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What is a Traction Motor? Functions and Classifications


Traction motors, also known as drive motors, are key components in intelligent assembly systems that generate mechanical motion. They are responsible for converting electrical energy into mechanical energy to drive the movement or rotation of assembly machinery for completing various assembly tasks.

 

The Functions of Traction Motor

 

1. Driving Function: Traction motors provide power to mechanical arms, conveyor belts, rotary tables, and other components in intelligent assembly systems, enabling them to move precisely along predetermined paths or at specified speeds.

2. Precise Control: By accurately controlling the motor’s speed and torque, it is possible to strictly control the assembly accuracy, thereby enhancing the quality and efficiency of the assembly process.

3. System Integration: Traction motors are often integrated with control systems, sensors, and other components to form an intelligent drive system that enables automated and intelligent assembly operations.

4. Energy Efficiency Optimization: The high efficiency of traction motors helps to reduce the energy consumption of the entire assembly system, meeting the modern manufacturing industry’s requirements for energy saving and emission reduction.

5. Adaptability: Traction motors can adapt to different assembly tasks and environmental conditions, exhibiting strong versatility and adaptability.

 

 

The Classification of Traction Motors

 

Traction Motors can be classified according to various criteria, and here are some common classification methods:

 

1. Based on power supply type, they can be divided into direct current traction motors and alternating current motors:

 

DC Traction Motor: Traction motors powered by direct current, which typically have good speed control performance and are simple and convenient to maintain, hence widely used.

 

AC Traction Motor: Traction motors powered by alternating current, including asynchronous traction motors and synchronous traction motors. And asynchronous motors have a simple structure are cost-effective, and are easy to maintain; synchronous motors, on the other hand ,have high efficiency and power factor, suitable for high-power drives.

 

2. Based on construction and working principle, they can be divided into induction motors, permanent magnet synchronous motors and switched reluctance motors:

 

Induction Motor: It is also known as an induction motor. It generates a rotating magnetic field through electromagnetic induction to drive the motor rotor.

 

Permanent Magnet Synchronous Motor (PMSM): It utilizes permanent magnets to produce a magnetic field, featuring high efficiency and power density.

 

Switched Reluctance Motor (SRM): It drives the motor rotor by changing the polarity of the magnetic field, typically with a simple, robust structure, but higher noise and vibration levels.

 

3. Based on the field of application, they can be divided into industrial motors and automotive motors:

 

Industrial Motor: It includes but is not limited to motors for automation and mechanical drives.

 

Automotive Motor: In new energy vehicles, the motor is a core component, including traction motors for driving and motors for auxiliary systems.

 

4. Based on performance characteristics, they can be divided into high-torque motors and high-speed motors:

 

High-Torque Motor: It commonly used in heavy machinery such as cranes and excavators, as well as in situations requiring high starting torque.

 

High-Speed Motor: It is suitable for applications requiring high speeds, such as machine tool spindles and high-speed centrifuges.

 

5. Based on cooling method, they can be divided into air-cooled motors and liquid-cooled motors:

 

Air-Cooled Motor: It uses air as the cooling medium, suitable for working environments that are not particularly high in temperature.

 

Liquid-Cooled Motor: It uses coolant for cooling, suitable for high-power density and high-temperature working environments.

 

 

6. Based on the installation method, they can be divided into internal motors and external motors:

 

Internal Motor: It usually designed as an integral part of the equipment, facilitating installation and maintenance.

 

External Motor: The motor is installed outside the equipment and needs to be connected to the load through a transmission device.

 

7. Based on the installation and control method, they can be divided into stepper motors and servo motors:

 

Stepper Motor: Can precisely control the number of steps and position, commonly used in situations requiring precise positioning.

 

Servo Motor: Has high-precision speed and position control capabilities, suitable for systems requiring rapid response and precise control.

 

The Working Principle of Traction Motor

 

The working principle of a traction electric motor is the same as that of a general direct current (DC) motor, but it operates under special conditions: the spatial dimensions are limited by the track gauge and the diameter of the driven wheels; it must withstand considerable impact and vibration when the locomotive passes over track joints and switches; strong torsional vibrations can occur on the armature when the engagement of large and small gears is poor; and it is used in harsh environments where rain, snow, and dust are easily infiltrated. Therefore, the design and structure of traction electric motors also have many requirements, such as making full use of the internal space of the machine to make the structure compact, using higher-grade insulating and magnetic materials, requiring parts to have higher mechanical strength and rigidity, and the entire motor needs to have good ventilation and heat dissipation conditions as well as dust and moisture resistance. Special measures must be taken to deal with the more difficult "commutation" conditions to reduce sparking under the brushes, and so on.

