Some recent innovations in the engine cooling system arena centre the introduction of stricter standards on emissions, requirement for reduced fuel consumption and new regulations on pedestrian protection. Although increased performance, reduced fuel consumption, longer durability and clear emissions may appear to be at odds with other, the engine cooling supplier must address them. Matthew Beecham reports how suppliers are responding.
“Engine cooling modules are essential users of electrical energy,” said Hermann Scherer, Marketing Director, Thermal Systems, Energy & Body Systems, Bosch Automotive Technology. “The prime driver is therefore centered on improving efficiency in order to save energy. Packaging is another driving force; engine cooling systems must fit into ever smaller spaces under the bonnet. Passenger comfort and safety are also important considerations.”
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Marshall Andrews, Global Business Line Executive, Climate Control & Powertrain Cooling Systems, Delphi Thermal & Interior, said: “The major forces driving innovation in the North American engine cooling arena are for better efficiency and packaging. The key is the ability to find how to deliver those improvements in a reliable and cost-effective package.”
Aluminium has taken the powertrain cooling sector by storm. The transfer from copper-brass to aluminium radiators is complete. Aluminium radiators are not only lighter, easier to recycle and cheaper than copper radiators but also demonstrate higher heat transfer performance and better durability.
The actual size of radiators has also gradually reduced. A modern aluminium radiator is about two-thirds the size of a unit produced in the late 1970s. The high cost of fuel, particularly in Europe, means that designers are seeking ways of reducing the airflow in the car, which is leading towards the use of smaller heat exchangers. In fact, one of the main challenges facing manufacturers in the heat transfer area is to get the same amount of heat rejection from thinner and thinner radiators.
Figure 1
Visteon‘s radiators:
Vistoen designs and manufactures thin, high performance radiators, from 10mm to 42mm, with plastic end tanks or all-aluminium design.
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Source: Visteon. |
Another trend in the engine cooling sector is for more component integration. Combinations of condensers and radiators to save packaging space, cost and yet achieve higher levels of cooling performance are driving innovation.
Interest in using electronics to monitor and control engine temperatures for maximum efficiency is gathering momentum in Europe. Manufacturers are considering the use of electronic thermostats and water pumps. Bosch’s Scherer added: “We are currently talking with customers about whether it makes sense to use electric water pumps or another device to control the coolant temperature. Generally speaking, an electric water pump is no more efficient than a mechanical water pump. The efficiency of using both types of pump is about 20%. It is not the type of pump – whether electric or mechanical – that matters. It is the design of the cooling circuit in the engine which brings the advantage.”
How quickly we will see that integration in North America depends, in part, on the development cost / fuel benefit ratio. Delphi’s Andrews said: “Electronic powertrain cooling is one of those technologies I see as continuing to be on the horizon. We can offer that today but the question has always been centered on a cost-benefit analysis. It still isn’t viable. Some day that will be. But I have not seen that yet.”
Manufacturers are forecasting growth for charge-air coolers driven by increased penetration of diesel engines in the light vehicle market and new emissions standards.. 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.
Cooling systems are also becoming more modular, thereby lowering costs and simplifying installation. The next transition, say manufacturers, is for total system suppliers. Although this trend began in Europe, it is now just beginning to catch on in the US. Tony Coats, General Sales Manager, North America, Modine Manufacturing Co, said: “We see modularity going in both directions right now with the OEMs. Certain OEMs have already opted for modularity and yet now seem to be making second decisions regarding their long-term position. Other OEMs who have not practiced modularity in the past are now evaluating it themselves. We can help them. We have been involved in modules for a very long time, working with many OEMS, including DaimlerChrysler and BMW. ”
As far as the use of engine cooling modules in Japan are concerned, Takaaki Sakane, general manager, Cooling Systems & Components Engineering Department, Denso Corp, said: “The effects of modules differ with each vehicle but there are carmakers in Japan that aggressively use front-end modules, and we think there are possibilities for this number to increase. We believe the focus is to add more value to modules, and not just think of them as an integration of components.”
