Bus A/C: Compressor Under Revolution

A/C compressors currently used on buses (school buses, city buses and coaches) have remained practically unchanged since the 1970s. These compressors are cumbersome — over 150 pounds, V-shaped and uneasy to mount. Their reciprocating technology using four or six crankshaft pistons requires devices called “unloader valves” to regulate their operation. These compressors have failed at tackling the goals of size reduction and fuel economy by solely focusing on durability and performance. The industry was longing for another solution; one that would be more complete and better adapted.

Valeo, a global designer and manufacturer of heavy-duty A/C compressors, rose to the challenge. After years of R&D/engineering homework, and laboratory/field trials under the toughest climates, Valeo released three swash plate compressors engineered to pioneer a new age of bus A/C: the TM65, TM55 and TM43.

These cubic-shaped compressors are about 50 percent lighter and smaller in volume than today’s average V-type reciprocating compressor. Three simple benefits — cubic, lighter, smaller — make them ideal to be mounted directly to, or right next to the engine. In addition to being easier to install, they save precious space to enable the integration of fuel economy parts such as the Ad-blue tanks. This innovative design is made possible by an internal technology, comprising more cylinders, an enhanced housing mounted clutch, and a unique anti-leakage shaft seal.

Fourteen cylinders and seven double-headed pistons for the TM65 and TM55 (10cyl, 5 pistons for TM43) make them the most efficient in their range through unmatched levels of performance and fuel economy. A result of their heavy-duty compact design, up to 40 percent less internal parts are used in the TM65/TM55 and TM43 vs. reciprocating compressors. Straightforward engineering: fewer parts mean less failure modes, which, in turn, increase reliability.

Being housing mounted as opposed to shaft mounted, the balanced clutch weight reduces the risk of clutch, bearing or shaft issue. It also lowers noise and vibration. Furthermore, Valeo’s clutch design regulates the compressor capacity, eliminating the need for unloader valves.

Thanks to its housing mounted clutch, the shaft rotates independently from the clutch movement, and its Valeo lip type shaft seal ensures flawless air tightness under any usage conditions, even in winter. No additional refrigerant or leakage check is required before using the A/C. In comparison, reciprocating compressors have non-rotating shafts that need mechanical seals, which notoriously do not maintain perfect air-tightness, leading to oil or refrigeration leakage.

The Valeo TM range is now one of the world’s largest A/C compressor lines, with displacements ranging from 82cc (TM08, tractor type) up to 635cc (TM65, large buses). For more information, visit http://www.valeocompressors.com