 

The Suspension Methods of Traction Motors

 

There are two types of suspension methods for traction electric motors:

 

One is the suspension method where the traction motor is connected to the driven wheel axle, known as the axle-hugging or semi-suspension. With this suspension method, the impact and vibration generated by the driven wheels passing over track joints and switches are directly transmitted to the traction motor. Axle-hugging suspension is suitable for locomotive vehicles with a structural speed of less than 120 kilometers per hour.

 

The other is the frame-supported suspension (also known as full suspension). With this suspension method, the traction motor is fixedly suspended on the bogie frame, and various elastic connecting elements are added between the motor shaft end and the small and large gears to reduce the impact of shock and vibration. Frame-supported suspension is suitable for locomotive vehicles with a structural speed of more than 120 kilometers per hour.

 

When a traction transformer reduces the voltage, which is then supplied to the DC series-wound traction motor through a silicon rectifier or high-power thyristor rectifier, the voltage applied to the traction motor is a pulsating voltage. Therefore, this type of traction motor is called a pulsed current traction motor. The "commutation" conditions for high-power pulsed current traction motors are even more difficult. In addition, there are some additional losses inside the motor, which cause the motor to heat up. Therefore, special measures must also be taken in the design and structure of pulsed current traction motors to address the prominent issues of "commutation" and temperature rise.

 

The Operating Conditions of Traction Motors

 

The working principle of traction motors is consistent with that of general motors, and their basic structure is also similar to that of general motors. However, the operating conditions of traction motors are quite different from those of general motors, so careful consideration must be given to the design, structure, materials, insulation, and processes of traction motors.

 

The main characteristics of the operating conditions of traction motors are:

 

1. Since locomotives require both large tractive force and high-speed operation, the voltage and current applied to the motor have a large range of variation. Therefore, the motor must be able to adapt to a large voltage regulation ratio and have a certain depth of magnetic field weakening capability.

 

2. Traction motors operate outdoors in harsh environments, often exposed to wind, sand, rain, and snow. There are significant differences in the altitude, environmental temperature, humidity, salt content (in coastal areas during the hot season), and dust content of the regions where they are used, all of which can deteriorate the motor insulation. Therefore, the insulating materials and structures of traction motors should have good dust and moisture resistance.

 

3. Since traction motors frequently start, brake, overload, and weaken the magnetic field during operation, and the impact and vibration experienced by the motor during locomotive operation are more severe than those of general motors, both electromagnetic and mechanical reasons can cause difficulties in commutation of the traction motor, with frequent sparking and even arcing on the commutator. It is particularly important to note that traction motors operating under pulsating voltage have even more challenging commutation and heating issues. Therefore, the structural selection for pulsed current traction motors must also consider these special aspects. The impact and vibration during operation not only worsen commutation but also easily damage the motor components, so the components of the traction motor must have high mechanical strength.

 

4. The installation space dimensions of traction motors are limited. Since traction motors are suspended on the locomotive bogie, the motor structure must consider both transmission and suspension issues. Its radial dimensions are limited by the diameter of the wheel pairs, the axial dimensions are limited by the track gauge, and it is also restricted by the distance between the centerline of the wheel pairs and other components of the locomotive running gear. Therefore, the structure of the traction motor must be compact, and high-grade insulating materials and high-performance magnetic materials are usually used.

 

 

Application Fields

 

Traction motors are suitable for various fields, including but not limited to:

 

Electric Vehicles: Traction motors provide the necessary power and torque for electric vehicles, driving the vehicle's movement.

 

Electric Trains: In railway transportation, traction motors are used to drive trains and subway vehicles for long-distance transportation.

 

Industrial Machinery: In industrial applications such as automated production lines, conveyor systems, and robots, traction motors are used for precise control of mechanical motion.

 

About HONEST

 

HONEST is a leading Chinese supplier focused on the innovation of electric motor equipment and automated production lines. We combine innovative technology with over a decade of expertise in automation to achieve efficient manufacturing of motors.

If you have any needs for motor production equipment or automatic production lines, please feel free to contact us at your convenience. We can provide you with detailed information and quotations for our products

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