Valve-operating mechanism in engine

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a valve-operating mechanism in an engine, including a cam operated in association with a crankshaft, cam followers turnably carried on an engine body, so that their tip ends are in slidable contact with the cam, rocker arms integrally connected to the cam followers and turnably carried on the engine body coaxially with the cam followers so that their tip ends are connected to valves mounted in the engine body, and valve springs for biasing the valves in closing directions, whereby the rocker arms are operated in association with the urging of the cam followers by the cam to open the valves against biasing forces of the valve springs.

2. Description of the Related Art

A conventional valve-operating mechanism in an engine has been already proposed by the assignee of the present application (see Japanese Patent Application No. 2000-276459). In this mechanism, a cam of a relatively large diameter is disposed on one side of an engine body, and a rocker arm and a rocker shaft of a relatively small diameter are disposed immediately above the engine body, whereby the upward overhanging of the valve-operating mechanism can be suppressed to reduce the entire height of the engine, and in turn to provide the compactness of the engine.

In this valve-operating mechanism, however, the following has been found by the present inventors: the cam follower and the rocker arm are obliged to be disposed at a distance along a turning shaft for the structural reason; when the cam followers ride on a base-circle portion of the cam, and in response to the release of urging forces on the cam followers, the valves are closed by biasing forces of the valve springs, the rocker arms are then pushed upwards by the valves and are swung upwards, to apply a couple of forces over the axes of the cam followers and the rocker shafts; such couple of forces cause turning support portions of the cam followers and the rocker arms to chatter, resulting in the generation of an abnormal sound or a striking wear.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a valve-operating mechanism in an engine, wherein the couple of forces generated over the axis of the cam follower and the rocker arm due to the biasing force of the valve spring are offset in a valve-closing process, whereby the abnormal sound or the striking wear can be prevented from generating at the turning support portions of the cam follower and the rocker arm.

To achieve the above object, according to the present invention, there is provided a valve-operating mechanism in an engine, comprising a cam operated in association with a crankshaft, cam followers turnably carried on an engine body so that their tip ends are in slidable contact with the cam, rocker arms integrally connected to the cam followers and turnably carried on the engine body coaxially with the cam followers so that their tip ends are connected to valves mounted in the engine body, and valve springs for biasing the valves in closing directions, whereby the rocker arms are operated in association with the urging of the cam followers by the cam to open the valves against biasing forces of the valve springs, wherein auxiliary springs are connected to the cam followers for biasing and turning the cam followers in the same directions as directions in which the valve springs bias and turn the rocker arms through the valves in a process of closing the valves.

With this feature, a couple of forces in one direction are applied over the axis of the cam follower and the rocker arm by a biasing/turning force of the auxiliary spring on the cam follower, and offset or weakened a couple of forces applied over the axis of the cam follower and the rocker arm by biasing and turning the rocker arm through the valve by the valve spring in the valve-closing process. Thus, it is possible to avoid the chattering of the turning support portions of the cam followers and the rocker arms to prevent the generation of an abnormal sound or a striking wear.

The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a vertical sectional side view of an engine including a valve-operating mechanism according to a first embodiment of the present invention.

FIG. 2

is an exploded view of an essential portion of FIG.

1

.

FIG. 3

is a sectional view taken along a line

3

—

3

in FIG.

1

.

FIG. 4

is a sectional view taken along a line

4

—

4

in FIG.

3

.

FIG. 5

is a sectional view taken along a line

5

—

5

in FIG.

4

.

FIG. 6

is a sectional view taken along a line

6

—

6

in FIG.

4

.

FIGS. 7A and 7B

are views similar to

FIG. 5

, but showing a process for assembling the valve-operating mechanism.

FIGS. 8A and 8B

are views similar to

FIG. 6

, but also showing the process for assembling the valve-operating mechanism.

FIG. 9

is a front view of a driven pulley/cam assembly in the valve-operating mechanism.

FIG. 10

is a sectional view taken along a line

10

—

10

in FIG.

9

.

FIG. 11

is a sectional view taken along a line

11

—

11

in FIG.

10

.

FIG. 12

is a sectional view taken along a line

12

—

12

in FIG.

4

.

FIG. 13

is a plan view of a valve-operating mechanism according to a second embodiment of the present invention.

FIG. 14

is a sectional view taken along a line

14

—

14

in FIG.

13

.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described by way of preferred embodiments with reference to the accompanying drawings.

