Internal-combustion engines – Combustion chamber means combined with air-fuel mixture...
Patent
1996-04-23
1998-01-13
Dolinar, Andrew M.
Internal-combustion engines
Combustion chamber means combined with air-fuel mixture...
F02D 4300
Patent
active
057067848
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and a device for controlling exhaust temperature for a combustion engine with knock control.
BACKGROUND INFORMATION
There will be frequent mention in the following of a load or of a load signal. This is a signal that essentially indicates the power output required at the moment from the engine. The load signal is dependent upon the momentary engine-control plan, e.g., either the adjustment angle of the throttle valve, the vacuum prevailing in the intake manifold, or the mass flow of intake air.
For years, the MOTRONIC control unit of Bosch Gmbh, Stuttgart, Germany has been provided with a cylinder-selective knock control and a global prolonging of injection time in conjunction with the knock control. When the knock control establishes knocking in a cylinder, it retards the ignition for this cylinder with a predetermined larger increment and then cancels this ignition retard again in small increments until there is either no longer an ignition retard or no new knocking occurs. When the ignition is retarded, less combustion energy is able to be converted into mechanical energy than before, so that an increased temperature of the exhaust (emissions) results. To prevent this from causing thermal overloading of the engine or of the exhaust manifold, when the sum of the ignition retards for all cylinders exceeds a predetermined value, the injection time is then prolonged to commensurate with an increasing value of the sum. The previously running lambda control is switched off. When the injection time is prolonged, the intake air/fuel mixture is enriched, so that a cooling is achieved.
Thus, the MOTRONIC control unit is a device where an injection time modification device is designed to prolong the injection time for all cylinders, the injection time being calculated by an injection-time control device as a function of the value of the named sum.
U.S. Pat. No. 4,825,836 describes a knock control for a combustion engine, where the ignition-advance angle is retarded for all cylinders as a function of the detected knocking. The rise in the exhaust temperature caused by retarding the ignition-advance angle is limited in that an enrichment of the intake air/fuel mixture is undertaken for all cylinders.
In a method described in British Patent Application No. 2 262 615, the fuel supply and the point of ignition are so adjusted for each individual cylinder that a detected knocking disappears. A direct relation is established between the supplied fuel quantity (or injection duration) and the degree of knocking. The supplied fuel quantity is not oriented here to the exhaust temperature.
SUMMARY OF THE INVENTION
The object of the present invention is to specify a method and a device for controlling the exhaust temperature of a combustion engine having knock control, which will make it possible to prevent local thermal overloading of an engine and of its exhaust manifold.
The present invention makes use of the realization that the cylinder-specific ignition-retard values output by the knock control constitute cylinder-selective values for the ignition, so that they represent a momentary measure of the temperature increase that is to be expected because of the ignition retard in one cylinder and in the corresponding exhaust manifold. As a result, the exhaust temperature can essentially be kept constant, selectively with respect to cylinders, in that a cylinder-selective fuel enrichment follows in dependence upon the retard value of the ignition for a specific cylinder.
A map is preferably used which stores maximum values (settings) for the fuel enrichment, these values being addressable by way of speed and load values and consisting of those values which apply when the ignition-advance angle is retarded in the maximally permissible manner and which, nevertheless, are not supposed to exceed a predetermined exhaust temperature. These maximum values are then only used fractionally for the enrichment (process) when an active ignition-retard (setting) remains
REFERENCES:
patent: 4825836 (1989-05-01), Hirose
Schreder Christian-Ernst
Steinbrenner Ulrich
Wagner Wolfgang
Dolinar Andrew M.
Robert & Bosch GmbH
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