DE9117244U1 - Portable implement, especially lawn mowers - Google Patents

Description

^GRÜNECKER, KINKELDEY, STOCKMAIR & SCHWANHÄUSSER

LAW FIRM

• · ·· ♦

LAW FIRM MAXIMIUANSTRASSE 58 D-80538 MUNICH GERMANY-

Applicant:

RYOBI-TECH LIMITED

INTELLECTUAL PROPERTY DEPT. 762 MESAKI-CHO, FUCHU-SHI HIROSHIMA-KEN, 726 JAPAN

Branch from P 41 39 411.9-13

LAWYERS

DR. HERMANN SCHWANHÄUSSER
DR. HELMUT EICHMANN
GERHARD BARTH
DR. ULRICH BLUMENRÖDER, LL. M.
CHRISTA NIKLAS-FALTER

YOUR REF.

OUR REF.

PATENT ATTORNEYS

EUROPEAN PATENT ATTORNEYS

AUGUST GRÜNEECKER

DR. HERMANN KINKELDEY

DR. WILFRIED STOCKMAIR (-1990)

DR. KLAUS SCHUMANN

PETER H. JAKOB

DR. GUNTER BEZOLD

WOLFHARD MEISTER ·

HANS HILGERS

DR. HENNING MEYER-PLATH

ANNELIE EHNOLD

THOMAS SCHUSTER

DR. WALTER LANGHOFF

DR. KLARA GOLDBACH

MARTIN AUFENANGER

GOTTFRIED KUTZSCH

DR. HEIKE VOGELSANG-WENKE

REINHARD KNAUER

DIETMAR KUHL

DR. FRANZ-JOSEF ZIMMER

BETTINA K. REICHELT

DR. ANTON K. PFAU

DR. UDO WEIGELT

DATE

G 3830-20/Sü

23.12.97

Portable work equipment, especially lawn mowers

TEL 089 / 21 23 50 · FAX (GR 4) 089 / 21 86 92 93 · FAX (GR 3) 089 / 22 02 87 · http://www.grunecker.de ■ e-mail: postmaster@grunecker.de · TELEX 529 380 MONA D MAXIMIUANSTRASSE 58 ■ D-80538 MUNICH DEUTSCHE BANK MUNICH, NO. 17 51734, BLZ 700 700 10 "

Portable work equipment, especially lawn mowers

The invention relates to a portable working device, in particular a lawn mower, with an internal combustion engine, a handle part and a working device that can be driven by the internal combustion engine, wherein the internal combustion engine is designed as a single-cylinder engine with a crankshaft, a connecting rod and a piston in a split engine housing having a cylinder block and a crankcase.

A tool of this type is known from US Patent 4,815,430. The combustion engine is a two-stroke engine, which means that when working with the tool the environment is polluted by dirty exhaust fumes and noise. In addition, the two-stroke engine is relatively expensive to produce and has high consumption.

Four-stroke combustion engines in single-cylinder design have been known for a long time. For example, JP 51-123416 A shows such an engine, the valve train of which has a crankshaft gear that is firmly connected to the crankshaft, a camshaft gear that is firmly seated on a camshaft in a cam chamber, and a single cam that is non-rotatably connected to the camshaft gear. The cam works together with two rocker tappets mounted on a tappet axis, which in turn actuate two pushrods. Each rocker arm sits on its own rocker arm axis, which runs parallel to the crankshaft.

Four-stroke engines, even single-cylinder versions with a structurally simple valve train, were not installed in portable work equipment, despite their well-known advantages in terms of running noise, purity of exhaust gases and lower consumption, because they were considered too heavy and bulky.

The invention is based on the object of designing a portable working device of the type described at the outset in such a way that it is less harmful to the environment in terms of exhaust gases and noise development and is inexpensive to manufacture.

This object is achieved according to the invention by the following features:

a) the internal combustion engine is a four-stroke engine (53) with valves (151,152) and a valve chamber (146);

b) the cylinder block (132) and the crankcase (130) of the four-stroke engine are made of an aluminium alloy;

c) a valve train (60) for controlling the valves (151,152) is arranged on the output side of the crankshaft (101) and consists of

C ₁ ) a crankshaft gear (102) firmly connected to the crankshaft (101),

C ₂ ) a camshaft gear (103) fixedly mounted on a camshaft (104) in a cam chamber (140) and meshing with the crankshaft gear,

C ₃ )" a single cam (120) connected to the camshaft gear in a rotationally fixed manner,

C ₄ ) two oscillating tappets (121,122) mounted on a tappet axis (123) and resting against the cam,

C ₅ ) two push rods (141,142) actuated by the oscillating tappets, and

C ₆ ) two rocker arms (143, 144) which can be acted upon by the push rods and act on the valves (151, 152), preferably mounted on a common rocker arm axis, wherein

C ₇ ) the axes of the cylinder and the crankshaft as well as the camshaft and the tappet axis lie in a common plane and the rocker arm axis is preferably perpendicular to the common plane, and

d) an oil mist lubrication device with an oil reservoir (139) and an oil swirling extension (138) immersed in the oil reservoir is provided on the crankshaft.

seen, by means of which an oil mist can be introduced into the cam chamber (140) and from there through a cover (145) of the push rods (141,142) into the valve chamber (146).

