Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-09-26
2003-05-20
Kwon, John (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S698000
Reexamination Certificate
active
06564784
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an exhaust gas recirculation control apparatus for an internal combustion engine and, more particularly, to an exhaust gas recirculation control apparatus for an engine having a turbocharger.
BACKGROUND OF THE INVENTION
In the present situation where tightening regulations against harmful matters exhausted from an internal combustion engine has been advanced in many places from the viewpoint of an environmental protection, as a method of reducing the harmful matters contained in an exhaust gas of the internal combustion engine, exhaust gas recirculation (EGR) has been widely known and used. It has the following operation. A part of an exhaust gas exhausted from a combustion chamber is recirculated from an exhaust manifold to an intake manifold and mixed to intake air, and the mixture is again supplied to the combustion chamber, so that the concentration of oxygen in the intake air is reduced and a combustion temperature is decreased. The EGR has such a large effect that the occurrence of the harmful matters contained in the exhaust gas, particularly, nitride oxide (hereinbelow, referred to as NO
X
) is suppressed.
FIG. 13
shows an intake and exhaust circuit diagram of an engine
14
with a turbocharger having a conventional exhaust gas recirculation circuit. The engine
14
comprises: a turbocharger
11
; an intake circuit
12
; an aftercooler
13
; an exhaust gas recirculation circuit
15
; an exhaust circuit
16
; and an exhaust pressure control valve
18
. An intake air compressed by a compressor
11
a of the turbocharger
11
passes through the intake circuit
12
, is cooled by the aftercooler
13
provided in the middle of the circuit
12
, and is introduced to an engine main body
14
a
through an intake manifold
12
a
. The exhaust gas exhausted from the engine main body
14
a
flows into the turbocharger
11
through the exhaust circuit
16
to drive a turbine
11
b
, and is then exhausted. The exhaust pressure control valve
18
capable of adjusting an outlet pressure in the turbine
11
b
is provided for the outlet of the turbine
11
b
. The exhaust gas recirculation circuit
15
is branchingly connected in such a manner that the one end is connected in the vicinity of an exhaust manifold
16
a
of the exhaust circuit
16
and the other end is connected in the vicinity of the intake manifold
12
a
of the intake circuit
12
. The exhaust gas recirculation circuit
15
has: an EGR valve
15
c
whose opening area can be controlled so that the exhaust gas recirculation circuit
15
can be opened or closed; and an EGR cooler
15
b
for cooling the circulated exhaust gas. When the exhaust gas is circulated, the EGR valve
15
c
is first opened. A part of the exhaust gas is separated in the exhaust circuit
16
and cooled by the EGR cooler
15
b
, and after that, it is mixed to the intake air in the intake circuit
12
. The mixture is introduced into the engine main body
14
a.
However, the above intake and exhaust circuit has the following problems.
(1) When the engine
14
is driven under certain conditions, for example, at a medium or high speed under high loads, the pressure in the intake manifold
12
a
is higher than that of the exhaust manifold
16
a
in some cases. Generally, the reason is that the engine is designed so that the characteristics of the turbocharger match with the frequently used driving conditions to raise the efficiency of the engine and obtain high power and low fuel economy. As the pressure on the intake side is higher and the pressure on the exhaust side is lower, an intake and exhaust resistance serving as a loss of power becomes smaller. In this case, since the exhaust gas is not circulated, the harmful component contained in the exhaust gas cannot be reduced. The exhaust gas is circulated only under such driving conditions that the pressure in the intake manifold
12
a
is lower than that in the exhaust manifold
16
a
, for example, during driving at a low speed under low loads. Accordingly, the driving conditions where the exhaust gas recirculation circuit is operated to enable the harmful component in the exhaust gas to be reduced are restricted.
(2) When the circulation amount of the exhaust gas increases or decreases in association with a change in opening degree of the EGR valve
15
c
, an intake flow rate to be introduced to the engine main body
14
a
is fluctuated due to a fluctuation in pressure in the intake manifold
12
a
. When the intake flow rate is fluctuated, the amount of oxygen to be used for combustion is fluctuated and a stable combustion state cannot be obtained, so that the rotational speed of the engine is varied.
In order to solve the above problem (1), as a method of raising the pressure of the exhaust manifold
16
a
so as to be higher than that of the intake manifold
12
a
, thereby realizing the circulation of the exhaust gas, there is a method of throttling the exhaust pressure control valve
18
. According to the method, the exhaust pressure control valve
18
is throttled to raise the outlet pressure of the turbine
11
b
, so that the pressure of the exhaust manifold
16
a
located on the upstream of the turbine
11
b
is raised and, even if the engine
14
is driven at a medium speed or under medium loads, the exhaust gas can be circulated.
However, there is a limitation in the driving conditions of the engine
14
in which the circulation of the exhaust gas can be performed by such a method. When the pressure in the exhaust manifold
16
a
is excessively raised, the exhaust efficiency of the engine
14
is decreases, so that the fuel economy is deteriorated. Accordingly, the pressure of the exhaust manifold
16
a
can be merely raised to such a degree that the deterioration in fuel economy can be permitted. Therefore, the range of the driving conditions of the engine
14
in which the circulation of the exhaust gas can be performed is wider than that of the engine having no exhaust pressure control valve
18
but it is limited to a narrow range.
SUMMARY OF THE INVENTION
According to the present invention, to solve the above problems, it is an object to provide an exhaust gas recirculation control apparatus for an internal combustion engine, in which while fuel economy is maintained and improved, an exhaust gas can be circulated under driving conditions of such a wide range from a low-speed and low-load area to a high-speed and high-load area and, further, a fluctuation in rotational speed accompanied with switching the circulation of the exhaust gas can be suppressed as much as possible.
To accomplish the above object, according to a first aspect of the present invention, there is provided an exhaust gas recirculation control apparatus for an internal combustion engine, in which between an intake circuit and an exhaust circuit, a turbocharger and an exhaust gas recirculation circuit that is openable by exhaust gas recirculation switching valves are provided, comprising: an intake and exhaust bypass circuit for connecting the downstream side of a compressor to the upstream side of a turbine of the turbocharger; and an intake and exhaust bypass valve whose opening area can be varied so that the intake and exhaust bypass circuit can be opened or closed, wherein an intake throttle valve whose opening area can be varied so that the intake circuit can be opened or closed is provided on the upstream side of the position of the intake circuit where the exhaust gas recirculation circuit is branchingly connected.
According to the first aspect of the present invention, a part of the exhaust gas is allowed to flow into the exhaust circuit through the intake and exhaust bypass circuit, its flow rate can be simultaneously adjusted by the intake and exhaust bypass valve, and a loss of pressure can be generated in the intake circuit by the intake throttle valve. Consequently, even under such driving conditions that the circulation of the exhaust gas cannot be performed because the pressure in the intake circuit is higher than that in the exhaust circuit, the pressure
Iino Takahisa
Kanzaki Yoshiki
Nishiyama Toshihiko
Onodera Yasuyuki
Sato Fumihide
Armstrong Westerman & Hattori, LLP
Komatsu Ltd.
Kwon John
LandOfFree
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