With the explosive growth of the global electric vehicle market, the maintenance demand of the driving motor, as the “power heart” of the vehicle, is rising at an unprecedented rate.
The maintenance experience of traditional industrial motors is often inadequate to deal with EV motors. Why does the performance of some motors decrease after disassembly? Why is the same fault code interpreted differently on different models?
Behind this is the unique design philosophy and working logic of EV motor.
We will take you in-depth analysis of the structural characteristics of the five mainstream drive motors, and provide a ready-to-use maintenance program.
Whether you are a novice in electric vehicle maintenance or an engineer who wants to improve efficiency, this strategy will become a “secret weapon” in your toolbox.
Let’s start with understanding the essential differences of EV motors and uncover the password of efficient maintenance step by step.
As the “power heart” of EV, the driving motor directly determines whether the vehicle can run and how stable it can run. However, in the face of various types of motors, many maintenance engineers often commit the problem of “not daring to install after disassembly, but also breaking down after repair”.
Combining with the practical operation scene, we will thoroughly explain the structure, principle and maintenance of the driving motor.
Core before maintenance: safety specifications and preparation
The maintenance of the drive motor involves high voltage (usually ≥ 300 V), and safety is the first prerequisite.
The preparation of the specification includes:
- Qualification and environment:The operator shall hold the electrician special operation certificate and the manufacturer’s certification. The operation area shall be dry and ventilated, with warning barrier, insulated gloves/shoes/glasses, water-based fire extinguisher and emergency sandbox.
- Vehicle pretreatment:turn off the power supply of the whole vehicle, hang the warning sign of “high voltage maintenance”, and disconnect the negative pole of the low voltage battery. After that, it must stand for more than 10 minutes and wait for the high-voltage capacitor to discharge.
- Electricity test confirmation:before operation, use a high-voltage electroscope to test the battery bus, motor controller and other key components, and confirm that the voltage is reduced to a safe range (such as ≤ 36V) before the next operation.
- First understand: EV drive motor is different from industrial motor.
When we repair, we should not take the standard set of EV motors of industrial motors-the two are very different, and it is easy to misjudge the fault. For example, the same “overload” requires completely different requirements:
- Overload capacity:EV motor needs to carry 4-5 times of overload (to cope with climbing and rapid acceleration), and 2 times of industrial motor is enough. Measure the motor current during maintenance. If there is no alarm when the current exceeds the fixed value by 4 times in a short time, don’t panic. It may be a normal working condition.
- Speed range:the maximum speed of EV motor is 4-5 times of the cruising speed (for example, the motor speed is 2000 R/min during cruising, and the maximum speed is 10000r/min), while the speed of industrial motor is only 2 times;
- Working environment:EV motor is installed at the bottom of the vehicle, which is resistant to high temperature (engine waste heat), vibration (bumpy road) and rain. Industrial motors are mostly in the constant temperature workshop. When disassembling and inspecting the motor during maintenance, be sure to clean sand in the shell first, and then check whether the sealing ring is aging (to prevent water from entering and short circuit).
Therefore, EV motors are “durable sprinters” and industrial motors are “stable long-distance runners”, so maintenance ideas should be separated.
- Five mainstream drive motors: structure + principle + maintenance focus
At present, the loaded motors are mainly divided into five categories, and the maintenance focus of each category is different. We will disassemble them one by one:
- DC motor: It is common in old cars, and the vulnerable parts are the “disaster area”.
Applicable models: Early low-speed electric vehicles (such as some of the old electric micro-face) are now mostly eliminated, but there are still maintenance needs.
- Stator:including main magnetic pole (to generate magnetic field), brush device (to transmit current)-maintenance focus on brush wear (if the thickness is less than 3mm, it must be replaced), brush spring pressure (too loose will lead to poor contact);
- Rotor (armature): the core is the commutator (converting DC into winding AC)-measure the diameter of the commutator with a micrometer during maintenance. If the wear exceeds 0.5mm or the surface is ablated, it must be turned and repaired.
How it works:
The energized conductor is forced to rotate in the magnetic field (simply speaking: the current passes through the brush → the armature winding → the magnetic field force → the rotor rotates).
