Reciprocating Compressor Rotor Positioning to Prevent Upper Dead Point Stopping
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Solution Overview
Problem
In refrigeration compressors with reciprocating pistons, the piston often stops at the upper dead point when the motor turns off, leading to reduced sealing capacity of the discharge valve, causing significant refrigerant fluid return from the condenser to the compressor, which increases thermal load and reduces energetic efficiency.
Innovation Solution
A reciprocating refrigeration compressor design that utilizes a cogging torque generated by the relative positioning of magnet segments on the rotor and stator teeth to prevent the piston from stopping at the upper dead point, ensuring sufficient pressure differential for valve closure by creating an unstable balance that forces the rotor and crankshaft to rotate to a stable position, displacing the piston away from the upper dead point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the compressor stops with the piston at the upper dead point, then the motor stops efficiently, but the discharge valve sealing capacity is significantly reduced causing refrigerant leakage
Solution Approach 1:
The patent applies preliminary anti-action by pre-positioning the rotor and crankshaft such that when the motor stops, the piston is automatically displaced from the upper dead point position. The rotor is positioned at an angle between 10° and 170° relative to the crankshaft, creating an unstable equilibrium that forces the piston away from the dead point before stopping occurs, thereby preventing valve sealing failure
Solution Approach 2:
The patent changes the angular parameter relationship between the rotor and crankshaft. By setting the rotor angular position within 10°-170° relative to the crankshaft, the system transforms the stopping position from a stable dead point (180°) to an unstable position that automatically displaces the piston, maintaining pressure differential and valve sealing capacity
2Productivity
If the piston stops at the upper dead point, then the compression cycle completes, but refrigerant fluid returns excessively from condenser to compressor increasing thermal load
Solution Approach 1:
The system prevents the harmful effect of refrigerant return by pre-positioning the rotor-crankshaft assembly to create an unstable equilibrium at the upper dead point. This preliminary positioning ensures that before the motor stops, the piston is already displaced, maintaining pressure differential and preventing the pressure equalization that would cause refrigerant to flow back through the expansion device to the evaporator
3Reliability
If the rotor and crankshaft are positioned to avoid upper dead point stopping, then valve sealing is maintained, but the motor stopping position becomes unstable
Solution Approach 1:
The patent inverts the traditional approach by creating an unstable equilibrium position instead of a stable one. By positioning the rotor at 10°-170° relative to the crankshaft, the system creates a position where any small disturbance causes the piston to move away from the upper dead point, using the instability itself as the mechanism to ensure valve sealing
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design stabilizes the rotor-crankshaft assembly in a position that maintains valve closure, reducing refrigerant leaks and enhancing the energetic efficiency of the refrigeration system by preventing excessive fluid return and thermal energy transfer.
Implementation Method 1
a cogging torque generated by the relative positioning of magnet segments on the rotor and stator teeth to prevent the piston from stopping at the upper dead point
Data Source
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AI summary
The compressor comprises: a crankcase (B) carrying a cylinder (11) and a bearing hub (50) which lodges a crankshaft (60); a valve plate (40) closing one end of the cylinder (11); a piston (20) reciprocating in the cylinder (11) and driven by the rotation of the crankshaft (60); an electric motor (M) having a stator (70) affixed to the crankcase (B) and provided with winding grooves (71) and teeth (72), each tooth carrying a respective shoe (72a), and a rotor (80) affixed to the crankshaft (60) and carrying magnet segments (81). 0 stator (70), the rotor (80) and the crankshaft (60) are mounted in an indexed way, in order to present, in relation to one another, a relative positioning which produces, upon the stop of the electric motor (M) and with the crankshaft (60) and rotor (80) being in the upper dead point condition of the piston (20), a cogging torque capable of taking the piston away from the upper dead point.