Compressor Flow Control for Oil Return in Dual Evaporator Cooling
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Solution Overview
Problem
In dual-type vehicle air conditioners, the low refrigerant flow rate leads to oil return issues and temperature variations in the evaporator, particularly due to the long refrigerant pipe path and pressure loss, which existing control methods fail to adequately address by intermittently changing compressor discharge displacement without proper temperature control.
Innovation Solution
A refrigerating cycle device that judges the refrigerant flow rate and adjusts compressor discharge flow rate accordingly, switching from intermittent to continuous control when the evaporation temperature change is gradual, and controls between a near-threshold and zero flow rate to prevent oil lack and temperature variations, using a variable displacement compressor with a control valve or electric compressor to manage rotation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the discharge flow rate of the compressor is reduced to address low refrigerant flow rate, then the cooling performance is improved, but the oil return to the compressor deteriorates
Solution Approach 1:
The control device implements periodic action by switching the compressor discharge flow rate between a first flow rate (when refrigerant flow rate is high) and a second flow rate lower than the first (when refrigerant flow rate is low). This periodic adjustment ensures that oil is periodically flushed back to the compressor during low flow rate conditions, preventing oil accumulation in the evaporator while maintaining cooling performance when conditions permit.
2Measurement precision
If the discharge flow rate of the compressor is controlled continuously according to evaporator cooling degree, then the cooling control precision is improved, but the oil return problem worsens when refrigerant flow rate is low
Solution Approach 1:
The control device employs feedback by continuously monitoring the refrigerant flow rate and adjusting the compressor discharge flow rate accordingly. When the refrigerant flow rate falls below a predetermined threshold, the system automatically switches to a lower discharge flow rate mode, ensuring oil return is prioritized. This feedback mechanism allows the system to adapt to changing operating conditions and prevent oil accumulation while maintaining efficient cooling when conditions are favorable.
3Reliability
If the compressor operates intermittently to prevent oil accumulation in evaporator, then the oil return is improved, but the temperature variations in evaporator discharged air worsen
Solution Approach 1:
The control device implements dynamics by continuously adjusting the compressor discharge flow rate based on real-time refrigerant flow rate conditions. Rather than simple intermittent operation, the system dynamically switches between two discharge flow rate levels, allowing smooth adaptation to changing conditions. This dynamic control maintains more stable evaporator temperatures while ensuring oil return when refrigerant flow rate is low, avoiding the temperature fluctuations associated with crude intermittent operation.
Data Source
AI summary
Whether or not a flow rate of a circulating refrigerant is higher than a predetermined threshold value is judged and when the flow rate is higher than the predetermined threshold value, the discharge flow rate of a compressor 11 is controlled in accordance with the degree of cooling of a front seat evaporator 9 and when the flow rate is lower than the predetermined threshold value, the discharge flow rate of the compressor 11 is controlled so as to intermittently change between a discharge flow rate near the predetermined threshold value and a flow rate of substantially zero and the operation time of the compressor 11 during the period of that control is measured and when the compressor operation time exceeds a predetermined time, the compressor is continuously controlled in accordance with a discharge flow rate near the predetermined threshold value.