Valve operating device for internal combustion engines

TECHNICAL FIELD

The present invention relates to a valve operating device for an internal combustion engine enabling valve timing and valve lift characteristic (valve lift and working angle or valve open period) of intake and/or exhaust valves to be varied depending upon engine operating conditions, and specifically to a variable valve timing and variable valve lift characteristic device applicable to an internal combustion engine equipped with an intake camshaft and an exhaust camshaft.

BACKGROUND ART

In recent years, there have been proposed and developed various variable valve timing and lift control devices each of which enables engine valve timing and valve lift characteristic of engine valves to be varied depending upon engine operating conditions, so as to reconcile improved fuel economy and enhanced combustion stability and driveability during low-speed low-load operation and enhanced intake-air charging efficiency and increased engine power during high-speed high-load operation. On such variable valve timing and lift control mechanism has been disclosed in Japanese Patent Provisional Publication No. 55-137305 (hereinafter is referred to as “JP55-137305”).

FIG. 21

shows the variable valve timing and lift device disclosed in JP55-137305. In the device shown in

FIG. 21

, a camshaft

2

is provided nearby an upper middle position of the upper deck of a cylinder head

1

. Camshaft

2

is integrally formed on its outer periphery with a cam

2

a

. A control shaft

3

whose axis is parallel to the axis of camshaft

2

is provided nearby the right-hand side of the camshaft (viewing FIG.

21

). An eccentric cam

4

whose axis is eccentric to the axis of control shaft

3

is fixed to the control shaft. A rocker arm

5

is oscillatingly or rockably supported on the eccentric cam of control shaft

3

. An intake valve

6

is slidably provided in cylinder head

1

. A rockable cam

8

is located at the upper end of intake valve

6

through a valve lifter

7

. Rockable cam

8

is oscillatingly or rockably supported by a pivot shaft

9

whose axis is laid out above valve lifter

7

in parallel with the axis of camshaft

2

. The lower cam surface

8

a

of rockable cam

8

is in abutted-engagement with the upper surface of valve lifter

7

. One end

5

a

of rocker arm

5

is in abutted-engagement with the cam contour surface of cam

2

a

, while the other end

5

b

of rocker arm

5

is in abutted-engagement with the upper end face

8

b

of rockable cam

8

, so as to transmit cam action (lift) of cam

2

a

through rockable cam

8

and valve lifter

7

to intake valve

6

, so that the intake valve is opened and closed. Control shaft

3

is rotatable within a predetermined angular range by means of an actuator (not shown). A spring

10

is provided to permanently bias the rockable cam

8

clockwise in such a manner as to force the upper end face

8

b

of rockable cam

8

into contact with the other end

5

b

of rocker arm

5

. By energizing the actuator in response to a control signal from a controller (not shown), control shaft

3

is adjusted to a desired angular position based on engine operating conditions such as engine speed and load, so that the center of eccentric cam shifts and thus the center of oscillating motion of rocker arm

5

also changes. As a result, the abutted position between the other rocker-arm end

5

b

and the rockable-cam upper end face

8

b

shifts in the vertical direction (viewing FIG.

21

), and thus the abutted position between the cam surface

8

a

of rockable cam

8

and the valve-lifter upper surface shifts. In this manner, a locus of oscillating motion of rockable cam

8

also changes, with the result that the valve timing of intake valve

6

, that is, both intake-valve open timing (IVO) and intake-valve closure timing (IVC), and the valve lift of intake valve

6

can be variably controlled. Furthermore, there is a possibility of a slight change in the distance between the axis of camshaft

2

and the axis of pivot shaft

9

during operation of the engine. This may deteriorates the accuracy of variable valve timing and lift characteristic control.

SUMMARY OF THE INVENTION

It is, therefore in view of the above disadvantages, an object of the invention to provide an improved valve operating device for an internal combustion engine enabling valve timing and valve lift characteristic to be varied depending on engine operating conditions.

In order to accomplish the aforementioned and other objects of the present invention, a valve operating device for an internal combustion engine enabling both valve timing and valve lift characteristic to be varied depending on engine operating conditions comprises intake and exhaust camshafts, an eccentric cam fixedly connected to a first one of the intake and exhaust camshafts so that an axis of the eccentric cam is eccentric to an axis of the first camshaft, a rockable cam supported on the first camshaft so that the rockable cam rotates or oscillates about the axis of the first camshaft, a rocker arm oscillatingly supported on an outer periphery of the eccentric cam so that a center of an oscillating motion of the rocker arm revolves around the axis of the first camshaft, and a control shaft that variably controls the center of the oscillating motion of the rocker arm.

According to another aspect of the invention, a valve operating device for an internal combustion engine enabling both valve timing and valve lift characteristic to be varied depending on engine operating conditions comprises intake and exhaust camshafts, a rockable cam oscillatingly supported on a first one of the intake and exhaust camshafts for operating an engine valve associated with the first camshaft by an oscillating motion of the rockable cam, a drive cam fixedly connected to an outer periphery of the second camshaft adapted to be driven by an engine crankshaft for operating an engine valve associated with the second camshaft, a power-transmission mechanism that produces the oscillating motion of the rockable cam by converting a rotary motion of the second camshaft into an oscillating motion, and a control mechanism that variably controls a valve lift characteristic of the engine valve associated with the first camshaft by controlling an angular position of the first camshaft and thus changing a sliding-contact position of the rockable cam with respect to the engine valve associated with the first camshaft.

According to a still further aspect of the invention, a valve operating device for an internal combustion engine enabling both valve timing and valve lift characteristic to be varied depending on engine operating conditions comprises intake and exhaust camshafts, both adapted to be driven by an engine crankshaft, a rockable cam oscillatingly supported on a first one of the intake and exhaust camshafts for operating an engine valve associated with the first camshaft by an oscillating motion of the rockable cam, a drive cam fixedly connected to an outer periphery of the second camshaft for operating an engine valve associated with the second camshaft, a power-transmission mechanism that produces the oscillating motion of the rockable cam by converting a rotary motion of the first camshaft into an oscillating motion, and a control mechanism that variably controls a valve lift characteristic of the engine valve associated with the first camshaft by controlling an attitude of the power-transmission mechanism and thus changing a sliding-contact position of the rockable cam with respect to the engine valve associated with the first camshaft.

The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a cross-sectional view showing the essential part of a first embodiment of a valve operating device.

FIG. 2

is a plan view showing the essential part of the valve operating device of the first embodiment.

FIGS. 3 through 5

are explanatory views of the operation of the valve operating device of the first embodiment.

FIG. 6

is a graph illustrating valve timing and valve lift characteristic curves of intake and exhaust valves, in the valve operating device of the invention.

FIG. 7

is a cross-sectional view showing the essential part of a second embodiment of a valve operating device.

FIG. 8

is a cross-sectional view showing the essential part of a third embodiment of a valve operating device.

FIG. 9

is a plan view showing the essential part of the valve operating device of the third embodiment.

FIGS. 10 through 12

are explanatory views of the operation of the valve operating device of the third embodiment.

FIG. 13

is a cross-sectional view showing the essential part of a fourth embodiment of a valve operating device.

FIG. 14

is an explanatory view showing the operation of the valve operating device of the fourth embodiment, during low valve lift.

FIGS. 15 and 16

are explanatory views showing the operation of the valve operating device of the fourth embodiment, during high valve lift.

FIG. 17

is a cross-sectional view of the essential part of a fifth embodiment of a valve operating device.

FIG. 18

is an explanatory view showing the operation of the valve operating device of the fifth embodiment.

FIG. 19

is a cross-sectional view of the essential part of a sixth embodiment of a valve operating device.

FIG. 20

is an explanatory view showing the operation of the valve operating device of the sixth embodiment.

FIG. 21

is a cross-sectional view of the essential part of the conventional variable valve timing and lift control device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

However, in the variable valve timing and lift control device disclosed in JP55-137305, camshaft

2

and control shaft

3

are constructed as two separate component parts, and additionally the control shaft is located above camshaft

2

. This undesirably increases the overall height of cylinder head

1

. Such a device requires a comparatively large installation space for control shaft

3

. Additionally, control shaft

3

is provided separately from camshaft

2

, and therefore the device of

FIG. 21

requires a supporting structure needed to rotatably support the control shaft on the cylinder head. In such a case, a great alteration in the upper structure of cylinder head

1

must be made. This results in complicated manufacturing processes, and thus increases total production costs. In addition to the two separate shafts, namely camshaft

2

and control shaft

3

, the device of

FIG. 21

requires pivot shaft

9

, thereby increasing the number of component parts.

