Single-Screw Compressor Pressure Equalization During Braking
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Solution Overview
Problem
In single screw compressors, the pressure equalization between high and low pressure units during rotation braking control is slow, leading to potential damage or wear of the gate rotor due to oil flow and counter-rotation, especially when the braking control time is limited.
Innovation Solution
A freezing device with a compressor that includes a communication flow path and a flow control valve, controlled by a controller to perform pressure equalization alongside rotation braking control, ensuring the pressures in the high and low pressure units are equalized quickly, thereby preventing counter-rotation and damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rotation braking control is performed by applying direct-current voltage to the motor stator to prevent motor rotor rotation, then the screw rotor counter-rotation is suppressed, but refrigerant flows through small flow paths (minute gap between screw rotor and casing, oil feed hole) causing long pressure equalization time
Solution Approach 1:
The invention divides the pressure equalization process into two independent pathways: (1) the original small flow paths (minute gap and oil feed hole) and (2) a newly introduced large flow path through the discharge port. This segmentation allows refrigerant to equalize pressure through multiple routes simultaneously, with the large discharge port pathway providing rapid pressure equalization while the small pathways continue to function for oil feeding and lubrication.
Solution Approach 2:
The discharge port acts as an intermediary element that mediates between the high pressure unit and low pressure unit. By opening the discharge port during braking control, it provides a controlled intermediate pathway for refrigerant flow, enabling fast pressure equalization without directly compromising the sealing and lubrication functions of the small gaps and oil feed holes.
2Reliability
If pressure equalization takes a long time during braking control, then the screw rotor and gate rotor are protected from counter-rotation damage, but oil continues to flow from high pressure unit into compression space causing potential liquid compression and gate rotor failure
Solution Approach 1:
The invention segments the oil feeding function from the pressure equalization function. The small oil feed hole continues to provide lubrication oil to the compression space through differential pressure, while the large discharge port pathway handles the bulk pressure equalization. This segmentation prevents excessive oil accumulation in the compression space while maintaining necessary lubrication.
Solution Approach 2:
The invention maintains continuous oil feeding through the oil feed hole during braking control, ensuring that the compression mechanism remains lubricated even while pressure equalization occurs. The continuous oil flow prevents dry friction and wear during the braking period, while the controlled pressure gradient prevents excessive oil accumulation that would cause liquid compression.
3Speed
If braking control time is limited by inverter capabilities, then the system responds quickly to stop commands, but pressure equalization cannot be completed and screw rotor counter-rotation damages the gate rotor
Solution Approach 1:
The invention segments the pressure equalization function into two time scales: rapid initial equalization through the large discharge port pathway and continued gradual equalization through the small oil feed hole and gap pathways. This segmentation allows the system to achieve sufficient pressure equalization within the limited inverter braking time window, preventing gate rotor damage even with short braking durations.
Solution Approach 2:
The invention performs preliminary pressure equalization action by opening the discharge port before the inverter braking control ends. This preliminary action reduces the pressure differential during the critical braking period, preventing excessive counter-rotation forces that would damage the gate rotor, while the braking control completes its fixed-duration protection function.
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
The solution reduces the time needed for pressure equalization, preventing damage to the compression mechanism and reducing the risk of oil flow issues during startup, thus protecting the gate rotor and maintaining compressor efficiency.
Implementation Method 1
refrigerant flows from a high pressure unit into a low pressure unit, and the pressure in the high pressure unit and the pressure in the low pressure unit are equalized with each other
Implementation Method 2
a direct-current voltage is applied from an inverter to a motor stator in the compressor to perform control such that the motor rotor does not rotate
Data Source
AI summary
A freezing device including a compressor that compresses sucked refrigerant using a compression mechanism and discharges compressed refrigerant includes a compressor, an inverter, and a controller. The compressor includes a motor, a low pressure unit, a compression space, a high pressure unit, a communication flow path, and a flow control valve. The inverter drives or stops the motor. The controller controls the inverter and the flow control valve. The controller performs, in stop control in which an operation of the compressor is stopped, braking control in which driving of the compression mechanism is prevented or suppressed, and pressure equalization control in which pressure in the high pressure unit is equalized with pressure in the low pressure unit.