Valve drive mechanism for an internal combustion engine

Description

BACKGROUND OF THE INVENTION

The present invention relates to a valve drive mechanism for an internal combustion engine for a portable, manually guided implement, especially a power chain saw.

Small four-stroke engines are known for portable, manually guided implements such as power chain saws, brush cutters, blowers, cut-off machines, or the like. Due to their type of construction with a valve drive mechanism, such engines have a greater overall size in the longitudinal axis of the cylinder than do port-controlled two-stroke engines. Portable, manually guided implements such as power chain saws have an implement housing with a rear handle, as viewed in the longitudinal direction of the housing, as well as a front, upper handle that is generally embodied as a tubular grip. The tubular handle extends form the region of the rear handle from one longitudinal side of the housing of the implement, over the upper side thereof, at an angle toward the front to a forward point of attachment, which is provided on the other longitudinal side of the housing. In order to be able to grip the handle with one hand, it must be appropriately spaced above the implement housing, i.e. above the internal combustion engine contained therein. In so doing, the tubular handle is disposed close to the cylinder head, so that due to the necessary free space relative to the handle a large cylinder requires a correspondingly greater path or orientation for the tubular handle. However, this results in a greater spacing of the handle relative to the center of gravity of the portable implement, which can adversely affect the ability to handle the implement. During use of a valve-controlled internal combustion engine, due to the valve drive that is disposed in the cylinder head the increased spacing of the tubular handle from the center of gravity must be accepted.

It is therefore an object of the present invention to provide a valve drive mechanism for a valve-controlled internal combustion engine such that when used in a portable implement a tubular handle that traverses the housing can be guided closer to the center of gravity of the implement.

BRIEF DESCRIPTION OF THE DRAWINGS

This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which:

FIG. 1

shows a four-stroke engine having poppet valves actuated by push rods;

FIG. 2

is a cross-sectional view through a portable, manually guided implement, namely a power chain saw having an internal combustion engine pursuant to

FIG. 1

;

FIG. 3

is a top view of the portable, manually guided implement of

FIG. 2

with the valve housing open;

FIG. 4

is an enlarged view of the valve housing of

FIG. 3

;

FIG. 5

is a schematic illustration of the cylinder and a protective tube, for push rods, that is spaced from the cylinder in the upright position of the cylinder; and

FIG. 6

shows a four-stroke engine of a modified embodiment having push rods actuated by a common control cam.

SUMMARY OF THE INVENTION

The valve drive mechanism of the present invention is provided for an internal combustion engine of a portable, manually guided implement having an implement housing and a handle that spans the housing and that has a tubular grip disposed adjacent to a cylinder head of the engine, wherein the tubular grip extends from one longitudinal side of the housing to the other longitudinal side thereof; the valve drive mechanism further comprises a valve control having a rocker arm that is pivotably mounted on the cylinder head between the ends of the rocker arm, wherein the rocker arm is pivotable about a pivot axis that is disposed transverse to the longitudinal axis of the rocker arm, wherein such longitudinal axis extends approximately parallel to the adjacent portion of the tubular grip, and wherein a control mechanism is provided that acts on one of the ends of the rocker arm for actuating a poppet valve having a valve stem on which the other end of the rocker arm acts.

By orienting the position of that rocker arm that is immediately adjacent to the tubular handle in conformity with the transverse position of the handle itself, it is possible to provide a guidance of the handle closely adjacent to the cylinder head without thereby adversely restricting the free space between the handle and the implement housing that is necessary for grasping the handle. Thus, even when used with a valve-controlled internal combustion engine, especially a four-stroke engine, in a power chain saw, the spacing of the front tubular handle relative to the center of gravity of the implement can be kept to a minimum. Especially with the greater weight of a four-stroke engine, due to the type of construction, the position of the tubular handle close to the center of gravity of the implement is advantageous for being able to operate the implement without fatigue.

The position of installation of the internal combustion engine in the power chain saw is expediently such that the rocker arm that is disposed approximately parallel to the adjacent portion to the tubular handle controls the exhaust valve of the internal combustion engine. The tubular handle itself extends above the exhaust channel of the internal combustion engine and, when viewed from above, preferably over the inlet into the muffler.

The second rocker arm, which controls the intake valve, is offset in the direction of the longitudinal axis of the first rocker arm by a distance that corresponds approximately to the axial width of a control cam of the valve control mechanism. As a result, in the longitudinal direction of the implement the valve drive mechanism can be narrow; the rocker arms that control the intake and exhaust valves are disposed closely adjacent to one another.

