Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2001-11-06
2003-06-24
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S278000, C060S287000, C060S291000, C060S297000, C123S688000, C073S118040
Reexamination Certificate
active
06581370
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a failure determination device for a humidity sensor that detects humidity of exhaust gases from an internal combustion engine and a control system for controlling an exhaust passage changeover valve capable of switching an exhaust passage for exhaust gases from the engine between a main exhaust passage and a bypass exhaust passage having an adsorber capable of adsorbing hydrocarbons and water contained in the exhaust gases.
2. Description of the Prior Art
Generally, in the exhaust system of a gasoline engine or the like, a three-way catalyst is arranged in an intermediate portion of the exhaust pipe in order to purify harmful substances (hydrocarbons, carbon monoxide and nitrogen compounds) in exhaust gases. However, immediately after the engine is started in a cold condition (e.g. before approximately 30 to 40 seconds have passed after the cold start of the engine), for instance, the three-way catalyst remains inactive, and the harmful substances cannot be purified sufficiently, so that particularly hydrocarbons are emitted from the engine as unburned combustible components. Therefore, in order to prevent emission of such hydrocarbons into the air, there has been proposed an engine which has, in addition to the three-way catalyst, an adsorber arranged in the exhaust pipe, for adsorbing hydrocarbons. Such an adsorber is arranged in a bypass exhaust passage which is branched from an intermediate portion of a main exhaust passage of the exhaust pipe having the three-way catalyst arranged therein. A changeover valve arranged in a bifurcating portion of the exhaust pipe switches the exhaust passage for exhaust gases between the main exhaust passage and the bypass exhaust passage. Thus, exhaust gases emitted immediately after the cold start of the engine are purified by the adsorber adsorbing hydrocarbons, and then discharged into the air.
The above-mentioned adsorber carries a zeolite on its surface. When exhaust gases are passing through the bypass passage, the molecules of hydrocarbons enter small holes of the zeolite whereby the hydrocarbons are adsorbed by the adsorber. The adsorber of this kind desorbs hydrocarbons once adsorbed thereby when it is heated to a temperature equal to or higher than a predetermined temperature (e.g. 100 to 250° C.). The desorbed hydrocarbons are recirculated to the engine e.g. via the EGR. As described above, the adsorber repeatedly carries out adsorption and desorption of hydrocarbons. However, the amount of undesorbed hydrocarbons permanently remaining in the adsorber may progressively increase or the small holes of the adsorber may be destroyed by a long-term use thereof. This results in the degradation of the adsorber, that is, a lowered adsorbing capacity of the adsorber for adsorbing hydrocarbons. If the engine is repeatedly started in such a state, an increasing amount of unadsorbed hydrocarbons is emitted into the air. Therefore, to carry out engine control for desorbing hydrocarbons (e.g. by elevating the temperature of the adsorber) to cope with the degraded state of the adsorber, or to notify the driver of the degradation of the adsorber, the present assignee has already proposed a degradation-detecting device for detecting degradation of a hydrocarbon adsorber by Japanese Patent Application No. 2000-66443.
In this degradation-detecting device, a humidity sensor is arranged at a location downstream of an adsorber in a bypass exhaust passage such that the humidity of exhaust gases having passed through the adsorber is detected by the humidity sensor, and degradation of the adsorber is detected based on the result of the detection. This degradation-detecting device utilizes proportionality between the adsorber's capabilities of adsorbing hydrocarbons and of adsorbing water. By detecting the humidity of exhaust gases having passed through the adsorber by using the humidity sensor, it becomes possible to detect lowered adsorbing capability of the adsorber for adsorbing hydrocarbons and water, that is, degradation of the adsorber.
Although the above degradation-detecting device can properly detect the degradation, once the humidity sensor of the degradation-detecting device has failed, the proper detection of the degradation cannot be performed, making it impossible to suitably carry out engine control or notify the driver of the degradation of the adsorber. Therefore, the conventional degradation-detecting device has room for improvement in this respect.
A control system of the above-mentioned kind has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 11-2115. The proposed control system includes a temperature sensor disposed in the exhaust pipe at a location between the three-way catalyst and the changeover valve, for detecting an exhaust temperature on a downstream side of the three-way catalyst, and based on the result of detection by the temperature sensor, controls the changeover valve in the following member: An exhaust temperature detected by the temperature sensor, and a predetermined temperature (e.g. 300° C.) defined in advance are compared with each other. When the exhaust temperature is lower than the predetermined temperature, it is determined that the three-way catalyst remains inactive, and the main exhaust passage is closed and at the same time the bypass exhaust passage is opened by the changeover valve. Thus, the exhaust gases are guided into the bypass exhaust passage, for causing hydrocarbons in the exhaust gases to be adsorbed by the adsorber, whereby the exhaust gases are purified. On the other hand, when the exhaust temperature is higher than the predetermined temperature, it is determined that the three-way catalyst has been activated, and the bypass exhaust passage is closed and at the same time the main exhaust passage is opened by the changeover valve, whereby the exhaust gases purified by the three-way catalyst are emitted without farther processing. It should be noted that the above adsorber adsorbs hydrocarbons when it is in a low temperature condition (e.g. lower than 100° C.) while desorbing the hydrocarbons once adsorbed thereby at temperatures equal to or higher than a predetermined temperature (e.g. 100 to 250° C.). The desorbed hydrocarbons are recirculated to the engine e.g. via an EGR pipe.
As described hereinabove, in the control system for the changeover valve, the exhaust temperature on the downstream side of the three-way catalyst is detected by the temperature sensor, and the condition of the three-way catalyst is estimated based on the result of the detection so as to control the changeover valve. In the above control system, however, the changeover valve is controlled irrespective of the actual state of adsorption of hydrocarbons by the adsorber. Moreover, generally, a temperature detected by the temperature sensor is slow in change, has low responsiveness, and is liable to be adversely affected by parameters including an outside air temperature, and the like. Therefore, in the above control system, it is sometimes impossible to control the changeover valve with appropriate timing, which causes insufficient purification of exhaust gases.
SUMMARY OF THE INVENTION
It is a first object of the invention to provide a failure determination device which is simple in construction and capable of properly determining failure of a humidity sensor that detects the humidity of exhaust gases from an internal combustion engine.
It is a second object of the invention to provide a control system for an exhaust passage changeover valve, which is capable of switching the changeover valve with appropriate timing, thereby making it possible to sufficiently purify exhaust gases.
To attain the first object, according to a first aspect of the invention, there is provided a failure determination device for a humidity sensor that detects humidity of exhaust gases from an internal combustion engine.
The failure determination device according to the first aspect of the invention is characterized by comprising:
operat
Akazaki Shusuke
Haga Takashi
Iwaki Yoshihisa
Miyahara Yasuyuki
Sato Masahiro
Arent Fox Kintner & Plotkin & Kahn, PLLC
Denion Thomas
Honda Giken Kogyo Kabushiki Kaisha
Tran Binh
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