Method and device for open-loop control of a solenoid-valve regulated fuel-metering system

A method and device for controlling a solenoid-valve-regulated fuel-metering system. Given the desired angular position of a fuel pump camshaft at the beginning of fuel delivery and the desired angular duration of fuel delivery, the method and device of the present invention, while accounting for the switching time of the solenoid valve, determines the trigger instant and shut-off instant for at least one solenoid valve. The present invention achieves more accurate and stable fuel-metering by treating the switching time of the solenoid valve as an angular quantity.

FIELD OF THE INVENTION 
The invention relates to a method and device for the control of 
fuel-metering systems for internal-combustion engines. More specifically, 
it pertains to the open-loop control of solenoid-valve-regulated 
fuel-metering systems. 
BACKGROUND OF THE INVENTION 
Devices and methods for controlling solenoid-valve-regulated fuel-metering 
systems are well known in the automotive technology. 
German Patent Application No. 40 04 110 discloses a method and device for 
controlling a diesel engine using a solenoid-valve-regulated fuel pump. 
The fuel pump described therein includes a pump piston, driven by a 
camshaft, which pressurizes the fuel and delivers it to the individual 
cylinders. The beginning and end of fuel delivery are actuated by means of 
at least one solenoid valve. A control unit calculates trigger instants 
for the solenoid valve in accordance with markings configured on a shaft. 
A problem with known systems arises by virtue of the fact that the 
fuel-metering control unit emits trigger signals based upon time 
quantities. The exact beginning of fuel injection must take place when the 
engine camshaft assumes a particular angular position. Injection ends when 
the camshaft has rotated through a specific angular displacement from its 
angular position at the beginning of injection. For this reason, time 
quantities must be converted into angular displacements and vice versa 
using the rotational speed of the camshaft as the conversion factor. The 
accuracy of this calculation depends directly on the accuracy of measuring 
the rotational speed. 
In the prior art, the instantaneous rotational speed at the sampling 
instant immediately prior to calculation is used to convert between time 
quantities and angular displacements. 
A method and device for so controlling a solenoid-valve-regulated fuel pump 
are described in German Patent Application No. 40 04 107. Given the 
desired starting point of injection and the desired duration of fuel 
delivery, the electronic control system, disclosed therein, determines the 
trigger instant and the shut-off instant for one or more solenoid valves. 
That system also accounts for the switching time of practical solenoid 
valves. The switching time of a solenoid valve is that time which elapses 
between the application of a triggering signal and the completed reaction 
of the solenoid valve. In the system described in the aforementioned 
patent, the switching times of the solenoid valves are handled as time 
quantities. Due to the fact that the switching time of the solenoid valves 
follows from a corresponding reduction in the residual times, the 
influence of the switching times is not adequately compensated for, 
causing inaccurate fuel-metering. 
The method and device of the present invention overcome the inaccuracies of 
fuel-metering in known systems. 
SUMMARY OF THE INVENTION 
In the device of the present invention, substantially more precise 
fuel-metering is possible because the switching times of the solenoid 
valves are handled as angular displacements. 
The advantage of representing the solenoid switching time TA as an angular 
displacement is particularly true in systems operating at high rotational 
speeds and using slow solenoid valves with long switching times. The 
device of the present invention determines the angular equivalent of a 
time quantity using an average rotational speed value. The angular range 
over which the rotational speed is averaged is flexibly adapted to the 
angular displacement corresponding to the switching time. This feature of 
the present invention makes it possible to minimize fluctuations in the 
switching time resulting from errors in sampling the instantaneous 
rotational speed. 
Furthermore, the reliability of the device of the present invention is 
improved over known systems. As rotational speed rises and the angular 
displacement representing the trigger time is kept constant, the solenoid 
valve switching times are compensated for simply by moving up the entire 
solenoid trigger pulse to an earlier time. This has the effect of reducing 
the quantity of fuel injected as rotational speed increases. This effect 
contributes considerably to the stability of operation of the 
internal-combustion engine. 
