Internal combustion engine

BACKGROUND OF THE INVENTION

CROSS-REFERENCES TO RELATED APPLICATIONS

This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2001-205174 filed in Japan on Jul. 5, 2001, and Patent Application No. 2001-205175 filed in Japan on Jul. 5, 2001, the entirety of each of which are herein incorporated by reference.

1. Field of the Invention

The present invention relates to an internal combustion engine, and more particularly to an internal combustion engine in which a piston slidably fitted in a cylinder is connected to a crankshaft through a connecting rod. The present invention specifically relates to a horizontally-opposed type internal combustion engine in which left and right pistons are slidably supported in left and right cylinder banks horizontally opposed to each other. A crankshaft is positioned between the pistons and is connected to the pistons through connecting rods.

2. Description of the Background Art

A horizontally-opposed type internal combustion engine has been known in the background art, e.g., as seen by the exemplary engine described in Japanese Patent Laid-open No. 2000-110661. The engine described in Japanese Patent Laid-open No. 2000-110661 has a structure in which left and right cylinders are disposed on both sides of a crankshaft. Pistons slidably fitted in the cylinders are each connected to the crankshaft through a connecting rod. A combustion chamber of each of the cylinders is provided at an end portions of the cylinders on the opposite side of the crankshaft. Therefore, each of the pistons is moved in the direction of approaching the crankshaft during an expansion stroke.

FIG. 7

is a schematic view of a general 4-cycle single-cylinder internal combustion engine according to the background art. The internal combustion engine E includes a cylinder

01

, a piston

02

slidably fitted in the cylinder

01

, a cylinder head

03

connected to the cylinder

01

, a combustion chamber

04

provided between a lower surface of the cylinder head

03

and the cylinder

01

, a crankshaft

05

, and a connecting rod

06

for connecting the piston

02

to the crankshaft

05

. The piston

02

is located at a position between the cylinder head

03

and the crankshaft

05

.

FIG.

7

(

a

) shows a condition where the piston

02

is located at a position of top dead center, e.g., when the crank angle θ is 0°. FIG.

7

(

c

) shows a condition where the piston

02

is located at a position of bottom dead center, e.g., when the crank angle θ is 180° (Position C in FIGS.

7

(

a

)-(

c

). FIG.

7

(

b

) shows a condition where the piston

02

is located at a middle position (Position B in FIGS.

7

(

a

)-(

c

) between top dead center (Position A in FIGS.

7

(

a

)-(

c

)) and bottom dead center (Position C), e.g., when the crank angle θ is not 90° but is an angle θa less than 90°. While the connecting rod

06

is on the axis L

1

of the cylinder

01

at top dead center and bottom dead center, the connecting rod

06

is inclined by an angle φ relative to the axis L

1

of the cylinder

01

at the middle position.

In

FIG. 6

, the relationship between the crank angle θ with reference to top dead center of the internal combustion engine E and the displacement x of the piston

02

with reference to top dead center is indicated by a chain line. The stroke between top dead center and bottom dead center of the piston

02

is 2R (R is the crank radius). As has been described with reference to FIG.

7

(

b

), when the piston

02

is located at the middle position, e.g., any intermediate point between, between top dead center and bottom dead center, e.g., at a point where the displacement x of the piston

02

is R, the crank angle θ is an angle θa which is less than 90°. In contrast, in a sine curve (x=Rsin(θ−90°)+R) indicated by a solid line, the crank angle θ is 90° when the piston

02

is located at the middle position between top dead center and bottom dead center.

Accordingly, in the case of the internal combustion engine E of the background art, the line (see the chain line) representing the relationship of the displacement x of the piston

02

to the crank angle θ is located on the upper side relative to the sine curve indicated by the solid line. When the piston

02

is lowered from top dead center in the beginning stage of the expansion stroke, the increase of the displacement x of the piston

02

with reference to the increase of the crank angle θ is greater when compared with the characteristics of the sine curve.

The present inventors have identified the following problems associated with the background art. In the internal combustion engine E of the background art shown in

FIG. 7

, the crankshaft

05

is disposed on the lower side of the direction of the axis L

1

of the cylinder

01

. Therefore, the engine E, and the mass dispersed in the direction of the axis L

1

, is enlarged in size in the direction of the axis L

1

.

