Internal combustion engine for a portable handheld work apparatus

The invention relates to an internal combustion engine for a portable handheld work apparatus such as a motor-driven chain saw or the like. The internal combustion engine includes a cylinder defining a combustion chamber and having an inlet passage for conducting a fuel mixture into the combustion chamber. The cylinder has an annular flange formed thereon and is disposed in surrounding relationship to the inlet passage. An intake pipe defines a longitudinal axis and has an end section. The end section and the annular flange are axially inserted one into the other in overlapping relationship to each other. The annular flange and the end section conjointly define an annular space therebetween radially of the longitudinal axis and a seal is clamped between the annular flange and the end section in the annular space.

FIELD OF THE INVENTION 
The invention relates to an internal combustion engine for a portable 
handheld work apparatus, such as a motor-driven chain saw. 
BACKGROUND OF THE INVENTION 
A device for mounting a carburetor on an internal combustion engine is 
disclosed in U.S. Pat. No. 4,835,866. In this device, the intake pipe is 
attached to a cylinder flange via a sealing ring. The end faces of the 
cylinder flange and the intake pipe face each other and are axially spaced 
relative to each other. The end faces have respective flanges which are 
surroundingly form tight engaged by corresponding ones of axial end 
sections of the sealing ring. The sealing ring is made of an elastic 
material, such as rubber, in order to ensure an adequately high elasticity 
for the assembly and in order to compensate for manufacturing tolerances 
of the cylinder flange and intake pipe. The elastic sealing ring 
attenuates the engine vibrations in order to substantially keep vibrations 
away from the carburetor attached to the intake pipe. 
The sealing ring can swell because of the influence of fuel whereby the 
attachment of the sealing ring to the cylinder flange and to the intake 
pipe can loosen. The integrity of the seal is affected. In this way, 
unwanted air can be inducted whereby the mixture supplied to the engine 
can be changed in a disadvantageous manner. The connection can loosen when 
mechanical loads occur such as intense vibrations or bumping. 
It is also known to fix the sealing ring via pipe clamps on the cylinder 
and on the intake pipe. This connection can withstand higher mechanical 
loading but the sealing ring is subjected to increased loading in the 
region of the pipe clamp connection because of the material being 
squeezed. In this region, the problem of fissure formation is increased 
with the result that the connection will no longer be tight. 
SUMMARY OF THE INVENTION 
It is an object of the invention to configure the connection of an intake 
pipe at the cylinder flange of a cylinder so that a permanent seal is 
ensured, even in the presence of unfavorable influences and so that a 
connection is provided which facilitates assembly and has excellent 
operating reliability. 
The internal combustion engine of the invention is for a portable handheld 
work apparatus, such as a motor-driven chain saw or the like. The internal 
combustion engine includes a cylinder defining a combustion chamber 
interior space and having an inlet passage for conducting a fuel mixture 
into the combustion chamber; the cylinder having an annular flange formed 
thereon and disposed in surrounding relationship to the inlet passage; an 
intake pipe defining a longitudinal axis and having an end section; the 
end section and the annular flange being axially inserted one into the 
other in overlapping relationship to each other; the annular flange and 
the end section conjointly defining an annular space therebetween radially 
of the longitudinal axis; and, a seal clamped between the annular flange 
and the end section in the annular space. 
The seal is tightly clamped radially between the cylinder flange and the 
end section of the intake pipe. This seal ensures a high degree of 
tightness even after being wetted with fuel and after swelling caused 
thereby since the seal is delimited on its radial inner-lying end as well 
as at its radially outer-lying end by the cylinder flange and the end 
section of the intake pipe. Swelling of the seal increases the radial 
pressure in the seal space whereby the seal function is improved. 
A further advantage is the small structural elevation of the connection 
because, as a result of the mutual insertion of parts, the cylinder 
flange, the seal and the end section of the intake pipe have essentially 
the same structural elevation. 
A further advantage is the low number of components and the simple assembly 
and disassembly. Especially for a seal configured to be oversized, the 
component to be inserted in or inserted over is axially fixed without 
additional attachment measures. Additional attaching measures are not 
perforce necessary. The friction lock is provided essentially via the 
total elevation on the radial outer side and inner side of the seal. High 
friction forces can be transmitted which become uniformly distributed over 
the seal wall so that the problem of fissure formation is reduced. 
The cylinder flange is advantageously configured as a radial outer-lying 
component in which the seal and the end section of the intake pipe are 
inserted. The cylinder flange can have an inner-lying annular shoulder 
which defines a stop for the seal to be inserted. The wall of the cylinder 
flange extends from the annular step and the axial structural elevation of 
the wall corresponds approximately to that of the seal. 