In addition, the rocker arms are advantageously disposed at an angle relative to one another, with the ends of the rocker arms that are actuated by the push rods of the control mechanism facing the apex of the angle. As a result, also the push rods can be disclosed closely adjacent to one another, so that the push rods themselves can be disposed in a common protective tube that, due to the position of the push rods close to one another, can be small.

To minimize disruption of the cooling of the air-cooled cylinder by the protective tube, the latter, at least in the direction of flow of the cooling air, is provided with a flow cross section that reduces the resistance to flow. The protective tube preferably has an outer configuration that is drop-shaped in cross section.

Further specific features of the present invention will be described in detail subsequently.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings in detail, the internal combustion engine

1

schematically illustrated in

FIG. 1

essentially comprises a cylinder

2

, in the cylinder head

3

of which are provided poppet valves

4

, which are not shown in detail.

FIG. 1

shows the valve springs

5

, which surround the valve stems

6

. One end of each valve spring

5

is supported on the cylinder head

3

, while the other end is supported on a valve disk

7

that is secured to the valve stem such that it is axially non displaceable.

Each valve stem

6

of the poppet valves

4

is actuated by means of a control mechanism

8

that by means of a push rod

12

engages one end

9

of a rocker arm

10

that is mounted on the cylinder head

3

. The end of the valve stem

6

of the poppet valve

4

rests against the other end

11

(see

FIG. 4

) of the rocker arm

10

.

The valve control mechanism

8

essentially comprises push rods

12

that are respectively associated with a rocker arm

10

. One end of each push rod

9

is held on a drag or contact lever

13

, while the other end is fixed in position in a recess

14

in the end

9

of the rocker arm

10

.

The drag lever

13

rests upon the cam surface of a control cam

15

and, in conformity with the cam configuration, actuates the drag lever

13

in the direction of the arrow

16

. In so doing, the push rod

12

is axially displaced in the same direction, as a result of which the rocker arm

10

is pivoted about its pivot axis

17

, which is disposed transverse to its longitudinal direction. For this purpose, the rocker arm

10

is held on the cylinder head

3

by means of a support pin

18

.

The mounting is formed by a ball socket

19

that is provided on the rocker arm

10

and that cooperates with a corresponding hemispherical bearing portion

20

of the support pin

18

(see FIG.

2

). In the illustrated embodiment, the support pin

18

is a stay bolt that is tapped into the cylinder head

3

; the bolt shaft

21

that projects from the cylinder head

3

is provided with a thread onto which is screwed a threaded head

22

that is embodied as a nut. In the illustrated embodiment, the threaded head

22

is monolithically formed with the hemispherical bearing portion

20

. By screwing the threaded head

22

on, the bearing distance to the cylinder head

3

can be altered, as a result of which the valve play can be adjusted.

Upon actuation of the push rod

12

, the rocker arm

10

pivots about the spherical mounting and presses the respective stem

6

of the poppet valve

4

down in order to open the intake or exhaust valve. The intake valve communicates with an intake channel

23

by means of which the fresh mixture is supplied. The exhaust valve communicates with an exhaust gas channel

24

that opens into a muffler

25

(see FIG.

2

).

The control cams

15

, which are embodied separately or in common for the intake valve and the exhaust valve, are driven by the crankshaft

26

of the internal combustion engine

1

, and preferably via a gear assembly, a chain drive or a belt drive. The crankshaft rotates in a crankcase

27

.

The rocker arm

10

of the valve drive mechanism is spring loaded by the respective valve spring

5

. The valve force acts via the end

11

of the rocker arm

10

upon the end

9

of the rocker arm that is at the push rod side, and acts further via the push rods

12

upon the drag lever

13

so that the latter is held in engagement against the cam surface of the control cam

15

. If the threaded head

22

is rotated on the threaded shaft

21

in a tightening direction, the bearing spacing “I” is shortened, so that, since the push rod

12

cannot deflect, a pivoting movement of the rocker arm

10

is effected and the valve stem

6

is pressed down. In the opposite direction of rotation of the threaded head

22

, the valve stem

6

is displaced by the valve spring

5

in the direction of a closing of the poppet valve

4

. By rotating the threaded head

22

and altering the bearing spacing, adjustment of the valve play at the poppet valve

4

is effected.

As can be seen from the illustrated embodiment of a power chain saw in

FIGS. 2 and 3

, in the installed position in the portable, manually guided implement the cylinder head

3

is disposed in the implement housing

28

in such a way that it is next to a front, upper tubular handle

30

. The handle

30

, which could also be made of solid material, extends from one longitudinal side

31

of the housing

28

to the other longitudinal side

32

of the housing. In the illustrated embodiment of a power chain saw, the point of attachment

33

on the longitudinal side

31

is disposed near a rear handle

29

, whereas the point of attachment

34

on the other longitudinal side

32

is disposed near the front end face

35

of the power chain saw. The only schematically illustrated guide bar

36

, with the circulating saw chain, is disposed at right angles to the front end face

35

and is held in a clamped manner between the chain or sprocket wheel cover

37

and the implement housing

28

.

