New energy vehicle driving motor type development trend
1.1 AC induction motor
At present, permanent magnet synchronous motor and induction motor account for the majority and a small part of all kinds of pure electric and hybrid new energy vehicles on the market. These two kinds of motors are basically all the driving motors of electric passenger vehicles.
Compared with permanent magnet synchronous motor, ac induction motor volume is larger, but the price is moderate, of course, have the operation of God, tesla rotor copper to make into a heterogeneous (patent), but the power of induction motor can be very big and there is no demagnetization problem, so some big cars or pursue performance of electric vehicles, such as the Tesla Model S and Wei to ES8, use the induction motor.
▲ Analysis of the cost proportion of each system of pure electric passenger vehicle
1.2 Permanent magnet synchronous motor
For small and medium-sized electric vehicles with high spatial layout and size requirements, a permanent magnet synchronous motor with higher power and torque density is the preferred choice. Moreover, the synchronous motor is more suitable for frequent start and stop working conditions and urban commuting application scenarios, which is also one of the reasons why Tesla Model 3 switched to the synchronous motor.
The online claim that China is rich in rare earth minerals and therefore China’s electric vehicles use synchronous motors with permanent magnets seems far-removed to me: Are various private enterprises and Internet car manufacturers taking national strategic security as their starting point instead of cost/performance considerations?
Unreliable, not to mention the extraction and processing of iron, rubidium, and boron in China’s technology does not have advantages, on the contrary, Japan has accumulated more in the application of rare earth materials.
▲ Comparison of PERMANENT magnet synchronous motor parameters between domestic and foreign drive motor enterprises
1.3 Switched reluctance motor
The motor structure is simple, firm, easy to maintain, or even maintenance-free, high torque and low current at starting and low speed; High-speed constant power range-wide, good performance, high output, and high efficiency in a wide speed and power range, and has good fault tolerance.
Generate torque on switch reluctance motor rotor is composed of a series of pulse torque superposition, due to the doubly salient structure and magnetic circuit saturation nonlinear influence, synthesis is not a constant torque, torque and harmonic component to a certain extent, affected the motor running at low-speed performance, so the transmission system of noise and vibration is larger than general motors.
The advantages and disadvantages of switched reluctance motors are very obvious. In the field of family vehicles, noise, and vibration caused by pulsation are difficult to control and greatly affect user experience, so they are not widely used. But in the field of commercial vehicles, it can be seen on many electric buses, buses, and trucks in China.
Therefore, it can be basically said that permanent magnet synchronous motors are mainly used in medium and small cars, large and high-performance passenger cars tend to induction motors, and switched reluctance motors are suitable for large commercial vehicles.
Development trend of new energy vehicle driving motor technology
2.1 Electrical steel sheet
Drive of the motor power, torque, efficiency, and life had a lot to do with the silicon steel sheet used, especially used in the motor rotor electrical steel piece without orientation, magnetic can decide the motor torque and efficiency, the lower the iron loss of motor efficiency is higher, increasing magnetic induction motor torque can increase mechanical properties determines the precision of the stator and rotor, bearing strength and the maximum speed.
Requirements for driving motor and electrical steel sheet for new energy electric vehicles:
The motor needs to provide high torque for starting, and to increase the torque must increase the current and magnetic sensitivity of the electrical steel
Motor efficiency is generally 85% ~ 93% under common driving mode. To improve energy conversion efficiency, it is required that electrical steel sheets used in the motor have excellent magnetic properties, that is, high magnetic sensitivity under medium and low magnetic field and low iron loss under high frequency
The motor speed is 6000 ~ 15000r/min, and the electrical steel sheet is required to have high enough strength to resist centrifugal force. This requires the use of high-strength electrical steel, especially the permanent magnet drive motor, whose magnetic poles are embedded in the rotor. Therefore, it is very important to ensure the strength of the rotor
Reducing the gap between rotor and stator can effectively improve magnetic flux density, which requires good stamping property of electrical steel sheet
During the service life of the automobile, the high-speed rotating electrical steel sheet in service can’t suffer fatigue damage, which requires a high fatigue life
2.2 Motor winding
In order to reduce the length of the winding line, reduce the volume of motor and with copper content, reduce the copper loss, improve the efficiency of the motor, reduce the motor weight and increase the power density, need a reasonable selection of motor winding way, can improve the motor winding magnetic potential sine, reduce the harmonic content of the stator magnetic potential, reduce motor iron loss and the motor stator winding cause ripple torque and improve the efficiency of the motor, the motor vibration and noise reduction, a reasonable choice of motor winding way, can improve the motor crown, to improve the magnetic resistance torque, reduce the winding current, reduce the motor copper loss.
