What is the mysterious wheel motor? Originally, it integrated the "power, transmission, and braking" system of a car into a set of motors, which were directly installed on the side of the wheels to drive them separately. BYD is equipped with four independent wheel side motors in each car, which are referred to as "Yi Sifang" technology, which means that it can achieve 360 degree rotation in place without relying on the steering mechanism and output through four wheel four motors.
Wheel side motor vs. wheel hub motor:
Structurally:
1. Wheel hub motor: The wheel hub is located inside the wheel, just in the original braking position of the tire, which will squeeze out some space to move the motor inside. The weight of the entire wheel will be relatively heavy, forming an unsprung mass. Additionally, due to its limited space, its power output is not very high. Generally, it can reach around 50-80 kilowatts. The larger the power output, the greater the unsprung mass, and the poorer the overall handling of the vehicle, especially when turning is required.
2. Wheel side motor: It does not fit inside the wheel hub, but rather leads it out, which is similar to the previous centralized drive. However, it no longer uses a differential and is driven by two motors transmitted to the wheels through the transmission shaft. However, the entire motor assembly is installed on the frame, forming a spring mass, so its handling is relatively good. At the same time, it is not limited by space, Its power can be very large, which means that the power on a single wheel can generally reach 200-300 kilowatts, and the power on the entire vehicle can reach about 800-1000 kilowatts. The power is very large, which means that normally, to make a sports car, it needs to be equivalent to 1000 horsepower.
Performance wise:
1. Wheel hub motor: Only suitable for vehicles below A-level, as it does not have particularly strong handling for the entire vehicle
2. Wheel motor: Some high-performance cars, such as those that are close to sports cars or above B-level. It can achieve greater power, better power, and better handling.
Parts increase or decrease:
1. Wheel hub: one with deceleration and the other without deceleration. Because of the existing motors, if you want to achieve high power, especially for cars, you must achieve high speed. If the reducer is not made, the power cannot be improved. For example, low-speed motors such as electric bicycles can only produce a maximum of 30-40 kilowatts, while those with a deceleration structure can achieve 50-80 kilowatts
2. Wheel edge: Generally, our motor can reach 15000-2000 revolutions per minute, which will result in a relatively high power output. Two wheel drive with added motor * 1+electronic control * 1+reducer * 1, reduced differential, output directly to the left and right wheels through gears. For four-wheel drive vehicles, direct * 2 is equivalent to not using the differential originally used to adjust the asymmetric speed of the left and right wheels, which will be impacted and rely on electronic differential in the rear.
3. ESP: Will not decrease, still need to monitor torque speed.
4. Air suspension: Because the wheel motor does not require a single motor to operate, its two half shafts can actually be separated from each other in terms of motion, so its suspension can be made better, but it will not affect the installation of the air suspension.
Advantages of wheel edge motors:
1. Traversibility: Each wheel is independently driven, with strong trafficability and the ability to quickly respond to torque. For example, when a wheel suddenly hovers, the entire vehicle is not affected, and in extreme environments, the stability and power of the body are not significantly affected.
2. Turning: Driven by an electric motor, each wheel can rotate forward and reverse, and each speed can be adjusted freely, theoretically achieving a very small turning radius. It's like drawing a circle.
3. Safe and stable: achieve rapid adjustment of vehicle stability, and drift can also be achieved at high speeds. When driving at high speeds, even if one of the front wheels suddenly experiences a tire blowout, if it recognizes the tilting of the vehicle body, it can quickly adjust the speed and torque of each motor to quickly adjust the vehicle body and still continue to drive forward without being offset.
Disadvantages of wheel motor:
1. High price, only suitable for high-end models
2. The difficulty of control is relatively high, even if there is a sudden front wheel loss of direction, the direction will deviate, which involves safety issues.
3. In terms of layout, it actually has an additional set of assemblies, which will increase its volume. Even if the normal shell is made of aluminum, it may involve the use of magnesium alloy and the need for silicon carbide to achieve volume reduction and further increase costs.
Value of bicycles:
BYD looks up at high-end models, which are all developed in a positive direction, with a wheel assembly and a single motor of about 200 kW * 4=the whole car is close to 800 kW. For the sake of small size, silicon carbide is used for electrical control. In addition, there are differential locks in both the front and rear of the assembly, which can lock the two motors and apply force to either wheel. There is also a lock in the middle. After calculation, it should cost 20000 yuan per unit on one side (2 motors+2 electronic controls), with a minimum cost of 40000 yuan for the front and rear.
The silicon carbide electronic control is around 4000-4500, the motor is around 3000-3500, and the remaining 1500 are reducers.
Electric control: Silicon carbide must be supplied by BYD itself, because it is much cheaper to make and package modules and components by themselves.
Motor housing: It is purchased from outside and also available internally.
Gears for reducers: Make your own gears, as well as rear ones like Chongda and Shuanghuan.
