Thermal management system software design based on SOA architecture

The development history of vehicle thermal management system

Traditional fuel vehicles have been the protagonist of the automotive industry for a long time, and the thermal management system is relatively simple, mainly including the thermal management of the air conditioning system and engine system.

Thermal management of the air conditioning system can be subdivided into passenger cabin cooling and passenger cabin heating. Passenger cabin refrigeration is a compressor driven by the engine. Through the refrigerant circuit formed by the compressor, condenser, expansion valve and evaporator, the air passing through the evaporator is cooled and sent to the passenger cabin to achieve passenger cabin refrigeration; passenger cabin heating It uses the waste heat generated by the engine to heat the coolant, and then heats the air passing through the heater core through the coolant circuit and then sends it into the passenger compartment to achieve heating of the passenger compartment.

Thermal management of the engine system is mainly responsible for the cooling needs of the engine. The high-temperature coolant that absorbs engine heat will be dissipated and cooled by the front-end module and then circulated back to the engine to achieve engine cooling.

With the development of the automobile industry, especially with the popularity of new energy vehicles in recent years, the thermal management system of pure electric vehicles has undergone great changes compared with traditional fuel vehicles. The differences in thermal management between pure electric vehicles and traditional fuel vehicles mainly include the following three points:

1) Both require thermal management of the air conditioning system. However, in the case of air conditioning and heating, traditional fuel vehicles can use the waste heat of the engine to heat the passenger compartment, while pure electric vehicles must use active heating.

2) Due to the different power systems of the two, the thermal management of the power system of traditional fuel vehicles mainly targets the engine module, while the thermal management of pure electric vehicles mainly targets the motor module.

3) Compared with traditional fuel vehicles, pure electric vehicles have added battery thermal management. Only by ensuring that the battery is maintained within a certain range can the best balance of battery life, charge and discharge performance, driving safety, etc. be achieved. Therefore, the battery needs to be Thermal management.

Figure 1 - Automotive Thermal Management Differences

Looking at the rapid development of pure electric vehicles in the past decade or so, the thermal management system has roughly gone through the following stages:

The first stage of the thermal management system of pure electric vehicles: using an electric compressor with individually controllable speed, and adding a Chiller battery cooling circuit to the refrigerant circuit of a traditional fuel vehicle. A water PTC is installed on the battery water circuit, and the water PTC heats the circuit coolant to achieve battery heating. An air PTC is installed in the air-conditioning box, and the air sent into the passenger compartment is heated by the air PTC to realize heating of the passenger compartment.

The second stage of pure electric vehicle thermal management system: Compared with the first generation, the system complexity is significantly increased. The most important feature is to apply heat pump technology to the passenger compartment heating, and at the same time couple the battery circuit, motor circuit and refrigerant circuit to realize the utilization of waste heat from the motor and battery. Heat pump technology can utilize low-grade heat in the environment or waste heat in the motor and battery circuits to improve the heating efficiency when heating the passenger compartment and increase the cruising range of pure electric vehicles in winter. However, the heat pump system at this stage generally uses refrigerant 134a or 1234yf. The heating capacity is seriously attenuated in low-temperature environments and cannot meet the heating capacity requirements of pure electric vehicles under low-temperature conditions. Therefore, it is still necessary to configure water PTC or air PTC for auxiliary heating. Moreover, although the thermal management system at this stage integrates the refrigerant, motor, and battery loop systems, the actuators and system heat exchangers are scattered and the integration level is not high. At the same time, the waste heat of the motor and battery is not used. Take full advantage of problem spots.

The third stage of pure electric vehicle thermal management system: In response to the problems existing in the thermal management system of the previous stage, a series of thermal management system improvement measures have been carried out in this stage. In order to improve low-temperature heating efficiency and capability, Volkswagen ID4 has successfully developed a thermal management system that replaces the refrigerant from 134a/1234yf to CO2. In terms of integration, the representative Tesla has highly integrated the thermal management system into the entire vehicle and applied it to the Model Y. At the same time, the system’s motor and battery waste heat utilization efficiency has also been improved to a certain extent. improvement.

The next stage of pure electric vehicle thermal management system: Although the thermal management of pure electric vehicles has made certain progress and results, it still has not reached the ideal of developing a set of safety and environmental protection, low temperature and high efficiency, space and lightweight, and low cost. Thermal management system. And with customer demands for shortening charging time as much as possible, meeting the high cooling capacity during super-fast charging is also a challenge that thermal management systems need to face. Moreover, with the development of automobile intelligent technology, the development of thermal management functions that adapt to the needs of different users will definitely be the general trend in the future. In other words, we want to realize the service-oriented thermal management function and allow users to choose their own preferences.

Next, this service-oriented software architecture SOA will be introduced in the next chapter.

Service-oriented software architecture (SOA)

After briefly understanding the development history of the thermal management system, let's get to know what SOA is.

Since entering the era of smart cars, software-defined cars have been widely accepted by industry personnel. The automobile industry is also transforming from the electronic era to the software era. Software has gradually become the core of differentiation for smart cars. In order to meet the rapid development of software and functions, service-oriented software architecture (SOA) has begun to be recognized by the industry.

