Valve train for internal combustion engine Number:7,367,297 from the United States Patent and Trademark Office (PTO) owispatent A valve train includes a primary rocker arm 50 oscillating about a primary oscillating center line L4 in response to the rotation of an inlet cam 21, a secondary rocker arm 60 oscillating about a secondary oscillating center line L5 so as to transmit a valve drive force via the primary rocker arm 50 to the inlet valve 14 and a holder 30 which supports the primary and secondary rocker arms 50, 60 in an oscillatory fashion in such a manner that the primary and secondary oscillating center lines L4, L5 oscillate together. A cam profile 55 has a lost motion profile 55a a drive profile 55b are formed on an abutment portion 54 of the primary rocker arm 50. A sectional shape of the lost motion profile 55a is an arc-like shape which is formed about the primary oscillating center line L4.<H combustion, internal, Valve, train, for, 7367297.html, Patent, pto, 7367297

Title: Valve train for internal combustion engine

Abstract: A valve train includes a primary rocker arm 50 oscillating about a primary oscillating center line L4 in response to the rotation of an inlet cam 21, a secondary rocker arm 60 oscillating about a secondary oscillating center line L5 so as to transmit a valve drive force via the primary rocker arm 50 to the inlet valve 14 and a holder 30 which supports the primary and secondary rocker arms 50, 60 in an oscillatory fashion in such a manner that the primary and secondary oscillating center lines L4, L5 oscillate together. A cam profile 55 has a lost motion profile 55a a drive profile 55b are formed on an abutment portion 54 of the primary rocker arm 50. A sectional shape of the lost motion profile 55a is an arc-like shape which is formed about the primary oscillating center line L4.

Patent Number: 7,367,297 Issued on 05/06/2008 to Tashiro

Inventors: Tashiro; Masahiko (Saitama, JP)
Assignee: Honda Motor Co., Ltd. (Tokyo, JP)

Appl. No.: 10/589,244

Filed: February 17, 2005

PCT Filed: February 17, 2005

PCT No.: PCT/JP2005/002965

371(c)(1),(2),(4) Date: August 14, 2006

PCT Pub. No.: WO2005/078244

PCT Pub. Date: August 25, 2005

Foreign Application Priority Data


Feb 17, 2004 [JP]			2004-040246
Feb 17, 2004 [JP]			2004-040247

Current U.S. Class: 123/90.16 ; 123/90.15; 123/90.39

Current International Class: F01L 1/34 (20060101)

Field of Search: 123/90.16,90.15,90.39

References Cited [Referenced By]

U.S. Patent Documents


6684832	February 2004	Codina et al.
2002/0007809	January 2002	Miyazato et al.

Foreign Patent Documents


2 486 440	Nov., 2003	CA
1 039 103	Sep., 2000	EP
2 186 337	Aug., 1987	GB
58-214610	Dec., 1983	JP
5-71321	Mar., 1993	JP
7-91217	Apr., 1995	JP
2002-235515	Aug., 2002	JP
2004/009967	Jan., 2004	WO

Primary Examiner: Denion; Thomas
Assistant Examiner: Eshete; Zelalem
Attorney, Agent or Firm: Arent Fox LLP

Claims

The invention claimed is:

1. A valve train for an internal combustion engine, comprising: a valve operating cam rotating around a rotational center line in synchronism with a rotation of an engine; an engine valve including at least one of an inlet valve and an exhaust valve; a transmission mechanism for transmitting a valve drive force of the valve operating cam to the engine valve so as to operate the engine valve in open and close states, the transmission mechanism including; a primary oscillating member oscillating about a primary oscillating center line; a secondary oscillating member oscillating about a secondary oscillating center line through abutment with the primary oscillating member so as to transmit the valve drive force via the primary oscillating member to the engine valve, and a holder supporting the primary and secondary oscillating members thereon in an oscillatory fashion; wherein the primary and secondary oscillating center lines oscillate together with the holder, and a drive abutment portion of the primary oscillating member abuts with a follower abutment portion of the secondary oscillating portion; a driving mechanism for driving the holder so as to control valve properties including opening and closing timings and maximum lift amount of the engine valve in accordance with a position of the holder which is driven by the driving mechanism, wherein the holder oscillates about a holder oscillating center line which differs from the rotational center of the valve operating cam in response to the operation of the driving mechanism, a cam profile having a lost motion profile for maintaining the engine valve in the closed state by abutting the drive abutment portion with the follower abutment portion and a drive profile for driving the engine valve in the open state is formed on at least one of the drive and follower abutment portions, and in a sectional shape of the lost motion profile in a plane which intersects at right angles with the primary oscillating center line is an arc-like shape of which center is the primary oscillating center line.

2. The valve train for the internal combustion engine as set forth in claim 1, wherein the primary oscillating member has a cam abutment portion which abuts with the valve operating cam, the secondary oscillating member has a valve abutment portion which abuts with the engine valve, a primary intersection point is defined as a point intersecting a plane which intersects at right angles with the holder oscillating center line and the primary oscillating center line, a secondary intersection point is defined as a point intersecting a plane which intersects at right angle with the holder oscillating center line and the secondary oscillating center line, and a distance between the holder oscillating center line and the primary intersection point is greater than a distance between the holder oscillating center line and the secondary intersection point.

3. The valve train for the internal combustion engine as set forth in claim 1, wherein the holder includes: an operative portion on which a drive force of the driving mechanism is applied; a base portion which extends from the holder oscillating center line toward the operative portion, and having a secondary support portion supporting the secondary oscillating member thereon in an oscillatory fashion; and a projecting portion projecting from the base portion to the valve operating cam, and having a primary support portion supporting a primary oscillating member thereon in an oscillatory fashion, wherein the primary and secondary support portions are disposed between the holder oscillating center line and the operative portion in a direction which intersects at right angles with a plane which includes a cylinder axis of the internal combustion engine and which is parallel to the rotational center line.

