What is the car ZCU that we talk about every day?

In recent years, more and more automotive OEMs and Tier 1s have mentioned the concept of ZCU (Zone Control Unit) for the entire vehicle. Since Tesla Model 3 first implemented the "central computing + zone control" framework and basically realized the centralized architecture, the centralization of the automotive electrical and electronic architecture (EEA) has become a major trend, and ZCU has also ushered in a big explosion.

To understand what ZCU is, you need to understand what changes have taken place in the entire system. In other words, the concept of ZCU was born along with the electrical architecture.

People in the chip industry must be familiar with the word integration. Whether it is digital chips or various power chips, they are all modularized and integrated. EEA is no exception. Nowadays, there are too many functions introduced in cars. Each function must be introduced as a new module, that is, the Electronic Control Unit (ECU). Now each of the latest vehicles requires more than 100 to 150 ECUs and related wiring harnesses. Not only do manufacturers lack space in their vehicles, but their wiring requirements are also close to saturation point. In summary, automotive E/E architecture is divided into three generations.

The first generation is Flat (distributed architecture), which has basically been eliminated.

Flat is like a tribe, each electronic function has its own ECU, such as one ECU for the radio and one ECU for the wiper. During this period, the architectural shortcomings were obvious, and the ECUs were basically in a closed network state, which could not achieve functional coordination and did not meet the conditions for OTA upgrades. More importantly, each of the hundreds of ECUs was independent, and if they wanted to exchange information, each ECU needed a wiring harness for control and transmission, so this architecture was very complex and difficult to expand.

The second generation is the Domain (domain control) architecture, which is the current mainstream.

Domain is like a feudal system, which classifies the computing needs in the car according to the function. For example, Bosch divides the whole vehicle architecture into five domains, namely the power domain (Power Train), chassis domain (Chassis), body domain (Body/Comfort), cockpit domain (Cockpit/Infotainment), and autonomous driving domain (ADAS). The core responsible for handling these tasks is the domain control unit (Domain Control Unit). On the surface, this classification is very clear, but the wiring in the car is very complicated, because the actual location of each function is spread throughout the car body, which eventually causes the wiring harness to be tangled in the car.

The third generation is the Zonal (regional control) architecture, which Tesla has already adopted and other OEMs are in the process of transitioning.

Although Zonal is also classified by region, it is different from Domain in that it is classified by physical location, more like a county system. Tesla Model 3's Zonal architecture is divided into three physical regions: front body, left body, and right body. Three regional controllers ZCU (Zonal Control Unit) are arranged accordingly. All end-side actuators are connected to the nearest ZCU, becoming a typical IT computing architecture, and the wiring harness is also simpler.

From the above introduction, it is not difficult to see that ZCU actually merges some of the past ECUs to form a module with greater computing power and stronger communication.

Some companies have begun to use Domain Plus, an intermediate state between Domain and Zonal, which is close to Zonal in form. However, most car companies are still in the transition stage of "distributed ECU + domain controller". It is expected that by 2025, some car companies will realize the integration of central computing and regional controllers; by 2030, Zonal architecture will become the mainstream in the industry.

Reduce overall ECU usage

The industry hopes for the best state to drive all systems with only one ZCU, but it is not economically feasible to assemble processors in one package with all the computing power required to handle the tera operations per second (TOPS) required for full vehicle autonomous driving. So now it is basically shared processing enabled by the regional controller (ZCU) and the central computing node, and the overall computing throughput and utilization of memory resources (such as solid-state drives SSD) are optimized without putting too much pressure on the system.

Have system processing redundancy

Zonal architectures are still zoning after all, and in particular offer an attractive option to avoid failure scenarios where one specific area of ​​the vehicle is affected, by connecting physically distant zone controllers into a ring.

Power architecture has advantages

In the Zonal architecture, the distribution box is redistributed so that each zone has its own distribution unit to power the modules in the corresponding zone. The design of the distribution module of the Zonal architecture can be similar throughout the vehicle. Using semiconductor solutions such as smart high-side switches instead of mechanical relays and fuses enables a more sensitive power distribution module design, placing the modules closer to the load rather than farther away for easier replacement.

Communication architecture is more optimized

The ZCU itself can be efficiently connected with other control units in the area through communication methods such as CAN bus, LIN bus or Ethernet. Under the Zonal architecture, all connections can be supported by Ethernet. You must know that CAN and CAN FD also need to be authorized by Bosch, which is not a small amount. Zonal converts all data into Ethernet frames and can be used for all domain controllers on the backbone network. Different virtual functions and virtual machines can reuse various functions. It is also possible to transfer tasks and improve virtual machines according to CPU load or power conditions (load balancing is very important for electric vehicles).

The software mechanism is better

The concept of software-defined cars will become more popular under the Zonal architecture. The difficulty of implementing software OTA is greatly reduced, so that cars can be updated in a timely manner even after they are delivered to end users. At the same time, the Zonal architecture transforms the automotive software integration mechanism from field bus signals to a service-oriented architecture (SOA). SOA decouples software from hardware.

Reduce the amount of wiring harnesses

The wiring harness cost of a Domain architecture vehicle can reach $1,000, and the length of the wiring harness is about 3 to 5 kilometers, accounting for an average of 45-55 kilograms of the vehicle weight, and the heaviest can reach 68 kilograms. The Zonal architecture can greatly shorten the wiring length (from 3 kilometers to 1.5 kilometers) and reduce the overall wiring harness weight by 85%.

In addition to the original control of interior and exterior lights, wipers, relays, etc., the zone controller (ZCU) also controls air conditioning dampers, rearview mirrors, doors and windows, door locks, PEPS, etc. Some even integrate gateway and VCU functions. The functional safety requirements have changed from the original QM to ASIL-B/ASIL-D (when VCU is integrated).

By merging the logical input/output (I/O) functions of multiple ECUs into the regional module and retaining the location of sensors and actuators, ZCU achieves the separation of physical and logical I/O functions. In terms of software, the IT industry's SOA (service-oriented architecture) concept has gradually become a design method for Zonal architecture.

Since the ZCU interfaces with all devices within its control area, it can interface with a wide range of devices using many different types of communication protocols. The following figure shows the circuit module of the ZCU:

From many ECUs to ZCU, greater centralization means more complex design, which will bring changes at the chip level.

Challenge 1: Time Awareness

As more data flows in more centralized topologies, the need for high-speed networks becomes more apparent. This will lead to the existing bus system CAN (with a maximum speed of a few Mbps) being gradually replaced by Ethernet, which can provide speeds of 100M or 1Gbps. At the same time, new computing resources will need to be combined with traditional systems. This hybrid design must take into account the need for precise timing, as many systems rely on time. The standards adopted will include IEEE 802.1AS-2020, the IEEE-approved time and synchronization standard for time-sensitive network (TSN) applications.

Challenge 2: Communications

The concept of regional networks is based on an Ethernet backbone that connects different regional controllers, domain controllers/central computers. Within each region, there will be multiple appropriate edge networks that connect regional modules and edge ECUs. These networks mainly include CAN FD and Ethernet, and their latest variants such as CAN XL and 10BASE-T1S. The communication challenge for regional modules is to be able to seamlessly abstract the regional network topology from the functionality.