On the whole, the amount of winding in the stator is an important factor to determine the motor power. The winding quantity is mainly determined by the number of turns the copper wire can make around the movement in the finite space. In terms of technology, the applicator is suitable for high power stator processing and has become the standard in the industry.
2.3 Coil design
To miniaturize the motor, Honda has increased the ratio of windings (the proportion of copper in the space) to make the stator smaller. By using square wires with large cross-sections as coils, the occupancy rate is achieved to 60%. In conventional motors, which use thin circular coils, the occupancy rate is typically only 48 percent.
To miniaturize the stator, the coil USES square wires with a large cross-sectional area. Square wires can increase the occupancy rate from 48% to 60% compared with traditional circular coils. However, because square lines are thicker than round ones, the “overcurrent loss” in conductors (copper) increases. The overcurrent loss is usually reduced by increasing the slot width of the stator or decreasing the thickness of each coil.
Bring about Tesla motor coil
To achieve miniaturization, Honda also shortened the coil portion (the “coil end”) that protrudes from the stator. Honda technicians said the end of the coil “does not contribute to motor work”.
In order to shorten the coil end, a new winding structure method is adopted:
First, the rectangular coil is molded into a U-shape to form a “parallel parting coil”.
Next, the split coil is inserted in the axial direction of the stator core.
After that, the inserted side and the opposite side protruding front end of the coil are welded together to form the coil.
The new winding process requires investment in new manufacturing equipment. The new process does not require tying or squashing the end of the coil, making it easier to automate than the traditional process. The result is high-efficiency mass production with reduced costs.
The main cooling methods of electric motors are natural cooling, air cooling, and water cooling. When the motor cooling system is at a low temperature, the coolant pump does not work. After the temperature rises, the coolant pump works.
Coolant pump operating temperature should not exceed 75 ℃, the most appropriate operating temperature should be less than 65℃.
The cooling system of the electric vehicle driving the motor and controller mainly relies on the cooling water pump to drive the coolant to circulate in the cooling pipe. Through the heat exchange in the radiator and other physical processes, the coolant takes away the heat generated by the motor and controller.
A fan is usually placed behind the radiator to give off more heat.
When a motor is working, a part of its loss is always converted into heat. It must continuously emit heat through the motor’s housing and surrounding media. This process of heat emission is known as cooling.
The trend of miniaturization and lightweight of 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 realize high efficiency, small size, and light weight, and reduce cost at the same time.
The hub motor, which installs the drive system in the wheel, further promotes miniaturization and lightweight.
The reason for the active mechatronics is that it can realize the small and lightweight driving system as well as reduce the cost and improve efficiency. If the motor and inverter are integrated, the inverter is configured next to the motor, the wiring harness connecting the motor and inverter can be shortened or replaced.
In this way, the size and weight are reduced, as well as the loss from the wiring harness is reduced. And if it is integrated with the reduction gearbox, the lubricating oil of the gear and the cooling coil of the motor can be Shared, simplifying the cooling mechanism, and can be easily miniaturized.
Machinery parts have advantages of manufacturers is the reducer as a strength. Schaeffler, for example, USES high-speed reducers with a reduction ratio of about 15 in its three-in-one drive system.
Other companies typically have a reduction ratio of about 10, even at high speeds of up to 13. The higher the deceleration ratio, the easier it is to increase the torque as a system. Therefore, compared with a drive system with a reduction ratio of about 10, it can achieve the same torque with a small motor spinning at a high speed and thus achieve miniaturization.
New energy vehicle driving motor suppliers supporting the trend
In terms of market share, Toyota is far ahead in the 2016 figures (the group’s main motor manufacturers include Denso and Aixin Seiji), while Honda ranks second, and both groups are global leaders in hybrid. Then there is BYD and Tomita Electric, a Taiwanese motor manufacturer that supplies Tesla.
In the early stage, the replacement speed of products is fast, and the upstream parts suppliers need to respond quickly and cooperate with each other, so the integrated production mode has a high-cost performance. However, in the middle and late stage of industry development, due to the expansion of the entire market scale, and the product upgrading speed does not need to be as fast as in the early stage, the scale effect of third-party suppliers taking the entire market as the customer object will be reflected.