4. The valve train for the internal combustion engine as set forth in claim 1, wherein the valve operating cam is a primary valve operating cam made up of one of an inlet cam and an exhaust cam which are provided on a camshaft, and the engine valve is a primary engine valve adapted to operate opening and closing operations by the primary valve operating cam and made up of one of the inlet valve and the exhaust valve, the valve train further comprises: a tertiary oscillating member adapted to be oscillated by a secondary valve operating cam made up of the other of the inlet cam and the exhaust cam so as to actuate a secondary engine valve made up of the other of the inlet valve and the exhaust valve to operate open and close state; and a support shaft which supports the tertiary oscillating member in an oscillatory fashion, and wherein an accommodation space in which the support shaft is accommodated is formed in the holder.

5. The valve train for the internal combustion engine as set forth in claim 4, wherein the accommodation space is formed in the primary oscillating member in which the drive abutment portion has the cam profile, and is located at a position defined between the primary oscillating center line and the lost motion profile in a radial direction which radiates from the primary oscillating center line as a center.

6. The valve train for the internal combustion engine as set forth in claim 1, wherein the valve operating cam is a primary valve operating cam made up of one of an inlet cam and an exhaust cam which are provided on a camshaft, and the engine valve is a primary engine valve adapted to operate opening and closing operations by the primary valve operating cam and made up of one of the inlet valve and the exhaust valve, the valve train further includes: a tertiary oscillating adapted to be oscillated by a secondary valve operating cam made up of the other of the inlet cam and the exhaust cam so as to actuate a secondary engine valve made up of the other of the inlet valve and the exhaust valve to operate open and close states; and a support shaft which supports the tertiary oscillating member in an oscillatory fashion, and wherein the accommodation space in which the support shaft is accommodated is formed in the primary oscillating member in which the drive abutment portion has the cam profile, and is located at a position defined between the primary oscillating center line and the lost motion profile in a radial direction which radiates from the primary oscillating center line as a center.

7. A valve train for an internal combustion engine comprising: a valve operating cam rotating around a rotational center line in synchronism with a rotation of the engine, an engine valve including at least one of an inlet valve and an exhaust valve; a transmission mechanism for transmitting a valve drive force of the valve operating cam to the engine valve so as to operate the engine valve in open and close states, the transmission mechanism including: a primary member which abuts with the valve operating cam; a rocker arm which oscillates about an oscillating center line by virtue of abutment with the primary member, and having a valve abutment portion having a valve abutment surface which abuts with the engine valve thereon; and a holder supporting the rocker arm in an oscillatory fashion and oscillating about a holder oscillating center line which differs from the rotational center line of the valve operating cam in response to the operation of the drive mechanism, wherein the oscillating center line oscillates together with the holder, and the rocker arm whose oscillating position relative to the holder is regulated by the primary member, a driving mechanism for driving the holder so as to control valve properties including opening and closing timings and maximum lift amount of the engine valve in accordance with a position of the holder which is driven by the driving mechanism, wherein in a rest state which is defined where the primary member which is in abutment with the valve operating cam abuts with the rocker arm, and where the rocker arm does not oscillate relative to the holder, a sectional shape of the valve abutment surface on a plane which intersects at right angles with the holder oscillating center line is an arc-like shape which is formed about the holder oscillating center line.

8. The valve train for the internal combustion engine as set forth in claim 7, wherein the primary member has a cam abutment portion which is brought into abutment with the valve operating cam and constitutes a primary rocker arm which is caused to oscillate about a primary oscillating center line, and the rocker arm constitutes a secondary rocker arm.

9. The valve train for the internal combustion engine as set forth in claim 8, wherein the holder oscillating center line intersects at right angles with the valve abutment portion of the secondary rocker arm which is in the rest state.

10. The valve train for the internal combustion engine as set forth in claim 8, wherein an operative portion on which a drive force of the drive mechanism acts is provided on the holder at a location thereof which is farthest apart from the holder oscillating center line on a plane which intersects at right angles with the holder oscillating center line.

11. The valve train for the internal combustion engine as set forth in claim 8, wherein the primary rocker arm is supported on the holder in an oscillatory fashion, and as an oscillating position of the holder approaches a predetermined position where a valve operating property is obtained where the maximum lift amount becomes maximum, a cam abutment position where the cam abutment portion and a cam lobe portion of the valve operating cam abut with each other approaches a specific straight line which passes through the holder oscillating center line and the rotational center line on the plane which intersects at right angles with the holder oscillating center line.

12. The valve train for the internal combustion engine as set forth in claim 8, wherein the primary rocker arm is supported on the holder in an oscillatory fashion in such a manner that the primary oscillating center line oscillates together with the holder, wherein one of a drive abutment portion of the primary rocker arm and a follower abutment portion of the secondary rocker arm which are brought into abutment with each other has a cam profile having, in turn, a lost motion profile which holds the engine valve in the closed state through abutment with the other abutment portion of the drive abutment portion and the follower abutment portion and a drive profile which puts the engine valve in the open state, and when the holder oscillates in an oscillating direction in which the holder moves apart from the rotational center line, a cam abutment position where the valve operating cam abuts with the cam abutment portion shifts, and at the same time an arm abutment portion where the cam profile abuts with the other abutment portion shifts in a direction in which the maximum lift amount is reduced and in a direction in which the arm abutment position moves apart from the rotational center line.

13. The valve train for the internal combustion engine as set forth in claim 2, wherein the valve abutment portion is provided with an adjusting unit which adjusts a valve clearance defined between the engine valve and the valve abutment portion.

14. The valve train for the internal combustion engine as set forth in claim 1, wherein the driving mechanism is provided on at least one of a cylinder.

