Engine with valve resting function

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an engine with a valve resting function, which is intended to rest at least one of a plurality of intake valves in a specific operational region.

2. Description of Background Art

The engine of this type has been known, for example, from Japanese Patent Publication No. Sho 62-56327.

The above-described related art engine is configured to rest one of a pair of intake valves in a specific operational region for allowing lean combustion by forming a swirl in a combustion chamber, thereby reducing fuel consumption. However, in a state in which one of the intake valves is rested, fuel remains in an intake passage corresponding to the rested intake valves, and consequently, when the operational state in which one of the intake valves is rested is switched into the operational state in which all of the intake valves are opened/closed, the remaining fuel flows in the combustion chamber to temporarily make dense the concentration of the fuel in the combustion chamber. This may reduce the engine output and increase the occurrence of unburned hydrocarbon.

SUMMARY AND OBJECTS OF THE INVENTION

In view of the foregoing, the present invention has been made, and an object of the present invention is to provide an engine with a valve resting function, which is capable of preventing the flow-in of the remaining fuel in a combustion chamber when the rested intake valve is switched to be opened/closed, thereby preventing the reduction in engine output and preventing the increase in unburned hydrocarbon.

To achieve the above object, according to the present invention there is provided an engine with a valve resting function, including a plurality of intake valve ports provided in a cylinder head in such a manner as to face to a combustion chamber. A plurality of intake passages are provided in the cylinder head in such a manner as to be individually connected to the intake valve ports; and a valve system is provided for driving a plurality of intake valves capable of individually opening/closing the intake valve ports, the valve system is configured such that it can rest at least one of the intake valves in a specific operational region. A communication passage for communicating the intake passage corresponding to the intake valve opened/closed even in the specific operational region to the intake passage corresponding to the intake valve rested in the specific operational region is provided in the cylinder head.

With this configuration, when at least one of a plurality of the intake valves is rested in a specific operational region, an air-fuel mixture flows from the intake passage corresponding to the rested intake valve to the intake passage corresponding to the opened/closed intake valve via the communication passage, with a result that it is possible to prevent the fuel from remaining in the intake passage corresponding to the rested intake valve. Accordingly, even if the operational state in which at least one of the intake valves is rested is switched into the operational state in which all of the intake valves are opened/closed, the remaining fuel does not flow in the combustion chamber, to prevent the mixing ratio of the air-fuel mixture flowing in the combustion chamber from being made unstable, thereby preventing the reduction in engine output and preventing the increase in occurrence of unburned hydrocarbon as much as possible.

According to the present invention an intake system including a carburetor common to the intake passages is connected to the intake passages. With this configuration, even if the intake system connected to a plurality of intake passages is configured to have the single carburetor, it is possible to avoid the inconvenience that the mixing ratio is made unstable when the operational state in which part of the intake valves is rested is switched into the operational state in which all of the intake valves are opened/closed. That is to say, it is possible to prevent the fuel from remaining in the intake passage corresponding to the intake valve which is rested due to the configuration of the present invention and hence to prevent the mixing ratio from being made unstable even by using the intake system with a simple structure in which the air-fuel mixture is formed by the carburetor common to respective intake passages.

According to the present invention the communication passage is formed as a hollow portion upon formation of the cylinder head by casting. With this configuration, it is possible to form the communication passage simultaneously with the formation of the cylinder head by casting, and hence to reduce the number of the steps of forming the cylinder head.

According to the present invention the communication passage is formed by cutting, from the combustion chamber side. With this configuration, the communication passage can be simply formed in the cylinder head without use of any special means.

According to the present invention, the communication passage is formed in such a manner as to be tilted toward the combustion chamber in the direction from the intake passage corresponding to the intake valve opened/closed even in the specific operational region to the intake passage corresponding to the intake valve rested in the specific operational region. With this configuration, the opening end of the communication passage to the intake passage corresponding to the intake valve rested in the specific operational region can be disposed at a position being as close to the combustion chamber as possible, so that when the intake valve is rested in the specific operational region, the intake passage corresponding to the rested intake valve can be communicated to the intake passage corresponding to the opened/closed intake valve at the position being as close to the combustion chamber as possible. This makes it possible to make the amount of the remaining fuel in the resting state of the intake valve as small as possible.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1

is a side view of a motorcycle according to a first embodiment;

FIG. 2

is a plan view seen from an arrow

2

of

FIG. 1

;

FIG. 3

is a partial vertical sectional view, taken on line

3

—

3

of

FIG. 5

, of an upper portion of an engine;

FIG. 4

is a transverse sectional view, taken on line

4

—

4

of

FIG. 5

, of the upper portion of the engine;

FIG. 5

is a bottom view, seen from arrows

5

—

5

of

FIG. 3

, of a cylinder head;

FIG. 6

is a partial transverse sectional view of the cylinder head near an intake port;

FIG. 7

is an enlarged vertical sectional view of a valve resting mechanism;

FIG. 8

is a perspective view seen from above a pin holder;

FIG. 9

is a perspective view seen from below the pin holder;

FIG. 10

is a perspective view of a slide pin;

FIG. 11

is a characteristic diagram showing the valve opening lift amounts of intake valves and exhaust valves;

FIG. 12

is a side view, seen from an arrow

12

of

FIG. 5

, of the cylinder head;

FIG. 13

is a sectional view showing a configuration of a hydraulic control valve;

FIG. 14

is a vertical sectional view showing a hydraulic passage of the cylinder block and a crank case; and

FIG. 15

is a sectional view, similar to

FIG. 6

, showing a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to

FIGS. 1 and 2

, a body frame

21

of this motorcycle includes a pair of right and left main frames

22

each being formed into an approximately U-shape opened upwardly. A head pipe

23

is provided at front ends of the main frames

22

. A connection frame

24

, that is formed into an approximately U-shape opened downwardly, is provided for connecting rear portions of the main frames

22

to each other. A seat stay

25

is connected to rear ends of the main frames

22

and extends rearwardly, obliquely upwardly therefrom. A front fork

26

for supporting a front wheel W

F

, is steerably supported by the head pipe

23

. A steering handle

27

is operatively connected to the front fork

26

. A rear fork

28

for supporting a rear wheel W

R

, is vertically swingably supported by a rear portion of one of the main frames

22

. A pair of cushion units

29

are provided between the seat stay

25

and the rear wheel W

R

.

An engine E is supported by the main frames

22

and the connecting frame

24

. Power from the engine E is transmitted to the rear wheel W

R

, via a transmission assembled in the engine E and a chain transmission

30

.

