Exhaust manifold for internal combustion engines

Details Exhaust manifold for internal combustion engines Exhaust manifold for internal combustion engines

1999-11-03

2001-05-15

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

Common receiver having inlets from plural cylinder

C060S321000

Reexamination Certificate

active

06230490

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an exhaust manifold for internal combustion engines. More specifically, the present invention relates to an exhaust manifold for internal combustion engines that allows early activation of a catalyst immediately after starting, reduces weight and costs, increases joining precision between plate materials, and improves welding precision.
Internal combustion engines have an exhaust manifold to collect exhaust gas discharged from gas columns. A catalyst is disposed following the exhaust manifold to purge harmful components of the exhaust gas from the exhaust manifold.
Exhaust manifolds for internal combustion engines include exhaust manifolds integrally formed by casting, as well as exhaust manifolds formed by joining a plurality of plate materials.
Examples of these exhaust manifolds for internal combustion engines are disclosed in Japanese examined utility model publication number 8-7055, Japanese laid-open patent publication number 10-89064, Japanese laid-open patent publication number 8-260958, Japanese laid-open patent publication number 9-317462, and Japanese laid-open patent publication number 10-89060.
Japanese examined utility model publication number 8-7055 discloses two plate materials joined to form an exhaust pipe collecting section. Of the two plate materials, the one that faces the main engine unit is formed thinner than the plate material positioned on the other side of the main engine unit. This difference in thickness generates a difference in vibration frequencies between the two plate materials, thereby reducing vibration noise. Also, the thicker plate material on the opposite side from the main engine unit restricts the transmission of exhaust noise.
Japanese laid-open patent publication number 10-89064 discloses the joining together of a front half, a partitioning body, and a rear half, each formed as plates. A plurality of exhaust pipes and confluence sections between two exhaust pipes are formed from the partitioning body and either the front half or the rear half. This allows for the reduced thickness and weight of the exhaust manifold.
Japanese laid-open patent publication number 8-260958 discloses junctures between the branching pipes that are made thicker than the other sections. The thickness is made greatest at the juncture disposed at the longitudinal center of the cylinder head. This increases the compressive stress generated at the junctures.
Japanese laid-open patent publication number 9-317462 discloses an outer pipe and an inner pipe, supported in the outer pipe, so that the two are separated by a gap. The outer pipe is formed so that the gap is larger near the engine attachment flange. This allows the thermal transfer from the inner pipe to the outer pipe to be reduced while allowing the exhaust temperature guided to the catalyst to quickly rise when the engine is started.
Japanese laid-open patent publication number 10-89060 discloses a vertically oriented engine having an exhaust port with an exit-side opening positioned higher toward the front or the rear of the automobile. The branching pipes, continuous with the exit-side opening, are positioned outward. This reduces the overlap between the branching pipes, when seen from the front of the automobile. As a result, the variations in the running airstreams that come into contact with the branching pipes are reduced and thermal warping is prevented.
Internal combustion engines use a catalyst to reduce harmful elements in the exhaust gas. The catalyst efficiently purges harmful elements when the catalyst temperature reaches its activation temperature.
In recent years, there has been an increasing demand for reducing harmful elements in the exhaust gas. In particular, there has been a demand to reduce the harmful elements in the exhaust gas that is discharged immediately after an internal combustion engine is started, since, at this time, the catalyst temperature is too low for the catalyst to be effective in removing the harmful elements.
For this reason, an exhaust manifold for internal combustion engines is formed by joining plate material having a smaller heat capacity than that of an exhaust manifold formed by casting. This allows the catalyst temperature to rise to the activation temperature quickly after the engine is started, thus providing early activation of the purging effect.
Referring to
FIG. 12
, there is shown an example of this type of exhaust manifold for internal combustion engines. Referring to
FIG. 12
, there is shown an engine compartment
102
for an automobile (not shown in the figure). An internal combustion engine
104
, a cylinder head
106
, and an exhaust manifold
108
are mounted in engine compartment
102
. Exhaust manifold
108
is formed by welding an upper case
110
and a lower case
112
. Upper case
110
and lower case
112
are formed as two metal sheets.
Exhaust manifold
108
attaches to cylinder head
106
with a head attachment flange
114
. A catalyst (not shown in the figure) is attached to a catalyst attachment flange
116
. When internal combustion engine
104
is mounted sideways in engine compartment
102
toward the front of the automobile (not shown in the figure), exhaust manifold
108
is disposed to the front of internal combustion engine
104
.
Exhaust manifold
108
is generally formed so that a sheet thickness t
1
of upper case
110
and a sheet thickness t
2
of lower case
112
are identical (t
1
=t
2
). Exhaust manifold
108
is cooled by air currents flowing through engine compartment
110
such as cooling air from a radiator fan (not shown in the figure) and running airflow.
Since upper case
110
is positioned further toward the front than lower case
112
, relative to the direction of the air currents, upper case
110
is cooled more than lower case
112
.
The stress tolerance of the metal sheets forming upper case
110
and lower case
112
increases for lower temperatures. Also, the heat capacity of the metal sheets is smaller if the thickness of the sheets is smaller.
Upper case
110
and lower case
112
are formed with the same sheet thickness (t
1
=t
2
) based on the stress tolerance of lower case
112
, which receives less cooling from air flows. As a result, there is excess strength in upper case
110
, which is cooled more than lower case
112
, and therefore has a larger stress tolerance. This increases the amount of required materials, the weight, and the production costs. Furthermore, upper case
110
has a higher heat capacity. In particular, the temperature of the exhaust gas sent to the catalyst immediately after internal combustion engine
102
is started is reduced, thus lengthening the time required for the catalyst to be heated to its activation temperature.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an exhaust manifold for an internal combustion engine which overcomes the foregoing problems.
It is a further object of the present invention to provide an exhaust manifold for an internal combustion engine which allows for activation of a catalyst immediately after starting the internal combustion engine.
It is another object of the present invention to provide an exhaust manifold for an internal combustion engine which reduces weight and costs, increases joining precision between plate materials, and improves welding precision.
The present invention provides an exhaust manifold disposed to collect exhaust gas from gas columns of an internal combustion engine mounted in an engine compartment of an automobile. The exhaust manifold is formed by joining at least two sheet materials. One of the sheet materials, positioned toward the front, relative to a direction of an air current flowing through the engine compartment, is formed with a thickness less than a thickness of an other sheet material, positioned toward the rear, relative to the current flow direction
Briefly stated, the present invention provides an exhaust manifold constructed of material varying in thickness. Auxiliary cooling, such as

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