Variable Displacement Pump Bypass Control for High Turn-Down Ratios
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Solution Overview
Problem
Conventional variable displacement pumps (VDPs) face inefficiencies due to high turn-down ratios, particularly in fuel delivery systems for gas turbine engines, where minimum pump pressure flows exceed the lowest flow requirements, leading to suboptimal performance and wear.
Innovation Solution
A system incorporating a bypass valve and a minimum pressure shutoff valve, controlled by a controller and sensors, recirculates flow to maintain optimal operation by adjusting flow based on demand, using electrohydraulic servo valves and solenoid valves to manage pressure and displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a variable displacement pump is designed to achieve high turn-down ratio, then the pump can operate across wide flow ranges, but the pump efficiency deteriorates throughout the operating range
Solution Approach 1:
The patent divides the pump's flow control into two separate functions: the VDP handles variable displacement control for normal operation, while a dedicated bypass valve with minimum pressure shutoff handles low flow recirculation. This segmentation allows each component to operate in its optimal efficiency range, resolving the contradiction between high turn-down ratio and pump efficiency.
Solution Approach 2:
The bypass valve acts as an intermediary component that recirculates flow from the pump outlet back to the inlet when minimum pressure is not achieved. This intermediary mechanism allows the VDP to maintain efficient operation across wide flow ranges by offloading the low flow control function to the bypass system.
2Temperature
If minimum pump pressure flow is increased to support cooling the VDP, then the pump can maintain proper cooling, but the pump cannot function with low flow requirements in fuel metering systems
Solution Approach 1:
The patent implements dynamic flow control through a minimum pressure shutoff valve that activates only when minimum pressure is not achieved. This dynamic mechanism allows the system to provide adequate cooling flow when needed while enabling low flow operation when the bypass valve recirculates flow, thus adapting to different operating conditions.
Solution Approach 2:
The system changes the flow parameters dynamically by introducing a bypass path that modifies the effective flow through the VDP. When minimum pressure is not achieved, the bypass valve opens to recirculate flow, changing the pressure and flow parameters to maintain proper cooling while allowing low demand operation.
3Device complexity
If conventional VDP control is used, then the system is simple, but wear increases due to excessive recirculation flow
Solution Approach 1:
The patent implements a feedback control mechanism where a pressure sensor monitors the pressure at the bypass valve inlet and provides feedback to a controller. The controller adjusts the bypass valve position based on this feedback to maintain minimum pressure, preventing excessive recirculation flow and reducing wear while keeping the control system manageable.
Solution Approach 2:
The patent replaces purely mechanical recirculation control with an electrohydraulic control system using a solenoid-actuated bypass valve and pressure-sensitive controller. This substitution allows more precise control of recirculation flow, reducing mechanical wear while adding only moderate complexity.
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 system enables efficient operation across wide flow ranges, reducing wear and maintaining pump efficiency by actively controlling flow and pressure, allowing high turn-down ratios without excessive wear.
Implementation Method 1
A bypass valve (BPV) includes a BPV inlet in fluid communication with the outlet line, and a BPV outlet in fluid communication with a bypass line that feeds into the inlet line upstream of the VDP
Implementation Method 2
The MPSOV is connected in fluid communication with the outlet line, configured to block flow through the outlet line for shutoff
Implementation Method 3
A first electrohydraulic servo valve (EHSV) can be connected in fluid communication with the BPV by a first control line. The first EHSV can be operatively connected to the controller for active control of the first EHSV to actuate the BPV
Implementation Method 4
A solenoid valve (SOL) can be connected in fluid communication with the outlet line and with the MPSOV control line for actuating the MPSOV between first and second states
Implementation Method 5
A flow sensing valve (FSV) can be connected in the outlet line, wherein the FSV includes a sensor configured to generate sensor data indicative of flow out of the outlet line
Implementation Method 6
The VDP includes a variable displacement mechanism configured to vary pressure to the outlet line
Data Source
AI summary
A system includes a variable displacement pump (VDP) in fluid communication with an inlet line and with an outlet line. The VDP includes a variable displacement mechanism configured to vary pressure to the outlet line. A bypass valve (BPV) includes a BPV inlet in fluid communication with the outlet line, and a BPV outlet in fluid communication with a bypass line that feeds into the inlet line upstream of the VDP. A minimum pressure shutoff valve (MPSOV) is connected in fluid communication with the outlet line, configured to block flow through the outlet line for shutoff. The MPSOV is connected in fluid communication with the BPV for triggering recirculation through the BPV.