Measuring and testing – Vehicle chassis – Steering
Reexamination Certificate
2002-12-12
2004-07-20
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Vehicle chassis
Steering
Reexamination Certificate
active
06763707
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a failure determination system and method for an internal combustion engine and an engine control unit, and more particularly to a failure determination system and method and an engine control unit, for determining a failure of a variable valve mechanism which inactivates a valve system associated with at least one of cylinders during a predetermined operation of the engine.
2. Description of the Prior Art
Conventionally, a control system for an internal combustion engine has been disclosed e.g. in the publication of Japanese Patent No. 2507550. The control system is used for controlling the fuel supply and cut-off of the fuel supply depending on a misfire condition of the engine. More specifically, the control system detects a misfire condition, on a cylinder-by-cylinder basis, based on variation in the rotational speed of a crankshaft, and cuts off the supply of fuel to a cylinder in which a misfire has been determined to occur, for a predetermined time period. Further, after that, the supply of fuel to the cylinder is resumed, and it is detected again whether or not a misfire occurs, thereby preventing continuation of the state in which the misfire has been determined to occur and fuel supply is cut off, in spite of the fact that a misfire actually no longer occurs.
However, the conventional control system suffers from the following problems: Internal combustion engines include a type which has a variable valve mechanism for inactivating predetermined ones of cylinders during deceleration of the vehicle. The variable valve mechanism is configured such that it keeps an intake valve and an exhaust valve of each of the predetermined cylinders capable of opening and closing when these cylinders are allowed to operate, and on the other hand, when they are inhibited from operation, it holds the intake and exhaust valves in a state incapable of opening and closing. As a result, in the case of this kind of engine, if a failure of the variable valve mechanism has occurred, the intake and exhaust valves, which should open and close for operation of the cylinders as their inherent function, are sometimes held closed, causing misfires in these cylinders. However, in the conventional control system, since detection of a misfire is carried out only based on variation in the rotational speed of the crankshaft, it is impossible to determine whether the misfire occurs due to a failure of the variable valve mechanism or due to unstable combustion in the misfiring cylinder (normal misfire). This makes it impossible to properly cope with a misfire in a manner suited to the cause of the misfire.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a failure determination system and method for an internal combustion engine and an engine control unit, which are capable of properly determining a failure of a variable valve mechanism by discriminating a misfire caused by the failure of the variable valve mechanism from a normal misfire.
To attain the above object, according to a first aspect of the present invention, there is provided a failure determination system for an internal combustion engine including a variable valve mechanism for inactivating a valve system associated with at least one of cylinders during a predetermined operation of the engine.
The failure determination system according to the first aspect of the invention is characterized by comprising:
cylinder-discriminating means for discriminating a particular one of the cylinders;
fuel injection valves for injecting fuel for the cylinders, on a cylinder-by-cylinder basis;
oxygen concentration-detecting means for detecting concentration of oxygen contained in exhaust gases exhausted from the engine;
misfire-detecting means for detecting a misfire condition of the engine, on a cylinder-by-cylinder basis;
fuel injection-stopping means for stopping fuel injection from the fuel injection valves to a cylinder of which occurrence of a misfire is detected by the misfire-detecting means; and
failure-determining means for determining that a failure of the variable valve mechanism has occurred, when an oxygen concentration parameter determined based on results of the detection by the oxygen concentration-detecting means assumes a value which indicates a richer value of an actual air-fuel ratio of the exhaust gases than a predetermined reference value does, under a condition of the stoppage of fuel injection being carried out by the fuel injection-stopping means.
According to this failure determination system, a misfire condition of the engine is detected on a cylinder-by-cylinder basis, and fuel injection to a cylinder of which occurrence of a misfire is detected by the misfire-detecting means via its associated fuel injection valve is stopped. When the oxygen concentration parameter determined based on results of the detection by the oxygen concentration-detecting means assumes a value which indicates a richer value of an actual air-fuel ratio of the exhaust gases than a predetermined reference value does, under the condition of the stoppage of fuel injection being carried out, it is judged that a failure of the variable valve mechanism has occurred. The variable valve mechanism, if normal, keeps the valve systems capable of opening and closing, when the engine is in an operating condition other than the predetermined condition. If the supply of fuel to a misfiring cylinder is cut off to supply only air to the cylinder, the oxygen concentration parameter responsive to oxygen concentration of exhaust gasses should indicate a leaner value of the air-fuel ratio of exhaust gases than when the fuel cut-off is not carried out, provided that the valve system is normally operating. Therefore, inversely, when the oxygen concentration parameter under the same conditions assumes a value indicating a richer value of the air-fuel ratio than a predetermined reference value does, it can be judged that the valve system of the misfiring cylinder is held closed and the variable valve mechanism is in a failure state in which it cannot control the valve system to a state capable of opening and closing. Further, in this case, the failure of the variable valve mechanism can be identified as the cause of the misfire, which makes it possible to clearly distinguish the misfire from a normal misfire.
Preferably, the fuel injection-stopping means cancels the stoppage of the fuel injection when the, oxygen concentration parameter assumes a value which indicates a leaner value of the actual air-fuel ratio of the exhaust gases than the predetermined reference value does.
According to this preferred embodiment, when the oxygen concentration parameter assumes a value which indicates a leaner value of the actual air-fuel ratio of the exhaust gases than the predetermined reference value does, i.e. when a misfire occurs due to some cause other than the failure of the variable valve mechanism, the stoppage of fuel injection is cancelled, whereby the engine can be properly and quickly restored to a state controlled to normal operation.
Preferably, the failure determination system includes engine rotational speed-detecting means for detecting a rotational speed of the engine, and the predetermined reference value is set such that the predetermined reference value indicates a richer value of the actual air-fuel ratio of the exhaust gases as the detected rotational speed of the engine is lower.
Preferably, the oxygen concentration parameter is an average value of a correction coefficient calculated in response to the detected oxygen concentration for use in air-fuel ratio feedback control of the engine.
Preferably, the failure determination system includes inhibition means for inhibiting the stoppage of the fuel injection by the fuel injection-stopping means and the determination by the failure-determining means, when a cylinder of which the occurrence of a misfire is detected does not belong to the at least one of the cylinders.
To attain the above object, according to a second aspect
Kitajima Shinichi
Kumagai Katsuhiro
Matsubara Atsushi
Nakaune Kan
Nishioka Futoshi
Davis Octavia
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
Laurentano Anthony A.
Lefkowitz Edward
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