A fuel tank

31

is mounted on the right and left main frames

22

and the connection frame

24

in such a manner as to be positioned over the engine E. A tandem seat

32

is mounted on the seat stay

25

, and a radiator

33

is disposed in front of the engine E.

Referring additionally to

FIGS. 3 and 4

, the engine E is a multi-cylinder for example, a four-cylinder/four-cycle engine. A plurality (for example, four) of cylinder bores

37

are formed in a cylinder block

36

of the engine E in such a manner as to be arranged along the width direction of the body frame

21

. The cylinder bores

37

are tilted upwardly, forwardly in the running direction of the motorcycle. To be more specific, cylinder liners

38

for forming the cylinder bores

37

are fixed in the cylinder block

36

in such a manner as to be spaced from each other at intervals along the width direction of the body frame

21

. Each cylinder liner

38

is partially inserted in an upper crank case

39

connected to a lower portion of the cylinder block

36

.

A cylinder block

40

is connected to an upper portion of the cylinder block

36

. Recesses

41

that individually correspond to the cylinder bores

37

are provided in a connection plane of the cylinder head

40

to the cylinder block

36

. Combustion chambers

43

including the recesses

41

are formed between the cylinder head

40

and top portions of pistons

42

slidably fitted in the cylinder bores

37

.

Referring additionally to

FIG. 5

, a plurality (for example, a pair) of first and second intake valve ports

44

1

and

44

2

opened to the combustion chamber

43

, and a plurality of (for example, a pair) of first and second exhaust valve ports

45

1

and

45

2

opened to the combustion chamber

43

are provided in the cylinder head

40

. The first intake valve port

44

1

and the first exhaust valve port

45

1

are substantially symmetrically disposed with respect to the center of the combustion chamber

43

, and the second intake valve port

44

2

and the second exhaust valve port

45

2

are substantially symmetrically disposed with respect to the center of the combustion chamber

43

.

Referring additionally to

FIG. 6

, a first intake passage

46

1

connected to the first intake valve port

44

1

a second intake passage

46

2

connected to the second intake valve port

44

2

and an intake port

47

commonly connected to the first and second intake passages

46

1

and

46

2

and opened to one side surface

40

a

of the cylinder head

40

are provided in the cylinder head

40

. The one side surface

40

a

of the cylinder head

40

to which each intake port

47

is opened is disposed on the back side along the running direction of the motorcycle.

A first exhaust passage

48

1

connected to the first exhaust valve port

45

1

a second exhaust passage

48

2

connected to the second exhaust valve port

45

2

and an intake port

49

commonly connected to the first and second exhaust passages

48

1

, and

48

2

and opened to the other side surface

40

b

of the cylinder head

40

are provided in the cylinder head

40

for each combustion chamber

43

. The other side surface

40

b

of the cylinder head

40

to which each exhaust port

49

is opened is disposed on the front side along the running direction of the motorcycle.

An intake system

51

including a carburetor

50

common to the intake ports

47

is connected to the intake ports

47

. An exhaust system

53

including an exhaust muffler

52

is connected to the exhaust ports

49

. The exhaust muffler

52

is disposed on the right side of the rear wheel W

R

in a state being directed forwardly in the running direction of the motorcycle.

Referring to

FIGS. 3 and 4

, the communication and cutoff between the first intake valve port

44

1

and the first intake passage

46

1

is switched from each other by a first intake valve

56

1

and the communication and cutoff between the second intake valve port

44

2

and the second intake passage

46

2

is switched from each other by a second intake valve

56

2

. Meanwhile, the communication and cutoff between the first exhaust valve port

45

1

and the first exhaust passage

48

1

is switched from each other by a first exhaust valve

57

1

as an engine valve, and the communication and cutoff between the second exhaust valve port

45

2

and the second exhaust passage

48

2

is switched from each other by a second exhaust valve

57

2

as an engine valve.

Each of the first and second intake valves

56

1

and

56

2

includes a valve body

58

capable of closing the associated one of the intake valve ports

44

1

and

44

2

and a valve stem

59

having the base end integrally connected to the valve body

58

. Each of the first and second exhaust valves

57

1

and

57

2

includes a valve body

60

capable of closing the associated one of the exhaust valve ports

45

1

and

45

2

and a valve stem

61

having the base end integrally connected to the valve body

60

.

The valve stem

59

of each of the first and second intake valves

56

1

and

56

2

is slidably fitted in a guide cylinder

62

provided in the cylinder head

40

. The valve stem

61

of each of the first and second exhaust valves

57

1

and

57

2

is slidably fitted in a guide cylinder

63

provided in the cylinder head

40

.

A retainer

64

is fixed via split cotters (not shown) to an intermediate point of a portion, projecting upwardly from the guide cylinder

62

, of the valve stem

59

of the first intake valve

56

1

. A coil valve spring

65

1

is provided between the retainer

64

and the cylinder head

40

, whereby the first intake valve

56

1

is biased in the direction of closing the first intake port

44

1

by the valve spring

65

1

. Meanwhile, a retainer

64

is fixed via split cotters (not shown) to the leading end of a portion, projecting upwardly from the guide cylinder

62

, of the valve stem

59

of the second intake valve

56

2

. A coil valve spring

65

2

is provided between the retainer

64

and the cylinder head

40

, whereby the second intake valve

56

2

is biased in the direction of closing the second intake port

44

2

by the valve spring

65

2

.

A retainer

66

is fixed via split cotters (not shown) to an intermediate point of a portion, projecting upwardly from the guide cylinder

63

, of the valve stem

61

of the first exhaust valve

57

1

. A coil valve spring

67

1

is provided between the retainer

66

and the cylinder head

40

, whereby the first exhaust valve

57

1

is biased in the direction of closing the first exhaust port

45

1

by the valve spring

67

1

. Meanwhile, a retainer

66

is fixed via split cotters (not shown) to the leading end of a portion, projecting upwardly from the guide cylinder

63

, of the valve stem

61

of the second exhaust valve

57

2

. A coil valve spring

67

2

is provided between the retainer

66

and the cylinder head

40

, whereby the second exhaust valve

57

2

is biased in the direction of closing the second exhaust port

45

2

by the valve spring

67

2

.

An intake side valve system

68

I for driving the first and second intake valves

56

1

and

56

2

of the combustion chambers

43

includes a cam shaft

70

, bottomed cylindrical valve lifters

71

1

and bottomed cylindrical valve lifters

71

2

. The cam shaft

70

has first intake side valve system cams

69

1

corresponding to the first intake valves

56

1

and the second intake side valve system cams

69

2

corresponding to the second intake valves

56

2

. The valve lifters

71

1

are supported by the cylinder head

40

in such a manner as to be slidably driven by the first intake side valve system cams

69

1

. The valve lifters

71

2

are supported by the cylinder head

40

in such a manner as to be slidably driven by the second intake side valve system cams

69

2

.

