Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1997-07-14
1999-07-20
Moulis, Thomas N.
Internal-combustion engines
Charge forming device
Fuel injection system
123448, 123445, F02M 4116
Patent
active
059244089
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a fuel metering system for feeding fuel from a storage tank to the cylinders of a combustion engine, comprising a fuel supply unit and a distributing device comprising at least one rotor, with the fuel supply unit continuously supplying fuel from the storage tank to the distributing device, and with the distributing device, depending on the angle of rotation of the rotor, sequentially feeding fuel to the cylinders of the combustion engine while determining for each cylinder during what period fuel is injected at the cylinder.
Such a system is known from, for instance, German Offenlegungsschrift 2921766. According to the German Offenlegungsschrift, the object contemplated is to provide a system in which the use of electromagnetic (on/off) injectors is avoided. This is realized by a rotor/stator combination, with the rotor being driven by a stepping motor. The angular displacement of the rotor is here time-controlled. The rotor is triggered by a reference on, for instance, a camshaft. After being triggered, the rotor rotates through a predetermined angle under the control of the stepping motor, wholly independently of the crankshaft and camshaft. Thereafter the rotor is stationary for a predetermined period. The period during which the rotor is stationary in an open position is dependent on the load of the engine and not directly on the speed of the engine, i.e., independent of the speed of rotation of the crankshaft and camshaft and hence independent of the instantaneous angle of rotation of the crankshaft and camshaft. During the period when the rotor stands still, fuel is fed to one of the cylinders, or fuel is fed to none of the cylinders. Here, as with systems in which injectors are used with a pulse width control, the fuel supply is switched on and off, respectively, under time control. Such a control of the fuel flow by variation of the open and/or closed time of a rotating valve with a discrete number of stable angular positions, is in practice difficult to realize, if at all. Stepping motors have a limited speed and therefore are generally not suited for such a control. The rotor/stator combination needs time to rotate through the closed position. The longer the mechanical valve (at a particular speed of the engine and the rotor) is in the open position, the more time to move through the closed position is lost. Conversely, the maximum time left for the open position is the time of the period minus the minimum closed time.
Further, the known rotor/stator combination involves a minimum open time: the time needed to move through the open position as fast as possible. That is also a disadvantage of that mechanical metering device over electromagnetic injectors, because the minimum pulse width thereof is zero. The control range of the known quantity control according to the Offenlegungsschrift is therefore by definition smaller than that of an electromagnetic one with pulse width control.
If several cylinders are provided with fuel by one mechanical distributor, an additional problem arises. The rotor rotates (in the case of a four-stroke engine) at half the crankshaft frequency. When the rotor must deliver fuel for all cylinders in one revolution, the frequency of the fuel pulses increases with the number of cylinders. The number of angular positions thereby increases proportionally to the number of cylinders. So at a given speed of the engine (and the rotor) the step time decreases proportionally. Or, at a given step time of the stepping motor, the maximum attainable speed of the rotor decreases proportionally.
The minimum open time is one stepping period. Without adjustments of the fuel pressure, this results in the minimum quantity of fuel being delivered even at zero load (no couple, so no fuel needed). If that quantity is made slight by reducing the passage, this in turn leads directly to unacceptable consequences for full load at high speeds. In that case the rotor cannot remain long in the opened position to deliver the required quantity of f
REFERENCES:
patent: 2955583 (1960-10-01), Dahl et al.
patent: 4184465 (1980-01-01), Nakazeki et al.
patent: 4200074 (1980-04-01), Kosuda et al.
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