In addition to the charge-air coolers, manufacturers see changes ahead for EGR (exhaust gas recirculation) coolers in Europe. Martin Green, Product Marketing Manager, Powertrain Cooling Products, Visteon Corp, said: “We are seeing a significant rise in product fitment. While some engine manufacturers and vehicle manufacturers were able to do without them for Stage 4 [Euro IV], as they ramp up for Stage 5 they have no alternative but to fit EGR coolers. There is obviously going to be some level of by-passing of the EGR cooler for some engine combustion reasons. For those applications there are different types of integration of these by-passes. The significant challenge that stills lays ahead, however, is their design to ensure robustness against soot.”
Keith Wilkins, Product Manager, Heat Exchangers, Visteon Corp added: “Our approach to EGR coolers has been very much one of integrated by-pass functions rather than having a completely different by-pass unit which is bolted to it.”
Figure 2
Visteon’s EGR coolers
Visteon has a range of EGR coolers that incorporate spiral-tube technology with integrated by-pass designs.
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Source: Visteon. |
Although hybrids have not really created a substantial change in the heat transfer philosophy of the engine, we asked manufacturers if this technology has created the need for additional product on the electronic side of the system.
Delphi’s Andrews explained how the North American market for hybrids is developing and the impact on cooling systems. He told us: “Hybrid technology is a very high growth area in the North American market. Almost all [carmakers] are expecting rapid growth. We are working with our customers to support both types of hybrid design [i.e. simple belt alternator driven and the more extensive full electrical system]. We are also working with a customer on battery cooling and ways in which to integrate it with the cabin cooling system. There is now an ever greater need for expertise in thermal management within the vehicle.”
Given that fuel cells emit a higher heat rejection to the cooling system than conventional gas or diesel engines, they pose a far bigger challenge to suppliers. For instance, around 50% of the energy fed into a fuel cell vehicle is emitted as heat rejection compared to just 30% for a gasoline or diesel engine.
Developing engine cooling systems for fuel-cell vehicles is therefore another main thrust of product development. Bosch’s Scherer added: “With fuel cell technology, we see even more use of auxiliary pumps. There will also be a high pressure, high speed charger. The cooling air requirement is even higher. So there will be a greater need for high voltage engine cooling fans.”
With hybrids and fuel cell vehicles in mind, Delphi has developed its so-called Centre Mounted Fan concept. Instead of stacking the condenser, radiator and fan module in the traditional order – electronic cooling fan, condenser and radiator – this concept packages the electronic cooling fan between the radiator and condenser. It addresses tight packaging requirements under the bonnet as Stefan Glober, Technical Director, Delphi Thermal and Interior Systems (Europe), said: “Any type of powertrain which uses a lot of electronics needs to be cooled. Our CMF concept can address a lot of those additional needs in a very effective package.”
Another challenge facing suppliers is the relentless push by vehicle makers to down-size engines for diesel as well as gasoline engines. Upgraded engine cooling modules capable of handling more heat rejection in a smaller space are being introduced. Visteon’s Wilkins told us: “It means we are trying to fit more and more things in. With the emergence of boosted engines, the space for an intercooler becomes pretty much a standard requirement for all car lines. Also, the level of energy that is discharged is steadily increasing. In fact, when you start going to the top end of the market in the luxury cars, heat rejection is doubling from about 25 kW up to 50 kW. It is reaching the point where we can no longer package an air-to-air intercooler.”
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.
Visteon’s Wilkins said: “Generally speaking, pedestrian protection is limiting the height of cooling packs. The laws effectively prevent manufacturers filling the space as fully as they may have done a few years ago. Nowadays, manufacturers must leave a crash space over the top of the radiator. That means finding yet more ways to squeeze more out of the same radiator package.”
Delphi’s Glober concluded: “The immediate impact [from the pedestrian safety legislation] is that our radiator height has to be reduced to allow for packaging a cross-bar on top. That bar helps with the pedestrian protection system yet means an overall 25% reduction in radiator height. As a result, we have developed a new line of radiators – called the AXR range – which offer even higher efficiency. Also, given the fact that the aspect ratio of the radiator has changed, we have designed a new way in which to package the heat exchangers in order to guide the air flow in a very effective manner. As the roll-out of the pedestrian standard occurs between now and 2012, we expect more and more requirements to come as a result of it. We also expect that front-end heat exchanger packages will have to be adopted in a modified manner.”
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