15. The valve train for the internal combustion engine as set forth in claim 1, wherein the driving mechanisms are provided on cylinders, respectively.

16. The valve train for the internal combustion engine as set forth in claim 1, wherein the holders provided in each cylinders are formed to be integral.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Stage entry of International Application Number PCT/JP2005/002965, filed Feb. 17, 2005. The disclosure of the prior application is hereby incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present invention relates to a valve train for an internal combustion engine, and more particularly to a valve train which can change the valve operating properties including opening and closing timings and maximum lift amount of an engine valve made up of at least one of an inlet valve and an exhaust valve.

BACKGROUND ART

A valve train for an internal combustion engine which can change the valve operating properties of engine valves is disclosed in, for example, Japanese Patent Unexamined Publication No. JP-A-58-214610. The valve train so disclosed includes a rocker arm (hereinafter, referred to as a primary rocker arm) supported in an oscillatory fashion on a fixed point or fulcrum which is eccentric to a rocker shaft and adapted to be oscillated by a primary cam which rotates in synchronism with the rotation of the engine and a oscillating cam which is rotatably supported on a camshaft which is in parallel with the rocker shaft. A cam profile made up of a base circle portion where an inlet valve remains not lifted and a lifting lobe portion where the inlet valve is lifted and a contact surface with which the primary rocker arm is brought into abutment are formed on the oscillating cam which opens and closes an inlet valve provided in a cylinder head. The inlet valve is opened and closed in accordance with rotational positions of the primary cam when the valve drive force of the primary cam is transmitted to the oscillating cam via the primary rocker arm. Then, opening and closing timings and maximum lift amount of the inlet valve are changed by displacing the fulcrum. Here, it is understood that the camshaft, which supports the oscillating cam, is not displaced relative to the cylinder head.

For other conventional apparatuses for changing the valve operating properties of engine valves of internal combustion engines, there are apparatuses which are disclosed, for example, in Japanese Patent Unexamined Publications Nos. JP-A-7-91217, and JP-A-5-71321. An apparatus disclosed in the JP-A-7-91217 includes a drive shaft which is driven to rotate by an internal combustion engine, a camshaft which is provided on an outer circumference of the drive shaft in such a manner as to rotate freely relative to the drive shaft and which has a cam for actuating an inlet valve to be opened and closed, a disk housing provided so as to oscillate freely about a pivot support pin as a fulcrum in a radial direction relative to the drive shaft, an annular disk rotatably supported on an inner circumferential surface of the disk housing, a drive mechanism for oscillating the disk housing and a rocker arm which is pivot supported in an oscillatory fashion on a rocker shaft which is supported on the disk housing at one end portion thereof and which abuts with the cam and the inlet valve. Then, when the disk housing is cause to oscillate by the drive mechanism, the center of the annular disk becomes eccentric to the axial center of the drive shaft, whereby the angular velocity of the camshaft is changed, and then the operation angle of the inlet valve is changed. At the same time, due to the displacement of the rocker shaft which oscillates together with the disk housing, the pivot support point of the rocker arm is changed, and the other end portion of the rocker arm shifts in a diametrical direction on an upper surface of a valve lifter, whereby a rocker ratio relative to the inlet valve is changed, the valve lift amount being thereby changed.

In addition, a variable valve train disclosed in the JP-A-5-71321 includes a rocker arm which is brought into contact with a rotating cam and an inlet valve, a lever which is rotatably supported on a fulcrum shaft so as to be joined to a back side of the rocker arm in an oscillatory fashion, a link which connects the fulcrum shaft to the rocker arm and a controller cam which changes over the position of the lever from a high lift position where the position of the lever approaches the cam to a low lift position where the position of the lever moves apart from the cam. In a state where the rocker arm contacts a base circle of the cam, a distal end of a joint portion of the lever which connects a point where the lever contacts the rocker arm at a low lift position to a point where the lever contacts the rocker arm at a high lift position is formed into a concentric arc-like sectional shape which is formed about the fulcrum shaft, and a joint portion of the rocker arm which contacts the inlet valve is formed into a concentric arc-like sectional shape. Then, by changing over the lever position to the low lift position or high lift position, the valve lift amount of the inlet valve is changed.

In valve trains of internal combustion engines, a clearance is provided, for example, between an engine valve and a rocker arm which abuts with the engine valve or between a cam and a rocker arm which abuts with the cam and an engine valve.

In the conventional valve train that has been described in the JP-A-58-214610, the cam profile of the oscillating cam abuts with a valve lifter, which is a member on the inlet valve side. This is because the cam profile of the oscillating cam cannot be brought into abutment with the inlet valve as the shift amount of an abutment position where the cam profile abuts with the member becomes large between the cam profile and the member which abuts with the cam profile, when the operating angle and lift amount (valve operating properties) of the inlet valve are changed. Thus, in the conventional valve train, since the cylindrical valve lifter with which the oscillating cam is brought into abutment and a holding portion for holding the valve lifter slidably need to be provided in the cylinder head, the cylinder head is enlarged. Due to this, in an internal combustion engine in which the width of the cylinder head is narrow in a direction which intersects at right angles with a plane which includes cylinder axes of the internal combustion engine and which is in parallel with the rotational center line of the primary cam, it is difficult to install such a valve train while maintaining the compactness of the internal combustion engine.