In addition, in order to enhance thermal efficiency of an internal combustion engine E, it is desirable to enhance the degree of an equal volume of a mixture gas at the time of combustion. The volume of the combustion chamber

04

on the upper side of the piston

02

is increased when the combustion of the mixture gas is started in the vicinity of top dead center of the piston

02

and the piston

02

is lowered. Accordingly, the equal volume is higher and thermal efficiency is higher as the increase of the volume of the combustion chamber

04

with reference to the increase of the crank angle θ is smaller. However, in the case of the internal combustion engine E of the background art, the increase of the volume of the combustion chamber

04

with reference to the increase of the crank angle θ from top dead center is enlarged and the equal volume degree is lowered. This arrangement is disadvantageous for enhancing the thermal efficiency of the internal combustion engine E.

The horizontal opposed type internal combustion engine described in Japanese Patent Laid-open No. 2000-110661 also suffers from the above-mentioned problems because it employs a structure in which the general single-cylinder internal combustion engines according to the prior art simply combine a pair of pistons opposed to each other.

Further, the horizontal opposed type internal combustion engine described in Japanese Patent Laid-open No. 2000-110661 requires complicated structures for the intake system and the valve mechanism, because the left and right cylinder heads are located away from each other.

SUMMARY OF THE INVENTION

The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.

An object of the present invention is to reduce the size of an internal combustion engine in the axial direction of the cylinder.

An object of the present invention is to enhance the equal volume degree at the time of combustion of a mixture gas of the internal combustion engine and to enhance thermal efficiency.

An additional object of the present invention is to provide the aforementioned improvements and advantages for a horizontally opposed type internal combustion engine. Specifically, an object of the present invention is to enhance the equal volume degree at the time of combustion of a mixture gas in a horizontal opposed type internal combustion engine, enhance thermal efficiency thereof, and to simplify the structures of the associated intake system and valve mechanism.

One or more of these and other objects are accomplished by an internal combustion engine comprising a cylinder; a cylinder head; a piston slidably fitted in the cylinder; an auxiliary cylinder coaxial with the cylinder; an auxiliary piston slidably fitted in the auxiliary cylinder; a first connecting rod integrating the piston and the auxiliary piston into a single unitary body; a combustion chamber provided in the cylinder head; a pair of left and right crankshaft halves; and a pair of second connecting rods connecting the auxiliary piston to the left and right crankshaft halves through an intermediate pin, wherein the left and right crankshaft halves are disposed along the outside of the cylinder with respect to a radial direction thereof and a piston sliding range of the cylinder.

One or more of these and other objects are accomplished by an internal combustion engine comprising a piston slidably fitted in a cylinder; a combustion chamber; a crankshaft; and a connecting rod connecting the piston to the crankshaft, wherein the crankshaft is positioned adjacent to the combustion chamber and outside of a piston sliding range of the cylinder with respect to a radial direction of the cylinder.

One or more of these and other objects are accomplished by a horizontally opposed internal combustion engine comprising a left cylinder block horizontally opposed to a right cylinder block; a left cylinder positioned in a left cylinder bank; a right cylinder positioned in a right cylinder bank; left and right pistons slidably supported respectively in the cylinders; a crankshaft positioned between the left and right pistons, the left and right pistons being connected to the crankshaft through a connecting rod; and left and right combustion chambers being provided between the left and right cylinders so that the left and right pistons are capable of being moved in opposite directions away from the crankshaft during an expansion stroke of the left and right pistons.

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 hereinafter 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 horizontal sectional view of an internal combustion engine for a motorcycle according to an embodiment of the present invention;

FIG. 2

is a sectional view taken along line

2

—

2

of

FIG. 1

;

FIG. 3

is a sectional view taken along line

3

—

3

of

FIG. 1

;

FIG. 4

is a sectional view taken along line

4

—

4

of

FIG. 2

;

FIG. 5

is an operational view of an internal combustion engine according to the present invention;

FIG. 6

is a graphical view showing a comparative relationship between crank angle θ and piston displacement x for internal combustions of the present invention and according to the background art;

FIG. 7

is a schematic view of the operation of a general 4-cycle single-cylinder internal combustion engine according to the background art;

FIG. 8

is a vertical sectional view of a horizontally-opposed type, internal combustion engine during an operating condition where a piston is located at bottom dead center;

FIG. 9

is a vertical sectional view taken along line

2

—

2

of

FIG. 8

;

FIG. 10

is a vertical sectional view taken along line

3

—

3

of

FIG. 8

;

FIG. 11

is an operational view of an internal combustion engine in which a piston is located at top dead center; and

FIG. 12

is an operational view of an internal combustion engine according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinafter be described with reference to the accompanying drawings.

