Scroll Compressor Back Pressure Cavity Reduces Motor Start-Up Load
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Solution Overview
Problem
Scroll compressors face a high start-up load on the motor due to the rapid filling of the back pressure chamber, which increases the resistance and load on the motor as the scroll members begin to orbit, preventing effective compression until they are biased together.
Innovation Solution
A large cavity is introduced in the back pressure chamber that must be filled with compressed refrigerant before the scroll members can engage, reducing the initial load on the motor by allowing them to move out of contact initially and then being driven into contact once the cavity is filled, effectively increasing the volume of the back pressure chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the back pressure chamber is filled quickly with compressed refrigerant, then the scroll members are biased together rapidly, but the start-up load on the motor increases significantly
Solution Approach 1:
The patent introduces a large cavity that must be filled with compressed refrigerant before the scroll members can engage. This preliminary filling action delays the engagement process, allowing the motor to accelerate the scroll members without immediately encountering full compression resistance. The large cavity acts as a buffer that absorbs the initial compression force, reducing the peak load on the motor during start-up.
2Power
If the back pressure chamber volume is increased, then the start-up load is reduced, but the time to reach full compression increases
Solution Approach 1:
The patent changes the volume parameter of the back pressure chamber by introducing a large cavity that is more than twice as deep as the seal grooves and extends for a greater radial distance. This parameter change increases the chamber volume, which delays the point at which compressed refrigerant can build sufficient pressure to bias the scroll members together. The increased volume allows the system to reach full compression later in the rotation cycle, reducing peak motor load during start-up.
3Power
If the scroll members are allowed to move out of contact initially, then the motor load is reduced, but compression efficiency decreases
Solution Approach 1:
The patent creates a periodic phenomenon where the scroll members alternately engage and disengage during rotation. During the first portion of the rotation cycle, the members remain out of contact, allowing the motor to operate with minimal load. As the rotation progresses and the large cavity fills with compressed refrigerant, the members are gradually biased together, increasing compression efficiency progressively rather than immediately. This periodic engagement pattern allows the system to optimize between motor load and compression efficiency at different stages of the rotation cycle.
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 solution reduces the start-up load on the motor by allowing the scroll members to move out of contact initially, minimizing motor resistance until the cavity is filled, thereby reducing the initial load and enabling normal operation once the members are biased together.
Implementation Method 1
A compressed refrigerant is tapped into this chamber, and creates a force tending to hold the two scroll members in contact with each other
Implementation Method 2
A separating force is created by the compressed refrigerant that tends to push the two scroll members away from each other
Data Source
AI summary
A scroll compressor is provided with a cavity in its back pressure chamber to increase a volume of the back pressure chamber. In this manner, at start-up, the back pressure chamber will not be effective to bias the two scroll members together until this enlarged volume is filled with a compressed refrigerant. This reduces the load on the electric motor at start-up.