Secondary components may be made internally, while tertiary components are mostly outsourced.
Layout of each enterprise:
1. Huawei: We have been producing wheel edge assemblies since 2020, and the B samples have already been produced. Currently, it seems that we cannot find a suitable car to ride on because making wheel edges definitely requires high-end brands.
2. BYD: It has an early patent layout, started in 2018, and has significant advantages.
3. Schaeffler: At the same time as BYD, they are researching and testing the entire vehicle in Europe at the end of 2019. They also have control algorithms for the entire vehicle.
4. Tesla: There is research on the Model s play three motor version, which uses wheel rims for rear wheel drive and DC drive for front wheel drive. The coordination between electronic differential and steering is necessary. In theory, the difficulty of controlling the front wheel motor and steering increases. So it's the wheel rim for rear wheel drive.
5. Volkswagen: There is also a car that is pure electric, with rear wheel drive using wheel rims and front wheel drive using DC drive. Equivalent to a dual motor scheme.
The difficulty of making wheel side motors with three electrical components:
1. Logically speaking, the applicable scope is D-class cars, which will not be low in price and involve issues defined by customers, so the logic for whole vehicle manufacturers to push is more streamlined than that for parts
2. Component technology: With a high degree of integration, it is necessary to master the core technology of the three electrical components:
1) In terms of power, including silicon carbide electronic control, the switching frequency of IGBT is about 10k, and silicon carbide can be used at a switching frequency of 20k or even 30k. When the switching frequency is high, the instantaneous voltage is very high, which involves the withstand voltage design of the motor;
2) High speed motors with speeds greater than 15000 rpm, involving dynamic balancing, NVH, and relatively difficult manufacturing;
3) A high-power assembly requires a high-power discharge battery that can be used. Generally, a thermal management battery is 3-5C, and 100 degrees Celsius is 500KW. However, a wheel motor of 200 * 4=800KW requires an 8C high rate battery, which is currently difficult to achieve (reducing the internal resistance of the battery cell and thermal management). If 200 degrees Celsius can be discharged, a discharge rate of 4C is sufficient, which is also a balance between battery energy density and discharge rate;
4) In addition, bearings, cooling lubrication, control algorithms, EMS, etc.
BYD's advantages:
In terms of thermal management: When the fourth generation was hybrid, it had already achieved refrigerant refrigeration cells and was also the most efficient cooling method.
In terms of batteries: The hybrid model has a front wheel drive 160KW motor and a rear wheel drive 200KW motor, with a total of 40 kWh corresponding to an 8C discharge rate. BYD is particularly good at this, and when using ternary lithium batteries before, it can achieve a discharge rate close to 15C, with a stable output of basically 12C. Lithium iron phosphate can achieve approximately 8-10c and stable output above 8c.
BYD has two types of batteries, one is called energy type and the other is called power type. The energy type has high density, the power type has a high discharge rate, the formula of the two batteries is different, and the cost of the power type will be higher.
BYD is unlikely to look up to lithium iron phosphate or lithium manganese iron, as the price of lithium manganese iron will be higher.
Application scenario:
BYD's plan requires at least 500000 vehicles to achieve this product. Some of Tesla and Volkswagen's solutions may include centralized front wheel drive and wheel drive in the later stages, which could potentially reach around 300000 yuan in car models.
Looking up at the car model:
The internal code is 1234, 1 is a hardcore off-road vehicle that has been released, 2 and 3 are coupes, and 4 is a city SUV.
Parameters: With a range of 1000 kilometers, the 0-100 km/h acceleration target is approximately 2.9, and the maximum speed may be above 260.
BYD has two good patent layouts internally, one is a U-shaped layout and the other is a ladder shaped layout.
R1 mainly uses a ladder layout: two gearboxes are placed in the middle, and two motors are placed next to the two gearboxes, which looks like a ladder. The electric control is placed on top of the motor and gearbox, and the height is relatively high. However, because there is a half shaft directly leading out of the gearbox, the assembly height will be relatively high, but the two on the left and right sides of the half shaft will be longer. It is more suitable for off-road vehicles because it is not an independent suspension and has a larger up and down travel, so it is suitable for this arrangement.
The arrangement of the R2-R3 assembly is U-shaped: two motors are placed in the middle, facing each other in a row, with the left and right arranged in a straight line. Then, two transmissions are placed on both sides of the motor, and the electronic control is placed in the U-shaped space position. The electronic control does not need to be placed on top of the assembly, and it can be pressed down by height, but the half shaft becomes shorter. He has a more compact layout, with lower requirements for the up and down movement of the wheels during turns. Combined with the high speed of silicon carbide, the power density can be reduced and placed inside.
Both of these are currently being developed simultaneously, and the progress is generally similar.
Source: Mechanical Branch of Shenzhen Hunan University Alumni Association
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Interpretation of Wheel Motor | BYD Looking Up at High end Models
View：188 Release Date：2023/12/17 9:25:41