Angled Tappet Contact Surface for Fuel Pump Plunger Alignment
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Solution Overview
Problem
Existing fuel pump mechanisms for internal combustion engines face issues with high contact stresses due to misalignment of components, leading to wear and potential failure, as the cam load is often transferred to the edge of the plunger contact surface, causing high point stresses despite attempts to distribute it evenly.
Innovation Solution
The intermediate member's contact surface is angled to ensure orthogonal contact with the plunger's axis during the pumping stroke, allowing for a larger radius on the plunger and reducing edge contact, thereby maintaining contact stresses within material capabilities and enabling higher pressure operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a radius is provided on the end of the plunger to distribute cam load, then contact stresses are reduced, but edge contact occurs when the tappet tilts within the tappet location bore
Solution Approach 1:
The contact surface of the tappet is given an asymmetric angled configuration rather than a symmetric flat surface. This asymmetric design allows the contact surface to remain orthogonal to the tappet location bore axis even when the tappet tilts, preventing edge contact while distributing cam load across the contact surface.
Solution Approach 2:
The angle of the tappet contact surface is specifically designed to match the anticipated tilt angle of the tappet. By changing the geometric parameter (contact surface angle) to correspond to the expected operational condition (tappet tilt angle), the system maintains optimal contact conditions throughout the pumping stroke.
2Ease of manufacture
If the contact surfaces of the plunger and tappet are both flat, then manufacturing is simpler, but misalignment of axes results in high point stresses at the edge
Solution Approach 1:
Instead of using two flat contact surfaces which would be simple to manufacture but cause edge stress under misalignment, the tappet contact surface is given an asymmetric angled configuration. This design choice prioritizes stress distribution over manufacturing simplicity, as the angled surface can be manufactured with standard machining operations.
3Reliability
If a larger radius is provided on the plunger to maintain contact stresses within material capabilities, then durability is improved, but edge contact occurs when the tappet tilts
Solution Approach 1:
The angled contact surface creates an asymmetric geometry that prevents edge contact during tappet tilt. This geometric configuration allows for optimal radius selection on the plunger end without the risk of edge contact, thereby improving durability while maintaining appropriate contact geometry.
Solution Approach 2:
The tappet contact surface is pre-angled to anticipate the tilt that will occur during operation. This preliminary geometric configuration ensures that even when the tappet tilts under cam load, the contact surface remains orthogonal to the tappet location bore axis, preventing edge contact before it can occur.
Data Source
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AI summary
Internal combustion engine fuel pumping mechanism (200), comprising a pumping element (214) such as a plunger, moveable within first location bore (220), an intermediate member (212) such as a tappet, movable within a second location bore, and a driving mechanism such as a cam (210), wherein during a pumping stroke, cam load is transferred to the plunger (214) via contact surfaces plunger (218) and tappet contact surfaces (216), the plunger contact surface (218) being radiused, and the tappet contact surface (216) being angled at a selected angle (A) with respect to an axial axis of the tappet (212), such that when the tappet (212) tilts within the second location bore on application of cam load, the tappet (212) contact surface becomes orthogonal with a longitudinal axis of the second bore and the plunger (214), ensuring a substantially central contact point between the contact surfaces. The inventive concept also extends to an intermediate member (212) comprising a contact surface (216) which is angled with respect to an axial axis of the intermediate member (212).