JPS61195573A - Rectifier for dc motor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rectifying device for a DC motor used in small audio equipment.

[Prior art and its problems] DC motors used in small audio equipment are generally required to rotate at a constant speed, and these often employ a bridge detection type speed control circuit.

This control circuit will be explained below with reference to FIG. M is a DC motor controlled at a constant speed, S is a DC power supply, and the control circuit is a bridge with the internal impedance of the DC motor M as one side and the other eight sides as resistors R, , R, and Rs. The motor detects the speed of the DC motor M using a back electromotive force (induced voltage Ea), and controls the transistors TRI and TR2 using this detection signal to maintain a constant rotation speed. Note that D is a reference voltage diode that sets the rotation speed of the DC motor M, and R4 is a resistor that sets the operating point of the diode D.

Now considering the case where Rat a, s R2, and Rs are in an equilibrium state, the voltage Eb between the bridge detection terminals 815 is Eb=αEa...
...It can be expressed as (1). Next, if the terminal voltage applied to the DC motor M is V1 and the armature current is (■), then the following relational expression is established between the induced voltage Ea of the DC motor M and the terminal voltage (■).

V = Ea 1 Ra Song 1...
...... (8) Then, the magnetic flux density (Wb/m p
Then, the induced electric power E generated in this armature conductor can be expressed by the following equation.

E=BAv (volt) ・・・・・・・・・・・・
(4) Therefore, the effective magnetic flux during one rotation of the DC motor M is constant, and if changes in the effective magnetic flux due to armature reaction are ignored, the induced current Ea of the DC motor M is proportional to the rotation speed. , is expressed by the following equation.

Ha == K a N ・・・・・・・・・
・Song/Song (5) However, Ka is a proportional constant.

The bridge detection type speed control method detects the voltage Eb between the detection terminals 815 and controls it so that it becomes a constant value. It is controlled so that Ea remains constant. That is, if the load on the DC motor M increases for some reason and the rotational speed decreases, the induced electric power Ea decreases and the potential at point a decreases. Then the transistor TR
The pace current and collector current of transistor I increase, the base current of transistor TR2 increases, the resistance between its emitter and collector decreases, the current increases, and the rotational speed of DC motor M increases.

By the way, in the bridge detection type speed control device,
Since the internal impedance Ra of the DC motor M is used as one side of the bridge circuit, Ra must remain unchanged during use, and if Ra changes, constant speed control becomes impossible. Therefore, in order to keep the internal impedance Ra of the DC motor M constant, it is necessary to sufficiently improve the materials and structures of the commutator, brushes, etc. that constitute the rectifier.

[Purpose of the Invention] Conventional DC motors employing a bridge detection type speed control system use silver for the commutator and palladium for the brushes, but the surface of the commutator is oxidized or sulfurized, causing contact resistance to increase. It tends to be large. In order to prevent this, gold plating has been applied to the surface of the commutator, but the gold plating wears away during long-term use, so the effect cannot be improved sufficiently. The present invention is intended to solve this problem, and it is an object of the present invention to provide a rectifier for a DC motor that has excellent durability and stability.

[Structure of the Invention] The rectifying device for a DC motor of the present invention rectifies the back electromotive force generated in the DC motor by a bridge circuit in which one side is the internal impedance of the DC motor and the other eight sides are configured with predetermined external resistances. In a DC motor equipped with a di-detection type speed control device, the commutator of the DC motor is made of a first layer of gold-silver alloy. , a second layer of silver alloy, and a third layer of copper or copper alloy.

FIG. 2 shows an embodiment of the rotor of a DC motor according to the present invention, in which symbol 2 is a rotating shaft, and 2 is a resin frame fixed to the rotating shaft l to hold the coil 8. 4 is a commutator mold,
5 is a commutator riser, and 6 is a brush made of palladium or palladium alloy. The commutator mold 4 is made of gold and silver alloy (
70-80% gold, 20-80% silver) and a silver alloy (90-94% silver, 4-8% copper, 1-4% cadmium).
) and a third layer of copper or a copper alloy. As a specific example of the cladding material forming this commutator 7, the first layer is a gold-silver alloy layer of 75% gold and 25% silver with a thickness of about 6μ, and the second layer is a gold-silver alloy layer with a thickness of about 20μ. 92% silver, 6% copper,
A silver alloy layer of about 2% cadmium is used, and the third layer is made of phosphor bronze or aluminum copper with a thickness of about 80 μm.

[Effects of the Invention] Since the present invention has the above configuration, it has the following effects. Since the first layer of the cladding material forming the commutator is a gold-silver alloy containing gold as its main component, oxidation and sulfidation of the surface of the commutator are prevented and contact resistance is reduced. Even if the first layer of gold-silver alloy is worn out, there is a second layer of silver alloy, and the gold of the first layer is diffused into the second layer, so the advantages of the first layer are maintained. The third layer is to obtain the necessary thickness as a structural material forming the commutator, and the brush 6 made of inexpensive copper alloy has excellent hardness and wear resistance. Suitable for commutator brushes.

As described above, the rectifier of the present invention eliminates the drawbacks of conventional silver commutators and gold-plated commutators, has low contact resistance, excellent wear resistance, and is durable and reliable. It has an excellent effect of providing a high rectifier.

[Brief explanation of drawings]

Figure 1: Electrical wiring diagram of the control circuit of the DC motor of the present invention Figure 2 is a diagram showing an embodiment of the rectifier of the present invention, (A)
is a side view, (b) is a plan view

Claims (2)

[Claims] (1) The back electromotive force generated in the DC motor is detected by a bridge circuit whose one side is the internal impedance of the DC motor and the other three sides are made up of predetermined external resistances, and this detection signal is used to detect the back electromotive force generated in the DC motor. In the DC motor equipped with a bridge detection type speed control device that controls the rotation of the DC motor at a constant speed, the commutator of the DC motor is made of a first layer of a gold-silver alloy, a second layer of a silver alloy, and a copper or silver alloy. A rectifying device for a DC motor, characterized in that it is formed of a cladding material comprising a third layer of copper alloy. (2) The first layer of the gold-silver alloy is 70-80% gold and 20% silver.
~30%, the second layer of silver alloy is 90-94% silver, 4-8 copper
%, 1 to 4% cadmium, and the third layer of the copper alloy is phosphor bronze or beryllium copper.