The cam shaft

70

has an axial line perpendicular to the extensions of the axial lines of the valve stems

59

of the first and second intake valves

56

1

and

56

2

and is rotatably supported between the cylinder head

40

and a holder

55

connected to the cylinder head

40

. The valve lifters

71

1

are slidably fitted in the cylinder head

40

in such a manner as to be slidably movable in the same axial direction as the axial lines of the valve stems

59

of the first intake valves

56

1

. The outer surface of the closed end of each valve lifter

71

1

is in slide-contact with the associated one of the first intake side valve system cams

69

1

. The valve lifters

71

2

are slidably fitted in the cylinder head

40

in such a manner as to be slidably movable in the same axial direction as the axial lines of the valve stems

59

of the second intake valves

56

2

. The outer surface of the closed end of each valve lifter

71

2

is in slide-contact with the associated one of the second intake side valve system cams

69

2

.

The leading end of the valve stem

59

of the second intake valve

56

2

is in contact with the inner surface of the closed end of the valve lifter

71

2

via a shim

72

. The second intake valve

56

2

is, during the operation of the engine E, usually operated to be opened/closed by the second intake side valve system cam

69

2

. On the other hand, a valve resting mechanism

73

I is provided between the valve stem

59

of the first intake valve

56

1

and the valve lifter

71

1

. The valve resting mechanism

73

I can switch an acting state and a non-acting state of a pressing force applied from the valve lifter

71

1

to the first intake valve

56

1

in the valve opening direction. To be more specific, in a specific operational region, typically, a low speed operational region of the engine E, the valve resting mechanism

73

I creates the non-acting state of the pressing force, thereby turning the first intake valve

56

1

into the resting state irrespective of the sliding motion of the valve lifter

71

1

.

Referring to

FIG. 7

, the valve resting mechanism

73

includes a pin holder

74

slidably fitted in the valve lifter

71

1

. A slide pin

76

is slidably fitted in the pin holder

74

in such a manner as to form a hydraulic chamber

75

between the inner surface of the valve lifter

71

1

and the slide pin

76

. A return spring

77

is provided between the slide pin

76

and the pin holder

74

, for biasing the slide pin

76

in the direction of reducing the volume of the hydraulic chamber

75

. A stopper pin

78

, functioning as a rotation stopping means, is provided between the pin holder

74

and the slide pin

76

, for stopping the rotation of the slide pin

76

around its axial line.

Referring additionally to

FIGS. 8 and 9

, the pin holder

74

includes a ring portion

74

a

slidably fitted in the valve lifter

71

1

and a bridging portion

74

b

, integrated with the ring portion

74

a

, for connecting the opposed inner peripheral portions of the ring portion

74

a

along one diameter line of the ring portion

74

a.

The inner periphery of the ring portion

74

a

and both the side surface portions of the bridging portion

74

b

are partially cut off to reduce the weight. The pin holder

74

is made from a steel or an aluminum alloy by lost-wax casting or forging, or made from a synthetic resin. The outer peripheral surface of the metal made pin holder

74

, that is, the outer peripheral surface of the metal made ring portion

74

a

and the inner peripheral surface of the valve lifter

71

, are subjected to carbonization.

An annular groove

79

is formed in the outer peripheral portion of the pin holder

74

, that is, the outer peripheral portion of the ring portion

74

a.

A bottomed sliding hole

80

is provided in the bridging portion

74

b

of the pin holder

74

. The sliding hole

80

has an axial line along one diameter line of the ring portion

74

a,

that is, an axial line perpendicular to the axial line of the valve lifter

71

1

. One end of the sliding hole

80

is opened to the annular groove

79

and the other end thereof is closed. An insertion hole

81

for allowing the leading end of the valve stem

59

of the first intake valve

56

1

to pass therethrough is formed at the center of a lower portion of the bridging portion

74

b

in such a manner as to be opened to the sliding hole

80

. An extension hole

82

for containing the leading end of the valve stem

59

of the first intake valve

56

1

is provided at the center of an upper portion of the bridging portion

74

b

in such a manner as to be coaxial with the insertion hole

81

with the sliding hole

80

put between the insertion hole

81

and the extension hole

82

.

A containing cylinder portion

83

coaxial with the axial line of the extension hole

82

is integrally formed on a portion, facing to the closed end of the valve lifter

71

1

of the bridging portion

74

b

of the pin holder

74

. A disk-like shim

84

for blocking the end of the extension hole

82

on the closed side of the valve lifter

71

1

is partially fitted in the containing cylinder portion

83

. A projecting portion

85

to be in contact with the shim

84

is integrally formed at a central portion on the inner surface of the closed end of the valve lifter

71

1

.

The slide pin

76

is slidably fitted in the sliding hole

80

of the pin holder

74

. If the pin holder

74

is made from a synthetic resin, only the slide-contact portion of the pin holder

74

with the slide pin

76

may be made from a metal.

The hydraulic chamber

75

communicated to the annular groove

79

is formed between one end of the slide pin

76

and the inner surface of the valve lifter

71

1

. The return spring

77

is contained in a spring chamber

86

formed between the other end of the slide pin

76

and the closed end of the sliding hole

80

.

Referring additionally to

FIG. 10

, a containing hole

87

, which can be coaxially communicated to the insertion hole

81

and the extension hole

82

and also can contain the leading end of the valve stem

59

, is provided at the intermediate portion in the axial direction of the slide pin

76

. The end of the containing hole

87

on the insertion hole

81

side is opened to a flat contact plane

88

formed on the outer surface of the lower portion of the slide pin

76

in such a manner as to face to the insertion hole

82

. To be more specific, the contact plane

88

is relatively longer along the axial line direction of the slide pin

76

, and the containing hole

87

is opened in the contact plane

88

at a position offset to the spring chamber

86

side.

Such a slide pin

76

is slid in the axial direction in such a manner that hydraulic pressure of the hydraulic chamber

75

acting to one end of the slide pin

76

is balanced against a spring force of the return spring

77

acting to the other end side of the slide pin

76

. In the non-acting state in which the hydraulic pressure of the hydraulic chamber

75

is low, the slide pin

76

is moved to the right in

FIG. 7

for containing the leading end of the valve stem

59

inserted in the insertion hole

81

in the containing hole

87

and the extension hole

82

. In the acting state in which the hydraulic pressure of the hydraulic chamber

75

is high, the slide pin

76

is moved leftward in

FIG. 7

for offsetting the containing hole

87

from the axial lines of the insertion hole

81

and the extension hole

82

thereby bringing the leading end of the valve stem

59

into contact with the contact plane

88

.