The rear handle

29

extends approximately in the direction of the longitudinal central axis

40

of the implement housing

28

; the guide bar

36

of the saw is disposed approximately parallel to the longitudinal central axis

40

.

Due to the selected points of attachment

33

and

34

, the handle

30

which spans and is spaced from the upper side of the implement housing

28

, is disposed transverse to the longitudinal central axis

40

, whereby the angle

38

of the handle portion

39

that is disposed above the implement housing

28

, which angle is directed toward the point of attachment

34

, is less than 90°. Thus, the handle portion

39

that extends above the implement housing

28

extends from the point of attachment

33

on the longitudinal housing side

31

at an incline in the direction toward the front end face

35

.

As can also be seen from

FIG. 4

, the handle portion

39

is disposed above the exhaust gas channel

24

of the internal combustion engine

1

approximately in the region over the inlet

41

of the muffler

45

. In order to provide an adequately large gripping space

42

between the upper handle portion

39

and the cylinder head

3

, the position of the rocker arm

10

that is disposed adjacent to the handle

30

is selected such that the longitudinal axis

44

of the rocker arm extends approximately parallel to the adjacent portion

39

of the handle

30

. Thus, while providing an adequately large gripping space

42

, the handle

30

can be guided close to the implement housing

28

without having disruptive portions of the valve housing, which the rocker arm spans, projecting into the gripping space.

In this connection, the position of the internal combustion engine

1

is selected such that the muffler

25

faces the front end face

35

, in other words the working region, and the rocker arm

10

that is disposed approximately parallel to the upper handle portion

39

controls the exhaust valve

43

. The internal combustion engine

1

, which is embodied as a valve-controlled two-stroke or four-stroke engine, is provided with a respective intake valve

45

and an exhaust valve

43

. The second rocker arm

10

, which is disposed in the valve housing, controls the intake valve

45

, whereby the pivot bearing of the intake valve that is formed on the support pin

18

is offset in the direction of the longitudinal central axis

44

of the first rocker arm

10

by a distance “a”. In conformity therewith, the recesses

14

in the ends

9

of the rocker arm

10

that are at the push rod side have an offset “a” relative to the longitudinal central axis

40

of the implement. In this connection, the distance or offset “a” corresponds approximately to the axial width of the control cam

15

of the control mechanism

8

to the extend that, as illustrated in

FIG. 1

, the control cams

15

for the intake valve

45

and the exhaust valve

43

are embodied separate from one another and respectively cooperate with a drag lever

13

. In this connection, the drag levers

13

can be mounted on a common shaft or axis

45

.

The first rocker arm

10

, which controls the exhaust valve

43

and is disposed approximately parallel to the handle portion

39

, i.e. to the longitudinal central axis

49

thereof, and the second rocker arm

10

which controls the intake valve

45

, have their longitudinal axes form an angle

46

relative to one another that in the illustrated embodiment is approximately 15°. The angle

46

can range from 10-30°.

Those ends

9

of the rocker arms

10

that are actuated by the push rods

12

of the control mechanism

8

face the apex

47

of the angle

46

, so that in the longitudinal direction of the longitudinal central axis

40

of the implement, i.e. of the internal combustion engine

1

, only a small overall width results so that, as shown in

FIG. 1

, the push rods can extend closely adjacent to one another.

The close position of the push rods

12

relative to one another structurally provides the possibility for guiding the push rods

12

in a common protective tube

50

, as schematically illustrated in FIG.

5

. The protective tube

50

has an inner, oval cross section

51

, in the oppositely disposed ends of which the push rods

12

extend. The cylinder

2

, which is similarly shown only schematically in

FIG. 5

, is an air-cooled cylinder having fins or ribs, as can be seen, for example, in

FIGS. 2 and 4

. The protective tube

50

extends next to the vertical cylinder

2

at a lateral spacing “b” therefrom. In order to ensure an adequate cooling of the cylinder

2

in the region of the protective tube

50

, the protective tube, at least on that side thereof that faces the direction of flow

52

of the cooling air

53

, is embodied as a flow body that reduces the resistance to flow, with the protective tube

50

preferably having an outer, drop-shaped flow cross section, as shown in FIG.