FIGS. 1

to

6

show a first embodiment of the present invention.

FIG. 1

is a horizontal sectional view of an internal combustion engine for a motorcycle according to an embodiment of the present invention.

FIG. 2

is a sectional view taken along line

2

—

2

of FIG.

1

.

FIG. 3

is a sectional view taken along line

3

—

3

of FIG.

1

.

FIG. 4

is a sectional view taken along line

4

—

4

of FIG.

2

.

FIG. 5

is an operational view of an internal combustion engine according to the present invention.

FIG. 6

is a graphical view showing a relationship between crank angle θ and piston displacement x.

FIG. 7

is a schematic view of the operation of a general 4-cycle single-cylinder internal combustion engine according to the background art.

FIGS. 8

to

12

show a second embodiment of the present invention.

FIG. 8

is a vertical sectional view of a horizontally-opposed type internal combustion engine during an operating condition where a piston is located at bottom dead center.

FIG. 9

is a vertical sectional view taken along line

2

—

2

of FIG.

8

.

FIG. 10

is a vertical sectional view taken along line

3

—

3

of FIG.

8

.

FIG. 11

is an operational view of an internal combustion engine in which a piston is located at top dead center.

FIG. 12

is an operational view of an internal combustion engine according to the present invention.

As shown in

FIGS. 1

to

4

, a four-cycle, single-cylinder engine E for a motorcycle includes a left engine block

11

and a right engine block

12

bisected along left and right sides. A cylinder block

13

is clamped between the left and right engine blocks

11

,

12

. The cylinder block

13

includes a cylinder

14

and an auxiliary cylinder

15

disposed along a common axis L

1

. A piston

16

is slidably fitted in the cylinder

14

, and an auxiliary piston

17

is slidably fitted in the auxiliary cylinder

15

.

A ring-shaped support portion

17

c

is provided in the inside of a generally cylindrical main body portion

17

a

of the auxiliary piston

17

through a pair of arm portions

17

b

,

17

b

. An intermediate pin

18

is fitted in two through-holes

17

d

,

17

d

penetrating through the main body portion

17

a

and the support portion

17

c

. Both ends of the intermediate pin

18

are slidably fitted in a pair of slits

15

a

,

15

a

provided in the auxiliary cylinder

15

along the direction of the axis L

1

.

The upper end of a first connecting rod

19

extending in the direction of the axis L

1

is connected to the piston

16

through a piston pin

20

. A bifurcated lower end portion of the first connecting rod

19

is connected to the intermediate pin

18

in the inside of the auxiliary piston

17

. The piston

16

and the auxiliary piston

17

are therefore moved as a unitary body through the first connecting rod

19

, and the first connecting rod

19

is constantly maintained along on the axis L

1

without oscillating.

A left crankshaft half

24

is rotatably supported on the left engine block

11

and by a left cover

21

connected to a left side surface thereof through two ball bearings

22

,

23

. A right crankshaft half

28

is rotatably supported on the right engine block

12

and by a right cover

25

connected to a right side surface thereof through two ball bearings

26

,

27

. The left crankshaft half

24

and the right crankshaft half

28

are located on a common axis L

2

(See FIG.

1

). A crank pin

29

provided on the left crankshaft half

24

and the left end of the intermediate pin

18

is connected by the second connecting rod

30

. Similarly, a crank pin

31

provided on the right crankshaft half

28

and the right end of the intermediate pin

18

is connected by the second connecting rod

32

.

A cylinder head

41

connected to the left engine block

11

and the right engine block

12

is provided with a combustion chamber

42

between a top surface of the piston

16

and a surface of the cylinder head

41

. The cylinder head

41

also includes an intake port

43

and an exhaust port

44

extending from the combustion chamber

42

, an intake valve

45

for opening and closing the intake port

43

, and an exhaust valve

46

for opening and closing the exhaust port

44

. An intake pipe

48

provided with a fuel injection valve

47

is connected to the intake port

43

, and the combustion chamber

42

is provided with a spark plug

49

.