In addition, a consideration is given to a valve train in which a separate rocker arm is adopted in place of the oscillating cam in the aforesaid conventional valve train for abutment with the inlet valve, and the separate rocker arm is made to be oscillated by the primary rocker arm. In this case, since the necessity of the valve lifter is obviated, it becomes possible for the valve train to be applied to the internal combustion engine which is narrow in the direction which intersects at right angles with the plane. However, since the fulcrum of the separate rocker arm is not displaced in contrast to the primary rocker arm whose fulcrum is displaced, it becomes difficult to maintain a clearance between the abutment portion of the primary rocker arm and the abutment portion of the separate rocker arm or the abutment state therebetween when the valve operating properties of the inlet valve are changed, thereby making it difficult to maintain an appropriate valve clearance. As a result, for example, due to an increase in valve clearance, noise is increased due to striking noise generated when the inlet valve starts to be opened, and noise is also increased due to collision of the rocker arms with each other when the internal combustion engine vibrates In addition, irrespective of a change in the valve operating properties, when attempting to maintain the clearance between the abutment portions or abutment state therebetween, the configurations of the abutment portions become complicated, leading to an increase in costs.

Furthermore, in the event that the fulcrum of the separate rocker arm is not displaced, the control range of valve operating properties is determined solely by the displace amount and displacement direction of the fulcrum of the primary rocker arm, and therefore, for example, when attempting to expand the control range of the opening and closing timings of the inlet valve, since the displacement amount of the primary rocker arm needs to be increased, the aforesaid maintenance of the appropriate valve clearance becomes more difficult, and therefore, the control range of valve operating properties cannot be actually set large.

Then, in the technique disclosed in the JP-A-7-91217, since the rocker arm abuts with the cam and the valve lifter, when the disk housing is caused to oscillate so that the rocker shaft oscillates together with the disk housing in order to change the operating angle and the valve lift amount (valve operating properties), while an abutment state is maintained between the rocker arm and the valve lifter, the clearance between the cam and the rocker are changes, and as a result, the valve clearance changes. In addition, in the technique disclosed in the JP-A-5-71321, since the rocker arm abuts with the cam and the inlet valve, when the position of the lever is changed over so that the rocker arm pivot supported by the link rotates about the fulcrum shaft in order to change the valve lift amount (valve operating properties), while the clearance or the abutment state is maintained between the joint portion of the rocker arm and the inlet valve, the clearance between the rocker arm and the cam changes, and as a result, the valve clearance changes.

Thus, in the valve train in which when the valve operating properties are changed, the oscillating center line of the rocker arm which abuts with the engine valve changes, when the valve operating properties are changed, the valve clearance changes. In this case, even in case the valve clearance is an appropriate value for a specific valve operating property, the valve clearance does not become an appropriate value in another valve operating property. Then, for example, when the valve clearance becomes larger than the appropriate value, noise is increased which results from striking noise generated when inlet and exhaust valves start to be opened.

DISCLOSURE OF THE INVENTION

The present invention is such as to have been made in view of these situations. An object of present invention is to provide a valve train for an internal combustion engine which can change valve operating properties of an engine valve, wherein even in the event that an oscillating center line of a rocker arm which abuts with an engine valve is shifted in order to change the valve operating properties, a valve clearance can be maintained constant, and moreover, a control range for the valve operating properties can be set large.

According to a first aspect of the invention, there is provided a valve train for an internal combustion engine, comprising:

a valve operating cam rotating around a rotational center line in synchronism with a rotation of an engine;

an engine valve including at least one of an inlet valve and an exhaust valve;

a transmission mechanism for transmitting a valve drive force of the valve operating cam to the engine valve so as to operate the engine valve in open and close states, the transmission mechanism including; a primary oscillating member oscillating about a primary oscillating center line; a secondary oscillating member oscillating about a secondary oscillating center line through abutment with the primary oscillating member so as to transmit the valve drive force via the primary oscillating member to the engine valve, and a holder supporting the primary and secondary oscillating members thereon in an oscillatory fashion; wherein the primary and secondary oscillating center lines oscillate together with the holder, and a drive abutment portion of the primary oscillating member abuts with a follower abutment portion of the secondary oscillating portion;

a driving mechanism for driving the holder so as to control valve properties including opening and closing timings and maximum lift amount of the engine valve in accordance with a position of the holder which is driven by the driving mechanism,

wherein the holder oscillates about a holder oscillating center line which differs from the rotational center of the valve operating cam in response to the operation of the driving mechanism,

a cam profile having a lost motion profile for maintaining the engine valve in the closed state by abutting the drive abutment portion with the follower abutment portion and a drive profile for driving the engine valve in the open state is formed on at least one of the drive and follower abutment portions, and

in a sectional shape of the lost motion profile in a plane which intersects at right angles with the primary oscillating center line is an arc-like shape of which center is the primary oscillating center line.

According to the construction, since, when the valve operating properties are changed through the movement of the primary and secondary oscillating members which abut with each other at the abutment portions thereof in accordance with the oscillating positions of the primary and secondary oscillating center lines which oscillate together with the holder, the relative positions of the primary and secondary oscillating center lines in the holder remain unchanged, and moreover, the sectional shape of the lost motion profile of the cam profile formed on one of the abutment portions is the arc-like shape which is formed about the primary oscillating center line, it becomes easy to maintain the clearance formed between the lost motion profile and the other abutment portion or the abutment state between the lost motion profile and the other abutment portion. In addition, even in the event that the holder supporting the primary and secondary oscillating members oscillates in a large oscillating amount so as to increase the control range of the valve operating properties, since the primary and secondary oscillating center lines oscillate together with the holder, when compared with a case where while one of the primary and secondary oscillating center lines shifts, the other oscillating center line remains stationary, the relative shift amount of the abutment position with the other abutment portion on the cam profile can be kept small, and consequently, also in this case, the maintenance of the clearance between the cam profile and the other abutment portion or the abutment state therebetween can be facilitated.

According to a second aspect of the invention as set forth in the first aspect of the present invention, it is preferable that the primary oscillating member has a cam abutment portion which abuts with the valve operating cam,

the secondary oscillating member has a valve abutment portion which abuts with the engine valve,

a primary intersection point is defined as a point intersecting a plane which intersects at right angles with the holder oscillating center line and the primary oscillating center line,

a secondary intersection point is defined as a point intersecting a plane which intersects at right angle with the holder oscillating center line and the secondary oscillating center line, and

a distance between the holder oscillating center line and the primary intersection point is greater than a distance between the holder oscillating center line and the secondary intersection point.

