4-cycle engine

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a 4-cycle engine, particularly, an improvement in a 4-cycle engine including an engine body which is comprised of a crankcase having first and second bearing portions for supporting opposite ends of a crankshaft, and a head-integral type cylinder barrel having a cylinder bore with a piston received therein.

2. Description of the Related Art

It is known, as disclosed, for example, in Japanese Patent Application Laid-open No. 8-177441, that in a 4-cycle engine of the mentioned type, the crankcase is comprised of first and second case halves which are coupled to each other at a parting plane extending to obliquely intersect the axis of the first and second bearing portions. The cylinder barrel and the first bearing portion are formed by being integrally molded on the first case half. The second bearing half is formed by being integrally molded on the second case half.

In this type of engine, it is effective to reduce the distance as much as possible between the first and second bearing portions for supporting the opposite ends of the crankshaft, in order to alleviate the bending moment generated on the crankshaft by a load applied from the piston to the crankshaft to enhance the durability of the crankshaft.

In the above conventional engine, however, a valve operating mechanism connected to the crankshaft is disposed adjacent the inside of the second case half. For this reason, when the distance between the first and second bearing portions is to be reduced, the valve operating mechanism is an obstacle. Namely, at least one of the bearing portions cannot be disposed adjacent a crank portion of the crankshaft, because it is hindered by the valve operating mechanism. When the engine is to be assembled, a portion of the valve operating mechanism is obliged to be temporarily assembled to the crankshaft before coupling the first and second case halves to each other. Hence, it cannot be said that assembling this type of engine is easy is good.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a 4-cycle engine of the above-described type, wherein the distance between the first and second bearing portions supporting the opposite ends of the crankshaft is reduced without being interfered with by the valve operating mechanism. The durability of the crankshaft is thereby enhanced. Moreover, the valve operating mechanism can be assembled to the crankshaft after coupling the first and second case halves to each other, which leads to easy assembling of the engine.

To achieve the above object, according to the present invention, there is provided a 4-cycle engine comprising an engine body which is comprised of a crankcase including first and second bearing portions for supporting opposite ends of a crankshaft. A head-integral type cylinder barrel has a cylinder bore in which a piston is received. The crankcase is comprised of first and second case halves which are coupled to each other at a parting plane extending to obliquely intersect an axis of the first and second bearing portions. The cylinder barrel and the first bearing portion are formed by being integrally molded on the first case half to form an engine block. The second bearing portion is formed by being integrally molded on the second case half. A side cover is coupled to an outer side surface of the engine block which is opposite from the parting plane, so as to define a valve operating chamber for accommodation of a valve operating mechanism between the side cover and the outer side surface.

With the arrangement of the present invention, the valve operating chamber is defined between the first case half and the side cover coupled to the outer side surface of the first case half. Therefore, the first and second bearing portions formed on the first and second case halves are disposed adjacent opposite ends of a crank portion of the crankshaft, respectively, without encountering any interference by the valve operating mechanism accommodated in the valve operating chamber and the distance between the first and second bearing portions is minimized. Thus, the bending moment applied from the piston to the crankshaft is reduced to enhance the durability the crankshaft.

Moreover, even after coupling of the first and second case halves, the assembling of the valve operating mechanism can easily be carried out in a state in which the side cover has been removed.

Further, it is possible to provide a 4-cycle engine at a low cost in various forms which can be applied for various uses, only by changing the shapes of the second case half and the side cover which are relatively small parts.

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a vertical sectional front view of a 4-cycle engine formed in a standard type;

FIG. 2

is a sectional view taken along a line

2

—

2

in

FIG. 1

;

FIG. 3

is a sectional view taken along a line

3

—

3

in

FIG. 1

;

FIG. 4

is a vertical sectional front view of a 4-cycle engine formed for driving a generator;

FIG. 5

is a vertical sectional front view of a 4-cycle engine formed for mowing a lawn; and

FIG. 6

is a vertical sectional front view of a 4-cycle engine formed in a hand-held type.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described as being applied to a standard horizontal type 4-cycle engine with reference to

FIGS. 1

to

3

.

