Electrohydraulic Propeller Pitch Control Without Oil Transfer Bearings
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Solution Overview
Problem
Existing turbomachine pitch change mechanisms face issues with complex and fragile Oil Transfer Bearings (OTBs) leading to oil leaks, reliability problems, and operational limitations, especially at low speeds, requiring additional pumps and protection systems, which are heavy, complex, and expensive.
Innovation Solution
A pitch change mechanism using an electrohydraulic actuator with a fixed displacement axial cylinder pump and hydraulic flow reversing valve, coupled with a high-pressure accumulator and safety valves, eliminates the need for rotating oil transfer, ensuring independent operation and feathering capabilities without electrical controllers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an OTB (Oil Transfer Bearing) is used to transfer hydraulic fluid from a fixed reference to a rotating reference, then pitch control is enabled, but the system becomes complex and fragile with significant oil leaks
Solution Approach 1:
The patent extracts and eliminates the OTB (Oil Transfer Bearing) from the system by reconfiguring the hydraulic architecture. The pump and accumulator are mounted on the rotating propeller hub, allowing direct local supply of hydraulic fluid to the pitch control mechanism without requiring fluid transfer across the rotating-stator interface. This removal of the OTB eliminates the source of oil leaks and mechanical fragility.
Solution Approach 2:
The patent introduces a high-pressure hydraulic accumulator as an intermediary energy storage device mounted on the rotating hub. This accumulator stores hydraulic energy locally and provides pressure compensation, enabling the pitch control system to operate independently of the stator-based hydraulic supply system and eliminating the need for rotating fluid seals.
2Power
If a high-pressure hydraulic pump driven by turbomachine shafts is used to provide high power density, then pitch control power is sufficient, but the system has operating limitations at low speeds and requires additional independent pumps
Solution Approach 1:
The patent uses a high-pressure hydraulic accumulator that is pre-charged and stores hydraulic energy in advance. This preliminary energy storage allows the pitch control system to maintain sufficient hydraulic power density during low-speed operations, engine shutdown, or startup conditions when the engine-driven pump cannot provide adequate flow or pressure. The accumulator acts as a buffer that delivers power when needed without requiring speed-dependent pump operation.
3Adaptability or versatility
If additional independent pumps and pitch lock devices are installed to ensure operation at low speeds and during shutdown, then operational coverage is improved, but system weight and complexity increase
Solution Approach 1:
The patent makes the rotating-mounted pump and accumulator serve multiple functions: they provide hydraulic power for pitch control during normal operation, low-speed operation, engine shutdown, and startup conditions. The same local hydraulic system also provides feathering capability through a simple manual valve. This multi-functionality eliminates the need for separate independent pumps, pitch lock devices, and feathering systems that would otherwise be required for different operational phases.
4Device complexity
If the lubrication unit operation is linked to turbomachine operation, then system simplicity is maintained, but protection functions fail in the event of overspeed or engine shutdown
Solution Approach 1:
The patent introduces a manually-operated hydraulic valve as an intermediary control device that provides protection functions independent of the automated lubrication unit. This simple manual valve allows the pilot to control the accumulator discharge for feathering or pitch lock in emergency conditions (overspeed, shutdown) without relying on the engine-linked lubrication system. The manual intervention capability ensures protection functions remain available even when the automated system fails or is inoperative.
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 solution reduces the risk of oil leaks and system oversizing, enhances reliability, and allows operation independent of turbomachine speed, providing efficient pitch control and feathering without electrical dependencies.
Implementation Method 1
a hydraulic pump (20) configured to pressurize a hydraulic fluid and store it in a high-pressure accumulator (17)
Implementation Method 2
An electrohydraulic actuator (11), configured to actuate a cylinder (15) which is mechanically connected to the propeller (13) in order to modify the pitch of the propeller blades (13a)
Implementation Method 3
The cylinder (15) comprises a first chamber (151) and a second chamber (152) supplied successively by the hydraulic pump (20)
Data Source
Figure 1~2
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AI summary
The present invention relates to a pitch-change mechanism for a turbine engine propeller, said turbine engine comprising a stator portion and a rotor portion, said pitch-change mechanism comprising an electrohydraulic actuator comprising: - a cylinder for actuating the propeller, comprising a first chamber and a second chamber; - a hydraulic pump suitable for selectively supplying the first chamber or the second chamber of the cylinder with pressurized hydraulic fluid; - a hydraulic fluid reservoir configured to store a pressurized hydraulic fluid; - a valve controlled between a first position in which the valve places the first chamber of the cylinder in fluid communication with the hydraulic pump, and a second position in which the valve places the first chamber of the cylinder in fluid communication with the hydraulic fluid reservoir.