Referring now to the drawings, particularly to

FIGS. 1 through 5

, the valve operating device of the first embodiment is exemplified in an internal combustion engine with a pair of intake valves (

12

,

12

) and a pair of exhaust valves (

13

,

13

) for each engine cylinder. The valve operating device of the first embodiment is mounted on a cylinder head

11

. As can be seen from the circles indicated by the one-dotted line of

FIG. 2

, a pair of intake valves (

12

,

12

) and a pair of exhaust valves (

13

,

13

) are provided for each engine cylinder. Valve lifters (

16

,

16

) for intake valves (

12

,

12

) and valve lifters (

17

,

17

) for exhaust valves (

13

,

13

) are provided on upper ends of valve stems (not numbered) of the intake and exhaust valves. The valve stems are integrally formed with respective valve heads or valve fillet portions (not shown) of the intake and exhaust valves. Each of valve lifters (

16

,

16

;

17

,

17

) is constructed as a direct-operated valve lifter or a direct-operated cam follower which is directly operated by means of a cam (that is, a drive cam

18

for the valve lifter

17

of the exhaust-valve side and a rockable cam

22

for the valve lifter

16

of the intake-valve side). Each of the valve lifters has a cylindrical bore closed at its upper end. Valve lifters (

16

,

16

;

17

,

17

) are slidably accommodated in respective cylindrical valve-lifter supporting bores formed in cylinder head

11

. Intake valves (

12

,

12

) and exhaust valves (

13

,

13

) are supported or guided by means of respective valve guides (not numbered) located on both sides of cylinder head

11

. An intake camshaft

14

and an exhaust camshaft

15

are laid out at the upper portion of cylinder head

11

. In the shown embodiment, intake camshaft

14

and exhaust camshaft

15

are arranged parallel to each other so that axes of the intake and exhaust camshafts extend in the longitudinal direction of the engine. A first eccentric cam

19

, which will be fully described later, is provided on exhaust camshaft

15

so that the axis of first eccentric cam

19

is eccentric to the axis of exhaust camshaft

15

. On the other hand, a rockable cam

22

is provided on intake camshaft

14

. A power-transmission mechanism (simply, a converter)

20

is provided to transmit an input motion (rotary motion) of first eccentric cam

19

to rockable cam

22

, while converting the rotary motion of first eccentric cam

19

to linear motion (output motion). A control mechanism

21

is provided for variably controlling a valve lift of each of the intake valves by controlling the angular position (the angular phase) of intake camshaft

14

, thus shifting or changing the sliding-contact position of rockable cam

22

relative to the associated intake valve

12

(exactly, the associated intake-valve lifter

16

). The valve operating mechanism of the first embodiment is comprised of the intake valve pair (

12

,

12

), exhaust valve pair (

13

,

13

), intake camshaft

14

, exhaust camshaft

15

, power-transmission mechanism (rotary-to-linear motion converter)

20

, and control mechanism

21

. A rotational force (torque) of an engine crankshaft is transmitted through a driven sprocket (not shown) and a timing chain (not shown) located at the front end of the engine to exhaust camshaft

15

. Exhaust-cam bearing caps

25

are bolted to the upper end of cylinder head

11

by means of bolts

25

a

, and thus the upper bearing halves of exhaust-cam bearing caps

25

are fitted to half-round sections of cylinder head

11

. Then, the bores in the cylinder head and caps

25

are bored to take the exhaust-cam bearings. In this manner, exhaust camshaft

15

is rotatably supported by way of the exhaust-cam bearings. Exhaust camshaft

15

is crank-shaped and integrally formed with drive cams (

18

,

18

) by which exhaust valves (

13

,

13

) are opened or closed via the respective exhaust-valve lifters (

17

,

17

). Exhaust camshaft

15

is also formed integral with the previously-noted first eccentric cam

19

(serving as a journal) outside of two adjacent drive cams (

18

,

18

) or between two adjacent engine cylinders (see FIG.

2

). Each of the drive cams is formed as a substantially raindrop-shaped circular cam (often called as a “convex cam”) in which a top circle and a base circle are joined by a third circular arc. Drive cams

18

have the same cam profile. As clearly shown in

FIG. 1

, the outer peripheral surface (cam contour surface) of drive cam

18

is in sliding-contact with the upper surface of the associated exhaust valve lifter. First eccentric cam

19

is crank-shaped so that the axis X

1

of first eccentric cam

19

is offset from the axis X of exhaust camshaft

15

by a predetermined distance (eccentricity) ε. The first eccentric cam is located outside of the two adjacent drive cams (

18

,

18

) or between two adjacent engine cylinders, in such a manner as to be axially spaced apart from the outside of two adjacent exhaust valve lifters (

17

,

17

).

On the other hand, intake camshaft

14

serves as a control shaft for control mechanism

21

. Each of intake-cam bearing brackets or each of intake-cam bearing caps

40

is bolted on both ends to the upper end of cylinder head

11

by means of bolts

40

a

, and thus the upper bearing halves of intake-cam bearing caps

40

are fitted to half-round sections of cylinder head

11

. Then, the bores in the cylinder head and caps

40

are bored to take the intake-cam bearings. In this manner, intake camshaft

14

is rotatably supported by way of the intake-cam bearings. Intake camshaft

14

rotatably or oscillatingly supports rockable cams (

22

,

22

) by which intake valves (

12

,

12

) are opened or closed via the respective intake-valve lifters (

16

,

16

). As shown in

FIGS. 1 and 2

, in particular as viewed from the axial direction in

FIG. 2

, cam profiles of rockable cams (

22

,

22

) are the same. Also, each of rockable cams (

22

,

22

) is formed into a substantially U shape (in side view). As best seen in

FIG. 2

, the rockable cam pair, namely the two adjacent rockable cams (

22

,

22

) are integrally connected to each other through a substantially cylindrical rockable-cam base portion

22

a

. Base portion

22

a

defines therein an axially-extending supporting bore in which intake camshaft

14

is rotatably supported. Base portion

22

a

is also formed with a pair of axially-spaced flanged portions (

22

b

,

22

b

). An intermediate portion of the outer peripheral surface of base portion

22

a

situated between the two flanged portions (

22

b

,

22

b

) serves as a journal. A rockable-cam bracket

23

for the rockable cam pair (

22

,

22

) is bolted on both ends to the upper end of cylinder head

11

by means of bolts

23

b

, and thus upper bearing halves of rockable-cam brackets

23

are fitted to half-round sections of cylinder head

11

. Then, the bores in the cylinder head and brackets

23

are bored to take the rockable-cam bearings. In this manner, the intermediate portion of base portion

22

a

of the rockable cam pair (

22

,

22

) is rotatably supported by way of the associated rockable-cam bearing. A cam nose portion

22

c

extends obliquely upwards from base portion

22

a

. Cam nose portion

22

c

is formed with a connecting-pin hole (simply, a pin hole). As can be seen from the cross-sectional view of

FIG. 1

, each of the two adjacent rockable cams (

22

,

22

) is formed on its lower surface with a base circle portion

24

a

, an intermediate cam surface portion

24

b

(simply, a cam surface portion), and a top circle portion

24

c

. A cam-contour surface

24

is constructed by these three portions

24

a

,

24

b

and

24

c

. Cam surface portion

24

b

is circular-arc shaped and extends from base circle portion

24

a

to top circle portion

24

c

. The cam profiles for base circle portion

24

a

and cam surface portion

24

b

are the same in the two adjacent rockable cams (

22

,

22

). Rockable cam

22

is designed to be brought into abutted-contact (sliding-contact) with a designated point or a designated position of the upper surface of the associated intake-valve lifter

16

depending on an angular position of rockable cam

22

oscillating. As can be appreciated from the cross sections shown in

FIGS. 1

,

3

,

4

and

5

, a predetermined angular range of base circle portion

24

a

functions as a base circle section. A predetermined angular range of the cam surface portion

24

b

being continuous with the base circle portion

24

a

functions as a ramp section. A predetermined angular range of the top circle portion

24

c

(or the cam nose portion

22

c

) being continuous with the ramp section of cam surface portion

24

b

functions as a lift section. Power-transmission mechanism

20

of the device of the first embodiment is comprised of the first eccentric cam

19

, a rocker arm

27

, a link arm

28

, and a link rod

29

. Rocker arm

27

is oscillatingly or rockably supported on intake camshaft

14

through a second eccentric cam

26

(described later) serving as a control cam included in control mechanism

21

. Link arm

28

mechanically links the first eccentric cam

19

to one end (a first end)

