Cam Shifting System for Variable Valve Actuation
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Solution Overview
Problem
Existing cam shifting systems in internal combustion engines have limited time for shifting movements, leading to high accelerations and obstacles during valve actuation, particularly when multiple lobes are involved, restricting the use of these systems.
Innovation Solution
The cam shifting system includes a shifting unit with a groove and a driving pin that allows the cam follower to engage a portion of the cam lobe during movement, extending the shifting arc and reducing acceleration by enabling contact with both the base circle and lobe surfaces, thereby increasing the available time for shifting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the shifting movement is performed only when the cam follower contacts the base circle, then the cam follower encounters no obstacles, but the available time for shifting is too short leading to high accelerations
Solution Approach 1:
The cam follower is prepared to contact the cam lobe surface in advance during the shifting movement, extending the shifting arc to include both base circle and lobe surface contact. This preliminary preparation of the contact path allows the shifting to occur over a longer duration without encountering obstacles, thereby reducing the required acceleration.
2Adaptability or versatility
If multiple lobes are provided on the cams, then variable valve actuation is enabled, but the base circle arc available for shifting is reduced
Solution Approach 1:
The invention extends the shifting movement from the traditional one-dimensional base circle contact into a two-dimensional path that includes both base circle and cam lobe surface contact. This dimensional expansion of the shifting arc provides additional time for shifting while maintaining the multiple lobe configuration needed for variable valve actuation.
3Duration of action of moving object
If the cam follower contacts the cam lobe during shifting movement, then the shifting arc is extended, but the cam follower may encounter obstacles
Solution Approach 1:
The cam lobe surface is designed with specific local qualities - a smooth, obstacle-free contact surface that allows the cam follower to move freely during shifting. This localized modification of the cam surface geometry ensures that the extended shifting path along the lobe does not introduce obstacles, maintaining reliability while extending shifting time.
Data Source
AI summary
An internal combustion engine includes a cam shifting system having a shifting unit rotatably fixed and axially moveable with respect to a camshaft. The shifting unit includes at least two cams configured to be selectively brought in contact with a cam follower and provided with a base circle and with at least one cam lobe. The shifting unit is provided with at least one groove having a shifting portion. A driving pin is operable to be selectively engaged with and disengaged from the shifting portion of the groove. Engagement between the driving pin and the shifting portion of the groove moves the shifting unit with respect to the camshaft. During the movement of the shifting unit the cam follower engages at least a portion of at least one cam lobe.