Fail-Fixed Hydraulic Actuator with Stepper-Controlled Pilot Valve
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Solution Overview
Problem
Helicopter hydraulic actuators face challenges in maintaining the last commanded position during electrical failures due to the nature of typical hydraulically powered control systems, which often default to a fail-safe position instead.
Innovation Solution
A fail-fixed hydraulic actuator system incorporating a stepper motor, pilot valve with a nulling sleeve, and an electronic controller that uses a cam and gear train to control the valve assembly, allowing for precise positioning and communication of high and low pressure fluids to maintain the actuator in the last commanded position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a typical hydraulically powered actuator is used, then the actuator can be controlled during normal operation, but in the event of an electrical failure it defaults to a fail-safe position instead of maintaining the last commanded position
Solution Approach 1:
The system dynamically adapts its fail-safe behavior based on the type of failure detected. During electrical failures, the actuator maintains the last commanded position through the stepper motor holding the cam in its current angular position. During hydraulic failures, it defaults to the mechanical fail-safe position. This dynamic adaptation resolves the contradiction by making the system's response contingent on the specific failure mode.
Solution Approach 2:
The system changes its operational parameters based on failure conditions. The stepper motor's holding torque parameter is utilized during electrical failures to maintain position, while the mechanical spring parameter dominates during hydraulic failures to provide fail-safe positioning. This parameter switching allows the system to maintain the last commanded position when needed while still providing fail-safe behavior when necessary.
2Reliability
If a stepper motor and cam mechanism are added to control the pilot valve, then precise positioning and maintenance of the actuator in the last commanded position is enabled, but the device complexity increases
Solution Approach 1:
The cam acts as an intermediary element that translates the stepper motor's rotational position into the linear positioning of the pilot valve spool. This mechanical intermediary allows precise control of hydraulic fluid flow without requiring complex electronic control valves, thereby achieving reliable position control while limiting the increase in overall system complexity.
Solution Approach 2:
The patent replaces a potentially complex electro-hydraulic control system with a simpler electromechanical-hydraulic system. The stepper motor controls a cam that mechanically positions a pilot valve, which then controls the main hydraulic actuator. This substitution uses well-understood mechanical principles (cam-follower geometry) to achieve precise control, reducing electronic complexity while maintaining reliability.
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
Enables tight control and maintenance of the actuator's position during electrical failures, ensuring flight control parameters are met by electromechanically controlling the cam and valve assembly to halt the actuator's motion when desired, using feedback from a position sensor to instruct the stepper motor.
Implementation Method 1
the feedback lever is elastically biased toward a surface of the ramp
Implementation Method 2
The actuator is hydraulically driven to move from an initial position upon a first movement of the spool relative to the housing
Data Source
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AI summary
A method of operating a fail-fixed hydraulic actuator system (13) is provided. The method includes providing an actuator (40) in an initial position, electromechanically operating a valve assembly (30) to hydraulically drive actuator movement and halting the hydraulic driving of the actuator movement by the valve assembly (30).