Vehicle Air Conditioner Startup Control for Low Suction Pressure
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Solution Overview
Problem
Conventional air conditioners for vehicles face issues with low pressure protection in the refrigerant circuit, leading to compressor and component damage due to rapid drops in suction refrigerant pressure, especially during startup in low outdoor temperatures, as the suction temperature sensor response delay prevents timely adjustment of compressor revolutions.
Innovation Solution
The air conditioner incorporates a control system that adjusts the compressor's revolution based on detected suction refrigerant temperature or pressure, setting a limiting upper limit initially and gradually decreasing it to a lower limit, with auxiliary heating on startup to prevent pressure drops, and uses data to adjust the upper limit number of revolutions according to outdoor temperature to maintain safe pressure levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the compressor number of revolution is rapidly increased on startup in heating mode, then the heating performance is improved, but the suction refrigerant pressure rapidly drops causing compressor damage
Solution Approach 1:
The system performs preliminary action by detecting startup conditions and pre-adjusting the compressor number of revolution to a predetermined value before rapid increase, ensuring suction pressure remains above the lower limit. This prevents pressure drop damage while enabling subsequent heating performance optimization.
Solution Approach 2:
The system dynamically adjusts the compressor number of revolution in stages: initially setting to a predetermined value, then rapidly increasing to a target value based on temperature difference, while continuously monitoring suction pressure. This dynamic control ensures both reliability and heating performance.
2Device complexity
If a fixed limiting target value is used for suction refrigerant temperature, then the control system is simple, but the actual suction pressure drops below the target value causing overshoot and component damage
Solution Approach 1:
The limiting target value is changed from a fixed value to a dynamic value that varies based on outdoor air temperature. The control unit stores multiple limiting target values corresponding to different temperature ranges and selects the appropriate value during operation. This dynamic adjustment prevents overshoot and ensures accurate compressor protection while maintaining reasonable control complexity.
Solution Approach 2:
The system changes the parameter of limiting target value based on outdoor temperature conditions. By storing predetermined limiting target values for different temperature ranges and selecting the appropriate value, the system adapts to varying operating conditions, preventing suction pressure from dropping below safe levels while avoiding overly complex real-time calculations.
3Device complexity
If the suction temperature sensor response delay is not compensated, then the detection system is simple, but the compressor number of revolution cannot be adjusted in time leading to pressure drop and damage
Solution Approach 1:
The system compensates for sensor response delay by performing preliminary action: when the suction temperature approaches the limiting target value, the control unit proactively decreases the compressor number of revolution before the actual pressure drop occurs. This anticipatory control ensures timely protection despite sensor delay.
Solution Approach 2:
The system uses feedback from the suction temperature sensor to continuously monitor the approaching limit condition and adjusts the compressor number of revolution accordingly. The feedback loop enables the system to respond to temperature changes and prevent pressure drop, compensating for the inherent sensor response delay.
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 approach enhances low pressure protection, preventing compressor and component damage by reducing overshoot and improving reliability through earlier and more accurate pressure management, even with response delays, and ensures stable operation across varying outdoor temperatures.
Implementation Method 1
a radiator disposed in this air flow passage to let the refrigerant radiate heat, thereby heating the air to be supplied to the vehicle interior
Implementation Method 2
an outdoor heat exchanger disposed outside the vehicle interior to let the refrigerant absorb heat, thereby heating the vehicle interior
Data Source
AI summary
Air conditioner for a vehicle in which low pressure protection is accurately performed to improve reliability. A controller adjusts a number of revolution Nc of a compressor 2 so that a detected value does not decrease below a limiting target value TGTs, on the basis of the detected value of a suction temperature sensor and a limiting target value TGTs set to a suction refrigerant temperature of the compressor 2. The controller has a predetermined limiting lower limit TGTsL and a predetermined limiting upper limit TGTsH which is higher than the predetermined limiting lower limit, and adjusts the number of revolution Nc of compressor 2 so that the limiting target value TGTs is the limiting upper limit TGTsH on startup of compressor 2, and the controller gradually decreases the limiting target value TGTs toward the limiting lower limit TGTsL, when the detected value decreases to the limiting upper limit TGTsH.