In

FIGS. 1 and 2

, reference character E designates a 4-cycle engine having an engine body

1

. The engine body

1

comprises a crankcase

3

which supports a crankshaft

2

horizontally, a cylinder barrel

5

having a cylinder bore

5

a

in which a piston

4

is slidably received, and a cylinder head

18

which defines a combustion chamber

6

between the cylinder head

18

and a top surface of the piston

4

. The crankshaft

2

has a crank portion

2

c

which is connected to the piston

4

through a connecting rod

7

. Intake and exhaust valves

8

and

9

and a spark plug

10

are mounted in the cylinder head

18

.

The crankcase

3

is comprised of a first case half

3

1

and a second case half

3

2

coupled to each other at a parting plane P which extends to obliquely intersect an axis of the crankshaft

2

. The three following parts are formed integrally together by casting to form an engine block

1

a

: the first case half

3

1

, the cylinder barrel

5

and the cylinder head

18

. The first and second case halves

3

1

and

3

2

are separatably coupled to each other by a plurality of bolts

11

(see FIG.

2

).

The crankshaft

2

includes first and second journal portions

2

j

1

and

2

j

2

formed thereon adjacent opposite sides of the crank portion

2

c

. First and second bearing portions

13

1

and

13

2

for supporting the first and second journal portions

2

j

1

and

2

j

2

through ball bearings

12

1

and

12

2

are formed by molding integrally molding them on the first and second case halves

3

1

and

3

2

, respectively.

A side cover

14

is coupled by a plurality of bolts (not shown) to that outer side surface of the engine block

1

a

which is opposite from the parting plane P, thereby defining a valve operating chamber

15

between the side cover

14

and the outer side surface. Oil seals

16

1

and

16

2

are mounted respectively to the side cover

14

and the second case half

3

2

to come into close contact with an outer peripheral surface of the crankshaft

2

.

The first case half

3

1

is provided with an opening

30

which permits the valve operating chamber

15

and the inside of the crankcase

3

to communicate with each other below the first bearing portion

13

1

. An oil reservoir

17

is defined to extend from the inside of the crankcase

3

to the valve operating chamber

15

for storing a lubricating oil in the bottom of the crankcase

3

and the valve operating chamber

15

.

An upper portion of the valve operating chamber

15

extends through a sidewall of the cylinder barrel

5

to above the cylinder head

18

, and an upper portion of the valve operating chamber

15

is closed by a head cover

18

a

which is coupled to an upper surface of the cylinder head

18

. A valve operating mechanism

19

is disposed in the valve operating chamber

15

for opening and closing the intake and exhaust valves

8

and

9

by rotating the crankshaft

2

.

As shown in

FIGS. 1 and 3

, the valve operating mechanism

19

includes a drive timing gear

20

secured to the crankshaft

2

outside the first bearing portion

13

1

. A driven timing gear

22

carried on an intermediate shaft

21

and driven at a reduction ratio of one half from the drive timing gear

20

. A cam

23

is connected to one end of the driven timing gear

22

. A pair of cam followers

25

,

25

are carried on a cam follower shaft

24

to be swung by the cam

23

. A pair of rocker arms

27

,

27

are carried on a rocker shaft

26

with one end thereof abutting against heads of the intake and exhaust valves

8

and

9

, respectively. A pair of push rods

28

,

28

connect the other ends of the rocker arms

27

,

27

to the cam followers

25

,

25

. Valve springs

29

,

29

bias the intake and exhaust valves

8

and

9

in closing directions. When the lift surface of the cam

23

pushes up the push rods

28

,

28

through the cam followers

25

,

25

, the intake valve

8

or the exhaust valve

9

is opened. When the base surface of the cam

23

faces the cam followers

25

,

25

, the intake valve

8

or the exhaust valve

9

is closed by a biasing force of the valve springs

29

,

29

.

The intermediate shaft

21

and the cam follower shaft

24

are supported at their opposite ends by the engine block

1

a

and the side cover

14

.