When the slide pin

76

is moved to the position at which the containing hole

87

is coaxial with the insertion hole

81

and the extension hole

82

, the first intake valve

56

, remains at rest. To be more specific, at this time, the pin holder

74

and the slide pin

76

&are moved on the first intake valve

56

1

side along with the sliding motion of the valve lifter

71

1

by the pressing force acting from the first intake side valve system cam

69

1

. However, only the leading end of the valve stem

59

is contained in the containing hole

87

and the extension hole

82

, and the pressing force is not applied from the valve lifter

71

1

and the pin holder

74

to the first intake valve

56

1

in the valve opening direction. When the slide pin

76

is moved to the position at which the leading end of the valve stem

59

is in contact with the contact plane

88

, the first intake valve

56

1

is operated to be opened/closed. To be more specific, at this time, the pin holder

74

and the slide pin

76

are moved toward the first intake valve

56

1

side along with the sliding motion of the valve lifter

71

1

by the pressing force acting from the first intake side valve system cam

69

1

, so that the pressing force is applied to the first intake valve

56

1

in the valve opening direction. In this way, the first intake valve

56

1

is operated to be opened/closed in accordance with the rotation of the first intake side valve system cam

69

1

.

If the slide pin

76

is rotated around its axial line in the pin holder

74

, the axial line of the containing hole

87

is offset from those of the insertion hole

81

and the extension hole

82

so that the leading end of the valve stem

59

cannot be brought into contact with the contact plane

88

. To cope with such an inconvenience, the stopper pin

78

is provided for stopping the rotation of the slide pin

76

around its axial line.

The stopper pin

78

is mounted in mounting holes

89

and

90

which are coaxially provided in the bridging portion

74

b

of the pin holder

74

in such a manner as to put part of the sliding hole

80

on its one end side therebetween. The stopper pin

78

passes through a slit

91

which is provided on the one end side of the slide pin

76

in such a manner as to be opened to the hydraulic chamber

75

side. To be more specific, the stopper pin

78

is mounted in the pin holder

74

in a state in which it passes through the slide pin

76

while permitting the axial movement of the slide pin

76

. Accordingly, the stopper pin

78

is brought into contact with the inner closed end of the slit

91

, so that the movement end of the slide pin

76

toward the hydraulic chamber

75

side is restricted.

A coil spring

92

is provided for biasing the pin holder

74

on the side on which the shim

84

mounted on the pin holder

74

is in contact with the projecting portion

85

provided at the central portion on the inner surface of the closed end of the valve lifter

71

1

. To be more specific, the coil spring

92

is disposed between the pin holder

74

and the cylinder head

40

in such a manner as to surround the valve stem

59

at a position where the outer periphery of the coil spring

92

is not brought into contact with the inner surface of the valve lifter

71

1

. A pair of projections

93

and

94

are integrally provided on the bridging portion

74

b

of the pin holder

74

. The projections

93

and

94

function to position the end of the coil spring

92

in the direction perpendicular to the axial line of the valve stem

59

.

Each of the projections

93

and

94

, formed into a circular-arc centered at the axial line of the valve stem

59

, projects from the pin holder

74

by an amount less than the diameter of the coil spring

92

.

The projection

93

has a stepped portion

95

which is brought into contact with the end portion, on the first intake valve

56

1

side, of the stopper pin

78

, thereby preventing the movement of the stopper pin

78

on the first intake valve

56

1

side.

To prevent a change in pressure in the spring chamber

86

by the axial movement of the slide pin

76

, the slide pin

76

has a communication hole

96

through which the spring chamber

86

is communicated to the containing hole

87

. Meanwhile, to prevent a change in pressure of a space between the pin holder

74

and the valve lifter

71

1

due to temperature change, the pin holder

74

has a communication hole

97

through which the space is communicated to the spring chamber

86

.

The cylinder head

40

has a supporting hole

98

for slidably supporting the valve lifter

71

1

and an annular recess

99

is provided in the supporting hole

98

in such a manner as to surround the valve lifter

71

1

. The valve lifter

71

1

has a communication hole

100

through which the annular recess

99

is communicated to the annular groove

79

formed in the pin holder

74

irrespective of the sliding motion of the valve lifter

71

1

in the supporting hole

98

, and also has a release hole

101

. The release hole

101

is provided in the valve lifter

71

1

at such a position as to allow, when the valve lifter

71

1

is moved at the uppermost position in

FIG. 71

1

communication between the annular recess

99

to the inside of the valve lifter

71

1

through the lower portion of the release hole

101

positioned under the pin holder

74

but to block, as the valve lifter

71

1

is moved downwardly from the uppermost position in

FIG. 7

, the communication between the annular recess

88

and the inside of the valve lifter

71

1

. Lubricating oil is jetted in the valve lifter

71

1

through the release hole

101

.

The cylinder head

40

also has working oil feed passages

103

communicated to the annular recesses

99

of the combustion chambers

43

.

An exhaust side valve system

68

E for driving the first and second exhaust valves

57

1

and

57

2

of the combustion chambers

43

includes a cam shaft

106

, bottomed cylindrical valve lifters

107

1

and bottomed cylindrical valve lifters

107

2

. The can shaft

106

has first exhaust side valve system cams

105

1

corresponding to the first exhaust valves

57

1

and the second exhaust side valve system cams

105

2

corresponding to the second exhaust valves

57

2

. The valve lifters

107

1

are supported by the cylinder head

40

in such a manner as to be slidably driven by the first exhaust side valve system cams

105

1

. The valve lifters

107

2

are supported by the cylinder head

40

in such a manner as to be slidably driven by the second exhaust side valve system cams

105

2

.

The cam shaft

106

has an axial line perpendicular to the extensions of the axial lines of the valve stems

61

of the first and second exhaust valves

57

1

and

57

2

and is rotatably supported between the cylinder head

40

and the holder

55

connected to the cylinder head

40

like the cam shaft

70

of the intake side valve system

68

I. The valve lifters

107

1

are slidably fitted in the cylinder head

40

in such a manner as to be slidably movable in the same axial direction as the axial lines of the valve stems

61

of the first exhaust valves

57

1

. The outer surface of the closed end of each valve lifter

107

1

is in slide-contact with the associated one of the first exhaust side valve system cams

105

1

. The valve lifters

107

2

are slidably fitted in the cylinder head

40

in such a manner as to be slidably movable in the same axial direction as the axial lines of the valve stems

61

of the second exhaust valves

57

2

. The outer surface of the closed end of each valve lifter

107

2

is in slide-contact with the associated one of the second exhaust side valve system cams

105

2

.