27

a

of rocker arm

27

. Link rod

29

is provided to mechanically link the other end (a second end)

27

b

of rocker arm

27

to the cam nose portion

22

c

of one of the two rockable cams (

22

,

22

). As shown in

FIG. 1

, rocker arm

27

is formed into a substantially boomerang shape. Rocker arm

27

has almost the same width dimension as the cam bracket

23

. In other words, rocker arm

27

is comparatively short and as wide as the cam bracket. A substantially central portion of rocker arm

27

is bored as a cam hole

27

c

, and thus rocker arm

27

is oscillatingly or rockably supported on second eccentric cam

26

rotatably fitted into the cam hole

27

c

. Rocker arm

27

is formed at its first end

27

a

with a connecting pin hole into which a tip end (or a front end) of a connecting pin

30

is loosely rotatably fitted. The first end

27

a

of rocker arm

27

is connected to link arm

28

by means of the connecting pin

30

. Additionally, rocker arm

27

is formed at its second end

27

b

with a connecting pin hole into which a connecting pin

31

is press-fitted. The second end

27

b

of rocker arm

27

is connected to link rod

29

by means of the connecting pin

31

. Link arm

28

is formed as a substantially straight link extending in the lateral direction of the engine (exactly, in a direction perpendicular to the axial direction of either one of intake and exhaust camshafts

14

and

15

). Link arm

28

is comprised of a comparatively large-diameter annular base portion

28

a

and a protruding end

28

b

extending from a predetermined angular position of the outer periphery of base portion

28

a

in the direction perpendicular to the axial direction of either one of intake and exhaust camshafts

14

and

15

. Base portion

28

a

of link arm

28

has a half-split structure. That is, base portion

28

a

is split into a first half-round section (i.e., a half-round bracket or a half-round cap

28

c

) and a second half-round section (a main link-arm base portion). When installing link arm

28

on first eccentric cam

19

, firstly, the first and second half-round sections are fitted onto the outer peripheral surface of first eccentric cam

19

, and then the first half-round section (half-round cap)

28

c

is bolted to the second half-round section of base portion

28

a

by means of bolts (

36

,

36

), and thus the first and second half-round sections are fitted to each other. At this time, a first fit groove

28

d

is defined between the first half-round section and the outer peripheral surface of first eccentric cam

19

, whereas a second fit groove

28

e

is defined between the second half-round section and the outer peripheral surface of first eccentric cam

19

, so as to permit first eccentric cam

19

to be rotatably fitted into the base portion

28

a

of link arm

28

. On the other hand, the protruding end

28

b

of link arm

28

has a connecting-pin hole into which the other end (or a rear end) of the previously-noted connecting pin

30

is press-fitted. Link rod

29

is formed as a comparatively short, straight link. Link rod

29

is formed on its both ends with a pair of circular portions

29

a

and

29

b

. A pair of connecting-pin holes are bored in the respective circular portions

29

a

and

29

b

. Pin

31

, press-fitted into the other end

27

b

of rocker arm

27

, is rotatably inserted into the connecting-pin hole of circular portion

29

a

. On the other hand, pin

32

, press-fitted into the cam nose portion

22

c

of rockable cam

22

, is rotatably inserted into the connecting-pin hole of circular portion

29

b

. Snap rings are fitted to the respective tip ends of pins

30

,

31

and

32

, to prevent these pins from falling out of the respective connecting-pin holes. A plug post

33

is provided at the transversely central position of cylinder head

11

. Control mechanism

21

is comprised of intake camshaft

14

(serving as a control shaft) and second eccentric cam

26

fixed to the intake camshaft. Control mechanism

21

also includes an actuator

34

by which the angular phase of intake camshaft

14

is varied. Second eccentric cam

26

is annular in shape. The axis P

1

of second eccentric cam

26

is eccentric to the axis X

2

of intake camshaft

14

(the axis P

2

of control shaft

14

) by a distance α. In the first embodiment of

FIGS. 1-5

, as the actuator for intake camshaft

14

, an electric actuator

34

is provided at the rear end of cylinder head

11

. In the shown embodiment, although the electric actuator is used as an actuator for intake camshaft

14

, in lieu thereof a hydraulic actuator may be used as the intake-camshaft actuator. In such a case, the hydraulic actuator is generally mounted directly on the cylinder head so as to simplify a hydraulic circuit and to reduce a fluid-flow resistance. This ensures a superior response for operation of the hydraulic actuator. Intake camshaft

14

is driven by actuator

34

so that the intake camshaft can be rotated within a predetermined angular range. Actuator

34

is driven in response to a control signal from a controller (not shown) or an electronic engine control unit (ECU). The controller generally comprises a microcomputer. The controller includes an input/output interface (I/O), memories (RAM, ROM), and a microprocessor or a central processing unit (CPU). The input/output interface (I/O) of the controller receives input information from various engine/vehicle switches and sensors, namely a crank angle sensor, an airflow meter, an engine coolant temperature sensor, and the like. Within the controller, the central processing unit (CPU) allows the access by the I/O interface of input informational data signals from the previously-discussed engine/vehicle sensors. The CPU of the controller determines the current engine operating condition based on the input information, and is responsible for carrying the variable valve timing and valve lift characteristic control program stored in memories and is capable of performing necessary arithmetic and logic operations. Computational results (arithmetic calculation results), that is, calculated output signals (containing an electric actuator drive current) are relayed via the output interface circuitry of the controller to output stages (containing the actuator

34

).

The valve operating device of the first embodiment shown in

FIG. 1

operates as follows.

Each of drive cams (

18

,

18

) is driven by exhaust camshaft

15

. As each of the drive cams revolves, the associated valve lifter

17

follows the cam surface of drive cam

18

by moving up and down. By virtue of the valve spring bias, during rotation of each of drive cams (

18

,

18

), each of exhaust valves (

13

,

13

) is opened and closed. As regards the exhaust valve lift characteristic, the valve operating device of the embodiment exhibits a fixed valve lift characteristic determined by the cam profile of each of the drive cams (see the exhaust valve lift characteristic indicated by the broken line in FIG.

6

), irrespective of the engine operating conditions.

On the other hand, each of intake valves (

12

,

12

) is driven as follows. As exhaust camshaft

15

rotates about its axis, first eccentric cam

19

revolves in a circle around the axis of exhaust camshaft

15

. Rotary motion (revolution) of first eccentric cam

19

is converted into linear motion of link arm

28

. The linear motion of link arm

28

is transmitted via connecting pin

30

to rocker arm

27

, and thus rocker arm

27

swings or oscillates around second eccentric cam

26

. The oscillating motion of rocker arm

27

is transmitted via link rod

29

to the rockable cam pair (

22

,

22

), so as to produce oscillating motion of the rockable cam pair. By way of the oscillating motion of the rockable cam pair (

22

,

22

), each of intake valves (

12

,

12

) is opened and closed through the respective intake-valve lifters (

16

,

16

). As discussed above, the axis P

1

of second eccentric cam

26

eccentrically fixed to intake camshaft

14

, that is, the center P

1

of oscillating motion of rocker arm

27

is shifted or displaced by controlling the angular position (phase angle) of intake camshaft (control shaft)

14

through actuator

34

. By virtue of control mechanism

21

, the intake valve lift characteristic can be changed depending on engine operating conditions (see the two different intake valve lift characteristics indicated by the one-dotted line and solid line in FIG.

6

). During low-speed and low-load operation, intake camshaft (serving as a control shaft)

14

is driven in its one rotational direction through actuator

34

, in response to a control signal from the controller. Then, as shown in

FIGS. 1 and 3

, the axis P

1

of second eccentric cam (control cam)

26

is held at an upper right angular position with respect to the axis P

2

(X

2

) of intake camshaft

14

. A radially-thick-walled portion

26

a

of second eccentric cam

26

is shifted or displaced or rotated to the upper right of intake camshaft

14

. Owing to the displacement of thick-walled portion

26

a

of second eccentric cam

26

, the rocker arm

27

itself is shifted upwards relative to intake camshaft

14

. At this time, the cam nose portion

22

c

of rockable cam

22

is slightly displaced or shifted downwards forcibly via link rod

29

, and thus the rockable cam pair (

22

,

22

) also rotates leftwards, that is, clockwise (viewing FIGS.