In systems embodying the present invention in which a pump element as well 
as a solenoid valve are allocated to each cylinder of an 
internal-combustion engine, only the average switching time of the several 
solenoid valves is represented as an angular displacement. Therefore, 
samples from control system are used to determine the angular equivalent 
from a time quantity. The advantage of this procedure is that the same 
extrapolation base for the trigger instant can be used for all working 
points independently of the particular solenoid valve. 
The method and system of the present invention works with standard valves. 
Furthermore, small injection quantities are possible, as are required, for 
instance, during preliminary fuel-injection. In addition, an improved 
reproducibility of working points is attained over various solenoid 
valves.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 illustrates a control system for a solenoid-valve-regulated fuel 
pump of a diesel engine. Fuel is pumped to the individual cylinders of an 
internal-combustion engine (not shown) via fuel pump 10 containing pump 
piston 15. A fuel pump 10 can be provided for each cylinder (pump-nozzle 
system), or one fuel pump (distribution pump) can alternately meter fuel 
for several cylinders. 
Fuel pump 10 is connected to solenoid valve 20. Valve 20 receives switching 
pulses, via power output stage 40, from electronic control unit 30 which 
includes read-only memory 35. Transmitter 70, which is located on solenoid 
valve 20 or on an injection nozzle (not shown), supplies signals to 
electronic control unit 30. 
Angular marks are located on incremental gear 55 mounted on pump camshaft 
60. Two marks define one increment. Incremental gear 50 has at least one 
increment gap. An increment gap can be realized, for example, by a 
removing a mark or by other appropriate means. 
Measuring device 50 generates an electrical pulse, which is supplied to 
control unit 30, as each angular mark passes by the measuring device. Thus 
the signal generated by measuring device 50 is indicative of the angular 
position of pump camshaft 60. The camshaft or crankshaft of the 
internal-combustion engine or a shaft coupled to it can act as the pump 
camshaft. As such, the rotary motion of the engine camshaft or crankshaft 
can be monitored instead of the rotary motion of the pump camshaft. An 
induction transducer, an eddy-current detector, or any other detector may 
be used to measure the position of the pump drive shaft. An example of 
such detector is measuring device 50. Other sensors 80, such as the 
average camshaft rotational speed N, temperature T, or load L (gas-pedal 
position), provide information about additional quantities to control unit 
30. The average rotational speed N is sampled over a larger angular range 
than is the pump camshaft position. For this function, a sensor which 
supplies a small number of pulses, e.g. 1-4, for each rotation of the 
shaft, is preferred. These pulses are evaluated to determine the average 
rotatonal speed N. Determination of the average rotational speed is 
implemented so as to allow the rotational speed to be averaged preferably 
over one engine cycle or one combustion process. 
Control unit 30 determines the angular position WB which is the desired 
angular position at which fuel delivery is to begin. It also determines 
the angular displacement, WD, representing the desired duration of the 
solenoid trigger signal. These angular quantities are shown in FIG. 2c. WB 
and WD are determined by control unit 30 in accordance with the parameters 
acquired by sensors 80 and the rotary motion of pump camshaft 60 as 
detected by measuring device 50. Based on the values WB and WD, control 
unit 30 then determines trigger instants A and E (shown in FIG. 3a) for 
activating power output stage 40. Among other things, one or more of the 
variables: rotational speed, air temperature, lambda (.lambda.) value, 
fuel temperature, other temperature values, or a signal characterizing the 
position of the gas pedal or the desired traveling speed can be entered as 
operating parameters. 
Pump camshaft 60 drives pump piston 15 causing it to pressurize the fuel in 
fuel pump 10. Solenoid valve 20 controls the fuel pressure. Valve 20 is 
configured so that no significant fuel pressure is established when it is 
open. Not until valve 20 is closed, does fuel pressure build up in fuel 
pump 10. Alternatively, valve 20 can be configured to cause fuel pressure 
to build up when it is open. 
