Variable Valve Mechanism Using Eccentric Sleeve
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Solution Overview
Problem
Existing valve train designs for internal combustion engines that achieve variable lift and event duration require three cams to avoid twisting forces, resulting in an expensive and bulky design, especially when using pushrods.
Innovation Solution
A valve train design utilizing two rotatable cams, a first rocker supported by an eccentric sleeve, and a second rocker that rotates the eccentric sleeve, allowing the cams to combine their action to achieve variable lift and event duration without the need for three cams, by cyclically moving the pivotal axis of the first rocker and using suitable phasing of the cams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If three cams are used to operate each valve to avoid large twisting forces, then the reliability and structural stability are improved, but the device complexity, cost, and bulk increase significantly
Solution Approach 1:
The invention divides the valve operation function into two separate cams: a first cam that provides the primary lift profile, and a second cam that provides a superimposed profile through the eccentric sleeve mechanism. This segmentation allows each cam to have a simpler, dedicated function rather than requiring one complex cam to handle all variations, thereby reducing the total number of cams needed while maintaining reliability
Solution Approach 2:
The invention introduces a dynamic element - the eccentric sleeve that can rotate relative to the rocker shaft. This dynamic mechanism allows the second cam to vary the lift profile on-the-fly by changing the phase relationship between the two cams, eliminating the need for multiple fixed cams for different operating conditions and reducing overall device complexity
2Adaptability or versatility
If three cams are used to operate each valve, then variable lift and event duration are achieved, but the manufacturing cost increases
Solution Approach 1:
The invention merges the functions of multiple cams into a two-cam system where the first cam provides base lift and the second cam provides variable adjustment through the eccentric sleeve. By combining these functions into fewer components, the manufacturing cost is reduced while still achieving variable lift and event duration capabilities
Solution Approach 2:
The eccentric sleeve mechanism serves multiple functions: it transmits the second cam's profile, provides the variable phase adjustment, and modifies the first cam's output. This multi-functionality reduces the need for separate dedicated components for each function, thereby lowering manufacturing costs while maintaining adaptability
3Force
If three cams are used to operate each valve, then the valve train can handle twisting forces, but the engine bulk and weight increase
Solution Approach 1:
The invention extracts the force management function from the cam count and places it in the eccentric sleeve mechanism. The eccentric sleeve acts as a mechanical advantage element that can handle and transmit forces efficiently, reducing the need for redundant cams purely for force management and thereby reducing the overall weight of the valve train
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
Enables variable valve lift and event duration with a more compact and cost-effective design, allowing for different valve operations by varying the eccentricity of the eccentric sleeves, and accommodating different valve events without the need for triple cam arrangements.
Implementation Method 1
a first rocker supported on a fixed rocker shaft by way of an eccentric sleeve that is rotatable relative to the rocker shaft
Data Source
AI summary
A valve train comprises a poppet valve 18 actuated by two rotatable cams 30, 32 which can preferably be phase shifted relative to one another. A first rocker 39 is supported on a fixed rocker 40 shaft by way of an eccentric sleeve 42 that is rotatable relative to the rocker shaft 40. A second rocker 37 directly supported on the rocker shaft 40 acts to rotate the eccentric sleeve 42 about the rocker shaft 40. In this way, the first rocker 39, which is operated by a first cam 30 and acts on the poppet valve 18 has its axis of rotation displaced cyclically towards and away from the valve 18 by the action of the second cam 32 and the second rocker 37.