Due to the four-stroke engine used as the drive, the tool according to the invention generates little noise and emits relatively clean exhaust gases. Due to the comparatively lower manufacturing costs and the lower consumption of the four-stroke engine, the tool can also be produced and operated inexpensively. The engine used in the tool according to the invention is light due to the use of an aluminum alloy for essential components and the use of a simple oil mist lubrication device and can be built compactly due to the design and arrangement of the valve train, so that the tool is surprisingly small and light enough to be carried without any problem despite the use of a four-stroke engine.

The camshaft gear and the cam are conveniently designed as one piece. This contributes to a short and simple design of the engine.

Preferably, the contact points between the oscillating tappets and the push rods are arranged in a plane perpendicular to the common plane. This measure also contributes to the compact design of the engine.

To further simplify and reduce the size of the engine, the cam chamber can be designed as a single piece with the cylinder.

A further weight reduction is achieved if the oscillating tappets are made of an aluminum alloy, whereby the service life can be increased if the oscillating tappets have a wear-resistant bearing sleeve and/or wear-resistant inserts at the contact points with the push rods.

Conveniently, the push rods consist essentially of an aluminum alloy and preferably have ferrous contact materials at their ends.

This also allows a reduction in weight without affecting the service life.

The cylinder head is expediently essentially a cast part made of a light metal alloy in particle dispersion form, in particular with a Si content of 13.5-16% by weight, in which valve guides and valve seats are integrated. This also results in a simple and lightweight construction in the cylinder head area.

Finally, it is advantageous if the crankshaft gear and/or the camshaft gear have a bearing body with a fitting opening for the associated shaft and a spur gear protruding axially from the bearing body. In this way, the gears can be built with a small radial diameter and still have a spur gear that is easy to manufacture and low-wear.

The invention is explained below using exemplary embodiments in conjunction with the drawing. They show:

Fig. 1 shows a perspective view of a working device according to the invention, carried by an operator,

Fig. 2 is a vertical section through the combustion engine of a first embodiment.

form of a working device according to the invention,

Fig. 3 is a detailed view from the front of a part of the valve train of the engine according to

Fig.2,

Fig. 4 is a detailed plan view of the oscillating tappets of Fig. 3,

Fig. 5 and 6 partial representations of the valve train of the engine according to Fig. 2 to illustrate the mode of operation,

Fig. 7A and 7B Diagrams to illustrate the relationships between the cam rotation angle and the stroke speed at the intake and exhaust

Exhaust side of the engine according to Fig. 2,

Fig. 8 is a diagram illustrating the opening and closing times of the

Valves of the engine according to Fig. 3,

Fig. 9 is a sectional view along the line IX in Fig. 2,

Fig. 10 is a sectional view along the line X in Fig. 2,

Fig. 11 is a sectional view along the line Xl - Xl in Fig. 9,

Fig. 12 a vertical section through the combustion engine of a second embodiment of the working device according to the invention,

Fig. 13-15 Views of modified oscillating tappets,

Fig. 16 is a view, partly in section, of a modified pushrod,

Fig. 17 is a partial section through the upper part of a

modified combustion engine for a working device according to the invention,

Fig. 18 a vertical section through another embodiment of an internal combustion engine for a working device according to the invention,

Fig. 19 is a perspective view of the crankshaft gear of the engine

according to Fig. 18,

Fig. 2OA is a front view, and

Fig. 20B shows a vertical section of the crankshaft gear according to Fig. 19.

A first preferred embodiment is explained in more detail with reference to Figs. 1 to 11, which relate to a portable working device, such as a lawn mower 50, which is shown in Fig. 1.

The lawn mower 50 according to Fig. 1 has a long power transmission part 51, an operating part 52 on which a handle part 52a is provided, a four-stroke internal combustion engine 53 which is fixedly attached to one end of the power transmission part 51, and a working device 54 with, for example, a mowing blade 54a which is fixedly attached to the other end of the part 51. The part 51 comprises an outer tube and an inner shaft which is connected to the crankshaft of the internal combustion engine via a coupling device. The shaft is rotatably mounted in the outer tube and transmits the power to the working device 54 and thus to the mowing blade 54a.