A camshaft

52

is supported in a valve chamber

51

surrounded by the cylinder head

41

and a head cover

50

. A driven sprocket

53

provided on the camshaft

52

is connected to a driving sprocket

54

provided on the left crankshaft half

24

through a timing chain

55

.

An intermediate portion of an intake rocker arm

57

is rotatably supported on an intake rocker arm shaft

56

provided at the cylinder head

41

. A first end of the intake rocker arm

57

makes contact with an intake cam

58

provided on the camshaft

52

. The other end of the intake rocker arm

57

engages with a stem end of the intake valve

45

. In addition, an intermediate portion of an exhaust rocker arm

60

is rotatably supported on an exhaust rocker arm shaft

59

provided at the cylinder head

41

. A first end of the exhaust rocker arm

60

engages with an exhaust cam

61

provided on the camshaft

52

, and the other end makes contact with a stem end of the exhaust valve

46

.

A balancer shaft

64

is supported through a pair of ball bearings

62

,

63

on the left engine block

11

and the left cover

21

. An output shaft

67

is supported through ball bearings

65

,

66

. A first gear

68

provided on the left crankshaft half

24

is meshed with a second gear

69

provided on the balancer shaft

64

, and a third gear

70

provided on the balancer shaft

64

is meshed with a fourth gear

71

provided on the output shaft

67

. A sector-shaped balancer weight

72

(See

FIGS. 1 and 3

) is provided at the inner end of the balancer shaft

64

, e.g., at a position adjacent to the cylinder

14

. The first gear

68

and the second gear

69

have an equal number of gear teeth, so that the balancer shaft

64

is rotated at the same speed as the left crankshaft half

24

. The output shaft

67

projecting from the left cover

21

is connected to an input shaft of a belt-type, direct drive (non-stage) transmission in a preferred embodiment.

A balancer shaft

75

is supported on the right engine block

12

and the right cover

25

through a pair of ball bearings

73

,

74

, and a fifth gear

76

provided on the right crankshaft half

28

is meshed with a sixth gear

77

provided on the balancer shaft

75

. A sector-shaped balancer weight

78

(See

FIGS. 1 and 2

) is provided at the inner end of the balancer shaft

75

, e.g., at a position adjacent to the cylinder

14

. The fifth gear

76

and the sixth gear

77

have an equal number of teeth, so that the balancer shaft

75

is rotated at the same speed as the right crankshaft half

28

. The right crankshaft half

28

is provided with a speed-detecting gear

80

positioned opposite to a pulser

79

for detecting the rotational frequency. As seen in

FIG. 2

, the engine E having the above-described structure includes a fitting portion

12

a

provided on the right engine block

12

supported by a vehicle body frame

83

through engine hangers

81

,

82

.

The action or effects of the above-described embodiment of the present invention will be described in greater detail hereinafter. The internal combustion engine E according to the present embodiment includes the cylinder

14

, the piston

16

slidably fitted in the cylinder

14

, an auxiliary piston

17

slidably fitted in the auxiliary cylinder

15

coaxial with the cylinder

14

, the first connecting rod

19

for integrating the piston

16

and the auxiliary piston

17

, the combustion chamber

42

provided in the cylinder head

41

, the left and right crankshaft halves

24

,

28

, and two second connecting rods

30

,

32

for connecting the auxiliary piston

17

to the left and right crankshaft halves

24

,

28

through the intermediate pin

18

. The left and right crankshaft halves

24

,

28

are disposed along the outside of the piston

16

with respect to a radial direction thereof.

FIG.

5

(

a

) shows a condition where the piston

16

is located at top dead center, e.g., when the crank angle θ is 0°. FIG.

5

(

c

) shows a condition where the piston

16

is located at bottom dead center, e.g., when the crank angle θ is 180°. FIG.

