Compressor With Variable Cylinder Displacement
The pistons are driven by a cam pulley, the angle of which can vary.
When the compressor is disengaged, the angle is determined by the springs.
When the compressor is engaged, the angle is determined by the pressure affecting the top side of the pistons (= intake pressure) and lower side (= pressure in the crank case) during the intake phase.
The pressure on the lower side of the pistons (= in the crank case) is governed by a valve which keeps the intake pressure constant.
High intake pressure = large cylinder displacement
The valve opens and lowers the pressure in the crank case. The back pressure on the reverse of the pistons is then reduced and the angle of the cam pulley increases.
An increased angle gives an increased cylinder stroke which results in a greater volume of refrigerant being sucked in and the outlet pressure dropping.
Low intake pressure = small cylinder displacement
The valve closes and the pressure in the crank case increases. The pressure is built up by the refrigerant which is led via a calibrated channel from the outlet side to the crankcase.
The back pressure on the reverse of the pistons is then increased and the angle of the cam pulley reduces.
A reduced angle gives an reduced cylinder stroke which results in a smaller volume of refrigerant being sucked in and the outlet pressure increasing.
The advantages of this type of compressor are:
The flow of refrigerant is continually adapted to requirements.
Few engagements/disengagements providing good driving comfort.