Assisting device and method for variable valve mechanism

Information

  • Patent Grant
  • 6742483
  • Patent Number
    6,742,483
  • Date Filed
    Monday, October 21, 2002
    22 years ago
  • Date Issued
    Tuesday, June 1, 2004
    20 years ago
Abstract
An output from each of output rods is converted into an assisting force via a corresponding one of rollers, while an outer peripheral surface of each of the rollers moving together with a control shaft serves as a conversion plane. This output is applied to the control shaft. Hence, as the control shaft is moved in such a direction as to increase valve lift amounts of intake valves, the assisting force can be correspondingly increased. Thus, a suitable assisting force that can act against a thrust force can be applied to the control shaft. As a result, there is no apprehension that a minimum hydraulic fluid pressure will not be ensured on the side of a larger valve lift amount or that responding properties in movements of the control shaft will deteriorate.
Description




INCORPORATION BY REFERENCE




The disclosure of Japanese Patent Application No. 2001-324757 filed on Oct. 23, 2001, including the specification, drawings, and abstract is incorporated herein by reference in its entirety.




BACKGROUND OF THE INVENTION




1. Field of Invention




The invention relates to an assisting device and method for a variable valve mechanism. More particularly, the invention relates to an assisting device for applying an assisting force acting against a thrust force generated in a control shaft to a variable valve mechanism that allows valve lift amounts to continuously change in such a manner as to interlock with an axial position of the control shaft by axially moving the control shaft.




2. Description of Related Art




As a related art, there is known a variable valve mechanism in which a cam shaft having three-dimensional cams whose cam noses (surfaces) gradually increase in height along an axial direction is moved in the axial direction so as to continuously adjust valve lift amounts of intake valves of an internal combustion engine in accordance with an operational state thereof (Japanese Patent Application Laid-Open No. 2000-54814).




In a variable valve mechanism in which a cam shaft is thus axially moved to allow valve lift amounts to continuously change, a thrust force is generated in such a direction as to reduce the valve lift amounts due to an axial inclination of cam surfaces of three-dimensional cams. Moreover, as the valve lift amounts are increased, compression strokes of valve springs are increased, which leads to a gradual increase in restoring forces thereof. As a result, the aforementioned thrust force is increased as well.




In the case where such a variable valve mechanism is utilized to regulate the amount of intake air in an internal combustion engine by adjusting valve lift amounts of intake valves instead of adjusting a throttle valve, an actuator for axially moving a cam shaft is required to have high responding properties. Especially in the case where a hydraulic actuator is employed, in order to accomplish high responding properties, it is required that the flow rate of a hydraulic fluid be reduced by reducing the diameter of pistons. However, if the diameter of the pistons is reduced, the actuator output cannot be adapted for an increase in the aforementioned thrust force, which causes an apprehension that a minimum hydraulic fluid pressure will not be generated or that the responding properties will deteriorate.




In order to address these problems, one might consider providing an assisting spring for assisting the operation of the actuator by generating an assisting force that acts against the aforementioned thrust force. However, as described above, while the thrust force is increased in proportion to an increase in the valve lift amounts, the restoring force of the assisting spring is reduced as the cam shaft is shifted to the high-lift side. Hence, this restoring force is inadequate as an assisting force.




Such a problem is caused in other types of variable valve mechanisms in which valve lift amounts can continuously change due to axial movements of a control shaft, as well as in a variable valve mechanism employing three-dimensional cams.




SUMMARY OF THE INVENTION




It is an object of the invention to provide an assisting device capable of applying a suitable assisting force to a variable valve mechanism that allows valve lift amounts to continuously change with changes in an axial position of a control shaft by axially moving the control shaft.




In order to achieve the aforementioned and/or other objects, an assisting device for applying an assisting force to counteract a thrust force generated in a variable valve mechanism according to one aspect of the invention comprises valves disposed in the variable valve mechanism, a control shaft for allowing valve lift amounts of the valves to continuously change with changes in an axial position of the control shaft, the control shaft receiving the thrust force from the valves, and an assisting force applying portion for generating and applying the assisting force on the basis of a restoring force of an elastic body or a pressure of a fluid and increasing the assisting force as the axial position of the control shaft is shifted to a high-lift side.




This structure allows a suitable assisting force capable of acting against a thrust force that is increased as the axial position of the control shaft is shifted to the high-lift side to be applied to the variable valve mechanism.











BRIEF DESCRIPTION OF THE DRAWINGS




The invention will be described with reference to exemplary embodiments illustrated in the drawings, in which:





FIG. 1

is a block diagram showing the overall structure of an engine equipped with an assisting device and a variable valve mechanism according to a first embodiment of the invention and a control system for the engine;





FIG. 2

is an explanatory view of the structure of a cylinder head portion of the engine;





FIG. 3

is a cross-sectional view of the internal structure of a slide actuator according to the first embodiment;





FIG. 4

is also a cross-sectional view according to the internal structure of the slide actuator;





FIG. 5

is a perspective view of a piston body of the first embodiment;





FIG. 6

is also a perspective view of the piston body;





FIGS. 7A-7C

are explanatory views of an assisting operation according to the first embodiment;





FIG. 8

is a graph showing how a thrust force Fs and an assisting force Fa are related to a moving distance of a control shaft;





FIG. 9

is a perspective view of the structure of an intermediary drive mechanism according to the first embodiment;





FIG. 10

is also a partially cutaway view of the internal structure of the intermediary drive mechanism;





FIGS. 11A-11C

are explanatory views of the shapes of a control shaft and a supporting pipe of the intermediary drive mechanism;





FIGS. 12A-12B

are explanatory views of a valve lift amount adjusting function of the intermediary drive mechanism according to the first embodiment;





FIGS. 13A-13B

are explanatory views of a valve lift amount adjusting function of the intermediary drive mechanism;





FIGS. 14A-14B

are explanatory views of a valve lift amount adjusting function of the intermediary drive mechanism;





FIG. 15

is a graph showing how the valve lift amount achieved by the intermediary drive mechanism according to the first embodiment changes;





FIG. 16

is an explanatory view of the structure of a variable valve mechanism and an assisting device according to a second embodiment of the invention;





FIG. 17

is an explanatory view of the functions of the variable valve mechanism and the assisting device according to the second embodiment;





FIG. 18

is an explanatory view of the structure of a modified example of the first embodiment; and





FIG. 19

is an explanatory view of the structure of a modified example of the second embodiment.











DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS





FIG. 1

is a block diagram of the overall structure of a gasoline engine (hereinafter referred to as the “engine”)


2


as an internal combustion engine equipped with an assisting device and a variable valve mechanism to which the aforementioned invention is applied, and of a control system for the engine


2


.




The engine


2


is installed in an automobile as a drive source for causing the automobile to run. The engine


2


includes a cylinder block


4


, pistons (not shown), a cylinder head


8


mounted on the cylinder block


4


, and the like. A plurality of cylinders are formed in the cylinder block


4


. For example, in this case, four cylinders


2




a


are formed in the cylinder block


4


. Each of the cylinders


2




a


has a corresponding one of combustion chambers


10


, each of which is defined by the cylinder block


4


, a corresponding one of the pistons, and the cylinder head


8


. In each of the combustion chambers


10


, four valves, namely, a corresponding one of first intake valves


12




a


, a corresponding one of second intake valves


12




b


, a corresponding one of first exhaust valves


16




a


, and a corresponding one of second exhaust valves


16




b


are disposed. Each of the first intake valves


12




a


opens and closes a corresponding one of first intake ports


14




a


. Each of the second intake valves


12




b


opens and closes a corresponding one of second intake ports


14




b


. Each of the first exhaust valves


16




a


opens and closes a corresponding one of first exhaust ports


18




a


. Each of the second exhaust valves


16




b


opens and closes a corresponding one of second exhaust ports


18




b.