According to the construction, the valve drive force is transmitted to the engine valve only via the primary and secondary oscillating members. In addition, since the shift amount of the primary oscillating center line becomes larger than the shift amount of the secondary oscillating center line, when the holder oscillates, while the shift amount of the abutment position between the valve operating cam and the cam abutment portion of the primary oscillating member can be increased, the shift amount of the abutment position between the valve abutment portion of the secondary oscillating member and the engine valve can be decreased.

According to a third aspect of the invention as set forth in the first aspect of the present invention, it is more preferable that the holder includes:

an operative portion on which a drive force of the driving mechanism is applied;

a base portion which extends from the holder oscillating center line toward the operative portion, and having a secondary support portion supporting the secondary oscillating member thereon in an oscillatory fashion; and

a projecting portion projecting from the base portion to the valve operating cam, and having a primary support portion supporting a primary oscillating member thereon in an oscillatory fashion,

wherein the primary and secondary support portions are disposed between the holder oscillating center line and the operative portion in a direction which intersects at right angles with a plane which includes a cylinder axis of the internal combustion engine and which is parallel to the rotational center line.

According to the construction, since the acting portion is situated farther than the primary and secondary support portions relative to the holder oscillating center line, the drive force of the driving mechanism can be reduced, and since the primary and secondary support portions disposed between the holder oscillating center line and the acting portion are provided on the projecting portion and the base portion separately, a space between the holder oscillating center line and the acting portion can be reduced. In addition, since the primary support portion provided on the projecting portion is disposed closer to the valve operating cam than to the base portion, in the primary oscillating member, a distance between the primary oscillating center line and the cam abutment portion becomes short when compared with a case where the primary support portion would otherwise be provided on the base portion.

According to a fourth aspect of the invention as set forth in the first aspect of the present invention, it is further preferable that the valve operating cam is a primary valve operating cam made up of one of an inlet cam and an exhaust cam which are provided on a camshaft, and

the engine valve is a primary engine valve adapted to operate opening and closing operations by the primary valve operating cam and made up of one of the inlet valve and the exhaust valve,

the valve train further comprises:

a tertiary oscillating member adapted to be oscillated by a secondary valve operating cam made up of the other of the inlet cam and the exhaust cam so as to actuate a secondary engine valve made up of the other of the inlet valve and the exhaust valve to operate open and close state; and

a support shaft which supports the tertiary oscillating member in an oscillatory fashion, and

wherein an accommodation space in which the support shaft is accommodated is formed in the holder.

According to the construction, since the support shaft is accommodated in the accommodation space defined in the holder, the both components can be disposed close to each other while the interference of the holder with the support shaft is avoided, and moreover, the oscillating range of the holder can be increased within a limited space.

According to a fifth aspect of the invention as set froth in the fourth aspect of the present invention, it is furthermore preferable that the accommodation space is formed in the primary oscillating member in which the drive abutment portion has the cam profile, and is located at a position defined between the primary oscillating center line and the lost motion profile in a radial direction which radiates from the primary oscillating center line as a center.

According to the construction, since the valve drive force or a reaction force from the primary engine valve acts least on the lost motion profile, the rigidity required at the part of the abutment portion where the lost motion profile is formed only has to be small, and the part can be made thin in thickness, whereby the accommodation space can be formed by making use of this thin part. Then, since this allows the support shaft to be accommodated in the accommodation space, the primary oscillating member and the support shaft can be disposed close to each other while the interference of the both components with each other is avoided, whereby the oscillating range of the holder, which supports the primary oscillating member, can be increased within the limited space.

According to a sixth aspect of the invention as set forth in the first aspect of the present invention, it is suitable that the valve operating cam is a primary valve operating cam made up of one of an inlet cam and an exhaust cam which are provided on a camshaft, and

the engine valve is a primary engine valve adapted to operate opening and closing operations by the primary valve operating cam and made up of one of the inlet valve and the exhaust valve,

the valve train further includes:

a tertiary oscillating adapted to be oscillated by a secondary valve operating cam made up of the other of the inlet cam and the exhaust cam so as to actuate a secondary engine valve made up of the other of the inlet valve and the exhaust valve to operate open and close states; and

a support shaft which supports the tertiary oscillating member in an oscillatory fashion, and

wherein the accommodation space in which the support shaft is accommodated is formed in the primary oscillating member in which the drive abutment portion has the cam profile, and is located at a position defined between the primary oscillating center line and the lost motion profile in a radial direction which radiates from the primary oscillating center line as a center.

According to the construction, a function similar to that provided by the invention set forth in the fifth aspect is provided.

According to a seventh aspect of the present invention, there is provided a valve train for an internal combustion engine comprising:

a valve operating cam rotating around a rotational center line in synchronism with a rotation of the engine,

an engine valve including at least one of an inlet valve and an exhaust valve;

a transmission mechanism for transmitting a valve drive force of the valve operating cam to the engine valve so as to operate the engine valve in open and close states, the transmission mechanism including: a primary member which abuts with the valve operating cam; a rocker arm which oscillates about an oscillating center line by virtue of abutment with the primary member, and having a valve abutment portion having a valve abutment surface which abuts with the engine valve thereon; and a holder supporting the rocker arm in an oscillatory fashion and oscillating about a holder oscillating center line which differs from the rotational center line of the valve operating cam in response to the operation of the drive mechanism, wherein the oscillating center line oscillates together with the holder, and the rocker arm whose oscillating position relative to the holder is regulated by the primary member,

a driving mechanism for driving the holder so as to control valve properties including opening and closing timings and maximum lift amount of the engine valve in accordance with a position of the holder which is driven by the driving mechanism,

wherein in a rest state which is defined where the primary member which is in abutment with the valve operating cam abuts with the rocker arm, and where the rocker arm does not oscillate relative to the holder, a sectional shape of the valve abutment surface on a plane which intersects at right angles with the holder oscillating center line is an arc-like shape which is formed about the holder oscillating center line.