The leading end of the valve stem

61

of the second exhaust valve

57

2

is in contact with the inner surface of the closed end of the valve lifter

107

2

via a shim

108

. The second exhaust valve

57

2

is, during operation of the engine E, usually operated to be opened/closed by the second exhaust side valve system cam

105

2

. On the other hand, a valve resting mechanism

73

E is provided between the valve stem

61

of the first exhaust valve

57

1

and the valve lifter

107

1

. The valve resting mechanism

73

E can switch an acting state and a non-acting state of a pressing force applied from the valve lifter

107

1

to the first exhaust valve

57

1

in the valve opening direction. To be more specific, in a specific operational region, typically, a low speed operational region of the engine E, the valve resting mechanism

73

E creates the non-acting state of the pressing force, thereby turning the first exhaust valve

57

1

into the resting state irrespective of the sliding motion of the valve lifter

107

1

. The valve resting mechanism

73

E has the same configuration as that of the valve resting mechanism

73

I of the intake side valve system

68

I.

In the non-acting state of the valve resting mechanism

73

I and

73

E, that is, in the state in which the first intake valve

56

1

and the first exhaust valve

57

1

are operated to be opened/closed, as shown by broken curves in

FIG. 11

, the first intake side valve system cam

69

1

and the first exhaust side valve system can

105

1

are operated in such a manner that the total opening angle is made relatively large and the angle at which the opening state of the first intake valve

56

1

is overlapped to that of the first exhaust valve

57

1

is made relatively large. However, as shown by solid curves in

FIG. 11

, the second intake side valve system cam

69

2

and the second exhaust side valve system cam

105

2

are operated in such a manner that the total opening angle is made relatively small and the angle at which the opening state of the second intake valve

56

2

is overlapped to that of the second exhaust valve

57

2

is made relatively small.

In accordance with such intake side and exhaust side valve systems

68

I and

68

E, in a low speed operational region as a specific operational region of the engine E, the first intake valve

56

1

and the first exhaust valve

57

1

are rested and only the second intake valve

56

2

and the second exhaust valve

57

2

are operated to be opened/closed. At this time, since the angle at which the opening state of the second intake valve

56

2

is overlapped to that of the second exhaust valve

57

2

is relatively small, the rear compression ratio in the combustion chamber

43

can be improved, and since swirl occurs by flow-in of the fuel-air mixture in the combustion chamber

43

only through the second intake passage

46

2

the fuel consumption can be reduced and the output torque is increased. In a high speed operational region, since the valve resting mechanisms

73

I and

73

E are turned into the acting state, not only the second intake valves

56

2

and the second exhaust valves

57

2

are usually operated to be opened/closed but also the first intake valve

56

1

and the first exhaust valve

57

1

are operated to be opened/closed, with a result that the output in the high speed operational region can be enhanced. Accordingly, in a wide operational region from a low speed operational region to a high speed operational region, it is possible to enhance the output and to reduce the fuel consumption.

As described above, in a low speed operational region of the engine E, the first intake valve

56

, is rested, and in such a state, fuel remains in the intake passage corresponding to the intake valve

56

1

, that is, the first intake passage

46

1

. When the operation for the low speed operational region is switched to the operation for a high speed operational region in which the intake valves

56

1

and

56

2

are operated to be opened/closed, the fuel thus remaining in the first intake passage

46

1

flows in the combustion chamber

43

, and thereby the concentration of the fuel in the combustion chamber

43

becomes temporarily dense. This may reduce the output of the engine E and cause an occurrence of unburned hydrocarbon.

To cope with such an inconvenience, as shown in

FIG. 6

, a communication passage

109

, which communicates the second intake passage

46

2

corresponding to the second intake valve

56

2

usually opened/closed upon operation of the engine E to the first intake passage

46

1

corresponding to the first intake valve

56

1

rested in a specific operation region upon the operation of the engine E, is formed in the cylinder head

40

. In the resting state of the first intake valve

56

1

the fuel-air mixture in the first intake passage

46

1

flows in the second intake passage

46

2

through the communication passage

109

as shown by an arrow

110

in FIG.

6

.

The communication passage

109

is formed in the cylinder head

40

obtained by casting, by cutting from the combustion chamber

43

side, in such a manner as to be tilted toward the combustion chamber

43

in the direction from the second intake passage

46

2

to the first intake passage

46

1

. The opening end of the communication passage

109

for communicating the first intake passage

46

1

to the second intake passage

46

2

is disposed at a position being as close to the combustion chamber

43

as possible.

Referring to

FIG. 5

, a containing hole

112

is provided in the cylinder head

40

at a position between the adjacent two, on the central side along the arrangement direction, of the four cylinder bores

37

. The cylinder head

40

is partitioned by the containing hole

112

into first and second head portions

40

1

and

40

2

.

A means such as a chain drive means for driving the cam shafts

70

and

106

of the intake side and exhaust side valve systems

68

I and

68

E is contained in the containing hole

112

.

Referring additionally to

FIG. 12

, a hydraulic control valve

113

is mounted on the one side surface

40

a

of the cylinder head

40

to which the intake ports

47

are opened at a position between a pair of the intake ports

47

disposed on the first head

40

1

side. The hydraulic control valve

113

is used for controlling a hydraulic pressure of working oil fed to the valve resting mechanism

431

and

43

E of the intake side and exhaust side valve systems

68

I and

68

E.

Referring to

FIG. 13

, the hydraulic control valve

113

is mounted on the one side surface

40

a

of the cylinder head

40

for switching the on/off of the communication between the opening end of a working oil intake passage

114

to the one side surface

40

a

of the cylinder head

40

and the opening end of a first working oil discharge passage

115

, to the one side surface

40

a

of the cylinder head

40

. The hydraulic control valve

113

includes an inlet

116

communicated to the working oil intake passage

114

, an outlet

117

communicated to the first working oil discharge passage

115

1

and a spool valve body

119

slidably fitted in a housing

118

mounted on the side surface

40

a

of the cylinder head

40

.

The housing

118

has a cylinder hole

121

with its upper end blocked by a cap

120

. The spool valve body

119

is slidably fitted in the cylinder hole

121

in such a manner as to form a hydraulic chamber

122

between the cap

120

and the spool valve body

119

. A spring chamber

123

is formed between the lower portion of the housing

118

and the spool valve body

119

. A spring

124

for biasing the spool valve body

119

upwardly, that is, in the closing direction is contained in the spring chamber

123

. The spool valve body

119

has an annular recess

125

for allowing communication between the inlet

116

and the outlet

117

. When the spool valve body

119

is moved upwardly as shown in

FIG. 13

, it blocks the communication between the inlet

116

and the outlet

117

.