1

and

3

). As a result, the abutted area (sliding-contact area) between the upper surface of each intake valve lifter

16

and the lower cam surface of the associated rockable cam

22

and ranging from the base circle portion

24

a

via the intermediate cam surface portion

24

b

to the top circle portion

24

c

forcibly shifts towards the base circle portion

24

a

. In other words, regarding the abutted area (sliding-contact area), the ratio of base circle portion

24

a

to cam surface portion

24

b

tends to increase during low-speed low-load operation. With the rocker arm

27

forcibly shifted upwards, during the low-speed low-load operation, when first eccentric cam

19

revolves by rotation of exhaust camshaft

15

and then the first end

27

a

of rocker arm

27

is pushed through the link arm

28

moving rightwards, the upward displacement (or upward lifting-up force or counterclockwise motion) of first end

27

a

(or pin

30

) is transmitted via link rod

29

to rockable cam pair (

22

,

22

), that is, intake-valve lifters (

16

,

16

). In this case, as shown in

FIG. 1

, a valve lift becomes a comparatively low valve lift L

1

. As discussed above, during the low-speed low-load operation, as can be seen from the low valve lift characteristic indicated by the one-dotted line in

FIG. 6

, the valve lift of each of intake valves (

12

,

12

) can be controlled to a comparatively low valve lift. Additionally, the intake valve open timing (IVO) tends to be retarded. The valve overlap (overlapping) of the intake-valve open period and the exhaust-valve open period tends to be decreased. This improves fuel economy and enhances combustion stability of the engine, during low-speed and low-load conditions.

In contrast to the above, when shifting from the low-speed low-load operation to high-speed high-load operation, intake camshaft

14

is driven in the opposite rotational direction through actuator

34

, in response to a control signal from the controller. As shown in

FIGS. 4 and 5

, actually, second eccentric cam

26

is rotated clockwise from the angular position shown in

FIG. 1

by the rotary motion of intake camshaft

14

. Thus, the axis P

1

of second eccentric cam

26

or the thick-walled portion

26

a

of second eccentric cam

26

shifts to the underside of the axis P

2

of intake camshaft

14

. Thus, the rocker arm

27

itself shifts downwards relative to intake camshaft

14

. At this time, the second end

27

b

of rocker arm

27

pushes down the cam nose portion

22

c

of rockable cam

22

via link rod

29

, and thus the rockable cam pair (

22

,

22

) also rotates counterclockwise (viewing

FIGS. 4 and 5

) by a predetermined displacement. As a result, the abutted-position (sliding-contact position) between the upper surface of each intake valve lifter

16

and the lower cam surface of the associated rockable cam

22

shifts rightwards (viewing FIGS.

4

and

5

). With the rocker arm

27

shifted downwards, during the high-speed high-load operation, when first eccentric cam

19

revolves by rotation of exhaust camshaft

15

and then the first end

27

a

is pushed through the link arm

28

moving rightwards, the upward displacement (or counterclockwise motion) of first end

27

a

(or pin

30

) is transmitted via link rod

29

to rockable cam pair (

22

,

22

), that is, intake-valve lifters (

16

,

16

). In this case, as shown in

FIG. 4

, a valve lift becomes a comparatively high valve lift L

2

. As discussed above, during the high-speed high-load operation, as can be seen from the high valve lift characteristic indicated by the solid line in

FIG. 6

, the valve lift of each of intake valves (

12

,

12

) is controlled to a comparatively high valve lift. Additionally, the intake valve open timing (IVO) tends to be advanced, while the intake valve closure timing (IVC) tends to be retarded. This enhances a charging efficiency of intake air entering the engine cylinders, and thus increases engine power, during high-speed high-load conditions.

As set forth above, in the valve operating device of the first embodiment shown in

FIGS. 1-5

, the intake valve open timing (IVO) and intake valve closure timing (IVC), and the intake valve lift characteristic (working angle as well as intake valve lift) can be variably controlled. In addition to the above, first eccentric cam

19

is formed as an integral section of exhaust camshaft

15

, whereas rockable cam pairs (

22

,

22

;

22

,

22

; . . . ) and rocker arms (

27

,

27

, . . . ) are oscillatingly provided on intake camshaft

14

. As a result of this, it is possible to effectively reduce the height of the valve operating device having the variable valve timing and valve lift characteristic control system, in other words, the overall height of cylinder head

11

. Hitherto, an additional cam shaft peculiar to first eccentric cam

19

was required, but in the device of the first embodiment the first eccentric cam can be driven by means of exhaust camshaft

15

generally used as one of engine parts. In addition, intake camshaft

14

is utilized as a control shaft included in a control mechanism as used in the conventional device, and all of the rockable cams (

22

,

22

) and rocker arm

27

are oscillatingly supported on the common intake camshaft. Therefore, it is possible to reduce the height of the valve train installed above cylinder head

11

, thus ensuring easier mounting of the valve operating device on internal combustion engines. The engine-hood height can also be reduced. Furthermore, it is possible to reduce the number of component parts of the valve operating device as much as possible. As a consequence, it is possible to enhance a manufacturing efficiency and to reduce total production costs. As can be appreciated from the above, in the device of the first embodiment, the construction of each of intake camshaft

14

, exhaust camshaft

15

, and their bearing sections (namely, rockable cam brackets

23

and intake-cam bearing caps

40

) is not changed. This eliminates the necessity of a design change in cylinder head

11

. Thus, the device of the embodiment can be easily mounted on the existing internal combustion engine, thus effectively suppressing an increase in manufacturing costs. Moreover, the second eccentric cam

26

and rocker arm

27

are axially offset from the rockable cam pair (

22

,

22

). The linkage composed of second eccentric cam

26

, rocker arm

27

and link arm

28

can be efficiently laid out within a dead space (simply, a space) defined outside of two adjacent drive cams (

18

,

18

) or between two adjacent engine cylinders. Additionally, first eccentric cam

19

is also laid out within the space defined outside of the two adjacent drive cams or between the two adjacent engine cylinders. Thus, it is possible to set the eccentricity E between the axis X

1

of first eccentric cam

19

and the axis X of exhaust camshaft

15

to a greater value. In the device of the embodiment, first eccentric cam

19

is mechanically linked to rocker arm

27

through link arm

28

, while rocker arm

27

is mechanically linked to rockable cam pair (

22

,

22

) through link rod

29

, so as to create a so-called six link structure. Therefore, it is possible to provide an increased rocker arm ratio (an increased leverage) of rocker arm

27

, and thus the motion of the input linkage (first eccentric cam

19

) can be converted through link arm

28

, rocker arm

27

and link rod

29

into a designated output oscillation (a desired oscillation angle) of rockable cam pair (

22

,

22

) without considerably increasing the eccentricity ε of first eccentric cam

19

to exhaust cam

15

, in other words, without setting the outside diameter of first eccentric cam

19

to an undesirably great value. As a result, it is possible to easily realize a considerably high valve lift characteristic and also to effectively downsize the device. As discussed above, there is no necessity to set the outside diameter of first eccentric cam

19

to a great value, and therefore it is possible to reduce a sliding-contact surface area between the inner peripheral surface of the annular base portion

28

a

of link arm

28

and the outer peripheral surface of first eccentric cam

19

. This contributes to a reduction in frictional resistance at the sliding-contact portion between annular base portion

28

a

and first eccentric cam

19

. Also, as described previously, first eccentric cam

19

is formed as an integral section of exhaust camshaft

15

. Suppose that first eccentric cam

19

is formed as a separate part. In this case, in order to integrally connect or fit the first eccentric cam to the exhaust camshaft, the mechanical strength of a portion of the first eccentric cam having a minimum wall thickness must be considered sufficiently. In case of first eccentric cam

19

formed as an integral section of exhaust cam

15

, it is possible to provide a comparatively great eccentricity without remarkably increasing the outside diameter of first eccentric cam

19

. This also contributes to the oscillation-angle enlarging effect of rockable cam pair (

22

,

22

). As set forth above, according to the linkage arrangement of the first embodiment, it is possible to provide the increased oscillation angle of rockable cam pair (

22

,

22

) and thus to effectively increase the ramp section of rockable cam

22

. Such an increased ramp section effectively lessens the collision velocity between valve lifter

16

and rockable cam

22

, thereby reducing noise and vibrations. Also, rockable cam

22

is oscillated or swung rightwards and leftwards forcibly by rocker arm

27

through link rod

29

. There is no necessity of a return spring used in the conventional device. Thus, it is possible to prevent an increase in friction created by a reaction force of the return spring. By driving only the exhaust camshaft by means of the engine crankshaft, exhaust valves

13

and intake valves

12

can be opened and closed. A structure of a wrapping power-transmission member such as a drive chain wound on the crankshaft and exhaust camshaft

15

can be simplified. This enhances a manufacturing efficient of the device, thus lowering production costs.

