What Is the Function of Commutator in DC Motor?

In the field of electromechanical systems, the brushed direct current (DC) motor remains a foundational technology. Its ability to produce continuous unidirectional rotation from a DC power supply relies on a critical electromechanical component: the commutator. From an engineering perspective, the commutator is not merely a conductive element—it functions as a synchronous rotary switch that enables the continuous generation of unidirectional torque. This article provides a technically rigorous analysis of the commutator’s function, its operating principles, and its essential role in the operation of brushed DC motors.

The Fundamental Challenge: Sustaining Unidirectional Torque

The operation of a DC motor is governed by the Lorentz Force Law: a current-carrying conductor in a magnetic field experiences a mechanical force. In a DC motor, the rotating component—the armature—contains conductors wound around a laminated core. When current flows through these conductors, the stationary magnetic field (produced by field windings or permanent magnets) exerts a force, generating torque and initiating rotation.

However, a fundamental challenge arises during rotation. As an armature coil approaches and passes through the magnetic neutral axis (MNA)—the position where the plane of the coil is perpendicular to the magnetic flux lines—the relative motion between the conductors and the magnetic field reverses. If the current direction in the coil remained constant, the Lorentz force on each conductor would reverse, leading to a reversal in torque direction. This would cause the armature to oscillate around the MNA rather than rotate continuously, resulting in motor stalling. This is the core problem that the commutator is designed to solve.

The Commutator’s Solution: Timed Current Reversal

The primary function of the commutator is to ensure that the electromagnetic torque on the armature remains unidirectional throughout the rotation cycle. It achieves this through a process known as commutation—the precise reversal of current in the armature windings at specific rotor positions.

The commutator is a cylindrical assembly mounted on the motor shaft, composed of multiple electrically isolated copper segments, typically made of high-conductivity copper. Each segment is connected to the ends of one or more armature coils. Carbon brushes, held in firm contact with the commutator by spring-loaded holders, deliver DC current from the external power source to the rotating armature.

As the armature rotates, the commutator turns with it. When a coil reaches the magnetic neutral axis, the brushes transition from one commutator segment to the next, crossing the insulating gap between them. This action:

1. Interrupts the current in the coil that has just passed the torque-zero point,
2. Reverses the polarity of the current supplied to that coil (by connecting it to the opposite brush polarity),
3. Ensures that the Lorentz force direction on the conductors remains aligned with the desired rotational direction.

This synchronized reversal—occurring for each coil as it passes the MNA—ensures that the net torque is always in the same direction. In motors with multiple coils and commutator segments, the overlapping commutation process further smooths torque output and reduces ripple, enabling continuous and stable rotation.

Conclusion: The Electromechanical Heart of the Brushed DC Motor

In summary, the commutator is the essential electromechanical interface that enables continuous rotation in brushed DC motors. Its function extends beyond simple current conduction; it acts as a precision-timed rotary switch that reverses armature current in synchronization with rotor position. By ensuring that the current in each coil reverses at the exact moment the torque direction would otherwise invert, the commutator maintains a net unidirectional torque, allowing the motor to deliver sustained mechanical power.

Without the commutator, a brushed DC motor would be incapable of continuous rotation. It is this dynamic interaction between the stationary brushes and the rotating, segmented commutator that resolves the fundamental challenge of torque reversal—making brushed DC motors reliable and effective across countless industrial, automotive, and consumer applications.

That concludes our introduction to “What Is the Function of the Commutator in a DC Motor?”. If you have any requirements for purchasing motors, please visit our online store: BLDC Motor Store.