An annular gap is provided between the annular step and the end face of the 
end section of the intake pipe. This annular gap has an outer end defined 
by the seal. Swelling of the seal causes the seal to expand radially into 
the annular gap thereby ensuring that the seal retains its elastic 
characteristics. 
The inner wall of the intake pipe and the inner wall of the inlet passage 
both lie in a common surface which is only interrupted by the axially 
narrow annular gap. In this way, an advantageous flow in the transition 
section between the end section and the inlet passage in the cylinder is 
obtained. It can be advantageous to provide here a conical configuration 
of the intake pipe. 
The seal advantageously includes a flange in which a pulse bore is 
introduced to transmit the crank case pressure to a membrane feed pump. 
The pulse bore lies approximately axially parallel to the opening defined 
by the seal and connects the pulse opening in the cylinder to a pulse 
channel which is formed in an edge section of the intake pipe. The flange 
mounted on a wall end of the seal, together with the pulse bore, ensures a 
defined assembly position of the seal in the cylinder flange.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
FIG. 1 shows the cylinder 2 of an internal combustion engine 1 which is 
especially a two-stroke engine in a portable handheld work apparatus such 
as a motor-driven chain saw, cutoff machine, brushcutter, or the like. An 
inlet opening 3 opens into the combustion chamber 24 of the cylinder 2 for 
conducting an ignitable air/fuel mixture. An outlet passage 25 is provided 
on the side of the combustion chamber 24 lying opposite the inlet passage 
23. Furthermore, transfer channels 26 are provided in the cylinder wall. A 
threaded opening 27 is provided in the head of the cylinder to accommodate 
a spark plug. 
The inlet passage 3 extends into a cylinder flange 4 configured as one 
piece integrally with the cylinder wall. An intake pipe 5 is inserted into 
the flange opening 8. A carburetor 22 supplies fuel to the intake pipe 5. 
The fuel is processed with supplied combustion air in the venturi section 
of the intake pipe 5 to form an ignitable mixture. The mixture is 
conducted in flow direction 28 to the combustion chamber 24 of the 
cylinder 2. 
The cylinder flange 4 on the cylinder 2 defines a receptacle into which the 
pipe end section 7 of the intake pipe 5 is inserted. An annularly-shaped 
flange wall 10 is formed on the cylinder flange 4 and delimits the flange 
opening 8 as shown in FIGS. 1 and 5. The flange wall 10 surroundingly 
engages the intake pipe 5 inserted into the flange opening 8. A seal 6, 
which is configured as a sealing ring, is seated in the annular space 
between the flange wall 10 and the pipe end section 7 of the intake pipe 
5. 
The axial structural elevation (h) of the seal 6 corresponds approximately 
to the axial structural elevation (H) of the flange wall 10 so that the 
sealing ring terminates axially with the end face 29 of the flange wall 10 
as shown in FIGS. 1, 4b and 5. The sealing ring is inserted completely 
into the flange opening 8 and is advantageously manufactured to have an 
oversize compared to the diameter of the flange opening 8 so that the seal 
ring is tightly held in the flange opening 8 after being pressed therein. 
The pipe end section 7 of the intake pipe 5 is inserted into the seal 6. 
The outer diameter D of the pipe end section 7 (FIG. 6) is manufactured 
with an oversize compared to the seal inner diameter so that the intake 
pipe 5 applies a radial contact pressure to the seal 6 which is taken up 
by the surroundingly engaging flange wall 10 of the cylinder flange 4. The 
intake pipe 5 is inserted into the flange opening 8. In this way, a 
uniform radial pressure is applied over essentially the entire axial 
structural elevation of the seal. The axial friction forces which occur 
between the tube end section 7 and the seal 6 and between the seal 6 and 
the flange wall 10 prevent an axial loosening of the attachment. 
An inner-lying annular step 9 is provided in the cylinder flange 4 and 
faces toward the intake pipe 5. The annular step defines the base of the 
flange opening as shown in FIG. 5 and delimits the insert depth of the 
seal 6 into the flange opening 8. The annular step 9 forms a stop for the 
seal 6 inserted into the flange opening. The radial thickness (w) of the 
seal wall (FIG. 4b) is less than the radial extent of the annular step 9. 
The remaining radial extent of the wall is filled out by the wall of the 
pipe end section 7 so that the inner wall 15 of the intake pipe 5 and the 
inner wall 14 of the inlet passage 3, which extends from the flange 
opening 8, both lie in a common imaginary generated surface of revolution. 
