Internal-combustion engines – Multiple cylinder – Cylinders radiating
Reexamination Certificate
2000-08-31
2001-12-25
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Multiple cylinder
Cylinders radiating
C123S055500, C123S055700, C123S1950HC
Reexamination Certificate
active
06332435
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a crank journal support portion structure of a horizontal opposed type engine and, especially, a crank journal support portion structure of a horizontal opposed type engine wherein an opening portion is provided in an area of crank journal support wall portions disposed between cylinders where the influence of stress concentration due to combustion load is small.
2. Description of Related Art
Generally, as for reciprocating engines whose cylinder disposition is of type other than a horizontally opposed type, such as straight-type or v-type engines, as shown in FIG.
4
and
FIG. 5
, a crank journal support wall portion
45
of a crank shaft
42
is disposed between respective cylinders
43
, in a crank case
41
defined at the bottom of an engine cylinder block
40
. Such engines are configured such that the crank shaft
42
is fit inside the crank case
41
, by arranging a crank journal
44
via a bearing on a semi-circular journal bearing portion
46
formed at this crank journal support wall portion
45
, and fixing with a bearing cap
47
from the engine bottom side.
In this case, a hole portion is often provided in respective crank journal support wall portion
45
penetrating in a thickness direction thereof such that respective cylinders can be in mutual ventilation through this hole portion. This hole portion is provided according to the following objects.
A first object is to solve engine pumping loss in the crank case.
Namely, during the piston vertical movement due to combustion in a certain cylinder, for example, in the explosion stroke, a piston is pushed down to the bottom of the cylinder by combustion energy generated by explosion in a combustion chamber. At this moment, air in the cylinder is compressed at the piston back side. In this case, this compressed air attenuates the kinetic energy of the descending piston, and energy transmitted to the crank via a connecting rod may be lost.
On the other hand, in the exhaust stroke, as the piston elevates in the cylinder while sucking air of the rear side of the piston, at the same time, a negative pressure is generated at the rear side of the piston and kinetic energy transmitted to the crank may be reduced.
Power loss caused by such piston movements is generally called “pumping loss” in the crank case, and a hole portion is provided in the respective crank journal support wall portion penetrating in the thickness direction thereof, in order to resolve such pumping loss in the crank case. It is configured such that respective cylinders can ventilate mutually through this hole portion.
Namely, for example, when a descending piston compresses air in the cylinder, power loss caused by the air compression generated at the piston back side can be reduced by discharging compressed air to adjacent other cylinders through the hole portion. Air led into the other adjacent cylinders can attenuate the negative pressure generated at the back side of the elevating piston.
As the result, for the multiple cylinder engine, such relation is created among a plurality of cylinders, allowing, consequently, to reduce generation of pumping loss in the crank case for the engine as a whole.
As another object of providing a hole portion in the crank journal support wall portion
45
, it serves to evacuate blow-by gas leaking from piston ring gap to the crank case
41
side in the compression stroke and explosion stroke of the engine. Further, it contributes to reduction of the engine weight.
For these objects, the hole portion is often opened at respective crank journal support wall portion
45
penetrating in thickness direction thereof; however, for the horizontal opposed type engine, its conditions made it difficult to open the hole portion.
In other words, as for the horizontal opposed type engine, a pair of crank cases are opposed to each other and joined to hold the crank journal. The combustion loads in horizontal opposed type engines, therefore, act in mutual opposition along the piston displacement direction.
As a result, stresses due to the combustion load are also generated in mutually opposed portions of the horizontal opposed type engine. Further, these stresses are concentrated in both of the right and left sides of a joint portion of the crank case joined in opposition. As a result, when a ventilation hole portion is provided in the vicinity of the crank journal support hole portion formed in the crank case, the possibility of concentrating stresses generated due to the combustion load in the vicinity of the hole portion and lowering the strength of the engine in the vicinity of the hole portion exists in either of the right or the left crank case where the hole portion is provided.
SUMMARY OF THE INVENTION
Therefore, the invention intends to prevent the problem of deterioration in engine strength by the concentration of the stress due to the combustion loads applied to the hole portion provided in the crank case. At the same time, the invention intends to reduce the pumping loss in the crank case caused by the vertical movement of the piston. Further, the invention intends to reduce the engine weight while discharging blow-by gas smoothly.
To solve the problem mentioned above, the invention provides a crank journal support portion structure disposed in a crank case
12
of a horizontal opposed type engine
10
, wherein a hole portion
21
communicating with an adjacent cylinder
11
is opened, at rotation angular positions of a crank journal
17
with small stress generated at a crank journal support wall portion
20
by combustion load transmitted to the crank journal
17
via a connecting rod
15
, in the vicinity of the crank journal support hole
19
of the crank journal support wall portion
20
disposed between respective cylinders
11
.
Therefore, operation of the invention is as follows.
Namely, the load generated by the combustion in a combustion chamber of the cylinder
11
is transmitted to the crank journal
17
via a piston
14
and the connecting rod
15
and acts as stress on a periphery of the support hole
19
of the crank journal of the crank journal support wall portion
20
of the crank case
12
.
For this case, according to the invention, a large stress generated by the combustion load does not act on the area where the hole portion
21
is disposed, because, in the vicinity of the crank journal support hole
19
of the crank journal support wall portion
20
, the hole portion
21
communicating with the adjacent cylinder
11
is provided at rotation angular positions of the crank journal
17
. Thus, small stress is generated at the crank journal support wall portion
20
by combustion loads transmitted to the crank journal
17
via the connecting rod
15
.
“Rotation angular positions of the crank journal with small stress generated at a crank journal support wall portion by combustion load” are areas C and D around the crank journal support hole portion
19
. The small stress rotation angular positions are defined by the rotation angle of the crank journal
17
during the period in which the piston
14
moves from a bottom dead center to a top dead center, for example, in the exhaust stroke, in the crank journal support wall portion
20
.
During the explosion stroke, the piston
14
moves from the top dead center to the bottom dead center. Because the combustion pressure increases in the state after the top dead center (ATDC), the combustion load attains its maximum in the state before arriving at the bottom dead center. At this moment, a large stress is generated in the area around crank journal support hole
19
defined by the rotation angle of the crank journal
17
.
However, when the explosion stroke is completed to transit to the exhaust stroke, the combustion load does not act. Therefore, the stress concentration to the hole portion
21
periphery can be prevented, even when the ventilation hole portion
21
is opened in the area defined by the crank journal
17
rotation angle corresponding to the transition of thi
McMahon Marguerite
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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