Pilot Bleed-Off Valve Control for Stable Idle Circuit Pressure
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Solution Overview
Problem
Existing work machines with pilot-driven bleed-off valves face challenges in maintaining stable circuit pressure for pilot primary pressure generation when actuators are not in operation, leading to inefficiencies in energy consumption.
Innovation Solution
A work machine with a pilot-driven bleed-off valve system that includes a spool movable by pilot secondary pressure, featuring a restrictor with stepwise and continuous changing opening areas, controlled by a controller to maintain stable pressure when actuators are idle or operated, ensuring pilot primary pressure generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a pilot-driven bleed-off valve is used to control circuit pressure, then energy consumption efficiency is improved by preventing unnecessary fluid relief, but the valve cannot generate pilot pressure when actuators are not being operated
Solution Approach 1:
The spool is designed to move dynamically between different positions based on actuator operation status. When actuators are not operated, the spool positions the restrictor to maintain circuit pressure. When actuators are operated with operation amount exceeding the predetermined value, the spool moves to allow fluid relief. This dynamic positioning resolves the contradiction by adapting the valve's pressure control behavior to the operational state of the system.
Solution Approach 2:
The spool's moving area is divided into multiple sections with different restrictor opening areas. The first moving area provides a first opening area for normal operation, while the second moving area provides a second opening area (smaller than the first) for maintaining pressure when actuators are idle. This segmentation allows the same valve mechanism to serve two different functional requirements, resolving the contradiction between energy efficiency and pressure generation reliability.
2Loss of energy
If the restrictor opening area is reduced to maintain circuit pressure when actuators are idle, then energy efficiency is improved, but the valve thrust required to move the spool increases with higher flow rate and pressure
Solution Approach 1:
The restrictor opening area is dynamically adjusted based on the operational state of actuators. When actuators are not operated, the spool moves to the second moving area, reducing the restrictor opening area to maintain circuit pressure and improve energy efficiency. When actuators are operated, the spool moves to the first moving area, increasing the opening area to reduce the thrust required to move the valve body. This dynamic adjustment resolves the contradiction between energy efficiency and valve thrust.
3Loss of energy
If the bleed-off valve is controlled to be in no-load communicating state to lower circuit pressure when no manual operation signals are present, then energy efficiency is improved, but pilot pressure for driving the bleed-off valve cannot be generated when manual operation signal is generated
Solution Approach 1:
The system performs preliminary action by maintaining circuit pressure in the second moving area when actuators are not operated, ensuring that pilot primary pressure is available and ready for immediate use when manual operation is required. This preliminary pressure maintenance eliminates the delay and ensures responsive manual operation, resolving the contradiction between energy efficiency and operational responsiveness.
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
Stable pressure maintenance in the main circuit for pilot primary pressure generation is achieved, enhancing energy efficiency by preventing unnecessary energy loss when actuators are not in use.
Implementation Method 1
a spool (141) which is moved in an axial direction by the pilot secondary pressure generated by the third pressure reducing valve (63)
Implementation Method 2
a restrictor (150) which gives a resistance to the working fluid passing therethrough
Data Source
AI summary
A work machine includes: a main circuit that supplies a working fluid from a pump to an actuator; a pilot circuit that introduces part of the working fluid from the pump, to a pilot pressure receiving section of a control valve; a bleed-off passage that connects the pump and a tank. The pilot circuit is provided with: a first pressure reducing valve that generates a pilot primary pressure; and second and third pressure reducing valves that generate a pilot secondary pressure to be applied to the control valve and a bleed-off valve. A moving area of a spool of the bleed-off valve has a first moving area where an opening area of a restrictor changes stepwise, and a second moving area where the opening area of the restrictor changes continuously. A controller controls the third pressure reducing valve such that the spool is positioned in the first moving area at the time of non-operation of the actuator, and the spool is positioned in the second moving area at the time of operation of the actuator. The restrictor of the bleed-off valve has a restricting hole that gives a resistance to the working fluid passing therethrough in a case the spool is positioned in the first moving area.