The first intake port


14




a


and the second intake port


14




b


of each of the cylinders


2




a


are connected to a surge tank


32


via a corresponding one of intake passages


30




a


formed in an intake manifold


30


. Disposed in each of the intake passages


30




a


is a corresponding one of fuel injectors


34


, which makes it possible to inject fuel into corresponding ones of the first intake ports


14




a


and the second intake ports


14




b.






The surge tank


32


is coupled to an air cleaner


42


via an intake duct


40


. It is to be noted herein that there is no throttle valve disposed in the intake duct


40


. An operation of an accelerator pedal


74


and an intake air amount control corresponding to an engine speed NE during an idle speed control are performed by adjusting valve lift amounts of the first intake valves


12




a


and of the second intake valves


12




b.






Lifting movements of intake cams


45




a


on an intake cam shaft


45


are transmitted via a corresponding one of later-described intermediary drive mechanisms


120


disposed in the cylinder head


8


as shown in

FIG. 2

, whereby it becomes possible to drive the intake valves


12




a


,


12




b


. In this transmission, a transmission state of lift by the intermediary drive mechanism


120


is adjusted through a function of a later-described slide actuator


100


, whereby the valve lift amounts are adjusted. The intake cam shaft


45


is interlocked with rotation of a crank shaft


49


of the engine


2


via a timing chain


47


and a timing sprocket (which may be replaced with a timing gear or a timing pulley) disposed at one end of the intake cam shaft


45


.




As shown in

FIG. 1

, each of the first exhaust valves


16




a


for opening and closing a corresponding one of the first exhaust ports


18




a


of a corresponding one of the cylinders


2




a


and each of the second exhaust valves


16




b


for opening and closing a corresponding one of the second exhaust ports


18




b


of a corresponding one of the cylinders


2




a


are opened and closed by a certain valve lift amount through rotation of exhaust cams


46




a


(

FIG. 2

) on an exhaust cam shaft


46


(

FIG. 2

) resulting from rotation of the engine


2


. The first exhaust port


18




a


and the second exhaust port


18




b


of each of the cylinders


2




a


are coupled to an exhaust manifold


48


. Thus, exhaust gas is discharged to the outside via a catalytic converter


50


.




An electronic control unit (hereinafter referred to as the ECU)


60


is constructed of a digital computer and includes components such as a CPU, a ROM, a RAM, various driver circuits, input ports, and output ports, which are interconnected via a bidirectional bus.




Various output voltages and various pulses are input to the input ports of the ECU


60


. The various output voltages include an output voltage proportional to a depression stroke of the accelerator pedal


74


as an output from an accelerator opening sensor


76


(hereinafter referred to as an “accelerator opening ACCP”), an output voltage corresponding to an amount GA of intake air flowing through the intake duct


40


as an output from an intake air amount sensor


84


, an output voltage corresponding to a coolant temperature THW of the engine


2


as an output from a coolant temperature sensor


86


disposed in the cylinder block


4


of the engine


2


, an output voltage corresponding to an air-fuel ratio as an output from an air-fuel ratio sensor


88


disposed in the exhaust manifold


48


, and an output voltage corresponding to an axial displacement as an output from a shaft position sensor


90


for detecting an axial moving distance of a later-described control shaft


132


that is moved by the slide actuator


100


.




The various pulses include a pulse that is output by a crank angle sensor


82


every time the crank shaft rotates by 30° and a pulse output from a cam angle sensor


92


for detecting cam angles of the intake cams


45




a


for driving the intake valves


12




a


,


12




b


via the intermediary drive mechanism


120


.




The ECU


60


calculates a current crank angle on the basis of an output pulse of the crank angle sensor


82


and a pulse of the cam angle sensor


92


and an engine speed NE on the basis of a frequency with which pulses are output from the crank angle sensor


82


.




Although various signals are input to the input ports of the ECU


60


in addition to the aforementioned output voltages and pulses, they are not shown in the drawings because they are not important in explaining the first embodiment.




Each of the output ports of the ECU


60


is connected to a corresponding one of the fuel injectors


34


via a corresponding one of drive circuits. The ECU


60


performs an opening control of the fuel injectors


34


in accordance with an operational state of the engine


2


and thus performs a fuel injection timing control and a fuel injection amount control. Furthermore, one of the output ports of the ECU


60


is connected to an oil control valve (hereinafter referred to as the “OCV”)


104


via a corresponding one of the drive circuits. The ECU


60


controls the slide actuator


100


through a hydraulic control by the OCV


104


in accordance with an operational state of the engine


2


such as a required intake air amount.




Each of

FIGS. 3 and 4

shows a cross-section of the internal structure of the slide actuator


100


.

FIG. 3

is a longitudinal cross-sectional view (taken along a line B—B in

FIG. 4

) when viewed from a location in front of the slide actuator


100


.

FIG. 4

is a longitudinal cross-sectional view (taken along a line A—A in

FIG. 3

) when viewed from a location on the right side of the slide actuator


100


.




The slide actuator


100


has a cylindrical space inside a housing


100




a


. The cylindrical space is formed so as to be coaxial with the control shaft


132


. This space is slightly reduced in diameter on the side of the control shaft


132


. A piston body


102


is axially movably disposed inside the space. As shown in perspective views of

FIGS. 5 and 6

, the piston body


102


includes a piston portion


102




a


and an assisting roller portion


102




b


. The piston portion


102




a


and the assisting roller portion


102




b


are integrally formed via a connecting portion


102




c.






The piston portion


102




a


is in the shape of a circular plate. A sealing groove


102




e


for accommodating a sealing ring


102




d


for oil seal is formed in an outer peripheral surface of the piston portion


102




a


. A leading end of the control shaft


132


is fitted into a fitting hole


102




f


formed in the center of the piston portion


102




a


. The control shaft


132


is fixed to the piston body


102


by a fixture bolt


102




h


penetrating from the right side in

FIG. 3

, through a bolt through-hole


102




g


axially penetrating the piston body


102


. As a result, the control shaft


132


is designed to be axially movable together with the piston body


102


.




The piston portion


102




a


is disposed on the smaller-diameter side (on the left side in the drawings) in the cylindrical space. Hence, the cylindrical space is divided into two pressure chambers


101




a


,


101




b


. The ECU


60


adjusts the supply and release of a hydraulic pressure for the two pressure chambers


101




a,




101




b


via the aforementioned OCV


104


, whereby the entire piston body


102


axially moves and adjusts an axial position of the control shaft


132


. The OCV


104


is a four-port three-position switching valve of an electromagnetic solenoid type. If the electromagnetic solenoid assumes a demagnetized state (hereinafter referred to as a “low-lift drive state”) as shown in

FIG. 3

, hydraulic fluid in the first pressure chamber


101




a


is returned to an oil pan


108


via a discharge passage


107


. A high-pressure hydraulic fluid is supplied from an oil pump P to the second pressure chamber


101




b


via a supply passage


106


. Hence, the control shaft


132


is moved in a direction indicated by L in

FIG. 3

, whereby it becomes possible to reduce valve operation angles and valve lift amounts of the intake valves


12




a


,


12




b


through the function of the intermediary drive mechanism


120


.




If the electromagnetic solenoid assumes an 100%-energized state (hereinafter referred to as a “high-lift drive state”), hydraulic fluid is supplied from the oil pump P to the first pressure chamber


101




a


via the supply passage


106


. Hydraulic fluid in the second pressure chamber


101




b


is returned to the oil pan


108


via the discharge passage


107


. Hence, the control shaft


132


is moved in a direction indicated by H in

FIG. 3

, whereby it becomes possible to increase valve lift amounts of the intake valves


12




a


,


12




b


through the function of the intermediary drive mechanism


120


.




