receiving the protection signal of the dedicated IC or the MPU/MCU when the detected temperature is above some set point, to shut down the controller or the relevant driving signal, and to shut down the motor. It is thus assured that the controller, the power devices and the motor will not be damaged by too high temperature.

The block diagram of Fig. 1 shows schematically a thermal protection scheme in the prior art, in which the motor driving dedicated IC serves as a main controller. Because the motor driving dedicated IC has a dedicated module and corresponding pin for shutting down an IC/motor driving signal, the main drawbacks are large encapsulated volume, great number of pins, and high development costs. Obviously, such an IC is detrimental to make a compact controller or motor.

The block diagram of Fig. 2 shows schematically another thermal protection scheme in the prior art, in which the MPU/MCU serves a main controller. Because the driving of the MPU/MCU which receives the thermal protection signal at a dedicated pin or a interrupt pin needs a dedicated program, resulting in the increase of development costs. Moreover, the main drawbacks of this scheme are also large encapsulated volume and great numbers of pins.

There is much room for improvements in thermal protection device for the motor.

Summary of the Invention

Accordingly, the present invention has been made to overcome the problems associated with the prior art, and an object thereof is to provide a thermal protection device for the motor which is small, inexpensive, and easy to accomplish, and thus to facilitate the miniaturization of the controller and the motor.

According to an aspect of the present invention, there is proposed a thermal protection device for a motor which is driven by a PWM signal outputted from a controller, the controller having a first terminal for receiving a controlling signal and a second terminal for outputting the PWM signal. When the controlling signal is uncoupled from the first terminal, the controller stops outputting the PWM signal at the second terminal. The thermal protection device comprises an overheating detecting module which includes a temperature sensor attached to a temperature measuring point and outputs an overheating detection result signal on the basis of the temperature measured by the temperature sensor, a switching element which is coupled to the first terminal of the controller and receives the overheating detecting result signal from the overheating detecting module to selectively couple or uncouple the controlling signal to or from the first terminal.

Preferably, the controller is a motor driving dedicated IC, and the controlling signal is selected from a torque/speed controlling signal, an oscillation-starting signal for controlling an operational oscillator and a signal for controlling the frequency of a carrier.

Preferably, the controller is a micro processor unit or a micro controller unit, and the controlling signal is a torque/speed controlling signal.

Preferably, the switching element is provided with a first terminal, a second terminal and a controlling terminal. The controlling signal is coupled to the first terminal of the switching element, and the first terminal of the controller is connected to the second terminal of the switching element, and the overheating detection result signal is coupled to the controlling terminal of the switching element.

More preferably, a capacitor is connected between the second terminal of the switching element and the earth. Even more preferably, the controlling signal is coupled to the first terminal of the switching element via a resistor.

More preferably, the first terminal of the controller is connected to the second terminal of the switching element via a resistor, and a capacitor is connected between the first terminal of the controller and the earth.

Preferably, the switching element has a first terminal, a second terminal and a controlling terminal. The controlling signal is coupled to the first terminal of the switching element, the first terminal of the controller is also connected to the first terminal of the switching element, the second terminal of the switching element is connected to the earth, and the overheating detection result signal is coupled to the controlling terminal of the switching element.

More preferably, a capacitor is connected between the first terminal of the switching element and the earth. Even more preferably, the controlling signal is coupled to the first terminal of the switching element via a resistor.

Preferably, the temperature measuring point is arranged at a heating element of the controller, a stator winding of the motor, a stator core of the motor, the housing of the motor and/or a heat sink.

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, further objectives, and advantages thereof, will be best understood by reference to the following detailed description of the illustrative embodiments when read in conjunction with the accompanying drawings.

Brief Description of the Drawings

The accompanying drawings are incorporated into and serve as a part of the specification, in which:

Fig. 1 schematically illustrates a block diagram of a thermal protection scheme according to the prior art.

Fig. 2 schematically illustrates a block diagram of another thermal protection scheme according to the prior art.

Fig. 3 schematically illustrates a block diagram of a overheating detecting module according to an embodiment of the invention.

Fig. 4 schematically illustrates the manner of coupling the overheating detection result signal to the controlling input of the controller according to an embodiment of the invention.

Fig. 5 schematically illustrates the manner of coupling the overheating detection result signal to the controlling input of the controller according to another embodiment of the invention.

Fig. 6 schematically illustrates the manner of coupling the overheating detection result signal to the controlling input of the controller according to another embodiment of the invention.