According to the construction, the sectional shape of the valve abutment surface is the arc which provides no clearance in the transmission path of the valve drive force reaching from the valve operating cam to the rocker arm via the primary member and which is formed about the holder oscillating center line in the state where the rocker arm is at rest, and even in the event that the holder oscillates about the holder oscillating center line in order to change the valve operating properties, the rocker arm, which has the oscillating center line which oscillates together with the holder, oscillates together with the holder, whereby the clearance between the valve abutment surface and the engine valve is maintained constant.

According to an eighth aspect of the present invention as set forth in the seventh aspect of the present invention, it is suitable that the primary member has a cam abutment portion which is brought into abutment with the valve operating cam and constitutes a primary rocker arm which is caused to oscillate about a primary oscillating center line, and

the rocker arm constitutes a secondary rocker arm.

According to the construction, in the valve train wherein the primary member is made up of the rocker arm, a similar function to that of the first aspect of the present invention is provided.

According to a ninth aspect of the present invention as set forth in the eighth aspect of the present invention, it is further suitable that the holder oscillating center line intersects at right angles with the valve abutment portion of the secondary rocker arm which is in the rest state.

According to the construction, since the valve abutment surface is situated close to the holder oscillating center line, even in the event that the secondary oscillating center line oscillates through the oscillation of the holder, whereby the abutment position between the valve abutment portion and the engine valve shifts, the shift amount thereof becomes small, thereby making it possible to make the valve abutment portion small in size.

According to a tenth aspect of the present invention as set forth in the eighth aspect of the present invention, it is furthermore suitable that an operative portion on which a drive force of the drive mechanism acts is provided on the holder at a location thereof which is farthest apart from the holder oscillating center line on a plane which intersects at right angles with the holder oscillating center line.

According to the construction, since the drive force which causes the holder to oscillate acts on the acting portion of the holder which is farthest apart from the holder oscillating center line, the distance on the holder from the holder oscillating center line to the acting portion on which the drive force is allowed to act can be substantially maximum, and therefore, the drive force of the drive mechanism can be reduced.

According to an eleventh aspect of the present invention as set forth in the eighth aspect of the present invention, it is preferable that the primary rocker arm is supported on the holder in an oscillatory fashion, and

as an oscillating position of the holder approaches a predetermined position where a valve operating property is obtained where the maximum lift amount becomes maximum, a cam abutment position where the cam abutment portion and a cam lobe portion of the valve operating cam abut with each other approaches a specific straight line which passes through the holder oscillating center line and the rotational center line on the plane which intersects at right angles with the holder oscillating center line.

According to the construction, since, when the cam abutment position is situated on the specific straight line, the line of action of the valve drive force is situated on the specific straight line, the moment acting on the holder based on the drive force acting via the primary rocker arm becomes zero. From this fact, since the maximum lift amount is increased as the oscillating position is approached where the valve operating property is obtained where the maximum lift amount becomes maximum, the valve drive force is also increased. However, since the cam abutment position on the cam lobe portion approaches the specific straight line, the moment acting on the holder can be reduced, thereby making it possible to reduce the drive force of the drive mechanism which oscillates the holder against the moment.

According to a twelfth aspect of the present invention as set forth in the eighth aspect of the present invention, it is more preferable that the primary rocker arm is supported on the holder in an oscillatory fashion in such a manner that the primary oscillating center line oscillates together with the holder,

wherein one of a drive abutment portion of the primary rocker arm and a follower abutment portion of the secondary rocker arm which are brought into abutment with each other has a cam profile having, in turn, a lost motion profile which holds the engine valve in the closed state through abutment with the other abutment portion of the drive abutment portion and the follower abutment portion and a drive profile which puts the engine valve in the open state, and

when the holder oscillates in an oscillating direction in which the holder moves apart from the rotational center line, a cam abutment position where the valve operating cam abuts with the cam abutment portion shifts, and at the same time an arm abutment portion where the cam profile abuts with the other abutment portion shifts in a direction in which the maximum lift amount is reduced and in a direction in which the arm abutment position moves apart from the rotational center line.

According to the construction, since the holder oscillates in the direction to move apart from the rotational center line of the inlet cam, the valve opening property can be obtained where the opening and closing timings are changed, and at the same time, the maximum lift amount is reduced. As this occurs, while the secondary rocker arm supported on the holder oscillates together with the holder in the direction to move apart from the rotational center line, the maximum lift amount of the engine valve which is actuated to be opened and closed by the secondary rocker arm is reduced at the same time, and therefore, the oscillating amount of the secondary rocker arm is reduced.

According to a thirteenth aspect of the present invention as set forth in the second aspect of the present invention, it is more preferable that the valve abutment portion is provided with an adjusting unit which adjusts a valve clearance defined between the engine valve and the valve abutment portion.

According to a fourteenth aspect of the present invention as set forth in the first aspect of the present invention, it is more preferable that the driving mechanism is provided on at least one of a cylinder.

According to a fifteenth aspect of the present invention as set forth in the first aspect of the present invention, it is more preferable that the driving mechanisms are provided on cylinders, respectively.

According to a sixteenth aspect of the present invention as set forth in the first aspect of the present invention, it is more preferable that the holders provided in each cylinders are formed to be integral.

