Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2001-03-05
2004-07-20
Tran, Binh (Department: 1764)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S276000, C060S285000, C060S287000, C060S297000
Reexamination Certificate
active
06763655
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catalyst state detector for an exhaust gas purifying catalyst which purifies exhaust gases emitted from an internal combustion engine, and more particularly, to a catalyst state detector for an exhaust gas purifying catalyst which purifies exhaust gases using an adsorbent for adsorbing hydrocarbons in exhaust gases.
2. Description of the Prior Art
Generally, in an exhaust system of a gasoline engine or the like, a three-way catalyst is arranged in an intermediate portion of an exhaust pipe in order to purify harmful substances (hydrocarbons, carbon monoxide and nitrogen compounds) in exhaust gases, the amount of which cannot be reduced sufficiently by engine modifications or EGR (exhaust gas recirculation). The three-way catalyst is heated by exhaust gases or by using additional means, and activated at temperatures equal to or higher than a predetermined temperature (300° C., for example), thereby purifying harmful substances flowing through the exhaust pipe by oxidation-reduction catalyst actions thereof. However, for approximately 30 to 40 seconds after the cold start of the engine, the temperature of the three-way catalyst is lower than the predetermined temperature, and the catalyst remains inactive, so that among the harmful substance, particularly hydrocarbons are emitted from the engine as they are as unburned combustible components. Therefore, in order to prevent emission of hydrocarbons in the air, there has been proposed an engine which incorporates not only the three-way catalyst but also an adsorbent, which is capable of adsorbing hydrocarbons, in an exhaust pipe of the engine (see, for example, Laid-open Japanese Patent Application No. 10-153112).
Such an adsorbent is arranged in a bypass exhaust passage branched from a main exhaust passage in which a three-way catalyst is arranged in exhaust pipes. When the three-way catalyst is not activated, for example, upon starting the engine, exhaust gases are introduced into the bypass exhaust passage such that hydrocarbons in the exhaust gases are adsorbed by the adsorbent. On the other hand, after the three-way catalyst is activated by worm-up of the engine, the exhaust gases are introduced into the main exhaust passage such that the exhaust gases are purified by the three-way catalyst. The adsorbent has, for example, zeolite on its surface, so that when the exhaust gases are passing through the bypass exhaust passage, molecules of hydrocarbons are caused to enter small pores of the zeolite, and the hydrocarbons are adsorbed. Also, when such an adsorbent is heated to a temperature equal to or higher than a predetermined temperature (for example, 100 to 250° C.) by the exhaust gases, the adsorbent desorbs hydrocarbons once adsorbed thereby. Then, the desorbed hydrocarbons are recirculated to the engine through an EGR pipe or the like.
As described above, while adsorption and desorption of hydrocarbons are repeated in the adsorbent, the amount of undesorbed hydrocarbons remaining in the adsorbent may gradually increase or cause destruction of pores of the adsorbent during a long-term use of the adsorbent. As a result, the adsorbent is deteriorated, i.e., experiences a gradually deteriorated capability of adsorbing hydrocarbons. If the engine is repeatedly started in such a state, hydrocarbons unabsorbed by the adsorbent will be emitted into the air. For this reason, it is required to detect the deterioration of the adsorbent in order to carry out engine control for desorbing hydrocarbons (e.g., by elevating the temperature of the adsorbent) to solve the deterioration of the adsorbent, or to notify the driver of the deterioration of the adsorbent. Among such methods of detecting the deterioration of the adsorbent, there are, by way of example, (1) a method which relies on a hydrocarbon sensor for the detection, (2) a method which relies on temperature sensors for the detection, and so on.
According to the method (1) relying on a hydrocarbon sensor, the hydrocarbon sensor is arranged at a location downstream of the adsorbent in the bypath exhaust passage. Then, the concentrations of hydrocarbons in exhaust gases introduced into the bypass exhaust passage and passing through the adsorbent is directly detected by the hydrocarbon sensor. Then, the deterioration of the adsorbent is detected based on the result of the detection. Specifically, when the concentrations of hydrocarbons in the exhaust gases introduced into the bypass exhaust passage and passing at a location downstream of the adsorbent (hereinafter referred to as the “post-adsorption exhaust gases” in the disclosure), which is active in adsorbing hydrocarbons, exceed a predetermined value or a predetermined allowable range, it is determined that the adsorbent is no longer capable of sufficiently adsorbing hydrocarbons, i.e., in a deteriorated state. Conversely, when the concentrations of hydrocarbons in the post-adsorption exhaust gases are equal to or lower than the predetermined value or within the predetermined allowable range, it is determined that the adsorbent is still capable of properly adsorbing hydrocarbons, i.e., in an undeteriorated or normal state.
According to the method (2) relying on temperature sensors, on the other hand, the temperature sensors are arranged both at locations upstream and downstream of an adsorbent in a bypass exhaust passage, respectively, for example, as described in Laid-open Japanese Patent Application No. 6-229234. These sensors detect the temperatures of the exhaust gases at locations upstream and downstream of the adsorbent to calculate a time period during which moisture in the exhaust gases is in a dew point state (dew point time) based on the result of the detection. Then, the deterioration of the adsorbent is detected based on the resulting dew point time. More specifically, a predefined standard dew point time (standard dew point time) is calculated in accordance with the result of the detection by the upstream temperature sensor and an engine operating condition, and an actual dew point time (actual dew point time) is calculated based on the result of the detection by the downstream temperature sensor. Then, these dew point times are compared with each other to determine that the adsorbent is more deteriorated as the actual dew point time is shorter than the standard dew point time, and conversely to determine that the adsorbent is less deteriorated as the actual dew point time is longer than the standard dew point time.
The foregoing detecting methods suffer from the following problems, respectively. In the method (1) relying on a hydrocarbon sensor, a generally employed hydrocarbon sensor is limited to detection of the concentration of a particular hydrocarbon (one kind of hydrocarbon having a predetermined number of carbons), so that it is difficult to accurately detect as a whole the concentrations of various hydrocarbons respectively having different numbers of carbons by such a hydrocarbon sensor. It is further difficult to correctly detect the deterioration of the adsorbent based on the result of the detection. In addition, the hydrocarbon sensor itself is quite expensive as compared with other sensors.
In the method (2) relying on temperature sensors, on the other hand, the deterioration of the adsorbent is indirectly detected by detecting temperatures of exhaust gases at two different locations, causing a susceptibility to an error in the detection of deterioration and a low detection accuracy. In addition, temperature sensors are expensive as is the case of the hydrocarbon sensor, and the use of two temperature sensors further results in a higher cost of the exhaust system as a whole.
OBJECT AND SUMMARY OF THE INVENTION
The present invention has been made to solve the problems as mentioned above, and its object is to provide a catalyst state detector for an exhaust gas purifying catalyst, which is capable of accurately detecting a state of an adsorbent of the exhaust gas purifying catalyst for adsorbing hydrocarbons, includ
Akazaki Shusuke
Endo Tetsuo
Haga Takashi
Iwaki Yoshihisa
Sato Masahiro
Arent & Fox PLLC
Honda Giken Kogyo Kabushiki Kaisha
Tran Binh
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