In a state in which the housing

118

is mounted on the one side surface

40

a

of the cylinder head

40

, an oil filter

126

is held between the inlet

116

and the working oil intake passage

114

. The housing

118

also has an orifice hole

127

for communicating the inlet

116

to the outlet

117

. Accordingly, even in a state in which the spool valve body

119

is located at the closing position, the inlet

116

is communicated to the outlet

117

through the orifice hole

127

, so that a hydraulic pressure restricted by the orifice hole

127

is fed from the outlet

117

into the first working oil discharge passage

115

1

.

The housing

118

also has a bypass port

128

which is communicated to the outlet

117

through the annular recess

125

only in the state in which the spool valve body

119

is located at the closing position. The bypass port

128

is communicated to the upper inside portion of the cylinder head

40

.

The housing

118

also has a passage

129

usually communicated to the inlet

116

. The passage

129

is connected via a solenoid valve

130

to a connection hole

131

which is formed in the cap

120

in such a manner as to be communicated to the hydraulic chamber

122

. When the solenoid valve

130

is opened, a hydraulic pressure is fed into the hydraulic chamber

122

, and the spool valve body

119

is driven to be opened by the hydraulic pressure thus introduced into the hydraulic chamber

122

.

The housing

118

also has a leak jet

132

communicated to the hydraulic chamber

122

. The leak jet

132

is also communicated to the upper inside portion of the cylinder head

40

. When the solenoid valve

130

is closed, the hydraulic pressure remaining in the hydraulic chamber

122

is released through the leak jet

132

.

Referring to

FIG. 14

, a lower crank case

136

constituting part of a mission case

135

is connected to a lower portion of the upper crank case

39

. A crank shaft

137

is rotatably supported between both the crank cases

39

and

136

.

An oil pan

138

is connected to a lower portion of the lower crank case

136

. An oil pump

139

for pumping up working oil remaining in the oil pan

138

is contained in the mission case

135

. A projecting portion

135

a,

which projects upwardly from the upper crank case

39

, is provided on the mission case

135

. A starter motor

140

having a rotational axial line parallel to the crank shaft

137

is mounted on the projecting portion

135

a

at a position over the upper crank case

39

.

The working oil intake passage

114

for introducing working oil from the oil pump

135

to the hydraulic control valve

113

is provided in the cylinder head

40

, the cylinder block

36

, the upper crank case

39

, and the lower crank case

136

.

The working oil intake passage

114

includes a connection port

114

a

connected to the inlet

116

of the hydraulic control valve

113

and opened to the one side surface

40

a

of the cylinder head

40

. A first passage

114

b

is provided in the cylinder head

40

in such a manner as to be connected to the connection port

114

a

and extends in a straight line along the one side surface

40

a.

A second passage

114

c

is provided in the cylinder block

36

in such a manner as to be coaxially connected to the first passage

114

b.

A third passage

114

d

is provided in the lower crank case

39

in such a manner as to be coaxially connected to the second passage

114

c

and to extend in straight line. A fourth passage

114

e

is provided in the lower crank case

136

in such a manner as to be connected to the lower end of the third passage

114

d

and to extend in the vertical direction. A fifth passage

114

f

is provided in the lower crank case

136

in such a manner as to be connected to the lower end of the fourth passage

114

e

and to extend substantially in the horizontal direction. A sixth passage

114

g

is provided in the lower crank case

136

in such a manner as to extend substantially in parallel to the fifth passage

114

f.

A filter

141

interposed between the fifth and sixth passages

114

f

and

114

g

is mounted in the lower crank case

136

, and the sixth passage

114

g

is connected to a discharge port of the oil pump

139

.

The working oil intake passage

114

for introducing working oil from the oil pump

139

to the hydraulic control valve

113

is provided in the cylinder head

40

, the cylinder block

36

, the upper crank case

39

, and the lower crank case

136

.

A water jacket

145

is provided in the cylinder block

36

and the cylinder head

40

. The first passage

114

b

and the second passage

114

c,

corresponding to the cylinder block

36

and the cylinder head

40

, of the working oil intake passage

114

are disposed outside the waterjacket

145

.

Referring to

FIGS. 5 and 12

, the first head portion

40

1

of the cylinder head

40

has a first working oil discharge passage

115

1

for feeding working oil to the valve resting mechanisms

73

I and

73

E for each of the combustion chambers

43

disposed on the first head portion

40

1

side, and the second head portion

40

2

has a second working oil discharge passage

115

2

for feeding working oil to the valve resting mechanisms

73

I and

73

E for each of the combustion chambers

43

on the second head portion

40

2

side. The working oil feed passages

103

provided in the cylinder head

40

for the valve resting mechanisms

73

I and

73

E (see

FIG. 7

) are branched from the first and second working oil discharge passages

115

1

and

115

2

.

A mounting seat

146

is mounted on the one side surface

40

a

of the cylinder head

40

in such a manner as to cross between the first and second head portions

40

1

and

40

2

. The first and second working oil discharge passages

115

1

and

115

2

are provided in the cylinder head

40

in such a manner that one end thereof is commonly opened to the mounting seat

146

and the other end thereof is closed at a position near the containing hole

112

.

A cover

147

is fastened to the mounting seat

146

, and the working oil discharge passage

115

1

and

115

2

are communicated to each other via the cover

147

.

Next, the function of the first embodiment will be described. The communication passage

109

for communicating the second intake passage

46

2

corresponding to the second intake valve

56

2

opened/closed even in a specific operational region to the first intake passage

46

1

corresponding to the first intake valve

56

1

rested in the specific operational region is provided in the cylinder head

40

. Accordingly, when the first intake valve

56

1

is rested, a fuel-air mixture flows from the first intake passage

46

1

corresponding to the rested first intake valve

56

1

to the second intake passage

46

2

corresponding to the opened/closed second intake valve

56

2

via the communication passage

109

, so that it is possible to prevent the fuel from remaining in the first intake passage

46

1

in the resting state of the first intake valve

56

1

as much as possible. As a result, when the operation for the above specific operational region is switched to the operation for an operational region in which the intake valves

56

1

and

56

2

are both opened/closed, it is possible to eliminate the inconvenience that the remaining fuel flows in the combustion chamber

43

. This makes it possible to prevent the mixing ratio of the fuel-air mixture flows in the combustion chamber

43

from being made unstable, and hence to prevent the reduction in engine output and the occurrence of unburned hydrocarbon as much as possible.

