Offset Idler Hub Geometry for Gear Backlash and NVH Control
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Solution Overview
Problem
Gear trains with symmetric idler hubs experience undesirable noise and vibration due to backlash issues when reversing direction, as manufacturing tolerances prevent exact gear tooth dimensions, leading to clearance between mated teeth.
Innovation Solution
An eccentrically-shaped offset idler hub is used to offset the idler gear centerline relative to the ring dowel centerline, reducing backlash between the crankshaft and idler gears while maintaining nominal backlash between the auxiliary and idler gears, achieved through a press-fit coupling with an engine block and a spring dowel pin for rotational constraint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a symmetric idler hub is used, then the gear train structure is simple and easy to manufacture, but backlash between gears causes noise and vibration
Solution Approach 1:
The patent applies asymmetry by using an offset idler hub where the idler gear centerline is deliberately offset from the hub centerline. This asymmetric configuration reduces backlash between the crankshaft gear and idler gear by pre-loading the gear mesh on one side, thereby eliminating the clearance that causes noise and vibration during direction reversals
2Manufacturing precision
If manufacturing tolerances are tightened to reduce backlash, then gear mesh precision improves, but manufacturing cost and complexity increase
Solution Approach 1:
The patent changes the geometric parameter of the idler hub by introducing an offset between the hub centerline and gear centerline. This parameter change allows the system to achieve reduced backlash without requiring tighter manufacturing tolerances on the gear teeth themselves, thereby maintaining manufacturing precision while avoiding increased complexity
3Reliability
If the idler gear centerline is offset from the hub centerline, then backlash between crankshaft gear and idler gear is reduced, but the structural symmetry and simplicity is lost
Solution Approach 1:
The patent deliberately introduces asymmetry through the offset idler hub design where the idler gear centerline is offset from the hub centerline by a predetermined distance. This asymmetric structure improves reliability by reducing backlash and controlling gear mesh clearance, while the offset amount is optimized to balance performance improvement with structural complexity
Data Source
AI summary
An apparatus includes a crankshaft gear operatively coupled to an engine. An auxiliary gear is operatively coupled to the engine. An idler gear is operatively coupled to the engine, and is in meshed engagement with each of the crankshaft gear and the auxiliary gear. A ring dowel is fixedly coupled to an engine block. An idler hub has an inner surface and an outer surface. The inner surface is fixedly coupled to the ring dowel and the idler gear is rotatably coupled to the outer surface. The idler hub is eccentrically-shaped so that an idler gear centerline is offset from a ring dowel centerline so as to reduce a crankshaft backlash between the crankshaft gear and the idler gear relative to a nominal crankshaft backlash, and so as to substantially maintain an auxiliary backlash between the auxiliary gear and the idler gear relative to a nominal auxiliary backlash.