Geared Turbofan Engine Gear Connection Reliability Check
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Solution Overview
Problem
In gas turbine engines with gear reduction systems, the potential failure of the transmission path between the turbine section and the fan rotor can lead to undesirable high speeds of the turbine section, posing safety risks, especially in three spool designs where the low pressure turbine is no longer driving the fan, potentially causing misalignment and increased risk.
Innovation Solution
The implementation of sensors to monitor the time of arrival and speed of the fan rotor and the turbine shaft, with an electronic engine control system that compares this information to expected values, allowing for real-time adjustments and shutdown or maintenance alerts if significant deviations occur, thereby preventing overspeed conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a gear reduction system is used to drive the fan rotor, then the turbine section can operate at higher speeds with reduced torque requirements, but the transmission path introduces potential failure points that could lead to undesirably high turbine speeds
Solution Approach 1:
The control system continuously monitors the relative positioning of the fan rotor and turbine shaft using sensors (proximity sensors, encoders, or resolvers) and compares actual positions to expected positions based on gear ratio. This preliminary detection of positional deviations allows the system to identify transmission failures before they lead to dangerous overspeed conditions, enabling preventive control actions.
Solution Approach 2:
The system employs feedback control by continuously measuring the actual positions of the fan rotor and turbine shaft, comparing these measurements to expected values calculated from the gear reduction ratio, and using this information to detect anomalies. When deviations exceed predetermined thresholds, the control system adjusts turbine operation or shuts down the engine to prevent harmful overspeed conditions.
2Ease of operation
If the gear connection fails, then the fan rotor may stop being driven, but the turbine section can reach undesirably high speeds creating safety risks
Solution Approach 1:
The control system proactively monitors the relative positioning between the fan rotor and turbine shaft using sensors that detect angular position and rotational speed. By continuously comparing actual positions to expected positions based on the gear reduction ratio, the system can detect transmission failures before they result in dangerous turbine overspeed conditions, enabling preventive control actions to be taken.
Solution Approach 2:
The system implements feedback control by measuring the actual angular positions and rotational speeds of both the fan rotor and turbine shaft, comparing these measurements against expected values derived from the gear reduction ratio, and using this information to detect anomalies. When positional deviations or speed discrepancies exceed predetermined thresholds, the control system responds by adjusting turbine operation or initiating engine shutdown to prevent harmful overspeed conditions.
3Reliability
If sensors and monitoring systems are added to detect transmission failures, then turbine overspeed can be prevented, but the device complexity increases
Solution Approach 1:
The monitoring system utilizes existing engine sensors and control units for multiple purposes: the same sensors that monitor fan rotor position for normal control operations are also used to detect transmission failures by comparing fan position to expected position based on turbine shaft position and gear ratio. This multi-functional use of existing components avoids adding dedicated failure detection hardware, thereby limiting the increase in device complexity while maintaining high reliability.
Solution Approach 2:
The control system performs self-diagnosis by using its own existing sensors and control algorithms to detect transmission failures. The electronic control unit processes signals from existing position sensors and compares actual fan rotor position against expected position calculated from turbine shaft position and the known gear reduction ratio. This self-monitoring capability enables failure detection without requiring separate dedicated monitoring hardware, thus limiting complexity increase while ensuring reliable turbine speed control.
Data Source
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AI summary
A gas turbine engine includes a fan and a compressor. A combustor drives a turbine, including a first turbine with a shaft to drive the compressor. A fan drive turbine drives the fan through a speed reduction. A sensor senses a speed of rotation of the fan and communicates sensed speed information to a control. The control develops an expected speed for the fan. A problem is identified should the sensed speed be less than the expected speed by more than a predetermined amount. A method is also described.