Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Patent
1992-07-06
1993-10-05
Argenbright, Tony M.
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
123481, F02D 4114, F02D 4122
Patent
active
052495620
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for protecting a catalytic converter from overheating. Overheating can take place when misfires occur in a cylinder. Uncombusted mixture then reaches the catalytic converter and combusts there. The resulting increase in temperature can destroy the catalytic converter and may even set the affected vehicle on fire.
BACKGROUND OF THE INVENTION
Numerous different methods are known for recognizing misfires. Their common purpose is to interrupt the supply of fuel to the affected cylinder. The air induced by this cylinder, however, is then still available for combustion in the catalytic converter. This becomes problematic when the other cylinders are operated with a rich mixture. This condition occurs particularly in the case of lambda control when lean mixture is initially indicated because of the excess air from the affected cylinder. In order to avoid the damaging effect of excess air, it is known from DE-A-23 40 541 to arrange a controllable flap in each induction pipe to the individual cylinders of an engine. If the fuel supply to a cylinder is interrupted, the associated flap is at the same time adjusted in such a way that the cylinder is cut off from the air supply. This protective measure, however, involves a substantial structural complexity.
Another measure for protecting a catalytic converter in the case of interrupted fuel supply to one cylinder consists in substantially reducing the power of the engine. In this case, post-combustion of air from the affected cylinder and fuel from the rich mixture in the other cylinders does not lead to overheating of the catalytic converter. Although this method does not require special structural measures, the substantial reduction in power is disadvantageous.
There is, therefore, the long-standing problem of providing a method for protecting a catalytic converter from overheating in the case of misfires in an engine which requires no special structural measures and which does not lead to a substantial reduction in power.
SUMMARY OF THE INVENTION
The method according to the invention for protecting a catalytic converter from overheating is distinguished in that
a conventional method for cylinder-selective misfire recognition is used to determine whether misfires are occurring in a cylinder,
and, if this is the case, the fuel supply to the affected cylinder is interrupted and the remaining cylinders are supplied with a lean mixture.
This measure ensures that no excess fuel, but only excess air, can reach the catalytic converter.
Making the mixture leaner in the full-load range can, however, lead to an unallowable increase in the manifold temperature because there is then no cooling by excess fuel. In various types of engines, it is therefore advantageous to limit the engine power in the full-load range. This, however, does not involve the substantial reduction in power necessary in the case of the known methods, which do not ensure a lean mixture. In these latter methods, power limitation to well below full load has to be effected.
In exceptional cases, misfires occur because an injection valve will no longer close and, in consequence, the mixture becomes so over-rich, particularly in the low-load range, that it can no longer be ignited. If, in this case, the injection valve of the affected cylinder is activated by the signal to interrupt the fuel supply, this measure remains ineffective. In this case, the mixture for all the cylinders is enriched so that the only oxygen available for the combustion of the substantial excess fuel from the affected cylinder is that induced by the affected cylinder itself .
BRIEF DESCRIPTION OF THE DRAWINGS
The single FIGURE shows a flow diagram to explain a method for protecting a catalytic converter from overheating.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
In the method shown in the FIGURE, the signal of any given conventional cylinder-selective misfire recognition method is called up in a step s1 after the start of the method. In a step s2 a chec
REFERENCES:
patent: 3983754 (1976-10-01), Deguchi et al.
patent: 4951773 (1990-08-01), Poirier et al.
patent: 4979481 (1990-12-01), Shimomura et al.
Kantschar Anton
Klenk Martin
Moser Winfried
Argenbright Tony M.
Ottesen Walter
Robert & Bosch GmbH
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