Comprehensive explanation of automotive domain controller technology

With the penetration and popularization of automobile intelligence and networking, the proportion of automotive electronic and electrical components in automobiles has gradually increased. Advanced driver assistance systems, in-vehicle multimedia entertainment systems, etc. have gradually become functional configurations that consumers pay attention to and influence their purchasing decisions. More and more complex systems have a demand for the number of sensors and electronic controllers (Electronic Control Unit, ECU), such as autonomous driving cameras, millimeter-wave radars, co-pilot entertainment screens for multimedia entertainment systems, HUD head-up display systems, ECM modules that control engine performance, BMS modules that manage new energy vehicle batteries, and AVM modules for 360-degree surround image fusion calculations, etc. According to Yanzhi Auto data, a modern luxury car usually contains 70 to 100 ECUs. The traditional distributed electrical and electronic architecture (EEA) can no longer meet development needs due to its: 1. The computing power is dispersed and cannot be used efficiently; 2. The cost and weight disadvantages of the wiring harness; 3. It cannot support high-bandwidth in-vehicle communication; 4. The subsequent upgrade and maintenance are difficult and other multi-dimensional reasons. Centralized electronic and electrical architecture came into being and will eventually move towards the form of a central computing platform in the future.

1. The computing power is dispersed and cannot be used efficiently.

In a distributed architecture, cars are equipped with dozens of controllers, and to ensure performance stability and safety, the hardware computing power of each controller chip is redundant relative to the program running on it. This results in the ability of each controller to "operate independently" from the perspective of the entire vehicle, and cannot be efficiently coordinated. On the contrary, in a centralized electronic and electrical architecture, computing power is used for assisted driving when driving, and can provide computing power for in-vehicle games when parking and resting.

2. Disadvantages in wiring harness cost and weight. A large number of ECUs also means complex and lengthy bus wiring harnesses. According to data from the Electronic Engineering World Network, the wiring harness used in a high-end car is about 2km long and weighs 20~30kg. In the wiring harness, the weight of the cable material itself accounts for about 75% of the total weight of the wiring harness. The introduction of a centralized electronic and electrical architecture and domain controllers can greatly reduce the use of wiring harnesses. 3. Unable to support high-bandwidth in-vehicle communications.

In the era of distributed ECUs, the core of computing and control is the MCU chip, and the basic core of transmission is based on traditional low-speed buses such as CAN, LIN and FlexRay. With the continuous increase of ECUs, the bus load has increased, basically reaching the upper limit of the allowable limit, which is easy to cause technical problems such as signal frame loss and bus congestion, thus leading to safety hazards. However, in the era of domain controllers, high-performance, highly integrated heterogeneous chips serve as the main control processor of the domain, with unified scheduling and control within the domain, and high-speed communication outside the domain through Ethernet. Currently, 100M and 1G Ethernet have been applied to many new models. The implementation cost per node of automotive Ethernet is higher than CAN and LIN, and is comparable to FlexRay. In the future, the restriction of data transmission speed will make it inevitable for automotive Ethernet to replace traditional buses.

4. System integration and OTA maintenance are difficult.

The development of each ECU is mainly provided by each Tier1 to the OEM, and the OEM is integrated by the internal team. This poses a high challenge to the OEM's integrated development capabilities and supplier management capabilities. In addition, the distributed architecture and scattered ECU layout are also difficult to support online upgrades of vehicle software (OTA), which increases the difficulty of later maintenance and iteration of the software. At present, OTA has gradually become popular from the unique skills of some new forces car companies, and the update and iteration frequency of various car companies is also increasing rapidly. According to data disclosed by the State Administration for Market Regulation, major car companies reported 351 OTA upgrades in 2021, an increase of 55% over the same period in 2020, and the number of vehicles involved reached 34.24 million, a surge of 307% over the same period in 2020. The electronic and electrical architecture of traditional vehicles is generally distributed, and its control center is connected by the electronic control unit ECU through the CAN bus and LIN bus. With the cooperation of sensors, power supplies, communication chips, actuators and other components, the control of the vehicle status and functions is realized. Each control system uses a separate ECU, and different electronic control system functions remain independent. Each additional function requires an additional ECU. Therefore, the increase and upgrade of traditional automotive intelligent functions mainly depends on the accumulation of ECUs and sensors.

