Put a smart ＂cerebellum＂ on the car, and VMC will be the first to be applied to the new Zhiji next year.

journalist | Gan Wenjia

Picture source | Enterprise official

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Beginners on the road may be at a loss in the face of difficult scenes such as narrow road sticking and turning around in place. Don’t worry, your car will automatically "pass"; When the city is congested, the car will automatically adjust (shock absorber, and at the same time control the opening of the switch or the braking force to cooperate), so that bad experiences such as starting to look up and nodding the brakes will no longer occur; The road ahead is sharp, and the car senses it earlier than you do. Steering, braking and suspension work together to reduce the turning radius, making the turning safer and more comfortable …

If the smart car is compared to a person, then the car also needs a smart "cerebellum", that is, the vehicle central coordinated motion controller (VMC) to dominate the whole body movement. As we all know, the brain is an organ that regulates the body’s functions and controls people’s movements and feelings, while the role of the cerebellum is to regulate muscle movements and maintain the balance of the human body. The cerebellum feeds back the information from the exercise to the brain, thus playing the role of regulating and correcting the exercise. The "cerebellum" of the intelligent chassis is not simply executed after receiving the instructions from the central computing and decision-making unit "Brain", but comprehensively considers the current application scenarios, optimizes the handling performance and ride comfort on the basis of ensuring vehicle safety, and then distributes the instructions to steering, braking and suspension, and finally realizes the coordinated control of six degrees of freedom (front and rear, left and right, up and down) in X, Y and Z directions, "muscle" and ""

In the next three years, SAIC will devote itself to building a brand-new "scientific and technological life". Including "intelligent brain", "agile body" and "strong heart". Among them, the "agile body" is the first to achieve a breakthrough in the "VMC technology of the whole vehicle", which keeps the vehicle body stable in different driving modes and various road conditions. It is reported that VMC will be first applied to the new Zhiji car next year. At present, SAIC’s intelligent solution integrating people, vehicles and environment is undergoing research and development, testing and verification.

In the new electronic architecture, the automobile execution system is also undergoing changes. From traditional chassis to electric chassis, and then to intelligent chassis, automobile chassis is welcoming brand-new changes.

Vehicle control is nothing more than longitudinal control represented by braking, lateral control represented by steering, and suspension control represented by up and down, which corresponds to six degrees of freedom of automobile movement. In order to meet the strict requirements of faster response speed and higher control accuracy of automatic driving, intelligent chassis needs brake, steering and suspension components by wire, and intelligent chassis has also become a wire-controlled chassis.

Chassis-by-wire system transmits the driver’s operation command to the actuator through the electronic controller, replacing the connection and execution from the traditional mechanical structure such as steering wheel and pedal, so it has the advantages of high precision, high safety and high response speed. By controlling the chassis with digital signals, the mechanical decoupling of the control system and the execution system can be realized. The drive-by-wire chassis can not only meet the requirements of higher-level automatic driving, but also enrich the imagination space of the intelligent cockpit and bring a safer and more comfortable driving experience to the occupants.

The chassis by wire mainly includes three core components: brake by wire, steering by wire and suspension system. Among them, brake-by-wire can not only meet the requirements of rapid response of automatic driving, but also meet the rigid requirements of energy recovery and increasing cruising range of new energy vehicles, and the market penetration rate is rapidly increasing. At present, the electro-hydraulic braking EHB system has been widely used in high-end pure electric vehicles. Although additional safety redundant equipment is needed, the intelligent Two-Box scheme is still more common in the short term, and the penetration rate of the intelligent One-Box will be significantly improved in the next few years.

Steer-by-wire steering is a rigid demand in the intelligent driving stage, which is gradually emerging. At present, it is in the stage of research and development verification and just getting on the bus, and it will also become a technical hotspot in the next few years. In the next 10 years, the penetration rate of steer-by-wire will reach 50%.

Since the beginning of this year, the air suspension system has been put on the market with some models, and the market popularity has also climbed once.