A regulating centrifugal governor

33

is mounted to the side cover

14

below the crankshaft

2

and driven by the drive timing gear

20

. The centrifugal governor

33

is comprised of a rotary board

35

supported on a support shaft

34

fixedly mounted on an inner wall of the side cover

14

. A cylindrical slider

36

is slidably fitted over the support shaft

34

. A plurality of pendulum-type centrifugal weights

37

swingably are carried on the rotary board

35

with the slider

36

interposed therebetween. Each of the centrifugal weights

37

includes an operating arm

37

a

which allows the slider

36

to slide in one direction, when the centrifugal weight

37

is swung in a radially outward direction by a centrifugal force. When the slider

36

slides in the one direction, a throttle valve (not shown) of a carburetor is operated in the closing direction through a link mechanism

38

, as is conventionally common, thereby controlling the engine speed to a preset value.

The support shaft

34

is fixedly mounted to the side cover

14

with an inclined attitude with its tip end directed toward the second bearing portion

13

2

, whereby the rotary board

35

is maintained in such an inclined attitude that its rotating plane is closer to the axis of the cylinder bore

5

a

toward its lower portion. The rotary board

35

is integrally formed, on an outer periphery thereof, with a driven gear

40

meshed with the drive timing gear

20

, and a plurality of oil splashing blades

41

adjacent the driven gear

40

. The rotary board

35

is disposed so that lower portions of the driven gear

40

and the oil splashing blades

41

are immersed in an oil in the oil reservoir

17

.

As shown in

FIG. 1

, an oil dipper

42

is secured to a lower end of the connecting rod

7

by a bolt

43

for splashing the oil in the oil reservoir

17

by the vertical movement and swinging movement of the connecting rod

7

.

A flywheel

45

having a cooling fan

44

integrally formed thereon is secured to one end of the crankshaft

2

which protrudes out of the second case half

3

2

, and a working equipment A used in a horizontal attitude, e.g., a rotor of a water pump is connected to the other end of the crankshaft

2

which protrudes out of the side cover

14

.

To assemble the engine E, the ball bearings

12

1

and

12

2

are mounted on the first and second journals

2

j

1

and

2

j

2

of the crankshaft

2

and are fitted into the first and second bearing portions

13

1

and

13

2

of the first and second case halves

3

1

and

3

2

, and the case halves

3

1

and

3

2

are coupled to each other by the bolts. Then, the valve operating mechanism

19

is assembled in the valve operating chamber

15

outside the first bearing portion

13

1

. Finally, the side cover

14

and the head cover

18

a

are coupled to the engine block

1

a

by the bolts. In this manner, in a state in which the first and second case halves

3

1

and

3

2

have been coupled to each other, and the crankshaft

2

has been reliably supported, the valve operating mechanism

19

is assembled. Therefore, it is unnecessary to perform a temporary assembling as in the prior art, leading to a easy assembling of the valve operating mechanism.

If a load is applied from the piston

4

through the connecting rod

7

to the crank portion

2

c

of the crankshaft

2

due to expansion or compression stroke during operation of the engine E, the load is supported by the first and second bearing portions

13

1

and

13

2

of the first and second case halves

3

1

and

3

2

. In response to this load, a bending moment is generated in the crankshaft

2

, particularly between the bearing portions

13

1

and

13

2

. However, this bending moment is smaller, since the distance L between the bearing portions

13

1

and

13

2

is shorter. As described above, the valve operating mechanism

19

is disposed in the valve operating chamber

15

outside the first bearing portion

13

1

, and the bearing portions

13

1

and

13

2

are disposed adjacent the opposite ends of the crankshaft

2

c

without being hindered by the valve operating mechanism

19

, so that the distance L between the bearing portions

13

1

and

13

2

is minimum. Therefore, the bending moment can be maintained to the minimum, which can contribute to an enhancement in durability of the crankshaft

2

.

The centrifugal governor

33

is driven by the crankshaft

2

during operation of the engine E. Therefore, the driven gear

40

and the splashing blades

41

of the rotary board

35

splash the oil in the oil reservoir

17

upwards while agitating the oil, whereby the valve operating mechanism

19

and the other portions can be lubricated by the splashed oil.

The second case half

3

2

and the side cover

14

are relatively small parts unlike the engine block

1

a

and hence, it is possible to provide at a low cost a 4-cycle engine E in various forms which can be applied for various uses which will be described below, only by changing the shapes and structures of the second case half

3

2

and the side cover

14

.

