Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2000-03-06
2001-10-30
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S447000
Reexamination Certificate
active
06308685
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and device for a transient operation of an internal combustion engine.
BACKGROUND INFORMATION
In vehicle engines with direct fuel injection, e.g. diesel engines or the recently developed direct injection gasoline engines, the fuel is compressed to a certain pressure in a pressure chamber and then distributed by injection valves to the individual combustion chambers. A constant fuel pressure is maintained, depending on the conditions.
In the case of direct gasoline injection (DGI), however, the fuel pressure takes on a greater significance because it is largely responsible for the quality of fuel preparation during injection as well as the depth of fuel penetration into the combustion chamber. To utilize the full potential of an internal combustion engine with direct gasoline injection, particularly in “stratified charge mode”—in which the fuel in the combustion chamber is distributed within channels or strata—different fuel pressures are set, depending on the working point. The fuel pressure is usually varied as a function of the load applied to the internal combustion engine as well as speed. This produces a transient change from one pressure level to another pressure level.
In contrast to the spark-ignition engine, in which a relatively constant pressure is applied to the fuel, the fuel pressure in direct-injection diesel or gasoline engines is set between approximately 40 bars and 120 bars. depending on the working point. In a direct-injection gasoline engine, the working points correspond, for example to the above-mentioned stratified charge mode, a homogeneous mode, or an idle mode.
A further operating parameter is the injection geometry selected for the injection nozzles, or rather the role it plays in the penetration geometry of the fuel injected into the combustion chamber.
Because this geometry and the injection nozzle properties are assumed to be constant, the injection geometry, i.e. the detailed variation of fuel in the combustion chamber, is almost entirely dependent on the fuel pressure present at the injection nozzle.
In conventional internal combustion engines, for example the diesel injection engine described in U.S. Pat. No. 4,777,921, the fuel is supplied by a high-pressure pump to a pressure chamber, referred to as a “fuel rail”. The pressurized fuel is then injected into combustion chambers from the pressure chamber by electrically driven injection valves according to the prevailing operating conditions in the internal combustion engine. The high-pressure pump is also driven by a control unit according to the prevailing operating conditions.
Due to cost and space constraints, the high-pressure pump is now becoming ever more compact. In contrast to this trend, the pressure chambers have a tendency to increase in capacity. since this inhibits, in particular, the formation of vapor bubbles in the pressurized fuel during hot operation or hot start. The main reason for this in particular is that a large-volume pressure chamber that extends almost all the way to the cylinder heads of the combustion chambers effectively prevents bubbles from forming in the pressure chamber area close to the cylinder head as a result of fuel convection. This increasingly prolongs the pressure buildup times needed in the pressure chamber due to necessary changes in fuel pressure. As a result, erroneous deviations from the desired pressure occur temporarily.
In the above-mentioned internal combustion engines with direct gasoline injection, the working points are subject to constant changes, which means that these engines are continuously within the transient range. Due to nitrogen oxide conversion, for example, the engine is constantly switching back and forth between homogeneous and stratified charge mode. In particular, this changeover is independent of the specific driver request. To this are added changes in the working point that are caused by new driver requests.
SUMMARY OF THE INVENTION
The present invention relates to a method and device for operating an internal combustion engine, in particular for a motor vehicle, in which fuel is delivered by a delivery pump to a pressure chamber where a corresponding pressure acting upon the fuel builds up. The pressure acting upon the fuel in the pressure chamber is measured. The fuel is injected by at least one injection valve directly into a combustion chamber of the internal combustion engine from the pressure chamber as a function of the measured pressure acting upon the fuel. The working point of the internal combustion engine changes upon a transition from a first pressure acting upon the fuel to a second pressure acting upon the fuel. The present invention also concerns a corresponding control unit for an internal combustion engine.
The object of the present invention is therefore to provide a method for operating an internal combustion engine as well as a corresponding internal combustion engine in which injection is controlled as accurately as possible even within the transient ranges. Another object is to provide a sufficiently comfortable driving performance even within the transient ranges, for example, avoiding momentary jolts due to the fact that the fuel pressure in the pressure chamber was not predicted or assumed with sufficient accuracy. In addition, the internal combustion engine must comply with legislated exhaust emission requirements even when operating within a transient range.
This object is achieved by the method according to the present invention in that the pressure acting upon the fuel is computed within the transient range between the first and the second pressures acting, upon the fuel in the pressure chamber, and the working point of the internal combustion engine is adjusted correspondingly to the actual pressure acting upon the fuel. According to the method, it is thus possible to set a fuel pressure according to need by predicting the actual value of the fuel pressure in the pressure chamber. Knowledge of this fuel pressure is then used to adjust the present working point of the internal combustion engine to this actual value. This ensures that the internal combustion engine remains fully controllable even when operating within a transient range as described above and can thus operate at the optimum working point even within this range.
According to one embodiment of the present invention, the method according to the present invention enables the pressure acting upon the fuel to be derived in each case on the basis of a model calculation. A model calculation of this type enables the fuel pressure to be determined with a relatively high degree of accuracy even within the transient range, thus allowing the corresponding working point of the internal combustion engine to be set with the same degree of accuracy.
According to a preferred embodiment of the method according to the present invention the actual pressure acting upon the fuel within the transient range can be derived from a variation over time in the pressure buildup and pressure release, respectively, using the input quantities of the first and second pressures acting upon the fuel, the delivery volume of the delivery pump, and the volume of the pressure chamber. The existing pressure buildup and pressure release, respectively, within the transient range can thus be modeled correspondingly on the basis of the difference between the first and second pressures acting upon the fuel. This requires a known delivery volume of the delivery pump and also generally represents a function that is dependent on the internal combustion engine speed. The volume of the pressure chamber must also be provided as a fixed quantity.
According to a further embodiment of the method according to the present invention, the determination of the actual pressure acting upon the fuel within the transient range can also take into account the pressure release caused by the fuel mass injected from the pressure chamber into the combustion chamber. Assuming a relatively large pressure chamber volume the pressure re
Gimie Mahmoud
Kenyon & Kenyon
Robert & Bosch GmbH
Yuen Henry C.
LandOfFree
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