Method and device for the open-loop and/or closed loop control of a final controlling element

A method and a device for the open-loop and/or closed-loop control of a final controlling element, in particular for influencing the fuel injected into an internal combustion engine, are described. A system deviation is defined starting from a setpoint and an actual value. On the basis of the system deviation, a loop controller specifies a manipulated variable to be received by the final controlling element. If the system deviation lies outside of a range defined by at least two values, a maximum value is specified for the manipulated variable.

FIELD OF THE INVENTION 
The present invention relates to a method and apparatus for open-loop 
and/or closed-loop control of a final controlling element. 
BACKGROUND OF THE INVENTION 
German No. 34 00 711 (corresponding to U.S. Pat. No. 4,638,782) describes 
an open-loop and/or closed-loop control of a final controlling element for 
influencing the metering of fuel into an internal combustion engine, 
wherein a system deviation is defined starting from a setpoint and an 
actual value. On the basis of the system deviation, a loop controller 
specifies a manipulated variable to be received by the final controlling 
element. A loop controller, preferably having Proportional-Plus-Integral 
(PI) action executes a closed-loop control at high rotational speeds. In 
certain operating states, particularly at low rotational speeds, only an 
open-loop control of the final controlling element takes place. 
Such PI controllers require a very high degree of complexity for 
applications, especially when different parameter sets are provided for 
high-level and low-level signal action. At low rotational speeds, no 
closed-loop control operation is possible. Instead, only an open-loop 
control of the final controlling element is provided. Another disadvantage 
of the known procedure is that it is very difficult to optimally design a 
loop controller. For example, for large system deviations, it is desirable 
to have very large gains (i.e., amplification factors) in the loop 
controller. On the other hand, when there are small system deviations 
(low-level signal action), it is advantageous to have very small gains. 
SUMMARY OF THE INVENTION 
The method and apparatus according to the present invention have an 
advantage of allowing the final controlling element to be optimally 
adjusted in all operating states. 
In accordance with the present invention, by providing at least one maximum 
value for the manipulated variable when the system deviation lies outside 
of a range defined by at least two values, a considerable improvement in 
the control response can be achieved. The degree of accuracy can be 
further improved for low-level signal action by applying a PI-controller 
within the above-defined range. 
At low rotational speeds, for example, the actual-value signal occurs only 
at larger time intervals. In such a situation, it is known to change over 
to an open-loop control. However, if one wants to retain closed-loop 
control, the control parameters must be adapted to these large time 
intervals between actual-value signals. This results in a very slow loop 
controller. Therefore, in accordance with an embodiment of the present 
invention, the actual value, or rather the system deviation between the 
discrete instants, is calculated by applying a model to the actual value 
acquired. This model requires only a very limited accuracy, since it is 
only the change in the actual value, or rather in the system deviation 
since the last acquisition of the actual value, that has to be calculated.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 depicts a block diagram of an illustrative device according to the 
present invention. Internal combustion engine 100 receives metered-in fuel 
from a pump 110. A drive circuit 120 triggers an injection-timing device 
in the pump 110 to adjust the start of pump delivery (the start of fuel 
injection). 
An output signal P from a loop controller 130 arrives via a first switch 
125 at the drive circuit 120 for the injection-timing device. An output 
signal D from a node 140 is fed via a second switch 135 to the loop 
controller 130. The output signal SBD from a summary point 145 is applied 
to the one input of the node 140. The output signal SBI from a 
needle-motion sensor 105, which is preferably mounted on the internal 
combustion engine, is applied to summary point 145 with a positive 
operational sign. The output signal SBS from a setpoint selection 150 
arrives with a negative operational sign at the summing point 145. 
By means of the first switch 125, the drive circuit 120 for the 
injection-timing device is able to alternatively receive an output signal 
PMAX from a maximum-value selection unit 132 or an output signal PMIN from 
a minimum-value selection unit 134. By means of the second switch 135, the 
loop controller is able to receive an output signal from an initialization 
module 165. 
