Indirect integrated charge air cooling—two technology leaders merge their expertise

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Stuttgart, September 2011—The trend toward downsizing, that is, reducing displacement while maintaining performance, but with better fuel economy, is one of the main approaches to the ongoing development of the combustion engine. The required charge air management perfectly illustrates the technological potential of the cooperation between MAHLE and Behr.

In practice, downsizing means turbocharging, and therefore requires effective cooling of charge air because hot charge air presents disadvantages, such as lower density, greater nitrogen oxide formation due to higher combustion temperature, increased tendency to knocking in gasoline engines, and a greater thermal load on the engine components.

Up to now, charge air is still primarily cooled directly with external air. This means that it is fed to the front end of the vehicle after exiting the compressor, then flows through a directly cooled charge air cooler, and is then returned to the engine.

Indirect charge air cooling has distinct advantages

For the indirect variant, the charge air is cooled by a coolant, which is then recooled by external air in a separate low-temperature coolant circuit. The indirect charge air cooler can be located close to the engine, between the compressor and the throttle valve. Despite its greater complexity, indirect charge air cooling has distinct advantages over conventional direct cooling:

  • Improved packaging: the LT cooler required can be made more compact for the same power output, thus opening up critical installation space in the front end of the vehicle. At the same time, the large-volume charge air hoses used for direct charge air cooling are replaced by much thinner coolant lines. This greatly simplifies integration of the engine in various vehicles.
  • Lower pressure loss: due its reduced volume, indirect charge air has up to 20 percent less pressure loss. This results in greater density recovery and higher volumetric efficiency in the cylinder.
  • Greater thermal inertia: in case of a sudden change in load, such as under strong acceleration on the freeway, the engine has cooler air available for a significantly longer period of time. This has a positive effect on performance, and is evident in the dynamic responsiveness of the engine.

For these reasons, and despite the greater complexity of the system, indirect charge air cooling is being used ever more often, even in high-volume production models.

All the advantages and more
In the next step, indirect charge air cooling is shifted even closer to the engine: the integrated indirect charge air cooler is installed in the intake pipe. This completely eliminates all the charge air lines, and amplifies all the advantages of indirect charge air cooling.

The pressure drop over the even shorter charge air line can be reduced by up to 80 percent in comparison with direct charge air cooling. The responsiveness, density recovery, and packaging are further optimized. Manufacturing is also simplified considerably by integrating the charge air cooler in the intake pipe. This results, for example, in optimum leak tightness of the system.

Great potential for both companies
In the course of downsizing, charge air cooling will grow in significance, while the share of indirect charge air cooling will continuously increase. The new integrated concept will gain acceptance in the next few years. It exemplifies the great potential of the cooperation between MAHLE and Behr. MAHLE develops intake pipes and Behr designs the matching charge air coolers, thereby merging the expertise of two technology leaders. Optimally tuned solutions from a single source can thus be provided for this rapidly growing market.

The MAHLE Group is one of the 30 largest companies in the automotive supply industry worldwide. With its two business units Engine Systems and Components and Filtration and Engine Peripherals, MAHLE ranks among the top three systems suppliers worldwide for piston systems, cylinder components, as well as valve train, air management, and liquid management systems. MAHLE's industrial activities are combined in the Industry business unit. These include, among others, the areas of large engines, industrial filtration, as well as cooling and air conditioning systems. The Aftermarket business unit serves the independent parts market, supplying MAHLE products in original equipment quality. In 2010, the MAHLE Group generated sales of approximately EUR 5.3 billion; around 47,000 employees work at over 100 production plants and eight research and development centers.

About Behr
Behr GmbH & Co. KG, Stuttgart, is a systems partner of the international automotive industry. A specialist for automotive air conditioning and engine cooling systems, the Behr Group is one of the world’s leading manufacturers and suppliers of original equipment for light vehicles and trucks. Group sales in the 2010 business year came to around 3.3 billion EUR. Currently, Behr employs some 16,500 staff at 9 development locations, 22 production sites and 10 joint ventures worldwide.