Maintenance focus:
If there is a “sizzling” sound when the rotor is rotating, do not just change the brush-first check whether the insulation between the commutator segments is broken down (use a multimeter to measure the adjacent commutator segments, if they are conductive, there will be a short circuit).
- Three-phase asynchronous induction motor: the mainstream of middle-end vehicles, with wrong connection of stator winding group
Applicable models: Nissan March EV, Ford ETX-1, etc., with large maintenance volume.
- Stator:including 3 sets of windings (connected to 380 V three-phase power), with star (Y) and delta (Δ) connections-check the wiring during maintenance (wrong connection will burn the motor: for example, Y is connected to Δ, the current is doubled, and the motor is overheated);
- Rotor:divided into cage type (common) and winding type-if the cage type rotor has a broken bar (showing that the motor is weak and makes abnormal noise), it can be quickly located with the “broken bar detector” without disassembly.
How it works:
Three-phase electricity energizes the stator → generates a rotating magnetic field → the rotor cuts the magnetic field to generate current → rotates by the magnetic field force (the rotor speed is always slower than magnetic field, so it is called “asynchronous”).
Maintenance focus:
Measurement of insulation class) — — For example, for class B insulation (130 ℃ resistance), use a 500V megohmmeter to measure the insulation of the winding to the ground. If the resistance is lower than 0.5MΩ, it is damp and needs to be dried.
- Permanent magnet synchronous motor: the first choice for new cars, for fear of “high temperature demagnetization”
Applicable models: Toyota RAV4 EV, BYD Han, Tesla Model 3 (some models), now more than 80% of new cars use it.
- Stator:It is similar to the asynchronous motor, but the rotor is embedded with a permanent magnet (rare earth material, strong magnetism)-do not use iron to attract the permanent magnet during maintenance! Do not get close to the strong magnetic environment (such as welding machine), which will lead to “demagnetization” (after demagnetization, the motor is weak and needs to be re-magnetized);
- Rotor position sensor:measure the rotor angle and send the phase change signal to the controller-if the motor is “stuck” during maintenance, check the sensor wiring first (mostly Hall type, no signal if the wire is broken).
How it works:
The permanent magnet generates a fixed magnetic field → the stator winding is electrified with alternating current → a rotating magnetic field is generated → the two magnetic fields “pull” the rotor to rotate synchronously (the rotating speed is consistent with the magnetic field, which is called “synchronization”).
Maintenance must be done:
When reassembling after disassembly and inspection, the polarity of permanent magnet must be aligned (marked with “N/S”), because reverse assembly will cause motor reverse rotation or seizure.
- Switched Reluctance Motor: small but durable, inverter is “difficult”
Applicable models:
For some low-speed electric vehicles, permanent magnet models can be used as hub motors.
Structural features:
Both the stator and rotor have salient poles (gear-like), no permanent magnets, and the current is controlled by a switching circuit-the maintenance difficulty is the “inverter” (more complex than other motors).
Maintenance focus:
If the motor does not rotate, first check the power converter: measure the IGBT tube (inverter core), and measure the positive and negative resistance values with the diode gear of the multimeter. If both the positive and negative are conductive, it indicates that the IGBT is broken down and needs to be replaced;
Rotor position sensor failure will lead to “phase loss” (motor jitter). Use an oscilloscope to measure the output waveform of the sensor. If there is no sine wave, replace the sensor.
- Wheel hub motor: future trend, wheels to be removed for maintenance
Applicable models: Tokyo Electric Power IZA, part of the new force concept car, directly installed in the wheel, save the transmission shaft.
Disassembly of structure: including the motor, reduction mechanism and brake-during maintenance, the wheels and brake calipers shall be removed first, and then the gear wear of the reduction mechanism shall be checked (lack of oil will cause “buzzing” sound, and special gear oil shall be added).
Maintenance note: The bearing preload must be calibrated when reassembling (too loose will cause shaking, too tight will cause overheating), and the “bearing preload detector” can be used to measure the torque, which conforms to the manufacturer’s standard (usually 0.5-1.2 N ・ m).
- Motor controller (MCU): Don’t just replace the assembly for maintenance. Check these four parts first.
