What are the structural components of the brush DC motor

What are the structural components of the brush DC motor

In industrial applications, when high torque is required mainly during acceleration and deceleration, the brush motor is very meaningful. A common example is dispensing equipment used in the medical and packaging fields. Coreless designs are also ideal for battery powered equipment because they consume very little current under no-load conditions. Their ability to produce fast and dynamic movements makes them very suitable for industrial robot applications. This paper mainly introduces the structure and working principle of the brush DC motor

We can see brushless or brushless DC motors on many mechanical equipment that need current to provide power. Their function is based on the same principle of attraction and repulsion between coils and permanent magnets. Both have advantages and disadvantages. You should choose one according to the requirements of the application.

DC motors can be mechanically or electronically commutated. Brushed DC motors rely on mechanical means, with brushes and commutators, while brushless DC motors use electronic means to achieve commutation. Although brushes and commutators are wear parts that can be avoided by brushless commutation, brushless DC motors do have some advantages over brushless motors, such as low friction, low starting voltage, high efficiency and good heat dissipation.

Structure Composition of Brushed DC Motor

Brushed motor is mainly composed of stator, rotor, carbon brush, magnetic steel and commutator. The part that does not rotate when a brush (or brushless) motor is working is called the stator. The motor shaft of a hub type brush (or brushless) toothless motor is also called the stator. This motor is also called the stator motor. The rotating part of the brush or brushless DC motor is called the rotor, also called the armature, and the casing of the hub type brush or brushless toothless motor is also called the rotor, which is also called the outer rotor motor.

Stator and rotor are only relative. The rotor is generally made of steel, and its inner wall is pasted with permanent magnet materials. The rotor of DC brushless motor for electric bicycle is usually pasted with 16 high efficiency rare earth magnets. The rotor is mainly composed of armature core, armature winding, commutator, shaft, bearing and fan.

Armature winding is used to pass current and generate induced electromotive force to realize electromechanical energy conversion. It is mainly composed of a certain number of armature windings connected according to a certain rule. The winding is embedded in the armature core slot in upper and lower layers with insulated circular or rectangular cross-section wire carbon brushes, and the arrangement sequence of the windings in the brushless motor is called phase sequence.

The function of the brush device is to introduce or lead the DC voltage and DC current. It is mainly composed of brushes, brush holders and conductive copper wires. The brush is a conductive block composed of graphite or metallic graphite. It is placed in the brush handle and is placed on the surface of the commutator with a compression spring under a certain pressure. When rotating, it forms a sliding contact with the commutator surface. The brush holder is clamped on the brush rod with screws.

Most brushless DC motors are composed of three main sub assemblies: stator, brush holder end cover and rotor. The stator consists of a central and cylindrical bipolar permanent magnet, an iron core supporting the bearing and a steel pipe with a closed magnetic circuit. High quality rare earth magnets ensure excellent performance in small packages. Sintered bearings and ball bearings are available according to the load and requirements of the mechanical equipment application.

The brush holder end cover is made of plastic material. Brushes can be of two different types depending on the intended use of the motor; Carbon or multi wire. The carbon type uses copper graphite or silver graphite, which is ideal for incremental motion applications requiring high continuous torque and peak torque. Multiwire uses precious metals to ensure low starting voltage and higher efficiency, which is the perfect match for portable battery powered applications. The electrical engineer can design the end cap to reduce electromagnetic noise to meet EMC requirements.

Working Principle of Brushed DC Motor

Brushed DC motor windings coils in the rotor, and the coils are surrounded by magnets contained in the stator. Both ends of the coil are connected with the commutator. The commutator is also connected to the electrode called the brush. As long as the brush contacts the commutator, DC will flow through the brush and coil.

Rotor is the core of brushless DC motor. The coil is directly and continuously wound on the cylindrical support and then removed, eliminating excessive air gaps and inactive coil heads, which do not contribute to torque generation. The self-supporting coil does not need iron structure, so the moment of inertia is low and there is no cogging effect (the rotor will stop at any position). Unlike other traditional DC coil technologies, there is no hysteresis, eddy current loss or magnetic saturation due to the absence of iron. The motor has perfect linear speed torque characteristics, and the operating speed only depends on the power supply voltage and load torque.

But when the coil rotates, it will reach the position where the brush and the commutator no longer contact, thus stopping the current flow in the coil. However, the momentum of the coil causes it to continue to rotate. This allows the brush to re contact the commutator, restoring the current that now flows through the different coils. This repeated switching of the current causes the brushless DC motor to continue to rotate. Brushed DC motors operate on DC, and their speed can be easily controlled by changing the applied voltage.

The brushless DC motor works by rotating the coil in the surrounding magnet. The rotation of the coil causes the contact between the commutator and the brush to alternate, thus switching the current flowing through the coil. Although the internal structure of the brush DC motor is simple, the continuous contact between the brush and the commutator will cause wear as the motor rotates, which requires regular maintenance to replace worn parts.

This paper mainly introduces the structure and working principle of the brush DC motor. Most of the brush DC motors in this paper are composed of three main sub components: stator, brush holder end cover and rotor. In addition, the paper also introduces its working principle. A coil is wound in the rotor of a brush DC motor, and the coil is surrounded by a magnet contained in the stator. Both ends of the coil are connected with the commutator. The commutator is also connected to the electrode called the brush. As long as the brush contacts the commutator, DC will flow through the brush and coil.