Variable valve actuation mechanism for an internal combustion engine

Abstract

Engaging portions 132c, each of which is engaged with a slider gear, are made of an iron based material, and coupler shafts 132d are made of an aluminum alloy material that is the same material as that of a cylinder head. Therefore, compared to a case where the control shaft 132 is entirely made of an iron based material, the thermal expansion coefficient of the control shaft 132 is closer to that of the cylinder head. Therefore, even if the ambient temperature changes, the position of each engaging portion 132c relative to the cylinder head is prevented from being displaced. Also, since the engaging portions 132c are made of an iron based material, the engaging portions 132c have a sufficient strength, which prevents the control shaft 132 from being deformed.

Description

[0001] This is a 371 national phase application of PCT / JP2005 / 000949 filed 19 Jan. 2005 claiming priority to Japanese Applications No. 2004-010896 filed 19 Jan. 2004, No. 2004-153936 filed 24 May 2004, and No. 2004-226145 filed 02 Aug. 2004, the contents of which are incorporated herein by reference.FIELD OF THE INVENTION [0002] The present invention relates to a variable valve actuation mechanism for an internal combustion engine that adjusts the actuation of valves by axially moving a control shaft with an actuator in the engine. BACKGROUND OF THE INVENTION [0003] For example, Japanese Laid-Open Patent Publication No. 2001-263015 discloses such a variable valve actuation mechanism. In this mechanism, a control shaft is axially moved with an actuator, so that a slider gear engaged with the control shaft is moved axially. Accordingly, the valve actuation such as the valve duration angle and the valve lift is adjusted. SUMMARY OF THE INVENTION [0004] Since the control shaft of a vari...

AI Technical Summary

Benefits of technology

[0004] Since the control shaft of a variable valve actuation mechanism axially moves the slider gear, a portion of the control shaft that is engaged with the slider gear receives a great force. Particularly, when the slider gear is moved in a direction for increasing the valve lift, the engaging portion is likely to receive a great force. Therefore, if the control shaft has an insufficient strength, the engaging portion can be deformed. To prevent such deformation, a control shaft is made of a high-strength material such as an iron based material.

[0005] However, in a case where the cylinder head of an engine is made of a light alloy material such as an aluminum alloy to reduce the weight of the engine, the thermal expansion coefficient of the cylinder head is significantly greater than that of the iron based material. Specifically, the thermal expansion coefficient of the cylinder head is about twice as great as that of the iron-based material. Thus, if an iron-based material is used for the control shaft of a variable valve actuation mechanism, the position of the engaging portion of the control shaft relative to the cylinder head is displaced between when the engine is cold and when the engine has been warmed up. Therefore, even if the actuator detects the amount of movement of the control shaft to control the movement amount of the control shaft, the axial displacement of the engaging portion due to a temperature change can hinder an accurate control of a valve actuation such as the valve lift.

Problems solved by technology

Particularly, when the slider gear is moved in a direction for increasing the valve lift, the engaging portion is likely to receive a great force.

Therefore, if the control shaft has an insufficient strength, the engaging portion can be deformed.

Therefore, even if the actuator detects the amount of movement of the control shaft to control the movement amount of the control shaft, the axial displacement of the engaging portion due to a temperature change can hinder an accurate control of a valve actuation such as the valve lift.

However, since a light alloy material such as an aluminum alloy is not as strong as an iron-based material, the engaging portion is likely to be deformed by a reaction force applied by the slider gear.

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