Under the SOA architecture, all service component interfaces are standardized, and software deployment no longer relies on specific hardware platforms, operating systems, etc. Its loose coupling, flexibility and ease of expansion truly realize the "separation of software and hardware" in automobiles. . SOA can divide different functions and hardware capabilities of the vehicle into services, and split the services into smaller-granularity interfaces based on the atomic capabilities of the entire vehicle. The interfaces of each service component are standardized and encapsulated, and they can access each other and expand combinations through established protocols; the core elements of SOA include loose coupling, standardized definitions, software reuse, etc. SOA enables application layer functions to be reused on different models, and can quickly respond to users' new functional requirements based on standardized interfaces. When software engineers modify or add a certain software function, they only need to code the corresponding service components of the upper layer. Writing without the need to recompile and repeatedly develop the basic software layer, runtime environment layer and other software components, which greatly reduces the complexity and cost of software upgrades and improves efficiency. Because of this, SOA is becoming a software trend for software-defined cars.

Figure 2-SOA design architecture

Currently, many OEMs and suppliers are involved in SOA software development, and it is expected that the mass production of SOA will reach its peak in the next five years.

Automotive SOA organizes the underlying capabilities of vehicle intelligence. The hardware capabilities and various functions of the car are SOA-based, divided into different services, and split into interfaces with smaller granularity. These services have interface designs based on SOA standards and communicate based on SOA standard protocols. In this way, each service component can access each other, thereby expanding the service combination form. It reduces the difficulty and expands more possibilities for continuous upgrades and services after the car leaves the factory.

The collision of thermal management and SOA

SOA was first used in vehicle intelligent driving and cockpit, and many domestic OEMs have already explored it. With the continuous development of technology, other software in the vehicle will inevitably need to follow the general trend to meet the SOA architecture.

The current stage of thermal management software development mostly relies on the development of traditional fuel vehicles. Most OEM thermal management software currently only meets Classic Autosar, and even some OEM thermal management software is not enough to meet the Classic Autosar architecture. So what should we do about SOA architecture? How to do it?

Figure 3-Differences in different software formats

First of all, it needs to be clear that Autosar software architecture and SOA software architecture are not conflicting. The author believes that the Autosar architecture is more of a specification that unifies software interfaces, exchange formats, and methodology standards. Among them, the separation of software and hardware achieved by Auotsar is exactly what the SOA architecture needs. But Autosar is a signal-oriented software architecture, while SOA is a service-oriented software architecture. This also shows that SOA focuses more on a guiding ideology at the architectural strategy level. It can be understood that SOA further layers ASW on the basis of AUTOSAR to achieve greater decoupling. Therefore, if the existing thermal management software does not currently meet the Classic Autosar architecture, it needs to be modified to meet the Classic Autosar architecture. Then perform the following conversion.

Secondly, the author believes that in order to meet SOA, thermal management software needs to implement the following two parts.

1) Exposure ability

The essence of SOA is to change from signal orientation to service orientation. Since SOA software needs to be service-oriented, it first needs to expose its capabilities for other services to call. The thermal management software is a software module that serves air conditioning and three electrical systems, so most of the service interfaces of the thermal management software are oriented to air conditioning and three electrical systems. It is based on the above situation that the author recommends arranging most of the logical algorithms of the thermal management software in the basic service layer of the SOA software architecture.

Since the thermal management system involves strong coupling of multi-component control strategies, only sensors and actuators of the thermal management software can be placed in the meta-service layer to release service interfaces for diagnosis and after-market use. That is to say, the sensor and actuator signal conversion and hardware diagnosis parts of the thermal management software need to be separated from the main thermal management software.

Note: Due to the strong coupling of the thermal management system, the forced driving of the actuator needs to consider system security, so the author does not recommend releasing this part of the service interface directly. Algorithms need to be added and protected.

2) Convert signal to service

The essence of SOA is to change from signal orientation to service orientation. In the traditional software development of the whole vehicle, module interaction is carried out in the form of signals. In order to realize the transformation of SOA, the interaction between modules must be changed to service orientation. Fortunately, AUTOSAR supports SOME-IP and can switch interactive modes.

Conclusion

Finally, let’s summarize the impact of thermal management software design based on SOA architecture on thermal management software development:

1)Can be customized as needed

Existing software development is mostly designed based on the experience of developers and vehicle model positioning. However, after all, there are thousands of people with different faces. Based on the SOA platform, developers can freely develop a large number of services and applications and put them on the shelves after passing testing and verification; users can freely subscribe to services to realize the use of cars by thousands of people. Therefore, after realizing SOA, thermal management can also achieve personalized customization by releasing decision-making power to users. For example, A is more concerned about the safety of the battery, so A chooses to prioritize battery thermal management. B cares more about the comfort of using the car, so B puts the priority of passenger compartment thermal management to the fullest. C cares about the smooth feeling of acceleration, so C cares more about the motor being always ready for full power output in the next second.

2) Rapid iteration of software can be achieved

Based on SOA architecture, we can increase the speed of software iteration. New feature development can have no or as little impact on existing software as possible. In the future, software iterations will be released more in the form of feature-added packages.

And it will also attract more software developers to carry out secondary development relying on the released API interface, just like mobile phones. There will definitely be many interesting apps developed by then. However, major OEMs must also pay attention to the management of relevant API interfaces and strengthen information security and functional safety construction to avoid malicious use by criminals.