JPH0591705A - Dc motor - Google Patents

Abstract

PURPOSE:To provide a motor wherein its large starting torque is generated and its rotational speed when applying no load to it is suppressed. CONSTITUTION:The field system of a DC motor comprises a magnet field system generated by permanent magnets 4 and a winding field system generated by field cores 2 and field windings 3. As the DC motor having six magnetic poles, which comprise two magnetic poles constituted with the permanent magnets 4 and four magnetic poles constituted with the field cores 2 and the field windings 3, the magnitude of the magnetic field generated when electrifying the field windings 3 is set larger than the one generated by the permanent magnets 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct current motor, and more particularly to a direct current motor using both a permanent magnet and a field winding for its field.

[0002]

2. Description of the Related Art Conventionally, as a DC motor, a series winding motor and a permanent magnet motor are known. The series-wound motor has an excellent characteristic (serial winding characteristic) that the starting torque is large and the torque decreases in a hyperbolic shape as the rotation speed increases. On the other hand, in a permanent magnet type electric motor, the field magnetic flux is constant irrespective of the load current (constant excitation characteristic), so the torque is proportional to the load current and decreases proportionally as the rotation speed increases. It has characteristics.

These electric motors are used in starter motors for vehicles, for example.

[0004]

However, when a series-wound electric motor is used as the starter motor, the series-wound electric motor generates a large starting torque as described above, but at the same time, the rotation speed increases significantly when no load is applied. Therefore, the time from turning off the starter switch to stopping the starter motor is long because inertial rotation is long. Therefore, if the starter motor is driven intermittently, such as during engine ignition failure, the starter-side pinion gear gets caught in the engine-side ring gear during inertial rotation of this motor, causing a large impact between the pinion and ring gear. There is a problem that the ring gear is damaged or the starter motor is damaged by this impact.

On the other hand, when the permanent magnet electric motor is used, the rotational speed under no load is suppressed, but the starting torque is small. Therefore, an object of the present invention is to provide an electric motor that generates a large starting torque and that suppresses the rotation speed under no load.

[0006]

In order to achieve the above object, the present invention uses a field of a DC motor as a magnet field of a permanent magnet and a winding field of a field core and a field winding. The magnetic field generated when the field winding is energized is set to be larger than the magnetic field generated by the permanent magnet.

[0007]

With the above construction, when the electric motor is started, the magnitude of the magnetic field generated by the field winding is larger than the magnitude of the magnetic field generated by the permanent magnet, and the proportion of the series winding characteristic of the field winding is high. On the other hand, when the motor is stopped, even if the current to the field winding is cut off, the magnetic field is always generated by the permanent magnet, and the rotor of the motor is inertially rotated, so that the motor is driven by the generator. And a force for braking the rotor acts on the rotor.

[0008]

Therefore, when the electric motor is started, a large starting torque is generated due to the series winding characteristic, and when the electric motor is stopped, the inertial rotation time of the rotor is shortened. When used as a motor, when the starter motor is intermittently driven, such as when the engine is ignited poorly, the starter side pinion gear is less likely to get caught in the engine side ring gear during inertial rotation of the motor. The possibility that the starter motor or the like will be damaged can be reduced as much as possible.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the electric motor of the present invention will be described below with reference to FIGS.
It will be explained based on. FIG. 1 is a cross-sectional view. When the stator, which is an essential part of the present invention, is described with a case of 6 poles as an example, the field around which the field winding 3 is wound around the inner peripheral surface of the cylindrical yoke 1. A magnetic core 2 is arranged and constitutes a winding field. Four
Is a permanent magnet, is arranged on the inner peripheral surface of the yoke 1 like the field iron core, and constitutes a magnet field. As shown in the figure, the permanent magnet 4 constitutes two magnetic poles, and the field core 2
The field winding 3 constitutes four magnetic poles. The size of the magnet, the number of turns of the winding, etc. are set so that the magnitude of the magnetic field generated when the field winding 3 is energized is larger than the magnitude of the magnetic field generated by the permanent magnet.

Reference numeral 5 denotes an armature core around which the armature winding 6 is wound, and constitutes a rotor including a commutator (not shown). Both the rotors are rotatably held by brackets (not shown) via bearings.

The case where the electric motor having the above configuration is used as a starter motor will be described below as an example. FIG. 2 is a schematic diagram showing the wiring configuration of the starter, in which 7 is an in-vehicle battery and 8 is a starter switch. Reference numeral 9 is a movable iron core, 10 is a switch coil, and 11 and 12 are positive side fixed contacts and negative side fixed contacts, respectively, which constitute a magnet switch as is well known.

The operation of the starter having the above structure will be described below.
When the starter switch 8 is closed, the switch coil 8 is supplied with current from the battery 7. When a magnetic flux is generated in the switch coil 8 and the movable iron core 9 is moved in the axial direction by this magnetic flux to close the fixed contacts 11 and 12, the field winding 3 and the armature winding 6 are energized. In the 6-pole fixed field, different poles are adjacent to each other, the magnetic flux generated by the field winding 3 forms a closed loop between the adjacent field windings, and the magnetic flux generated by the permanent magnet 4 is Since a closed loop is formed between the opposing magnets, the magnetic field of the main pole winding field and the magnetic pole of the main pole winding field and the magnetic pole of the complementary pole magnet field Without forming the closed loop and reducing the high torque, which is the merit of the direct winding type, the windings that form 4 poles and 2
It is possible to obtain a performance close to a series winding characteristic that is proportional to the constituent ratio (ratio of the magnitude of the generated magnetic field) of the magnets that form the poles, that is, a starting torque that is proportional to the constituent ratio.

When there is no load, the rotation speed can be suppressed by the shunt winding characteristic of the magnet, and when the starter switch 8 is opened, the rotor crosses the magnetic flux generated by the permanent magnet 4 while inertially rotating. Therefore, since a voltage (power generation voltage) opposite to that at the time of operation is generated, the force for braking this inertial rotation acts and the inertial rotation is quickly stopped.

Further, by providing a high-permeability auxiliary pole in a part of the permanent magnet, the magnetic flux generated by the field winding can be increased and the torque generated by the electric motor can be increased.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an electric motor of the present invention.

FIG. 2 is a diagram showing a wiring structure when the electric motor is used as a starter motor.

[Explanation of symbols]

 1 yoke 2 field iron core 3 field winding 4 permanent magnet 5 armature iron core 6 armature winding

Claims (1)

[Claims] 1. A field of a direct current motor is constituted by a magnet field of a permanent magnet and a winding field of a field iron core and a field winding, and is generated when the field winding is energized. A direct current motor characterized in that a magnitude of a magnetic field is set to be larger than a magnitude of a magnetic field generated by the permanent magnet.