Once a certain fuel pressure has been attained in fuel pump 10, a valve 
(not shown) opens and the fuel is injected, via an injection nozzle (not 
shown), into a combustion chamber of the engine. Transmitter 70 indicates 
at which instant solenoid valve 20 opens or closes. Transmitter 70, which 
can also be installed on the fuel injection nozzle, generates a signal 
that indicates the actual beginning or end of the injection of fuel into 
the combustion chamber. In lieu of the output signal from transmitter 70, 
a signal indicating the position of solenoid valve 20 can also be used. 
Such a signal can be obtained by monitoring the currents or voltages 
applied to the solenoid. 
FIG. 2 depicts the conversion of angular displacements into time 
quantities. FIG. 2a shows a typical pump camshaft rotational speed profile 
over one fuel-metering cycle. The rotational speed values fluctuate 
discretely from increment to increment. Within the course of the 
fuel-metering cycle, the rotational speed decreases over time. FIG. 2b 
shows the pulses generated by measuring device 50, caused by the rotation 
of incremental gear 55. Each angular mark on gear 55 generates a pulse in 
the measuring device 50. Two pulses define one angular increment. It is 
particularly advantageous when the distance between two angular marks is 
smaller by a so-called increment than the smallest possible trigger angle 
WD. An angular increment of 3 degrees is typically satisfactory. 
The solenoid valve trigger signal is shown in FIG. 2c with angular 
quantities determinative of the desired fuel-metering. The quantity of 
fuel metered depends on the angular displacement WD which determines the 
duration of fuel delivery. WD is defined by the angular position WB, which 
indicates the beginning of fuel delivery, and WE, which indicates the end 
of fuel delivery. 
As represented in FIG. 2c, the angular positions WB and WE are divided, 
respectively, into angular components WBG and RWB, and WEG and RWE. The 
components WBG and WEG are integral multiples of angular increments. The 
residual angular components, RWB and RWE, correspond respectively to the 
residual times TB and TE. The conversion of residual angular components 
RWB and RWE into residual times TB and TE is accomplished using the 
instantaneous rotational speed n of pump camshaft 60. The relationship of 
a residual time Ti to its corresponding residual angular component RWi is 
expressed by the following expression: 
EQU Ti=RWi/(6.times.n) (1) 
The instantaneous rotational speed n is determined over a measuring angular 
range, MW, which represents the angular displacement of one or more 
angular increments delineated by points M and W in FIG. 2b. These points 
are selected to precede, as closely as possible, the particular residual 
time segment to be calculated. Camshaft 60 rotates through the measuring 
angular range MW in the measuring time MT. MW and MT are used to calculate 
the momentary rotational speed n from which the residual time TB or TE is 
calculated in accordance with the expression above. 
The time required to perform the above calculations is represented by the 
computational time TR. The computation of TB must be completed before fuel 
delivery begins. Thus the rotational speed of the camshaft must be 
determined and the calculation of TB must commence earlier than a time 
interval equal to the sum of the measuring time MT and the computational 
time TR, before the desired beginning of fuel delivery as defined by WB. 
This process is repeated to determine TE for the end of fuel delivery. 
The trigger signal for solenoid valve 20 is shown in FIG. 3a. At the 
trigger instant E, the solenoid valve receives a signal causing it to 
assume a position in which the fuel delivery begins. After the period of 
time represented by the angular displacement WD, the trigger signal ends 
at the trigger instant A. 
The solenoid valve position is represented by FIG. 3b. Switching time TA 
elapses between E, the point at which triggering begins, and the actual 
closing of solenoid valve 20. Likewise, a switching time TA elapses 
between A, the point at which triggering ends, and the actual opening of 
solenoid valve 20. The angular displacement WTA corresponds to switching 
time TA. Although the switching angular displacements for both transitions 
are shown with the same designation in this example, in practice they will 
typically be different. 
