Switchable Cam Follower Conical Taper Edge Contour
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Solution Overview
Problem
The existing cam followers, such as roller tappets, experience increased contact forces and lash due to tilting pistons during coupling, leading to deformation and potential jamming, especially under high loads, due to a two-point contact at the edge region which intensifies with shape and parallelism variations.
Innovation Solution
The piston's entraining surface tapers conically from the front end to the rear, with a cylindrical, outwardly arched contour at the edge region, shifting the contact zone from the inner edge to the outer counter surface, reducing wear and allowing for coarser manufacturing tolerances, and optionally featuring a convex shape for easier hydraulic displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat entraining surface is used on the piston, then manufacturing is simpler, but contact forces concentrate at the edge region causing deformation and jamming
Solution Approach 1:
The entraining surface is configured with a conical taper and an outwardly arched cylindrical contour instead of a flat surface. This curved geometry redistributes the contact forces from the edge region to the radially outer counter surface, preventing stress concentration that would cause deformation and jamming, while maintaining manufacturing feasibility through standard machining and shaping methods.
Solution Approach 2:
The piston features a composite surface geometry where the edge region has a cylindrical outwardly arched contour and the main surface has a conical taper. This local differentiation of surface properties ensures that contact occurs at the optimized radially outer position rather than at the vulnerable edge, improving reliability without significantly complicating manufacturing.
2Ease of operation
If the contact zone is at the edge region, then coupling is achieved, but contact forces rise extremely causing wear and lash increase
Solution Approach 1:
The conical taper and outwardly arched cylindrical contour of the entraining surface redirect the contact zone from the edge region to the radially outer counter surface. This geometric modification maintains the coupling function while distributing contact forces over a larger area, preventing extreme force concentration and reducing wear.
3Manufacturing precision
If manufacturing tolerances are tight for the entraining surface angle, then contact zone positioning is accurate, but manufacturing costs increase
Solution Approach 1:
The conical taper angle of the entraining surface is designed within a preferred range (5-15 degrees) to optimize the redistribution of contact forces. This parameter optimization allows for coarser manufacturing tolerances while still achieving reliable contact zone positioning at the radially outer counter surface, reducing manufacturing costs without sacrificing performance.
Data Source
AI summary
The invention proposes a switchable cam follower (1) for a valve train of an internal combustion engine, said cam follower comprising two elements (2, 3) telescoped into each other and, axially displaceable relative to each other. A bore (4) comprising at least one piston (5) extends in the inner element (2). The piston (5) has, on a portion of its outer peripheral surface (7), a stepped entraining surface (8) that starts from the first front end (6) of the piston (5) facing the outer element (3). For achieving coupling, the piston (5) can be displaced with this entraining surface (8) onto a flat counter surface (10) of the other element (3). The entraining surface (8) of the piston (5) extends, starting from the first front end (6), toward a second front end (11) of the piston (5) while tapering into a conical shape generally in the direction toward a longitudinal axis of the piston (5). Besides this, an edge region (12) of the entraining surface (8) on the first front end (6) is additionally provided with a cylindrical, outwards arched (with reference to a starting point of the radius (R)) contour (13) that extends orthogonally to the longitudinal axis of the piston (5). In this way, during the coupled state of the piston (5) and its inevitable tilting, the edge abrasion feared in the prior art does not occur any longer. The manufacturing tolerances in the region of coupling can be coarsened, i.e. slackened.