The demands on modern engine cooling systems are many and varied. Although increased performance, reduced fuel consumption, longer durability and clear emissions may appear to be at odds with each other, the engine cooling supplier must address them. Matthew Beecham takes a glimpse at tomorrow's technology.
Fuel economy pressures have long since driven innovation in the powertrain cooling arena, prompting engineers to consider alternatives to copper-brass, steel and plastics. Aluminium radiators for passenger cars and light trucks are not only lighter, thinner, easier to recycle and cheaper than their copper-brass counterparts but also demonstrate higher heat transfer performance and better durability. The actual size of radiators has gradually reduced, too. A modern aluminium radiator is about two-thirds the size of a unit designed in the late 1970s.
It's not just radiators that use more aluminium but other engine cooling components. Traditionally produced in the US using stainless steel, oil coolers are now starting to be produced using aluminium. Europeans are already some way ahead of Americans in this respect.
In terms of packaging, combinations of condensers and radiators to save space, cost and yet achieve higher levels of cooling performance are also driving innovation. New radiator designs are emerging, too. A patented Valeo radiator that can be bent into curved shapes made its debut in the Renault concept car Wind at this year's Geneva motor show. The segmented 'spinal architecture' of Valeo's new radiator allows it to take on a curved shape, thereby saving space and easily adapting to all types of front-end designs. The innovation has allowed Renault to develop the new front-end theme of the Wind concept car, in which a radiator is located on each side of the car fascia.
New EU laws designed to protect pedestrians and cyclists, and effective from 1st October 2005, are set to create major changes in the design of European cars. This will inevitably influence the front-end architecture of the car and the geometry of the radiator. Behr says it is working on "totally new" cooling module designs in order to meet those demands.
With fuel economy in mind, we can also expect to see an influx of electronic capability in next generation powertrain cooling systems. Integration of electronics to monitor and control engine temperatures for maximum efficiency is gathering momentum in Europe. A lot of development work is currently centred on electronic thermostats and electronic water pumps.
Cooling systems are also becoming more modular, thereby lowering costs and simplifying installation. "Our sales today in North America are more than 50% modules," said Tony Coats, general sales manager for Modine's North American automotive division. The next transition is for total system suppliers where the major OEMs assign all their heat transfer requirements to one supplier. Although this trend began in Europe, it is now just beginning to catch on in the US.
Manufacturers also forecast growth for charge-air coolers driven by increased penetration of diesel engines in the light vehicle market, new emissions standards and higher module sales. Performance can be increased by liquid cooled charge air coolers using a low temperature coolant circuit.
As boost pressures and engine temperatures rise, there is a tendency for vehicle makers to opt for all-aluminium charge-air coolers over plastic tanked parts for passenger cars. Visteon observes how some vehicle makers are now specifying 2.5 bar as against 1.5 bar a few years ago. Keith Wilkins, product line manager for Visteon's powertrain cooling business, said: "Although some exotic plastics can cope with these higher tolerances, they are more expensive. It will soon reach a point when they will not be financially viable."
In addition to the charge-air coolers, manufacturers see changes ahead for EGR (exhaust gas recirculation) coolers in Europe. A spokeswoman for Denso said: "Many trucks will have both charge-air coolers and EGR coolers to meet severe emission regulations. We can see a similar situation occurring in Japan with regard to charge-air coolers and EGR gas coolers. The number of light vehicles having charge-air coolers and EGR coolers will increase both in Europe and Japan." Although manufacturers report EGR cooler growth in the US heavy duty market, the surge in demand is far greater in Europe.
Developing powertrain cooling systems for fuel-cell vehicles is another main thrust of product development. Given that fuel cells emit a higher heat rejection to the cooling system than conventional petrol or diesel engines, they pose a far bigger challenge to suppliers. "Fuel cells are quite a different animal," said Jim Giardino, director of engineering for Delphi Thermal & Interior business. "One of the challenging elements of developing fuel cells themselves is how to deal with the thermal environment, such as extreme differences in temperatures compared to conventional engines. We see fuel cells as the next major challenge for powertrain cooling."
Behr also see some cooling challenges ahead for hybrid and fuel cell cars, such as cooling of power electronics, electrical motors and the battery. "We are working in all of these fields mostly in joint projects with our customers," said Dr.Ing. Thomas Heckenberger, head of Behr Group's technology centre. "Simulation helps us to design thermal management systems including powertrain cooling and air conditioning and to specify the cooling components needed."
The cooling aftermarket, as a whole, is in decline. The once large independent sector shrank first in the US and then in Europe. It is estimated that the coolant package and cooling system reliability has improved by a factor of five since the mid-1980s. Much of this is due to improvements in build quality and introduction of plastic tanks, aluminium cores and seamless welded radiator tubes. It is reckoned that only 2.5% of radiators fail during their first five years. In the late 1980s this figure was almost 9%. In the US alone, the radiator repair business has all but collapsed barring crash repairs. Aluminium has stretched a normal repair cycle of 3 - 5 years of copper-brass to near life-of-vehicle. Longer life coolants, introduced in the mid-1990s and now found in most new cars, means that maintenance takes place every 4 - 5 years instead of 1 - 2 years.