Furthermore, if the supply of electricity to the electromagnetic solenoid is controlled so as to assume an intermediate state (hereinafter referred to as a “neutral state”), the pressure chambers


101




a


,


101




b


are sealed and connected to neither the supply passage


106


nor the discharge passage


107


. Hence, axial movements of the control shaft


132


are stopped, whereby it becomes possible to hold valve lift amounts of the intake valves


12




a


,


12




b.






The assisting roller portion


102




b


will now be described. A space


102




i


penetrating in a direction perpendicular to the axial direction is formed in a body of the assisting roller portion


102




b


. Two shaft portions


102




j


penetrating the space


102




i


are symmetrically disposed across the fixture bolt


102




h


. Axes “as” (

FIG. 5

) of the two shaft portions


102




j


are disposed parallel to a virtual plane (PS) that is perpendicular to an axis of the control shaft


132


. Each of rollers


102




k


is freely rotatably fitted to a corresponding one of the shaft portions


102




j.






Each of two push portions


103


is disposed in the housing


100




a


in such a manner as to face a corresponding one of the two rollers


102




k


. Each of the push portions


103


has an output rod


103




a


, a linear bearing


103




b


for axially movably supporting the output rod


103




a


, and a spring


103




c


for urging the output rod


103




a


toward the piston body


102


.




The direction in which the output rod


103




a


is urged is perpendicular to the axis of the control shaft


132


. Furthermore, although the direction in which the output rod


103




a


is urged is parallel to a virtual plane (QS) perpendicular to the axes “as” of the rollers


102




k


, the output rod


103




a


has an offset doff toward the control shaft


132


from the axes “as” (FIG.


3


). Accordingly, as shown in

FIG. 7A

, a pressure Fo


1


is diagonally applied to an outer peripheral surface of the roller


102




k


from a leading end portion


103




d


of the output rod


103




a


. Hence, a radial force Fr


1


is applied to the shaft portion


102




j


. As a result, an axial force Fa


1


is applied to the piston body


102


from the output rod


103




a


. That is, the pressure Fo


1


of the output rod


103




a


is converted into the axial force Fa


1


with the cylindrical outer peripheral surface of the roller


102




k


serving as a conversion plane. The force Fa


1


is applied in the direction H and acts as an assisting force that acts against a thrust force generated by the later-described intermediary drive mechanism


120


in the direction L.

FIG. 7A

shows a state where the piston body


102


is located at a critical position in the direction L and the offset doff is a minimum offset distance doff


1


.




If the piston body


102


is moved in the direction H as shown in FIG.


7


B through adjustment of hydraulic pressures in the pressure chambers


101




a


,


101




b


by the ECU


60


based on an OCV signal, the offset doff is an intermediate offset distance doff


2


. Hence, a pressure Fo


2


is applied to the cylindrical outer peripheral surface of the roller


102




k


from the leading edge portion


103




d


of the output rod


103




a


in a further inclined direction. Hence, a radial force Fr


2


is applied to the shaft portion


102




j


. As a result, an assisting force Fa


2


(>Fa


1


) is applied to the piston body


102


.




Furthermore, if the piston body


102


is moved to a critical position in the direction H as shown in

FIG. 7C

, the offset doff is a maximum offset distance doff


3


. Hence, a pressure Fo


3


is applied to the cylindrical outer peripheral surface of the roller


102




k


from the leading portion


103




d


of the output rod


103




a


in a most inclined direction. Hence, a radial force Fr


3


is applied to the shaft portion


102




j


. As a result, a maximum assisting force Fa


3


(>Fa


2


) is applied to the piston body


102


.




A solid line in

FIG. 8

indicates a relationship between an assisting force Fa and a moving distance of the control shaft


132


in the direction H which has been actually designed on the basis of the aforementioned relationship. That is, if the moving distance of the control shaft


132


in the direction H is “0(mm)” (at the critical position in the direction L), the assisting force Fa assumes a minimum value that is almost 0(kgf). The assisting force Fa increases as the control shaft


132


moves in the direction H. The assisting force Fa assumes a maximum value at the critical position in the direction H. An alternate long and short dash line in

FIG. 8

indicates a thrust force Fs (applied in the opposite direction) generated by the later-described intermediary drive mechanism


120


. The assisting force Fa is set so as to become substantially equal to the absolute value of the thrust force Fs. Such an ascending pattern of the assisting force Fa can be suitably set by the shape of the leading end portion


103




d


of the output rod


103




a


, the diameter of the roller


102




k


, and the initial offset doff


1


. Although the ascending pattern of the thrust force Fs generated by the intermediary drive mechanism


120


slightly changes depending on the speed of the engine


2


, it is appropriate that the ascending pattern of the assisting force Fa be adapted for, for example, a thrust force Fs at an average engine speed, a thrust force Fs at an engine speed during idling, or a thrust force Fs at a maximum engine speed.




The intermediary drive mechanism


120


will now be described.

FIG. 9

is a perspective view of the intermediary drive mechanism


120


. The intermediary drive mechanism


120


includes a shaft input portion


122


disposed at the center in the drawing, a first rocking cam


124


disposed on the left side in the drawing (corresponding to an “shaft output portion”), and a second rocking cam


126


disposed on the right side in the drawing (corresponding to an “shaft output portion”). A housing


122




a


of the shaft input portion


122


and housings


124




a


,


126




a


of the rocking cams


124


,


126


have a cylindrical shape and are equal in outer diameter.





FIG. 10

is a perspective view of the housings


122




a


,


124




a


,


126




a


that have been horizontally cut away. It is to be noted herein that an axially extending space is formed in the housing


122




a


of the shaft input portion


122


and that a helical spline


122




b


that axially spirals like a right-handed screw is formed in an inner peripheral surface of the space. Further, two arms


122




c


,


122




d


are formed so as to protrude from an outer peripheral surface in parallel with each other. A shaft


122




e


is hung between leading ends of the arms


122




c


,


122




d


. The shaft


122




e


is parallel to an axis of the housing


122




a


. A roller


122




f


is rotatably fitted to the shaft


122




e.






An axially extending space is formed in the housing


124




a


of the first rocking cam


124


, and a helical spline


124




b


that axially spirals like a left-handed screw is formed in an inner peripheral surface of the internal space. A ring-like bearing portion


124




c


having a center hole with a reduced diameter covers a left end of the internal space. A generally triangular nose


124




d


is formed so as to protrude from an outer peripheral surface. One side of the nose


124




d


constitutes a cam surface


124




e


that is concavely curved.




An axially extending space is formed in the housing


126




a


of the second rocking cam


126


, and a helical spline


126




b


that axially spirals like a left-handed screw is formed in an inner peripheral surface of the internal space. A ring-like bearing portion


126




c


having a center hole with a reduced diameter covers a right end of the internal space. A generally triangular nose


126




d


is formed so as to protrude from an outer peripheral surface. An upper side of the nose


126




d


constitutes a cam surface


126




e


that is concavely curved.




The first rocking cam


124


and the second rocking cam


126


are disposed such that their end surfaces are respectively in contact with opposed ends of the shaft input portion


122


in a coaxial manner with the bearing portions


124




c


,


126




c


facing outwards. As a whole, the first rocking cam


124


, the shaft input portion


122


, and the second rocking cam


126


assume a generally cylindrical shape having an internal space as shown in FIG.


9


.




A slider gear


128


is disposed in the internal space that is constituted by the shaft input portion


122


and the two rocking cams


124


,


126


. The slider gear


128


has a generally cylindrical shape, and an input helical spline


128




a


that spirals like a right-handed screw is formed at the center of an outer peripheral surface of the slider gear


128


. A first output helical spline


128




c


that spirals like a left-handed screw is formed at a left end portion of the input helical spline


128




a


, with a small-diameter portion


128




b


being interposed between the input helical spline


128




a


and the first output helical spline


128




c


. A second output helical spline


128




e


that spirals like a left-handed screw is formed at a right end portion of the input helical spline


128




a


, with a small-diameter portion


128




d


being interposed between the input helical spline


128




a


and the second output helical spline


128




e


. It is to be noted herein that the output helical splines


128




c


,


128




e


are smaller in outer diameter than the input helical spline


128




a.






