Fault determining apparatus for exhaust passage switching valve

Details Fault determining apparatus for exhaust passage switching valve Fault determining apparatus for exhaust passage switching valve

2001-04-13

2002-11-12

Vrablik, John J. (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

Having sensor or indicator of malfunction, unsafeness, or...

C060S288000, C060S292000, C060S297000, C060S324000

Reexamination Certificate

active

06477830

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a fault determining apparatus for an exhaust passage switching valve, and more particularly, to such an apparatus for determining a fault of an exhaust passage switching valve which switches an exhaust passage for exhaust gases discharged from an internal combustion engine from a main exhaust passage to a bypass exhaust passage having an adsorbent capable of adsorbing hydrocarbons and moisture contained in the exhaust gases, and vice versa.
2. Description of the Prior Art
Generally, in an exhaust system of a gasoline engine or the like, a three-way catalyst is arranged at an intermediate portion of an exhaust pipe in order to purify harmful substances (hydrocarbons, carbon monoxide and nitrogen compounds) in exhaust gases. However, since the three-way catalyst has not been activated, for example, immediately after a cold start of the engine (for example, for about 30-40 seconds from the start), the harmful substances may not be sufficiently purified, 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 the exhaust pipe. 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 addition, a switching valve is arranged in the exhaust pipe for switching an exhaust passage for exhaust gases. This switching valve opens/closes the bypass exhaust passage in accordance with the state of the three-way catalyst to switch the exhaust passage from the main exhaust passage to the bypass exhaust passage, and vice versa.
Specifically, when the three-way catalyst remains inactive, for example, at a start of the engine, the switching valve opens only the bypass exhaust passage to introduce exhaust gases into the bypass exhaust passage and adsorb hydrocarbons in the exhaust gases to the adsorbent, thereby purifying the exhaust gases. On the other hand, when the three-way catalyst has been activated by a warm-up operation of the engine, the switching valve closes the bypass exhaust passage to pass the exhaust gases only to the main exhaust passage to purify the exhaust gases with the three-way catalyst. The adsorbent adsorbs hydrocarbons in a low temperature state (for example, below 100° C.), and desorbs the once adsorbed hydrocarbons when it has been heated to a predetermined temperature or higher (for example, 100-250° C.). The desorbed hydrocarbons are recirculated to the engine through an EGR pipe and so on.
While the switching valve normally operates as described above to permit appropriate purification of exhaust gases from the engine immediately after the start thereof, a fault in the switching valve, if any, disables appropriate purification of exhaust gases, so that it is necessary to monitor the switching valve for a fault. A fault determining apparatus for determining such a fault in a switching valve is known, for example, from Laid-open Japanese Patent Application No. 10-159544.
This fault determining apparatus has a temperature sensor arranged at a location downstream of an adsorbent in a bypass exhaust passage. For determining a fault in a switching valve during an operation of the engine, the fault determining apparatus forces the switching valve to perform a predetermined switching operation, and determines a fault in the switching valve based on a change in temperature of exhaust gases (hereinafter called the “post-adsorption exhaust gases” in this disclosure) downstream of the adsorbent, which is adsorbing hydrocarbons, before and after the switching operation. More specifically, when the engine is, for example, in a steady-state operating condition (for example, during idling), the switching valve is forcedly switched to cause a temporary change in the state of the exhaust passage from a state in which the bypass exhaust passage is closed and the main exhaust passage is opened to the reverse state, i.e., a state in which the bypass exhaust passage is opened and the main exhaust passage is closed. Then, the fault determining apparatus determines that the switching valve is faulty if a changing amount of the temperature detected by the temperature sensor respectively before and after the switching operation is equal to or less than a predetermined value. It should be noted that this determination takes advantage of the fact that the adsorption of hydrocarbons by the adsorbent involves an endothermic action.
As described above, the fault determining apparatus forces the switching valve to operate, after the start of the engine, when the three-way catalyst has been activated so that exhaust gases can be purified by the three-way catalyst and when the engine remains in a steady-state operating condition, to thereby open the bypass exhaust passage and close the main exhaust passage, and determines whether the switching valve fails. As such, the fault determining apparatus can determine a fault in the switching valve only when the engine is operating in a steady-state condition after the temperature of exhaust gases has been stabilized, but cannot directly determine whether or not the switching valve is actually operating under conditions in which the switching valve should essentially operate. In addition, since the detected temperature is generally slow in change, low in responsibility, and susceptible to the influence of various parameters including external air temperature and so on, an erroneous determination is likely to result when the fault determination of the switching valve is based on the detected temperature. Also, the fault determining apparatus must delay the execution of the switching valve fault determination until the engine enters the steady-state operating condition after the start, causing the fault determination to be time-consuming. Furthermore, the switching valve must be forcedly operated only for determining a fault in the switching valve in the steady-state operating condition in which the switching valve need not be essentially operated. For implementing this switching valve operation for the fault determination, a switching valve fault determining mode must be specially provided.
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 fault determining apparatus for an exhaust passage switching valve which is capable of directly, rapidly and properly determining a fault in an exhaust passage switching valve, under conditions such as immediately after the start of an internal combustion engine, in which the switching valve should be essentially operated, without the need for setting a special fault determining mode.
To achieve the above object, the present invention provides a fault determining apparatus for determining a fault in an exhaust passage switching valve for switching an exhaust passage of exhaust gases discharged from an internal combustion engine between a first exhaust passage having a three-way catalyst and a second exhaust passage branched off at a location downstream of the three-way catalyst of the first exhaust passage and having filled in an intermediate portion thereof an adsorbent capable of adsorbing hydrocarbons and moisture in the exhaust gases in accordance with an activated state of the three-way catalyst. The fault determining apparatus includes a humidity sensor arranged at a location downstream of the adsorbent in the second exhaust passage for detecting a humidity of the exhaust gases introduced into the second exhaust passage, and switching valve fault determining means for determining a fault in the exhaust passage switching valve based on a result of detection performed by the humidity sensor when the exhaust passage should have been switched to the seco

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