The electrical control system and the supply chain of the main engine factory can be divided into two modes: the third party electrical control system and the main engine factory’s independent research and development.
In the long – term development of the motor industry, the rise of third-party suppliers will be the trend. If we observe the current situation of the industrial chain of The Japanese automobile industry, it is not difficult to find that the top three leading companies (Toyota, Honda, and Nissan) are all inclined to provide their own motor products, which is not only related to the traditional genes of Japanese manufacturing enterprises but also related to the development stage of the industry.
According to our incomplete statistics on domestic new energy vehicle enterprises, the proportion of motor third-party matching (joint venture + supplier matching) from 2014 to 2017 was 54.9%, 50.4%, 52.8%, and 61.8% respectively, and the proportion of electric control third-party matching was 51.2%, 46.8%, 49.6%, and 57.6% respectively. The proportion of third-party matching continued to rise, and the growth was mainly due to the increase of the market share of joint venture electrical control suppliers.
The new energy motor industry is no exception, from the current point of view, Honda has announced a partnership with Hitachi to produce motor. Nissan also mentioned at an investor conference that it might start outsourcing electric motors in the future.
In October 2017, Mitsubishi Electric announced it would supply Daimler-Benz with motors and inverters. With the popularity of efficient and low-cost products of third-party motor manufacturers, it is an inevitable trend for the motor industry to transfer its market share from main engine manufacturers to third-party enterprises.
At present, Japan’s electrical enterprises have started to respond to the trend of electric change. We expect Denso and Aixin to be the first to take advantage of their existing scale and take market share at a lower cost, followed quickly by power generation and residential units.
In terms of its own brand, BYD has accumulated rich research and development ability of electric motor control in the early stage and achieved an independent supporting power system. Large electric automobile manufacturers such as BAIC choose joint ventures with professional electric motor manufacturing companies, while other independent brand manufacturers focus on vehicle design and manufacturing, and electric motor control is mainly provided by a third party. With the Internet car companies entering the market in the future, the third party supporting is expected to continue to penetrate the passenger car market.
New energy vehicle driving motor market development trend
The motor system of new-energy vehicles mainly consists of two parts: electric motors and inverters. Although these two parts, like most other auto parts, are under pressure of price reduction for a long time, the industry as a whole still has a large room for growth due to the increase of the total number of new-energy vehicles.
With the rapid development of global electrification of vehicles, the motor system market of new energy vehicles will expand rapidly, and the market size is expected to grow from 15 billion yuan in 2015 to 200 billion yuan in 2030. It is expected that the average annual growth rate of market size will be about 18-20% by 2030.
The cost of an electric drive system accounts for 20% of the total vehicle cost. According to the Medium and Long Term Development Plan for The Automobile Industry jointly issued by three ministries and commissions in May 2017, the production of new energy vehicles in China will reach 7 million in 2025, which will bring significant benefits to enterprises if each vehicle is equipped with a set of electric drives.
In addition, as one of the three core components of new-energy vehicles, the electric drive system is the main execution structure of electric vehicles, and its driving characteristics determine the main performance indexes of vehicles. Benefiting from the rapid expansion of the market scale of new energy vehicles, the production and sales of new energy vehicle driving motors also increase accordingly. At the end of the “13th Five-Year Plan”, the market capacity of new energy vehicle driving motors in China is expected to reach about 250 billion yuan.
It is estimated that 20 million electric vehicles will be sold in 2030, less than 20% of the total vehicle volume. But under an optimistic scenario, in which battery prices fall sharply and environmental policies become more stringent, 30 million electric vehicles are likely to be sold, accounting for 25-27% of the total vehicle sales that year.
In terms of the unit price of the system, the motor system as a whole develops towards a high power direction, which also brings the improvement of the system price. Expected to:
The power demand of a single motor hybrid car is about 30KW, and the price is about 1500 yuan
The power of the dual motor is about 50-100KW, and the price is about 6000 yuan
The electric motor power of a pure electric vehicle is about 200KW, and the price is about 9000 yuan
It is expected that the sales of electric motors will reach 49 million units in 2030. Meanwhile, the number of single-motor motors is expected to decline, but the unit price of electric motors will be further increased, mainly driven by the wider application of high-priced high-power motors.