In use, the lawn mower 50 is carried by an operator 55 who, for example, stands on the right side of the engine 53 as shown in Fig. 1, and holds and grips the handle 52a. With this working position in mind, an exhaust silencer 56 is provided to prevent the operator from being exposed to heated exhaust gases and is provided on the side of the engine 53 facing away from the operator. An air intake opening 57 of a carburetor is provided on the side of the operator.

As shown in Figs. 2 to 4, the internal combustion engine 53 for the lawn mower is equipped with a valve train 60 which is arranged in a main body 131 of the engine 53. The engine has a crankcase 130 and a crankshaft 101 arranged therein, one end of which is formed integrally with a power output shaft 101a which is connected to the shaft of the power transmission part 51. A crankshaft gear 102 is seated on the crankshaft 101 in a rotationally fixed manner, which gear meshes with a camshaft gear 103. Therefore, when the crankshaft gear 102 is set in rotation, the camshaft gear 103 follows this rotational movement and rotates in the opposite direction.

The camshaft gear 103 is mounted on a camshaft 104 which is rotatably mounted on the crankcase 130 and carries a cam 120 which is non-rotatably connected to the cam gear 103. As shown in Fig. 3, a pair of reciprocating or pivoting oscillating tappets 121 and 122 are provided which are arranged such that they come into contact with the cam 120 with their ends. The oscillating tappets 121 and 122 can be pivoted about a common tappet axis 123, via which the two tappets are operatively connected to one another. The tappet axis 123 and the camshaft 104 are arranged in a plane which is formed by the plane of the drawing in the illustration of Fig. 2. Furthermore, a camshaft 101 and the cylinder center axis Oa are shown. The tappet axis 123, the camshaft 104 and the crankshaft 101 are arranged parallel to each other.

One of the rocker tappets 121 is connected to a push rod 141 for the exhaust valve and the other rocker tappet 122 is connected to a push rod 142 for the intake valve. The push rods 141 and 142 are moved back and forth. The rocker tappets 121 and 122 are made of one and the same material and are arranged so that they face each other, as can be seen in plan view in Fig. 4. The rocker tappets are bent so that the left end of the tappet 121 points upwards and the right end of the tappet 122 points downwards, as shown in Fig. 4. Consequently, a contact point 141a with the push rod 141 and a contact point 142a with the push rod 142 are located on the same plane K, which is perpendicular to the push rod axis 123. Furthermore, the center axes 121a and 122a of the rocker tappets 121 and 122 are designed to intersect at an angle at the center of the cam shaft 104 when the rocker tappets come into contact with the cam peripheral part 120a of the cam 120. The rocker tappets 121 and 122 have free ends which are designed as flat plate-like sections 121b and 122b and which come into contact with the periphery of the cam 120. The contact points 141a and 142a are arranged symmetrically to the tappet axis 123, as can be seen from Fig. 3.

As described above, the exhaust valve 151 and the intake valve 152 (see Fig. 2) are actuated by a cam 120 via a pair of rocker tappets and associated pushrods. The valve train 60 therefore comprises the rocker tappets 121, 122, the cam gear 103 and the cam 120, which are arranged in a cam

chamber 126, which is fastened to the crankcase 130, for example by means of screws.

The reciprocating push rods 141 and 142 for the exhaust valve and the intake valve are respectively connected to a pair of rocker arms 143 and 144, which are pivotally provided in a valve chamber 146 formed in an upper part of the engine main body 131. The rocker arms 143 and 144 are respectively connected to the exhaust valve 151 and the intake valve 152, which are arranged in the cylinder head 136 at the upper end of the cylinder 132. Thus, these valves 151 and 152 are operated by the rocking movements of the rocker arms 143 and 144.

The crankshaft 101 is rotatably supported by bearings 101b and 101c and carries a flywheel 133 on the side of the output shaft 101a.

