Open-Circuit Pump Pressure Control With Spool Stop Protection
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Solution Overview
Problem
Existing variable displacement pumps face challenges in precise control of displacement, particularly in open hydraulic circuits, where abrupt pressure changes can lead to system instability and potential damage, and require additional safety measures like pressure compensators.
Innovation Solution
A pump control assembly with a spool valve system, including spring-loaded pistons and a proportional pressure reducing valve, which allows for step-less pressure control and includes a mechanical stop to prevent over-stroking, eliminating the need for separate pressure compensators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate pressure compensator device is included to safeguard against abrupt pressure changes and electronic failures, then system safety is improved, but device complexity increases
Solution Approach 1:
The patent combines the pressure control function and safety protection function into a single integrated pump control assembly. The spool valve system with spring-loaded pistons and mechanical stop structure performs both displacement control and over-pressurization prevention, eliminating the need for separate pressure compensators while maintaining system safety.
Solution Approach 2:
The pump control assembly is designed to perform multiple functions: controlling pump displacement through spool valve actuation and simultaneously preventing over-pressurization through the mechanical stop structure. This multi-functional design reduces overall system complexity while improving reliability.
2Ease of operation
If traditional swash plate control using spring-loaded piston cylinder or solenoid is used, then displacement control is achieved, but precision and stability deteriorate due to abrupt pressure changes
Solution Approach 1:
The patent employs a dynamic spool valve system with spring-loaded pistons that can respond rapidly to pressure changes. The mechanical stop structure provides a hard limit that prevents over-stroking, ensuring stability while maintaining operational flexibility for precise displacement control.
Solution Approach 2:
The spring-loaded pistons in the spool valve system provide inherent feedback mechanisms where spring force balances against hydraulic pressure, automatically adjusting the spool position to maintain stable pump operation despite pressure fluctuations in the hydraulic circuit.
3Productivity
If the swash plate angle is increased to increase pump displacement, then productivity is improved, but system stability worsens due to higher pressure and risk of over-pressurization
Solution Approach 1:
The mechanical stop structure is pre-positioned to prevent the spool valve from moving beyond a safe displacement limit. This preliminary protective measure prevents over-pressurization before it can occur, allowing the system to operate at high displacement for improved productivity without compromising stability.
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 solution provides stable, precise control of pump displacement, enhancing system stability and safety by preventing over-pressurization, thus improving overall hydraulic system performance.
Implementation Method 1
proportional pressure reducing valve (114) controlled by a solenoid
Implementation Method 2
first and second springs (118, 120) positioned on either side of the piston
Implementation Method 3
The first chamber (168) is in fluid communication with the pump output port (133)... The second chamber (138) is in fluid communication with the tank port (137)
Data Source
AI summary
A pump control assembly for controlling a variable displacement hydraulic pump includes a spool mounted within a valve block. The spool is configured to move between a first and a second position within the valve block so as to selectively control the displacement of the attached pump. The pump control assembly further includes first and second chambers that each apply a force to opposite ends of the spool. The first chamber is positioned at a first end of the spool in fluid communication with a pump output port. The second chamber is positioned at a second end of the spool and in fluid communication with a hydraulic tank port and a proportional pressure reducing valve. The second chamber also includes a piston and first and second springs positioned on either side of the piston. The proportional pressure reducing valve provides a regulated pressure to a first side of the piston along with the first spring, and the hydraulic tank port provides a tank pressure on the opposite side of the piston along with the second spring. The pump control assembly also includes a stop structure having a positive stop that limits movement of the piston in a direction toward the first chamber.