Vehicle A/C Compressor Cycling Limits for Stable Discharge Air
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Solution Overview
Problem
Existing compressor cycling control methods in air conditioning systems struggle to achieve an optimal tradeoff between compressor cycling frequency and discharge air temperature variation across different operating conditions, leading to inadequate occupant comfort and compressor durability.
Innovation Solution
A dynamic control methodology adjusts the compressor cycling limits based on discharge air temperature, re-heating conditions, and ambient temperature to maintain a constant discharge air temperature variation or comfort level, using mathematical models to determine the required evaporator outlet temperature variation and set compressor switching thresholds accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the compressor is cycled on and off with fixed thresholds to control cooling capacity, then the system energy efficiency is improved by reducing over-dehumidification and series re-heating, but the discharge air temperature variation increases leading to inadequate occupant comfort
Solution Approach 1:
The patent applies dynamics by transitioning from fixed compressor cycling thresholds to dynamically adjusted thresholds. The controller continuously monitors system operating conditions (ambient temperature, solar load, vehicle speed, airflow rate) and adjusts the compressor on/off thresholds in real-time. This dynamic adjustment allows the system to maintain optimal evaporator outlet temperatures that prevent both over-dehumidification and excessive temperature variation in discharge air, thereby resolving the contradiction between energy efficiency and comfort.
Solution Approach 2:
The patent implements parameter changes by modifying the compressor cycling thresholds based on multiple operating parameters. Instead of using fixed temperature thresholds, the system changes the threshold parameters dynamically according to ambient temperature, solar radiation, vehicle speed, and airflow conditions. This parameter adaptation enables the system to optimize the balance between energy efficiency (reducing over-cooling) and comfort (maintaining stable discharge air temperature).
2Temperature
If the compressor cycling thresholds are adjusted to reduce discharge air temperature variation for occupant comfort, then the occupant comfort is improved, but the compressor cycling frequency increases reducing compressor and clutch durability
Solution Approach 1:
The patent resolves this contradiction through dynamic threshold adjustment that adapts to operating conditions. By continuously monitoring parameters such as ambient temperature, solar load, and airflow rate, the system dynamically sets compressor cycling thresholds that maintain acceptable discharge air temperature variation while avoiding excessive cycling frequency. This dynamic approach prevents the compressor and clutch from undergoing too many on/off transitions, thereby protecting their durability while maintaining comfort.
Solution Approach 2:
The system employs feedback mechanisms by continuously monitoring discharge air temperature, evaporator outlet temperature, and other operating parameters. This feedback information is used by the controller to adjust compressor cycling thresholds in real-time, creating a closed-loop control system that balances comfort requirements with compressor durability. The feedback ensures that threshold adjustments do not lead to excessive cycling frequency.
3Device complexity
If a fixed displacement compressor is used with on/off cycling to control capacity, then the device complexity is reduced compared to variable displacement compressors, but the ability to optimize cooling capacity across varying operating conditions is limited
Solution Approach 1:
The patent compensates for the limitations of fixed displacement compressors by implementing parameter changes in the control strategy. The system monitors multiple operating parameters (ambient temperature, solar radiation, vehicle speed, airflow rate) and dynamically adjusts compressor cycling thresholds to optimize cooling capacity delivery. This parameter-based adaptation enables a simple fixed displacement compressor to achieve performance comparable to more complex variable displacement systems.
Solution Approach 2:
The patent replaces mechanical complexity (variable displacement compressor mechanisms) with control system intelligence. Instead of using mechanically complex variable displacement compressors, the invention uses a microprocessor-based controller that dynamically adjusts cycling thresholds based on operating conditions. This substitution of mechanical complexity with electronic control achieves similar optimization benefits while maintaining simpler hardware.
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 ensures consistent occupant comfort and improved compressor and clutch durability by dynamically adjusting compressor cycling limits, optimizing the tradeoff between cycling frequency and temperature variation across varying operating conditions.
Implementation Method 1
the orifice tube 20 allows the cooled high-pressure refrigerant in line 30 to expand in isenthalpic fashion before passing through the evaporator 22
Implementation Method 2
an air intake duct 32 disposed upstream of evaporator 22 houses a motor driven ventilation blower 34 for forcing air past the evaporator tubes
Implementation Method 3
a heater core 40 formed as an array of finned tubes through which flows engine coolant. The heater core 40 effectively bifurcates the outlet duct 38
Implementation Method 4
The refrigerant flows through a closed circuit including a condenser 18... The cooling fans 30 are electrically activated to provide supplemental airflow for removing heat from high-pressure refrigerant in condenser 18
Data Source
AI summary
A control methodology for dynamically adjusting the switching limits of a cycled refrigerant compressor in an air conditioning system with the objective of achieving an optimal or specified tradeoff between compressor cycling frequency and discharge air temperature variation under all operating conditions. In a first embodiment, the compressor cycling limits are controlled to maintain a virtually constant discharge air temperature variation for all operating conditions. In a second embodiment, the compressor cycling limits are controlled so that the discharge air temperature variation changes in relation to the discharge air temperature to provide a virtually constant human comfort level for the occupants. And in a third embodiment, the compressor cycling limits are controlled so that the discharge air temperature variation changes in relation to the ambient or outside air temperature to provide a virtually constant human comfort level for the occupants.