Via a third switch 162, an output signal SBIM from a model 160 is applied 
to the second input of the node 140. The model 160 receives the output 
signal SBI from the needle-motion sensor 105 and the current manipulated 
variable PI. In the simplest exemplified embodiment, the model is a 
PT1-element or an integrator. However, the model can also be conceived as 
an observer, or rather as a more or less comprehensive computer program. 
The output signal from the node 145 arrives, in addition, at the 
initialization module 165, as well as via a fourth switch 175 at a 
switching module 170. By means of the switch 175, the switching module can 
optionally receive the output signal from the node 140. The switching 
module 170 applies appropriate trigger signals to the switches 135 and 
125. 
The switches are usually situated in the position that is drawn in with a 
solid line. In such a case, the functioning of the device is as follows. 
Starting from the comparison between the setpoint value SBS, which is able 
to be specified by the setpoint selection 150, and the actual value SBI 
for the start of injection, the loop controller 130 defines a signal P to 
be applied to the drive circuit 120 for the injection-timing device. The 
loop controller 130 preferably exhibits PI action. However, the invention 
is not limited to loop controllers having PI action. It can also be 
applied to systems in which loop controllers having a different action are 
used. 
The signal P controls the adjustment angle of the fuel injection. This 
adjustment angle is preferably realized by the drive circuit for the 
injection-timing device by triggering a solenoid valve with a pulse duty 
factor. The pressure in the injection-timing device is able to be 
influenced by means of this solenoid valve. The injection-timing device 
assumes a specific position in dependence upon the pressure. Depending on 
the position of the injection-timing device, the injection begins at 
different instants. The exact instant of the beginning of injection is 
able to be acquired, for example, by means of a needle-motion sensor 105. 
This acquired actual value SBI is compared with respect to the start of 
injection to the setpoint value SBS and fed to the loop controller. 
If large system deviations occur, for example, when there is a substantial 
change in the setpoint value SBS, then the injection-timing device 
requires a certain time to reach the new setpoint value. Therefore, the 
present invention provides for the system deviation SBD to be fed to the 
switching module 170. If the switching module recognizes that the system 
deviation SBD is greater than an upper threshold value, or smaller than a 
lower threshold value, then the second switch 135 is switched into its 
position shown with a dotted line. 
Moreover, depending on whether the system deviation falls below a lower 
threshold value or rises above an upper threshold value, the switch 125 is 
switched to its upper (to 132) or its lower (to 134) position. Thus, the 
drive circuit 120 for the injection-timing device receives either a 
maximum value PMAX or a minimum value PMIN. The result is that the 
injection-timing device and, consequently, the actual value, assume their 
new value very quickly. If the system deviation SBD lies outside of a 
range defined by the upper and lower threshold values, then the loop 
controller is switched off and a maximum value is specified for the 
manipulated value. If the system deviation lies within the defined range, 
then the loop controller 130 is active. 
In accordance with a further embodiment of the present invention, several 
ranges can be defined. In this case, it is possible for different values 
to be selected in the various ranges. 
When the loop controller is switched off, i.e., when the switch 135 and 125 
are opened, the I-component of the loop controller is frozen. This means 
that the output quantity P from the loop controller is stored. When the 
loop controller is switched on again, i.e., when the switch 125 goes over 
again into its position drawn with a solid line, the switch 135 returns to 
its original position after a slight delay. 
Referring to FIG. 2, in a first step 200, the setpoint value SBS and the 
actual value SBI are acquired (or determined) for the start of injection. 
The system deviation D2 is determined in a second step 205. The defined 
range within which a closed-loop control and outside of which an open-loop 
control take place is then specified in step 210. 
The magnitude of this range is usually constant. In accordance with a still 
further embodiment of the present invention, the magnitude of this range, 
the upper and lower threshold values FEN- and FEN+, are specified as a 
function of the rotational speed. In the simplest case, the threshold 
values are selected to be inversely proportional to the rotational speed 
N. Thus, they can be selected in accordance with the formula: 
EQU FEN=K/N. 