Fig. 7 schematically illustrates the manner of coupling the overheating detection result signal to the controlling input of the controller according to another embodiment of the invention.

Fig. 8 schematically illustrates a modification of the thermal protection device shown in Fig. 5.

Preferential Embodiments

In the following, the illustrative embodiments of the present invention will be explained more fully with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless expressly stated otherwise. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. As used herein the term "and/or" includes any and all combinations of one or more of the associated listed items.

In the novel thermal protection device for a motor proposed in the present invention, a normal motor driving dedicated IC or a MPU/MCU without any dedicated overheating protection function is used as the electronic controller for driving the motor. Since there is not any dedicated pin or interrupt pin for inputting the overheating protection signal, in the present invention, the signal outputted from the overheating detecting module is used to control the ON/OFF of a switch coupled to a pin of the controller for inputting the torque/speed controlling signal, and thus to accordingly control the coupling/uncoupling of the torque/speed controlling signal to/from that pin.

Fig. 3 schematically illustrates a block diagram of the thermal detecting module according to an embodiment of the invention. As illustrated, a comparator OA1 forms the kernel of the overheating detecting module. The comparator OA1 compares the potentials at the non-inverting input and the inverting input, respectively, and outputs the comparison result as the overheating detection result signal. A divider network composed of resistors R33 and R35 provides a reference voltage to the comparator OA1 , with which the voltage across a thermal resistor Rt is to be compared by the comparator OA1 . Because the resistance of the thermal resistor Rt is varied as the environment temperature varies, the compared voltage varies accordingly. When the temperature is below a predetermined threshold, the overheating detection result signal is kept at a low level. As the temperature rises beyond the predetermined threshold, the signal outputted from the comparator OA1 reverses to a high level, which is used to activate certain overheating protection actions. As the overheating protection measures are carried out, when the temperature decreases below the predetermined threshold, the comparator output becomes a low level again, which restarts the operation of the motor.

The temperature sensor can be attached onto heating elements such as the controller, the power devices, the stator windings of the motor, the stator core of the motor, or arranged in the vicinity of the heating elements. If the generated heat is eliminated through the housing of the motor or some heat sinks, the temperature sensor can be attached to the housing or the heat sinks. In the embodiment shown in Fig. 3, a thermal resistor Rt is used as the temperature sensor, and the overheating detection result signal is generated by a comparator OA1 . However, it will be appreciated that the temperature sensor may take a form other than the thermal resistor, and that other types of overheating detecting module may be used.

As the above-mentioned, the overheating detection result signal is arranged to control the switch which is coupled to the controlling input pin of the controller for the motor. When overheating is detected, the torque/speed controlling signal is uncoupled from the controlling input pin of the controller, to make the controller stop outputting the PWM signal which is needed in the operation of the motor. In contrast, if overheating is not detected, the torque/speed controlling signal is coupled to the controlling input pin of the controller, and thus the controller outputs the PWM signal to drive the motor.

Fig. 4 schematically illustrates the manner of coupling the overheating detection result signal to the controlling input of the controller according to an embodiment of the invention. When the temperature is detected as too high by the overheating detecting module, under the control of the overheating detection result signal, a transistor, SW41 is switched ON, which pulls the level of the controlling input terminal of the controller low, i.e. interrupts the inputting of the torque/speed controlling signal to the controller. As a result, the controller stops outputting the PWM signal, and thus stops the operation of the motor. When it is detected that the temperature drops below the predetermined threshold, under the overheating detection result signal, the transistor SW41 is switched OFF, recovering the inputting of the torque/speed controlling signal to the controller, and recovering the operation of the motor.

With respect to the case where the electronic controller for the motor is formed by a motor-driving dedicated IC, the overheating detection result signal can be coupled to the pin for controlling the oscillation-starting of an operational oscillator or the pin for controlling the frequency of a carrier, to selectively control the operating state of the IC. Thus, the motor can be controlled to start/stop based on the temperature detection result, and protects the controller, the power device and the motor from damages for overheating.

It is to be noted that, in Fig.4, the torque/speed controlling signal is coupled to the switching element SW41 and the controlling input of the controller via a resistor-capacitor network formed of a resistor R41 and a capacitor C41 . When the measured temperature falls from the protection action point to the restarting point, owe to the process of charging the capacitor C41 , the motor is "soft-started", with an advantage of small starting current and small impact to the power supply.