A first embodiment of the present invention will be first described below. Referring to

FIGS. 1

to

4

and

6

, an engine body

1

of an engine E comprises a crankcase

2

having a crank chamber

2

a

, a cylinder block

3

having a single cylinder bore

3

a

, and a cylinder head

4

having a combustion chamber

5

and intake and exhaust ports

6

and

7

which open into the combustion chamber

5

.

A crankshaft

10

accommodated in the crank chamber

2

a

is carried on laterally opposite sidewalls of the crankcase

2

with bearings

11

and

11

′ interposed therebetween.

An oil tank

12

is integrally connected to the left sidewall of the crankcase

2

adjacent the outer side thereof, and one end of the crankshaft

10

is oil-tightly passed through the oil tank

12

.

A belt guide tube

13

flat in section is integrally connected to a ceiling wall of the oil tank

12

to extend vertically through the ceiling wall. A lower end of the belt guide tube

13

extends to the vicinity of the crankshaft

10

within the oil tank

12

. An upper end of the belt guide tube

13

is integrally connected to the cylinder head

4

so that it shares a partition wall

14

jointly with the cylinder head

4

. A series of annular seal beads

15

are formed at peripheral edges of the cylinder head

4

and the upper end of the belt guide tube

13

, and the partition wall

14

protrudes upwards from the seal beads

15

.

An annular seal groove

16

is defined in a lower end face of a head cover

8

coupled to an upper end of the cylinder head

4

to correspond to the seal beads

15

. A linear seal groove

17

is defined in an inner surface of the head cover

8

to permit the communication between opposite sides of the annular seal groove

16

. An annular packing

18

is mounted in the annular seal groove

16

, and a linear packing

19

is formed integrally with the annular packing

18

is mounted in the linear seal groove

17

. The head cover

8

is coupled to the cylinder head

4

by a bolt so that the seal beads

15

are brought into pressure contact with the annular packing

18

, and the partition wall

14

is brought into pressure contact with the linear packing

19

.

A first valve-operating chamber

21

a

is defined by the belt guide tube

13

and one of halves of the head cover

8

. A second valve-operating chamber

21

b

is defined by the cylinder head

4

and the other half of the head cover

8

. The valve-operating chambers

21

a

and

21

b

are partitioned from each other by the partition wall

14

.

An intake valve

22

i

and an exhaust valve

22

e

for opening and closing the intake port

6

and the exhaust port

7

respectively are disposed in the cylinder head

4

in parallel to the cylinder bore

3

a.

A valve-operating mechanism

23

for opening and closing the intake valve

22

i

and the exhaust valve

22

e

according to the present invention will be described below.

Referring to

FIGS. 1

to

6

, the valve-operating mechanism

23

comprises a timing transmitting device

23

a

disposed to extend from the inside of the oil tank

12

into the first valve-operating chamber

21

a

, and a cam device

23

b

disposed to extend from the first valve-operating chamber

21

a

into the second valve-operating chamber

21

b.

The timing transmitting device

23

a

comprises a driving pulley

24

fixedly mounted on the crankshaft

10

within the oil tank

12

, a driven pulley

25

rotatably supported at an upper portion of the belt guide tube

13

, and a timing belt

26

reeved between the driving and driven pulleys

24

and

25

. A hub

30

and a cam

29

are integrally formed on the driven pulley

25

, thereby constituting a driven pulley/cam assembly

50

. In this way, the cam

29

is disposed along with the driven pulley

25

on one side of the cylinder head

4

. The driving and driven pulleys

24

and

25

are toothed so that the driving pulley

24

drives the driven pulley

25

at a reduction ratio of ½ through the belt

26

.

A support wall

27

is integrally formed on an outer sidewall of the belt guide tube

13

, so that it rises inside the annular seal beads

15

to abut against or extend to near the inner surface of the head cover

8

. A support shaft

39

is rotatably supported at its opposite ends in a through-bore

28

a

provided in the support wall

27

and a bottomed bore

28

b

provided in the partition wall

14

. The hub

30

is rotatably supported at an intermediate portion of the support shaft

39

. The support shaft

39

, before mounted to the head cover

8

, is inserted from the through-bore

28

a

, through a shaft bore

135

of the driven pulley

25

and the cam

29

, into the bottomed bore

28

b

. After the insertion of the support shaft

39

, when the head cover

8

is coupled to the cylinder head

4

and the belt guide tube

13

, the inner surface of the head cover

8

is opposed to an outer end of the support shaft

39

, to prevent the slipping-out of the support shaft

39

.