FIG. 3c shows the output signal of measuring device 50, which detects the 
rotation of incremental gear 55. Control unit 30 specifies the angular 
displacement WB, between a reference pulse R and the instant at which the 
solenoid valve is to be completely closed. This instant corresponds to the 
beginning of fuel delivery. As described above with regards to FIG. 2, WB 
is broken down into an integral angular component, WBG, and a residual 
angular component, RWB. RWB is converted into the residual time value TB. 
Triggering of the solenoid occurs after residual time TB elapses. 
In order to compensate for the solenoid valve switching time, TA, the 
residual angular displacement to the beginning of solenoid triggering, 
RWB, must be reduced by the angular displacement corresponding to TA, WTA. 
It is assumed that determining the trigger instant E requires a 
computational time, TR, which cannot be disregarded. The angular 
displacement representing the computational time is denoted WR. Thus, as 
is apparent from FIG. 3c, residual angular component RWB must be greater 
than the sum of WTA and WR. In order to meet this constraint, integral 
angular component WBG must be selected accordingly. The calculation of 
switching angular displacement WTA, given switching time TA, is based on 
the camshaft rotational speed determined over the measuring angular range 
MW. The same procedure is followed when determining the shut-off instant 
A. 
The flow chart of FIG. 4 shows the order in which the various quantities 
are calculated. Step 405 estimates how large the measuring angular range 
MW should be optimally. The average camshaft rotational speed N is used to 
estimate how many angular increments the switching time TA spans. This 
rotational speed signal is continuously available and is accurate enough 
for purposes of estimation. Given the average rotational speed and TA, an 
estimated value can be calculated for the switching angular displacement 
WTA. This value is then divided by the angular displacement of one 
increment. The result of this division yields an estimated number of 
angular increments over which WTA extends. Preferably, the measuring 
angular range MW is selected to be nearly equivalent to the estimated 
switching angular displacement WTA. This means that the difference between 
MW and the estimated value of WTA should be no greater than one angular 
increment. 
Step 410 entails determining the angular position WB of the pump camshaft 
at the beginning of fuel delivery. As is known in the prior art, WB is 
selected in accordance with various operating conditions. WB can be stored 
in a table of engine characteristics. 
In step 420, WB is broken down into integral component WBG and residual 
component RWB. As discussed above, the values of these components are 
selected in accordance with the time constraints attributable to the 
computation time. 
In step 430, the solenoid valve switching time TA is separated into an 
average switching component, TAM, and an individual switching component, 
TAI. This approach is appropriate in systems with multiple solenoid valves 
as where a separate pump element with a solenoid valve is allocated to 
each cylinder of an internal-combustion engine. TAM denotes the average 
switching time of all solenoid valves in the system. The individual 
switching time TAI allows for deviations of the individual solenoid valves 
from the average value. 
The average component TAM is then converted in step 440 into the 
corresponding angular displacement WTAM. This conversion is carried out in 
accordance with the following equation 
EQU WTAM=6.times.n.times.TAM (2) 
where n represents the instantaneous rotational speed of the pump camshaft. 
The residual angular displacement RWB is subsequently reduced in step 450 
by the average switching angle WTAM. The reduced RWB is then converted in 
step 460 into the residual time TB. 
The varying individual switching times TAI are accounted for in step 470, 
in which the calculated residual time TB for each solenoid is reduced or 
increased by the corresponding individual switching time TAI. The 
advantage of this procedure is that the calculation of step 460 need only 
be performed once each fuel-metering cycle for all solenoid valves. Only 
step 470, which involves a simple subtraction, need be carried out 
individually for each solenoid valve. 
