Droop-Mode Engine Control for Transport Refrigeration Cooling Capacity
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Solution Overview
Problem
Current transport refrigeration systems (TRS) face limitations in cooling capacity due to power-limited engines, as they operate within a constant speed isochronous mode, restricting compressor speed and refrigerant flow, which cannot be increased without exceeding emission standards.
Innovation Solution
The system operates the electronically governed engine in a droop mode, allowing engine speed to vary with load, increasing compressor speed and refrigerant flow without exceeding power limits, by alternately switching between droop and isochronous modes based on load parameters, such as box temperature or prime mover load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the engine operates in isochronous mode to maintain constant speed, then engine stability is improved, but cooling capacity deteriorates due to restricted compressor speed
Solution Approach 1:
The patent applies dynamics by transitioning from static isochronous speed control to dynamic droop mode control, where engine speed varies dynamically with load conditions. The ECU continuously adjusts fuel injection based on load sensor feedback, allowing the engine to operate at higher speeds under partial load conditions, thereby increasing compressor speed and cooling capacity while maintaining stability when needed.
2Productivity
If the engine speed is increased beyond rated speed, then cooling capacity is improved through increased refrigerant flow, but emission standards are violated due to excessive power output
Solution Approach 1:
The patent changes the operating parameters of the engine by implementing droop mode control, which allows engine speed to vary with load rather than maintaining a fixed rated speed. This parameter change enables the engine to operate efficiently at different speed-power points, increasing cooling capacity through higher refrigerant flow while staying within emission compliance boundaries by not exceeding the rated power output.
Solution Approach 2:
The system employs feedback control through load sensors that continuously monitor engine load and provide signals to the ECU. The ECU uses this feedback to adjust fuel injection quantities dynamically, ensuring the engine operates optimally within emission standards while maximizing cooling capacity. The feedback loop prevents excessive power output by adjusting fuel delivery based on actual load conditions.
3Object-affected harmful factors
If the governor restricts fuel flow to limit engine power, then emission standards are met, but compressor speed and refrigerant flow are reduced
Solution Approach 1:
The patent replaces the static mechanical governor with a dynamic electronic control system. The ECU dynamically adjusts fuel injection based on real-time load conditions, allowing the engine to operate at higher speeds when load is reduced, thereby increasing compressor speed and refrigerant flow while still meeting emission standards through intelligent fuel management.
Solution Approach 2:
The patent substitutes the mechanical governor system with an electronic control unit (ECU) that uses sensors and electronic signals to control fuel injection. This replacement allows for more precise and flexible control of engine power output, enabling the system to optimize compressor speed and refrigerant flow while maintaining emission compliance through electronic rather than purely mechanical means.
Data Source
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AI summary
There is disclosed a transport refrigeration system (10) comprising an electronically governed engine (60) that drives a refrigeration circuit (80) of the system (10). The engine control unit (65) is configured to operate the engine (60) in a droop mode of operation, in which the engine speed increases with decreasing engine loads from the refrigeration circuit (80), so as to maximise the cooling capacity of the system (10) at low engine load conditions.