DOHC Engine Axial Size Reduction via Idle Gear Overlap
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Solution Overview
Problem
The existing internal combustion engine designs with DOHC-type valve trains have a larger size due to the increased axial length of camshafts and protruding driven gears, which necessitate a reduction in camshaft protrusion and driven gear positioning to minimize engine size.
Innovation Solution
The engine configuration includes an idle chain sprocket positioned axially overlapping with the bearing wall and camshaft holder, allowing the idle gear to be closer to the bearing wall, and the driven gears to be positioned with reduced protrusion, thereby reducing the engine's axial size by integrating the idle chain sprocket with the bearing wall and camshaft holder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the camshafts are supported by bearings at directly upper portions of the bearing wall without axial displacement, then the camshaft support structure is simplified, but the driven gears must be positioned axially apart from the bearing wall which increases the axial length of camshafts and overall engine size
Solution Approach 1:
The patent repositions the idle chain sprocket in the axial dimension to overlap with the bearing wall and camshaft holder axially. This dimensional rearrangement allows the driven gears to be positioned closer to the bearing wall, reducing the axial length of camshafts while maintaining the simplified bearing support structure.
2Ease of operation
If the idle gear is positioned adjacent to the cylinder head outside wall axially apart from the bearing wall, then the idle gear can mesh with driven gears, but the driven gears must be positioned beyond the idle chain sprocket which enlarges the engine size
Solution Approach 1:
The patent repositions the idle chain sprocket axially to overlap with the bearing wall and camshaft holder, creating space for the driven gears to be positioned closer to the bearing wall. This axial dimensional change allows gear meshing while reducing the overall engine size.
Solution Approach 2:
The patent merges the axial positions of the idle chain sprocket, bearing wall, and camshaft holder by positioning them to overlap axially. This consolidation of components in the axial dimension eliminates unnecessary spacing and reduces engine size while maintaining proper gear engagement.
Data Source
AI summary
An internal combustion engine is provided with a DOHC-type valve train in a cylinder head. The valve train includes an intake side camshaft with an intake side driven gear, and an exhaust side camshaft with an exhaust side driven gear. The cylinder head supports therein a spindle with an idle gear with an idle chain sprocket fixed thereto. The idle gear is in meshing engagement with both the intake and exhaust side driven gears. Rotary power of a crankshaft is transmitted via a cam chain to the idle gear to rotate both the intake and exhaust side camshafts. These camshafts are supported by bearings of a bearing wall and a camshaft holder. These bearings and camshaft holder are located, for compact arrangement, at a position axially coinciding or overlapping with the idle chain sprocket.