Variable Displacement Compressor
A variable displacement compressor eliminates the need for a cycling clutch by altering the compressors volume based on system demands. The compressor does not contain a cycle switch to cycle the compressor on and off. The displacement or output of the compressor is altered by changing the stroke of the pistons.
The pistons are attached to an axial wobble plate that changes angle based on the difference in pressure between the top of the piston and the back or housing side. When cabin temperatures are warm and air conditioning performance is high suction pressure will also be high. During this time the compressors wobble plate is moved to its greatest angle providing maximum displacement. As demand decreases the wobble plate is moved to a lesser angle providing lesser or minimum output.
This is accomplished with a control valve connected to the suction and discharge ports in the compressors head. This valve may be a mechanical or computer controlled valve. The mechanical valve has a diaphragm that responds to changes in low side pressure. As this valve opens it increases piston stroke. As piston stroke increases so does the volume or displacement of the refrigerant flow through the compressor.
A computer controlled system contains temperature and pressure sensors. An ECM or air conditioning module controls the valve adjusting compressor displacement. They offer a reduced potential for noise and drain on the system. This type of compressor puts less load on the engine resulting in slightly improved fuel economy and a smoother idle.
