Half Thrust Bearing Geometry for Crankshaft Misalignment
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Solution Overview
Problem
The reduced diameter of modern crankshafts in internal combustion engines leads to increased deflection and vibration, causing the thrust collar surface to become inclined and resulting in frequent direct contact with the sliding surface of the half thrust bearing, leading to damage (seizure) and increased friction loss due to misalignment and uneven clearance between the thrust collar and the bearing surfaces.
Innovation Solution
A half thrust bearing with a semi-annular shape featuring a flat surface portion parallel to the reference plane and inclined flat surface portions on either side, with varying axial distances to maintain a constant thickness and reduce contact with the thrust collar surface, preventing continuous direct contact and promoting effective oil film formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the crankshaft diameter is reduced to decrease engine weight, then the engine weight is reduced, but the crankshaft rigidity decreases causing increased deflection and vibration
Solution Approach 1:
The half thrust bearing employs a non-uniform thickness design with a thick portion positioned at a specific circumferential location and a thin portion at another location. This local variation in thickness allows the bearing to adapt to crankshaft deflection and vibration while maintaining overall structural integrity, resolving the contradiction between reduced crankshaft diameter and sufficient rigidity support.
2Speed
If the crankshaft deflection increases due to reduced diameter, then the vibration becomes larger, but the clearance between the thrust collar surface and sliding surface becomes uneven causing direct contact and seizure
Solution Approach 1:
The half thrust bearing features a thick portion and a thin portion at different circumferential positions. This local quality variation allows the bearing to maintain appropriate clearance under dynamic crankshaft deflection conditions, preventing direct contact between the thrust collar surface and sliding surface, thereby maintaining reliability during high-speed rotation.
Solution Approach 2:
The invention addresses the clearance issue by introducing circumferential position as an additional dimension for thickness variation. Instead of uniform thickness in one dimension, the bearing thickness varies circumferentially, creating a three-dimensional configuration that accommodates crankshaft deflection and prevents seizure.
3Force
If the sliding surface near circumferential end portions comes into direct contact with the thrust collar surface, then the contact area increases, but the friction loss increases and damage (seizure) occurs
Solution Approach 1:
The half thrust bearing has a thick portion and a thin portion positioned at different circumferential locations. This local quality differentiation ensures that during crankshaft rotation, the sliding surface maintains appropriate clearance with the thrust collar surface, preventing continuous direct contact and reducing friction loss while still bearing axial force when needed.
4Ease of manufacture
If the thrust relief is formed with constant length and depth, then the manufacturing is simplified, but the misalignment of end surfaces cannot be adequately absorbed
Solution Approach 1:
The half thrust bearing employs a non-uniform thickness design with thick and thin portions at different circumferential positions. This local quality approach provides greater flexibility in absorbing end surface misalignment compared to uniform thrust relief, while still maintaining manufacturability through a systematic design approach.
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
The configuration prevents continuous contact between the sliding surface and the thrust collar surface, reducing the likelihood of damage and minimizing friction loss by allowing the contact position to move circumferentially with the crankshaft rotation and maintaining an effective oil film.
Implementation Method 1
promoting effective oil film formation
Data Source
Figure 1
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Figure 5~7
AI summary
A half thrust bearing (8) includes a sliding surface (81) for receiving an axial force (f) of a crankshaft of an engine, and a rear surface (84a) on an opposite side thereto. The sliding surface includes a flat surface portion (81a) near a circumferentially central portion (85), and two inclined flat surface portions (81b) on both circumferential sides of the flat surface portion. The axial distance between the rear surface and the sliding surface is maximum at the flat surface portion. At any radial positions, the axial distance in each inclined flat surface portion is maximum on a circumferentially central portion side and is reduced toward a circumferential end portion (86) of the half thrust bearing. Each inclined flat surface portion is arranged to form one constant thickness portion (M) extending linearly from a radially inner end to a radially outer end at a circumferential angle of 45°.