Referring now to

FIG. 7

, there is shown the valve operating device of the second embodiment. The device of the second embodiment of

FIG. 7

is different from that of the first embodiment of

FIG. 1

, in that a protruded portion (or a driving pin or a sliding pin)

35

having width across flats (two parallel flat faces) is provided at the other end

27

b

of rocker arm

27

and a cam slot (or a slit)

42

is provided at a boss-shaped portion

41

formed at the rightmost end (the upper end in

FIG. 7

) of base circle portion

24

a

of rockable cam

22

, instead of using the link rod

29

. With the linkage arrangement (the pin-slot engagement) shown in the right-hand side of

FIG. 7

, during the oscillating motion of rocker arm

27

, the protruded portion

35

serves to directly drive or oscillate rockable cam

22

, while sliding in the cam slot

42

. This enhances a power-transmission efficiency, reduces the number of component parts, and also simplifies the linkage structure.

Referring now to

FIGS. 8-12

, there is shown the valve operating device of the third embodiment. Exhaust camshaft

15

to which the rotational force (torque) of the engine crankshaft is transmitted through a sprocket

50

, is not crank-shaped, but formed rectilinearly. First eccentric cam

19

is circle in shape, and located outside of the two adjacent drive cams (

18

,

18

) or between two adjacent engine cylinders, in such a manner as to be axially space apart from the outside of two adjacent exhaust valve lifters (

17

,

17

). First eccentric cam

19

is fixed to the exhaust camshaft. The device of the third embodiment of

FIGS. 8-11

is different from that of the first or second embodiments, in that rocker arm

27

is located at a side of the exhaust camshaft. As shown in

FIG. 8

, rocker arm

27

is oscillatingly supported on the outer peripheral surface of first eccentric cam

19

through the cam hole

27

c

formed in rocker arm

27

. The first end

27

a

of rocker arm

27

is mechanically linked via link arm

28

to second eccentric cam

26

fixed to the intake camshaft

14

. On the other hand, the second end

27

b

of rocker arm

27

is mechanically linked via link rod

29

to one of the rockable cam pair (

22

,

22

). As best seen in

FIGS. 8

,

10

and

11

, link rod

29

extends transversely substantially in parallel with link arm

28

. The other end or right-hand end

29

b

(viewing

FIG. 8

) of link rod

29

has a substantially inverted L shape such that the right-hand side link-rod end

29

b

is moderately curved downwards or bent towards the rockable cam

22

. As can be appreciated from comparison between the linkage arrangements shown in

FIGS. 1 and 8

, the rockable cam

22

of the device of

FIG. 8

is different from that of

FIG. 1

, in layout and shape. As clearly shown in

FIG. 8

, cam nose portion

22

c

of the device of the third embodiment is directed transversely outwards and faced apart from the central plug post. Conversely, cam nose portion

22

c

of the device of the first (see

FIG. 1

) or second (see

FIG. 7

) embodiments is directed transversely inwards and faced to the central plug post. Rockable cam

22

is formed at its upper end with a boss-shaped portion

43

. The other end

29

b

of link rod is linked and pined to the boss-shaped portion

43

of rockable cam

22

by means of a connecting pin

32

. In the first, second and third embodiments, the basic structural design that the angular position of intake camshaft

14

is adjusted or controlled by actuator

34

is the same.

The valve operating device of the third embodiment shown in

FIG. 8

operates as follows.

During low-speed low-load operation, intake camshaft

14

is driven in its one rotational direction through actuator

34

, in response to a control signal from the controller. Then, as shown in

FIGS. 8 and 10

, the axis P

1

of second eccentric cam

26

is held at an upper right angular position with respect to the axis P

2

of intake camshaft

14

. Therefore, the thick-walled portion

26

a

of second eccentric cam

26

is upwardly rightwards spaced apart from intake camshaft

14

. At this time, rocker arm

27

itself is rotated counterclockwise through the link rod

28

, and held at a counterclockwise position, and thus rockable cam pair (

22

,

22

) is rotated to a predetermined counterclockwise position (see

FIGS. 8 and 10

) through link rod

29

. As a result, the abutted area (sliding-contact area) between the upper surface of each intake valve lifter

16

and the lower cam surface of the associated rockable cam

22

and ranging from the base circle portion

24

a

via the intermediate cam surface portion

24

b

to the top circle portion

24

c

slightly shifts towards the base circle portion

24

a

. In other words, regarding the abutted area (sliding-contact area), the ratio of base circle portion

24

a

to cam surface portion

24

b

tends to increase during low-speed low-load operation. As set forth above, during the low-speed low-load operation, when first eccentric cam

19

revolves by rotation of exhaust camshaft

15

and then rocker arm

27

oscillates, the displacement or oscillating motion of rocker arm

27

is transmitted via link rod

29

to rockable cam pair (

22

,

22

), that is, intake-valve lifters (

16

,

16

). In this case, as shown in

FIG. 8

, a valve lift becomes a comparatively low valve lift L

1

. For the reasons set out above, in the same manner as the device of the first embodiment, in the device of the third embodiment, during the low-speed low-load operation, as can be seen from the low valve lift characteristic indicated by the one-dotted line in

FIG. 6

, the valve lift of each of intake valves (

12

,

12

) can be controlled to a comparatively low valve lift. Also, the intake valve open timing (IVO) tends to be retarded. The valve overlap of the intake-valve open period and the exhaust-valve open period tends to be reduced. This improves fuel economy and enhances combustion stability, during low-speed and low-load conditions.

When shifting from the low-speed low-load operation to high-speed high-load operation, intake camshaft

14

is driven in the opposite rotational direction through actuator

34

, in response to a control signal from the controller. As shown in

FIGS. 11 and 12

, actually, second eccentric cam

26

is rotated counterclockwise from the angular position shown in

FIG. 8

by the rotary motion of intake camshaft

14

. Thus, the axis P

1

of second eccentric cam

26

or the thick-walled portion

26

a

of second eccentric cam

26

shifts to the upper left angular position with respect to the axis P

2

of intake camshaft

14

. Thus, the first end

27

a

of rocker arm

27

is slightly pushed out by link arm

28

, and as a result rocker arm

27

itself is rotated clockwise through the link rod

28

, and held at a clockwise position. Rockable cam pair (

22

,

22

) is thus rotated to a predetermined clockwise position (see

FIGS. 11 and 12

) through link rod

29

. As a result, the abutted area (sliding-contact area) between the upper surface of each intake valve lifter

16

and the lower cam surface of the associated rockable cam

22

and ranging from the base circle portion

24

a

via cam surface portion

24

b

to top circle portion

24

c

slightly shifts towards the cam nose portion

24

c

. In other words, regarding the abutted area (sliding-contact area), the ratio of base circle portion

24

a

to cam surface portion

24

b

tends to decrease during high-speed high-load operation. As set forth above, during the high-speed high-load operation, when first eccentric cam

19

revolves by rotation of exhaust camshaft

15

and then the first end

27

a

of rocker arm

27

is pushed out through link arm

28

, as shown in

FIG. 11

, a valve lift becomes a comparatively high valve lift L

2

. Therefore, during the high-speed high-load operation, as can be seen from the high valve lift characteristic indicated by the solid line in

FIG. 6

, the valve lift of each of intake valves (

12

,

12

) is controlled to a comparatively high valve lift. Additionally, the intake valve open timing (IVO) tends to be advanced, while the intake valve closure timing (IVC) tends to be retarded. This enhances a charging efficiency of intake air entering the engine cylinders, and thus increases engine power. As discussed above, the device of the third embodiment shown in

FIGS. 8-12

can provide the same effects (that is, good engine performance suited to various engine operating conditions, such as low-speed low-load operation, high-speed high-load operation and the like, and reduced height of the valve operating device or reduced overall height of cylinder head

1

) as the device of the first embodiment shown in

FIGS. 1-5

.

In the first, second and third embodiments described previously, although the cam profiles of two adjacent rockable cams (

22

,

22

) for the intake valve pair (

12

,

12

) are the same, a cam profile of one of the rockable cams (

22

,

22

) may be different from a cam profile of the other, so as to provide a valve-lift difference between the two intake valves (

12

,

12

) for each engine cylinder. Due to the valve-lift difference, swirl flow in each engine cylinder can be effectively strengthened, thereby improving the combustibility of the engine. In the first, second and third embodiments discussed above, as can be appreciated from the characteristic curves shown in

FIG. 6

, in order to mainly vary valve timing and valve lift characteristics of intake valves (

12

,

12

), the second camshaft to which at least first eccentric cams

19

are attached is set or used as an exhaust camshaft

15

, whereas the first camshaft to which at least rockable cams

22

and rocker arms

27

are attached is set or used as an intake camshaft

14

. Alternatively, in order to mainly vary valve timing and valve lift characteristics of exhaust valves (

13

,

13

), the second camshaft to which at least first eccentric cams

19

are attached may be set or used as an intake camshaft

14

, whereas the first camshaft to which at least rockable cams

22

and rocker arms

27

are attached may be set or used as an exhaust camshaft

15

.

