Cooling system for a variable frequency drive in a transport refrigeration unit
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Solution Overview
Problem
The internal air-cooling system of transport refrigeration units is insufficient in high ambient conditions, causing the variable frequency drive (VFD) to overheat, especially due to heat generated by diesel gensets, leading to reduced performance or shutdown.
Innovation Solution
A cooling system comprising a conduit that directs ambient air towards the VFD, with a flexible section, a grill cover to filter and direct airflow, and a flap that automatically opens and closes based on vehicle movement, ensuring efficient cooling and thermal separation from the engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the internal air-cooling system is used in high ambient conditions, then the cooling system structure is simple, but the VFD temperature increases beyond safe limit causing reduced performance or shutdown
Solution Approach 1:
The patent extracts the VFD from the hot engine compartment and positions it in a separate location within the TRU cabinet. A dedicated cooling air passage is created that bypasses the engine compartment, allowing the VFD to be cooled by ambient air without being exposed to engine heat. This spatial separation resolves the contradiction by maintaining simple cooling structure while ensuring reliable VFD operation.
Solution Approach 2:
The patent introduces a dedicated cooling air passage as an intermediary channel between the ambient environment and the VFD. This passage acts as a mediator that delivers cool ambient air directly to the VFD while preventing hot engine air from reaching it. The passage includes features like water drainage capability and insect screen protection, ensuring reliable cooling without complex systems.
2Volume of moving object
If the VFD is positioned close to the engine for space efficiency, then the TRU cabinet space utilization is improved, but the VFD is heated by the diesel genset causing temperature increase
Solution Approach 1:
The patent segments the TRU cabinet into distinct thermal zones: a hot engine compartment and a cool VFD compartment. By creating separate air passages for each zone, the patent prevents thermal mixing while maintaining compact overall layout. The cooling air passage is specifically routed to serve the VFD without passing through or near the engine compartment, resolving the spatial-thermal conflict.
Solution Approach 2:
The patent applies local quality by providing targeted cooling to the VFD through a dedicated air passage that delivers cool ambient air directly to the VFD location. The cooling system is not uniformly applied throughout the cabinet but is specifically directed where needed (at the VFD) while leaving other areas (engine compartment) with their own thermal characteristics. This resolves the contradiction by maintaining compact layout with localized thermal management.
3Productivity
If the cooling air passage is open to ambient air for effective cooling, then the VFD cooling efficiency is improved, but water and outside objects can enter the passage
Solution Approach 1:
The patent employs an insect screen (mesh) at the ambient air intake opening of the cooling air passage. This porous material allows air to pass through freely for effective cooling while blocking water, insects, and other outside objects from entering the passage. The screen is positioned at the opening where ambient air enters, maintaining cooling efficiency while providing protection against harmful contaminants.
Solution Approach 2:
The patent incorporates a water drainage capability into the cooling air passage design. Instead of trying to completely prevent water entry (which would compromise cooling efficiency), the system is designed to allow water to enter and then drain it away through designated drainage paths. This converts the potential harm of water entry into a manageable condition, maintaining cooling efficiency while preventing water damage to the VFD.
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
The system effectively maintains the VFD at a safe operable temperature by providing fresher ambient air and preventing heat transfer from the engine, enhancing the reliability and performance of the VFD in transport refrigeration units.
Implementation Method 1
the conduit directs the ambient air towards the VFD to enable cooling of the VFD
Implementation Method 2
a predefined length of the conduit at the first end is elevated by a predefined angle from a longitudinal axis of the opening to restrict entry of water towards the second end of the conduit and allow automated discharge of water from the conduit through the opening
Data Source
AI summary
A cooling system for a variable frequency drive (VFD) of a transport refrigeration unit (TRU) is disclosed. The system comprises a conduit disposed within the vehicle and extending between a opening provided at a first predefined position on the outer body of the vehicle and the VFD being positioned at a second predefined position within the vehicle. The opening facilitates the inflow of ambient air within the conduit that carries the ambient air towards the VFD to enable cooling of the VFD. The system includes a grill cover adapted to be removably attached to the opening and/or the first end of the conduit, which allows entry of the ambient air within the conduit and restricts entry of outside objects and/or living organisms within the conduit.