JP2877481B2 - Overload protection device for DC motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a DC motor provided with an overheat protection element.

(Prior Art) Conventionally, in a DC motor such as a brushless motor, as shown in FIG. 3, when the motor 1 is overloaded, or when the rotor of the motor 1 is The motor 1 is provided with an overheat protection element 2 in order to protect the motor 1 when it is in a locked state or to stop the rotation so that the motor 1 does not emit smoke or fire.

The overheat protection element 2 is provided in the vicinity of the coil 3 and both terminals thereof are connected in series with the coil 3. When the overheat protection element 2 detects an abnormal temperature, the inside of the element 2 is closed. When the electrical connection is broken, the coil 3
Thus, no current flows and the motor 1 can be stopped.

Particularly, in the case of a three-phase brushless motor, even if power supply to one coil is stopped, current flows to the other coil, so that two overheat protection elements 2 are required.

(Problems to be Solved by the Invention) However, in this three-phase brushless motor, the timing of energizing the coil 3 is determined by a Hall element or the like, and a rectangular wave having an electrical angle of 120 ° is applied to each coil 3. By doing so, the motor 1 is rotated. During rotation, the current may not flow to the coil 3 sequentially, so there is little problem. However, particularly, when the motor 1 is stopped in a completely locked state, the Hall element Therefore, a current always flows through the coil 3 to which energization is determined. Then, in this case, since the temperature of the coil 3 rises, the overheat protection element 2
Works to cut off the current supply to the coil 3, but because a direct current is constantly flowing, an arc discharge occurs between the fixed contact and the movable contact of the overheat protection element 2, The melting and welding of these contacts causes a problem that the current cannot be cut off and the function cannot be sufficiently achieved. In order to prevent this, an overheat protection element having a larger capacity than necessary so as not to weld is required.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a DC motor that can be reliably stopped in the event of an abnormality without using an overheat protection element having an unnecessarily large capacity. is there.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above-described object, the present invention provides an AC power supply unit, which is connected to the AC power supply unit via a noise filter, and is connected to the A DC power supply that rectifies the current to obtain a DC current, and a DC motor that is connected to and rotates with the DC power supply, detects abnormal temperatures near the stator coil and opens the contacts inside the element to open and close the element. An overload protection device for a DC motor, comprising an overheat protection element for disconnecting electrical connection between the units, and connecting the element between the noise filter and the DC power supply unit.

(Operation) When the contact type overheat protection element provided in the vicinity of the stator coil operates due to the DC motor generating an abnormality such as a locked state and generating heat, the current flowing between both terminals of the element is an AC current. Therefore, since the contacts inside the element are not welded, the electrical connection at both ends of the element can be surely cut off, so that the current to the stator coil can be cut off.

(Embodiment) An embodiment of the present invention applied to a three-phase brushless motor will be described below with reference to FIGS. 1 and 2. First, in FIG. 2 showing the overall configuration of the motor,
Reference numeral 11 denotes a stator made of a laminated plate and having 24 teeth, which is sandwiched by upper and lower frames 12 and 13 from both directions and fixed by rivets 14, and a stator coil 15 is wound around the teeth. . Reference numeral 16 denotes a rotor having a rotating shaft 17 at the center. The rotor 16 has an iron core 18 made of a laminated plate, four permanent magnets 19 provided separately on the outer circumference of the iron core 18, and aluminum provided on the outer circumference. And a substantially cylindrical metal cover 20 made of a non-magnetic material such as that described above, and is disposed inside the stator 11. Reference numeral 21 denotes an overheat protection element disposed in contact with the stator coil 15, and both terminals 21 a and 21 b of the overheat protection element 21 are drawn out of an opening provided in the lower frame 13. This overheat protection element 21 disconnects the contact inside the element by detecting an abnormal temperature of the stator coil 15, thereby disconnecting the electrical connection between both ends of the element. Krickson 17M (Texas Instruments trademark) and non-reusable thermal fuses. Reference numeral 22 denotes a Hall element disposed opposite to the inner peripheral surface side of the permanent magnet 19, and the stator coil 15 is sequentially energized based on a signal from the Hall element 22, and a three-phase brushless motor is used. Make up.

