Variable Valve Actuation Mechanism with Dual Roller Cam Follower

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Solution Overview

Problem

Variable valve actuation mechanisms in internal combustion engines experience wear due to harsh conditions and high cycle numbers, particularly from edge contact and skidding issues with existing single-roller cam followers.

Innovation Solution

A variable valve actuation mechanism using two concentrically arranged camshafts with a cam follower comprising two rollers, each adapted to follow a respective cam, reducing edge contact and skidding risks through individual rotational speed adaptation and crowned contact surfaces, which are designed to minimize axial misalignment and edge contact.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single roller cam follower is used, then the device complexity is reduced, but wear increases due to edge contact and skidding

Engineering Contradiction:

Improvecam follower structureVSAvoidwear resistance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The cam follower is segmented into two separate rollers instead of a single roller. Each roller independently contacts a respective cam, allowing them to rotate at different speeds and preventing edge contact and skidding, thereby reducing wear while maintaining reasonable structural complexity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The solution transitions from a single-point contact in one dimension to a distributed contact system across two dimensions. The two rollers are arranged to contact different cams, creating a multi-dimensional contact pattern that eliminates the edge contact problems of single-roller designs

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If two concentric camshafts with two rollers are used, then wear is reduced by preventing edge contact and skidding, but device complexity increases

Engineering Contradiction:

Improvewear resistanceVSAvoidcamshaft and cam follower arrangement

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The camshafts are arranged concentrically with one camshaft inside the other, creating a nested configuration. The two rollers are positioned to contact the respective cams on these concentric camshafts, achieving compact space utilization while maintaining the wear-reducing two-roller architecture

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The two camshafts and two rollers are merged into a single integrated valve actuation mechanism. The concentric arrangement combines the camshafts spatially, while the shared rocker arm combines the actuation function, reducing overall system complexity despite using two rollers

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If rollers are allowed to rotate independently at different speeds, then skidding is prevented, but manufacturing precision requirements increase

Engineering Contradiction:

Improveskidding preventionVSAvoidroller alignment and contact surface geometry

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The roller design allows independent rotational movement of each roller about its own axis. This dynamic capability enables each roller to rotate at the speed required by its respective cam profile, preventing skidding. The crowned contact surfaces further adapt to minor misalignments, reducing manufacturing precision requirements

Inventive Principle:

Principle #15Dynamics

4Reliability

If crowned contact surfaces are used on rollers, then edge contact is minimized and wear is reduced, but manufacturing complexity increases

Engineering Contradiction:

Improvewear reductionVSAvoidroller contact surface fabrication

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The contact surfaces of the rollers are crowned with a curved profile rather than being flat. This spherical/curved geometry concentrates contact on the central portion of the roller-cam interface, minimizing edge contact and reducing wear. While crowned surfaces require slightly more complex manufacturing than flat surfaces, the benefit in wear reduction justifies the added fabrication step

Inventive Principle:

Principle #14Spheroidality (Curvature)

Data Source

PatentEP3337960B2A variable valve actuation mechanism, an internal combustion engine, and a vehicle

Publication Date: 2022.11.16 VOLVO TRUCK CORP

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AI summary

The invention provides a variable valve actuation mechanism for an internal combustion engine comprising at least one valve (201) and comprising - two concentrically arranged camshafts (301, 302), - a cam set comprising two cams (303, 304), each fixed to a respective of the camshafts (301, 302), whereby the camshafts (301, 302) are arranged to be turned in relation to each other, so as to change the combined profile of the cams (303, 304), and - a cam follower (311) adapted to follow the combined profile of the cams (303, 304) and to actuate at least one of the at least one valve (201) in dependence on the combined profile of the cams (303, 304), - wherein the cam follower (311) comprises two rollers (312, 313), each roller (312, 313) being adapted to follow a respective of the cams (303, 304).