Overview of Motor Commutator
English: commutator Commonly known as a commutator.
The commutator is composed of brushes and commutator rings and is a component on a DC permanent magnet series-excited motor to enable the motor to keep rotating. On some motors, we can see that its rotor is equipped with a conductive ring composed of many copper sheets. This is connected to an external power source through a pair of brushes. For a motor, we call it a commutator, and for a generator, we call it a rectifier.
The commutator includes: mechanical commutator, semi-plastic commutator, and all-plastic commutator. The commutators used in automotive starters mainly use mechanical arched commutators and plastic commutators.
Structurally, the commutator is a circle formed by several contact pieces, each connected to each contact on the rotor. The two electrodes connected externally are called brushes and are in contact with them, while only in contact with two of them at the same time.
The principle is that when a coil passes current, it will rotate through attraction and repulsion under the action of a permanent magnet. When it rotates to balance with the magnet, the contact piece corresponding to the wire that was originally energized separates from the brush on the commutator, and the brush is connected to the contact piece corresponding to the coil group that generates the driving force. This repeats continuously, and the DC motor rotates.
If there is no function of the commutator, the motor can only rotate less than half a circle and get stuck, and can only be used as an electric brake. A device that uses the centrifugal force generated during the rotation of the motor as the power to control the size of the starting resistance, achieving the reduction of the starting current of the motor, increase of the starting torque, and enabling the wound asynchronous motor to achieve brushless self-control operation. It mainly consists of a casing, starting fluid, moving electrode plate, spring, terminal post, safety valve, exhaust valve, etc. This liquid resistance starter has the characteristics of small starting current, large starting torque, automatic adaptation to changes in the power supply and load, and protection of the motor. The commutator is a high-speed rotating equipment, and its rotor winding is subjected to the effects of electric force and centrifugal force. Although it has always been operating under rated parameters, the solder joint at the junction of the rotor winding and the commutator riser is a weak link of the commutator rotor, and the traditional soldering tin process is used. Combined with the measurement results of the DC resistance between the sheets, it is judged that the solder joint between the rotor winding and the commutator riser is loose, resulting in fatigue of the end wire, increased contact resistance, increased heat generation, accelerated oxidation of the contact surface, further increased contact resistance, and further increased heat generation. This vicious cycle eventually leads to insulation burnout of the commutator rotor at high temperatures, arc discharge to ground, and damage to the commutator. The results of the disassembly inspection of the commutator show that the test-related data and judgment conclusions of the rotor winding are accurate and correct. When the motor commutator is working, in addition to transmitting longitudinal current, there is also the task of current commutation in the short-circuited armature coil.
These currents are the reverse current and reactance voltage generated when the main current commutator of the motor occurs, causing edge sparks and arcs when the brush slides on the surface of the motor commutator. The influence of the motor commutator on the performance of the motor depends on the process of realizing circuit conduction when it slides at a relatively high speed with the brush under certain conditions. Although the description of this process is relatively complex and theoretical research is still developing, through the comparative analysis of the operation status of micro-motors at home and abroad, it can be determined that wear is the most crucial factor leading to changes in contact resistance. The commutator mainly has specifications such as hook type, slot type, and planar type. It is refined from imported raw materials, and the performance of the product reaches the international advanced level. It is widely used in fields such as power tools, household appliances, automobiles, and motorcycle motors; collector rings, carbon brush holders, and terminal boards have various specifications and models of products, and are applied in fields such as automotive generators and gasoline generators. The commutator plays the role of rectification, and its function is to make the current direction in the armature winding alternating to ensure that the direction of the electromagnetic torque remains unchanged. In a generator, the commutator can convert the alternating potential of the component into the DC potential between the brushes; in a motor, it can convert the applied DC current into the alternating current in the component, generating a constant-direction torque.
