Piston-crank mechanism

Details Piston-crank mechanism Piston-crank mechanism

1999-12-15

2001-05-08

Yuen, Henry C (Department: 3747)

Internal-combustion engines

Transmission mechanism from piston

Crankshaft and connecting rod

Reexamination Certificate

active

06227161

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piston-crank mechanism for use in automobile engines and so forth.
2. Description of the Related Art
Piston-crank mechanisms for converting reciprocating movement of a piston into rotational movement have been widely used in steam engines since the invention up to contemporary automobile engines. This piston-crank mechanism has sliding portions such as the sliding surface between the cylinder and the piston and bearing portions of crank pins, which produce frictional resistance forces, so that power loses due to severe variations in load, variations in frictional forces, and generation of heat are increased. These are known as causes of reduced transmission efficiencies and hastening of wear and tear in the piston, the cylinder, bearings, etc.
In order to improve the transmission efficiencies and prevent wear and tear in the piston, the cylinder, bearings, etc., various improvements in materials, structures, lubrication, cooling, and so forth have been conventionally made. A conventional piston-crank mechanism has been basically a structure shown in
FIG. 7
; however no innovative improvements on this mechanism have been made.
In a structure of a conventional piston-crank mechanism for one cylinder, as schematically shown in
FIGS. 7
a
to
7
d
, a piston
101
, a piston rod
106
, and a crankshaft
103
are arranged on one straight line. At the top dead center of the piston
101
(
FIG. 7
a
), a cylinder chamber
102
is just before the explosion process or the suction process while at the bottom dead center (
FIG. 7
c
) is just before the exhaustion process or the compression process, and the piston
101
at both the positions is in an almost stationary state. In these positions, the crankshaft
103
is rotated in the “A” direction owing to the explosive force of another cylinder or inertial forces of the crankshaft
103
and a crank arm
104
integrated in the crankshaft
103
; the bending moment is scarcely applied to the piston rod
106
and neither the side pressure nor the frictional force due to the side pressure are applied to the sliding surface “D” between the cylinder
102
and the piston
101
because connecting portions between the crank arm
104
and the connection rod
105
and between the connection rod
105
and the piston rod
106
are pivoted with a crank pin
107
and a piston pin
108
, respectively.
On the other hand, in an intermediate position from the top to the bottom of the piston stroke (
FIG. 7
b
), the rotation “A” of the crankshaft
103
mainly depends on the downward thrust of the piston
101
shown in the drawing, i.e., explosive forces in the cylinder
102
, in the explosion process. At this time, the rotational force is applied to the crank arm
104
via the connection rod
105
which is much inclined “&thgr;” toward the piston rod
106
. Since the piston rod
106
is fixed to the piston
101
in unison, the reaction force of the rotational driving force strongly pushing the crank arm
104
with the connection rod
105
is applied to the piston pin
108
to apply the bending moment to the piston rod
106
. Thereby, the high side pressure and the frictional force accompanied thereby are applied to the sliding surface
As shown in “P01” of
FIG. 8
illustrating variations in the side pressure and the frictional force due to the side pressure in the crank pin
107
, pressures are low in the top and bottom dead centers (
FIGS. 7
a
and
7
c
) while is high in the intermediate position (
FIG. 7
b
) of the explosion process.
In the suction process of the piston-cylinder, the driving direction is switched so that the crank arm
104
drives the connection rod
105
which in turn pushes up the piston rod
106
in the axial direction thereof. At this time, the side pressure and the frictional force accompanied thereby are applied to the sliding surface “D” by the inclination “&thgr;” of the connection rod
105
to the piston rod
106
. Since the resistance force against the suction is smaller than the driving force from the crank arm
104
, the pressure is rather lower as shown in “P02” of
FIG. 8
; however just like “P01”, the maximum pressure is shown in the intermediate position of the stroke of the piston
101
.
In
FIG. 7
d
that is the exhaustion process or the compression process of the piston
101
, the crank arm
104
is rotated in the “A” direction of the crankshaft
103
owing to the explosive force of another cylinder or inertial forces of the crankshaft
103
or a crank arm
104
so as to push the sliding portion of the crank pin
107
which is the connecting portion to the connecting rod
105
. Since this pushing force is used only for the exhaustion or the compression by pushing up the connecting rod
105
, the piston rod
106
, and the piston
101
, it is not so large as that in the explosion process, resulting in the same line “P02” as that of the suction process.
Among respective processes of suction, compression, explosion, and exhaustion, in the intermediate positions (
FIGS. 7
b
and
7
d
) in which the speed of the piston
101
is the highest, the side pressure/the frictional force in the sliding surface “D” between the piston
101
and the cylinder
102
is the maximum as shown in FIG.
8
.
The above-mentioned problem of the side pressure/the frictional force in the sliding surface “D” between the piston
101
and the cylinder
102
also arises almost similarly in a piston-crank mechanism for use in fuel-injection-type engines in which suction and compression of fuel are not performed.
As described above, in the conventional piston-crank mechanism, since in the intermediate positions in which the speed of the piston
101
is the highest, the side pressure/the frictional force in the sliding surface “D” between the piston
101
and the cylinder
102
is the maximum, the cylinder
102
and the piston
101
sliding within the cylinder
102
have to tolerate the extremely severe state. In particular, in the intermediate portion of the cylinder
102
, the speed and the side pressure/the frictional force of the piston
101
are the maximums, so that the state thereof is most severe.
When a piston-cylinder after long term use or having scoring is disassembled, the intermediate portion “C” of the cylinder
102
and the sliding surface “D” of the piston
101
are severely damaged as shown in
FIG. 9
a
, so that the severe state in which the speed and the side pressure/the frictional force of the piston
101
are the maximums can be supposed. The speed and the side pressure/the frictional force of the piston
101
not only reduce an operating life of the piston
101
-cylinder
102
but also deteriorate the transmission efficiency of the piston-cylinder mechanism and engine efficiencies because some engine power is consumed by the useless side pressure/the frictional force.
On the other hand, when the piston
101
approaches the top and bottom dead centers of the reciprocating stroke thereof, the frictional force in the sliding surface “D” between the piston
101
and the cylinder
102
is small so as to bring about such a state that brakes are not applied to overrunning of the piston
101
. Therefore, the crank arm
104
is meaninglessly pushed and pulled in the top and bottom dead centers, so that bearings of the crankshaft
103
, the crank pin
107
, and the piston pin
108
are laterally pressed on impact to be hastened to damages of these parts in vain.
When a crank pin after long term use or having scoring is disassembled, the damaged surfaces “E” of the crank pin
107
are concentrated in an angular position in which the above-mentioned impact is produced, as shown in
FIG. 9
b
, thereby, the above-mentioned situation can be confirmed. This impactive force also reduces the transmission efficiency of the piston-cylinder mechanism and engine efficiencies by consuming some engine power.
The above-mentioned arrangement of the piston
101
, the piston rod
106
, and the crankshaft
103
on one straight line has been also a restriction on engine desig

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