Rockerless Desmodromic Valve System Eliminates Return Springs
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Solution Overview
Problem
Desmodromic valve systems face challenges such as design complexity, poor reliability, and valve train binding, limiting their application in production automobiles, and existing solutions like stiffer return springs increase stress and wear.
Innovation Solution
A rockerless desmodromic valve system utilizing a semirigid band or 'basket' that surrounds cams on a camshaft, engaging the valve stem to provide bidirectional drive without rocker arms, ensuring positive reciprocating action and reduced stress on engine components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a stiffer return spring is used to prevent valve float, then valve seat pressure increases and valve float is reduced, but stress on valve drive system parts increases and wear accelerates
Solution Approach 1:
The patent removes the return spring from the valve drive system entirely, extracting the harmful element that causes stress and wear. The desmodromic mechanism uses direct mechanical linkage between the cam and valve stem, eliminating the spring and its associated problems while maintaining reliable valve closure through positive mechanical action.
Solution Approach 2:
The patent replaces the spring-based mechanical system with a direct mechanical linkage system. The cam profile directly controls valve opening and closing through a follower and rocker arm mechanism, substituting the elastic energy storage system with a rigid mechanical transmission system that provides positive control without stress concentration.
2Reliability
If a desmodromic valve system is implemented to prevent valve float, then valve closure is positively controlled, but design complexity increases
Solution Approach 1:
The cam mechanism performs multiple functions: it provides the primary driving force for valve opening, controls the timing and duration of valve opening through its profile, and enables positive valve closure through the desmodromic linkage. This multi-functionality reduces the need for separate components and simplifies the overall system architecture.
Solution Approach 2:
Instead of using a spring to push the valve closed and accepting passive control during opening, the desmodromic system inverts the approach by using the cam mechanism to actively control both opening and closing. The follower and rocker arm are designed to maintain positive mechanical contact throughout the cycle, reversing the conventional approach of using springs for closure.
3Reliability
If a desmodromic valve system is implemented to prevent valve float, then valve float is reduced, but valve train binding occurs
Solution Approach 1:
The rocker arm is designed with a fulcrum point that allows it to pivot dynamically during operation. This dynamic movement accommodates thermal expansion and manufacturing tolerances, preventing binding while maintaining the positive mechanical linkage required for desmodromic operation. The geometry of the rocker arm and follower are optimized to maintain proper clearance and contact throughout the valve cycle.
Solution Approach 2:
The patent optimizes geometric parameters of the valve train components, including the rocker arm length, fulcrum position, and follower contact surfaces. By carefully selecting these parameters, the system achieves the necessary mechanical advantage for positive valve control while maintaining adequate clearance to prevent binding under operating conditions.
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 system effectively prevents valve float and reduces stress on engine parts, enhancing reliability and performance by eliminating the need for return springs, thus improving engine efficiency and longevity.
Implementation Method 1
a first cam rotating on a camshaft and cyclically pushing a valve stem
Implementation Method 2
a second cam on the camshaft, and a band extending circumferentially around the second cam and engaging the valve stem, the second cam rotating within the band and causing it to reciprocate so as to cyclically lift the valve stem
Data Source
AI summary
A desmodromic valve system which provides direct bidirectional displacement of a valve stem of an internal combustion engine without the aid of a rocker arm, utilizing a semirigid basket operating in conjunction with a plurality of cams for each valve. The basket is disposed about the camshaft of the engine and secured to the valve stem by an integral retainer on a bottom portion of the basket, and is constrained to motion along the valve stem axis. The basket has a pair of downwardly oriented cam followers in the upper portion thereof, spaced apart from the valve stem axis. A central cam and a parallel pair of side cams are fixedly mounted on the camshaft so as to rotate therewith, the cams substantially surrounded by the basket and cooperating therewith to provide reciprocating valve action with positive bidirectional drive. The central cam is aligned with the valve stem axis, and the side cams are spaced apart from the valve stem axis, parallel to the central cam and respectively aligned with the cam followers. During a first part of a valve cycle, the central cam pushes the valve stem down so as to positively open the associated valve, and the valve stem pulls said basket down with it via the retainer. During a second part of the valve cycle, the side cams push the basket up via their respective cam followers and thereby cause the basket to pull the valve stem so as to positively close the valve.