New energy electric/hybrid vehicle driving motor development trend

01. Development trend of new energy vehicle driving motor type

1.1 ac induction motor

At present, a variety of pure electric and hybrid new energy vehicles on the market, permanent magnet synchronous motor accounted for the majority, induction motor accounted for a small part, these two kinds of motor is basically all the electric passenger car drive motor.Compared with permanent magnet synchronous motor, ac induction motor is larger, but the price is moderate, and the induction motor can do a lot of power and there is no demagnetization problem.

1.2 permanent magnet synchronous motor

For small and medium-sized electric vehicles with high requirements on space layout size, permanent magnet synchronous motor with higher power and torque density is the preferred choice. Moreover, synchronous motor is more suitable for frequent start and stop conditions and suitable for the application scenarios of urban commuting. This is one of the reasons for Tesla Model 3 to use synchronous motor.

1.3 switched reluctance motor

The switched reluctance motor is simple in structure, strong in structure, easy to maintain and even maintenance-free.High speed constant power area has wide range, good performance, high output and high efficiency and good fault tolerance ability in a wide range of speed and power.The rotor torque of switched reluctance motor is superposed by a series of impulse torque, and the resultant torque is not constant torque, so there is a lot of vibration and noise.

The advantages and disadvantages of switched reluctance motors are very obvious. In the field of domestic vehicles, noise and vibration caused by pulsation are really difficult to control and have a great impact on the user experience, so they are not applied on a large scale.But in commercial vehicles, it can be seen on many electric buses, buses and vans.

Therefore, it can be basically said that: medium and small cars are dominated by permanent magnetic synchronization, large and high-performance passenger vehicles tend to induction motor, switched reluctance motor is suitable for large commercial vehicles.

02. New energy vehicle driving motor technology development trend

2.1 electrical steel sheet

The power, torque, efficiency and life of drive motor had a lot to do with the silicon steel sheet used, especially non-oriented electrical steel used in the motor rotor . Magnetic ability can decide the motor torque and efficiency, the lower the iron loss of motor the efficiency is higher. When increasing magnetic field motor torque can increase. Mechanical properties determines the precision of the stator and rotor, bearing strength and the maximum speed.
For stator and rotor, it is mainly composed of thin electromagnetic steel layers.The first Toyota prius in 1997 used a 0.35mm layer of steel, which was subsequently reduced to 0.3mm, and most recently to 0.25mm in 2016.In general, the number of thin steel layers can increase the motor efficiency, but also help control the motor temperature.

2.2 motor winding

Reasonable selection of motor winding mode and reduction of winding wire length can reduce the volume and copper consumption of the motor, reduce copper loss, improve motor efficiency, reduce motor weight, improve power density, reduce motor core loss and motor ripple torque, reduce motor vibration and noise.

2.3 coil design

To miniaturize the motor, manufactures increased the winding percentage (the proportion of copper in the space) to make the stator smaller.By using a large section of the square wire as the coil, the groove full rate is greatly improved.

2.4 cooling

The main cooling modes of the motor are natural cooling, air cooling ,water cooling and oil cooling.It is mainly water-cooled.When the motor cooling system is at a low temperature, the coolant pump does not work.After the temperature rises, the coolant pump works.

3. The trend of miniaturization and lightweight of the driving motor of new energy vehicles

In recent years, the research on the integration of electric vehicle driving system is very active. Through the integration of motor, inverter and reduction gear, it can achieve high efficiency, small size and light weight, and reduce the cost at the same time.

The hub motor, which is installed in the wheel of the driving system, further promotes miniaturization and lightweight.

If the motor and the inverter are integrated, the inverter is configured next to the motor, and the wiring harness connecting the motor and the inverter can be shortened or replaced.

Thus, the size and weight are reduced, and the loss of wire harness is also reduced.And if integrated with the gearbox, the gear lubricating oil and motor cooling oil can be Shared, streamline the cooling mechanism, can easily achieve miniaturization.