5

(

c

) shows the condition where the piston

16

is located at a middle point between top dead center and bottom dead center, e.g., when the crank angle θ is not 90°, but is an angle θb greater than 90°. Accordingly, while the second connecting rods

30

,

32

are located on the axis L

1

of the cylinder

14

at top dead center and bottom dead center, the second connecting rods

30

,

32

are inclined by an angle φ with reference to the axis L

1

of the cylinder

14

at the time of an intermediate piston position between top dead center and bottom dead center. In addition, the first connecting rod

19

merely integrates the piston

16

and the auxiliary piston

17

as a unitary body, and is therefore maintained without oscillation along the axis L

1

.

In

FIG. 6

, the relationship between the crank angle θ with reference to top dead center of the internal combustion engine E and the displacement x of the piston

16

with reference to top dead center is indicated by a broken line. Here, the stroke between top dead center and bottom dead center of the piston

16

is 2R (R is the crank radius). As has been described with reference to FIG.

5

(

b

), when the piston

16

is located at the middle point (the point where the displacement is R) between top dead center and bottom dead center, the crank angle θ is the angle θb greater than 90°. In contrast, the crank angle θ is 90° when the piston

16

is located at the middle point between top dead center and bottom dead center, e.g., as seen in the sine curve indicated by a solid line.

Thus, in the internal combustion engine E according to this embodiment, the line (See the broken line) indicating the relationship of the displacement x of the piston

16

with the crank angle θ is located on the lower side of the sine curve indicated by the solid line, and it is seen that x<Rsin(θ−90°)+R is established with the present invention. When the piston is lowered from top dead center in an expansion stroke, the increase of the displacement x of the piston

16

with reference to the increase of the crank rangle θ is smaller then when compared to the characteristics of the sine curve.

As has been described above, in order to enhance thermal efficiency of the internal combustion engine E, it is desirable to enhance the equal volume degree at the time of combustion of a mixture gas. For this, the equal volume degree is higher and the thermal efficiency is higher as the increase of the volume of the combustion chamber

42

with reference to the increase of the crank angle θ is smaller when the piston

16

is lowered from top dead center in the expansion stroke.

As seen in the expansion stroke portion with the crank angle θ from 0° to 180° in

FIG. 6

, the displacement x of the piston

16

from top dead center of the internal combustion engine E according to the present embodiment indicated by the broken line is smaller than the displacement x of the internal combustion engine E of the background art indicated by the chain line. Therefore, the equal volume degree in the expansion stroke and thermal efficiency is enhanced.

In addition, since the auxiliary piston

17

is moved away from the left and right crankshaft halves

24

,

28

during the expansion stroke in which the largest load is exerted on the first and second connecting rods

19

,

30

,

32

, an advantageous tensile load is achieved that is opposite to the load exerted on the second connecting rods

30

,

32

in the case of the internal combustion engine E of the background art. More particularly, the exertion of the tensile load on the second connecting rods

30

,

32

in the present invention is advantageous since it provides more strength than the case of the exertion of a compressive load experienced with the internal combustion engine E of the background art. Accordingly, it is possible to make the second connecting rods

30

,

32

of the present invention relatively slender and to thereby achieve a reduction in overall weight.

Since the left and right crankshaft halves

24

,

28

are disposed on the outside in the radial direction of the range of sliding of the piston

16

of the cylinder

14

, it is possible to reduce the size of the internal combustion engine E in the direction of the axis L

1

of the cylinder

14

. Accordingly, it is possible to achieve a concentration of mass.

In addition, even though the crankshaft is bisected into the left and right crankshaft halves

24

,

28

and disposed on both sides of the cylinder

14

, the two second connecting rods

30

,

32

disposed on both sides of the cylinder

14

are connected respectively to the left and right crankshaft halves

24

,

28

. It is also possible to avoid exertion of an unbalanced load on the auxiliary piston

17

, the piston

16

and the first and second connecting rods

19

,

30

,

32

and to prevent generation of abnormal wear.

Any interference of the left and right crankshaft halves

24

,

28

with the cylinder

14

is simultaneously avoided with the present invention. The balancer weights

72

,

78

rotated in conjunction with the left and right crankshaft halves

24

,

28

are disposed in the surrounding of the cylinder

14

and it is therefore possible to concentrate the mass of the balancer weights

72

,

78

in the surrounding of the cylinder

14

and to enhance a vibration-damping effect.

While the embodiment of the present invention has been described in detail hereinabove, the present invention includes various design modifications within the spirit and scope of the invention. For example, the internal combustion engine E for a motorcycle can be applied to multi-cylinder and/or other internal combustion engine applications for other vehicles and engine applications.

