Change-over Valve Offset Axial Passage Drilling
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Solution Overview
Problem
Existing change-over valves face difficulties in precisely applying pilot pressure due to air bubbles, requiring a small hole for air discharge, which is challenging to drill and prone to tool damage, especially with larger spool diameters.
Innovation Solution
The design features an axial passage offset from the center axis and a small hole formed in an angular position with the shortest distance from the spool's outer periphery, allowing for easier drilling and reducing the risk of tool damage by shortening the hole's length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a small hole is provided for discharging air in the pilot chamber, then air discharge function is improved, but the hole is difficult to drill and tool damage risk increases
Solution Approach 1:
The air discharge passage is segmented into two parts: a small hole formed in the spool outer periphery and an axial passage formed inside the spool. This segmentation allows the small hole to be positioned at the outer periphery where drilling is easier, while the axial passage completes the discharge path to the pilot chamber without requiring a long radial drill through the spool center.
Solution Approach 2:
The air discharge path transitions from a purely radial direction (drilling from outer periphery to center) to a combined radial-axial path. The small hole is formed radially at the outer periphery, then the axial passage carries the air discharge axially through the spool, changing the discharge direction to avoid the difficult center drilling operation.
2Productivity
If the small hole has a large sectional area, then air discharge efficiency is improved, but pilot chamber pressure is lowered
Solution Approach 1:
The discharge passage has different cross-sectional areas at different locations: the small hole at the outer periphery has a small area to maintain pilot chamber pressure, while the axial passage inside the spool provides additional discharge capacity. This local variation in passage area allows efficient air discharge while maintaining the pressure needed for spool operation.
Data Source
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AI summary
A change-over valve comprises a spool housed in a spool housing, and a pilot chamber facing at least an end of the spool. An axial passage is formed in the spool along the axial direction. While being connected to a pilot chamber, the axial passage communicates with a tank passage via a small hole having an opening on an outer periphery of the spool in accordance with displacement of the spool, to discharge the air in the pilot chamber to the tank passage. Since the axial passage is formed at a location offset from a center axis of the spool, a length of the small hole is shortened and the small hole is easily processed.