A through-hole


128




f


is formed in the slider gear


128


in the direction of a center axis thereof. A long hole


128




g


for opening the inside of the through-hole


128




f


to the outer peripheral surface is formed in one of the small-diameter portions


128




d


. The long hole


128




g


has a circumferentially extended length.




A supporting pipe


130


as shown in

FIG. 11

is circumferentially slidably disposed in the through-hole


128




f


of the slider gear


128


. It is to be noted herein that

FIG. 11A

is a plan view, that

FIG. 11B

is a front view, and that

FIG. 11C

is a right side view. As shown in

FIG. 2

, the supporting pipe


130


is commonly provided for all the intermediary drive mechanisms


120


(the number of the intermediary drive mechanisms


120


is four in this case). For each of the intermediary drive mechanisms


120


, a corresponding one of axially extended long holes


130




a


is opened in the supporting pipe


130


.




Furthermore, a control shaft


132


axially slidably penetrates the supporting pipe


130


. As is the case with the supporting pipe


130


, the control shaft


132


is also commonly provided for all the intermediary drive mechanisms


120


. For each of the intermediary drive mechanisms


120


, a corresponding one of engaging pins


132




a


protrudes from the control shaft


132


. Each of the engaging pins


132




a


is formed so as to penetrate a corresponding one of the axially extended long holes


130




a


formed in the supporting pipe


130


. Furthermore, the leading end of each of the engaging pins


132




a


of the control shaft


132


is inserted through the circumferentially extended long hole


128




g


formed in the slider gear


128


of a corresponding one of the intermediary drive mechanisms


120


.




Because of the axially extended long holes


130




a


formed in the supporting pipe


130


, even if the supporting pipe


130


is fixed to the cylinder head


8


, each of the engaging pins


132




a


of the control shaft


132


can be axially moved and thus makes it possible to axially move the slider gear


128


. In addition, the slider gear


128


itself is engaged in the circumferentially extended long hole


128




g


with a corresponding one of the engaging pins


132




a


and is thereby axially positioned. On the other hand, however, the slider gear


128


can rock around the axis.




The input helical spline


128




a


of the slider gear


128


is engaged with the helical spline


122




b


inside the shaft input portion


122


. Further, the first output helical spline


128




c


is engaged with the helical spline


124




b


inside the first rocking cam


124


. The second output helical spline


128




e


is engaged with the helical spline


126




b


inside the second rocking cam


126


.




As shown in

FIG. 2

, each of the intermediary drive mechanisms


120


thus constructed can rock around the axis but is prevented from being axially moved while being interposed between rising wall portions


136


,


138


formed in the cylinder head


8


on the side of the bearing portions


124




c


,


126




c


of the rocking cams


124


,


126


. Holes are formed in the rising wall portions


136


,


138


at positions corresponding to the center holes of the bearing portions


124




c


,


126




c


, respectively. The supporting pipe


130


is passed through the holes and fixed thereby. Accordingly, the supporting pipe


130


is fixed to the cylinder head


8


and does not axially move or rotate.




The control shaft


132


in the supporting pipe


130


axially slidably penetrates the supporting pipe


130


and is connected at one end thereof to the piston body


102


of the slide actuator


100


shown in

FIGS. 3 and 7

. Thus, the axial position of the control shaft


132


can be adjusted by adjusting hydraulic pressures applied to the pressure chambers


101




a


,


101




b


. Hence, the difference in phase between the roller


122




f


of the shaft input portion


122


and the noses


124




d


,


126




d


of the rocking cams


124


,


126


can be adjusted by way of the control shaft


132


and the slider gear


128


. That is, as shown in

FIGS. 12

to


14


, valve lift amounts of the intake valves


12




a


,


12




b


can be made continuously variable by driving the slide actuator


100


.




It is to be noted herein that

FIGS. 12A and 12B

shows the intermediary drive mechanism


120


in a state where the control shaft


132


has been moved to the critical position in the direction H by the slide actuator


100


. That is,

FIGS. 12A and 12B

correspond to the state shown in FIG.


7


C. While

FIGS. 12

to


15


show a mechanism in which the second rocking cam


126


drives the first intake valve


12




a


, the same holds true for a mechanism in which the first rocking cam


124


drives the second intake valve


12




b


. Therefore, the following description will be accompanied by reference symbols of the first rocking cam


124


and the second intake valve


12




b


as well.




In

FIG. 12A

, a base circle portion (a portion other than the nose


45




c


) of the intake cam


45




a


is in contact with the roller


122




f


of the shaft input portion


122


in the intermediary drive mechanism


120


. Although not shown, the roller


122


is urged by a spring so as to be always in contact with the side of the intake cam


45




a


. In this state, the noses


124




d


,


126




d


of the rocking cams


124


,


126


are not in contact with a roller


13




a


of a rocker arm


13


. The base circle portion adjacent to the noses


124




d


,


126




d


is in contact with the roller


13




a


of the rocker arm


13


. Hence, the intake valves


12




a


,


12




b


are closed.




If the nose


45




c


of the intake cam


45




a


depresses the roller


122




f


of the shaft input portion


122


through rotation of the intake cam shaft


45


, rocking movements are transmitted from the shaft input portion


122


to the rocking cams


124


,


126


via the slider gear


128


in the intermediary drive mechanism


120


, and the rocking cams


124


,


126


rock in such a manner as to depress the noses


124




d


,


126




d


respectively. Hence, curved cam surfaces


124




e


,


126




e


formed on the noses


124




d


,


126




d


immediately come into contact with the roller


13




a


of the rocker arm


13


. As shown in

FIG. 12B

, the rocking cams


124


,


126


depress the roller


13




a


of the rocker arm


13


by means of the entire cam surfaces


124




e


,


126




e


, whereby the rocker arm


13


rocks around the side of a base end portion


13




c


supported by an adjuster


13




b


and a leading edge portion


13




d


of the rocker arm


13


greatly depresses a stem end


12




c


. Thus, the intake valves


12




a


,


12




b


open the intake ports


14




a


,


14




b


respectively with a maximum valve lift amount.





FIGS. 13A and 13B

show a state of the intermediary drive mechanism


120


in the case where the control shaft


132


has been returned by the slide actuator


100


from the state shown in

FIGS. 12A and 12B

in the direction L. That is,

FIGS. 13A and 13B

correspond to the state shown in FIG.


7


B.




In

FIG. 13A

, the base circle portion of the intake cam


45




a


is in contact with the roller


122




f


of the shaft input portion


122


in the intermediary drive mechanism


120


. In this state, the noses


124




d


,


126




d


of the rocking cams


124


,


126


are not in contact with the roller


13




a


of the rocker arm


13


. A base circle portion that is spaced slightly further apart from the noses


124




d


,


126




d


in comparison with the case of

FIGS. 12A and 12B

is in contact with the roller


13




a


of the rocker arm


13


. Hence, the intake valves


12




a


,


12




b


are closed. This is because the slider gear


128


has moved in the direction L in the intermediary drive mechanism


120


and thus the difference in phase between the roller


122




f


of the shaft input portion


122


and the noses


124




d


,


126




d


of the rocking cams


124


,


126


has become small.




If the nose


45




c


of the intake cam


45




a


depresses the roller


122




f


of the shaft input portion


122


through rotation of the intake cam shaft


45


, rocking movements are transmitted from the shaft input portion


122


to the rocking cams


124


,


126


via the slider gear


128


in the intermediary drive mechanism


120


, and the rocking cams


124


,


126


rock in such a manner as to depress the noses


124




d


,


126




d


respectively.