From the reality, with the acceleration of intelligent by-wire control system in smart electric vehicles to improve the competitiveness of brand models, by 2025, the domestic smart chassis market is expected to expand rapidly, which is expected to reach more than 50 billion yuan. Among them, the technical reserve of brake-by-wire is relatively mature, and the market is expected to grow at a compound annual growth rate of 34% from 2022 to 2025; In the next 4-5 years, the improvement of its assembly rate will provide a core increment for the smart chassis market, while steer-by-wire and air suspension are expected to enter the pre-assembly lead-in period in 2025.

From a technical point of view, at present, there is a trend of integration of various systems of automobiles, such as intelligent cockpit and intelligent driving, which are being integrated across domains. Zhang Ying, president of Bosch Chassis Control System in China, said that compared with the traditional chassis control system, in which all components are relatively independent for longitudinal, lateral and vertical vehicle dynamic control, VMC can adapt the chassis that was basically "just for itself" to the trend, and integrate the functions of transmission system, driving system, steering system and braking system into multiple systems, which greatly improves the vertical integration ability of chassis development, and can be flexibly deployed in pairs.

Steering and braking integration. It is very difficult for ordinary drivers to slam the steering wheel or make a big correction if they turn a corner on the icy road. When steer-by-wire and brake can be combined, the steering wheel angle and brake controller of steer-by-wire can be controlled in coordination, and the brake and actuator of steer-by-wire are integrated. Ordinary drivers can turn with the help of technological innovation, without worrying about oversteering or understeering, avoiding obstacles successfully and easily turning corners smoothly.

Brake and suspension fusion. Suspension system should not only meet the requirements of comfort, but also take into account the requirements of handling stability. Comfort is also related to the braking system. If the braking is too urgent, there will be phenomena such as braking nodding and unstable control. Comfortable braking function makes you an "old driver" in seconds. Through the precise software control of the system, a part of the braking pressure can be released smoothly in an instant before the vehicle stops, which can greatly alleviate the vehicle nodding and ensure the vehicle to stop very safely.

Integration of braking and power system. When the car starts on smooth roads such as snow and ice, the driving wheels may slip and the direction will be out of control, which will lead to danger. The driving torque vector control and braking control are combined with each other, and the acceleration potential of the vehicle is fully tapped, the curve limit is exerted and the dynamic response is optimized through the optimal distribution of axle or wheel torque.

Integration of VMC and ADAS. In order to meet the richer functional experience in NAD autopilot scene, the chassis needs to provide a bearing platform for autopilot system, cockpit system and power system. In the NAD autopilot scenario, VMC can integrate four-wheel drive distribution, brake-by-wire and variable suspension functions to maximize the dynamic performance of the vehicle, while supporting high-level autopilot scenarios. Through FOTA upgrade, it can be flexibly upgraded and quickly iterated.

As a safety component, intelligent chassis has the highest functional safety level requirements. Functional safety is the core requirement of intelligent chassis and autonomous driving development. If the high-order automatic driving system comes, redundant braking and fail-safe will become the most important. Only on the basis of safety can driving be pleasant, comfortable, agile and personalized.

When the smart car develops to L3 or above, the driver will no longer control the car for a considerable part of the driving process, and the main responsibility of driving has changed from the driver to the system itself, which brings great challenges to the performance and safety of the whole chassis. For the drive-by-wire chassis, the most important requirements are safety and redundancy, and redundancy is also safe in essence. VMC has two backup schemes of independent actuators. When the main controller fails, the redundant controller takes over, which can systematically reduce the risk of failure of key functions.

The intelligent chassis is divided into two important parts: one is the chassis execution part, which realizes the coordinated control in X, Y and Z directions and the coordinated wire control optimization; Second, the chassis domain control system, based on the advantages of strong hardware and high performance chassis, further realizes the whole domain fusion control and rapid iteration of chassis through experience drive.

With the development trend and evolution of centralized electronic and electrical architecture, chassis control will be promoted to the concept of "domain". Combined with the chassis hardware system, the intelligent chassis domain controller can comprehensively design and adjust the chassis comfort and handling.

