Author: Michelin

Recently, BYD (Build Your Dreams) has been a bit “drifty”.

At the beginning of the year, at the launch event of the “Looking Up” brand, BYD showcased its million-level electric car, the “Looking Up U8,” which can “walk horizontally” and “float on water”. Recently, they also showed off their ability to turn around in place on a bridge.

If BYD used to be known as a national electric vehicle in everyone’s mind, with the appearance of the “Looking Up” brand, they have become more and more focused on showing off their muscles as a “circus performer” in the automotive industry.

Recently, at the E4 technical conference held by the Looking Up brand, they gave a comprehensive explanation of the underlying technical logic and scenario capabilities of their E4 technology platform. After participating in this technical conference, I have to say: the “Mustang Walk” of Looking Up is not accomplished by Mecanum wheels.

E4, the “restart” of the Four-Motor Dream

Let’s go back to 2004 when the domestic automobile market was still dominated by joint-venture brands and foreign car companies. BYD, which we are familiar with today, had just been established for one year. During that year’s Beijing International Auto Show, BYD, known as a “small and medium-sized car company” by mainstream media outlets, released a pure electric concept car — the ET. 

At that time, BYD, with its blue sky and white cloud logo, equipped the concept car with four wheel-side electric motors that could independently control the four-wheel torque.

As the saying goes, “being ahead is advanced, being two steps ahead is a pioneer, and being three steps ahead is a martyr.” Eighteen years ago, people’s acceptance of electric vehicles was far lower than it is today, and BYD was far from being the “BYD King” it is now. This four-motor technology can be said to be a bad timing.

However, BYD did not give up back then but rather tried to improve the four-motor technology in commercial vehicles. Eighteen years later, they have improved and optimized this technology and created a new technical platform, the E4 technology platform, which allows the Looking Up U8 to “turn around in place” and “walk horizontally” with ease.

If there’s one thing that kept BYD holding on to this technology for eighteen years, it must be the flexibility and performance advantage that the four-motor configuration provides for four-wheel drive under an electric platform.

In the era of traditional fossil fuel vehicles, the most familiar four-wheel drive representative is quattro. In order to distribute the power output by the same engine to four wheels, it is necessary to use the central differential to distribute the power to the front and rear axles, and then the front and rear axle differentials to distribute the torque to the two wheels. This determines that power needs to go through a complex structure; it needs to go through at least two differentials; and it needs to distribute as much torque as possible to the non-slipping wheels under the limited torque distribution ratio of the mechanical differential.

However, even the most outstanding quattro technology cannot transmit power 100% to the non-slipping side when a wheel is stuck in slip, and there is energy loss after several power allocations, not to mention the “fantasy” of outputting negative torque. But in the era of electrification, all of these can be achieved.

When the driving force of the driven wheels changes from the engine to the electric motor, if an in-wheel motor is equipped for each wheel, not only can four wheels be controlled independently by four motors, but also the wheels can switch between forward and reverse. The four in-wheel motors are independent of each other, without the mechanical linkage in the lateral direction, with a short transmission path and strong synchronicity, which improves efficiency. In the future, through standardized chassis platforms, electric drive and chassis platforms can be deeply integrated, and they can be developed as a power source and a basic carrier to achieve complete decoupling of the upper and lower bodies, which is the embryonic form of skateboard chassis.

In fact, more than just BYD has discovered the technological advantage of four-motor drive. In the past year or two, four-motor drive design can be found in the HUMMER EV, Rivian RT1, Hyundai IONIQ 5, and even in BMW M4 pure electric version spy photos. However, compared with them, the Easee4U U8, which will be launched this year, may be the first mass-produced car with four motors that Chinese consumers can get their hands on.

Refactoring Car Driving, How Difficult Is It?

Maybe every driver who drives a large or medium SUV or other huge vehicle has encountered such a problem when parking: Why can’t a car turn on the spot like a tank?

The tank can make a U-turn in place by controlling the two tracks of the tank to rotate in opposite directions, with the outer track rotating forward and the inner track rotating backward. From the principle, it is not difficult to understand why one side rotates forward and the other side rotates backward. The difficult part is how to control the torque of the wheels on the inside and outside of the car separately, and even how to control the four wheels of the car separately.

The principle to be implemented is also simple. If each wheel is equipped with an electric motor, not only can four motors independently control the four wheels, but the wheels can also switch between forward and backward rotation. This is the principle that the Yiqi Square technology platform uses to implement the tank’s turning on the spot.

The problem is, when using a four-motor drive system, how to precisely control the coordinated cooperation between the four motors, how to accurately perceive the road conditions, and how to make the performance finally presented the most optimized. What is needed is not just four motors, but the close cooperation between the three dimensions of perception, control, and execution.

To achieve this effect, in terms of perception, Yiqi Square took the lead in giving full play to the powerful perception ability of the wheel-side motor. Compared with the full-time four-wheel drive technology of traditional fuel vehicles, which monitors the speed difference between the two wheels to perceive whether the wheels are slipping, Yiqi Square uses intelligent driving sensing data such as cameras, lidars, and millimeter-wave radars to continuously sense the vehicle’s motion state in all directions, providing a perception data foundation for subsequent decision-making and execution stages.

In the control link, Yiqi Square’s technology platform is different from the mechanical power transmission system of fuel vehicles. It uses a centralized computing platform and a domain control architecture that collaborates closely with the electronic and electrical architecture to enable real-time communication of perception information and control strategies, and can independently adjust the dynamics of the four wheels with millisecond response speed. Taking a vehicle’s single-wheel blowout as an example, it can precisely adjust the torque of the remaining three wheels at a frequency of 1000 times per second and use the drive wheel to make a strong compensation intervention in the vehicle’s posture in time to help the driver stop the vehicle stably and controllably.“`

At the operational level, the Yiqi Si Fang Technology Platform is equipped with four wheel-driven motors, which can achieve pure four-wheel independent drive and precisely control the power of all four wheels according to driving scenarios.

In addition to the inherent high-power advantage of electric vehicles, the maximum power of the electric drive assembly system equipped on the Yi Si Fang technology platform can exceed 1100 horsepower, with a maximum speed of 20500rpm. In order to further improve traditional efficiency, all models in the Yi Si Fang technology platform are equipped with 800V SiC electric control system as a standard, with the highest efficiency of up to 99.5%.

The coordinated cooperation of the three dimensions of perception, control, and execution, and the 800V SiC platform, enable the Yi Yang U8 to not only have good off-road performance such as turning on the spot and climbing extreme slopes, but also improve the limit of vehicle control on the ice and snow road. In the event of inadvertently entering deep water, it can also maintain driving force and obtain short-term floating and escape capability through the emergency water-floating mode, relying on precise four-wheel torque vector distribution.

Finally

Rereading the reports on the Beijing International Auto Show in 2004, there were quite a few doubts about the BYD ET concept car. Those who raised questions that year could not have imagined that the “original aspiration” of four-motor independent drive would be adhered to by BYD for eighteen years. BYD seems to have been holding its breath, waiting for the right time and the right product to bring out its nearly 20-year-old technology, just to prove that BYD as an independent car maker can also make high-end brands and top-notch technology.

The fact that “Yi Yang” can “walk sideways” is not just talk.
“`

This article is a translation by ChatGPT of a Chinese report from 42HOW. If you have any questions about it, please email bd@42how.com.