A pair of bearing bosses

31

i

and

31

e

are integrally formed on the cylinder head

4

to protrude from the partition wall

14

in parallel to the support shaft

39

toward the second valve-operating chamber

21

b

. The cam device

23

b

comprises the cam

29

, an intake rocker shaft

33

i

and an exhaust rocker shaft

33

e

rotatably supported in bearing bores

32

i

and

32

e

in the bearing bosses

31

i

and

31

e

, respectively, an intake cam follower

34

i

and an exhaust cam follower

34

e

each press-fitted to one end of each of the rocker shafts

33

i

and

33

e

to extend toward the cam

29

, an intake rocker arm

35

i

and an exhaust rocker arm

35

e

press-fitted to the other ends of the intake and exhaust rocker shafts

33

i

and

33

e

in the second valve-operating chamber

21

b

to extend toward the intake valve

22

i

and the exhaust valve

22

e

, and an intake valve spring

38

i

and an exhaust valve spring

38

e

mounted on the intake valve

22

i

and the exhaust valve

22

e

for biasing these valve

22

i

and

22

e

in closing directions. The intake cam follower

34

i

and the exhaust cam follower

34

e

are disposed so that slipper faces

36

,

36

formed on upper surfaces of their tip ends are in sliding contact with the lower surface of the cam

29

. The intake rocker arm

35

i

and the exhaust rocker arm

35

e

are disposed so that adjusting bolts

37

,

37

threadedly mounted in their tip ends are in abutment against upper ends of the intake valve

22

i

and the exhaust valve

22

e.

The support shaft

39

and the intake and exhaust rocker shafts

33

i

and

33

e

are disposed above the annular seal beads

15

at the cylinder head

4

and the upper end of the belt guide tube

13

. Therefore, in a state in which the head cover

8

is removed, the assembling and disassembling of the support shaft

39

and the intake and exhaust rocker shafts

33

i

and

33

e

can be conducted above the seal bead

15

without being obstructed by the seal beads

15

in any way, leading to excellent assemblability and maintenance.

Referring to

FIGS. 5

to

8

, abutment faces

40

i

and

40

e

are formed respectively on backs of the intake cam follower

34

i

and the exhaust cam follower

34

e

opposite from the slipper faces

36

,

36

, in parallel to axes of the rocker shafts

33

i

and

33

e

. Abutment faces

41

i

and

41

e

are formed respectively on backs of the intake rocker arm

35

i

and the exhaust rocker arm

35

e

opposite from protruding portions of the adjusting bolts

37

,

37

. On the other hand, reference faces

42

i

and

42

e

as well as reference faces

43

i

and

43

e

are formed on the cylinder head

4

so that the reference faces

42

i

and

42

e

face the abutment faces

40

i

and

40

e

when the intake cam follower

34

i

and the intake rocker arm

35

i

are turned outwards and sideways of the cylinder head, and so that the reference faces

43

i

and

43

e

confront the abutment faces

41

i

and

41

e

, when the exhaust cam follower

34

e

and the exhaust rocker arm

35

e

are turned outwards and sideways of the cylinder head.

If phases of the intake cam follower

34

i

and the intake rocker arm

35

i

are appropriate relative to each other around the intake rocker shaft

33

i

, the abutment faces

40

i

and

41

i

and the reference faces

42

i

and

43

i

abut against each other simultaneously. If the phases of the exhaust cam follower

34

e

and the exhaust rocker arm

35

e

are likewise appropriate relative to each other around the exhaust rocker shaft

33

e,

the abutment faces

40

e

and

41

e

and the reference faces

42

e

and

43

e

abut against each other simultaneously. All the reference faces

42

i

,

42

e

,

43

i

and

43

e

are disposed at the same height, so that they can be worked simultaneously.

