Variable Pitch Sprocket Timing Chain Drive Tension Control
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Solution Overview
Problem
Conventional timing chain drive units in internal combustion engines face challenges with cyclic variations in chain tension, leading to excessive weight, noise, and vibration due to cyclic changes in torque load and rotational speed, which are not effectively addressed by existing solutions.
Innovation Solution
The timing chain drive system incorporates sprockets with teeth pitches that cyclically increase and decrease over their circumference, synchronizing with fluctuations in the driving sprocket's speed to absorb tension changes without applying forces perpendicular to the chain's direction, thereby reducing noise and vibration while allowing for downsizing and weight reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional timing chains are designed with high tensile strength to withstand peak tension, then the chain can handle cyclic load variations, but the chain becomes excessively heavy
Solution Approach 1:
The patent changes the geometric parameters of the sprocket teeth by varying the pitch cyclically around the sprocket circumference. This parameter change allows the timing chain to operate with reduced tensile strength requirements because the varying pitch absorbs tension fluctuations, enabling weight reduction while maintaining adequate strength
2Strength
If conventional timing chains are designed to withstand peak tension values, then the chain can handle load variations, but the overall weight of the drive unit increases
Solution Approach 1:
The varying pitch of sprocket teeth changes the operational parameters of the timing chain system. By adjusting the pitch distribution, the system reduces peak tension requirements, allowing for lighter chain and drive unit design while maintaining sufficient strength to handle load variations
3Strength
If conventional timing chains are designed with high tensile strength, then the chain can withstand peak tension, but excessive noise is generated
Solution Approach 1:
The patent varies the pitch parameter of sprocket teeth cyclically to absorb tension fluctuations. This parameter change reduces the impact loads and vibrations that cause noise, allowing the use of lighter chains with lower tensile strength while actually reducing noise levels
4Stability of the object's composition
If non-circular sprockets are used to address tension variations, then chain tension fluctuations can be reduced, but forces are applied perpendicular to chain travel causing displacement and increased noise
Solution Approach 1:
Instead of making the entire sprocket non-circular, the patent applies local quality by varying the pitch only in specific locations around the sprocket circumference. This localized pitch variation absorbs tension fluctuations without requiring the chain to move perpendicular to its travel direction, avoiding the noise and vibration problems caused by non-circular sprockets
Data Source
AI summary
In a timing chain driving system in which the speed of a driving sprocket fluctuates cyclically, the tooth pitch of a driven sprocket from which a tension span of the chain travels toward the driving sprocket varies cyclically around the circumference of the driven sprocket so that the tooth pitch at the point at which the timing chain disengages from the driven sprocket is at a minimum when the rotational speed of the driving sprocket is maximum, moderating fluctuations in chain tension. A similar effect can be achieved in the case of a driving sprocket having a cyclically varying tooth pitch by arranging the driving sprocket so that its tooth pitch is maximum at the point at which it is engaged by the chain when its rotational speed is maximum.