Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2002-01-17
2004-02-10
Kwon, John (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C123S690000, C060S274000
Reexamination Certificate
active
06691021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a failure determination system, a failure determination method, and an engine control unit for a variable-cylinder internal combustion engine which is capable of switching a cylinder operation mode between an all-cylinder operation mode in which all of a plurality of cylinders are operated and a partial-cylinder operation mode in which part of the plurality of cylinders are made idle, the failure determination system being capable of determining whether or not the valve-actuating system associated with the part of the plurality of cylinders for being made idle has failed.
2. Description of the Prior Art
A failure determination system of this kind has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 7-63097. In the variable-cylinder internal combustion engine disclosed in this publication, all the four cylinders of the engine are operated during the all-cylinder operation mode, whereas two of the four cylinders are made idle, i.e. inhibited from operating, during the partial-cylinder operation mode. In the exhaust system of the variable-cylinder engine, an oxygen concentration sensor is arranged for detecting the concentration of oxygen in exhaust gases. The oxygen concentration sensor delivers a signal indicative of the sensed oxygen concentration, based on which is calculated an actual air-fuel ratio. In the failure determination system, during the all-cylinder operation mode, the count of a failure counter is incremented if the ratio of the actual air-fuel ratio to a reference air-fuel ratio becomes equal to or smaller than a predetermined reference value, that is, if the actual air-fuel ratio is considerably richer than the reference air-fuel ratio. Then, if the count of the failure counter becomes equal to or larger than a predetermined value, it is determined that the valve-actuating system associated with the cylinders for being made idle has failed. This method of failure determination is based on a phenomenon that when the intake valves and exhaust valves of the cylinders for being made idle are in a normally closed state due to the failure of the valve-actuating system associated therewith, the air-fuel ratio of a mixture supplied to the other two cylinders is controlled to a richer value than when the valve-actuating system is normally operating, so that the actual air-fuel ratio undergoes a shift to the richer side.
In the above conventional failure determination system, however, all the cylinders are allowed to operate normally in the all-cylinder operation mode. In this state, it is determined that the valve-actuating system associated with the cylinders for being made idle has failed if the actual air-fuel ratio is shifted to a richer value indicative of failure of the valve-actuating system, since the air-fuel ratio of a mixture supplied to the other cylinders is controlled to a richer value due to the failure of the valve-actuating system of the cylinders for being made idle. Therefore, it takes much time to determine that the valve-actuating system has failed, after the failure has actually occurred. Further, under conditions in which the air-fuel ratio tends to be lean, e.g. when the engine temperature is low or fuel is difficult to vaporize depending on the type thereof, there can be a case where the actual air-fuel ratio is drifted to a leaner value to fall short of the above-mentioned richer value indicative of failure of the valve-actuating system, even though the valve-actuating system has actually failed. In such a case, there occurs an erroneous determination that the valve-actuating system is normally operating although it has failed.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a failure determination system for a variable-cylinder internal combustion engine, which is capable of promptly and accurately carrying out failure determination of the valve-actuating system of cylinders for being made idle during the partial-cylinder operation mode.
To attain the above object, the invention provides a failure determination system for a variable-cylinder internal combustion engine including a plurality of cylinders each having at least one intake valve and at least one exhaust valve, and a valve-actuating system including a valve-actuating mechanism for actuating the at least one intake valve and the at least one exhaust valve of each of the cylinders, the engine being capable of switching a cylinder operation mode between an all-cylinder operation mode in which all of the plurality of cylinders are operated, and a partial-cylinder operation mode in which fuel supply to part of the plurality of cylinders is stopped and at the same time the part of the plurality of cylinders are made idle by stopping the valve-actuating mechanism from actuating the at least one intake valve and the at least one exhaust valve of each of the part of the cylinders.
The failure determination system is characterized by comprising:
oxygen concentration-detecting means for detecting a concentration of oxygen in exhaust gases exhausted from the plurality of cylinders;
failure-determining operation mode-executing means for executing a failure-determining operation mode for causing the valve-actuating mechanism to resume actuation of the at least one intake valve and the at least one exhaust valve of at least one of the part of the cylinders in a state in which the fuel supply to the part of the cylinders is stopped, when the cylinder operation mode is switched from the partial-cylinder operation mode to the all-cylinder operation mode; and
failure determination means for determining whether or not the valve-actuating system including the valve-actuating mechanism has failed, based on an oxygen concentration detected by the oxygen concentration-detecting means when the failure-determining operation mode is executed.
In this variable-cylinder internal combustion engine incorporating the failure determination system according to the first aspect of the invention, the cylinder operation mode is switched between the all-cylinder operation mode and the partial-cylinder operation mode. In the partial-cylinder operation mode, fuel supply to part of the plurality of cylinders by a fuel supply mechanism is stopped, and at the same time the valve-actuating mechanism associated with the part of the cylinders is stopped from actuating the intake valves and exhaust valves of the part of the cylinders, to thereby make the part of the cylinders idle in operation. According to the failure determination system, the failure-determining operation mode is executed by the failure-determining operation mode-executing means when the cylinder operation mode is switched from the partial-cylinder operation mode to the all-cylinder operation mode. In the failure-determining operation mode, the actuation of the intake valves and exhaust valves of at least one of the part of the cylinders is resumed in a state in which fuel supply to the part of the cylinders is stopped. Therefore, when the valve-actuating system associated with the part of the cylinders is normally operating, air taken into combustion chambers from the intake system via the intake valves is directly exhausted to the exhaust system of the engine via the exhaust valves, and hence an oxygen concentration detected at this time by the oxygen concentration-detecting means becomes higher than that detected before the start of the failure-determining operation mode.
On the other hand, when the valve-actuating system of the part of the cylinders has failed, the intake valves and exhaust valves thereof remain held in a closed state to inhibit air from being exhausted to the exhaust system, whereby the concentration of oxygen in exhaust gases is hardly changed in comparison with that before execution of the failure-determining operation mode. As described above, by execution of the failure-determining operation mode, if the valve-actuating system is normally operating, a state is forcibly produced in which the concentration of oxyge
Asaki Yasuaki
Fujiwara Mikio
Takagi Jiro
Arent Fox Kintner Plotkin & Kahn
Honda Giken Kogyo Kabushiki Kaisha
Kwon John
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