Multi-link Engine Geometry Reduces Crank Journal Load
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Solution Overview
Problem
In a multi-link internal combustion engine, the load acting on a crank journal is particularly large when pistons are at bottom dead center, leading to increased inertial forces and potential bearing cap issues.
Innovation Solution
The link geometry is optimized by setting specific relationships between the lower link attitude angle, lower link aperture angle, and control link geometry, such that cos(θl+α) < cos(θl+π) when the piston is at bottom dead center, reducing the load on the crank journal through controlled link angles and pin loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a multi-link mechanism is used to adjust piston stroke, then piston stroke can be optimized, but the load on the crank journal increases due to greater inertial forces
Solution Approach 1:
The patent applies parameter changes by optimizing the lower link aperture angle α and lower link attitude angle θl to satisfy specific geometric relationships. By adjusting these angular parameters, the invention reduces the inertial forces transmitted to the crank journal while maintaining the desired piston stroke, thus resolving the contradiction between stroke optimization and load reduction.
Solution Approach 2:
The invention utilizes the dynamic characteristics of the multi-link mechanism by controlling the motion trajectory of the piston through precise geometric configuration. The lower link aperture angle and attitude angle are designed to optimize the dynamic force distribution, reducing peak loads on the crank journal during piston acceleration and deceleration phases.
2Strength
If the bearing cap is fastened tightly to resist large load, then the crank journal can withstand the load, but the fastening bolt and bearing cap increase in size
Solution Approach 1:
By changing the geometric parameters of the link mechanism (lower link aperture angle and attitude angle), the patent reduces the peak load on the crank journal. This parameter optimization directly decreases the force that the bearing cap must resist, allowing for a reduction in the size and weight of the bearing cap and fastening bolt while maintaining adequate strength.
3Length of moving object
If multi-link mechanism is used, then piston stroke can be adjusted, but the number of constitutional components and inertial mass increases
Solution Approach 1:
The patent segments the connection between the piston and crankshaft into multiple links (upper link, lower link, control link) with defined geometric relationships. This segmentation allows independent optimization of each link's function while achieving the overall goal of stroke adjustment with reduced inertial forces.
Solution Approach 2:
The invention employs dynamic geometric relationships in the multi-link mechanism, where the lower link aperture angle and attitude angle are optimized to control the motion and force characteristics. This dynamic approach allows the mechanism to achieve stroke adjustment while minimizing the inertial mass effects through proper timing and force distribution.
Data Source
AI summary
In an internal combustion engine, comprising: an upper link (11) connected via a piston pin (21) to a piston (32) that reciprocates within a cylinder; a lower link (12) attached to a crank pin (33b) of a crankshaft (33) to be free to rotate and connected to the upper link (11) via an upper pin (22); and a control link (13) which is connected to the lower link (12) via a control pin (23) and oscillates about an oscillation central shaft (24), the following equation is established when the piston (32) is at bottom dead centercos(θl+α)<cos(θl+π)where:θl is a lower link attitude angle; andα is a lower link aperture angle.As a result, a load acting on a crank journal when the piston is at bottom dead center can be reduced.