In addition, while the engine E according to the embodiment comprises the left and right crankshaft halves

24

,

28

on both sides of the cylinder

14

, a structure may be adopted in which either one of the left and right crankshaft halves

24

,

28

is provided. While the 4-cycle internal combustion engine E has been described as an example in the foregoing embodiments, the present invention may also be applied to an overhead valve type, 2-cycle internal combustion engine.

As described above, according to an embodiment of the invention, the crankshaft is disposed on the outside in the radial direction of the piston sliding range of the cylinder. Therefore, it is possible to reduce the size of the internal combustion engine in the axial direction of the cylinder and to achieve a concentration of mass when compared with the conventional internal combustion engine in which the crankshaft is provided on the outside on the axis of the cylinder and on the outside of the piston sliding range.

In addition, the connecting rod is split into the first connecting rod having one end connected to the piston side and the second connecting rod having one end connected to the crankshaft side, and the other ends of both of the connecting rods are connected to each other through the intermediate pin moved in the axial direction of the cylinder. In contrast to the conventional internal combustion engine having the crankshaft provided on the axis of the cylinder and on the outside of the piston sliding range, the increase of the volume of the combustion chamber corresponding to the increase of the crank angle with reference to top dead center of the piston can be reduced with the present invention. Accordingly, it is possible to enhance the equal volume degree at the time of combustion of a mixture gas and to enhance thermal efficiency.

In addition, the pair of crankshaft halves bisected with the cylinder therebetween is connected respectively to both ends of the intermediate pin through the second connecting rod. Therefore, it is possible to avoid exertion of an unbalanced load on the piston and the first and second connecting rods. Further, the present invention prevents the generation of abnormal wearing, while avoiding an interference of the crankshaft with the cylinder.

The balancer weights provided on the balancer shafts rotated in conjunction with the crankshaft are advantageously disposed in the surroundings of the cylinder. Therefore, it is possible to concentrate the mass of the balancer weights in the surrounding of the cylinder and to enhance a vibration-damping effect.

A second embodiment of the present invention will be described hereinafter with respect to

FIGS. 8-12

of the accompanying drawings.

FIGS. 8

to

12

show a second embodiment of the present invention.

FIG. 8

is a vertical sectional view of a horizontally-opposed type internal combustion engine during an operating condition where a piston is located at bottom dead center.

FIG. 9

is a vertical sectional view taken along line

2

—

2

of FIG.

8

.

FIG. 10

is a vertical sectional view taken along line

3

—

3

of FIG.

8

.

FIG. 11

is an operational view of an internal combustion engine in which a piston is located at top dead center.

FIG. 12

is an operational view of an internal combustion engine according to the present invention.

As shown in

FIGS. 8

to

10

, the horizontally-opposed type two-cylinder internal combustion engine E having left and right banks B, B includes left and right bisected cylinder heads

11

,

11

, left and right cylinder blocks

12

,

12

connected to the outside of the cylinder heads

11

,

11

, left and right cylinders

13

,

13

supported in the inside of the cylinder blocks

12

,

12

, left and right pistons

14

,

14

slidably fitted withn the cylinders

13

,

13

, and a crankshaft

15

supported at a split surface of the left and right cylinder heads

11

,

11

. Two pairs of left and right connecting rods

17

for connecting piston pins

16

,

16

supported at outer ends of the pistons

14

,

14

to crank pins

15

a

, and cup-shaped covers

18

,

18

for covering outer end portions of the cylinder blocks

12

,

12

are included in the engine E.

The left and right cylinders

13

,

13

are not offset in the axial direction of the crankshaft

15

, but are located on a common axis L (See FIG.

9

). An outer end portion of each cylinder block

12

and cylinder

13

is provided with two slits

19

,

19

extending in the direction of the axis L, and the piston pin

16

is slidably guided by the slits

19

,

19

. A driven gear

22

provided at a single camshaft

21

supported at a mating surface of the left and right cylinder heads

11

,

11

is meshed with a driving gear

23

provided at one end of the crankshaft

15

. The camshaft

21

is rotated at one half of the rotational frequency of the crankshaft

15

.

