TI Group Automotive Systems, the world's leading supplier of fluid carrying and delivery systems, is aiming to revolutionise the manufacture of vehicle air-conditioning systems with the development of a concentric tube.

TI Group Automotive Systems has accumulated more than 30 year's expertise in heating, ventilation and air conditioning systems, specialising in rigid tube, flexible tube, receiver driers, accumulators and connector technology. The patented design of this two-in-one tube, called the Co-tube, offers significant benefits to the vehicle manufacturer.

The design simplifies the installation process by eliminating the requirement of separate tubes to carry the forward and counter flows between the compressor and expansion device. As a result of its stronger design, the manufacturer will use a lesser number of fittings to support the tube, while installation times are shortened. The Co-tube will also complement vehicle design as it frees up valuable space saved by the double purpose tube.

In addition to a more efficient installation process, extensive testing has shown that the concentric tube can improve the efficiency of the air conditioning system, especially in rear systems. This is a result of the benefits of the heat exchange between both the forward and counter flows which are carried alongside each other.

Product development manager, Charles Thrift, has been involved in the project since the start, working alongside a team of experts in materials technology and engineering.

He explains: "The pressure today is to provide manufacturers with ever more compact and lightweight components and this is the point we started from in formulating our design. The principle of combining an inflow and outflow tube in one has already been established within the refrigeration industry. We wanted to see if the same principle could be applied to the tubing for an air-conditioning unit, whilst still meeting all the stringent criteria required to meet or even exceed the needs of the automotive industry.

"In anticipation of these needs we set forth with the objectives of not only saving space and reducing packaging but also of improving performance, strength and flexibility.

"We looked at a number of types of designs using Cad-Cam technology and then started prototyping. We were interested in establishing the best method and the most efficient materials for facilitating two separate flows, as well as the most efficient way to engineer and manufacture the product with the aim of making it as cost-efficient as possible.

"All the product development team's expertise was drawn from in-house at our facilities in Florida, where the new Co-tube has undergone extensive testing. Our testing laboratory, like 70 other TI Automotive system sites around the world, is QS - 9000 certified and covers current industry testing requirements as well as customer specific needs. In the laboratory environment, using system simulation, noise evaluation, vibration, thermal/pressure cycling and coupling testing, we can ensure that all our components meet or exceed the strict criteria and standards each customer demands. Testing under various conditions, including how well it works in the vehicle, has been an important part of the process to getting it to the point where manufacturers can be confident in this exciting new product. We are buying vehicle components to continue simulation tests to ensure that this new component performs under any conditions.

"The need for Co-tube was evident in the problems inherent in traditional designs. Typically, vehicle air conditioning units include supply and return conduits for carrying pressurised liquid or vapour. These conduits require certain thermal conductivity properties for maintaining fluid phases, structural integrity for supporting the pressurised fluid, and flexibility for packaging within the unit in the engine. Because these systems generally comprise bulky, independent supply and return lines, packing can be problematic. Again, limited space requirements in the vehicle as a result of weight reduction goals compound this problem.

"The Co-tube overcomes these shortcomings by providing a way to convey fluids in opposing directions via inner and outer tubes positioned concentrically and connected by one or more radially extending ribs. The inner tube is adapted to carry the first fluid in one direction, and channels formed between the inner and outer tubes carry a second fluid in the opposite direction. The design significantly reduces space requirements in comparison to traditional systems without loss of structural integrity of heat transfer characteristics. The lightweight, bendable design enables easy packaging in the vehicle and includes a novel coupling for connecting the inner tube and the channels with the supply and return pipes.

"More specifically, the Co-tube provides a way of conveying fluids in a vehicle air conditioning system in a configuration which maintains the high pressure liquid refrigerant below its evaporating point prior to reaching the evaporator. In effect the outer tube acts as a suction-side heat exchanger between the evaporator and compressor, thereby helping to ensure that no liquid refrigerant reaches the compressor.

"The outer tube, inner tube, and radially extending ribs are an aluminium extrusion, which is bendable to facilitate packaging the apparatus in the vehicle, while the double tubing provides extra strength and rigidity.

"Originally designed for Chrysler's Jeep Cherokee, we have been talking to a number of other manufacturers interested in the advantages afforded by the new tubing. We have been presenting to a number of them and the Co-tube continues to undergo rigorous tests under their specific environments prior to its acceptance on vehicles. We expect most of this testing to be completed by the end of the year and are extremely excited by the positive response it is already receiving," concluded Thrift.

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TI Group plc
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