Internal-combustion engines – Charge forming device – With fuel pump
Reexamination Certificate
2000-01-28
2001-05-15
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Charge forming device
With fuel pump
C060S274000
Reexamination Certificate
active
06230689
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a four-stroke internal combustion engine comprising one or more cylinders each having a combustion chamber, a fuel injector opening into each cylinder room, a fuel pump device for feeding fuel to the respective injector, an exhaust line leading from the respective combustion chamber and opening into a catalytic converter device for catalytic reduction of NO
x
in the exhaust, and means for supplying fuel to the catalytic converter device.
DESCRIPTION OF THE RELATED ART
It is known to use so-called DENOX catalytic converters for catalytic reduction of nitrogen oxides in diesel engine exhaust. It is also a known fact that such catalytic converters have a relatively low efficiency and a narrow temperature range within which they function and that addition of hydrocarbons can increase the efficiency and broaden the temperature range. This can be effected by adding extra diesel fuel in such a manner that it reaches the catalytic converter in vapour form. Where the fuel is supplied is of no consequence as long as no combustion occurs prior to the catalytic converter.
Different methods and systems for supplying fuel to the catalytic converter are known. One method uses a separate fuel system which injects fuel into the exhaust line prior to the catalytic converter. In another method, which is known by WO96/03572 for example, the ordinary fuel injector of the engine is to inject, after the ordinary fuel injection phase, a small amount of fuel directly into one or more of the engine combustion chambers during the exhaust phase, so that the fuel in vapour form is transported with the exhaust to the catalytic converter. For this purpose a fuel injection system is used in the engine which is known as “common rail” and comprises a high-pressure vessel which is kept continually under high pressure with the aid of a high-pressure pump between the vehicle fuel tank and the high-pressure vessel and which communicates with all of the injectors via electronically controlled valves cooperating with the respective injectors. Since the system is under constant pressure, fuel can be theoretically injected at an arbitrary number of times any time during the work cycle of the engine. The control of the injection both at the ordinary injection phase and at the extra post-injection phase is achieved with the aid of a control unit (control computer), which opens and closes the valves depending on various engine data fed into the control unit. With a common rail fuel injection system, the post-injection phase can be freely selected since the system does not have a varying fuel pressure cycle to take into account, as would be the case in usually occurring cam shaft-driven fuel injection systems.
SUMMARY OF THE INVENTION
The purpose of the present invention is to achieve, in an internal combustion engine of the type described by way of introduction, the above mentioned post-injection without using the known common rail system or any other separate dosage system.
This is achieved according to the invention by virtue of the fact that the fuel pump device comprises individual fuel pump means for each injector, and a cam shaft driven by the engine crankshaft, and having a cam element for each fuel pump means, said cam element having a first cam ridge, which is arranged to effect, once per work cycle, a first pump stroke in the associated fuel pump means, and at least a second cam ridge which is arranged to effect, once per work cycle, a second pump stroke in the associated fuel pump means, a predetermined number of crankshaft degrees after the first pump stroke, and that an electronic control unit is arranged to control a by-pass valve, cooperating with each injector, to regulate the amount of injection and the time during the respective pump stroke, depending on various control parameters fed into the control unit.
The time interval for the second injection phase is in this case determined by the geometric position of the second cam ridge relative to the first while the exact injection time and injection amount from each injector can be varied depending on the operational state of the engine with the aid of by-pass valves which are also used to determine if any injection should occur at all, i.e. the amount can be controlled to zero.
In one embodiment of the engine according to the invention with at least two cylinders, a cam element has a second cam ridge with a cam curve which achieves a second pump stroke a certain number of crankshaft degrees from the first pump stroke, and a second cam element has a second cam ridge with a cam curve which achieves a second pump stroke at another predetermined number of crankshaft degrees after the first pump stroke. The control unit is in this case arranged to control the by-pass valves of the injector depending on the engine load, so that extra fuel to the catalytic converter is injected through an injector having an earlier post-injection when the engine load is low (partial load) and through an injector with a later post-injection when the load is high (full load). In this manner a system is achieved which in practice provides essentially the same freedom as regards the injection time as a common rail system.
REFERENCES:
patent: 5094215 (1992-03-01), Gustafson
patent: 5787708 (1998-08-01), Lane et al.
patent: 5826425 (1998-10-01), Sebastiano et al.
patent: 5956942 (1999-09-01), Sebastiano et al.
patent: 5986871 (1999-11-01), Forck et al.
patent: 6016653 (2000-01-01), Glassey et al.
patent: 0 621 400 (1994-10-01), None
Larsson Bengt
Tengroth Stellan
Gimie Mahmoud M
Kamen Noah P.
Volvo Lastvagnar AB
Young & Thompson
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