Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2000-01-13
2001-02-27
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S307000
Reexamination Certificate
active
06192678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a secondary air supply control system for an internal combustion engine, which controls the supply of secondary air to an upstream side of a catalyst arranged in an exhaust pipe of the engine to activate the catalyst, thereby enhancing exhaust emission characteristics.
2. Description of the Prior Art
In general, a catalyst, such as a three-way catalyst, arranged in an exhaust pipe of an internal combustion engine is not active enough for purification of exhaust gases until it is heated up to a predetermined temperature. To cope with this inconvenience, some conventional internal combustion engines are provided with a secondary air supply control system for supplying secondary air to the upstream side of the catalyst at the start of the engine by operating an electromagnetic valve and an electric air pump to burn unburned combustible components in exhaust gases, such as CO and HC, thereby activating (warming up) the catalyst. A secondary air supply control system of this kind was proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 6-129241. In this secondary air supply control system, an engine coolant temperature THWST at the start of the engine is sensed by an engine coolant temperature sensor, then a supply time period CDANKIX is calculated based on the sensed engine coolant temperature THWST, and secondary air is supplied to the upstream side of the catalyst over the calculated supply time period CDANKIX to thereby control activation of the catalyst. That is, the secondary air supply control system uses the engine coolant temperature THWST sensed at the start of the engine as a parameter reflecting a temperature of the catalyst at the start of the engine to determine the supply time period CDANKIX over which secondary air is to be supplied. More specifically, as the engine coolant temperature THWST is lower, the supply time period CDANKIX is set to have a larger value.
However, since the above secondary air supply control system uses the engine coolant temperature THWST as the parameter reflecting the catalyst temperature, secondary air can be supplied excessively or insufficiently. This results from the fact that the engine coolant temperature THWST sensed when the engine is restarted cannot always reflect the catalyst temperature accurately because the catalyst temperature at the restart of the engine depends on an operating condition of the engine before stoppage, a stop time period between the stoppage and the restart of the engine, and so forth, even if the engine coolant temperature THWST is identical. The excessive supply of secondary air can cause overheating of the catalyst and generate untoward noises. In addition, an excessively long operation time period over which the electromagnetic valve and the electric air pump are operated for supplying the secondary not only shortens the service life of the electromagnetic valve and that of the electric air pump but also degrade fuel economy and fast consumption of a battery. On the other hand, the insufficient supply of secondary air causes degradation of exhaust emission characteristics due to insufficient activation of the catalyst.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a secondary air supply control system for an internal combustion engine, which is capable of supplying an appropriate amount of secondary air to a catalyst of the engine to thereby activate the catalyst properly.
To attain the above object, the present invention provides a secondary air supply control system for an internal combustion engine including an exhaust passage, and a catalyst arranged in the exhaust passage, for purification of exhaust gases, the secondary air supply control system controlling supply of air to the catalyst, and comprising:
air supply means for supplying air to the catalyst;
engine coolant temperature-sensing means for sensing a temperature of an engine coolant within the engine;
intake air temperature-sensing means for sensing a temperature of intake air within the engine;
operation time-determining means for determining an operation time period over which the air supply means is to be operated;
storage means for storing a value of the temperature of the engine coolant sensed by the engine coolant temperature-sensing means at a stoppage of the engine;
arithmetic operation means for calculating a temperature difference between the value of the temperature of the engine coolant sensed at the stoppage of the engine and stored in the storage means and a value of the temperature of the engine coolant sensed at a start of the engine after the stoppage of the engine;
determination means for determining whether or not a stop time period between the stoppage of the engine and the start of the engine is short, depending on the temperature difference calculated by the arithmetic operation means; and
operation time-correcting means for correcting the operation time period, based on a temperature difference between the value of the temperature of the engine coolant sensed at the start of the engine and a value of the temperature of the intake air sensed at the start of the engine, when the determination means determines that the stop time period is short.
According to the secondary air supply control system of the invention, it is determined whether or not the stop time period of the engine is short, depending on the temperature difference between a value of the engine coolant temperature sensed at the stoppage of the engine and a value of coolant temperature sensed at the start of the engine. In this case, the temperature of the engine coolant which circulates within a cooling system of the engine tends to fall continuously after the engine is stopped, so that it is possible to determine accurately from the temperature difference whether the stop time period of the engine is long or short. If the stop time period is short, the operation time period over which the air supply means is to be operated is corrected based on the temperature difference between the value of the engine coolant temperature and a value of the intake air temperature both sensed at the start of the engine. In general, when the stop time period of the engine is short, the temperature of the engine coolant continues falling as described above, but the temperature of the intake air, which has been held close to a temperature of fresh air continuously taken in before the stoppage of the engine, tends to rise temporarily with a temporary rise in temperature of the whole intake pipe caused by heat remaining in the engine after the stoppage thereof, since the fresh air ceases to be taken in. Therefore, the temperature difference between the value of the engine coolant temperature and the value of the intake air temperature both sensed at the start of the engine accurately reflects the stop time period of the engine and hence a decrease in temperature of the catalyst due to the stoppage of the engine. Thus, differently from the prior art in which a time period for supplying secondary air is determined simply based on the engine coolant temperature sensed at the start of the internal combustion engine, the present embodiment makes it possible to supply an appropriate amount of secondary air to the catalyst according to the decrease in temperature of the catalyst by correcting, based on the temperature difference, the operation time period over which the air supply means is to be operated, thereby activating the catalyst properly. Further, it is possible to obtain the above effects without sensing the catalyst temperature directly, so that a sensor for sensing the catalyst temperature can be dispensed with, which prevents an increase in manufacturing costs.
Preferably, the secondary air supply control system further comprises:
remaining time storage means for storing therein a remaining time period of the operation time period at the stoppage of the engine;
comparison means for performing a comparison between the operation time period determined at the
Arent Fox Kintner & Plotkin & Kahn, PLLC
Denion Thomas
Honda Giken Kogyo Kabushiki Kaisha
Nguyen Tu M.
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