Hybrid Vehicle HVAC Control for Engine-Off Cabin Cooling
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Solution Overview
Problem
In hybrid vehicles with belt-driven refrigerant compressors, there is a conflict between maintaining passenger thermal comfort and achieving fuel economy, as the compressor cannot operate when the engine is off, leading to increased energy costs with electric compressors as an alternative.
Innovation Solution
A method for controlling the HVAC system that determines the maximum allowed compressor off time and adjusts the system to maximize cooling or heating with minimum energy usage, allowing for engine shut-off while ensuring thermal comfort, by monitoring and adjusting components like the blower, blend door, and auxiliary coolant pump.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the engine is shut off to improve fuel economy, then fuel consumption is reduced, but the belt-driven refrigerant compressor cannot operate leading to degraded thermal comfort
Solution Approach 1:
The system performs preliminary cooling of the passenger compartment before engine shut-off, and pre-chills the HVAC system components (evaporator, coolant) to extend the duration of thermal comfort during engine-off periods. This allows the engine to remain off longer while maintaining acceptable thermal conditions.
Solution Approach 2:
The patent replaces the mechanical belt-driven compressor with an electrically-driven compressor that can operate independently of engine operation. This substitution allows the compressor to run during engine-off periods, maintaining thermal comfort without requiring the engine to be running.
2Temperature
If an electric driven compressor is used to maintain thermal comfort during engine off, then thermal comfort is improved, but energy cost and system complexity increase
Solution Approach 1:
The electric compressor is integrated into the existing HVAC system architecture, serving both as a cooling compressor and working in conjunction with the thermal energy storage system for heating. This multi-functionality reduces the need for separate systems and minimizes overall complexity.
Solution Approach 2:
The patent introduces a thermal energy storage system (ice storage, chilled water storage) as an intermediary between the compressor and the passenger compartment. This intermediary allows decoupling of compressor operation from immediate cooling demands, enabling the compressor to run less frequently while maintaining thermal comfort.
3Temperature
If the compressor operates continuously to maintain thermal comfort, then thermal comfort is improved, but fuel consumption increases
Solution Approach 1:
The system uses periodic compressor operation instead of continuous operation. The compressor runs in cycles, taking advantage of thermal inertia and stored cold energy to maintain comfort during off periods. This periodic operation significantly reduces fuel consumption while maintaining acceptable thermal conditions.
Solution Approach 2:
The thermal energy storage system provides self-service by maintaining cooling capacity without active compressor operation. The stored cold energy in the ice storage or chilled water system automatically maintains passenger compartment temperature during engine-off periods, reducing the need for continuous compressor operation.
4Use of energy by moving object
If the engine is shut off for extended periods to maximize fuel savings, then fuel economy is improved, but thermal comfort and system reliability degrade
Solution Approach 1:
The system continuously monitors passenger compartment temperature, HVAC system temperatures, and thermal storage levels to dynamically adjust compressor operation and HVAC component operation. This feedback control ensures thermal comfort is maintained within acceptable ranges while maximizing engine-off periods for fuel savings.
Solution Approach 2:
The system builds up thermal energy storage (ice, chilled water) before extended engine-off periods to cushion against thermal comfort degradation. This beforehand cushioning provides a buffer that maintains acceptable thermal conditions during prolonged engine-off periods, enhancing reliability of thermal comfort.
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 maintains thermal comfort while maximizing fuel savings, reducing compressor operation, minimizing fogging, re-fogging, and temperature swings, and allowing for extended engine off time while providing heat to the passenger compartment.
Implementation Method 1
an evaporator to cool air for the passenger compartment
Implementation Method 2
a heater core to heat air for the passenger compartment
Data Source
AI summary
A method of controlling a HVAC system for a hybrid vehicle having a refrigerant compressor driven by an engine is disclosed. The method may comprise: determining a requested air conditioning operating point for a passenger compartment; estimating a time to reach the requested operating point; based on the previous steps, estimating a maximum allowed compressor off time; determining if the allowed compressor off time is greater than a minimum engine off time; if the allowed compressor off time is greater than the engine off time, determining if the vehicle is entering an allowable engine off mode; if so, commencing engine shut-off mode; if engine shut-off is anticipated, prior to commencing the shut-off mode, adjusting the HVAC system to maximize cooling of the passenger compartment with minimum energy usage; and if the engine shut-off is commenced, monitoring the HVAC system to determine when engine restart is needed to maintain comfort.