As described above, in the state shown in

FIG. 13A

, the base circle portion that is spaced apart from the noses


124




d


,


126




d


is in contact with the roller


13




a


of the rocker arm


13


. Hence, even if the rocking cams


124


,


126


have rocked, the roller


13




a


of the rocker arm


13


remains in contact with the base circle portion for a while without coming into contact with the curved cam surfaces


124




e


,


126




e


formed on the noses


124




d


,


126




d


. Thereafter, the curved cam surfaces


124




e


,


126




e


come into contact with the roller


13




a


and depress the roller


13




a


of the rocker arm


13


as shown in FIG.


13


B. Hence, the rocker arm


13


rocks around the base end portion


13




c


. However, since the roller


13




a


of the rocker arm


13


is spaced apart from the noses


124




d


,


126




d


at the beginning, the cam surfaces


124




e


,


126




e


have a correspondingly reduced area available. Thus, the rocking angle of the rocker arm


13


is reduced, and the amount by which the leading end portion


13




d


of the rocker arm


13


depresses the stem end


12




c


, namely, the valve lift amount is reduced. Hence, the intake valves


12




a


,


12




b


open the intake ports


14




a


,


14




b


respectively with a valve lift amount smaller than the maximum valve lift amount.





FIGS. 14A and 14B

show a state of the intermediary drive mechanism


120


in the case where the control shaft


132


has been returned by the slide actuator


100


to the maximum extent in the direction L. That is,

FIGS. 14A and 14B

correspond to the state shown in FIG.


7


A. In the state shown in

FIG. 14A

, the base circle portion that is spaced far apart from the noses


124




d


,


126




d


is in contact with the roller


13




a


of the rocker arm


13


. Hence, for an entire period of rocking movements, the roller


13




a


of the rocker arm


13


remains in contact with the base circle portion without coming into contact with the curved surfaces


124




e


,


126




e


formed on the noses


124




d


,


126




d


. That is, as shown in

FIG. 14B

, even if the nose


45




c


of the intake cam


45




a


has depressed the roller


122




f


of the shaft input portion


122


to the maximum extent, the curved cam surfaces


124




e


,


126




e


are not used to depress the roller


13




a


of the rocker arm


13


. Hence, the rocker arm


13


does not rock around the base end portion


13




c


, and the amount by which the leading end portion


13




d


of the rocker arm


13


depresses the stem end


12




c


, namely, the valve lift amount is “0”. Thus, even if the intake cam shaft


45


rotates, the intake valves


12




a


,


12




b


hold the intake ports


14




a


,


14




b


closed respectively.




By thus adjusting the axial position of the control shaft


132


by means of the slide actuator


100


, it becomes possible to continuously adjust valve lift amounts of the intake valves


12




a


,


12




b


as indicated by solid lines in a graph shown in FIG.


15


.




In the case where the intake valves


12




a


,


12




b


are opened, forces are applied from valve springs


12




d


of the intake valves


12




a


,


12




d


via the rocker arm in such a direction as to narrow an angle between the arm


122




c


and the noses


124




d


,


126




d


. Thus, a thrust force is generated in the slider gear


128


so as to cause a movement in the direction L. Hence, a thrust force Fs for moving the control shaft


132


in the direction L is applied via the engaging pins


132




a


. The more the valve lift amounts of the intake valves


12




a


,


12




b


are increased, the more firmly the valve springs


12




d


are compressed. Hence, the thrust force Fs generated in the control shaft


132


is increased as the slide actuator


100


moves the control shaft


132


in the direction H, as indicated by an alternate long and short dash line in FIG.


8


.




In the aforementioned structure of the first embodiment, a combination of the piston body


102


and the push portion


103


corresponds to an assisting force applying portion, the push portion


103


corresponds to an assisting force output portion, and the outer peripheral surface of the roller


102




k


corresponds to a conversion plane.




The following effects are obtained from the first embodiment that has been described above.




(a) A force output by the output rod


103




a


is converted into an assisting force via the roller


102




k


while the outer peripheral surface of the roller


102




k


moving together with the control shaft


132


serves as a conversion plane. The force thus converted is applied to the control shaft


132


. Hence, as shown in

FIG. 8

, as the control shaft


132


moves in such a direction as to increase valve lift amounts of the intake valves


12




a


,


12




b


, the assisting force can be correspondingly increased. Accordingly, a suitable assisting force that can act against a thrust force generated in the intermediary drive mechanism


120


can be applied to the control shaft


132


.




As a result, even if the pressure-receiving area of the piston portion


102




a


has been reduced for the sake of responding properties, there is no apprehension that a minimum hydraulic fluid pressure will not be ensured on the side with a large valve lift amount or that a delay will be caused in responding properties during movements of the control shaft


132


.




(b) A restoring force of the spring


103




c


is used in an output from the output rod


103




a


. Thus, the more easily the axial position of the control shaft


132


is shifted to the high-lift side with a relatively simple structure, the more the assisting force can be increased. Moreover, unlike the case of a magnetic force or the like, the restoring force is not weakened suddenly. That is, an assisting force that is sufficient even for axial movements of the control shaft


132


over an extensive range is generated.




(c) In particular, the slide actuator


100


is applied to the intake valves


12




a


,


12




b


and used to adjust their valve lift amounts. Even for such a use, a suitable assisting force can be applied to the control shaft


132


due to the aforementioned structure. Therefore, the intake air amount of the engine


2


can be regulated with a quick response.




In a second embodiment, valve lift amounts of intake valves


212




a


,


212




b


are adjusted by a slide actuator


300


through axial movements of an auxiliary shaft


250


that is connected to an intake cam shaft


245


via a roller bearing portion


250




a


as shown in FIG.


16


. The intake cam shaft


245


is interlocked with rotation of the crank shaft of the engine via a timing sprocket (which may be replaced with a timing gear or a timing pulley) disposed at one end of the intake cam shaft


245


. However, since the auxiliary shaft


250


is connected to the intake cam shaft


245


via the roller bearing portion


250




a


, it does not rotate in such a manner as to interlock with rotation of the intake cam shaft


245


. The auxiliary shaft


250


moves together with the intake cam shaft


245


only in the axial direction. It is to be noted herein that a timing sprocket


252


connected to the intake cam shaft


245


is supported so as to be rotatable with respect to the cylinder block of the engine but immovable in the axial direction. However, the timing sprocket


252


is connected at a central portion thereof to the intake cam shaft


245


via a straight spline mechanism


252




a


, thus allowing axial movements of the intake cam shaft


245


.




It is to be noted herein that intake cams


245




a


on the intake cam shaft


245


are designed as three-dimensional cams that continuously change in profile in the axial direction. More specifically, the intake cams


245




a


are formed such that their cam noses are reduced in height toward the right side in FIG.


16


and increased in height toward the left side in FIG.


16


. Such changes in profile make it possible to change valve lift amounts substantially in the same manner as shown in FIG.


15


.




The slide actuator


300


includes a piston portion


310


and an assisting portion


320


. The piston portion


310


is designed such that a piston


310




b


is accommodated in a cylinder


310




a


. The piston


310




b


is connected to the auxiliary shaft


250


. In accordance with a state of supply of a hydraulic pressure from the OCV


104


that is controlled by the ECU, the piston


310




b


moves as indicated by an arrow, whereby the intake cam shaft


245


can be axially moved via the auxiliary shaft


250


and the bearing portion


250




a.






The assisting portion


320


includes a slide cam


322


in a housing


320




a


. In this case, the slide cam


322


has a generally hemispherical shape and is connected in a rotational center axis portion on the spherical side to a coupling shaft


350


. The coupling shaft


350


is coaxially connected to the piston


310




b


on the other side of the auxiliary shaft


250


. Accordingly, the axial position of the slide cam


322


is interlocked with a position of displacement of the piston


310




b.






