Dual Camshaft Structure With Segmented Base Pipe

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Solution Overview

Problem

Conventional dual camshaft structures face challenges in ensuring rigidity, securing cams to the inner shaft, controlling clearance between components, and maintaining a smooth outer peripheral surface, leading to issues with valve timing, noise, and increased costs due to the need for multiple units for different engine types.

Innovation Solution

A dual camshaft structure featuring a first cylindrical member with a secured cam and a second cylindrical member with a variable cam, where the second member is rotatably installed outside the first member and secured to the inner shaft via a connection member through notches on both members, enhancing rigidity and allowing for precise control of clearances and surface smoothness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If plural cams are fitted into a single base pipe to form a single unit, then the structure is simplified and can be used across different engine types, but the area for securing the cams to the inner shaft by pins is insufficient and the connection strength is reduced

Engineering Contradiction:

Improveapplicability to different engine typesVSAvoidconnection strength of cams to inner shaft

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

The base pipe is divided into separate base pipes for each cam, rather than using a single base pipe for multiple cams. This segmentation allows each cam to have its own dedicated base pipe and pin arrangement, ensuring sufficient connection area and strength while still allowing the same design to be applied across different engine types.

Inventive Principle:

Principle #1Segmentation

2Strength

If two notches are formed on the outer shaft to allow pin penetration, then the cams can be secured to the inner shaft, but the rigidity of the outer shaft is reduced

Engineering Contradiction:

Improveconnection strength of cams to inner shaftVSAvoidrigidity of outer shaft

Core Design Contradiction:

StrengthVSStability of the object's composition

Solution Approach 1:

The notches are removed from the outer shaft and transferred to the base pipe. The base pipe now carries the notches that allow pin penetration, while the outer shaft remains intact without notches, preserving its rigidity. The base pipe acts as the intermediate structure that provides both the notch features and the connection function.

Inventive Principle:

Principle #2Taking out (Extraction)

3Stability of the object's composition

If the outer shaft is made thick to compensate for the reduction in rigidity caused by notches, then the rigidity is improved, but the cam bearing becomes larger and weight saving is hindered

Engineering Contradiction:

Improverigidity of outer shaftVSAvoidweight of camshaft assembly

Core Design Contradiction:

Stability of the object's compositionVSWeight of moving object

Solution Approach 1:

The notches are extracted from the outer shaft and placed in the base pipe instead. This allows the outer shaft to maintain its original thickness and rigidity without requiring additional material, thereby avoiding weight increase while still providing the necessary pin penetration features through the base pipe.

Inventive Principle:

Principle #2Taking out (Extraction)

4Ease of operation

If the outer peripheral surface of the outer shaft is made smooth for sliding contact with the cam, then the sliding performance is improved, but the surface becomes rough when the cam is installed by press-fitting

Engineering Contradiction:

Improvesliding performance of cam on outer shaftVSAvoidsurface smoothness of outer peripheral surface

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The outer shaft is segmented into two functional zones: an upper portion with a smooth outer peripheral surface for sliding contact with the cam, and a lower portion that receives the base pipe. The base pipe, rather than the outer shaft, is press-fitted to the outer shaft, so the press-fitting operation does not affect the smooth sliding surface of the outer shaft.

Inventive Principle:

Principle #1Segmentation

5Device complexity

If a single base pipe with multiple cams is used, then the structure is simplified, but different units have to be prepared for different engine types increasing cost

Engineering Contradiction:

Improvestructural complexity of camshaft assemblyVSAvoidcompatibility across different engine types

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The camshaft assembly is segmented into modular components: individual base pipes for each cam, each cam, and the outer shaft. These standardized modules can be independently manufactured and then assembled in different configurations to suit different engine types, reducing the need for completely different units while maintaining structural simplicity.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS8833202B2Dual camshaft structure and method for assembling dual camshaft structure

Publication Date: 2014.09.16 TOYOTA JIDOSHA KK

AI summary

In a dual camshaft structure, an inner shaft provided with a variable cam is inserted into an outer shaft provided with a secured cam. In the dual camshaft structure, the secured cam is provided on a first cylindrical member, the first cylindrical member is secured to the outside of the outer shaft, the variable cam is provided on the second cylindrical member, and the second cylindrical member is installed at the outside of the first cylindrical member and is secured to the inner shaft by a connection member via a notch provided on the first cylindrical member and a notch provided on the outer shaft. Therefore, the rigidity of the dual camshaft structure can be ensured, and a slidable surface of a cam rotatable at the outside of the outer shaft can be held.