The definition of a brushless motor in electric vehicles

With the growing popularity of electric bicycles, scooters and cars, there is often discussion of battery range, smart features and stylish designs. However, behind these ostentatious features lies the fundamental technology that genuinely propels us forward—the brushless DC motor.

Like the beating heart of an electric vehicle, it is a rarely mentioned yet crucially determining factor in performance, efficiency, and reliability. The subject of this article is the world of brushless motors. The article provides a deep dive into the subject, revealing the reasons for brushless motors' emergence as the silent leaders in modern electric transportation.

Chapter One: From “Brushed” to “Brushless”—A Design Revolution

The grasping of the ingenuity of brushless motors is dependent on a prior revisiting of their predecessor, the brushed DC motor.

The operating principle of a brushed motor is simple:

A stationary permanent magnet (stator) and a rotating electromagnet (rotor) are contained within.

To accomplish uninterrupted rotation, it depends on a vital element: the brushes and commutator. Typically made of carbon, the brushes remain in a stationary position and maintain constant physical contact with the rotating commutator mounted on the rotor.

The continuous reversal of the direction of current flowing into the rotor coils results in the generation of a changing magnetic field by the commutator. This interacts with the permanent magnet, driving the rotor to spin endlessly.

The limitations of brushed motors are evident:

Friction and wear: The inevitable cause of friction is physical contact, leading to the gradual wear of the brushes, which require periodic replacement.

Energy loss and heat generation: The production of sparks and resistance by contact points reduces efficiency and results in electrical energy being wasted as heat.

Noise and interference: Noise is generated by friction between brushes and commutators, while electromagnetic interference affecting electronic devices may be caused by sparks.

These drawbacks spurred the development of more advanced and reliable brushless motor technology. Brushless motors represent not merely an improvement over brushed designs, but a revolutionary “inside-out” transformation in fundamental principles.

Chapter 2: Unveiling Brushless Motors: An Electronically Orchestrated Magnetic Dance

The design philosophy of brushless motors is nothing short of ingenious:

Structural Inversion:

Rotor: Composed of high-performance permanent magnets (such as neodymium iron boron magnets), it no longer requires any electrical connections.

Stator: Composed of multiple copper wire coils, fixed externally and stationary.

Source of Driving Force:

Since the rotor is a “passive” permanent magnet, how is it made to rotate? The answer lies in creating a rotating magnetic field to “drag” it along.

This process is orchestrated by an intelligent electronic controller. Serving as the “brain” of the brushless motor, this controller executes a precise task:

Position sensing: Through Hall sensors or back-EMF detection, the controller precisely determines the rotor's permanent magnet position at any given moment.

Precise power delivery: Based on the rotor's position, the controller rapidly supplies current to different coil groups on the stator in a specific sequence.

Generating a rotating magnetic field: Energized coils produce electromagnetic fields that attract or repel the rotor's permanent magnets, generating torque. By continuously and rapidly switching which coils are energized, a “running” magnetic field is generated within the stator. This field acts like an invisible hand, persistently pulling the rotor to rotate in sync.

A vivid analogy:

Imagine an elegant waltz. The rotor is the lead dancer (permanent magnet), while the stator coils are three partners circling around it. The electronic controller acts as the orchestra conductor. Based on the position of the lead dancer, the conductor directs the three partners to extend their hands in sequence, generating magnetic fields and guiding the lead dancer to rotate continuously and smoothly. This dance involves no physical contact, only the seamless coordination of magnetic forces, resulting in unparalleled fluidity, efficiency and quiet operation.

Chapter 3: Why Are Brushless Motors the Ideal Choice for Electric Transportation?

The inherent advantages of brushless motors perfectly address all core requirements of electric vehicles:

1. Exceptional Efficiency

By eliminating friction and resistance losses caused by brushes, brushless motors convert up to 90%-95% of battery power into mechanical energy for propulsion. In contrast, brushed motors typically operate at 75%-85% efficiency. This directly translates to extended range—a crucial win for users concerned about “range anxiety.”

2. Brushless motors are fantastic because they can provide a great deal of power and torque in a compact space. The provision of massive starting and low-speed torque enables electric vehicles to accelerate quickly from a standstill and climb hills with ease, thereby enhancing the riding experience.

3. Remarkable longevity and low maintenance

Without any major wear components (brushes), brushless motors have vastly extended lifespans.  Their service life typically depends only on bearing durability, which can last thousands or even tens of thousands of hours. For most users, this means the motor requires zero internal maintenance throughout the vehicle's entire lifecycle.

4. Quiet, smooth operation is achieved through electronic commutation replacing mechanical switching. This results in the elimination of brush friction noise and sparks. The motor produces only a faint electromagnetic hum. This creates a quieter, more enjoyable ride. It also has a futuristic technological feel.

5. Superior heat dissipation

The positioning of the heat-generating coils (stator) on the motor housing allows for direct conduction of heat to the casing and dissipation through its large surface area. The enabling of more effective regulation of heat accumulation under substantial loads by brushless motors allows for continuous high-power output over extended durations without activation of thermal protection.

Chapter 4: Trade-offs and Considerations

Well, obviously, every technology's got its pros and cons, and brushless motors are no different.

Higher manufacturing costs: So, brushless motor systems have these precision permanent magnet rotors and multi-phase stator windings, right? And they've also got these complex electronic controllers, which are pretty much essential. All of that means that, compared to brushed motors, they're more expensive to make.Absolute Dependence on Controllers: The brushless motor itself is a “dumb” component that cannot function without a controller. The system's performance and reliability also depend heavily on the quality and algorithms of the controller.

Despite these considerations, the market's unequivocal choice of brushless motors as the standard for high-end electric vehicles is driven by the immense value they deliver in performance, efficiency, and reliability.

Chapter 5: Looking Ahead: The evolution and trends of brushless motors.

Brushless motor technology continues to advance.

More Advanced Control Algorithms: The increasing prevalence of techniques such as Field-Oriented Control (FOC/Vector Control) is evident. The operation of the FOC technology is characterised by exceptional smoothness and quietness. The delivery of optimal torque efficiency is consistent across the entire speed range, with particular elimination of vibration at low speeds.

Direct Drive and Mid-Drive Motors: In the e-bike sector, brushless technology has spawned powerful hub motors and efficient mid-drive motors (integrating the motor with the vehicle's drivetrain), further optimizing power delivery and riding experience.

Application of New Materials: Stronger permanent magnets, more efficient electromagnetic steel laminations, and better thermal conductive materials are continually pushing the performance limits of motors.