A roller


324




b


disposed at a leading end of an output rod


324




a


provided in a push portion


324


is in contact with a generally spherical cam surface


322




a


of the slide cam


322


. It is to be noted herein that the push portion


324


is different only in a roller portion


324




b


and basically identical in structure with the push portion


103


of the aforementioned first embodiment. That is, the output rod


324




a


presses the cam surface


322




a


of the slide cam


322


by means of a compressed spring


324




c


, and applies an assisting force acting in the direction H to the intake cam shaft


245


via the piston


310




b


, the auxiliary shaft


250


, and the bearing portion


250




a


. A stroke sensor core


360




a


is mounted in a central portion of the slide cam


322


on the other side of the coupling shaft


350


. A leading edge of the stroke sensor core


360




a


is inserted into a stroke sensor coil


360




b


that is attached to the housing


320




a


. Hence, a shaft position of the intake cam shaft


245


is detected, and a signal corresponding to the shaft position is output to the ECU from the stroke sensor coil


360




b.






As shown in the drawings, the intake cams


245




a


designed as three-dimensional cams are designed such that their valve lift amounts are increased toward the left side. Thus, restoring forces received from the valve springs


212




d


of the intake valves


212




a


,


212




b


generate a thrust force applied to the intake cam shaft


245


in the direction L by means of the cam surfaces of the intake cams


245




a


. Hence, the cam surface


322




a


of the slide cam


322


is inclined in a curved manner and reversely with respect to the cam surfaces of the intake cams


245




a


and thus generates an assisting force that acts against the aforementioned thrust force. If the piston


310




b


exists at a critical position in the direction L as shown in

FIG. 16

, the aforementioned thrust force is small. Therefore, the roller


324




b


is in contact with the cam surface


322




a


of the slide cam


322


at a position with a slight inclination with respect to the axis of the intake cam shaft


245


. If the piston


310




b


has been moved toward a critical position in the direction H, the restoring forces received from the valve springs


212




d


of the intake valves


212




a


,


212




b


are increased, and the thrust force is increased as well. Hence, the inclination of the cam surface


322




a


at a position for contacting the roller


324




b


is gradually increased, which causes an increase in the assisting force. If the piston


310




b


reaches the critical position in the direction H as shown in

FIG. 17

, the absolute values of the thrust force and the assisting force are maximized. The thrust force and the assisting force counterbalance each other as in the case of the aforementioned first embodiment shown in FIG.


8


.




In the structure of the aforementioned second embodiment, the intake cam shaft


245


corresponds to a control shaft and the cam surface


322




a


of the slide cam


322


corresponds to a conversion plane.




The following effects are obtained from the second embodiment that has been described above.




(a) A force output by the output rod


324




a


is converted into an assisting force while the cam surface


322




a


of the slide cam


322


axially interlocked with the intake cam shaft


245


serves as a conversion plane. The force thus converted is applied to the intake cam shaft


245


. Hence, as the intake cams


245




a


are moved by the intake cam shaft


245


in such a direction as to increase valve lift amounts, the assisting force can be correspondingly increased. Accordingly, a suitable assisting force that can act against a thrust force applied to the intake cam shaft


245


from the intake cams


245




a


can be applied to the intake cam shaft


245


.




As a result, even if the pressure-receiving area of the piston


310




b


has been reduced for the sake of responding properties, there is no apprehension that a minimum hydraulic fluid pressure will not be ensured on the side with a large valve lift amount or that responding properties will deteriorate.




(b) The effects (b) and (c) of the aforementioned first embodiment also are obtained.




In the aforementioned embodiments, the urging force of the springs


103




c


,


324




c


is utilized to apply a pressing force for the roller


102




k


or the slide cam


322


to the output rods


103




a


,


324




a


. However, it is also appropriate that a pressing force be applied to the output rods


103




a


,


324




a


through a fluid pressure such as an oil pressure or an air pressure. In this case, almost no drop in pressure is caused even by movements of the control shaft


132


and the intake cam shaft


245


. Therefore, a suitable assisting force that can be sufficient even for movements of the control shaft


132


and the intake cam shaft


245


over a more extensive range can be generated.




The slide actuator


300


of the second embodiment may be employed in the first embodiment instead of the slide actuator


100


. Further, the slide actuator


100


of the first embodiment may be employed in the second embodiment instead of the slide actuator


300


.




In the aforementioned embodiments, the number of the output rods


103




d


,


324




a


provided for the slide actuator


100


,


300


is two. However, it is also appropriate that this number be one, or three or more. Further, it is not absolutely required that the single slide actuator


100


or


300


be provided for the control shaft


132


or the intake cam shaft


245


. That is, two or more slide actuators may be axially coupled in series so as to strengthen an assisting force.




In the aforementioned embodiments, the output rods


103




a


,


324




a


protrude in the direction perpendicular to the axis of the control shaft


132


or the intake cam shaft


245


. However, as shown in

FIGS. 18

,


19


, even if the output rods


103




a


,


324




a


protrude in a direction that is not perpendicular to the axis but parallel to a virtual plane (PY, QY) perpendicular to the axis, an assisting force can be generated.





FIG. 18

shows a modified example of the first embodiment. In

FIG. 18

, each of two shaft portions


402


J disposed parallel to a piston body


402


is provided with a corresponding pair of rollers


402




k


. Axes “az” of the rollers


402




k


are parallel to a virtual plane (PY) that is perpendicular to an axis “ax” of a control shaft. Output rods


403




a


having axes “ay” protrude parallel to the virtual plane (PY) in such a manner as to be in contact with outer peripheral surfaces of the rollers


402




k


. Even in such a structure, the four rollers


402




k


receive pressing forces output by the four output rods


403




a


, whereby the pressing forces are converted into assisting forces acting in the direction of an axis “ax” of the control shaft on the outer peripheral surfaces of the rollers


402




k


. Thus, even if a large thrust force is generated in the intermediary drive mechanism, those assisting forces can act against the thrust force.





FIG. 19

shows a modified example of the second embodiment. Although the slide cam


322


of the second embodiment assumes a generally hemispherical shape, a slide cam


522


of this modified example assumes a generally semicolumnar shape. A coupling shaft


550


is fitted to the center of an outer peripheral surface of the slide cam


522


. Output rods


524




a


having axes “by” protrude parallel to a virtual plane (QY) perpendicular to an axis “bx” in such a manner as to be in contact with a cam surface


522




a


constructed of the outer peripheral surface. Rollers


524




b


are provided on the ends of the rods


524




a


. Even in such a structure, the cam surface


522




a


receives pressing forces output by the four output rods


524




a


(the lower two are not shown), whereby the pressing forces are converted into assisting forces acting in the direction of the axis “bx” of the coupling shaft


550


. Thus, even if a large thrust force is generated, those assisting forces can act against the thrust force.




In the aforementioned first embodiment (FIG.


3


), the rollers


102




k


are disposed on the side of the piston portion


102




a


. However, it is also appropriate that each of the rollers


102




k


be disposed at the leading end of a corresponding one of the output rods


103




a


and that a protrusion identical in shape to the leading end portions


103




d


of the output rods


103


(or a salient strip identical in cross-sectional shape to the leading end portions


103




d


of the output rods


103


) be formed on the side of the piston portion


102




a


. In this case, the same function as in the first embodiment can be substantially achieved. In the second embodiment (

FIG. 16

) as well, it is appropriate that the roller


324




b


be disposed on the side of the coupling shaft


350


and that a cam having a generally cylindrical surface identical in shape to the cam surface


322




a


of the slide cam


322


be disposed on the side of the output rod


324




a


. In this case, the same function as in the second embodiment can be substantially achieved. As for the examples described with reference to

FIGS. 18 and 19

as well, the structure in which the rollers are disposed at the leading ends of the output rods and the structure in which the rollers are disposed on the side of the control shaft or the coupling shaft may be interchanged. In this case as well, the same function as described above can be substantially achieved.