Therefore, when the crankshaft 101 rotates in the counterclockwise direction W ₂ due to the movement of the piston 134 in the cylinder 132, the camshaft gear 103, which meshes with the crankshaft gear 102, is rotated in the clockwise direction W ₃ as shown in Fig. 3. At the same time, the cam 102, which is fixedly attached to the camshaft gear 103, is also rotated in the clockwise direction W _3. In response to this rotation, the rocker tappet 121 is first moved clockwise, and the push rod 141 for the exhaust valve 151 is displaced upward to thereby open the exhaust valve 151 via the movement of the rocker arm 143. Then, the cam 120 continues to rotate and the contact point of the rocker tappet 121 slides over the projecting portion 120b (Fig. 5) of the cam 120. From this point on, the rocker tappet 121 is moved in the counterclockwise direction, so that the exhaust valve 151 is then actuated in the closing direction. Immediately before the closing of the exhaust valve 151, the intake valve 152 is actuated in the opening direction. In particular, during the further rotation of the cam 120, the other rocker tappet 122 is pivoted in the counterclockwise direction and the push rod 142 for the intake valve 152 is moved upward to thereby open the intake valve 152 via the movement of the rocker arm 144. The exhaust valve 151 is then closed. Then, when the cam 120 continues to rotate, the

Rocker tappet 122 is moved clockwise and intake valve 152 is actuated in the closing direction by movement of pushrod 142 and rocker arm 144. When intake valve 152 is closed, one operating cycle of the exhaust and intake valves is completed.

As shown in Fig. 5 or 6, the cam 120 has an outer contour which includes a circular portion 120a, the maximum protruding portion 120b and portions 120c and 120d with symmetrical shape and reduced diameter of the intermediate arrangement.

As described above, in this preferred embodiment, since the pivotable rocking tappets 121 and 122 are rocked back and forth by the cam 120, the length of the cam 120 in the axial direction of the camshaft 101 can be made short to obtain the length i ₂ which, as shown in Fig. 2, is shorter than the length required for a conventional four-stroke internal combustion engine. The weight can also be reduced due to the position and arrangement of this one cam 120. Furthermore, in the conventional design, it is necessary to have a large space available in order to be able to arrange the tappets. In the preferred embodiment according to the invention, however, this space can be reduced.

The operations of the cam 120 and the rocker arms 121 and 122 are explained in more detail below with reference to Figs. 5 to 7.

Referring to Fig. 5, the cam 120 has a symmetrical external configuration. That is, the outer peripheral surfaces 120a and 120d of the ascending side and the descending side with respect to the associated push rods 141 and 142 are formed symmetrically to the maximum lift position, ie, to the most protruding portion 120b of the cam 120. The cam 120 rotates about the rotation center A ₀ which is the center of the cam shaft 104. The paired rocking tappets 121 and 122 are reciprocated about the center B ₀ of the rocking movement of the tappet axis 123.

According to the cam design form described above, the lift curves of the exhaust valve 151 and the intake valve 152 can be designed differently.

Specifically, referring to Figs. 5 and 6, if the radius of the central portion 120a of the cam 120 is R, the tilt angles of the rocking tappets 121 and 122 are α and β, and the distance between the tilting motion center B ₀ of the rocking tappets 121 and 122 and the push rods 141 and 142 are respectively denoted by L. The stroke amounts of the push rods 141 and 142 can thus be expressed by this distance in the following manner: (L χ α) and (L χ β). The quantity X denotes a coordinate axis which is fixedly assigned to the cam 120, and the quantity θ denotes a coordinate axis which is fixedly assigned to the cam 120. denotes a relative angle to the axis X at the time when the cam 120 and the contact points 121b and 122b move on the outer contour of the cam 120.

When the angle θ is not equal to the rotation angle of the cam shaft 104, this angle becomes φ. Under this condition, a distance between the contact points P and Q with the cam 120 (Q: contact point with the circular portion 120a of the cam 120) is expressed as dy/d9 according to the design equation, and assuming that the angle α (or β) of the contact surface 121b (or 122b) which contacts the circular portion of the cam 120 is denoted as Ct ₀ (or β ₀ ), the distance between the rocking motion center B ₀ of the rocking tappets 121,122 and the rotation center A ₀ of the cam 120 is expressed as C according to the following equation.

C χ sin (α + Ot ₀ ) = (R + y + a)

α + OC ₀ = sin' ¹ [(R + y + a) / C]

φ = θ + (α +

From these equations we then obtain the following equations: dct/cty = (dy/de) / [dy/de + Ccos (α + α ₀ )]

Since the lifting speed of the push rod 141 for the exhaust valve can be expressed as L · dy/de, the lifting speed Mi of the push rod 141 at the time of lifting becomes smaller than at the time of lowering (at the time of lowering) even if the absolute value of dy/de is the same at both times of operation. The reason for this is that the value of dy/de becomes negative during lifting, while it becomes positive during lowering.

From the foregoing, it can be seen that in the preferred embodiment of the invention, in which the outer peripheral shape of the portions of the cam 120 which act on the push rod to perform a lifting movement and a lowering movement are designed symmetrically, the lifting speed of the push rod 141 for the exhaust valve according to Fig. 7A is lower than the lowering speed, thereby obtaining more favorable characteristics than usual.