With the need for electronic and intelligent development, the traditional distributed architecture has gradually evolved into a domain-centralized architecture, and "domains" and "domain controllers" have emerged. The domain controller was first proposed by Tier 1 manufacturers such as Bosch, Continental, and Delphi. By using multi-core CPU/GPU chips with stronger processing power, introducing Ethernet and integrating scattered ECUs into domain controllers with stronger computing power to relatively centrally control each domain, it solves the limitations of distributed architecture such as cost and computing power.

The advantages of the domain-centralized architecture mainly include: 1) The domain-centralized architecture can save costs and reduce assembly difficulty. In the distributed architecture, the large number of internal communication requirements generated by the increase in the number of ECUs leads to an increase in the cost of wiring harnesses and an increase in the difficulty of assembly; while the domain-centralized architecture separates sensing from processing, and sensors and ECUs are no longer one-to-one, which makes management more convenient, effectively reducing the number of ECUs and wiring harnesses, thereby reducing hardware costs and labor installation costs, and is more conducive to component layout. 2) The domain-centralized architecture can improve communication efficiency, achieve software and hardware decoupling, and facilitate vehicle OTA upgrades. In the distributed architecture, the software development framework and underlying code of ECUs from different suppliers are different, resulting in redundancy and increasing the difficulty of maintenance and OTA unified upgrades; while the domain-centralized architecture achieves unified management and information interaction of each ECU, and unifies the underlying software development framework, thereby facilitating future OTA upgrades and the realization of expanded functions. 3) The domain-centralized architecture can further concentrate computing power and reduce redundancy. The computing power of each ECU in the distributed architecture cannot be coordinated, and there is mutual redundancy, resulting in great waste. The domain control architecture centralizes the computing power of the originally dispersed ECUs, processes data in a unified manner, reduces computing power redundancy, and better meets the high computing power requirements of advanced autonomous driving.

Based on the centralized functional zoning, traditional Tier 1 companies such as Bosch divide automotive electronic control systems into five domains: power domain (safety), chassis domain (vehicle motion), cockpit domain (entertainment information), autonomous driving domain (driving assistance) and body domain (body electronics).

The power domain is used for the optimization and control of the powertrain, and also has functions such as electrical intelligent fault diagnosis, intelligent power saving, and bus communication. The power domain controller is an intelligent powertrain management unit that uses CAN/FLEXRAY to achieve transmission management, lead management, battery monitoring, and alternator regulation. Its advantages are that it calculates and distributes torque for a variety of power system units (internal combustion engines, motor generators, batteries, and gearboxes), achieves CO2 emission reduction through predictive driving strategies, and communication gateways. It is mainly used for the optimization and control of the powertrain, and also has functions such as electrical intelligent fault diagnosis, intelligent power saving, and bus communication.

The chassis domain will integrate the vehicle's lateral, longitudinal, and vertical control functions such as braking, steering, and suspension to achieve integrated control. The transmission system is responsible for transmitting the engine's power to the drive wheels, and can be divided into mechanical, hydraulic, and electric types; the driving system connects the various parts of the car into a whole and supports the entire vehicle; the steering system ensures that the car can drive in a straight line or turn according to the driver's wishes; the braking system forces the road surface to exert a certain external force on the car's wheels that is opposite to the direction of the car's travel, and performs a certain degree of forced braking on the car. Its function is to slow down and stop, and parking brake. The chassis domain can integrate multiple functions in the transmission system, driving system, and braking system. The more common ones are air spring control, suspension damper control, rear wheel steering function, electronic stabilizer bar function, steering column position control function, etc. If sufficient computing power is reserved in advance, the chassis domain will integrate the vehicle's lateral, longitudinal, and vertical control functions such as braking, steering, and suspension to achieve integrated control. To realize the functions of the chassis domain, it is necessary to integrate the chassis domain drive, braking, and steering algorithms.