According to the invention set forth in the first aspect of the present invention, the following advantages are provided. Namely, since the maintenance of the clearance formed between the abutment portions of both the primary and secondary oscillating members or the abutment state therebetween is facilitated, the maintenance of the appropriate valve clearance is facilitated even when the valve operating properties are changed. This prevents the increase in noise level which would otherwise be caused by virtue of valve striking noise and collision of both the oscillating members with each other, both of which are triggered by, for example, an increase in valve clearance. In addition, even in the event that the holder oscillates in a large oscillation amount, since the maintenance of the clearance between the two abutment portions or the abutment state therebetween is facilitated, the control range of the valve operating properties can be set large.

According to the invention set forth in the second aspect of the present invention, in addition to the advantages provided by the invention set forth in the first aspect referred to therein, the following advantages are provided. Namely, the valve drive force is transmitted to the engine valve only via the primary and secondary oscillating members, the transmission mechanism is made compact in size, and hence the valve train is also made compact in size. Furthermore, since, when the holder oscillates, the shift amount of the abutment position where the valve operating cam abuts with the cam abutment portion can be increased, the control range of opening and closing timings of the engine valve can be set large, and moreover, since the shift amount of the abutment position where the valve abutment portion abuts with the engine valve can be decreased, the wear of the valve abutment portion can be suppressed, thereby making it possible to extend the period when the appropriate clearance is maintained.

According to the invention set forth in the third aspect of the present invention, in addition to the advantages provided by the invention set forth in the second aspect referred to therein, the following advantages are provided. Namely, since the drive force of the driving mechanism can be reduced, the driving mechanism is made compact in size, and since the space between the holder oscillating center line where the primary and secondary support portions are disposed and the acting portion can be made narrow, the hold is made compact between the holder oscillating center line and the acting portion. In addition, since the distance between the primary oscillating center line and the cam abutment portion is made short, the required rigidity against the valve drive force is ensured, while the primary oscillating member is made light in weight.

According to the invention set forth in the fourth aspect of the present invention, in addition to the advantages provided by the invention set forth in the third aspect referred to therein, the following advantages are provided. Namely, since the holder and the support shaft can be disposed close to each other, the valve train is made compact in size, and moreover, since the oscillating range of the holder can be increased, the control range of the valve operating properties can be increased.

According to the invention set forth in the fifth aspect of the present invention, in addition to the advantages provided by the invention set forth in the fourth aspect referred to therein, the following advantages are provided. Namely, since the part of the drive abutment portion of the primary oscillating member where the lost motion profile is formed can be made thin, the primary oscillating member is made light in weight. Furthermore, since the holder, the primary oscillating member and the support shaft can be disposed close to one another by virtue of the accommodation space, the valve train can be made more compact in size, and moreover, since the oscillating range of the holder which supports the primary oscillating member can be increased further, the control range of the valve operating properties can be set large.

According to the invention set forth in the sixth aspect of the present invention, in addition to the advantages provided by the invention set forth in the fifth aspect referred to therein, the following advantages are provided. Namely, similarly to the invention set forth in the fifth aspect, the primary oscillating member is made light in weight. Furthermore, since the primary oscillating member and the support shaft can be disposed close to each other, the valve train is made compact in size, and moreover, since the oscillating range of the holder which supports the primary oscillating member can be increased, the control range of the valve operating properties can be set large.

According to the invention set forth in the seventh aspect of the present invention, the following advantage is provided. Namely, since, when the holder oscillates in order to change the valve operating properties, the clearance between the valve abutment surface and the engine valve is maintained constant in the state, the valve clearance existing from the valve operating cam to the engine valve is maintained constant.

According to the invention set forth in the eighth aspect of the present invention, in the valve train in which the primary member is made up of the rocker arm, a similar advantage to that provided in the eighth aspect can be provided.

According to the invention set forth in the ninth aspect of the present invention, in addition to the advantage, the following advantages are provided. Namely, the wear of the valve abutment portion is suppressed, whereby a period of time is extended when the appropriate valve clearance is maintained.

According to the invention set forth in the tenth aspect of the present invention, the following advantages are provided further. Namely, since the drive force of the drive mechanism which oscillates the holder can be reduced, the drive mechanism is made compact. In addition, since the valve abutment portion can be made small in size, the secondary rocker arm is miniaturized.

According to the invention set forth in the eleventh aspect of the present invention, in addition to the advantages, the following advantage is provided. Namely, since when the holder approaches the oscillating position where the valve drive force is increased, the moment acting on the holder based on the valve drive force can be reduced, the drive force of the drive mechanism which oscillates the holder against the moment can be reduced, whereby the drive mechanism is made compact in size.

According to the invention set forth in the twelfth aspect of the present invention, in addition to the advantage, the following advantages are provided. Namely, since when the valve operating property can be obtained where the opening and closing timings are changed and at the same time, the maximum lift amount is reduced, the oscillating amount of the secondary rocker arm which shifts together with the holder in the direction to move apart from the rotational center line is reduced, the operation space occupied by the secondary rocker arm is made compact, thereby making it possible to dispose the valve train in the relatively compact space.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of a main part of an internal combustion engine having a valve train of the invention, which shows a first embodiment of the invention.

FIG. 2 is an enlarged view of the main part in FIG. 1, which is a sectional view taken along the line indicated by arrows IIa-IIa and as viewed in a direction indicated by the same arrows in FIG. 3 as to a cylinder head, and which is a sectional view taken along the line indicated by arrows IIb-IIb and as viewed in a direction indicated by the same arrows in FIG. 3 as to a transmission mechanism.

FIG. 3 is a view of the valve train with a cylinder head cover of the internal combustion engine being removed, as viewed in a direction indicated by an arrow III in FIG. 1.

FIG. 4 is a sectional view taken along the line indicated by arrows IV-IV and as viewed in a direction indicated by the same arrows in FIG. 3.

FIG. 5 is a graph showing valve operating properties of the valve train shown in FIG. 1.