Furthermore, taking into account the push rod 142 for the intake valve according to Fig. 6, the reciprocating direction of the oscillating tappet 122 is selected to be the opposite of that of the oscillating tappet 121, which is assigned to the push rod 141 for the exhaust valve. This gives the following equations:

C x sin (ß + ßo) = (R + y + a)
β + ßo = sin" ¹ [(R + y + a)/C]
φ = θ-(β + β ₀ )

From these equations, the following equation can be derived: dß/αφ = (dy/αφ) / [-dy/de + C χ cos (ß + ß ₀ )]

Thus, since the lift speed M ₂ (Fig. 7B) of the push rod 142 for the intake valve at the lift time is greater than that at the downward movement time (lowering time) even if the absolute value dy^ is equal on both sides, in the preferred embodiment according to the invention in which the portions of the cam 120 which act on the push rod in the lift direction and in the lowering direction

beat, are arranged symmetrically, select the lifting speed of the push rod 142 for the intake valve according to Fig. 7B to be greater than the lowering speed, so that the rotational speed of the crankshaft 101 becomes greater and thus the output power is greater.

The reference symbols N ₁ and N ₂ in Fig. 7A and 7B indicate the stroke sizes.

Various tests have shown that it is desirable for the ratio of the lifting speed of the push rod 141 (and 142) to the lowering speed of the same to be in a range of 120 to 170% on the exhaust side but in a range of 83 to 58% on the intake side.

Fig. 8 is a timing chart showing the valve opening/closing timing of the exhaust valve 151 and the intake valve 152.

Referring to Fig. 8, the intake valve 152 is opened at an angle φ 2 of 20°, for example, before the suction top dead center e ₀ and is closed at an angle φ ₂ of 60°, for example, after the suction bottom dead center ei . On the other hand, the exhaust valve 151 is opened at an angle φ ₂ of 60°, for example, before the expansion bottom dead center and is closed at an angle φ _; of 20°, for example, after the suction top dead center (φ 2 and φ ₂ : rotation angle of the crankshaft 101).

Since the cam 120 has mutually symmetrical parts on the push rod lifting and lowering movement sides, the maximum lift size of the push rod 141 for the exhaust valve is at a location according to the following angle before the upper suction dead center e ₀

0.5(ϕ&igr; + ϕ ₂ + 180) - ϕ&igr; = 0.5(180 + ϕ ₂ -ϕ,).

The maximum stroke of the push rod 142 for the intake valve is obtained at a point according to the following angle after the upper suction dead center e ₀ :

+ ϕ ₂ + 180) - ϕ! = 0.5(180 + ϕ ₂ -

Thus, the relative angle (Fig. 3) subtended by the center lines 121a, 122a of the rocker arms 121, 122, which is expressed as 0.5 (180 + _φ2 - φα) taking into account the angle of rotation of the cam 120, is half (1/2) of the crankshaft 101. As described above, the value of the angle is selected to be 0.5 (180 + φ2 - φα), for example, 0.5 (180 + 70 - 20)° = 110°, and is equal to the angular difference of the maximum lift amounts of the intake and exhaust sides assuming that _φ1 = 20° and φ2 = 1. ₂ = 60°, these calculations being based on the valve opening and closing times. Thus, the upper part of the cam is arranged lying towards the central direction of the lift axis 123, and this means that the line connecting the upper part 120a of the cam 120 to the center of rotation A ₀ of the camshaft coincides with the direction of the reciprocating movement of the piston, whereby the valve opening/closing times of both the exhaust valve and the intake valves 151 and 152 can be maintained.

The precise assembly of the crankshaft gear 102 and the camshaft gear 103 at the time of assembling the internal combustion engine 53 will be explained in more detail below with reference to Figs. 9 to 11, taking the following statements into account.

The crankshaft gear 102 is fixedly connected to the crankshaft 101 by means of two keys or bolts 170, and the cam 120 is fixedly connected to the camshaft gear 103 by means of two keys or bolts 172. When the crankshaft 101 is moved to top dead center, the keys 170 lie on a line 171 which connects the center of the crankshaft 101 to the center of the crank pin 135. In this state, the center portion of a gear tooth 102a, which is located on the upper part of the crankshaft gear 102, also lies on this line 171. In this state, the splines 172 of the camshaft gear 103 lie on a line 174 which connects the center of the camshaft gear 103 with the upper cam portion 120b of the cam 120, and an intermediate position 173 of two teeth 103a and 103b, which are adjacent to each other on the camshaft gear 103, is obtained, and

these are arranged opposite the upper cam section 120b and also lie on the line 174. Since the camshaft 104, to which the camshaft gear 103 is firmly connected, is rotatably mounted on the crankcase 130, the positional assignment of the camshaft gear 103 and the crankshaft gear 102 can be easily achieved during assembly.