The present invention also provides for the average switching angle to be 
entered at the time of the setpoint selection of the beginning-of-delivery 
angle WB. This can be accomplished by use of an engine characteristics map 
for the beginning-of-delivery angle WB containing the appropriate values 
while allowing for the average switching time TAM of the solenoid valves 
or by reducing the beginning-of-delivery angle WB by the amount of the 
switching angle. 
The accuracy of converting the time quantity TAM into its corresponding 
angular displacement WTAM, per the above expression, will be adversely 
affected by errors in determining the instantaneous camshaft rotational 
speed n. In known systems, in order to obtain the most current possible 
value, the camshaft rotational speed is evaluated over only one increment. 
This increment immediately precedes the calculation of the trigger signal. 
This practice leads to problems, particularly in the case of systems 
operating at high rotational speeds or with slow solenoid valves having 
long switching times. In these cases, the solenoid switching time TA will 
have a relatively large corresponding angular displacement WTA which will 
extend over several increments. 
Measurement of rotational speed over just one increment is susceptible to 
errors. Such errors can be caused, for example, by computational 
inaccuracy or sampling error. The effect of even a small error occurring 
when the rotational speed is measured over one increment will be 
multiplied when applying this value over a considerably larger angular 
range. 
To avoid this multiplying effect, the method of the present invention calls 
for matching the measuring angular range MW over which the rotational 
speed is determined, to the size of the switching angular displacement 
WTA. If WTA extends over several increments, then MW is likewise selected 
to span several angular increments. Preferably, the number of increments 
over which the measuring range extends is equal to the number of 
increments over which the switching displacement extends. 
A further improvement of the present invention over the prior art is 
obtained by keeping WD, the angular duration of solenoid triggering, 
constant, regardless of the rotational speed. Referring to the first 
expression above, it is clear that as rotational speed n increases, the 
residual times TB and TE decrease accordingly. The result is that the 
trigger beginning instant E and the trigger ending instant A are shifted 
up to an earlier time. Furthermore, referring to the second expression 
above, as rotational speed n increases, WTA increases accordingly. With WD 
remaining constant, as WTA increases with rotational speed, the angular 
range over which the solenoid valve is actually closed, and, thus, over 
which fuel is delivered, decreases. Thus, given a rising rotational speed 
with a constant solenoid trigger angular duration, WD, a decreasing 
quantity of fuel delivery results. 
FIG. 5 shows the solenoid trigger signal for three different rotational 
speeds, and how WTA, RWB and E vary accordingly. It is important to note 
that the horizontal scale is angular position and not time. Fuel-metering 
is independent of rotational speed at the desired beginning-of-delivery 
angle WB. The desired angular position WB of the fuel pump at the time 
fuel delivery begins is represented by the dashed perpendicular line. 
The solenoid trigger signal for a low rotational speed is shown in FIG. 5a. 
The switching angular displacement WTAI of the solenoid valve is very 
short. The trigger instant E1 shortly precedes WB. The majority of the 
solenoid trigger duration follows WB, the desired angular position at 
which fuel delivery begins. 
The solenoid trigger signal for a higher rotational speed is shown in FIG. 
5b. WTA2 is perceptibly larger than WTA1. The trigger instant E2 has 
perceptibly moved up to an earlier angular position. Only a small part of 
the trigger angular duration WD still lies after WB. Thus, the quantity of 
fuel delivered is less in this case than in that depicted in FIG. 5a. 
The solenoid trigger signal for a very high rotational speed is shown in 
FIG. 5c. The switching angular displacement WTA3 is virtually as large as 
the trigger angular duration WD. The trigger instant E3 is moved up to an 
even earlier angular position. Only an extremely small part of the trigger 
duration still lies beyond WB. The quantity of injected fuel is now even 
less than in the case of FIG. 5b. 
The terms and expressions which are employed herein are used as terms of 
expression and not of limitation. There is no intention, in the use of 
such terms and expressions, of excluding the equivalents of the features 
shown and described, or of portions thereof, it being recognized that 
various modifications are possible within the scope of the invention.