Method and arrangement for controlling the metering of fuel in an internal combustion engine

The invention relates to a method and arrangement for controlling the fuel metered to an engine and especially to a diesel engine. The engine includes a fuel pump drive by a shaft for which injection start and injection end is fixed by a corresponding control of the electromagnetically actuated valve. The drive pulses for pump-delivery start and pump-delivery end are generated in dependence upon the analog signal of an angle sensor.

FIELD OF THE INVENTION 
The invention relates to a method and an arrangement for controlling the 
fuel metered to an internal combustion engine such as a diesel engine 
having a pump driven by a shaft. Injection start and injection end is 
fixed by correspondingly driving an electromagnetically actuated valve. 
BACKGROUND OF THE INVENTION 
Such a method and arrangement is disclosed in published patent application 
DE 35 40 811. In this publication, arrangement and method for controlling 
the metering of fuel in an internal combustion engine is described. A fuel 
pump includes a pump piston guided in a pump cylinder and driven by the 
cam shaft as well as a pump work chamber communicating with the injection 
nozzle via a pressure channel. Fuel is supplied to the pump work chamber 
via an electromagnetic valve. An electronic control arrangement determines 
the drive pulses for the electromagnetic valve in dependence upon control 
pulses initiated by marks on the crank shaft and by counting pulses 
triggered by marks on the cam shaft. The metering is very imprecise since 
the marks on the cam shaft have a finite spacing. The pump-delivery start 
and the pump-delivery end takes place only in discrete time intervals 
which are defined by the spacing of the marks on the cam shaft. The 
metering precision is therefore dependent upon the spacing of the marks. 
However, these markings cannot be as small as desired and therefore an 
imprecise metering occurs perforce. 
Published German patent application DE 36 42 678 discloses a measuring 
arrangement for rotation angles. This measuring arrangement supplies an 
analog output signal proportional to the rotation angle and an 
approximately linear interrelationship is present between rotation angle 
and output signal. 
Summary of the Invention 
It is an object of the invention to provide a method of the kind described 
above wherein the injection start and the injection end and therefore the 
quantity of fuel injected can be precisely controlled as desired. 
The method of the invention is for controlling the metering of fuel in an 
internal combustion engine such as a diesel engine, the engine having a 
fuel pump actuated by a shaft of the engine and an electromagnetically 
actuated valve for controlling the metering of the fuel to the engine. The 
method includes the steps of: fixing the injection start and the injection 
end by correspondingly driving the electromagnetically actuated valve; 
and, generating control pulses for pump-delivery start and pump-delivery 
end in dependence upon an analog signal of the analog sensor. 
With respect to the state of the art, the invention affords the advantage 
that the control of the pump-delivery start and the pump-delivery end can 
take place with substantially greater precision.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
As shown in FIG. 1, the internal combustion engine 10 is linked to a 
fuel-metering arrangement comprising an electromagnetically actuated valve 
40 and a fuel pump 30. An electronic control arrangement 20 detects 
signals of a measuring unit 60 which recognizes the state of the 
fuel-metering device. The control arrangement 20 further detects the 
signals of a measuring unit 101 which, in turn, detects the operating 
characteristic variables of the engine and the control arrangement 20 also 
detects signals of additional sensors 50. In dependence upon these 
signals, the electronic control arrangement 20 generates signals for 
driving the fuel-metering device of the engine. 
The fuel-metering device comprises at least an electromagnetically actuated 
valve and a fuel pump. The fuel-metering device meters fuel to the engine 
10 at pump-delivery start computed by the electronic control arrangement 
20 up to pump-delivery end. The fuel-metering device can be so configured 
that each cylinder is provided with an electromagnetic valve and a fuel 
pump. Another possibility is that only one electromagnetically actuated 
valve and one fuel pump 30 incorporating a distributing arrangement are 
provided for effecting the fuel supply. If the fuel-metering device 
comprises only one electromagnetic valve and one fuel pump, then this 
fuel-metering device meters fuel sequentially to the individual cylinders. 