Referring now to

FIGS. 13 through 16

, there is shown the valve operating device of the fourth embodiment. The device of the fourth embodiment is exemplified in an internal combustion engine with one intake valve

12

and one exhaust valve

13

for each engine cylinder. The device of the fourth embodiment of

FIGS. 13-16

is similar to the device of the first embodiment of

FIGS. 1-5

. Thus, the same reference signs used to designate elements in the first embodiment shown in

FIGS. 1-5

will be applied to the corresponding reference signs used in the device of the fourth embodiment in

FIGS. 13-16

, for the purpose of comparison of the first and fourth embodiments. The valve operating device of the fourth embodiment is mounted on cylinder head

11

. An intake-valve lifter

16

and an exhaust-valve lifter

17

are provided on upper ends of valve stems of intake and exhaust valves

12

and

13

. Each of valve lifters (

16

,

17

) is constructed as a direct-operated valve lifter which is directly operated by means of a cam (that is, drive cam

18

for exhaust-valve lifter

17

and rockable cam

22

for intake-valve lifter

16

). Each of the valve lifters has a cylindrical bore closed at its upper end. Valve lifters (

16

,

17

) are slidably accommodated in respective cylindrical valve-lifter supporting bores formed in cylinder head

11

. Intake valve

12

and exhaust valve

13

are supported or guided by means of respective valve guides located on both sides of cylinder head

11

. Intake camshaft

14

and exhaust camshaft

15

are laid out at the upper portion of cylinder head

11

. Inlet and outlet camshafts

14

and

15

are arranged parallel to each other so that their axes extend in the longitudinal direction of the engine. Drive cam

18

is fixed to the exhaust camshaft

15

for opening exhaust valve

13

against the exhaust valve spring bias. Rockable cam

22

is oscillatingly supported on the intake camshaft

14

for opening intake valve

12

against the intake valve spring bias. Power-transmission mechanism (simply, a converter)

20

is provided to transmit an input motion (rotary motion) of second eccentric cam

26

to rockable cam

22

, while converting the rotary motion of second eccentric cam

26

to oscillating motion (output motion). Control mechanism

21

is provided for variably controlling a valve lift of intake valve

12

by controlling the attitude of power-transmission mechanism

20

, thus shifting or changing the sliding-contact position of rockable cam

22

relative to the associated intake valve

12

(exactly, the associated intake-valve lifter

16

). The valve operating device of the fourth embodiment is comprised of the intake valve

12

, exhaust valve

13

, intake camshaft

14

, exhaust camshaft

15

, drive cam

18

, rockable cam

22

, power-transmission mechanism (rotary-to-oscillating motion converter)

20

, and control mechanism

21

. A rotational force (torque) of the engine crankshaft is transmitted through driven sprockets (not shown) and a timing chain (not shown) located at the front end of the engine to intake and exhaust camshafts

14

and

15

. Exhaust-cam bearing caps

25

are bolted to the upper end of cylinder head

11

, and thus the upper bearing halves of exhaust-cam bearing caps

25

are fitted to half-round sections of cylinder head

11

. Then, the bores in the cylinder head and caps

25

are bored to take the exhaust-cam bearings. In this manner, exhaust camshaft

15

is rotatably supported by way of the exhaust-cam bearings. In a similar manner, intake-cam bearing caps

40

are bolted to the upper end of cylinder head

11

, and thus the upper bearing halves of intake-cam bearing caps

40

are fitted to half-round sections of cylinder head

11

. Then, the bores in the cylinder head and caps

40

are bored to take the intake-cam bearings. In this manner, intake camshaft

14

is rotatably supported by way of the intake-cam bearings. Exhaust camshaft

15

is integrally formed with drive cam

18

by which exhaust valve

13

is opened or closed via exhaust-valve lifter

17

(see the left-hand side of FIG.

13

). The drive cam is formed as a substantially raindrop-shaped circular cam (often called as a “convex cam”) in which a top circle and a base circle are joined by a third circular arc. The outer peripheral surface (cam contour surface) of drive cam

18

is in sliding-contact with the upper surface of the associated exhaust valve lifter. Second eccentric cam

26

is fixed to the outer periphery of intake camshaft

14

(see the right-hand side of FIG.

13

). In the device of the fourth embodiment, second eccentric cam

26

constructs part of power-transmission mechanism

20

. Second eccentric cam

26

is located between two adjacent engine cylinders. Intake camshaft

14

rotatably or oscillatingly supports rockable cam

22

by which intake valve

12

is opened or closed via the intake-valve lifter

16

. As shown in

FIGS. 13 and 14

, rockable cam

22

is formed into a substantially U shape (in side view). Rockable cam

22

is formed at its substantially cylindrical base portion

22

a

with an axially-extending supporting bore into which intake camshaft

14

is rotatably inserted and fitted. A cam nose portion

22

c

extends obliquely upwards from base portion

22

a

. Cam nose portion

22

c

is formed with a connecting-pin hole (simply, a pin hole). As can be seen from the cross-sectional view of

FIG. 13

, rockable cam

22

is formed on its lower surface with a base circle portion

24

a

, an intermediate cam surface portion

24

b

(simply, a cam surface portion), and a top circle portion. Cam surface portion

24

b

is circular-arc shaped and extends from base circle portion

24

a

to top circle portion. Rockable cam

22

is designed to be brought into abutted-contact with a designated point or a designated position of the upper surface of the associated intake-valve lifter

16

depending on an angular position of rockable cam

22

oscillating. As can be appreciated from the cross sections shown in

FIGS. 13-16

, a predetermined angular range of base circle portion

24

a

functions as a base circle section. A predetermined angular range of the cam surface portion

24

b

being continuous with the base circle portion

24

a

functions as a ramp section. A predetermined angular range of the top circle portion or the cam nose portion

22

c

being continuous with the ramp section of cam surface portion

24

b

functions as a lift section. Power-transmission mechanism

20

of the device of the fourth embodiment is comprised of the second eccentric cam

26

, rocker arm

27

oscillatingly supported on the outer periphery of the second eccentric cam, and link rod

29

mechanically linking the second end

27

b

of rocker arm

27

and the cam nose portion

22

c

of rockable cam

22

. Second eccentric cam

26

is substantially disc-shaped. As shown in

FIG. 13

, second eccentric cam

26

is offset from intake camshaft

14

, so that the axis X

1

of second eccentric cam

26

is eccentric to the axis X

2

of intake camshaft

14

by an eccentricity ε. On the other hand, as shown in

FIG. 13

, rocker arm

27

is formed into a substantially boomerang shape in such a manner as to extend in the transverse direction of the engine. Rocker arm

27

is dimensioned to be comparatively short in length. A substantially central portion of rocker arm

27

is bored as a cam hole

27

c

, and thus rocker arm

27

is oscillatingly or rockably supported on second eccentric cam

26

rotatably fitted into the cam hole

27

c

. Rocker arm

27

is formed at its first end

27

a

with a connecting pin hole into which a tip end (or a front end) of a connecting pin

30

is loosely rotatably fitted. The first end

27

a

of rocker arm

27

is connected to a control arm

62

(described later) by means of the connecting pin

30

. Additionally, rocker arm

27

is formed at its second end

27

b

with a connecting pin hole into which a connecting pin

31

is press-fitted. The second end

27

b

of rocker arm

27

is connected to link rod

28

by means of the connecting pin

31

. Link rod

29

is formed as a comparatively short, boomerang-shaped link. Link rod

29

is formed on its both ends with a pair of circular portions each having a connecting-pin hole. Pin

31

, press-fitted into the connecting-pin hole formed in the second end

27

b

of rocker arm

27

, and pin

32

, press-fitted into the connecting-pin hole formed in the first end

27

a

, are rotatably inserted into the respective connecting-pin holes of both ends of link rod

29

. Snap rings are fitted to the respective tip ends of pins

30

,

31

and

32

, to prevent these pins from falling out of the respective connecting-pin holes. Control mechanism

21

is comprised of a control shaft

61

, a third eccentric cam

70

(serving as a control cam), a control arm

62

, and the same actuator as denoted by reference sign

34

in the first embodiment). Control shaft

61

is rotatably supported on the exhaust-cam bearing

25

. Third eccentric cam

70

is fixed to control shaft

61

. Control arm

62

is provided to mechanically link the third eccentric cam

70

to the first end

27

a

of rocker arm

27

. Control shaft

61

is located between intake and exhaust camshafts

14

and

15

, and situated close to the exhaust camshaft. Control shaft

61

extends in the longitudinal direction of the engine. Control shaft

61

is driven by the actuator provided at the rear end of cylinder head

11

, so that control shaft

61

is rotated within a predetermined angular range. Third eccentric cam

70

is annular in shape. The axis P

1

of third eccentric cam

70

is eccentric to the axis P

2

of control shaft

61

by a distance α. Control arm

62

is formed as a substantially straight link and has a relatively large-diameter portion

62

a

at its one end and a relatively small-diameter portion

62

b

at the other end. The large-diameter portion

62

a

is formed therein a cam hole

62

c

in which third eccentric cam

70

is slidably fitted. On the other hand, the small-diameter portion

62

b

is rotatably connected to the first end

27

a

of rocker arm

27

by means of pin

30

.