FIG. 6 is a drawing explaining the operation of an inlet operation mechanism when a maximum valve operating property of the valve train shown in FIG. 1 is obtained.

FIG. 7 is a drawing explaining the operation of the inlet operation mechanism when a minimum valve operating property of the valve train shown in FIG. 1 is obtained.

FIG. 8 is a drawing explaining the operation of the inlet operation mechanism when an intermediate valve operating property of the valve train shown in FIG. 1 is obtained.

FIG. 9 is a drawing showing a second embodiment of the invention, which corresponds to FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be described below by reference to FIGS. 1 to 9.

FIGS. 1 to 8 are drawings which describe a first embodiment of the invention. Referring to FIG. 1, an internal combustion engine E provided with a valve train of the invention is an overhead camshaft, water-cooled, in-line four-cylinder, four-stroke internal combustion engine, and is installed transversely in a vehicle in such a manner that a crankshaft thereof extends in a transverse direction of the vehicle. The internal combustion engine E includes a cylinder block 2 in which four cylinders 1 are formed integrally, a cylinder head 3 connected to an upper end portion of the cylinder block 2 and a cylinder head cover 4 connected to an upper end portion of the cylinder head 3, the cylinder block 2, the cylinder head 3 and the cylinder head cover 4 making up an engine main body of the internal combustion engine E.

Note that in this specification, it is understood that a vertical direction denotes a direction which coincides with a cylinder axis direction A1 of the cylinder 1 and that upward denotes a direction in which the cylinder head 3 is disposed relative to the cylinders 1 in the cylinder axis direction A1. In addition, a sectional shape means a sectional shape in a plane (hereinafter, simply referred to as an orthogonal plane) which intersects at right angles with a holder oscillating center line L3, a primary oscillating center line L4, a secondary oscillating center line L5 or a rotational center line L2, all of which will be described later on. Then, this orthogonal plane also constitutes an oscillating plane which is a plane parallel to an oscillating direction of a holder 30, a primary rocker arm 50 or a secondary rocker arm 60, all of which will be described later on.

A cylinder bore is formed in each cylinder 1 in which a piston 5 connected to the crankshaft by a connecting rod 6 fits in such a manner as to reciprocate freely therein. In the cylinder head 3, a combustion chamber 7 is formed in a surface which faces the cylinder bores in the cylinder axis direction A1 in such a manner as to correspond to each cylinder 1, respectively, and an inlet port 8 having a pair inlet openings and an exhaust port 9 having a pair of exhaust openings are also formed in the cylinder head 3 in such a manner as to open to each combustion chamber 7. A spark plug 10 is installed in the cylinder head 3 in such a manner as to be inserted into an insertion hole formed in the cylinder head 3 on an exhaust side thereof together with an ignition coil 11 connected to the spark plug 10.

Here, the inlet side of the internal combustion engine E means a side where an inlet valve 14 or an entrance 8a to the inlet port 8 is disposed relative to a reference plane H1 which includes cylinder axes L1 and which is parallel to a rotational center line L2 of an inlet cam 21 and an exhaust cam 22 which also constitutes a rotational center line L2 of a camshaft 20, and the exhaust side of the internal combustion engine E means a side where an exhaust valve 15 or an exit 9a from the exhaust port 9 is disposed. Then, the inlet side is one of one side and the other side relative to the reference plane H1, whereas the exhaust side is the other of the one side and the other side.

In the cylinder head 3, a pair of inlet valves 14 functioning as primary engine valves and a pair of exhaust valves 15 functioning as secondary engine valves are provided for each cylinder 1, the inlet valves 14 and the exhaust valves 15 each being made up of a poppet valve which is supported in a valve guide 12 in such a manner as to reciprocate therein and is biased in a normally closed direction. The pair of inlet valves 14 and the pair of exhaust valves 15 which belong to each cylinder 1 are operated to be opened and closed by a valve train V so as to open and close the pair of inlet openings and the pair of exhaust openings, respectively. The valve train V, excluding an electric motor 28 for driving a drive shaft 29, which will be described later on, is disposed within a valve chamber 16 defined by the cylinder head 3 and the cylinder head cover 4.

The internal combustion engine E includes further inlet system 17 and an exhaust system 18. The inlet system 17, which includes an air cleaner, a throttle valve and an inlet manifold 17a for induction of air for combustion into the inlet port 8, is mounted on a side on the inlet side of the cylinder head 3 to which the openings 8a of each port 8 are made to open, whereas the exhaust system 18, which includes an exhaust manifold 18a for guiding exhaust gases flowing thereinto from the combustion chambers 7 via the exhaust ports 9 to the outside, is mounted on a side on the exhaust side of the cylinder head 3 to which the openings 9a of each exhaust port 9 are made to open. In addition, a fuel injection valve 19, which is a fuel supply system for supplying fuel for intake air, is installed in the cylinder head 3 in such a manner as to be inserted into an insertion hole provided on the inlet side of the cylinder head 3 so as to face the inlet port 8 of each cylinder 1.

Then, air drawn in through the inlet system 17 is drawn further into the combustion chamber 7 from the inlet port 8 via the inlet valves 14 which are opened in an induction stroke where the piston 5 descends and is compressed in a compression stroke where the piston 5 ascends in a state in which the air is mixed with fuel. The air/fuel mixture is ignited by the spark plug 10 in a final stage of the compression stroke for combustion, and the piston 5, which is driven by virtue of the pressure of combustion gases in a power stroke where the piston descends, drives and rotates the crankshaft via the connecting rod 6. Combustion gases are discharged from the combustion chamber 7 into the exhaust port 9 as exhaust gases via the exhaust valves 15 which are opened in an exhaust stroke where the piston 5 ascends.

Referring to FIG. 2, the valve train V provided on the cylinder head 3 includes a single camshaft 20 which is rot