Crankshaft With Offset Unsupported Section
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Solution Overview
Problem
Crankshafts in engines with an odd number of cylinders, such as three cylinder engines, experience increased bending and vibration due to non-symmetric bearing arrangements, leading to reduced efficiency and shorter longevity when traditional bearing configurations are modified to reduce friction.
Innovation Solution
A crankshaft design with only three bearing journals and three rod journals, featuring an unsupported section with a larger diameter than the bearing journals, offset from the longitudinal centerline, which reduces friction, bending, and torsion, while maintaining desired rotational characteristics and allowing for cost and weight reduction by eliminating unnecessary components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional bearing configurations are modified to reduce friction by removing bearing journals, then fuel economy is improved, but crankshaft bending and vibration increase beyond desirable levels
Solution Approach 1:
The patent applies local quality by making the unsupported section have a larger diameter than standard bearing journals. This localized dimensional change increases stiffness precisely where needed to support the reduced bearing arrangement, resolving the contradiction between friction reduction and maintaining structural integrity.
Solution Approach 2:
The patent employs asymmetry by positioning the unsupported section and inner bearing journal offset from the longitudinal centerline of the crankshaft. This asymmetric arrangement maintains desired spacing of cylinders while accommodating the reduced three-bearing configuration, preventing excessive bending in the unsupported section.
2Device complexity
If the number of bearing journals is reduced from four to three, then device complexity and cost are reduced, but crankshaft bending increases due to non-symmetric bearing arrangement
Solution Approach 1:
The unsupported section is designed with a larger diameter than standard bearing journals, creating a localized reinforcement zone. This local quality enhancement compensates for the reduced number of bearings by providing increased stiffness in the critical unsupported region, maintaining strength while reducing complexity.
Solution Approach 2:
The patent addresses the bearing reduction by transitioning to a different dimensional approach - increasing the diameter (radial dimension) of the unsupported section rather than maintaining the original bearing journal dimensions. This dimensional change provides the necessary structural support with fewer bearings.
3Ease of manufacture
If bearing journals are removed to reduce friction and cost, then fuel economy and manufacturing cost are improved, but crankshaft longevity decreases due to increased bending
Solution Approach 1:
By creating a localized unsupported section with enlarged diameter, the patent provides targeted reinforcement that extends crankshaft life. This local quality enhancement ensures the crankshaft can withstand operational stresses despite having fewer bearings, maintaining longevity while reducing manufacturing cost.
Solution Approach 2:
The patent changes the dimensional parameter of the unsupported section by increasing its diameter beyond that of standard bearing journals. This parameter change optimizes the balance between friction reduction (fewer bearings) and longevity (increased stiffness), allowing cost reduction without sacrificing service life.
Data Source
AI summary
A crankshaft in an engine is provided. The crankshaft includes only two outer bearing journals configured to attach to two outer crankshaft bearings, only a single inner bearing journal positioned axially between the two outer bearing journals configured to attach to an inner crankshaft bearing, an unsupported section positioned axially between the inner bearing journal and one of the outer bearing journals, and only three rod journals each configured to attach to a separate piston rod.