Variable Valve Timing Speed Reduction Control for Engine Stop
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Solution Overview
Problem
Variable valve timing systems in engines, particularly those driven by electric motors, face challenges in accurately controlling valve timing in cold environments or during engine starting due to insufficient hydraulic pressure or slow camshaft response, leading to undesirable changes in valve timing when the engine is stopped.
Innovation Solution
An engine system with a speed reduction control mechanism that adjusts the engine speed reduction pattern to ensure the valve timing is accurately changed into a specific phase region before engine stoppage, using a determination unit to assess the speed reduction enabled state and restrict or permit engine speed reduction operations accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the speed reduction ratio is reduced in the phase region where valve timing is delayed, then the valve timing can be changed more effectively, but the valve timing may undesirably change due to output shaft rotation caused by reaction force when the engine is stopped
Solution Approach 1:
The speed reduction ratio is made variable rather than fixed. The transmission mechanism dynamically adjusts the speed reduction ratio based on the current valve timing phase, using a variable transmission mechanism that changes the reduction ratio according to the phase region, thereby optimizing performance across different operating conditions
Solution Approach 2:
The speed reduction ratio parameter is changed based on the phase region. When the valve timing phase is in the delayed region, a lower speed reduction ratio is applied, while in other regions, a higher speed reduction ratio is used, allowing the system to adapt its mechanical advantage to the specific timing requirements
2Adaptability or versatility
If hydraulic pressure is used to drive the camshaft, then the variable valve timing control can be implemented, but the control accuracy is insufficient in cold environments or during engine starting
Solution Approach 1:
An electric motor is introduced as an intermediary actuator between the control system and the camshaft. This electric motor-driven system replaces or supplements the hydraulic drive, providing precise control of the camshaft position independent of hydraulic pressure conditions, thereby ensuring accurate valve timing control in all operating environments
Solution Approach 2:
The hydraulic drive system is replaced with an electric motor-driven system. The electric motor provides direct mechanical drive to the camshaft through a reduction mechanism, eliminating the reliance on hydraulic pressure and its associated limitations in cold environments and during engine starting
Data Source
AI summary
When a command to stop an engine is issued, it is determined whether a current state is a speed reduction enabled state where an intake valve phase is brought into a phase region, in which speed reduction ratio is high, by the time the engine is stopped if an engine speed reduction control according to a predetermined speed reduction pattern is started at the present moment. If it is determined the current state is not the speed reduction enabled state, starting of the engine speed reduction control is not permitted, or the engine speed reduction control is restricted by reducing the deceleration, and then an intake valve phase control is executed. Thus, a required length of time before the engine is stopped is ensured, namely, a required length of period in which the intake valve phase is changed is ensured.