Since the phenomenon in which the fuel remains in the first intake passage

46

1

in the resting state of the first intake valve

56

1

can be prevented as described above, even if the intake system

51

is simply configured to have the carburetor

50

common to the intake passages

46

1

and

46

2

it is possible to avoid the inconvenience that the mixing ratio of the fuel-air mixture flowing in the combustion chamber

43

is made unstable when the operation for the specific operational region in which the first intake valve

56

1

that is in a rest position is switched to the operation for the operational region in which the intake valves

56

1

and

56

2

are both opened/closed.

The communication passage

109

can be simply formed in the cylinder head

40

, having been obtained by casting, by cutting from the combustion chamber

43

side. Since the communication passage

109

is tilted toward the combustion chamber

43

in the direction from the second intake passage

46

2

to the first intake passage

46

1

the opening end of the communication passage

109

for communicating the first intake passage

46

1

that is rested in a specific operational region to the second intake passage

46

2

can be disposed at a position being as close to the combustion chamber

43

as possible. As a result, when the first intake valve

56

1

is rested in the specific operational region, the first intake passage

46

2

corresponding to the rested first intake valve

56

1

can be communicated to the second intake passage

46

2

at a position being as close to the combustion chamber

43

as possible, so that the remaining amount of fuel in the resting state of the first intake valve

56

1

can be made as small as possible.

The hydraulic control valve

113

for controlling the hydraulic pressure of working oil to the hydraulic valve resting mechanism

73

I and

73

E for resting the first intake valve

56

1

and the first exhaust valve

57

1

in a specific operational region are mounted on the side surface

40

a

of the cylinder head

40

to which a plurality of the intake ports

47

provided in the cylinder head

40

are opened. To be more specific, the hydraulic control valve

113

is mounted on the side surface

40

a

of the cylinder head

40

in the direction perpendicular to the arrangement direction of the cylinder bores

37

, that is, in the forward or rearward direction (in the rearward direction in this embodiment) of the body frame

21

. As a result, it is possible to avoid an inconvenience that the length of the multi-cylinder engine E extending along the arrangement direction of the cylinder bores

37

becomes large due to the mounting of the hydraulic control valve

113

to the cylinder head

40

. That is to say, in the motorcycle in which the engine E is mounted on the body frame

21

with the arrangement direction of the cylinder bores

37

set in the width direction of the body frame

21

, the length of the multi-cylinder engine E extending along the width direction of the body frame

21

can be made as small as possible.

Since the hydraulic control valve

113

is mounted on the side surface

40

a

of the cylinder head

40

at a position between the adjacent two of the intake ports

47

by making effective use of a space therebetween, it is possible to decrease the length of the multi-cylinder engine E along the width direction of the body frame

21

.

Since the working oil intake passage

114

for introducing working oil from the oil pump

139

to the hydraulic control valve

113

is provided in the cylinder head

40

, the cylinder block

36

, and the crank cases

39

and

136

, it is possible to eliminate the necessity of the provision of an additional pipe line for introducing the working oil from the oil pump

139

to the hydraulic control valve

113

, and hence to simplify the appearance of the multi-cylinder engine E.

Since the water jacket

145

is provided in the cylinder block

36

and the cylinder head

40

and the two parts, corresponding to the cylinder block

36

and the cylinder head

40

, of the working oil intake passage

114

are disposed outside the water jacket

145

, it is possible to effectively cool the working oil flowing in the working oil intake passage

114

.

The working oil intake passage

114

has at least the first passage

114

b

provided in the cylinder head

40

in such a manner as to extend in straight line along the side surface

40

a

between the one side surface

40

a

of the cylinder head

40

and the water jacket

145

. A second passage

114

c

is provided in the cylinder block

36

in such a manner as to be coaxial with the first passage

114

b.

A third passage

114

d

is provided in the upper crank case

39

in such a manner as to be coaxial with the second passage

114

c

and extend in straight line therefrom. As a result, it is possible to make the working oil passage from the oil pump

139

to the hydraulic control valve

113

as short as possible, and hence to make a loss in hydraulic pressure in the working oil intake passage

114

as small as possible.

The containing hole

112

, which contains the means for driving the cam shafts

70

and

106

, is provided in the cylinder head

40

at a position between the adjacent two, on the central side along the arrangement direction, of the four cylinder bores

37

. The cylinder head

40

is partitioned by the containing hole

112

into the first and second head portions

40

1

and

40

2

. As a result, it is possible to desirably keep the balance between the cylinder heads

40

along the arrangement direction of the cylinder bores

37

, and thereby the balance of the multi-cylinder engine E as a whole.

The first working oil discharge passage

115

1

for supplying working oil to the valve resting mechanism

73

I and

73

E for each of the combustion chambers

43

on the first head portion

40

1

side is provided in the first head portion

40

1

in such a manner as to be connected to the hydraulic control valve

113

mounted on the side surface

40

a

of the cylinder head

40

between a pair of the intake ports

47

disposed on the first head portion

40

1

side. The second working oil discharge passage

115

2

is provided for supplying working oil to the valve resting mechanism

73

I and

73

E for each of the combustion chambers

43

on the second head portion

40

2

side is provided in the second head portion

40

2

. The one-ends of the first and second working oil discharge passages

115

1

and

115

2

are opened to the mounting seat

146

which is formed on the side surface

40

a

of the cylinder head

40

in such a manner as to cross between the first and second head portions

40

1

and

40

2

. The first and second working oil discharge passages

115

1

and

115

2

are communicated to each other via the cover

147

fastened to the mounting seat

146

. Accordingly, the first and second working oil discharge passages

115

1

and

115

2

provided in the cylinder head

40

on both of the sides of the containing hole

112

can be simply communicated to each other, and thereby working oil discharged from the single hydraulic control valve

113

can be effectively supplied to the valve resting mechanism

73

I and

73

E for each of the combustion chambers

43

.

In the valve resting mechanism

73

I (or

73

E), the pin holder

74

is slidably fitted in the valve lifter

71

1

(or

107

1

) driven by the valve system cam

59

1

(or

105

1

). The slide pin

76

slidably fitted in the pin holder

74

is slidable between the position at which the leading end of the valve stem

59

(or

61

) is contained in the containing hole

87

and the position at which the leading end of the valve stem

59

(or

61

) is in contact with the contact plane

88

as the outer side surface of the slide pin

76

in accordance with the balance between the hydraulic force and the spring force applied to both the ends of the slide pin

76

. As a result, by controlling the hydraulic force applied to one end of the slide pin

76

, it is possible to switch the resting state and the opening/closing state of the first intake valve

56

1

(or the first exhaust valve

57

1

) from each other.

