Rolled Chain Tensioner Threads to Prevent Bulge Interference
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Solution Overview
Problem
Conventional chain tensioners with cut internal threads on the plunger face interference issues due to bulges formed during rolling, which hinder smooth and stable movement of the plunger relative to the screw rod, leading to difficulties in quickly absorbing chain looseness.
Innovation Solution
The chain tensioner features rolled internal threads with a surface roughness less than Ra 1.0 µm and a chamfer at the intersection of the protruding-side flank and thread top face to prevent bulge interference, allowing smooth and reliable movement of the plunger relative to the screw rod.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If internal threads are formed on the plunger by rolling to reduce surface roughness, then the plunger and screw rod can slide more smoothly and the plunger can quickly protrude to absorb chain looseness, but bulges are formed on the thread top faces which interfere with the root surfaces of external threads
Solution Approach 1:
The harmful bulges generated during rolling are extracted and removed from the thread top faces through a finishing operation. This eliminates the interference between bulges and external thread root surfaces while preserving the smooth rolled surfaces on the thread flanks for reliable sliding movement.
Solution Approach 2:
Different regions of the internal thread are given different surface qualities: the thread flanks (push-in-side and protruding-side) maintain the smooth rolled surface for low friction and reliable sliding, while the thread top faces are finished to remove bulges and prevent interference. This local differentiation of surface quality resolves the contradiction between smooth sliding and bulge interference.
2Force
If the plunger moves to a large degree into the cylinder to absorb chain tension, then the chain tension is absorbed, but when the engine is started later the chain could slack to such an extent as to cause flapping and/or skipping of teeth of sprockets
Solution Approach 1:
The return spring is pre-loaded to apply a preliminary biasing force to the plunger in the protruding direction. This preliminary action ensures that the plunger maintains a minimum protrusion position even when chain tension increases, preventing excessive retraction and ensuring the chain remains sufficiently taut during engine operation and startup.
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 design enables the plunger to quickly and smoothly protrude from the cylinder to absorb chain looseness, ensuring reliable and stable operation by preventing bulge interference and enhancing surface contact between the internal and external threads.
Implementation Method 1
since a rolled surface has a smaller surface roughness than a cut surface, the plunger and the screw rod should be capable of more smoothly slide relative to each other between the protruding-side flanks of the internal threads on the inner periphery of the plunger, and the protruding-side flanks of the external threads on the outer periphery of the screw rod
Implementation Method 2
provide a return spring disposed between the screw rod and the plunger, and biasing the plunger in the direction in which the plunger protrudes from the cylinder
Implementation Method 3
when the tension of the chain increases during the operation of the engine, due to the tension of the chain, the plunger moves in the direction in which the plunger is pushed into the cylinder, thereby absorbing the tension of the chain
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
A chain tensioner is provided which is formed with internal threads (21) each including a push-in-side flank (27), a protruding-side flank (28) and a thread top face (29). The push-in-side flank (27) has a flank angle (θ1) larger than the flank angle (θ2) of the protruding-side flank (28). The push-in-side flank (27) and the protruding-side flank (28) are rolled surfaces formed by rolling, and have a surface roughness smaller than Ra 1.0 µm. Each internal thread (21) further includes, at its position at which the protruding-side flank (28) intersects with the thread top face (29), a chamfer (32) configured to receive a bulge (33) moving from the protruding-side flank (28) during rolling.