As described above, an embodiment according to one aspect of the invention is designed such that the assisting force applying portion increases the assisting force as the axial position of the control shaft is shifted to the high-lift side. Hence, a suitable assisting force capable of acting against a thrust force that is increased as the axial position of the control shaft is shifted to the high-lift side can be applied to the variable valve mechanism. Since the assisting force is generated on the basis of a restoring force of the elastic body or a pressure of the fluid, it is not weakened all of a sudden as in the case of a magnetic force. That is, an assisting force that is sufficient even for axial movements of the control shaft over an extensive range can be generated.




As a result, the apprehension that a minimum hydraulic fluid pressure will not be ensured on the side of a larger valve lift amount or that responding properties will deteriorate can be eliminated.




The assisting device of the aforementioned variable valve mechanism can be characterized as follows. The assisting force applying portion includes the assisting force output portion and the conversion plane. The assisting force output portion outputs a restoring force of an elastic body or a pressure of a fluid parallel to the virtual plane intersecting with the axis of the control shaft. The conversion plane receives a force output from the assisting force output portion, converts it into a force acting in the direction of the axis of the control shaft, and makes it available as an assisting force. The assisting force applying portion changes the inclination of the conversion plane at a position to which a force from the assisting force output portion is transmitted, in such a manner as to interlock with axial movements of the control shaft. Thus, as the axial position of the control shaft is shifted to the high-lift side, the assisting force can be correspondingly increased.




Since the aforementioned conversion plane is provided, the force output by the assisting force output portion is converted into a force acting in the direction of the axis of the control shaft. The inclination of the conversion plane to which the force is transmitted changes while interlocking with axial movements of the control shaft, whereby the assisting force is increased in proportion to a shift to the high-lift side. Therefore, a suitable assisting force that can act against the aforementioned thrust force can be applied to the variable valve mechanism.




In the embodiment according to one aspect of the invention, the output rod transmits a force by means of the conversion plane.




The output thus constructed makes it possible to easily transmit a force to the conversion plane and adjust the magnitude of an assisting force through an inclination of the conversion plane. Thus, a suitable assisting force that can act against a thrust force can be applied to the variable valve mechanism.




Furthermore, in the embodiment according to one aspect of the invention, the conversion plane is designed as a cam surface and a cam having the cam surface is designed to be moved in the direction of the axis of the control shaft, whereby the assisting force can be easily increased by means of a restoring force of the elastic body or a pressure of the fluid as the axial position of the control shaft is shifted to the high-lift side. Thus, a suitable assisting force that can act against a thrust force can be applied to the variable valve mechanism.




In addition, in the embodiment according to one aspect of the invention, the conversion plane is designed as an outer peripheral surface of a ring and the position of the output rod for contacting the outer peripheral surface is axially moved in such a manner as to interlock with the control shaft, whereby the assisting force can be easily increased by means of a restoring force of the elastic body or a pressure of the fluid as the axial position of the control shaft is shifted to the high-lift side. Thus, a suitable assisting force that can act against a thrust force can be applied to the variable valve mechanism.




Instead of the structure of the aforementioned embodiments in which the output rods protrude in the direction substantially perpendicular to the axis of the control shaft, it is also appropriate that the output rods be in contact with the conversion plane by protruding parallel to the virtual plane that is substantially perpendicular to the axis of the control shaft as described above. This also makes it possible to easily increase the assisting force by means of a restoring force of the elastic body or a pressure of the fluid as the axial position of the control shaft is shifted to the high-lift side. Thus, a suitable assisting force that can act against a thrust force can be applied to the variable valve mechanism.




The variable valve mechanism may also include the cam shaft, the cams, the intermediary drive mechanism, the control shaft, and the actuator. In such a structure as well, the structure of the aforementioned assisting force applying portion makes it possible to easily increase the assisting force by means of a restoring force of the elastic body or a pressure of the fluid as the axial position of the control shaft is shifted to the high-lift side. Thus, a suitable assisting force that can act against a thrust force can be applied to the variable valve mechanism.




The variable valve mechanism may also include the three-dimensional cams and the control shaft. Even in such a structure, the structure of the aforementioned assisting force applying portion makes it possible to easily increase the assisting force by means of a restoring force of the elastic body or a pressure of the fluid as the axial position of the control shaft is shifted to the high-lift side. Thus, a suitable assisting force that can act against a thrust force can be applied to the variable valve mechanism.




Further, it is also appropriate that the control shaft be used as the cam shaft having the three-dimensional cams as well. In this case as well, a suitable assisting force that can act against a thrust force can be applied to the variable valve mechanism.




As in the case of the aforementioned embodiments, the assisting device generates an assisting force by means of a restoring force of the spring. Thus, the spring can be used as the elastic body. Accordingly, since the assisting force can be easily increased by means of the restoring force of the spring as the axial position of the control shaft is shifted to the highlift side, a suitable assisting force that can act against the thrust force can be applied to the variable valve mechanism with a relatively simple structure.




Further, the assisting device can use oil as a fluid for generating an assisting force. Accordingly, the assisting force can be easily increased by means of a hydraulic pressure as the axial position of the control shaft is shifted to the high-lift side. Thus, a suitable assisting force that can act against the thrust force can be applied to the variable valve mechanism.




Furthermore, as in the case of the aforementioned embodiments, the variable valve mechanism makes it possible to continuously change valve lift amounts of the intake valves of the internal combustion engine.




By applying the aforementioned assisting device to the variable valve mechanism for adjusting valve lift amounts of the intake valves of the internal combustion engine, it becomes possible to apply a suitable assisting force to the variable valve mechanism and to adjust the amount of intake air in the internal combustion engine with a quick response.




While the invention has been described with reference to preferred exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or constructions. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more less or only a single element, are also within the spirit and scope of the invention.



