Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Patent
1995-06-01
1997-08-12
Hart, Douglas
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
60300, F01N 328
Patent
active
056553641
DESCRIPTION:
BRIEF SUMMARY
This application has been filed under 35 USC 371 for the invention described and claimed in international application number PCT/GB93/02456, filed Nov. 30, 1993.
FIELD OF THE INVENTION
The present invention relates to a control system for an internal combustion engine having a catalytic converter and heating means for raising the temperature of the catalyst in the catalytic converter.
BACKGROUND OF THE INVENTION
In an engine which has means for heating the catalytic converter, be it an afterburner or an electrical heating element, a system is required for controlling the heating means in order to avoid possible damage to the catalytic converter through overheating. The control system should, for example, switch off the heating means once the catalytic converter has reached its light off temperature, prevent the heating from working during a warm start, and reactivate the heating means if the catalytic converter should drop below its light off temperature through prolonged low load operation of the engine.
Clearly, it is possible to make a direct measurement of the temperature of the catalytic converter. This of course is disadvantageous from the point of view of cost but a more serious objection to the use of a temperature sensor is the issue of reliability. Proposed legislation requires vehicles to comply with emission regulations not only when they are first manufactured but also after several tens of thousands of miles of use (currently 50,000 miles, 100,000 miles in the future) and the lifetime of a sensor operating in such a hostile environment cannot be guaranteed over such a period.
OBJECT OF THE INVENTION
The object of the present invention is therefore to provide a control system that will safeguard the durability of the catalytic converter and at the same time ensure effective operation of the catalyst when needed, which system does not rely on direct measurement of the temperature of the catalytic converter.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a control system for an internal combustion engine having a catalytic converter and heating means for raising the temperature of the catalyst in the catalytic converter, the control system comprising an electrical circuit for estimating the temperature of the catalyst and means for controlling the heating means of the catalytic converter based on the estimated catalyst temperature, wherein the electrical circuit for estimating the temperature of the catalyst comprises a storage means for storing a signal indicative of the estimated catalyst temperature and means for modifying the stored signal to take into account the difference between the estimated exhaust gas temperature and the estimated catalyst temperature, the heating effect of the heating means and the heat lost by the catalyst to the ambient atmosphere.
The storage means may be a capacitor and the means for modifying the stored charge may comprise charging and discharging resistors. Such an embodiment has the advantage of ease of calibration. The various sources of heat loss and heat gain, be they conduction, convection or radiation, can each be simulated by a separate resistor and each may readily be set by a calibration engineer.
Alternatively, the storage means may be a digital memory and the means for modifying the value stored in the memory may comprise a digital processor programmed to increment and decrement the stored value in accordance with any mathematical model designed to emulate the temperature changes in the catalyst.
In a preferred embodiment of the invention, the means for modifying the value of the stored signal comprise means for estimating the temperature of the exhaust gases arriving at the catalytic converter after having passed through a pipe of the exhaust system, the exhaust gas temperature at the catalytic converter being estimated by taking into account the quantity of fuel burnt in the engine combustion chambers, the estimated temperature of the exhaust pipe and the thermal capacity of the exhaust gases.
The tempera
REFERENCES:
patent: H1113 (1992-12-01), Yoshizaki
patent: 4656829 (1987-04-01), Creps
patent: 5303168 (1994-04-01), Cullen
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