Calsonic Kansei Corporation manufactures and sells automotive parts, primarily in Japan, North America, Europe, and Asia.
Air conditioning (AC) is considered a “must-have” by consumers for most new cars. But the fluorocarbon refrigerant HFC-134a – the global standard – is believed to be a cause of climatological change. With these concerns, the European Union (EU) has passed regulations phasing out the compound beginning in 2011 and mandating the use of alternatives with less environmental impact. By 2018, HFC-134a will be banned in new cars sold in the EU. Japan is expected to soon follow suit.
At the top of the alternative list is the refrigerant CO2 (carbon dioxide), also known as R-744. This gas is believed to be significantly more eco-friendly than fluorocarbons and provides 25 percent faster cool-down. Moreover, CO2 systems can be reversed and thereby serve as a passenger cabin heater in cold weather, a definite plus for electric cars that otherwise drain power from batteries as well as internal combustion engines (particularly diesels) that need high operating temperatures to run efficiently.
However, moving to CO2 won’t be easy. Gas pressures can be 10 times greater than fluorocarbon-based systems, requiring compressors, seals and other major components to be specially designed. For the most-efficient performance, the CO2 refrigerant must be kept above its super critical temperature of 31degrees Celsius (C), so a gas cooler must replace a classic R134a loop condenser. CO2 systems also require a special heat exchanger separating the high- and low-pressure sides. According to some industry observers, these design complexities – plus a longer development cycle and additional physical prototype testing to refine the designs – could mean that some of the first CO2-based systems could cost 30 percent more than conventional units.
Compounding these difficulties, CO2 has not been established as a global standard. On the contrary, the United States has no plans to discontinue HFC-134a, and China has made major investments in producing HFC-134a. Moreover, fluorocarbon suppliers are actively pursuing alternative blends, such as HFO-1234yf, which has lower ozone-depletion potential and are direct “drop-in” substitutes for HFC-134a in current air conditioning systems. Consequently, AC suppliers must develop systems for different global regions based on refrigerant specifications that may change at any time.
Right now, AC suppliers are challenged to meet these varying requirements with systems that integrate smoothly into the total vehicle to provide optimal cool-down performance and passenger comfort with minimal engine drag and pollutant emissions. With faster and faster development cycles in the automotive sector, AC suppliers are striving to develop these complex designs better, faster and less expensively than competitors, and to be the first to demonstrate optimal system performance to automakers. Design speed is critical, as is the ability to account for all complex thermal, mechanical and electronic control issues relating to an AC system.
Many AC suppliers and carmakers use the Simcenter Amesim Vehicle Thermal Management solution to handle the AC system design and predict performance. The solution enables engineers to analyze component behavior in relation to engine temperature, exhaust levels, auxiliary equipment, cabin environment and other factors to find the best combination.
Using Simcenter Amesim™ software, part of the Simcenter portfolio from Siemens Digital Industries Software, engineers can easily access the required tools and libraries to build simulation models, run simulations and display results graphically.
One of the automotive suppliers using this Siemens PM Software is Japanese supplier Calsonic Kansei. With more than 50 years of experience in the field, it is one of the few suppliers that designs and manufactures the complete AC system. Calsonic Kansei has made sure that its modular designs and compact units align with vehicle manufacturers’ requirements to reduce cabin space. Moreover, the company’s position as a Tier 1 AC supplier is strengthened by its experience in designing and manufacturing engine cooling systems, vehicle air circulation units, exhaust systems, dashboard modules and electronic climate control systems.
Junichiro Hara, senior engineer and project manager for Innovative AC and Engine Cooling Module Systems Development at Calsonic Kansei, explains that no expert programmers are needed to build the models and run simulations using the Simcenter Amesim software. Engineers drag, drop and interconnect simple icons – pre-defined 1D elements selected from libraries in the different physical domains – to create a unified physicsbased model. The block diagram is a fairly simple sketch, but underlying it is all validated dynamics information, a real working one-dimensional representation of all the different parts of the AC system. Not only did the Calsonic Kansei engineers model all the parts of the system, but they linked together the subsystems to simulate the complete interaction between the AC, cabin and engine.
First, engineers selected the icons for each individual AC component, like the compressor, evaporator and piping as well as refrigerant tubes in the gas cooler and evaporator. Different size components were swapped according to vehicle requirements and connected to represent the warm and cool refrigerant loops. Refrigerant thermal-physical properties for CO2 were then modeled, and the 1D simulation was run to study AC thermal output performance as well as individual part behavior.
Simcenter Amesim lets engineers access a variety of plots and charts to evaluate different aspects of the AC system. Mollier pressure-enthalpy diagrams show the state of the refrigerant in each phase of the cooling cycle. They can also review pressure levels at the compressor inlet and outlet as well as heat exchange in the gas cooler. Changes in gas mass fraction levels can be plotted at various locations in the refrigerant circuit. With in-depth information like this, Calsonic Kansei engineers could easily perform sensitivity analysis on critical parameters to determine the best possible AC performance.
Meanwhile, engineers worked in parallel on the cabin interior model, using various icons to represent blowers, air ducts, windows, thermal properties of walls, solar heat flux, internal and external convection and ambient thermal radiation. By linking the model of the cabin and model of the AC system, engineers could calculate cool-down rate, cabin temperature and humidity, even incorporating different weather and driving conditions. Using the one-dimensional model this early in the process lets engineers accurately size critical system components, such as ducts and fans and test climate control strategies. Simcenter Amesim Vehicle Thermal Management solution was also used to perform a durability analysis regarding the impact of corrosion and contamination on the heat exchangers and other parts.
After this, the team took the Simcenter Amesim solution one step further to examine the overall energy balance between the engine and lubrication and cooling systems, combustion chamber, air intake and exhaust pipes. By linking the engine model with the AC system and cabin models, engineers could then optimize engine performance, fuel consumption and exhaust emissions while providing the best passenger comfort.
“Using our previous internally-developed programs, creating engineering estimations and acquiring experimental data was very time-consuming, even to roughly approximate AC performance under transient conditions such as cool-down and vehicle speed variations,” says Hara. “Furthermore, including engine characteristics into the development process was impossible before. The Simcenter Amesim Vehicle Thermal Management solution enables us to quickly and accurately predict how the complete AC system will operate, taking into account a wide range of conditions that otherwise would not be included.
“The beauty of Simcenter Amesim Vehicle Thermal Management solution is that the model – once created and verified – can be used as a basis for a wide range of future designs without starting from scratch each time,” says Hara. “Engineers merely enter new parameters to reflect different vehicle applications and run simulations to quickly predict AC system performance.
“When fully operational and integrated into system development, indications are that the simulation-based process using Siemens Digital Industries Software solutions will be at least 80 percent more accurate than current methods, and reduce the number of physical prototypes by half, a definite business benefit in terms of lowering development costs and shortening the time to respond to customer requests for quotes.”
One of the most exciting prospects of Simcenter Amesim Vehicle Thermal Management solution for Calsonic Kansei is its use as a sales tool in demonstrating cool-down and other performance characteristics.
“Demonstrating precisely the level of passenger comfort and the impact of the system on engine performance and exhaust emissions is a powerful capability,” says Hara. “In the coming years, simulation-based design processes will certainly give us a competitive edge in growing our business as the global automotive AC market shifts to more ecologically friendly refrigerants.”