A combustion chamber

24

provided at the cylinder head

11

of each bank B is provided with an intake valve

25

and an exhaust valve

26

. An intake rocker arm

28

rotatably supported on a rocker arm shaft

27

fixed to the cylinder head

11

engages with stem ends of an intake valve

25

and an intake cam

29

provided at the camshaft

21

. An exhaust rocker arm

30

rotatably supported on the rocker arm shaft

27

makes contact with stem ends of an exhaust valve

26

and an exhaust cam

31

provided at the camshaft

21

.

The upstream side of an intake port

32

opened and closed by the intake valve

25

is connected to a throttle valve

33

. A fuel injection valve

34

is provided directly under the throttle valve

33

. An exhaust port

35

opened and closed by the exhaust valve

26

is connected to an exhaust pipe

36

. A guide tube

38

for detachably fitting a spark plug

37

engaging with the combustion chamber

24

extends from the cylinder block

12

of the bank B on the opposite side in a skewed orientation.

As seen in

FIG. 9

, the left and right guide tubes

38

,

38

are not parallel with the axes L of the cylinders

13

,

13

in plan view, and their opening end sides are inclined to both end sides of the crankshaft

15

. With this layout, it is unlikely that the guide tubes

38

,

38

will interfere with the lower surfaces of the cylinder blocks

12

,

12

. As a result, it is possible to reduce the inclination angle of the downward inclination of the opening end sides of the guide tubes

38

,

38

relative to the axes L of the cylinders

13

,

13

in FIG.

6

. Accordingly, the engine E according to the present invention can incorporate the aforementioned features and achieve an advantageous reduction in overall size.

An AC generator

39

and a starter gear

40

are provided on the other end of the crankshaft

15

. The engine E is started by a driving force of a pinion

42

provided on a starter motor

41

transmitted to the crankshaft

15

through intermediate gears

44

,

45

supported on an intermediate shaft

43

, the starter gear

40

, a one-way clutch

46

and the ACgenerator

39

.

FIG. 12

schematically shows the bank B on one side of the internal combustion engine E according to the second embodiment of the present invention. The internal combustion engine E of the present includes a cylinder

13

, a piston

14

slidably fitted in the cylinder

13

, a cylinder head

11

connected to the cylinder

13

, a combustion chamber

24

formed in the cylinder head

11

and by the piston

14

, a crankshaft

15

, and connecting rods

17

,

17

for connecting the piston

14

to the crankshaft

15

. The cylinder head

11

is disposed at a position between the piston

14

and the crankshaft

15

.

FIG.

12

(

a

) shows a condition where the piston

14

is located at top dead center, e.g., when the crank angle θ is 0°. FIG.

12

(

c

) shows a condition where the piston

14

is located at bottom dead center, e.g., when the crank angle is 180°. FIG.

12

(

b

) shows a condition where the piston

14

is located at an intermediate point between top dead center and bottom dead center, e.g., when the crank angle θ is not 90° but is an angle θb greater than 90°.

While the connecting rods

17

,

17

are located on the axis L of the cylinder

13

at top dead center and bottom dead center, the connecting rods

17

,

17

are inclined by an angle φ with reference to the axis L of the cylinder

13

at the time of the intermdiate point.

Since the left and right combustion chambers

24

,

24

are concentrated at a central portion of the engine E, the intake system, e.g., such as the fuel injection valves

34

,

34

and the throttle valves

33

,

33

connected to the combustion chambers

24

,

24

, can be laid out in a compact form, and the pipe length of the intake pipes can be shortened. Further, the noise generated from the combustion chambers

24

,

24

and the valve mechanisms

20

,

20

is less likely to leak to the exterior of the engine E. In addition, relatively heavy members can be concentrated at a central portion of the engine E.

Since the valve mechanisms

20

,

20

of the left and right banks B, B are driven by the common camshaft

21

provided at the center of the left and right cylinder heads

11

, it is possible to minimize the number of required camshafts

21

. This reduces the number of component parts and achieves a reduction in size of the engine E. Since the common camshaft

21

is disposed between the intake port

32

and the exhaust port

35

of the left bank B and the intake port

32

and the exhaust port

35

of the right bank B, it is possible to effectively utilize the dead space between the left and right intake ports

32

,

32

and the dead space between the left and right exhaust ports

35

,

35

, respectively.