VMC can uniformly adjust and control air spring height, shock absorber damping, electronic parking and other functions. The controller detects the vehicle state through the signal received by the sensor, determines the optimal parameter instruction according to the algorithm or control strategy, adjusts the spring stiffness and damping state of the shock absorber, and increases the correction of pitch and roll to enhance the control of the vehicle body. For example, when driving in the field with poor road conditions and encountering a protruding obstacle in front, VMC system will "command" the air spring to raise the height of the car body, and at the same time adjust the electric shock absorber to make the vehicle smooth. In the face of bumpy roads, the system will also use compensation braking to alleviate jitter.

Thanks to VMC, after adjusting a large number of key components such as tires, air suspension and steering system, each car realizes the combination of comfort and handling, and develops various driving modes such as sports, comfort and energy saving according to road conditions and driving habits of users to meet the individual needs of users. At the same time, VMC relies on continuous collection and identification of users’ personalized driving data, and provides driving experience that meets users’ psychological expectations through human-vehicle interaction and self-learning iteration.

The Roadmap of Intelligent Chassis Technology for Electric Vehicles establishes the development goal of intelligent chassis, and the overall goal is that by 2030, intelligent chassis will meet the requirements of first-class products and leading technology. "The next 10 years will be a major strategic opportunity period for China’s intelligent chassis technology innovation and industrial development." Li Jun, then chairman of China Automotive Engineering Society, pointed out at the 2023 Electric Vehicle Intelligent Chassis Conference. At the same time, the intelligent chassis industry has also entered a critical stage of technical competition. Among them, the chassis domain controller has become a battleground for intelligent chassis development.

In the past, the international Tier 1 controlled the core of chassis control technology and provided "black box" chassis solutions for car companies. Many car companies, especially China brands, are highly dependent on suppliers’ development support, and the development time is long and the constraints are high, resulting in the lack of deep-seated chassis function integration development ability of the main engine factory, which makes the vehicles only meet some simple basic driving experiences, with few extended functions and relatively single driving experience.

On the one hand, with the rapid launch of new models, car companies urgently need to change the current situation. In the view of some OEMs, the high integration of software and hardware and cross-domain integration control ability are the core competencies that car companies must have in the era of smart cars, and they must be in their own hands. At present, some OEMs, such as BYD, Ideality and Weilai Automobile, have started full-stack self-research in this respect, and tend to plan chassis domain, convergence domain and other architectures, and lead the development of application software, and also put forward the requirements of "white box" delivery software for suppliers.

On the other hand, the international Tier 1 will obviously not give up the current market interests. Bosch China said that ABS and ESP are one of Bosch’s main products at present, and we are taking smart chassis as our next goal. ZF and Jidu have jointly developed the next generation of intelligent chassis technology to support automobile robots to "move freely".

With the continuous upgrading of R&D technology, coupled with the advantages of stable supply chain, rapid development and market response, China suppliers are likely to catch up with others. Among them, since the mass production of One-box line control products in 2021, Bethel has carried a number of models to the market. At the same time, local start-ups such as Nathan, Tongyu, Likun and Grubo have successfully mass-produced brake-by-wire products based on the Two-box scheme, achieving a new breakthrough in localization.

There are various indications that in the field of intelligent chassis, especially in VMC, the boundary between OEMs and suppliers in the technical field has become blurred, and the technical route of domain controllers will also be "contended by a hundred schools of thought". Borders are often fought out, but at the same time, there are opportunities for cooperation in competition.

Zhang Jinhua, chairman of the China Society of Automotive Engineering, suggested that we should advocate adhering to the sense of cooperation, deepen the whole-scale cooperation, cross-border cooperation and international cooperation, and deepen the synergy between the industrial chain.

Although the full-stack self-developed chassis domain control allows the main engine factory to master more autonomy, it also needs to consider the cost and efficiency. The drive-by-wire chassis products need a lot of adjustment work and the full cooperation of the parts manufacturers. The advantage of the main engine factory is to integrate the parts control provided by suppliers. In the future, the direction of cooperation between the two parties is likely to be to jointly define the system architecture and development design, and all parties will contribute their own "points" and unite to achieve a "breakthrough". Specifically, the supplier may only be responsible for providing the hardware and doing the underlying driver, and then open the control right to the OEM to do in-depth joint development with the OEM, so as to improve the development efficiency and software reusability, speed up the iteration and reduce the cost.