Passenger Car Braking System Requirements: Changes and Continuities in the New National Standard
Jun 28, 2024
The Ministry of Industry and Information Technology recently sought public opinions on the "Passenger Car Braking System Technical Requirements and Test Methods" (Draft for Comments) on its official website. This has sparked heated discussions within and outside the industry, especially regarding the "one-pedal braking" system used by some models represented by Tesla, which may be phased out with the introduction of the new national standard.
While the public debate on the draft mainly revolves around a certain brand's model and its one-pedal braking function, the new national standard does not outright ban specific technologies; safety remains the primary concern.
"The public's debate or worries about the one-pedal mode are more related to drivers' habits and should not be simply understood as the new national standard stopping or restricting the one-pedal braking function. The draft proposes that 'the braking effect achieved by releasing the accelerator pedal in gear should not be able to slow the vehicle to a stop,' without specifying the limit of deceleration. I believe that this gives car companies as much autonomy as possible under the premise of ensuring safety," said Fu Zhengjun, Director of Braking Products, Electronics, and Software R&D at Jingxi Group China, to the reporter of China Automotive News.
Zhou Xuan, Director of Wan'an Technology Center, introduced to the reporter that the energy recovery of the Type B regenerative braking system can be divided into two types: superimposed braking energy recovery and coordinated braking energy recovery. Superimposed braking energy recovery, where the motor drags the brake superimposed on the normal hydraulic/air braking (friction braking), will produce normal pedal opening hydraulic/air braking and partial electrical braking (i.e., energy recovery) as long as the brake is stepped on. This method may lead to actual braking force greater than needed in some working conditions, causing the vehicle to enter the anti-lock braking state abnormally. Usually, after the vehicle enters the anti-lock braking state, the electrical braking will be quickly canceled, and the sudden loss of deceleration given by the electrical braking will cause the vehicle to surge forward and cause an accident. Superimposed braking energy recovery is usually used on traditional non-decoupled braking systems. With the iteration of technological development, the line control braking system has gradually taken to the stage. Due to its mechanical decoupling characteristics, the line control braking system can achieve coordinated braking energy recovery, that is, the braking force required by the vehicle is equal to the sum of the electrical and hydraulic braking, maximizing the use of electrical braking to increase the recovery efficiency. For drivers and vehicles, the demand for braking force and the final output are equal, which is more safe and reliable, and this is one of the reasons why the industry is vigorously developing the line control braking system.
In addition to the widespread attention caused by the one-pedal mode, there are several detailed changes in the draft that confirm the positive interaction between the revision of the standard and the technological progress of the industry. Specifically, the draft adds the requirement that "when the ECU has an electrical failure at one point, or the internal wiring of the electronic control transmission between the ECU and the actuator (excluding the power supply line) is damaged at one point, it should be possible to perform parking braking from the driver's position and keep the fully loaded vehicle stationary on an 8% uphill or downhill slope," which is a response to the technological progress of the parking braking system.
Compared with the original national standard, the draft clarifies and refines the meaning of the control circuit, that is, a backup requirement for a failure of the electronic control parking brake (internal control circuit). This requirement actually clarifies that it is possible to use dual control dual redundancy EPB (electronic parking brake system), separate EPB and other electronic control methods to achieve the parking brake requirement of 8% under single point failure.
Such changes are in line with technological progress while maintaining the safety bottom line. It focuses on system redundancy, that is, even if the main control system fails, the vehicle can still achieve basic braking functions through the backup system. This requirement focuses on the driver's control issues, and when the key braking system fails, the driver should use the control device at the driver's position to achieve parking braking to avoid the vehicle from getting out of control; it focuses on terrain adaptability, the vehicle must have enough braking force to remain stationary on an 8% slope when fully loaded, which means that the braking system must have enough braking force to cope with emergencies under different terrain conditions; at the same time, it also focuses on fault mode management, car companies need to design systems that can still function under specific fault modes, which helps to reduce safety hazards caused by single failures.
Another detail worth noting in the draft is that it clarifies the scope of application of functional safety requirements for braking electronic control systems, that is, "braking electronic control systems with functions such as anti-lock braking, regenerative braking, electronic transmission parking braking, and electronic transmission driving braking." Functional safety standards provide a set of detailed methods and processes for the design, verification, and maintenance of electronic control systems, and the development process of functional safety helps to reduce vehicle risks caused by electronic control system failures as much as possible, improving the safety and reliability of the system.
Chen Yujue, a professor from a domestic university's automotive engineering department, believes that the definition of this scope of application not only includes the traditional anti-lock braking system but also covers the emerging regenerative braking and electronic parking system in recent years. The clarification of the scope of "functional safety requirements for braking electronic control systems" in the draft aims to ensure the safety and reliability of the braking system under various working conditions, which is crucial for improving the overall safety performance of the vehicle. At the same time, it also provides clear research and development and production guidelines for companies, helping to promote the innovation and development of braking technology.
The safety of the braking system is the bottom line requirement. The draft promotes the industry to build a solid bottom line with the standard and "urges" the industry to continuously upgrade the product safety with technological iteration, which is a distinctive feature of the new national standard.
It is understood that the draft clearly stipulates the requirement for M1 vehicles to be mandatorily equipped with Class 1 ABS. Although ABS is basically standard on the relevant vehicles at present, writing it into the standard still has great significance for progress.
Fu Zhengjun said that this measure not only enhances the standardization of the standard but also strengthens the public's safety awareness. Although ABS is already a standard configuration for most vehicles, the explicit requirement for installation can further enhance the public's awareness of vehicle safety, especially for some relatively low-end or cost-sensitive models. Moreover, it further protects consumer rights and interests, and the clarity of the standard means that consumers can expect all M1 vehicles to have at least Class 1 ABS, providing an important reference for consumers when choosing vehicles.
Zhang Junhui, a research and development engineer from a domestic brand's whole vehicle company, said that the rapid development of technology and the continuous upgrading of demand have made the introduction of the draft a response to the industry's demands. Based on the original national standard, the draft encourages enterprises to continue technological innovation with higher standards, puts forward new requirements for emerging braking technologies (such as energy recovery braking, intelligent braking), and leads the industry to develop in a more efficient, environmentally friendly, and intelligent direction. At the same time, it also raises the threshold for access to the braking field, promoting technological progress and optimizing the industrial structure.
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