Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2001-06-28
2003-08-26
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
Reexamination Certificate
active
06609506
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas recirculation system (EGR system) incorporated into an internal combustion engine to recirculates part of the exhaust gas discharged from the internal combustion engine at a controlled flow controlled by a recirculation control valve to an intake passage and, more specifically, to the construction of a flow passage connecting an exhaust passage and the recirculation control valve.
2. Description of the Related Art
A conventional internal combustion engine is provided with an exhaust gas recirculation system for recirculating part of the exhaust gas to an intake passage to suppress the generation of NO
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by lowering maximum combustion temperature and to improve fuel consumption by reducing pumping loss. In the exhaust gas recirculation system, a recirculation control valve for controlling the flow of the recirculation exhaust gas is attached to the cylinder head of the internal combustion engine, and a recirculation exhaust gas inlet through which part of the exhaust gas flowing through an exhaust passage is extracted is formed in an exhaust manifold or an exhaust pipe connected to the lower end of the exhaust manifold.
When the recirculation exhaust gas inlet is formed in a lower part of the exhaust manifold, the exhaust pipe or a part of the exhaust pipe below a part of the exhaust pipe where a catalytic converter is placed, the recirculation exhaust gas inlet is at a relatively lower position on the exhaust passage with respect to the flowing direction of the exhaust gas. Therefore, a relatively long recirculation passage is needed to connect the exhaust gas passage and the recirculation control valve attached to the cylinder head. Thus the recirculation exhaust gas taken out of the exhaust passage dissipates heat into the atmosphere and is subject to cooling while the same flows through the recirculation passage to the recirculation control valve. Consequently, carbon and hydrocarbons (HC) contained in the recirculation exhaust gas are not oxidized and deposit deposits including carbon on the valve element of the recirculation control valve and in the gas passage of the recirculation control valve. The deposits in the passages obstruct the flow of the recirculation exhaust gas and make the recirculation control valve unable to function properly for flow control.
Heat dissipation while the recirculation exhaust gas is flowing through the recirculation passage may be reduced by reducing the length of the recirculation passage. However, the length of the recirculation passage cannot be reduced below a minimum necessary length dependent on the positional relation between the recirculation gas outlet and the recirculation control valve. Even if the recirculation passage is formed in the shortest possible length, the recirculation exhaust gas is still apt to dissipate heat into the atmosphere and to be cooled. Thus the reduction of the length of the recirculation passage cannot be an effective means for suppressing the deposition of deposits on the recirculation passage.
The present invention has been made in view of such circumstances and it is therefore an object of the present invention to provide an exhaust gas recirculation system of simple construction capable of suppressing the drop of the temperature of a recirculation exhaust gas flowing through a recirculation passage between an exhaust passage and a recirculation control valve and of suppressing the deposition of deposits including carbon on the components of the recirculation control valve.
Another object of the present invention is to provide an exhaust gas recirculation system for a multicylinder internal combustion engine having a plurality of cylinders, capable of preventing the extraction of part of an exhaust gas from an exhaust passage as a recirculation exhaust gas from making the ratios of effect of the cylinders on a measured value measured by an exhaust gas analyzer placed in the exhaust passage to acquire data for estimating an air-fuel ratio differ from each other.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, an exhaust gas recirculation system includes: a recirculation passage having one end connected to an exhaust passage included in an internal combustion engine and the other end connected to an intake passage included in the internal combustion engine to extract part of an exhaust gas as a recirculation exhaust gas from the exhaust passage and to recirculate the same to the intake passage; and a recirculation control valve placed in the recirculation passage to control the flow of the recirculation exhaust gas into the intake passage; wherein a recirculation pipe forming a part of the recirculation passage has a section extended close to and along an exhaust pipe forming a part of the exhaust passage.
The section, extended close to and along the exhaust pipe, of the recirculation pipe for carrying the recirculation exhaust gas extracted from the exhaust passage to the recirculation control valve is included in an environment heated at a high temperature by the heat radiated by the exhaust pipe heated at a high temperature by the exhaust gas. Therefore, heat dissipation from the recirculation pipe into the atmosphere is small even if the recirculation pipe is long and the drop of the temperature of the recirculation exhaust gas flowing through the recirculation pipe is suppressed. Consequently, the recirculation exhaust gas is maintained at a high temperature, the oxidation of carbon and hydrocarbons contained in the recirculation exhaust gas is promoted and hence the deposition of deposits including carbon on the valve element and the walls of a valve case of the recirculation control valve can be suppressed.
Thus simple construction including the recirculation pipe extended close to the exhaust pipe suppresses the deposition of deposits including carbon in the recirculation control valve and prevents the recirculation control valve from becoming incapable of properly controlling the flow of the recirculation exhaust gas due to the deposition of deposits in the recirculation control valve.
In the exhaust gas recirculation system according to the first aspect of the present invention, both the recirculation pipe of the recirculation passage, and the exhaust pipe of the exhaust passage may be covered with a heat insulating cover. When both the recirculation pipe and the exhaust pipe are covered with the heat insulating cover, a hot atmosphere heated by heat radiated by the exhaust passage is created in a space enclosed by the heat insulating cover. Since the recirculation pipe is extended in the hot atmosphere, the amount of heat radiated by the recirculation pipe into the atmosphere is reduced, the drop of the temperature of the recirculation exhaust gas flowing through the recirculation pipe is suppressed and the oxidation of carbon and hydrocarbons contained in the recirculation exhaust gas is promoted. Consequently, the deposition of deposits including carbon on the valve element of the recirculation control valve and in the exhaust gas passage of the recirculation control valve can be suppressed. Thus simple construction including covering both the recirculation pipe and the exhaust pipe with the heat insulating cover enhances the aforesaid effect of the exhaust gas recirculation system.
According to a second aspect of the present invention, an exhaust gas recirculation system includes: a recirculation passage having one end connected to an exhaust passage included in an internal combustion engine and the other end connected to an intake passage included in the internal combustion engine to extract part of an exhaust gas as a recirculation exhaust gas from the exhaust passage and to recirculate the same to the intake passage; and a recirculation control valve placed in the recirculation passage to control the flow of the recirculation exhaust gas into the intake passage; wherein the internal combustion engine is mounted on a vehicle, an exhaust pipe forming a par
Matsuura Hiromi
Shinkai Takahiro
Takashiba Kazuhiro
Yamamoto Takuji
Armstrong Westerman & Hattori, LLP.
Castro Arnold
Yuen Henry C.
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