It will be apparent for those skilled in the art that modifications and variations to the details of the above described scheme are possible without departing from the scope of the invention. For an example, Fig. 5 schematically illustrates another manner of coupling the overheating detection result signal to the controlling input of the controller. According to Fig. 5, based on the overheating detection result signal from the overheating detecting module, the transistor SW 51 is accordingly switched ON/OFF, making the torque/speed controlling signal being coupled or uncoupled to or from the controlling input of the controller. The thermal protection device in Fig. 5 also includes a resistor-capacitor network to carry out the soft starting. However, either or both of the resistor and the capacitor can be arranged in other device/circuit/module other than the thermal protection device, for an example, in the circuit which generates the controlling signal inputted to the controller. Fig. 8 schematically illustrates a modification of the thermal protection device shown in Fig. 5, in which the elements enclosed in dotted block are separated from the thermal protection device, and the soft-starting can be accomplished as well.

It will be apparent for those skilled in the art that the switching element being switched between the ON and OFF states under the control of the overheating detection result signal may take other various forms. Figs. 6 and 7schematically illustrates two examples among them. Although the resistor is arranged in different locations in these Figs. 6 and 7, the soft-starting function is accomplished in both cases.

The controller for the motor according to the present invention can comprise a motor-driving dedicated IC or a MPU/MCU without the dedicated protection function or pin. The number of the pins is decreased, resulting in a relatively small volume and low costs, which enables a relatively compact package of the electronic controller and the motor. In the case where a MPU/MCU serves as the controller for the motor, the present invention needs no extra software workload, shortens the development circle and decreases the development costs relative to the prior solutions.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It will be apparent for those skilled in the art that modifications and variations to the details of the above described embodiments are possible without departing from the scope of the invention. For example, two or more temperature measuring points can be arranged in different locations, respective overheating detection modules can be arranged therefor, and respective switching elements being controlled by each overheating detection result signal can be connected in parallel (for Fig. 4) or series (for Fig. 5). Otherwise, in another efficient alternative embodiment, two or more thermal resistors which carry out the overheating detection at two or more temperature measuring points can be connected in series to replace the single thermal resistor Rt in Fig. 3. Thus, it is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

1 . A thermal protection device for a motor which is driven by a PWM signal outputted from a controller, the controller having a first terminal for receiving a controlling signal and a second terminal for outputting the PWM signal, when the controlling signal being uncoupled from the first terminal, the controller stopping outputting the PWM signal at the second terminal, said thermal protection device comprising:

an overheating detecting module which includes a temperature sensor attached to a temperature measuring point, and outputs an overheating detection result signal on the basis of the temperature measured by the temperature sensor,

a switching element which is coupled to the first terminal of the controller and receives the overheating detecting result signal from the overheating detecting module, to selectively couple or uncouple the controlling signal to or from the first terminal.

2. The thermal protection device of claim 1 , wherein the controller is a motor driving dedicated IC, and the controlling signal is selected from a torque/speed controlling signal, an oscillation-starting signal for controlling an operational oscillator and a signal for controlling the frequency of a carrier.

3. The thermal protection device of claim 1 , wherein the controller is a micro processor unit or a micro controller unit, and the controlling signal is a torque/speed controlling signal.

4. The thermal protection device of claim 1 , wherein the switching element is provided with a first terminal, a second terminal and a controlling terminal, the controlling signal is coupled to the first terminal of the switching element, the first terminal of the controller is connected to the second terminal of the switching element, and the overheating detection result signal is coupled to the controlling terminal of the switching element.

5. The thermal protection device of claim 4, wherein a capacitor is connected between the second terminal of the switching element and the earth.

6. The thermal protection device of claim 4 or 5, wherein the controlling signal is coupled to the first terminal of the switching element via a resistor.

7. The thermal protection device of claim 4, wherein the first terminal of the controller is connected to the second terminal of the switching element via a resistor, and a capacitor is connected between the first terminal of the controller and the earth.

8. The thermal protection device of claim 1 , wherein the switching element has a first terminal, a second terminal and a controlling terminal, the controlling signal is coupled to the first terminal of the switching element, the first terminal of the controller is connected to the first terminal of the switching element, the second terminal of the switching element is connected to the earth, and the overheating detection result signal is coupled to the controlling terminal of the switching element.

9. The thermal protection device of claim 8, wherein a capacitor is connected between the first terminal of the switching element and the earth.

10. The thermal protection device of claim 8 or 9, wherein the controlling signal is coupled to the first terminal of the switching element via a resistor.

1 1 . The thermal protection device of claim 1 , wherein the temperature measuring point is arranged at a heating element of the controller, a stator winding of the motor, a stator core of the motor, the housing of the motor and/or a heat sink.