To assemble the intake cam follower

34

i

and the intake rocker arm

35

i

to the intake rocker shaft

33

i

, for example, the intake cam follower

34

i

is first press-fitted and secured to one ends of the rocker shafts

33

i

and

33

e

, and the rocker shaft

33

i

and

33

e

are inserted into the bearing bores

32

i

and

32

e

. Then, as shown in

FIGS. 7B and 8B

, the intake rocker arm

35

i

is turned outwards and sideways from the cylinder head

4

, and the abutment faces

40

i

and

40

e

are put into abutment against the corresponding reference faces

42

i

and

42

e

. In this state, if the intake rocker arm

35

i

is press-fitted and secured to the other ends of the rocker shafts

33

i

and

33

e

while putting its abutment faces

41

i

and

41

e

into abutment against the corresponding reference faces

43

i

and

43

e

, the phases of the intake cam follower

34

i

and the intake rocker arm

35

i

can be appropriately established relative to each other around the intake rocker shaft

33

i

. Of course, the phases of the exhaust cam follower

34

e

and the exhaust rocker arm

35

e

can be appropriately established relative to each other around the exhaust rocker shaft

33

e

in the same manner. The same effect is also obtained in the case where the rocker arms

35

i

and

35

e

are first press-fitted to the rocker shafts

33

i

and

33

e

. After the assembling, the cam followers

34

i

and

34

e

and the rocker arms

35

i

and

35

e

are turned to service positions at a central portion of the cylinder head

4

, as shown in

FIGS. 7A and 8A

.

Referring to

FIGS. 4 and 5

, auxiliary springs

45

i

and

45

e

are mounted under compression respectively between the cylinder head

4

and the intake cam follower

34

i

and between the cylinder head

4

and the exhaust cam follower

34

e

, and adapted to bias and turn the intake and exhaust cam followers

34

i

and

34

e

in the same directions as directions in which the intake and exhaust valve springs

38

i

and

38

e

bias and turn the intake and exhaust rocker arms

35

i

and

35

e

through the intake and exhaust valves

22

i

and

22

e

in the process of closing the intake and exhaust valves

22

i

and

22

e

. Each of the auxiliary springs

45

i

and

45

e

is a torsion spring including a coil portion

46

fitted over an outer periphery of corresponding one of the rocker shafts

33

i

and

33

e

, a stationary end

47

is locked to a locking portion

49

of the cylinder head

4

, and a movable end

48

connected to corresponding one of the cam followers

34

i

and

34

e

to bias the cam follower

34

i

,

34

e

upwards.

Referring to

FIGS. 9

to

11

, the cam

29

is formed of a sintered alloy integrally along with the cylindrical hub

30

rotatably carried on the support shaft

39

. In this case, the hub

30

is disposed to protrude one end face of the cam

29

, and has a chamfer

30

a

provided on an outer peripheral surface of its tip end. The cam

29

is provided at its one end face with a recess

51

surrounding the hub

30

, and a radial projection

52

protruding on a bottom surface of the recess

51

. The recess

51

is of a shape substantially similar to an outer peripheral surface of the cam

29

, so that the wall thickness of the cam

29

around the recess

51

is set substantially constant.

The driven pulley

25

made of a synthetic resin is mold-coupled to the hub

30

and the cam

29

. In this process, the outer peripheral surface of the hub

30

as well as the chamfer

30

a

are wrapped by the material of the driven pulley, i.e., the synthetic resin, and the recess

51

in the cam

29

is filled with the synthetic resin. In this manner, the driven pulley/cam assembly

50

is constituted.

Referring again to

FIGS. 1 and 2

, a specified amount of a lubricating oil O injected through an oil supply port

12

a

is stored in the oil tank

12

. A pair of oil slingers

55

a

and

55

b

are secured by press-fitting or the like to the crankshaft

10

in the oil tank

12

, and arranged axially on opposite sides of the driving pulley

24

. The oil slingers

55

a

and

55

b

extend in radially opposite directions, and are bent so that their tip ends are axially going away from each other. When the oil slingers

55

a

and

55

b

are rotated by the crankshaft

10

, at least one of the oil slingers

55

a

and

55

b

agitates and scatters the oil O stored in the oil tank

12

to produce an oil mist, even in any operative position of the engine E. At this time, the produced oil mist enters the first valve-operating chamber

21

a

to lubricate the timing transmitting device

23

a

, and, on the other hand, is circulated to the crank chamber

2

a

, the second valve-operating chamber

21

b

and the oil tank

12

to lubricate various portions within the crank chamber

2

a

and the cam device

23

b.

The operation of this embodiment will be described below.

When the driving pulley

24

rotated along with the crankshaft

10

during rotation of the crankshaft

10

drives the driven pulley

25

and the cam

29

through the belt

26

, the cam

29

properly swings the intake and exhaust cam followers

34

i

and

34

e

. The swinging movements are transmitted through the corresponding rocker shafts

33

i

and

33

e

to the intake and exhaust rocker arms

35

i

and

35

e

, to swing the intake and exhaust rocker arms

35

i

and

35

e

. Therefore, the intake and exhaust valves

22

i

and

22

e

can be opened and closed properly by cooperation with the intake and exhaust springs

38

i

and

38

e.