A linear identification mark Z-Z for indicating the position of the camshaft gear 103 is formed in the surface 103c of the camshaft gear 103 on the side of the flywheel 133 so as to be perpendicular to the line 174. When the crankshaft 101 is at the top dead center, a distance f between the center of the camshaft 104 and the identification mark Z-Z becomes substantially equal to a distance D between a mounting surface F-F (see Fig. 2) of the cylinder 132 to the crankcase 130 and the center of the camshaft 104 (see Fig. 2). The identification mark Z-Z is formed as a linear groove. If necessary, it may be replaced by points Za and Zb provided on the surface 103c of the camshaft gear 103.

In assembling the transmission device having the above-described structure, the crankshaft 101 is first rotated to position the piston 134 at the top dead center, as shown in Fig. 10. This operation is normally carried out before the cylinder head 136 is mounted so that the operations required for this can be easily carried out. Then, the camshaft gear 103 is mounted so that it is in meshing engagement with the crankshaft gear 102, while at the same time the identification mark Z-Z (or the points Za and Zb) provided on the surface 103c of the camshaft gear 103 is moved to a part which is parallel to or overlaps the mounting surface F-F (state in Fig. 9). According to this alignment assembly process, the tooth 102a of the crankshaft gear 102 is precisely engaged with the intermediate portion between the two teeth 103a and 103b of the camshaft gear 103, so that a reliable and secure engagement state is obtained.

If, according to the above explanations, the meshing between the gears 102,103 cannot be checked visually during the assembly step, the

The exact meshing can be easily monitored visually by observing the identification marking Z-Z.

A second embodiment of the internal combustion engine is explained in more detail below with reference to Fig. 12.

In this, identical or similar parts are provided with the same reference numerals as in the first embodiment according to Figs. 1 to 11.

As shown in Fig. 12, the cam chamber 126a in which the cam 120, the cam gear 103 and the rocker tappets 121 and 122 are housed is designed integrally with the cylinder 132a. According to this design, the distance between the chamber 126a and the cylinder 132a can be reduced as much as possible. This means that the valve gear 60 and the flywheel 133 can be arranged in close proximity to the crankcase 130 and therefore the distance l _z between the outer surface 25a of the housing 25b and the central portion of the piston becomes small, so that a compact design of the internal combustion engine 53a is achieved.

The crankcase 130, the cylinder 132, the cylinder head 136, etc., which are shown in Fig. 2, for example, are made of an aluminum alloy to reduce the overall weight of the engine. In such a configuration, in general, the push rods 141, 142, the rocker tappets 121, 122, etc., which constitute the valve gear 60, are made of a ferrous material such as steel or cast iron, which has a smaller coefficient of thermal expansion than the aluminum alloy, so that the amount of thermal expansion of the crankcase, the cylinder, the cylinder head, etc. is larger than that of the push rods and the rocker tappets with a temperature rise in the driving state of the engine. This adversely affects the timing of opening or closing the intake/exhaust valve in the cold and warm states of the engine. This difference may cause noise to be generated and may require the valves 151 and 152 and the valve seats to be made of a material having high heat resistance.

_t » φφφφφ « I _t &phgr;&phgr; « ,

In view of the foregoing, the push rods 141, 142 and the rocker arms 121, 122 of the valve train 60 may be formed of an aluminum alloy which is substantially the same as the material from which the crankcase 130, the cylinder 132 and the cylinder head 136 are made, so as to substantially eliminate the differences in the thermal expansion coefficients between these parts.

With reference to Fig. 2, an oil swirling extension 138 is provided on the connecting rod 137 of the piston 134, which swirls up an extremely hot lubricating oil 139 in the crank chamber. The resulting oil mist enters the part 140 of the cam chamber 126 via a gap on the bearing 101 b and spreads into the valve chamber 146 via a cover 145 of the push rods 141 and 142 or lies over them. During this process, the extremely hot oil 139 contacts the swing tappets 121, 122 and the push rods 141, 142, so that these parts expand under heating. However, when these parts are made of an aluminum alloy, the amount of thermal expansion is large compared to the case where ferrous materials are used, and thus a gap between the rocker arms 143, 144 and the valves 151, 152 does not change in size due to heating.

