Engine Valve Gear Synchronous Cam Switching Mechanism
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Solution Overview
Problem
Conventional valve gears for engines suffer from a 'flick phenomenon' where the connected state between rocker arms is abruptly canceled when the intake or exhaust valve is not closed, leading to potential damage due to impact loads on the valves and rocker arms.
Innovation Solution
A valve gear system incorporating a synchronous cam that pushes a cam follower to switch the drive form of the intake or exhaust valve only when the valve is closed, using a switching mechanism with a pivot shaft and projecting pieces to ensure smooth movement and prevent the flick phenomenon by synchronizing the switching action with the valve's closed state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the slide pin is pushed by oil pressure to connect the first rocker arm and second rocker arm, then the drive form switching is achieved, but the slide pin cannot return to the non-connecting position when frictional force is large
Solution Approach 1:
The patent applies preliminary action by canceling the oil pressure before the frictional force becomes large during the rocker arm swing. The control unit cancels the oil pressure when the swing angle difference between the first and second rocker arms exceeds a predetermined threshold, ensuring the slide pin can return smoothly to the non-connecting position without being blocked by excessive friction.
2Adaptability or versatility
If the slide pin moves to the connecting position during valve operation, then the flick phenomenon occurs causing impact loads on valves and rocker arms
Solution Approach 1:
The patent implements feedback control by continuously monitoring the swing angle difference between the first and second rocker arms. The control unit uses this feedback information to determine the appropriate timing for canceling oil pressure, ensuring the slide pin returns to the non-connecting position only when the rocker arms are sufficiently aligned, thereby preventing the flick phenomenon and impact loads on the valves.
3Manufacturing precision
If the pin holes are aligned on the same axis only when swing angles are equal, then the connecting position is limited, but the switching mechanism cannot operate during valve lift
Solution Approach 1:
The patent applies dynamics by allowing the slide pin to move between the first and second rocker arms during the valve closed period when the swing angle difference is within a predetermined range. This dynamic approach enables the switching mechanism to operate flexibly during the period when the valves are closed, increasing the opportunities for drive form switching without requiring perfect pin hole alignment throughout the entire valve cycle.
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 solution effectively prevents the flick phenomenon, ensuring the intake or exhaust valves are not abruptly closed, reducing the risk of damage and allowing for smooth operation by synchronizing the switching mechanism with the valve's closed state, thereby maintaining optimal performance and component reliability.
Implementation Method 1
a synchronous cam configured to rotate in synchronism with the valve drive cam, and a switching mechanism configured to switch a drive form of one of the intake valve and the exhaust valve
Implementation Method 2
a valve drive cam configured to drive one of an intake valve and an exhaust valve, and a rocker arm having a function of converting a rotation of the valve drive cam into a reciprocating motion
Data Source
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AI summary
A valve gear for an engine includes a camshaft (14) including a valve drive cam (12), a rocker arm (9), a synchronous cam (13) configured to rotate in synchronism with the valve drive cam (12), and a switching mechanism (3) configured to switch a drive form of an intake valve or an exhaust valve (5) in a period defined by the synchronous cam (13). The switching mechanism (3) includes a switching unit (21) and a drive unit (23). The switching unit (21) switches the drive form by moving some of components which constitute a valve gear system from the valve drive cam (12) to the rocker arm (9). The drive unit (23) includes a cam follower (22) that is pushed by the synchronous cam (13) and moves, and drives some of the components which constitute the valve gear system in directions to switch the drive form by force received from the cam follower (22). A period when the synchronous cam (13) pushes the cam follower (22) is a period when the intake valve or the exhaust valve (5) is kept closed. There is provided a valve gear for an engine, which synchronizes the period when the intake valve or the exhaust valve is kept closed with the period when the members configured to switch the drive form of the intake valve or the exhaust valve are driven.