During this process, the cam

29

and the hub

30

are lubricated by the oil mist produced within the oil tank

12

. However, the cam

29

and the hub

30

are made of a sintered alloy having an infinite number of pores, and hence the oil is retained in the pores. Thus, portions of the cam

29

and the hub

30

in sliding contact with the cam followers

34

i

and

34

e

and portions of the cam

29

and the hub

30

rotated and slid on the support shaft

39

are effectively lubricated so that the wear thereof is prevented. This can contribute to an enhancement in durability of such portions.

Moreover, the hub

30

is rotatably carried on the support shaft

39

, and the support shaft

39

is also rotatably carried on the opposite sidewalls of the first valve-operating chamber

21

a

. Therefore, during rotation of the driven pulley

25

and the cam

29

, the support shaft

39

is also rotated, dragged by the friction, and hence a difference between rotational speeds of the hub

30

and the support shaft

39

is decreased. This can provide a reduction in wear of the rotated and slid portions, which can contribute to a further enhancement in durability of the rotated and slid portions.

In addition, the driven pulley

25

driven by the driving pulley

24

through the belt

26

is made of the synthetic resin, and hence is relatively lightweight in spite of its relatively large diameter, which can contribute to a reduction in weight of the driven pulley/cam assembly

50

and in its turn to a reduction in weight of the engine E.

Moreover, because the driven pulley

25

is mold-coupled to the cam

29

and the hub

30

, the driven pulley/cam assembly

50

can be constructed without a special member, leading to a further reduction in weight of the assembly

50

.

Further, when the driven pulley

25

is mold-coupled to the cam

29

and the hub

30

, the outer peripheral surface of the hub

30

as well as the chamfer

30

a

are wrapped by the material of the driven pulley

25

, i.e., the synthetic resin, and the recess

51

in the cam

29

is filled with the synthetic resin, and hence coupling forces between the driven pulley

25

and the hub

30

as well as the cam

29

in rotational and axial directions can be increased.

Particularly, because the recess

51

is of the shape substantially similar to the outer peripheral surface of the cam

29

, the coupling force between the driven pulley

25

and the cam

29

particularly in the rotational direction can be effectively increased. Moreover, because the wall thickness of the cam

29

around the recess

51

is substantially constant, the thermal deformation of the cam

29

during sintering thereof can be suppressed to contribute to an enhancement in accuracy of a cam profile.

On the other hand, when the intake cam follower

34

i

and the exhaust cam follower

34

e

respectively ride on a base-circle portion of the cam

29

, and in response to the release of downward urging forces on the cam followers, the intake valve

22

i

and the exhaust valve

22

e

are closed by biasing forces of the intake valve spring

38

i

and the exhaust valve spring

38

e

, the rocker arms

35

i

and

35

e

are then pushed upwards by the intake valve

22

i

and the exhaust valve

22

e

and are swung about their axes, to act on one end of each of the rocker shafts

33

i

and

33

e

so as to push them up and to apply a couple of forces Ma over the rocker shafts

33

i

and

33

e

, as shown in FIG.

12

.

However, the cam followers

34

i

and

34

e

push the other ends of the rocker shafts

33

i

and

33

e

upwards while being biased and turned upwards by the auxiliary springs

45

i

and

45

e

. Thus, a couple of forces Mb (see

FIG. 12

) applied over the rocker shafts

33

i

and

33

e

offset or weaken the couple of forces Ma. As a result, the rocker shafts

33

i

and

33

e

are entirely urged against upper surfaces of the bearing bores

32

i

and

32

e

, and hence it is possible to avoid the chattering due to the couple of forces and to prevent generation of an abnormal sound and a striking wear.

The cam

29

of the relatively large diameter is disposed along with the driven pulley

25

on one side of the cylinder head

4

, and only the intake and exhaust rocker arms

35

i

and

35

e

and the intake and exhaust rocker shafts

33

i

and

33

e

of the relatively small diameter are disposed immediately above the cylinder head

4

. Therefore, the valve-operating mechanism

23

cannot overhang largely above the cylinder head

4

, and hence it is possible to provide a reduction in entire height of the engine E, and in turn provide the compactness of the engine E.

