Switchable Finger Follower Radial Play Elimination
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Solution Overview
Problem
Existing switchable finger followers for internal combustion engine valve trains face issues with radial play between the inner or outer levers and the shaft, leading to potential switching errors and risk of damage due to displacement, especially during cam approach flank contact.
Innovation Solution
The use of a pointed arch profile, composed of two circular arcs, in the bore of the inner or outer lever eliminates radial play by providing a rotatable and secure line contact with the shaft, ensuring proper alignment and coupling without radial movement, which can be enhanced by an angle of approximately 45° between the contact points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a radial clearance fit is used for mounting the inner or outer lever on the shaft, then the lever can rotate freely, but radial play occurs leading to switching errors and potential damage
Solution Approach 1:
The bore profile is changed from a standard circular shape to a pointed arch profile composed of two circular arcs. This geometric parameter change eliminates radial play while preserving rotational capability, as the pointed arch shape provides line contact that prevents radial displacement but allows angular movement.
Solution Approach 2:
The bore is designed with a curved pointed arch profile consisting of two circular arcs instead of a straight or simple circular bore. This curvature design creates a Gothic-like arch shape that provides both rotational freedom and eliminates radial clearance through its geometric configuration.
2Ease of operation
If the coupling piston is only slightly moved into the counter-contour, then switching is possible, but edge contact occurs leading to breakage or smearing of the contact
Solution Approach 1:
The pointed arch bore profile prevents radial displacement of the lever before the switching operation occurs. By eliminating radial play in advance, the system prevents the conditions that lead to edge contact and subsequent contact breakage or smearing during the switching process.
Solution Approach 2:
The geometric parameter of the bore profile is changed to a pointed arch shape, which fundamentally alters the contact mechanics between the lever and shaft. This parameter change ensures that the lever maintains a stable, radially fixed position while allowing rotation, thereby preventing premature edge contact.
3Adaptability or versatility
If the inner lever is at a slight angle to the outer lever, then partial coupling occurs, but the coupling slider does not enter its counter-contour with entire width leading to unreliable switching
Solution Approach 1:
The bore profile parameter is changed to a pointed arch shape that eliminates radial play while preserving rotational freedom. This ensures that the lever maintains proper angular alignment with the shaft, preventing the slight angular deviations that cause incomplete coupling and unreliable switching.
Solution Approach 2:
The curved pointed arch profile of the bore provides a geometric constraint that guides the lever into the correct angular position. The two circular arcs forming the arch create a natural alignment feature that ensures complete coupling of the slider with the counter-contour while allowing necessary rotational movement.
Data Source
AI summary
A switchable finger follower for a valve train of an internal combustion engine includes an outer and an inner lever, which at a first longitudinal end run pivotably relative to one another via respective bores on a common shaft. At this longitudinal end, the finger follower has a gas-exchange valve contact face on an underside. The outer lever has a pivot bearing on the underside at a further longitudinal end, and at least the inner lever has a cam running face on an upper side. The inner and outer levers are connectable to one another via at least one coupling slide, which spans a separation area between the levers. The outer and inner levers are braced relative to one another via a cam return spring, and the shaft is connected to the bore of the outer lever by an interference fit. To mount the inner lever relative to the shaft without radial play but in a rotatable fashion, the bore of the inner lever includes, in its semi-circular segment facing the upper side, a pointed arch composed of two circular arcs as contact means.