The motor can rotate and adjust the speed, and it all depends on the controller to “give orders”. When repairing, don’t replace the assembly as soon as it is broken (the cost is high). First check according to these four steps:
| Controller composition | Function | Maintenance and detection method |
| DSP control unit | Receiving command and calculating switch signal | Read the data stream with the diagnosis instrument. If the “motor target speed” has a value but the “actual speed” does not, check the DSP output signal. |
| IGBT drive circuit | Amplify signal and drive IGBT | Measure the voltage at the driving end (normally 12-15 V). If there is no voltage, check the quarantine circuit (the optocoupler is easy to be damaged). |
| Control power supply | Power supply for DSP and driver | Measure the power supply output (usually 5V, 12V), and replace the power supply module if the voltage is unstable |
| Cooling system | Cool down the IGBT | Touch the heat sink. If the temperature is normal but “overtemperature fault” is reported, check the temperature sensor (NTC resistance, about 10 kΩ at normal temperature) |
4.Maintenance comparison table: distinguish the priority of each motor
| Motor type | Wearing parts | Maintenance difficulty | Common faults | Emergency treatment plan |
| DC motor | Brush, commutator | ★★☆ | Poor contact, commutator ablation | Temporary replacement of electric brush for emergency |
| Three-phase asynchronous motor | Stator winding | ★★★ | Winding short circuit, rotor bar breaking | The broken bar can be temporarily wound with copper wire. |
| Permanent Magnet Synchronous Motor | Permanent magnet, sensor | ★★★★ | Loss of excitation, sensor fault | Trailer is required for loss of excitation. Do not drive by force. |
| Switched Reluctance Motor | IGBT, sensor | ★★★★ | Inverter fault and phase loss | Unplug the sensor for test run (emergency) |
| Hub Motor | Reduction gear, bearing | ★★★★ | Worn gear and abnormal sound of bearing | Gear oil can be supplemented temporarily due to oil shortage. |
- A complete motor maintenance follows a standardized process
Repair process:
Diagnosis: read the MCU fault code with special diagnostic equipment, and conduct preliminary appearance and electrical inspection.
Disassembly and depth detection: disassemble after power off, check the winding and magnetic steel, and use a megohmmeter to detect the insulation (standard value ≥ 1 MΩ).
Repair/replacement: repair (such as stator rewinding) or replace (such as bearing, IGBT module) damaged parts.
Test: Carry out no-load/load test after reassembly to ensure that the torque output conforms to the original parameters (error within ± 5%).
6.Verification after maintenance
After the repair is completed, strict verification must be carried out to ensure safety and performance:
High-voltage system verification: test the insulation resistance of the high-voltage circuit of the whole vehicle (≥ 10 MΩ), and use the diagnostic instrument to execute the high-voltage power-on command to confirm that the communication of each component is normal and there is no fault code.
Power performance verification: conduct road test to test whether the acceleration performance and energy recovery strength are normal, and monitor whether there is abnormal noise. For the hub motor, the wheel temperature shall be checked after the road test. If the temperature exceeds 60 ℃, it may mean that the bearing preload is too tight.
Compliance and rights protection: Maintenance Certificate shall be obtained after maintenance, and the new warranty period shall be confirmed. It should be noted that unauthorized disassembly and repair or failure to maintain according to the manual may lead to the invalidation of the original warranty.
The core of drive motor maintenance is to “recognize the type first, then focus on the key points”-remember the “vulnerable parts” and “taboos” of each motor (for example, permanent magnet motor is afraid of strong magnetism, asynchronous motor is afraid of wrong wiring), so as to avoid detours. The next time the motor is repaired, the efficiency can be doubled by checking the drawing.
By mastering these core techniques, you’ve surpassed most repairers who rely on “trial and error.”. But there is no end to technology iteration.
In the future, with the popularity of 800 V high voltage platforms and silicon carbide devices, motor maintenance will focus more on data diagnosis and preventive maintenance.
It is recommended to attend the manufacturer’s training regularly and establish your own fault case base: record the motor model, symptoms and solutions of each repair, and over time, you will form an intuitive judgment.