Accessory Gear Box Ventilation via Interface Compartment
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Solution Overview
Problem
Turbojet engine accessory gear boxes face challenges in managing heat generated by continuously rotating hydraulic pumps, leading to increased temperature and potential overheating, and there is a need to ventilate the fan compartment while the aircraft is stationary with the engine running.
Innovation Solution
An interface compartment with air circulation, including a blower driven by the accessory's drive shaft, is integrated into the accessory gear box to actively insulate and ventilate the heat-generating accessories, with optional thermally insulating materials and communication between compartments for enhanced heat management and ventilation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If hydraulic pumps are continuously rotated to drive accessories, then power transmission function is maintained, but heat generation increases causing gear box temperature to exceed limits
Solution Approach 1:
An interface compartment is introduced as an intermediary between the hydraulic pump and the gear box housing. This compartment contains circulating air that acts as a thermal mediator, absorbing heat from the pump through convection and preventing direct thermal conduction to the gear box, thereby resolving the contradiction between maintaining power transmission and controlling temperature
Solution Approach 2:
A blower device is used to circulate air through the interface compartment, creating a forced convection current. This pneumatic system actively transports heat away from the hydraulic pump and dissipates it through the air circulation, enabling continuous operation while maintaining safe temperature levels in the gear box
2Temperature
If insulating material is placed between accessory and gear box housing, then heat conduction to gear box is reduced, but temperature gradient creates overheating risk in equipment
Solution Approach 1:
Instead of relying solely on static thermal insulation, the invention introduces a dynamic air circulation system within the interface compartment. The blower-driven air flow actively manages heat transfer by convecting thermal energy from the equipment, through the air medium, and away from the gear box, preventing both overheating and excessive temperature gradients
Solution Approach 2:
The invention changes the thermal management approach from passive conduction-based insulation to active convection-based heat control. By modifying the heat transfer mechanism from conductive to convective, the system dynamically adjusts thermal parameters to maintain safe operating temperatures for both equipment and gear box
3Productivity
If fan compartment is sealed for pressurization, then flight performance is improved, but ventilation capability is lost when aircraft is stationary
Solution Approach 1:
The air circulation system in the interface compartment serves multiple functions: during flight, it contributes to overall fan compartment ventilation; when stationary, it provides dedicated cooling for the hydraulic pump and gear box. This multi-functional design resolves the contradiction between maintaining sealed pressurization for flight performance and enabling ventilation when stationary
Solution Approach 2:
The blower is driven by the hydraulic pump's own operation, creating a self-service cooling system. When the pump operates, it automatically drives the blower to circulate cooling air, providing continuous thermal management without requiring external ventilation systems, thus maintaining flight performance while enabling stationary ventilation
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
Effectively reduces heat absorption by the gear box and allows for ventilation of the fan compartment even when the aircraft is stationary, effectively managing heat and maintaining equipment within safe temperature thresholds.
Implementation Method 1
air to circulate inside the interface compartment to insulate the accessory gear box from the heat generated by the accessories
Implementation Method 2
the interface compartment comprises a blower circulating air between said air inlet and outlet openings
Data Source
AI summary
An accessory gear box configured to be mounted on a fan casing of a turbojet engine, including: an input shaft; a plurality of accessory drive shafts; and a compartment forming an interface with an accessory arranged on the housing of the accessory gear box at a site of the accessory, the interface compartment including an inlet and an outlet configured to allow air to circulate inside the compartment, to insulate the accessory gear box from heat generated by the accessories.