With EU Directive2006/40/EC taking effect in the year 2011, air conditioner systems in cars will have to be equipped with new coolants as well. Starting in 2017, this regulation will apply not only to new vehicle types launched on the market, but the old refrigerant types will then also be forbidden in all new vehicles that are sold starting at that point in time.
Developers at ContiTech Fluid Technology are already working on new products that will make it possible to comply with these regulations. A global warming potential (GWP) of less than 150 will be required to minimise environmental pollution. There are currently two competing coolants: the HFC-based 1234yf and the natural coolant CO2 - and ContiTech has a solution for each of them.
The VDA (Association of the German Automotive Industry) has already chartered a course for greater efforts in the direction of climate protection. In so doing, it has garnered praise from critical organisations such as Greenpeace.
Starting in 2011, CO2, a natural refrigerant, is the only refrigerant to be used in German cars. With a global warming potential (GWP) of 1, the natural gas CO2 is by far the most eco-friendly choice. And it makes it possible already today to completely satisfy the vehicle makers' demands for safe, economical and reliable solutions. ContiTech Fluid Technology is ready. Thanks to years of development work in the area of CO2 ac technology, it is already supplying the refrigerant lines of the future today. "Investments early on in modern plant technology will make it possible for us to supply our customers CO2 line technology from volume production before the current year is out," reports Mike Eismann, head of R&D Air Conditioning Systems at ContiTech Fluid Technology.
CO2 is highly environmentally compatible because its greenhouse potential is just 1/1300th of the value of the R134a refrigerant used today. If CO2 is obtained for the air conditioning system as a waste product from industrial processes, it is even environmentally neutral. In addition, modern CO2 systems are much more efficient than current R134a systems, which is why air conditioners with CO2 as refrigerant require approximately 14 to 25 per cent less fuel for the same cooling power. This reduces not only the exhaust emissions but operating costs as well. Moreover, the complex service and recycling infrastructure required by a coolant such as R134a, which serves as a replacement for CFCs, is not needed for the natural CO2. Taking all of these effects into account, CO2 as refrigerant can reduce the greenhouse effect of air conditioning systems in cars by 40 per cent.
In view of heightened environmental awareness and more stringent regulations, tight hose connections in air conditioning systems are becoming ever more important. Developers at ContiTech Fluid Technology have come up with new products for CO2 that will make it possible to comply with these stringent regulations. However, the system can only be as tight as the connections between the lines. With the ContiLock R forming connection technology, ContiTech has developed the ideal solution for these critical points.
In the ContiLock R sealing concept, a sealing washer made of spring steel and coated paper-thin with elastomer is clamped between the male and female parts. The flexible sealing component compensates for temperature changes and vibrations. "The elastomer layer in this case is so thin as to provide the refrigerant practically no corrosion surface," explains Eismann. It ensures that both parts form a perfectly tight connection - with a leakage rate well below 0.5g per year.
The technology has long since established itself many times over in large-volume manufacturing. It is used for cylinder-head gaskets in modern diesel engines. The principle developed by ContiTech allowed for elimination of leakage problems automotive manufacturers initially had to deal with on account of the radial seals in general use at the time.
In addition to their leakproof quality, the seals exhibit high temperature and pressure stability (up to 176bar and 165°c). Depending on industrial demands, the flange material can be selected from a wide range of options. Seals can be easily installed and are reliably shielded from contamination.
In terms of process reliability and serviceability, the ContiLock R offers customers advantages they cannot realise with seals made completely of metal. Whether it is a matter of installation-related reworking or in conjunction with servicing - after an accident, for instance - the seals can always be loosened and retightened without fear of jeopardising their positive properties. The seals can be replaced without having to remove the lines.
"Because the ContiLock R is cold formed, there are no soldering and welding joints that might pose a leakage risk," explains Eismann. What is more, cold forming is less work and much more cost-effective.
The leakproof quality of the lines themselves is also growing in importance - for CO2 as well as for 1234yf. In the past, stainless steel corrugated tubing was the only way to ensure that the lines for CO2 were leakproof.
ContiTech Fluid Technology has now developed a hose for air conditioning lines with the natural refrigerant CO2 that no longer requires corrugated stainless steel tubing to form a barrier layer as it did in the past. A polymer barrier layer inside the hose keeps permeation to a minimum. "The hose is much more flexible than the previous solution, and makes tighter bending radii possible," says Eismann, listing important benefits of this solution. In addition, the elastomer hose with the barrier layer demonstrates much better acoustic properties and offers significant cost advantages in comparison with the corrugated tube hose solutions.
Permeation describes the penetration of a gas through a solid. Permeation occurs in three steps, always in the direction of lower concentration: sorption (absorption on the surface of the solid), diffusion (passage through the solid via pores or gaps between the molecules) and desorption (escape from the solid via the surface).
For developers of an air conditioning line for the refrigerant CO2, the crux of the problem was finding a material that reliably contains CO2 in supercritical situations, even at temperatures and pressures above the critical level of 31°c and 73bar (ca.1059psi). In air conditioners, a change in condition, combined with a sudden drop in CO2 density, can lead to what is called explosive decompression, which destroys the polymer materials.
The problem was solved by using a polymer barrier layer which effectively holds back the CO2, combined with an inner elastomer lining, both of which are resistant to the system's pressure and high temperature.
At low- and high-pressure ranges, the permeation rate of the elastomer hose with a barrier layer is about 3g per meter and year, which is a considerable improvement over the current customer requirement of 15g. The only area where this new product does not yet represent an alternative is in hot gas service, where it needs to withstand temperatures up to 180°c. At present, it is only able to withstand temperatures of up to 100°c.
Trials with various HFC-based refrigerants show that the polymer barrier layer reduces permeation to nearly 0g. This is not merely eco-friendly. It also guarantees maintenance-free operation of the future ac unit. It will be ready for volume production by 2011.
More demanding requirements for the leakproof features of air conditioning lines automatically ups the quality demands for permeation measurements. To satisfy these demands, ContiTech has invested in a modern permeation test rig that measures the values for the gases R134a and CO2.
The test piece is flushed by a nitrogen mass flow that transports the permeated molecules to the analyser. With the help of infrared spectrometry, permeation is recorded to an accuracy of 0.01g per year. Alongside an enormous increase in accuracy, measurements that previously required weeks can now be taken care of in days.
Enter 20 or at www.engineerlive.com/ede
Mario Töpfer is with ContiTech AG, Hanover, Germany. <a href="http://www.contitech.de"target=_blank>www.contitech.de</a>
