Braking plays an important role in automatic driving. No matter how good the intelligent driving system is and how strong the redundancy is, the final vehicle control still needs to rely on the longitudinal execution unit. The higher the level of automatic driving is, the more stringent the requirements for braking, steering and power systems will be.

On September 21, 2022, at the 2022 Second Automatic Driving Conference of Commercial Vehicles hosted by Geshi Motors, Zhang Qi, Technical Director of Automatic Driving of Geely New Energy Commercial Vehicle Research Institute, mentioned that Geely commercial vehicles had studied the line control system and concluded that the current EBS system can only achieve the redundancy between mechanical circuits. After going through the stages of brake system redundancy, horizontal and vertical control system redundancy, and multi cooperative redundancy, It will eventually develop to an integrated chassis system controlled by wire.

Zhang Qi, Technical Director of Automatic Driving of Geely New Energy Commercial Vehicle Research Institute

The following is the content of the speech:

Geely Commercial Vehicles was established in 2014 under the background of the new four modernizations, focusing on new energy brands, with five product lines: heavy truck, light truck, LCV, bus and pickup truck.

Braking plays an important role in automatic driving. No matter how well the intelligent driving system and ADAS system are done, and how strong the redundancy is, the longitudinal execution unit is still required to control. With the higher level of automatic driving, the requirements for braking, steering and power systems will be higher and higher. Today I will share the brake by wire system suitable for intelligent driving of commercial vehicles from three aspects.

The relationship between intelligent driving system and braking system of commercial vehicles

At present, the current mandatory regulations for intelligent driving of domestic commercial vehicles include the requirements for FCW, LDWS, AEBS, LKA, BSD and DMS systems, among which the AEBS system is related to braking.

At present, the matching amount of FCW on tractors is far greater than that of AEBS. The laws and regulations require that trucks with a gross vehicle weight of more than 12 tons, a maximum speed of more than 90 km/h and tractors with a maximum speed of more than or equal to 90 km/h must be equipped with AEBS system.

AEBS regulations, namely GB/T 38186-2019, follow the requirements of phase I of ECE-R131. JT/T 1242-2019 has more strict requirements on AEB performance and requires pedestrian identification. The performance of trucks and tractors equipped with AEBS shall meet the requirements of GB/T 38186-2019 of the Ministry of Industry and Information Technology. The LKA regulations for commercial vehicles have also been submitted for approval, and are first implemented on commercial buses.

Photo source: Geely

By comparing the current mainstream AEB regulations 1242, 38186 and R131, the three regulations have the same requirements for moving targets and traversing, but different requirements for stationary targets, crossing pedestrians and curve performance, and 1242 will have higher requirements.

The definition of AEBS in the 1242 regulation is that the AEB system can detect the driving environment in front of the vehicle in real time, and automatically start the vehicle's braking system when the risk of collision may occur, so as to slow down the vehicle and avoid or mitigate the collision. It can be seen that the composition of AEB system includes sensing, fusion and control, and execution.

The AEB system's requirements for the performance of the executive system are embodied in torque limiting and cruise back for the power system. The braking system needs to respond quickly. Once the ADAS system sends a deceleration request, the braking system must respond quickly; There is also high precision. The ADAS requests deceleration, and the precision must be between 10% and 30%; The deceleration is large. As a "life saving system", the AEB system needs to provide the maximum deceleration for the vehicle in an emergency.

Photo source: Geely

The braking systems of commercial vehicles supporting AEB are usually ABS+ESC and EBS+ESC systems. The tractor loading of ABS+ESC system is relatively large, and EBS+ESC will be more and more loaded as required by 7258. Compared with ABS and EBS systems, EBS is superior to ABS in braking sense, deceleration control, response accuracy and response time, and its cost is higher than ABS.

Development Trend of Control System for Commercial Vehicle Line

Next, let's talk about the development trend of the control system of commercial vehicle line. Since 1980, the international mainstream commercial vehicle brake system suppliers began to develop the ABS system, which was gradually improved around 2000, and the EBS system of the brake by wire system started around 1995. In this process, domestic commercial vehicle brake system suppliers represented by Ruili Kemi and Wan'an followed up quickly, and ABS and EBS both had mass production experience. The EMB electric braking system represented by Hande Wanan has also developed new solutions for commercial vehicle braking systems.