The rocker tappets 121 and 122 according to this preferred embodiment are made of an aluminum alloy. As shown in Fig. 13, the rocker tappets 121f and 122f are firmly connected to a bearing sleeve 181 which has a small thickness and good wear resistance and which is fitted into a tappet axis hole 180. According to Fig. 14, ferrous inserts 182 and 183 are firmly cast at the contact point of the rocker tappets 121g and 122g with the push rods 141, 142.

The rocker arms 121h and 122h shown in Fig. 15 are made substantially entirely of an aluminum alloy.

The push rods 141b and 142b are made essentially of an aluminum alloy. However, as shown in Fig. 16, ferrous contact materials 184

be firmly provided on those parts where contact is made with the rocker arms 121, 122 and the rocker arms 143, 144. These parts can be attached by means of a press fit.

By making the rocker arms 121, 122 and the pushrods 141, 142 from aluminum alloy, the dead weight of the valve train can be reduced considerably. Therefore, the use of an aluminum alloy as the material for the rocker arms 143 and 144 results in an extremely advantageous and effective design.

In the first preferred embodiment shown in Fig. 2, a valve guide 190 for guiding the valves 151 and 152 and a valve seat 191 are formed as independent, separate parts. According to the embodiment shown in Fig. 17, the cylinder head 136a can be formed as an integrally designed casting comprising the valve guide and the valve seat, the cylinder head 136a being made of an aluminum alloy containing silicon at 13.5 to 16 wt.%. According to this embodiment, the difference in thermal expansion between the cylinder head and the other parts made of the aluminum alloy can be substantially eliminated, and excellent wear properties can be obtained. Furthermore, the number of individual parts to be assembled and the number of machining operations can be reduced. Furthermore, in the case where the cylinder head 136a is formed of a light metal alloy by means of particle diffusion, high strength is achieved and favorable wear resistance properties can be obtained.

A further embodiment according to the invention is explained in more detail below with reference to Figs. 18, 19, 20A and 20B, in which the same or similar parts as in the embodiments described above are provided with the same reference numerals.

In this embodiment, the design of the crankshaft gear 102 (Fig. 2) is improved. The crankshaft gear shown in Fig. 2 is designed as a spur gear. Such a gear generally has a central circular portion and a toothed portion formed on the outer circumference of the central portion. In a spur gear with this design, it is necessary to have a predetermined thickness.

ke in the radial direction of the central portion 352a to prevent breakage of the gear. Therefore, when using a conventional spur gear as the crankshaft gear, there are limits to the reduction in diameter.

To overcome this difficulty, according to the embodiment of Figs. 18, 19, 20A and 20B, the crankshaft gear is improved in its construction. In particular, referring to Figs. 18 and 19, a crankshaft gear 302 is formed as an annular gear having an inner columnar cavity, and the outer periphery and the inner periphery of this gear 302 are formed concentrically. The crankshaft gear 302 thus has a hollow bearing body 352 having an inner fitting hole 351 and a toothed portion 354 having a plurality of teeth forming the gearing formed in an axially projecting manner on a side surface of the bearing body 352, as can be seen most clearly from Fig. 19. The toothed part of the camshaft gear 103 is in spur gear engagement with the toothed part 354 of the crankshaft gear 302 to thereby cause the camshaft gear 103 to rotate in accordance with the rotational movement of the crankshaft 101 via this meshing engagement.

The diameter of the base circle of the crankshaft gear 302 is denoted by Dp in Fig. 20A, B, and the diameter of the fitting hole 351 is denoted by Di. The diameter Dp of the base circle with respect to the axial diameter Dj of the crankshaft 101 which is suitably fitted into the fitting hole 351 can be expressed as follows: Dp = Dj + αδ, that is, αδ = Dp - Dj. Further, since the diameter Dj is almost equal to the inner diameter Di, Dj» Di ₁ holds, thus obtaining the following expression: cti = Dp - Di. Now, denoting a height of a tooth base line of each tooth of the toothed part 354 by Dm as shown in Fig. 20A, the diameter Dp can be expressed as Dp = Di + 2 × Dm, thus obtaining αδ. = Di + 2 &khgr; Dm - Di = 2 &khgr; Dm. Thus, the diameter Dp can be expressed as Dp = Dj + 2 &khgr; Dm!

On the other hand, the diameter Dp of a conventional spur gear can be expressed as Dp = Dj + ßi, in which P ₁ = Dp - Dj and Dj« Di, as well as P ₁ = Dp - Dj. Thus, one obtains

Dp = Di + 2 × Db + 2 × Dm, where, β&ig; = Dj + 2 × Db + 2 × Dm - Di = 2 × Db + 2 × Dm (Dm: height of a tooth radius of the respective gearing on the toothed part; Db: thickness of the bearing part). Consequently, the equation Dp = Dj + 2 × Db + 2 × Dm is obtained.

