Air compressors affect the functioning of a number of vehicle components, perhaps the most crucial being the truck's air braking system. With this in mind, manufacturers such as Bendix Commercial Vehicle Systems, Haldex Brake Systems, and Meritor WABCO Vehicle Control Systems all continually strive to improve the oil carryover performance of this component, since even small amounts of oil in the air passages can lead to problems in air-brake systems.
The effort to reduce oil carryover is described by Bendix as an "evolutionary" process made up of many small design changes, as well as changes in the manufacturing process itself to make those design changes possible. Design enhancements include better finishes on mating parts and changes in ring tension and thickness, as well as ring design. And according to Meritor WABCO, its proprietary bore finishing process has substantially reduced oil passage.
Manufacturers point out that new machining technology can be as important as design changes in reducing oil carryover. In fact, changing design parameters is only the first step. The second step is making air compressors with greater precision. For example, Bendix has been able to take advantage of technology that reduces from three to one the number of machining centers necessary to make an air compressor crankcase, eliminating the variability inherent in a multi-step production process.
Focus on efficiency Another trend in air compressor design is the development of products that are smaller and lighter, yet at the same time more efficient. Weight reduction has been accomplished through the use of aluminum parts by both Meritor WABCO and Bendix, although higher cost and concerns over strength capacity are two disadvantages that limit the use of aluminum.
The need for more efficient air compressors has evolved primarily out of the demand for increased air output on today's vehicles. For example, aerodynamic truck design and increased road congestion mean that air brakes have to work harder. In addition, more and more fleets are spec'ing air suspensions to provide a more comfortable ride for drivers.
One example of an approach to this problem is Bendix's use of reed valves to improve the control of air into and out of the compressor.
The industry can expect to see even more dramatic changes in air compressor technology in the future. According to Haldex, air compressors could run much more efficiently if they had "smart" governors that would tell the compressors to work only while vehicles are coasting. Counted among the benefits of this type of intelligent system might be better fuel economy and perhaps even a decrease in the size of the compressor. In fact, in Germany smart governors are already being made with just such a feature for use in Europe's commercial truck market.
Haldex also talks about the possibility of a new kind of drive that would maintain a constant compressor speed regardless of engine speed, enabling a smaller air compressor design. With current technology, air compressor size is determined by output at idle, making them in effect "oversized" for what's needed at engine speed.
Less is more Increased efficiency has led to the introduction of air compressors that use fewer cylinders to generate the same output. Bendix offers the DuraFlo 359, a single-cylinder air compressor for the linehaul market that accomplishes what the company's previous generation two-cylinder unit did. And for extra heavy-duty applications, a unit with only two cylinders now replaces one with four.
According to Meritor WABCO, its System Saver 318 is a single-cylinder design that can meet the needs of applications that would usually require two cylinders, including linehaul and some off-road applications. It can also be spec'd on medium-duty trucks with air-brake systems. In addition, Meritor WABCO is currently looking at the need for a high-output product for extremely heavy-duty applications.
Haldex offers the EL 850, a single-cylinder compressor that's targeted to medium-duty applications. The company's EL 1300 and EL 1600 two-cylinder units are designed for linehaul operations. Larger air compressors for the extra-heavy-duty market are also available from Haldex.