Claims
  • 1. An assisting device for applying an assisting force to counteract a thrust force generated in a variable valve mechanism, comprising:valves disposed in the variable valve mechanism; a control shaft that is movable to cause valve lift amounts of the valves to continuously change with changes in an axial position of the control shaft, the control shaft receiving the thrust force from the valves; a force applying member coupled to the control shaft and that receives an adjusting force from a first source of force to adjust the axial position of the control shaft; and an assisting force applying portion that generates and applies the assisting force to the control shaft on the basis of a restoring force of an elastic body or a pressure of a fluid, which is a second source of force that is in addition to the first source of force, the assisting force applying portion increasing the assisting force as the axial position of the control shaft is shifted to a high-lift side.
  • 2. An assisting device for applying an assisting force to counteract a thrust force generated in a variable valve mechanism, comprising:valves disposed in the variable valve mechanism; a control shaft that is movable to cause valve lift amounts of the valves to continuously change with changes in an axial position of the control shaft, the control shaft receiving the thrust force from the valves; and an assisting force applying portion that generates and applies the assisting force to the control shaft on the basis of a restoring force of an elastic body or a pressure of a fluid, the assisting force applying portion increasing the assisting force as the axial position of the control shaft is shifted to a high-lift side, wherein the assisting force applying portion comprises: an assisting force output portion that outputs the restoring force of the elastic body or the pressure of the fluid parallel to a virtual plane perpendicular to an axis of the control shaft, and a conversion plane that converts a force output from the assisting force output portion into a force acting in a direction of the axis of the control shaft so as to use the force as the assisting force, and changes an inclination of the conversion plane at a position to which the force from the assisting force output portion is converted as the control shaft moves axially so as to increase the assisting force as the axial position of the control shaft is shifted to the high-lift side.
  • 3. The assisting device according to claim 2, wherein:the assisting force output portion comprises an output rod protruding toward the conversion plane due to the restoring force of the elastic body or a pressure of the fluid; and the force from the output rod is transmitted to the conversion plane through contact of the output rod with the conversion plane.
  • 4. The assisting device according to claim 3, wherein:the smaller an angle of the output rod with respect to an abutment surface between the output rod and the conversion plane becomes, the larger the force transmitted to the control shaft becomes; and the closer to a right angle the angle of the output rod with respect to the abutment surface between the output rod and the conversion plane becomes, the smaller the assisting force transmitted to the control shaft becomes.
  • 5. The assisting device according to claim 4, wherein:the output rod protrudes in a direction substantially perpendicular to the axis of the control shaft; the conversion plane is formed as a cam surface on a cam moving in a direction of the axis of the control shaft while interlocking with the control shaft; and a position of the output rod that contacts the cam surface is axially moved as the control shaft axially moves, whereby the assisting force is increased as the axial position of the control shaft is shifted to the high-lift side.
  • 6. The assisting device according to claim 4, wherein:the output rod protrudes in a direction substantially perpendicular to the axis of the control shaft; the conversion plane is formed as an outer peripheral surface of a ring that moves in the direction of the axis of the control shaft as the control shaft axially moves, with an axis parallel to the virtual plane substantially perpendicular to the axis of the control shaft serving as an axis of rotation; and a position of the output rod that contacts the outer peripheral surface is moved in the direction of the axis of the control shaft as the control shaft axially moves, whereby the assisting force is increased as the axial position of the control shaft is shifted toward the high-lift side.
  • 7. The assisting device according to claim 4, wherein:the output rod protrudes parallel to the virtual plane substantially perpendicular to the axis of the control shaft; the conversion plane is formed as an outer peripheral surface of a ring that moves in the direction of the axis of the control shaft as the control shaft axially moves, with an axis parallel to the virtual plane substantially perpendicular to the axis of the control shaft serving as an axis of rotation; and a position of the output rod that contacts the outer peripheral surface is moved in the direction of the axis of the control shaft as the control shaft axially moves, whereby the assisting force is increased as the axial position of the control shaft is shifted toward the high-lift side.
  • 8. The assisting device according to claim 1, wherein the variable valve mechanism comprises:a cam shaft that is rotationally driven by a crank shaft of an internal combustion engine; cams disposed on the cam shaft; intermediary drive mechanisms each of which is pivotally supported by a shaft other than the cam shaft and each of which has a shaft input portion and a shaft output portion so that a corresponding one of the valves is driven at the output portion in response to the driving of the input portion by a corresponding one of the cams; the control shaft whose axial moving distance is based on a difference in phase between the input portion and the output portion of each of the intermediary drive mechanisms; and an actuator for axially moving the control shaft and thus adjusting the difference in phase between the shaft input portion and the shaft output portion of each of the intermediary drive mechanisms, and thus allows valve lift amounts to continuously change with changes in the axial position of the control shaft.
  • 9. The assisting device according to claim 1, wherein:the variable valve mechanism is a mechanism that allows valve lift amounts to continuously change by axially moving three-dimensional cams whose cam profile changes in the axial direction; and an axial moving distance of the control shaft changes with an axial moving distance of the three-dimensional cams.
  • 10. The assisting device according to claim 9, wherein the control shaft also serves as a cam shaft for the three-dimensional cams.
  • 11. The assisting device according to claim 1, wherein the assisting force applying portion generates the assisting force on the basis of a restoring force of a spring.
  • 12. The assisting device according to claim 1, wherein the assisting force applying portion generates the assisting force on the basis of a hydraulic pressure.
  • 13. The assisting device according to claim 1, wherein the variable valve mechanism allows valve lift amounts of intake valves of an internal combustion engine to continuously change.
  • 14. An assisting method for applying an assisting force to counteract a thrust force generated in a variable valve mechanism, comprising the steps of:allowing valve lift amounts of valves disposed in the variable valve mechanism to continuously change with changes in an axial position of a control shaft; adjusting the axial position of the control shaft by applying an adjusting force to a force applying member that is coupled to the control shaft, the adjusting force is supplied from a first source of force; and increasing the assisting force that is applied to the control shaft on the basis of a restoring force of an elastic body or a pressure of a fluid as the axial position of the control shaft that receives the thrust force is shifted to a high-lift side, the elastic body that supplies the restoring force or the fluid that supplies the pressure being a second source of force that is in addition to the first source of force.
  • 15. An assisting method for applying an assisting force to counteract a thrust force generated in a variable valve mechanism, comprising the steps of:allowing valve lift amounts of valves disposed in the variable valve mechanism to continuously change with changes in an axial position of a control shaft; and increasing the assisting force that is applied to the control shaft on the basis of a restoring force of an elastic body or a pressure of a fluid as the axial position of the control shaft that receives the thrust force is shifted to a high-lift side, wherein: the restoring force of the elastic body or the pressure of the fluid is output to a virtual plane that intersects with an axis of the control shaft; the force output to the virtual plane is converted by a conversion plane into a force acting in a direction of the axis of the control shaft as the assisting force; and an inclination of the conversion plane at a position to which the force is transmitted to the conversion plane is changed with changes in axial movement of the control shaft, whereby the assisting force is increased as the axial position of the control shaft is shifted to the high-lift side.
  • 16. The assisting method according to claim 14, wherein the force applying member includes a piston, and the first source of force is a source of hydraulic force that applies pressure to the piston.
  • 17. The assisting device according to claim 1, wherein the force applying member includes a piston, and the first source of force is a source of hydraulic force that applies pressure to the piston.
  • 18. The assisting device according to claim 2, wherein the variable valve mechanism comprises:a cam shaft that is rotationally driven by a crank shaft of an internal combustion engine; cams disposed on the cam shaft; intermediary drive mechanisms each of which is pivotally supported by a shaft other than the cam shaft and each of which has a shaft input portion and a shaft output portion so that a corresponding one of the valves is driven at the output portion in response to the driving of the input portion by a corresponding one of the cams; the control shaft whose axial moving distance is based on a difference in phase between the input portion and the output portion of each of the intermediary drive mechanisms; and an actuator for axially moving the control shaft and thus adjusting the difference in phase between the shaft input portion and the shaft output portion of each of the intermediary drive mechanisms, and thus allows valve lift amounts to continuously change with changes in the axial position of the control shaft.
  • 19. The assisting device according to claim 2, wherein:the variable valve mechanism is a mechanism that allows valve lift amounts to continuously change by axially moving three-dimensional cams whose cam profile changes in the axial direction; and an axial moving distance of the control shaft changes with an axial moving distance of the three-dimensional cams.
  • 20. The assisting device according to claim 19, wherein the control shaft also serves as a cam shaft for the three-dimensional cams.
  • 21. The assisting device according to claim 2, wherein the assisting force applying portion generates the assisting force on the basis of a restoring force of a spring.
  • 22. The assisting device according to claim 2, wherein the assisting force applying portion generates the assisting force on the basis of a hydraulic pressure.
  • 23. The assisting device according to claim 2, wherein the variable valve mechanism allows valve lift amounts of intake valves of an internal combustion engine to continuously change.
Priority Claims (1)
Number Date Country Kind
2001-324757 Oct 2001 JP
US Referenced Citations (7)
Number Name Date Kind
5289806 Hurr Mar 1994 A
5445117 Mendler Aug 1995 A
5497737 Nakamura Mar 1996 A
6105551 Nakano et al. Aug 2000 A
6182623 Sugie et al. Feb 2001 B1
6244230 Mikame Jun 2001 B1
6318313 Moriya et al. Nov 2001 B1
Foreign Referenced Citations (1)
Number Date Country
A 2000-54814 Feb 2000 JP