Cool and Green: Vehicle Thermal Management

Mollier pressure-enthalpy diagrams show the state of the refrigerant in each of the four phases of the cooling cycle: compression, gas cooling, expansion, and evaporation. The area of the semi-ellipse enclosed by the red box indicates the “supercritical” operational range where the CO2 refrigerant is most efficient.
One of the automotive suppliers using this LMS solution is Japanese supplier Calsonic Kansei. With over fifty years experience in the field, they are one of the few suppliers that designs and manufactures the complete AC system. Their modular designs and compact units coincide with vehicle manufacturers’ requirements to reduce cabin space. Moreover, Calsonic Kansei’s position as a tier-one AC supplier is strengthened by the company’s 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 LMS models and run simulations. Engineers themselves drag, drop and interconnect simple icons – pre-defined 1D elements selected from libraries in the different physical domains – to create a unified physics- based model. The block diagram is a fairly simple sketch, but underlying it is all actual 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, they linked together the subsystems to simulate the complete interaction between the AC, cabin and engine.

Easy as 1-2-3

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.

LMS Imagine.Lab 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. The LMS 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 LMS 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 then could optimize engine performance, fuel consumption and exhaust emissions while providing the best passenger comfort.

Business value of 1D simulation

“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. Furthermore, including engine characteristics into the development process was impossible before,” Junichiro Hara noted. “The LMS Vehicle Thermal Management solution lets us 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 project is still on-going at Calsonic Kansei. Calsonic Kansei plans to base future AC designs on this LMS Imagine.Lab AMESim simulation model.

“The beauty of LMS Vehicle Thermal Management 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,” he said. “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 LMS software will be at least 80% more accurate than current methods and reduce the number of physical prototypes by half – definite business benefits in lowering development costs and shortening the time to respond to customer requests of quotes.”

One of the most exciting prospects of the LMS 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,” he noted. “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.”

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