Hydromechanical Pressure Compensation for Variable Displacement Pump
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Solution Overview
Problem
High-speed centrifugal pumps used in fuel systems for aircraft engines do not provide sufficient fuel pressure for engine start-up until engine speed is high, leading to size and weight issues when considering all operating conditions, and existing solutions require excessive power consumption when using variable displacement pumps for pressure compensation.
Innovation Solution
A pump unit combining a high-speed centrifugal pump with a variable displacement pump, controlled by a hydromechanical pressure compensation system that adjusts operation based on pressure differentials across metering and throttling valves, allowing the variable displacement pump to supplement pressure only when needed, thereby maintaining efficient power use and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high-speed centrifugal pump is used to reduce power consumption and weight, then power efficiency and weight are improved, but the pump cannot provide sufficient pressure for engine start-up at low speeds
Solution Approach 1:
The pump system is segmented into two distinct pumping stages: a high-speed centrifugal pump for efficient operation during cruise and climb, and a variable displacement pump for engine start-up. Each stage operates independently to address specific operating conditions, allowing the centrifugal pump to be optimized for power efficiency while the variable pump provides necessary pressure during start-up.
Solution Approach 2:
The variable displacement pump incorporates a pressure compensation mechanism that dynamically adjusts its displacement based on system pressure requirements. This dynamic adjustment allows the pump to automatically engage when pressure drops below a threshold and disengage when the centrifugal pump suffices, optimizing both power consumption and pressure delivery across varying operating conditions.
2Reliability
If a variable displacement pump is added to provide pressure compensation, then pressure delivery capability is improved, but system complexity and size increase
Solution Approach 1:
The variable displacement pump and centrifugal pump are merged into a single integrated pump unit with a common drive shaft. This combination allows both pumping mechanisms to be controlled by a single engine-driven motor, reducing the number of independent power sources and simplifying the overall system architecture while maintaining the pressure compensation capability.
Solution Approach 2:
The pressure compensation system operates autonomously using a hydraulic control mechanism that automatically adjusts the variable pump's displacement based on downstream pressure conditions. The system uses pressure differential signals from the fuel control assembly to trigger pump engagement without requiring external control systems, thereby reducing complexity while maintaining reliable pressure delivery.
3Reliability
If the variable displacement pump operates continuously to ensure pressure requirements, then pressure delivery is maintained, but power consumption increases
Solution Approach 1:
The variable displacement pump operates periodically rather than continuously, engaging only when the centrifugal pump cannot meet pressure requirements. The pressure compensation mechanism monitors system pressure and triggers the variable pump in periodic cycles during transition phases (such as engine start-up or rapid throttle changes), allowing the centrifugal pump to handle steady-state operation efficiently.
Solution Approach 2:
The system changes operational parameters by adjusting the variable pump's displacement ratio based on real-time pressure conditions. During cruise and climb when the centrifugal pump operates efficiently, the variable pump maintains minimal displacement or idle operation. During start-up or transient conditions, the displacement parameter is increased to provide necessary pressure compensation, optimizing power consumption across different operating regimes.
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
The system ensures consistent pressure delivery across varying engine conditions while minimizing power consumption and system size, with the variable displacement pump automatically engaging only when necessary to provide additional pressure beyond the centrifugal pump's capabilities.
Implementation Method 1
a high speed centrifugal pump
Implementation Method 2
receives first and second signals indicative of a pressure differential across at least the throttling valve
Data Source
Figure 1~2
Figure 3A
Figure 3B
AI summary
A pump assembly includes a pump unit having a centrifugal pump and a variable pump supplying pressurized flow. A fuel control assembly receives flow from the pump unit and includes at least one metering valve and at least one throttling valve. A control for the variable pump receives first and second pressure signals indicative of a pressure differential across the throttling valve, or across the metering valve/throttling valve combination, for altering operation of the variable pump in response to the pressure differential.