As shown in FIGS. 1 and 2, this imaginary generated surface is only 
interrupted by an annular gap 12 which is formed in that the axial 
structural length L of the pipe end section 7 of the intake pipe 5 is less 
than the structural elevation H of the flange wall 10 (see FIGS. 5 and 6). 
An annular step 13 is formed in the outer surface of the intake pipe and 
delimits the insert depth of the intake pipe into the flange opening 8 in 
that the annular step 13 can be inserted maximally up to the stop on the 
end face 29 of the flange wall 10 or to the end face of the seal. The 
annular gap 12 provides a compensating space for swelling seal material 
when a possible swelling of the seal 6 occurs because of being wetted with 
fuel. The annular gap ensures that the structurally elastic 
characteristics of the seal are retained. 
An axial intermediate space can be retained into which the seal material 
can extend. The axial intermediate space is disposed between the annular 
step 13 on the intake pipe 5 and the end face 29 of the flange wall 10 and 
provides a further compensating space for swelling seal material. 
As shown in FIGS. 1 and 6, the interior of the pipe defines a conical trace 
when viewed in projection on a longitudinal plane extending along the 
cylinder 2. The pipe interior tapers in the direction of the combustion 
chamber 24. The interior of the pipe conically expands in the direction of 
the combustion chamber 24 in a plane perpendicular to the longitudinal 
axis 30 of the cylinder as shown in FIG. 2. 
From FIGS. 3 and 4a, it can been seen that the flange opening 8 of the 
cylinder flange 4 and the seal 6 inserted therein have an approximately 
oval cross section. The intake pipe 5 is correspondingly formed so as to 
be oval. 
FIG. 4a shows that a flange section 16 is provided on a longitudinal end of 
the oval-shaped seal 6. This flange section is formed as one piece with 
the seal. A pulse bore 17 is provided in the approximately 
semicircular-shaped flange section 16 and runs approximately axially 
parallel to the clear opening 18 of the seal. 
According to FIG. 3, the cylinder flange 4 has a correspondingly formed 
cross section in order to completely accommodate the seal 6. In this way, 
a defined insert position of the seal in the flange opening 8 is provided. 
The flange section 16 functions as a seal for a pulse channel 20 shown in 
FIG. 1. The pulse channel 20 is in a wall section 21 of the intake pipe 5 
and runs approximately parallel to the longitudinal axis 31 of the pipe. 
The pulse channel 20 transmits the pressure fluctuations from the interior 
space of the crankcase via a pulse opening 19 introduced into the cylinder 
wall and via the pulse bore 17 in the flange section 16 to a membrane feed 
pump (not shown). 
A liquid-tight and pressure-tight connection is provided between the pulse 
opening 19 in the cylinder wall and the pulse channel 20 in the wall 
section 21 of the intake pipe. This is achieved in that cylindrical stubs 
(32, 33) are provided on the cylinder wall and the intake pipe, 
respectively. The stubs (32, 33) engage friction-tight in the pulse bore 
17 at both ends of the seal as shown in FIGS. 5 and 6. The pulse opening 
19, the pulse bore 17 in the seal 6 and the pulse channel 20 in the intake 
pipe 5 are advantageously aligned coaxially to each other. 
The intake pipe 5 and the carburetor housing 23 advantageously conjointly 
define a one-piece component thereby ensuring that the intake pipe is held 
on the cylinder flange so as to be essentially inseparable therefrom 
because the carburetor housing is fixedly attached on the engine housing. 
According to FIG. 2, it can be advantageous to attach the intake pipe 
and/or the carburetor housing directly to the cylinder 2. For this 
purpose, an attachment bore 36 is provided in a wall section 35 configured 
as one piece with the intake pipe. An attachment element can be guided 
through the attachment bore 36 and hold the intake pipe on the cylinder. 
The axis 34 of the attachment bore 36 advantageously lies at a lateral 
distance with respect to the longitudinal axis 31 of the intake pipe so 
that the intake pipe can move axially by a small amount as a consequence 
of the one-sided lateral attachment. In this way, intense vibrations of 
the engine block can be compensated. 
The outer surface of the end section 7 of the intake pipe can also have a 
slight conical inclination in order to facilitate introduction of the pipe 
end section into the seal 6. For this reason, the end face of the pipe end 
section can be provided with a bevel. 
It is understood that the foregoing description is that of the preferred 
embodiments of the invention and that various changes and modifications 
may be made thereto without departing from the spirit and scope of the 
invention as defined in the appended claims.