The fuel pump 30 comprises essentially a pump piston driven by a drive 
shaft as well as a pump work chamber communicating with the injection 
nozzle via a pressure channel. The fuel reaches the pump work chamber from 
a low pressure fuel source via an electromagnetic valve. The pump piston 
is driven by the movement of the drive shaft 110 and the pump piston 
places the fuel in the pump work chamber under pressure and delivers the 
same via the injection valve into the cylinder of the engine 10. The 
opening and closing times of the electromagnetically actuated valve 40 fix 
injection start and injection end. The injected fuel quantity is dependent 
upon the rotation angle of the drive shaft between the time point of 
injection start and the time point of injection end. The drive must be 
dependent upon the position of the drive shaft to obtain a precise fuel 
injection. 
In conventional systems, markings are applied to the cam shaft or the 
crankshaft. Since these markings cannot be arranged as narrowly as 
desired, the precision of the fuel metering is limited by the spacing of 
these marks. 
The electronic control arrangement 20 first computes the desired quantity 
of fuel to be injected and the desired injection start in dependence upon 
the operating characteristic variables of the engine such as rotational 
speed, temperature values, and the output signals of various sensors 50. 
The control arrangement 20 determines the drive pulses for the 
electromagnetically actuated valves in dependence upon the desired values 
for the quantity and the injection start as well as further variables such 
as the actual injection start, the reaction time of the 
electromagnetically actuated valves and possibly data stored in the 
control apparatus. The computation of the switch-on time point and the 
switch-off time point is not made in dependence upon the markings on the 
cam shaft or crankshaft; instead, they are computed in dependence upon an 
analog signal of an angle sensor 100 which characterizes the position of 
the drive shaft of the pump piston and therefore also the position of the 
pump piston. 
FIG. 2 shows a possible interrelationship between the position of the drive 
shaft W and the output signal U of the measuring unit 60. In the angular 
range in which metering can occur, the output signal U of the measuring 
unit 60 increases as a function of the rotation angle W of the drive shaft 
and then drops again to the original value. If the electronic control 
arrangement 20 now computes a desired fuel delivery from the rotation 
angle W1 up to the rotation angle W2 of the cam shaft, then the control 
arrangement generates a drive pulse in the presence of an output signal U1 
of the measuring unit and a decontrol pulse for the electromagnetically 
actuated valve in the presence of the measuring signal U2. The fuel 
metering then takes place when the output signal of the measuring unit 
lies between the values U1 and U2 which correspond to angles Wl and W2, 
respectively. In this way, the start and end can take place at any desired 
angular position and is not dependent upon the discrete markings. The 
metering takes place precisely between the desired pump-delivery start and 
the desired pump-delivery end. A precise metering takes place by assigning 
a voltage value to each position of the pump piston. In the simplest case, 
a linear relationship is present between the cam shaft angle and the 
measuring signal. 
The measuring unit for detecting the rotation angle of the drive shaft can 
be mounted on the crankshaft, cam shaft or on the pump drive shaft. An 
especially advantageous configuration is obtained by providing a 
transducer for each cylinder on the particular drive shaft. In this way, 
torsion vibrations on the shaft can be compensated with pump-nozzle 
systems. The measuring unit 60 includes a transducer and an evaluation 
circuit. 
FIGS. 3a and 3b show an especially simple configuration of the transducer 
which is in the form of a so-called dragon transducer. A carrier disc 130 
is mounted on the shaft 110 whose rotation angle is to be detected. A 
coating 120 is applied to the carrier disc 130 and has a width which can 
be varied in dependence upon angle. Different coating materials can be 
used in dependence upon the principle according to which the transducer 
operates. Different ways of operating are known for the transducer, for 
example, eddy current or Hall effect. For an eddy current transducer, a 
conductive material such as copper can be used. One or more sensors 100 
then detect a signal which is dependent upon the width of the coating. The 
functional relationship between angle and measuring signal can be varied 
by the width of the coating in dependence upon rotation angle. 
Accordingly, and as shown in FIG. 2, a linear relationship between angle W 
and output signal U can be defined. The further evaluation is especially 
simple if a linear relationship exists between angle W and output signal 
U. An especially advantageous arrangement is one wherein the signal U 
increases greatly in an angular range wherein high precision is required 
and the signal U changes only slightly in an angular range in which 
reduced precision is required. This signal is then processed in the 
evaluation circuit and a voltage value is present at the output of this 
circuit or a current value U which is dependent upon the angular position. 
Such a measuring unit is disclosed, for example, in published German 
patent application DE 36 42 678. 
It is understood that the foregoing description is that of the preferred 
embodiments of the invention and that various changes and modifications 
may be made thereto without departing from the spirit and scope of the 
invention as defined in the appended claims.