When a car engine is running, be it diesel or petrol, unluckily not all the energy contained in the fuel is turned into power available to make the vehicle move. In different proportions, depending on engine speed and running conditions, approximately 30% of the “chemical energy” contained in the fuel is dispersed as heat generated by combustion. If this heat is not controlled, the increase in temperature it produces may reach values which are critical to the structural integrity of the engine itself. The main purpose of the cooling system is that of maintaining the temperature of the metal parts of the engine within foreseen limits, so as to guarantee the engine’s good performance and reliability.

The main components of the engine cooling system are the heat exchangers that guarantee the disposal into the atmosphere of that part of energy which is contained in the fuel and is not turned into energy available to move the vehicle. Car heat exchangers are made of a bundle of small tubes containing the hot fluid to be cooled. Thin fins are fixed onto the tubes: by conduction of their metal they “extract” the heat from the tubes and by convection they dissipate it into the air all around. A DENSO radiator with a 0.2 sq. m front surface has over 6 sq. m cooling surface on the fins.

The tubes and fins of an automotive heat exchanger are made of metals with a high level of conductivity and light weight, allowing for small surface thicknesses to be machined. Copper and aluminium have these features. Contact between tubes and fins is achieved with two kinds of technologies, braze welding and mechanical deformation (pressing” the tube against the fin).

DENSO develops and produces heat exchangers using both technologies. In the 1st case the contact is established by braze welding in controlled atmosphere continuous furnaces, in the 2nd case by mechanical expanding on automated production lines.

The performance of the heat exchanger actually depends on the technology used. Welding produces a “closer” contact between tube and fin and guarantees a more efficient transmission of heat if compared with the contact produced by mechanical deformation. However, the production costs of braze welded heat exchangers are higher vis-a-vis the machine expanded ones, thus assuring a balance between cost and performance.

Within this range of technologies, DENSO develops heat exchangers which are appropriate for the car and the engine they are to be fitted to using its capability of calculating on forehand the performances of the products and of checking the effectiveness of the decisions made with the help of advanced testing equipment.

Heat exchanger development in DENSO is based on a procedure involving a set of rigorous tests to make sure all product features are inspected before mass production. Mechanical resistance tests, high temperature, pressure resistance and corrosion tests are carried out before approval, to check product reliability.