Since the rotation of the slide pin

76

around its axial line in the pin holder

74

is prevented only by the simple configuration in which the stopper pin

78

is mounted in the pin holder

74

, the valve resting mechanism

73

I (or

73

E) can be easily assembled with the stem

59

(or

61

) of the first intake valve

56

1

(or the first exhaust valve

57

1

) by mounting the valve lifter

71

1

(or

107

1

) to the cylinder head

40

in the state that the pin holder

74

in which the slide pin

76

has been fitted is fitted in the valve lifter

71

1

(or

107

1

).

The pin holder

74

has the insertion hole

81

into which the leading end of the stem

59

(or

61

) of the first intake valve

56

1

(or the first exhaust valve

57

1

) can be inserted, and also has the extension hole

82

, disposed coaxially with the insertion hole

81

, for containing the leading end of the valve stem

59

(or

61

). The sliding hole

80

in which the slide pin

76

is slidably fitted is put between the insertion hole

81

and the extension hole

82

. Accordingly, since in the resting state of the first intake valve

56

1

(or the first exhaust valve

57

1

), the leading end of the valve stem

59

(or

61

) is contained not only in the containing hole

87

but also in the extension hole

82

, the length of the containing hole

87

, that is, the diameter of the slide pin

76

can be made small. This makes it possible to miniaturize the pin holder

74

and hence to the miniaturize the entire valve resting mechanism

73

I (or

73

E).

The shim

84

for blocking the end portion of the extension hole

82

on the closed end side of the valve lifter

71

1

(or

107

1

) is mounted on the pin holder

74

in such a manner that it can be brought into contact with the closed end of the valve lifter

71

1

(

107

1

). To be more specific, it is required to block the end portion of the extension hole on the closed end side of the valve lifter for applying a pressing force from the valve lifter

71

1

(or

107

1

) to the pin holder

74

, and in this embodiment, the end portion of the extension hole

82

is blocked with the shim

84

which is brought into contact with the closed end of the valve lifter

71

1

(or

107

1

). Accordingly, it is possible to simplify the structure of the pin holder

74

, and to suitably adjust a gap at the valve head of the first intake valve

56

1

(or first exhaust valve

57

1

) by changing the thickness of the shim

84

.

The containing cylinder portion

83

coaxial with the axial line of the extension hole

82

is integrally formed on the pin holder

74

at a position facing to the closed end of the valve lifter

71

1

(or

107

1

), and the disk-like shim

84

is partially fitted in the containing cylinder portion

83

. As a result, it is possible to simply mount the relatively small shim

84

on the pin holder

74

.

The projecting portion

85

to be in contact with the shim

84

is integrally formed on the inner surface of the closed end of the valve lifter

71

1

(or

107

1

), and accordingly, the sliding motion of the valve lifter

71

1

(or

107

1

) with respect to the cylinder head

40

can be certainly performed along the axial line of the valve stem

59

(or

61

) in such a manner that the pressing force is applied from the valve lifter

71

1

(or

107

1

) to the pin holder

74

on the extension of the axial line of the valve stem

59

(or

61

) of the first intake valve

56

1

(or the first exhaust valve

57

1

). As a result, the sliding motion of the valve lifter

71

1

(or

107

1

) can be smoothened.

The coil spring

92

for biasing the pin holder

74

toward the closed end side of the valve lifter

71

1

(or

107

1

) is provided between the pin holder

74

and the cylinder head

40

. To be more specific, the coil spring

92

is disposed in such a manner as to surround the valve stem

59

(or

61

) at a position at which the outer periphery of the coil spring

92

is not in contact with the inner surface of the valve lifter

71

1

(or

107

1

). The projections

93

and

94

for positioning the end portion of the coil spring

92

in the direction perpendicular to the axial line of the valve stem

59

(or

61

) are provided on the pin holder

74

. As a result, it is possible to allow the spring force of the coil spring

92

to be certainly applied along the axial line of the valve stem

59

(or

61

), and to prevent the occurrence of frictional loss due to slide-contact of the outer periphery of the coil spring

92

with the valve lifter

71

1

(or

107

1

).

Since the projecting amount of each of the projections

93

and

94

is less than the diameter of the coil spring

92

, even if the coil spring

92

is contracted, it is not in slide-contact with the pin holder

74

. As a result, it is possible to prevent the occurrence of the frictional loss due to the slide-contact of the coil spring

92

with the pin holder

74

.

FIG. 15

shows a second embodiment of the present invention. As shown in

FIG. 15

, a communication passage

149

for communicating a first intake passage

46

1

corresponding to a first intake valve

56

1

rested in a specific operational region of the engine E to a second intake passage

46

2

corresponding to a second intake valve

56

2

opened/closed in the specific operational region is formed as a hollow portion upon the formation of the cylinder head

40

by casting.

According to the second embodiment, the communication passage

149

can be formed upon the formation of the cylinder head

40

by casting. As a result, it is possible to more easily form the communication passage

149

while reducing the number of the steps of forming the cylinder head

40

, and to increase the degree of freedom in shape and the arrangement position of the communication passage

149

.

While the embodiments of the present invention have been described in detail, the present invention is not limited thereto, and it is to be understood that many changes in design may be made without departing from the scope of the claims.

As described above, according to the present invention, it is possible to prevent the fuel from remaining in the intake passage corresponding to the rested intake valve, and hence to prevent the remaining fuel from flowing in the combustion chamber when the operational state in which part of the intake valves is rested is switched into the operational state in which all of the intake valves are opened/closed. As a result, it is possible to prevent the mixing ratio of the air-fuel mixture flowing in the combustion chamber from being made unstable, and hence to prevent the reduction in engine output and the increase in occurrence of unburned hydrocarbon as much as possible.

According to the present invention, even if the intake system connected to a plurality of intake passages is configured to have a single carburetor, it is possible to avoid the inconvenience that the mixing ratio is made unstable when the operational state in which part of the intake valves is rested is switched into the operational state in which all of the intake valves are opened/closed.

According to the present invention, it is possible to form the communication passage simultaneously with the formation of the cylinder head by casting, and hence to reduce the number of the steps of forming the cylinder head.

According to the present invention, the communication passage can be simply formed in the cylinder head without use of any special means.

According to the present invention, the opening end of the communication passage to the intake passage corresponding to the intake valve is positioned in the specific operational region can be disposed at a position being as close to the combustion chamber as possible, so that when the intake valve is positioned in the specific operational region, the intake passage corresponding to the position of the intake valve can be communicated to the intake passage corresponding to the opened/closed intake valve at the position being as close to the combustion chamber as possible. This makes it possible to make the amount of the remaining fuel in the resting state of the intake valve as small as possible.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Engine with valve resting function

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

Foreign Referenced Citations (1)