Technical Information
– Optimization focus: thermal management –
MAHLE Behr Industry: the expert in innovative cooling and air-conditioning solutions
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Stuttgart, September, Germany 2010—Thermal management plays an important role in reducing fuel consumption and emissions in modern engines. As part of its greater commitment to this market, MAHLE now offers a wide range of systems and component solutions. Following its acquisition of Behr Industry, MAHLE is now active in the market of complete cooling and air-conditioning solutions for off-highway vehicles and industrial applications.
Off-highway vehicles include building machines, agricultural machines such as tractors, railroad vehicles, military vehicles, and ships. MAHLE Behr Industry supplies complete cooling and air-conditioning solutions not only for this segment, but also for buses as well as industrial applications such as large engines, diesel engine-driven generators for electricity production, and wind power stations.
Among other things, these systems comprise coolers for coolant, charge air, hydraulic fluid, transmission fluid, and exhaust gases, as well as fans, fan drives, and air guides. Water and oil pumps, thermostats, and expansion tanks round out the systems as needed. In developing these systems, MAHLE Behr Industry draws on experience and makes use of components from Behr's passenger car and truck operations.
However, the requirements for cooling and air-conditioning systems in off-highway and stationary engines are completely different than for such systems in passenger cars and trucks. These differences include small production numbers or even made-to-order production; different exhaust gas legislations and engine operating cycles; high loads in some cases due to aggressive media, mud, dust, or fibers; as well as restrictions in terms of cooling requirements, mounting position, and package constraint.
Even the development and production processes are different from those involved in large-scale production in automotive manufacturing: Small-lot production, for instance, requires flexible manual assembly systems and highly skilled employees. Due to high investment costs, semiautomatic or fully automatic production facilities are hardly cost-effective.
Focusing on future emission standards
To meet ever-stricter emission standards in off-highway applications while increasing specific output, processes both inside and outside the engine are being employed in much the same way as in the truck sector; these include cooled exhaust gas recirculation and dual-stage tubocharging with charge air cooling, as well as exhaust gas aftertreatment measures, such as SCR or diesel particulate filters.
For an off-highway diesel engine in the 56 to 560 kilowatt performance range, there are various ways to meet future emission standards. Engines with an SCR system or a two-stage high- and low-temperature EGR system with a high recirculation rate form the cornerstones of compliance. In between these, a number of hybrid formats with varying degrees of SCR and EGR are conceivable. Systems with high recirculation rates, which will likely be capable of fulfilling even the upcoming EURO VI emissions regulations, require no additional operating agents. Moreover, the EGR components can be integrated into a module at low cost and require less interfacing.
To define the requirements for charge air and coolant cooling systems, MAHLE Behr Industry has taken a closer look at two scenarios: one that uses exclusively exhaust gas recirculation and another that uses primarily exhaust gas recirculation, but also SCR technology. In both cases, the diesel engines have twin turbocharging, a common-rail injection system with an injection pressure of over 2,500 bar, and a two-stage high-and low-temperature EGR system.
The hybrid system operates with an EGR rate of 23–27%, resulting in very low NOx emissions; in combination with the SCR system, future Tier IV (USA) and EURO VI (Europe) emission standards can reliably be undercut. The EGR-only engine operates with an extremely high recirculation rate of 35–40% and consequently produces extremely low NOx emissions. Emission standards can thus be fulfilled without an additional SCR system—even in large-volume diesel engines in locomotives and ships with power outputs greater than 560 kilowatts.
Integration and modularization
The cooling system in both scenarios comprises two circuits. The first circuit cools the engine and the high-temperature EGR cooler. A second, independent, low-temperature circuit dissipates the heat from the second EGR cooler and the two indirect charge air coolers.
Indirect cooling of charge air presents several advantages: during warm-up or at partial load, the coolers can be bypassed so that the engine can reach its operating temperature more quickly and continue to maintain this temperature afterward. Apart from the second EGR cooler, additional cooling elements can also be connected to the low-temperature circuit; these include elements for the power electronics of a hybrid drive, for transmission oil, or for hydrostatic drives. The location of the charge air cooler in the engine bay reduces pressure losses by up to 50% and increases the engine's efficiency, among other advantages.
Both coolers have a disk-type design, similar to coolers used in trucks; the number, length, and width of the disks determines the power output of the coolers. For large diesel engines with power outputs of up to 10 megawatts, charge air coolers are available in the proven round tube technology with expanded tubes made of nonferrous metal, as well as in an innovative disk design available both in aluminum and nonferrous metal.
The two EGR coolers are also located in the engine bay, but are integrated into a housing requiring no special care. This module also encompasses the EGR valve, along with a mass-flow sensor or EGR cooler bypass if necessary. Given the stringent dynamic and thermal requirements for off-highway engines, MAHLE Behr Industry relies on stainless-steel flaps for its EGR valves and brushless DC motors, providing forces that are both extremely accurate and powerful.
To a large extent, the exhaust gas coolers are the same as those used in trucks, since the basic conditions are similar for the most part. For the higher performance requirements of large diesel engines, MAHLE Behr Industry offers a modular concept comprising several individual coolers in a single cast housing, as well as specific fin/tube geometries and tube bundling systems. By modifying the coolant ports, two-stage cooling systems can be accommodated here as well.
For coolant coolers and charge air coolers in the off-highway and stationary segments, MAHLE Behr Industry has developed a modular concept that makes it possible to create a number of high-performance cooler configurations based on a few standardized components.
The tubes in the cooler are standardized and can be arranged in single-row, two-row, or three-row systems. This system can be enhanced by suitable cooling fins of various heights and thicknesses to achieve superior cooling performance or greater resistance to soiling. Thus a wide range of solutions are available, from the flat high-performance cooler all the way to the robust deep cooler. For average production numbers, these fin/tube technologies are used; for smaller numbers, the coolers are constructed in a packet design.
Special solution for bus air conditioners
One of MAHLE Behr Industry's innovative air-conditioning solutions is the driver's seat air-conditioning unit for buses. At only 16–17 kilograms, this front box weighs only half as much as the previous solution, owing to its intelligent, lightweight design. Its major features include polypropylene plastic instead of sheet steel for the housing, a recycling-friendly, all-aluminum heat exchanger instead of the copper-tube variant, and aluminum flaps from extruded hollow-cast profiles instead of sheet-steel flaps.
Besides providing air conditioning to the driver and co-driver seat, the front box also maintains a fog-free windshield. This is accomplished primarily by a powerful heat exchanger for heating and a high air delivery rate. The air-conditioning unit's air and heat performance is more than 50% higher than units used for large-volume cabs in long-haul trucks.
The variety of formats required—six variants for left- and right-hand drive vehicles with three different housing sets—renders the already challenging conditions of small-scale production all the more difficult. To minimize costs, all housings are produced from a single, flexible toolset.
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. The newly formed Industry business unit bundles the MAHLE Group's industrial activities. These include the areas of large engines, industrial filtration, as well as cooling and air-conditioning systems.
In 2009, the MAHLE Group generated sales of approximately EUR 3.9 billion; around 43,000 employees work at over 100 production plants and eight research and development centers.
Press contact
MAHLE GmbH
Birgit Albrecht
Corporate Communications/Public Relations
Pragstrasse 26–46
70376 Stuttgart
Germany
Phone: +49 (0) 711/501-12506
Fax: +49 (0) 711/501-13700
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