Photo source: Geely

The development direction of commercial vehicle braking system is first integration. The left side of this figure shows the ABS+ESC system we have built before, and the right side shows the system to be mass produced soon, integrating the front axle module and the correction valve together to achieve high integration.

The other direction is electrification. The EMB of Hande Wan'an has been engaged in the corresponding development for several years. At present, it has made some sample vehicles, which have the advantage of no high-pressure air medium, fewer brake system parts, and a high degree of modularization. The system has redundancy, including the supply chain, communication, and implementation.

Research on the Line to Line Control Technology of Geely Commercial Vehicles

Photo source: Geely

Geely commercial vehicle has explored the line control technology based on the vehicle model project. This is the demand of the commercial vehicle automatic driving function on the characteristics of the braking system. The above part is the development trend and corresponding functions of auxiliary driving, automatic driving and high-level automatic driving. Around 2020, front collision warning, AEB, LKE, parking aid and other functions have been mass produced. By 2023, some OEMs will realize high-speed intelligent driving assistance, speed limit assistance and traffic congestion assistance. In 2025, the driving of expressways, ports and fixed lines will also achieve conditional automatic driving. In 2026, HWP warehouse to warehouse, toll station to toll station and line driving will realize mass production. In 2027, trunk logistics will gradually cover the long tail effect of automatic driving and realize high or complete automatic driving.

In order to realize these functions, there are also requirements for the line control system. Starting from partial automatic driving, the line control system is required to be used as the execution system, which needs to meet ADAS related braking requirements. When ADAS system develops to conditional automatic driving, the braking system will reach the full redundancy state and meet the design strategy of full redundancy.

Photo source: Geely

At present, the redundancy of EBS line control motor is commonly in this form of architecture. The architecture is divided into front axle control module, rear axle control module and EBS master control module, plus other ABS valves or pipelines to achieve the main control of EBS. At present, the redundancy between mechanical circuits can be realized under the driving condition of a pure driver.

The next step is the redundancy of the braking system, such as the redundancy of communication between two arithmetic processors in the main control module. There are two trunk lines, one using CAN and the other using Ethernet. Each has different strategies. This will also serve as the redundancy of the EBS system. If the EBS stops, the EPB can finally accept the braking request from the ADAS system and stop the vehicle safely. At present, several major parts suppliers are also studying the redundancy of this part.

The third stage is the functional redundancy between horizontal and vertical control systems. For example, when the steering gear and electric hydraulic power steering fail, and ADAS is still working, how to make the car stop stably? The braking system will perform some steering functions as a backup scheme, for example, the single wheel braking can meet the requirements of steering in emergency.

The fourth part is multi system redundancy. There are two sets of control algorithms in the original EBS controller, and two ECUs are conducting corresponding control. If the system or EPB is down, the spare electronic brake system module and EBS will share the same wheel speed sensor. When the EBS master control module is down, the standby electric braking system can continue to accept the request of ADAS for longitudinal deceleration control.

Eventually, it will develop to a more integrated chassis system controlled by wire, which may combine braking, steering, power and other parts to form a large domain control, so that faster redundant control can be achieved within the domain, which is the direction of our current efforts.

Based on redundancy related research, Geely commercial vehicles are also taking the road of electric and intelligent revolution. Through the electrification revolution, we have built our own electric vehicles, light trucks, LCVs, etc. have achieved pure electrification; Accordingly, we also have our own pure electric chassis. With the development of intelligent revolution, we may build an intelligent chassis, which combines braking, steering and power together to achieve more integrated control and create more ADAS functions. Through the electric revolution and intelligent revolution, Geely commercial vehicles have integrated the corresponding production lines or models, realizing the multi-dimensional of commercial vehicles.

To sum up, to achieve full automatic driving, you still need strong support from your colleagues. The automatic driving road for commercial vehicles is very long, so let's go to the remote.

(The above content comes from the keynote speech "Exploring the Brake by Wire System Suitable for Intelligent Driving of Commercial Vehicles" delivered by Zhang Qi, Technical Director of Automatic Driving of Geely New Energy Commercial Vehicle Research Institute, on September 21, 2022 at the 2022 Second Commercial Vehicle Automatic Driving Conference hosted by Geshi Motors.)