FIG. 4

shows an example in which the second case half

3

2

is modified, whereby the engine E is formed for driving a generator. More specifically, a plurality of stator mounting bosses

47

are integrally provided on an outer side surface of the second case half

3

2

so as to protrude therefrom. A stator

48

s

of a generator

48

is secured to the bosses

47

by a bolt

49

, and a rotor

48

r

is secured to the crankshaft

2

to surround the stator

48

s

. An alert mounting bore

50

is provided in a bottom wall of the second case half

3

2

, and a housing

52

of an oil alert

51

is mounted in the alert mounting bore

50

. Thus, the rotor

48

r

can be rotated by the operation of the engine E to generate an electric power.

A liquid-tight switch tube

53

is integrally formed at a central portion of a bottom wall of the housing

52

, and a lead switch

54

is accommodated within the switch tube. An annular float

56

having a permanent magnet

55

embedded in an inner peripheral surface thereof is liftably fitted over an outer periphery of the switch tube

53

. The housing

52

has a through-bore

57

provided therein with its inside communicating with the oil reservoir

17

in the crankcase

3

, so that the oil can flow into and out of the oil reservoir

17

. Therefore, when the oil level in the oil reservoir

17

is dropped until it is equal to or lower than a defined level, the float

56

on the oil is also lowered so that the magnet

55

is closer to the lead switch

54

. Thus, an alarm which is not shown can be automatically operated by closing the switch

54

due to an action of the magnetic force of the magnet

55

.

FIG. 5

shows an example in which the side cover

14

is modified, whereby the engine E is formed into a vertical type for driving a lawn mower. More specifically, a plurality of housing mounting bosses

59

are integrally formed on an outer side surface of the side cover

14

. The engine E is mounted on a cutting edge housing

60

for a lawn mower with the side cover

14

directed downwards, and the cutting edge housing

60

is secured to the housing mounting bosses

59

by a bolt

61

. A cutting edge

62

and a driven pulley

63

for driving a driven wheel through a belt (both not shown) are mounted to the crankshaft

2

within the cutting edge housing

60

.

In this way, when the engine E is used as a vertical type, the oil reservoir

17

is defined in the valve operating chamber

15

with the side cover

14

directed downwards, so that a portion of the valve operating mechanism

19

is immersed in an oil. Thus, the valve operating mechanism

19

can be lubricated without hindrance.

On the other hand, the lower portion of the centrifugal governor

33

is placed in a state in which it is still immersed in the oil of the new oil reservoir

17

. Therefore, the driven gear

40

and the splashing blades

41

of the rotary board

35

splash the oil upwards while agitating the oil to reflect the oil on the inner surface of the crankcase

3

, whereby the crankshaft

2

and the piston

4

as well as the portions around them can reliably be lubricated.

In a case of such vertical-type engine E, the oil dipper

42

mounted to the connecting rod

7

cannot exhibit an intrinsic oil splashing function and hence, no problem occurs even if the oil dipper

42

is removed.

FIG. 6

shows an engine E which is formed into a hand-held type which drives a power trimmer, for example, by modifying the second case half

3

2

. More specifically, an oil tank

65

for storing an oil in a given amount is formed in the second case half

3

2

, and an oil slinger

66

for agitating the oil to produce an oil mist is secured to the crankshaft

2

. The oil mist produced in the oil tank

65

is passed through a through-bore

67

in the second case half

3

2

into the crankcase

3

, thereby lubricating the crankshaft

2

and the piston

4

as well as the portions around them. Further, the oil mist is passed into the valve operating chamber

15

to lubricate the valve operating mechanism

19

. The oil liquefied after finishing of the lubrication is returned to the oil tank

65

through a return pipe

68

provided in the second case half

3

2

. In this way, the various portions of the engine are lubricated by the oil mist and therefore, even if the engine E is used in any inclined state, the lubrication cannot be hindered.

The flywheel

45

secured to the crankshaft

2

is provided with a centrifugal clutch

69

which is operable to connect the flywheel

45

and a working machine B to each other, when the rotational speed of the crankshaft

2

is equal to or higher than a given value.

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

4-cycle engine

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)