The cam followers

34

i

and

34

e

and the rocker arms

35

i

and

35

e

secured to the opposite ends of the rocker shafts

33

i

and

33

e

have their abutment faces

40

i

and

40

e

put into abutment against the reference faces

42

i

,

42

e

,

43

i

and

43

e

of the cylinder head

4

during assembling of the cam followers

34

i

and

34

e

and the rocker arms

35

i

and

35

e

, whereby the phases of the intake cam follower

34

i

and the intake rocker arm

35

i

around the rocker shafts

33

i

and

33

e

are appropriately established. Therefore, the intake and exhaust valves

22

i

and

22

e

can be opened and closed with a good timing by rotation of the cam

29

.

Particularly, during assembling, for example, each of the cam followers

34

i

and

34

e

is press-fitted to one end of each of the rocker shafts

33

i

and

33

e

, and the rocker shafts

33

i

and

33

e

are fitted into the bearing bores

32

i

and

32

e

in the bearing bosses

31

i

and

31

e

and thereafter, the rocker arms

35

i

and

35

e

are press-fitted to the other ends of the rocker shafts

33

i

and

33

e

. At this time, the abutment faces

41

i

and

41

e

of the rocker arms

35

i

and

35

e

are press-fitted to the corresponding reference faces

43

i

and

43

e

, while being put into abutment against the corresponding reference faces

43

i

and

43

e

. Therefore, the appropriate phases of the cam followers

34

i

and

34

e

and the rocker arms

35

i

and

35

e

can be confirmed simultaneously with the coupling of the cam followers

34

i

and

34

e

and the rocker arms

35

i

and

35

e

to the rocker shafts

33

i

and

33

e

, whereby both the quality and the productivity of them can be satisfied.

A second embodiment of the present invention will now be described with reference to

FIGS. 13 and 14

.

In the second embodiment, an intake cam follower

34

i

and an intake rocker arm

35

i

are integrally formed of a steel plate, and an exhaust cam follower

34

e

and an exhaust rocker arm

35

e

are also integrally formed of a steel plate. The intake cam follower

34

i

and the intake rocker arm

35

i

, as well as the exhaust cam follower

34

e

and the exhaust rocker arm

35

e

, respectively, have a pair of support walls

60

and

60

′ opposed to each other. A bridge portion

61

connects the support walls

60

and

60

′ to each other. The support walls

60

and

60

′ are disposed to sandwich corresponding bearing bosses

31

i

or

31

e

of the cylinder head

4

, and turnably carried at opposite ends of the rocker shafts

33

i

and

33

e

supported on the bearing bosses

31

i

and

31

e

. Also in the present embodiment, auxiliary springs

45

i

and

45

e

are mounted under compression respectively between the intake and exhaust cam followers

34

i

and

34

e

and between the bearing bosses

31

i

and

31

e,

for biasing and turning the intake and exhaust cam followers

34

i

and

34

e

in the same directions as directions in which the intake and exhaust valve springs

38

i

and

38

e

bias and turn the intake and exhaust rocker arms

35

i

and

35

e

in the process of closing the intake and exhaust valves

22

i

and

22

e

. Each of the auxiliary springs

45

i

and

45

e

is a torsion coil spring including a coil portion

46

fitted over an outer periphery of corresponding one of the rocker shafts

33

i

and

33

e.

In the process of closing the intake and exhaust valve

22

i

and

22

e

, the couple of forces Ma produced on the rocker shafts

33

i

and

33

e

due to the biasing forces of the intake and exhaust valve springs

38

i

and

38

e

are offset or weakened by the couple of forces Mb applied to the rocker shafts

33

i

and

33

e

by the biasing forces of the auxiliary springs

45

i

and

45

e.

The other constructions are basically the same as those in the first embodiment, and hence portions or components corresponding to those in the first embodiment are denoted by the same reference numerals in

FIGS. 13 and 14

, and the descriptions thereof are omitted.

Although the embodiments of the present invention have been described in detail, it will be understood that the present invention is not limited to the above-described embodiments, and various modifications in design may be made without departing from the spirit and scope of the invention defined in the claims.

Number	Name	Date	Kind
5080054	Nakamura	Jan 1992	A
6349688	Gracyalny et al.	Feb 2002	B1

Valve-operating mechanism in engine

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CPC

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Priority Claims (1)

US Referenced Citations (2)

Foreign Referenced Citations (1)