Moreover, since the camshaft

21

is disposed in proximity to the crankshaft

15

, a timing chain or a timing belt in the power transmission system from the crankshaft

15

to the camshaft

21

is not required, and it is possible to make the power transmission system compact and to further reduce the number of required component parts.

In addition, since the opposed cylinders

13

,

13

of the left and right banks B, B are located on the common axis L, e.g., the offset in the axial direction of the crankshaft

15

is avoided, it is possible to suppress the generation of an inertia couple of forces attendant on the reciprocation of the pistons

14

,

14

and to reduce the vibration of the engine E.

While the second embodiment of the present invention has been described in detail hereinabove, the present invention allows various design modifications within the spirit and scope of the invention. For example, while a 4-cycle internal combustion engine E has been described as an example in the embodiment, the present invention can be applied also to a 2-cycle internal combustion engine. In addition, while the cylinders

13

,

13

of the left and right banks B, B are disposed on a common axis L in the embodiment, the axes L, L of the left and right cylinders

13

,

13

may be offset from each other in the case of a small-type engine E in which generation of an inertia couple of forces is not as critical.

While the two left and two right connecting rods

17

of the left and right banks B, B are alternately disposed on the inner and outer sides in the above-described embodiment, the two connecting rods

17

,

17

of one bank B may be disposed on the inside with respect to the axial direction of the crankshaft

15

. The two connecting rods

17

,

17

of the other bank B may be disposed on the outside with respect to the axial direction of the crankshaft

15

. In addition, while the two-cylinder horizontally-opposed type internal combustion engine E has been described in the embodiment, the present invention can be applied also to a four-cylinder (or other multi-cylinder) horizontally-opposed type internal combustion engine E.

Thus, according to the second embodiment of the present invention the increase of the volume of the combustion chamber corresponding to the increase of the crank angle with reference to top dead center of the piston can be reduced, e.g., as compared with the horizontally-opposed type internal combustion engine of the background art in which the left and right combustion chambers are provided on the outside of the left and right cylinders.

Accordingly, it is possible to enhance the equal volume degree at the time of combustion of the mixture gas and to enhance thermal efficiency. In addition, since a tensile load is exerted on the connecting rods during the expansion stroke, the typical considerations of buckling are unnecessary in contrast to the internal combustion engine of the background art where a compressive load is experienced. Therefore, it is possible to reduce the required strength of the connecting rods and to thereby reduce the weight thereof.

Since the left and right combustion chambers are concentrated at a central portion of the engine, a compact layout of the intake systems connected to the combustion chambers is achieved. Further, it is difficult for the noise generated from the combustion chambers and the valve mechanisms adjacent thereto to leak to the exterior. Typically heavier members can be concentrated at central portions of the engine and engine size is reduced.

A common camshaft disposed between the left and right cylinders is used for the valve mechanisms of the left and right banks. Therefore, it is possible to minimize the number of required camshafts. The axes of the opposed cylinders of the left and right banks are generally disposed coaxially. Therefore, it is possible to suppress the generation of an inertia couple of forces attendant on the reciprocation of the pistons, and to reduce the vibration of the engine.

In addition, the camshaft disposed between the intake passages or between the exhaust passages of the left and right banks aids in effectively utilizing the dead space between the left and right intake passages or the dead space between the left and right exhaust passages and to therefore reduce the size of the engine. The guide tube for detachably fitting the spark plug is inclined to a shaft end side of the crankshaft with reference to the axes of the cylinders. Therefore, the guide tube is unlikely to interfere with the cylinders, in contrast to the case where the guide tube is disposed directly under or directly over the axes of the cylinders. Accordingly, it is possible to reduce the angle of vertical inclination of the guide tube so as to part from the axes of the cylinders for avoiding interference with the cylinders and to reduce the size of the engine.

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.

Number	Date	Country	Kind
2001-205174	Jul 2001	JP
2001-205175	Jul 2001	JP

Number	Name	Date	Kind
4694785	Timmerman et al.	Sep 1987	A
5092293	Kaniut	Mar 1992	A

Internal combustion engine

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

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US

International Classifications

Abstract

Description

Claims

Priority Claims (2)

US Referenced Citations (2)

Foreign Referenced Citations (1)