Next, in FIG. 1 showing the electrical configuration, reference numeral 23 denotes an AC power supply unit, which is connected to a rectifying bridge 29 through a current fuse 24, and a noise filter 28 composed of coils 25 and 26 and a capacitor 27. The overheat protection element 21 is connected to a constant voltage unit 31 which is a DC power supply unit configured by a smoothing capacitor 30 to generate a DC power supply, and is connected to one bus 23a between the noise filter 28 and the constant voltage unit 31. Terminals 21a and 21 of
When b is connected, it is electrically connected. Reference numeral 32 denotes a drive circuit connected to the constant voltage section 31. The drive circuit 32 sequentially outputs rectangular wave signals having a phase difference of 120 ° based on the signal output from the Hall element 22 to the stator coil 15 sequentially. Turn on electricity.

Next, the operation of the above configuration will be described. When the motor assumes a locked state or is overloaded, the temperature of the stator coil 15 increases. Element 21
Detects the abnormal temperature, and the movable contact inside moves away from the fixed contact. Then, the electrical connection between the terminals 21a and 21b is disconnected, so that the current from the AC power supply unit 23 stops flowing to the constant voltage unit 31, so that the supply of the current to the stator coil 15 also stops, and the motor rotates. To stop. In this case, since the current flowing between the fixed contact and the movable contact of the overheat protection element 21 is an alternating current, the voltage between the fixed contact and the movable contact temporarily becomes zero when the fixed contact and the movable contact are separated. Since there is a moment, the arc discharge does not continue between the fixed contact and the movable contact, so that both contacts are melted by the arc discharge, so that the welding does not occur.

According to the above embodiment, the overheat protection element 21 provided in contact with the stator coil 15 is electrically connected between the AC power supply section 23 and the constant voltage section 31.
Since an alternating current flows through 21, the overheat protection element 21 is activated due to the motor malfunction.If the arc discharge continues, the fixed and movable contacts inside the overheat protection element 21 will weld. Since the overheat protection element 21 works reliably without using a device having a capacity larger than necessary so as not to cause a problem, it is possible to reliably prevent a situation such as smoking or ignition from occurring.

Further, even when the present invention is applied to a motor having three-phase stator coils, if only one overheat protection element 21 is used, power supply to all the stator coils 15 can be stopped. Since the number of overheat protection elements 21 can be reduced, it is possible to provide an inexpensive motor with good assembling workability.

Furthermore, since the overheat protection element 21 is provided between the noise filter 28 and the constant voltage unit 31, noise generated from the stator coil 15 and transmitted through the overheat protection element 21 is absorbed by the noise filter 28. Therefore, noise is not transmitted to the AC power supply unit 23, so that the influence of noise on other devices having the same power supply as the AC power supply unit 23 can be reduced.

The present invention is not limited to the above-described embodiment, and can be applied to all DC motors in which a DC current flows through a stator coil even if the motor is not a three-phase brushless motor.

Further, the mounting position of the overheat protection element 21 may be, for example, a stator if it is disposed near the stator coil to such an extent that an abnormal temperature of the stator coil can be detected, even if it is not in contact with the stator coil. Various modifications are possible, for example, they may be provided on the frame.

[Effects of the Invention] According to the present invention, the overheat protection element is electrically connected between the AC power supply unit and the DC power supply unit. Therefore, when the motor generates heat due to an abnormality such as a locked state, the stator is heated. When the contact-type overheat protection element provided near the coil is activated, the current flowing between both terminals of this element is an alternating current, so that the contacts inside the element will not be welded. Even without using a large capacity element,
Since the electrical connection between both ends of the element can be reliably cut off, and the current supply to the stator coil can also be cut off, it is possible to prevent the motor from generating smoke or ignition.

Furthermore, since an overheat protection element is provided between the noise filter and the DC power supply unit, noise generated from the stator coil and transmitted through the overheat protection element is absorbed by the filter. No noise is transmitted, and the influence of noise on other devices that use the same power supply as the AC power supply can be reduced.

[Brief description of the drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 is a circuit diagram showing an electric configuration, FIG. 2 is a sectional view of a motor,
FIG. 3 is a diagram corresponding to FIG. 1 of a conventional example. In the drawing, 15 is a stator coil, 21 is an overheat protection element, 23
Denotes an AC power supply unit, and 31 denotes a constant voltage unit (DC power supply unit).

Claims (1)

(57) [Claims] An AC power supply, a DC power supply connected to the AC power supply via a noise filter, and a DC power supply for rectifying a current from the AC power supply to obtain a DC current; and a DC power supply connected to the DC power supply. In a DC motor that rotates by rotating, a contact element inside the element is opened by detecting an abnormal temperature in the vicinity of the stator coil to disconnect an electric connection between both ends of the element, and an overheat protection element is provided. An overload protection device for a DC motor connected between the DC power supply unit and the DC power supply unit.