As can be seen from the comparison given above, in the embodiment according to Fig. 18, the diameter Dp of the base circle of the crankshaft gear 302 with respect to the crankshaft 101 is reduced compared to the conventional spur gear.

In particular, in a conventional gear, in order to reduce the diameter of the base circle, it is necessary to make a shaft which is to be fitted in a suitable manner thin or to make the thickness of the bearing part of the gear small, which, however, results in the strength of the shaft and the gear being reduced. In the embodiment of the invention described above, however, the diameter of the base circle can be made small without changing the diameter of the shaft which is to be fitted in a suitable manner and the thickness of the bearing part of the gear. Therefore, by selecting one and the same diameter for the base circle, the diameter of the shaft can be made large in the embodiment of the invention, so that a crankshaft gear with sufficient strength can be obtained.

The improvement described is not limited to the crankshaft gear. The design of the gear described above can also be used for other gears, such as a camshaft gear. The number and shape of the gear teeth as well as the teeth and gear teeth of the bearing part can be selected accordingly.

Furthermore, it is possible to provide a connecting flange with a thin disk-like design shape at a bottom part of the tooth part of the end face, so that the gearing can be formed integrally in a corresponding manner. Sintering technology or cutting processes can be used to form these gears, and a gear thus produced can be used not only in connection with un-

Not only can this type of gear be used in different internal combustion engine units, but it can also be used in other areas.

Claims (8)

Expectations 1. Portable working device, in particular a lawn mower, with an internal combustion engine (53), a handle part (52a) and a working device (54) which can be driven by the internal combustion engine, wherein the internal combustion engine is designed as a single-cylinder engine with a crankshaft (101), a connecting rod (137) and a piston (134) in a divided engine housing (131) having a cylinder block (132) and a crankcase (130), characterized by the following features: a) the internal combustion engine is a four-stroke engine (53) with valves (151,152) and a valve chamber (146); b) the cylinder block (132) and the crankcase (130) of the four-stroke engine are made of an aluminium alloy; c) a valve train (60) for controlling the valves (.151,152) is arranged on the output side of the crankshaft (101) and consists of C ₁ ) a crankshaft gear (102) firmly connected to the crankshaft (101), C ₂ ) a camshaft gear (103) fixedly mounted on a camshaft (104) in a cam chamber (140) and meshing with the crankshaft gear, C ₃ ) a single cam (120) connected to the camshaft gear in a rotationally fixed manner, C ₄ ) two oscillating tappets (121,122) mounted on a tappet axis (123) and resting against the cam, C ₅ ) two push rods (141,142) actuated by the oscillating tappets and C ₆ ) two rocker arms (143, 144) which can be acted upon by the push rods and act on the valves (151, 152), preferably mounted on a common rocker arm axis, wherein C ₇ ) the axes of the cylinder and the crankshaft as well as the camshaft and the tappet axis lie in a common plane and the rocker arm axis is preferably perpendicular to the common plane, and d) an oil mist lubrication device with an oil reservoir (139) and an oil swirling extension (138) immersed in the latter is provided on the crankshaft, by means of which an oil mist can be introduced into the cam chamber (126) and from there through a cover (145) of the push rods (141, 142) into the valve chamber (146). 2. Tool according to claim 1, characterized in that the camshaft gear (103) and the cam (120) are designed as one piece. 3. Tool according to claim 1 and/or 2, characterized in that the contact points (141a, 142a) between the oscillating tappets (121, 122) and the push rods (141, 142) lie in a plane (K) perpendicular to the common plane. 4. Tool according to one of claims 1 to 3, characterized in that the cam chamber (126a) is designed as one piece with the cylinder (132a). 5. Tool according to one of claims 1 to 4, characterized in that the oscillating tappets (121f - h, 122f - h) consist of an aluminum alloy and are preferably provided with a wear-resistant bearing sleeve (181) and/or wear-resistant inserts (182) at the contact points with the tappet rods (141, 142). 6. Tool according to one of claims 1 to 5, characterized in that the push rods (141b, 142b) consist essentially of an aluminum alloy and are preferably provided with iron-containing contact materials at their ends. 7. Tool according to one of claims 1 to 6, characterized in that the cylinder head (136a) is essentially a cast part made of a light metal alloy in particle dispersion form, preferably with a Si content of 13.5-16 wt.%, in which valve guides and valve seats are integrated. 8. Tool according to one of claims 1 to 7, characterized in that the crankshaft gear (302) and/or the camshaft gear has a bearing body (352) with a fitting opening (351) for the associated shaft and a spur gear toothing (354) projecting axially from the bearing body.