The valve operating device of the fourth embodiment shown in

FIG. 13

operates as follows.

Drive cam is driven by exhaust camshaft

15

. As the drive cam revolves, the associated valve lifter

17

follows the cam surface of drive cam

18

by moving up and down. By virtue of the valve spring bias, during rotation of drive cam

18

, the exhaust valve is opened and closed. As regards the exhaust valve lift characteristic, the valve operating device of the fourth embodiment exhibits a fixed valve lift characteristic determined by the cam profile of drive cam

18

(see the exhaust valve lift characteristic indicated by the broken line in FIG.

6

.), irrespective of the engine operating conditions.

On the other hand, intake valve

12

is driven as follows. As intake camshaft

14

rotates about its axis, second eccentric cam

26

revolves in a circle around the axis of intake camshaft

14

. Rotary motion of second eccentric cam

26

is converted into oscillating motion of rocker arm

27

. The oscillating motion of rocker arm

27

is transmitted via link rod

29

to rockable cam

22

, and thus the rockable cam swings or oscillates around intake camshaft

14

. By way of the oscillating motion of rockable cam

22

, intake valve

12

is opened and closed through the intake-valve lifter

16

. As discussed above, the axis P

1

of third eccentric cam

70

eccentrically fixed to control shaft

61

is shifted or displaced by controlling the angular position (phase angle) of control shaft

61

through actuator

34

, and as a result the attitude of power-transmission mechanism

20

can be changed. In other words, by changing the angular phase of the axis P

1

of third eccentric cam

70

relative to the axis P

2

of control shaft

61

, the attitude of power-transmission mechanism

20

can be changed and therefore the center of oscillating motion of rocker arm

27

, which is rockably or oscillatingly supported on the outer periphery of second eccentric cam

26

so that the center of oscillating motion of rocker arm

27

is capable of revolving in a circle around the axis X

2

of intake camshaft

14

, is variably controlled by the control shaft

61

. By virtue of control mechanism

21

, the intake valve lift characteristic can be changed depending on engine operating conditions (see the two different intake valve lift characteristics indicated by the one-dotted line and solid line in FIG.

6

). During low-speed and low-load operation, control shaft

61

is driven in its one rotational direction through actuator

34

, in response to a control signal from the controller. Then, as shown in

FIGS. 13 and 14

, the axis P

1

of third eccentric cam (control cam)

70

is held at a lower right angular position with respect to the axis P

2

of control shaft

61

. A radially-thick-walled portion

70

a

of third eccentric cam

70

is shifted or displaced or rotated to the lower right of control shaft

61

. Owing to the displacement of thick-walled portion

70

a

of second eccentric cam

70

, the first portion

27

a

of rocker arm

27

is pulled down and as a result the rocker arm itself is rotated counterclockwise. At this time, the cam nose portion

22

c

of rockable cam

22

is forcibly pulled upwards via the link rod

29

by the second end

27

b

of rocker arm

27

. In this manner, as a whole the right-hand linkage section comprised of rocker arm

27

, link rod

29

, and rockable cam

22

shifts counterclockwise. As a result, the abutted area (sliding-contact area) between the upper surface of intake-valve lifter

16

and the lower cam surface of the associated rockable cam

22

and ranging from the base circle portion

24

a

via the intermediate cam surface portion

24

b

to the top circle portion slightly shifts towards the base circle portion

24

a

(see FIGS.

13

and

14

). In other words, regarding the abutted area (sliding-contact area), the ratio of base circle portion

24

a

to cam surface portion

24

b

tends to increase during low-speed low-load operation. With the rocker arm

27

forcibly shifted counterclockwise, during the low-speed low-load operation, when second eccentric cam

26

revolves by rotation of intake camshaft

14

and thus rocker arm

27

swings or oscillates, the oscillating motion of rocker arm

27

(or upward lifting-up force of second end

27

b

of rocker arm

27

) is transmitted via the link rod

29

through rockable cam

22

to intake-valve lifter

16

. In this case, as shown in

FIG. 14

, a valve lift becomes a comparatively low valve lift L

1

. Therefore, during the low-speed low-load operation, as can be seen from the low valve lift characteristic indicated by the one-dotted line in

FIG. 6

, the valve lift of intake valve

12

can be controlled to a comparatively low valve lift. Additionally, the intake valve open timing (IVO) tends to be retarded. The valve overlap of the intake-valve open period and the exhaust-valve open period tends to be decreased. This improves fuel economy and enhances combustion stability of the engine, during low-speed and low-load conditions.

Contrary, when shifting from the low-speed low-load operation to high-speed high-load operation, control shaft

61

is driven in the opposite rotational direction through actuator

34

, in response to a control signal from the controller. As shown in

FIGS. 15 and 16

, actually, control shaft

61

is rotated clockwise and thus third eccentric cam (control cam)

70

is rotated clockwise from the angular position shown in

FIGS. 13 and 14

. Thus, the axis P

1

of third eccentric cam (control cam)

70

or the thick-walled portion

70

a

of third eccentric cam

70

shifts to the upper left (almost to the left) of the axis P

2

of control shaft

61

. Thus, rocker arm

27

itself rotates clockwise. At this time, the cam nose portion

22

c

of rockable cam

22

is forcibly pulled down via the link rod

29

by the second portion

27

b

of rocker arm

27

. In this manner, as a whole, the right-hand linkage section comprised of rocker arm

27

, link rod

29

, and rockable cam

22

shifts clockwise (note a relatively greater angle between the neutral axis of control arm

62

indicated by the one-dotted line in

FIGS. 15 and 16

and the neutral axis of rocker arm

27

indicated by the one-dotted line in

FIGS. 15 and 16

as compared to an angle between the neutral axis of control arm

62

indicated by the one-dotted line in

FIGS. 13 and 14

and the neutral axis of rocker arm

27

indicated by the one-dotted line in FIGS.

13

and

14

). As a result, the abutted area (sliding-contact area) between the upper surface of intake-valve lifter

16

and the lower cam surface of the associated rockable cam

22

and ranging from the base circle portion

24

a

via the intermediate cam surface portion

24

b

to the top circle portion slightly shifts towards the cam surface portion

24

b

(see FIGS.

15

and

16

). In otherwords, regarding the abutted area (sliding-contact area), the ratio of base circle portion

24

a

to cam surface portion

24

b

tends to decrease during high-speed high-load operation. With the rocker arm

27

forcibly shifted clockwise, during the high-speed high-load operation, when second eccentric cam

26

revolves by rotation of intake camshaft

14

and thus the second end

27

b

of rocker arm

27

is pushed down via the link rod

29

, as shown in

FIG. 16

, a valve lift becomes a comparatively high valve lift L

2

. Therefore, during the high-speed high-load operation, as can be seen from the high valve lift characteristic indicated by the one-dotted line in

FIG. 6

, the valve lift of intake valve

12

can be controlled to a comparatively high valve lift. Additionally, the intake valve open timing (IVO) tends to be advanced, while the intake valve closure timing (IVC) tends to be retarded. This enhances a charging efficiency of intake air entering the engine cylinders, and thus increases engine power, during high-speed high-load conditions.

