Rotary vane compressor improves AC efficiency

Vancouver, BC, Canada--Since the phase-out of Freon(TM), many car air-conditioning systems have suffered performance losses. As evidence, you can probably recall switching the AC onto MAX (or recirculate) mode in late models just to get passable cooling in the nastiest hot, humid weather.

This cooling crunch occurs primarily because of Freon's replacement, HFC-134a. It transfers heat only half as well as Freon. In an attempt to maintain cooling power, engineers have raised system pressures,

increased flow rates, and (where possible) upsized components. But upsizing runs counter to the major new trend towards cab-forward design, which seeks to reduce under-the-hood real estate.

Fortunately for drivers, the Big Three will soon be examining a compact cooling solution. REG Technologies, in an arrangement with a major automaker, has prototyped a smaller, more efficient compressor design based on its patented Rand Camengine design.

Half the size of the unit it's designed to replace, the new positive-displacement compressor measures about the same 4 inches in diameter but half the length. It runs at 1.5engine speed--to 10,000 rpm--and displaces a required 10 cu-inches per revolution. Yet it provides 15 to 20% more cooling capacity than the unit now used. And its volumetric efficiency is 15 to 20% greater than the axial-piston compressor it may replace.

According to Pat Badgley, manager of technology development at REG Technologies, the Rand Camcompressor achieves a compression ratio between 200 and 300, and operates on a two-stroke cycle. The unit's operational inlet and outlet pressures vary greatly, he says, but can't be divulged because they are proprietary automobile manufacturer's knowledge.

The valveless Rand Cam compressor contains a rotor with six axial vanes that slide in milled slots. This assembly rotates within a cam housing made up of two stator halves. Each stator has a single-cycle toroidal trough that is 180 degrees out of phase with the other. This arrangement creates six captured volumes per side to create12 full compression cycles per revolution.

In operation, as the rotor rotates, the vanes ride the axial cam profile through a bottom dwell section, an upward ramp, a top dwell section, and a downward ramp. The cycle pulls vaporized refrigerant inward through a simple port as the volume expands, compresses it to a liquid as the volume decreases, and then pushes it through another port and on to the condenser. The ports do not overlap, and the cam's dwell sections provide the two-stroke operation alluded to above and the high efficiency.

Engineers used diecast aluminum for the prototype compressor's housing and rear cover. In production, the cams may be fabricated from powder metal (aluminum). Groove-seated polymeric metal seals ensure sealing between vanes. To protect the parts in sliding contact, a friction-reduction, anti-wear, and corrosion-inhibition coating is applied to the inner, outer, and cam housings in which the seals ride.

West Virginia University provided analytical assistance during the design of the compressor. Various geometric, volume, surface area, thermodynamic, and force analyses were conducted at WVU using custom Fortran codes and SDRC's IDEAS(TM), as well as with software from Algor and ANSYS. These models ran on Digital Alpha-based equipment and computers made by Silicon Graphics.

When the compressor is employed in the engine of a vehicle, its one-lift cam profile ensures reduced wear at high rpms. But a switch to multiple-lift cam profiles can enable engineers to achieve greater pumping efficiency at lower rpms. This capability makes the Rand Cam compressor unmatched, says Badgley. "If you really want to pump a lot of fluid with a small package, be it air or oil or hydraulics or whatever, we don't know of any other mechanism that can do what this one does."

Additional details...Pat Badgley, REG Technologies, #185-10751 Shellbridge Way, Richmond, BC V6X 2W8, Canada, (604) 278-6996.