5

. This configuration forces the cooling air

53

into the gap

54

between the cylinder

2

and the protective tube

50

. The danger of clogging due to dirt, wood chips, or the like is minimized while at the same time ensuring a good air cooling of the cylinder

2

, even in the region of the protective tube

50

.

It can be expedient to embody the control mechanism

8

of the valve control in such a way that each push rod

12

a

,

12

b

via a separate drag lever

13

a

,

13

b

runs on a common cam surface

48

. In this connection, only a single control cam

15

is provided, on the cam surface

48

of which the drag levers

13

a

,

13

b

are disposed one after the other as viewed in the direction of rotation

55

. Both of the drag levers

13

a

and

13

b

are towed or dragged; due to the identical cam contour, the stroke of both drag levers is the same. Each drag lever is expediently mounted via its own axis of rotation

45

a

,

45

b

. In other respects, the construction of the internal combustion engine

1

of

FIG. 6

corresponds to that of

FIG. 1

, for which reason the same reference numerals have been used for the same part.

The rocker arms

10

are advantageously produced as shaped parts that are made in particular from a sheet of steel. As shown in

FIG. 4

, each rocker arm

10

has a base

60

that is provided with the ball socket

19

between its ends

9

and

11

. To reinforce the base

60

, the longitudinal edges thereof are provided with side walls

61

and

62

, which are preferably monolithically formed on the base. The rocker arm

10

has a U-shaped cross-sectional configuration as can also be seen from FIG.

2

. In this connection, the open side of the U-shaped cross section faces away from the cylinder head

3

.

The specification incorporates by reference the disclosure of German priority document 100 43 232.8 filed Sep. 2, 2000.

The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.

Claims

1. A valve drive mechanism for an internal combustion engine of a portable, manually guided implement having an implement housing and a handle that spans the housing and that has a tubular grip disposed adjacent to a cylinder head of the internal combustion engine, wherein said tubular grip extends from one longitudinal side of said implement housing to another longitudinal side thereof, said valve drive mechanism further comprising:a valve control having a rocker arm that is pivotably mounted on said cylinder head between end of said rocker arm, wherein said rocker arm is pivotable about a pivot axis that is disposed transverse to a longitudinal axis of said rocker arm, and wherein said longitudinal axis extends approximately parallel to an adjacent portion of said tubular grip; and a control mechanism that acts on one, of said ends of said rocker arm for actuating a poppet valve having a valve stem on which the other end of said rocker arm acts.
2. A valve drive mechanism according to claim 1, wherein said rocker arm that is disposed approximately parallel to said adjacent portion of said tubular grip controls an exhaust valve of said internal combustion engine.
3. A valve drive mechanism according to claim 1, wherein said control mechanism is provided with at least one push rod that is actuated by a control cam, and wherein that end of said push rod that is remote from said control cam rests against said rocker arm.
4. A valve drive mechanism according to claim 1, wherein a second rocker arm is provided, and wherein a mounting of said second rocker arm is offset, in a direction of said longitudinal axis of said first mentioned rocker arm, by a distance relative to a mounting of said first mentioned rocker arm.
5. A valve drive mechanism according to claim 4, wherein said distance corresponds approximately to an axial width of a control cam of said control mechanism.
6. A valve drive mechanism according to claim 4, wherein said second rocker arm controls an intake valve of said internal combustion engine.
7. A valve drive mechanism according to claim 4, wherein said first mentioned rocker arm, which is disposed approximately parallel to said adjacent portion of said tubular grip, and said second rocker arm are disposed at an angle relative to one another, and wherein said ends of said rocker arms that are actuated by said control mechanism are directed toward an apex of said angle.
8. A valve drive mechanism according to claim 7, wherein said control mechanism includes push rods for said rocker arm, and wherein said push rods are disposed in a common protective tube.
9. A valve drive mechanism according to claim 8, wherein said internal combustion engine has an air-cooled cylinder, wherein said protective tube is spaced from said cylinder, and wherein said protective tube has a flow cross section that relative to a direction of flow of cooling air reduces resistance to flow.
10. A valve drive mechanism according to claim 9, wherein said protective tube has an outer drop-shaped flow cross section.
11. A valve drive mechanism according to claim 8, wherein said protective tube extends over an exhaust channel of said internal combustion engine.
12. A valve drive mechanism according to claim 11, wherein said protective tube is disposed over an inlet of a muffler.
13. A valve drive mechanism according to claim 7, wherein a single control cam is provided for actuating said push rods.

Priority Claims (1)

Number	Date	Country	Kind
100 43 232	Sep 2000	DE

US Referenced Citations (1)

Number	Name	Date	Kind
5029393	Nagashima et al.	Jul 1991	A

Valve drive mechanism for an internal combustion 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)

US Referenced Citations (1)