As discussed above, in the valve operating device of the fourth embodiment shown in

FIGS. 13-16

, the intake valve open timing (IVO) and intake valve closure timing (IVC), and the intake valve lift characteristic (working angle as well as intake valve lift) can be variably controlled. In addition to the above, second eccentric cam

26

is formed as an integral section of intake camshaft

14

, whereas rockable cam

22

and rocker arm

27

are oscillatingly provided on intake camshaft

14

. As a result of this, it is possible to effectively reduce the height of the valve operating device having the variable valve timing and valve lift characteristic control system, in other words, the overall height of cylinder head

11

. Hitherto, an additional cam shaft peculiar to second eccentric cam

26

was required, but in the device of the fourth embodiment the second eccentric cam can be driven by means of intake camshaft

14

generally used as one of engine parts. In addition, rockable cam

22

and rocker arm

27

are both oscillatingly supported on the common intake camshaft. Therefore, it is possible to reduce the height of the valve train installed above cylinder head

11

, thus ensuring easier mounting of the valve operating device on internal combustion engines (including various types of engines, such as V-type engines and in-line engines). The engine-hood height can also be reduced. Furthermore, it is possible to reduce the number of component parts of the valve operating device as much as possible. As a consequence, it is possible to enhance a manufacturing efficiency and to reduce total production costs. Additionally, as can be appreciated from the layout of rocker arm

27

mounted on intake camshaft

14

via second eccentric cam

26

(see FIG.

13

), it is possible to arrange control shaft

61

within a space defined between intake and exhaust camshafts

14

and

15

and to locate control shaft

61

closer to the exhaust camshaft, utilizing the exhaust-cam bearings

25

. Thus, it is possible to set the installation height of control shaft

61

to a properly low level, and as a result it is possible to adequately reduce the height of the valve train installed above cylinder head

11

. Also, in the device of the fourth embodiment, control shaft

61

, third eccentric cam (control cam)

70

, and control arm

62

are laid out within a dead space (a space) defined between intake and exhaust camshafts

14

and

15

, and thus it is possible to efficiently use the dead space. Within the dead space, there are less obstacles that prevent rotary motion (pivotal motion) of each of control shaft

61

, third eccentric cam (control cam)

70

, and control arm

62

. This ensures the enhanced design flexibility (increased operating angle of each of the control shaft

61

, control cam

70

, and control arm

62

, increased eccentricity a between the two axes P

1

and P

2

, and the like). The increased eccentricity a acts to increase or amplify the oscillating motion of rocker arm

27

. The increased oscillating motion of rocker arm

27

contributes to a remarkable change in valve lift characteristic. In the same manner as the device of first embodiment, in the device of the fourth embodiment, the construction of each of intake camshaft

14

, exhaust camshaft

15

, and their bearing sections (namely, rockable cam brackets

23

and intake-cam bearing caps

40

) is not changed. This eliminates the necessity of a design change in cylinder head

11

. Thus, the device of the embodiment can be easily mounted on the existing internal combustion engine, thus effectively suppressing an increase in manufacturing costs. As set forth above, according to the linkage arrangement of the fourth embodiment, owing to the increased eccentricity α, it is possible to provide the increased oscillation angle of rockable cam

22

and thus to effectively increase the ramp section of rockable cam

22

. Such an increased ramp section effectively lessens the collision velocity between valve lifter

16

and rockable cam

22

, thereby reducing noise and vibrations. Also, rockable cam

22

is oscillated or swung rightwards and leftwards forcibly by rocker arm

27

through link rod

29

. There is no necessity of a return spring used in the conventional device. Thus, it is possible to prevent an increase in friction created by a reaction force of the return spring.

Referring now to

FIGS. 17 and 18

, there is shown the valve operating device of the fifth embodiment. The device of the fifth embodiment of

FIGS. 17 and 18

is different from that of the fourth embodiment of

FIGS. 13-16

, in that the previously-noted control cam (third eccentric cam)

70

is eliminated and in lieu thereof the large-diameter portion

62

a

of control arm

62

(formed as a comparatively short straight link), is directly fixed to the control shaft

61

(formed as a cylindrical hollow shaft), while the small-diameter portion

62

b

of control arm

62

is mechanically linked via a straight link arm

63

to the first end

27

a

of rocker arm

27

. In case of the linkage layout of

FIGS. 17 and 18

, the amount of rotary motion of the small-diameter portion

62

b

of control arm

62

tends to increase, and thus the operating angle of control shaft

61

can be set to a relatively small operating angle. This contributes to the reduced load of actuator

34

. Thus, it is possible to downsize the actuator, thereby reducing the total size of the device, and consequently reducing power consumption.

Referring now to

FIGS. 19 and 20

, there is shown the valve operating device of the sixth embodiment. The device of the sixth embodiment of

FIGS. 19 and 20

is different from the fourth (

FIGS. 13-16

) and fifth (

FIGS. 17-18

) embodiments, in that the control cam (third eccentric cam)

70

and link arm

63

are eliminated and in lieu thereof a cam slot (or a slit)

64

is provided at the first end of rocker arm

27

so that the cam slot

64

is partly formed along the rocker-arm neutral axis indicated by the one-dotted line in

FIG. 19

, and a sliding pin

65

is attached to the small-diameter portion of control arm

62

so that the sliding pin

65

is slidably engaged with the cam slot

64

. The root portion of sliding pin

65

is rotatably supported in a pin holding hole

66

bored in the small-diameter portion of control arm

62

. Sliding pin

65

has width across flats (two parallel flat faces) formed at its tip end. The two parallel flat faces formed at the tip of sliding pin

65

are in sliding-contact with the respective opposing inner peripheral wall surfaces of cam slot

64

. Actually, a snap ring (not shown) is fitted to the root portion of sliding pin

65

, to prevent the sliding pin from falling out of the pin holding hole

66

. According to the device of the sixth embodiment shown in

FIGS. 19 and 20

, the two parallel flat-faced portion of the tip end of sliding pin

65

variably controls the center of oscillating motion of rocker arm

27

, while sliding in the cam slot

64

owing to rotation of control shaft

61

. The linkage arrangement (the sliding-pin-slot engagement) shown in

FIGS. 19 and 20

enhances the accuracy of variable control for the center of oscillating motion of rocker arm

27

. Due to the pin-slot engagement, the number of parts of the device can be decreased, and the linkage structure can be simplified, thereby reducing production costs.

In the fourth, fifth and sixth embodiments described previously, although the improved valve operating device is applied to an internal combustion engine with one intake valve

12

and one exhaust valve

13

for each engine cylinder, it will be appreciated that the device of the fourth, fifth and sixth embodiments can be applied to an internal combustion engine with a pair of intake valves (

12

,

12

) and a pair of exhaust valves (

13

,

13

) for each engine cylinder. In this case, the cam profiles of two adjacent rockable cams (

22

,

22

) for the intake valve pair (

12

,

12

) may be the same. Alternatively, a cam profile of one of the rockable cams (

22

,

22

) may be different from a cam profile of the other, so as to provide a valve-lift difference between the two intake valves (

12

,

12

) for each engine cylinder. Due to the valve-lift difference, swirl flow in each engine cylinder can be effectively strengthened, thereby improving the combustibility of the engine. In the fourth, fifth and sixth embodiments discussed above, as can be appreciated from the characteristic curves shown in

FIG. 6

, in order to mainly vary valve timing and valve lift characteristic of intake valve

12

, the first camshaft to which at least second eccentric cams

26

, rocker arms

27

and rockable cams

22

are attached is set or used as an intake camshaft

14

, whereas the second camshaft to which at least drive cams

18

are attached is set or used as an exhaust camshaft

15

. Alternatively, in order to mainly vary valve timing and valve lift characteristics of exhaust valves (

13

,

13

), the second camshaft to which at least drive cams

18

are attached may be set or used as an intake camshaft

14

, whereas the first camshaft to which at least second eccentric cams

26

, rocker arms

27

and rockable cams

22

are attached may be set or used as an exhaust camshaft

15

.

The entire contents of Japanese Patent Application Nos. P2000-286341 (filed Sep. 21, 2000) and P2000-293573 (filed Sep. 27, 2000) are incorporated herein by reference.

While the foregoing is a description of the preferred embodiments carried out the invention, it will be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the scope or spirit of this invention as defined by the following claims.

Number	Date	Country	Kind
2000-286341	Sep 2000	JP
2000-293573	Sep 2000	JP

Number	Name	Date	Kind
4397270	Aoyama	Aug 1983	A
6311659	Pierik	Nov 2001	B1

Valve operating device for internal combustion engines

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Term Extension

Abstract

Description

Claims

Priority Claims (2)

US Referenced Citations (2)

Foreign Referenced Citations (1)