In this case, K is a constant which corresponds to the magnitude of the 
range given a defined rotational speed. N is the current, average 
rotational speed. 
A query 215 checks whether the system deviation D2 is greater than the 
upper threshold value FEN+. If this is the case then the maximum possible 
manipulated variable PMAX is selected in step 220. This means that the 
second switch 135 is switched to its lower position, and the first switch 
125 is switched to its upper position. 
If the query 215 determines that the system deviation is less than the 
upper limit FEN+, then the second query 225 checks whether the system 
deviation D2 is less than the lower limit FEN-. If this is the case, then 
the minimum value PMIN for the manipulated variable P is selected in step 
230. This means that switch 135 and switch 125 are brought to their lower 
positions. In this case, the minimum setpoint selection 134 applies the 
minimum manipulated variable PMIN to the drive circuit 120 for the 
injection-timing device. 
Steps 220 and 230, in which switch 135 is opened, are followed by step 235, 
in which a storage device R is occupied by the value 1. This value 1 
indicates that the loop controller is becoming inactive and that the drive 
circuit 120 for the injection-timing device is receiving its minimum or 
maximum value. 
If the query 225 reveals that the system deviation D2 lies within the 
specified range, then it is checked in step 240 whether the loop 
controller was switched off during the preceding program run. This means 
that it is checked whether the storage device R holds the value 1. If R 
does not equal 1, this means that the loop controller was active during 
the preceding program run. The program then continues with step 255. If 
the query 225 determines that the loop controller was not active during 
the preceding program run, then the initialization module 165 calculates 
the manipulated variable IS2 in step 245. This is preferably done in 
accordance with the following formula: 
EQU IS2=IS1+D1-D2 
In the above formula, IS1 is the I-component of the manipulated variable 
when the loop controller is switched off; D1 is the system deviation when 
it is switched off; and D2 is the current system deviation when the loop 
controller is switched on again. 
The constant R is subsequently set to zero in step 250. This indicates that 
the loop controller is now active again. In step 255, switch 125 and 
switch 135 are subsequently switched into their position that is drawn in 
with a solid line. In the subsequent step 260, the values for the 
manipulated variable IS1 and for the system deviation D1 are occupied with 
the current values. The next program run starts subsequently with step 
200. 
The manipulated variable is preallocated in the same manner when the 
initialization module 165 consists of a differentiator. For this purpose, 
the differentiator continually applies its output quantity to the loop 
controller while the switch 135 is in its lower position. 
In any case, the device specifies the largest (or smallest) possible 
manipulated variable PMAX (PMIN), and switches off the loop controller 
when the system deviation SPD lies outside of a range defined by two 
threshold values FEN+ or FEN. If the system deviation again lies within 
the range, the loop controller 130 is switched back on. 
A smooth changeover is effected when the initialization module 165 is 
switched on at the time the loop controller is coupled back into the 
circuit. The optimal adjusting speed is able to be achieved for the 
injection-timing device within the large-signal range by utilizing only 
two additional parameters FEN+ and FEN. 
The above-mentioned embodiments work optimally when the check-back 
indication of the actual quantity SBI occurs relatively frequently. If 
this is not the case at lower rotational speeds, a changeover to an 
open-loop control may be used in some instances. However, as already 
described, it is possible to specify the range within which the loop 
controller is active in dependence upon rotational speed. 
One can eliminate adapting the control parameters when the loop controller 
supplies a new manipulated variable P only when a new actual value is 
present. This means that the injection-timing device is adjusted more 
slowly given a falling rotational speed, but it is still adjusted with 
closed-loop control. The range selected at low rotational speeds is 
preferably larger than that at high rotational speeds, since the time 
duration between the occurrence of the actual values is greater at low 
rotational speeds. 
In accordance with a still further embodiment of the present invention, a 
model 160 is employed. This model simulates the movement of the 
injection-timing device 120 since the last acquisition of the actual value 
SBI. Thus, this model continually operates a simulated actual value SBIM, 
which replaces the acquired start-of-injection actual value SBI. In this 
case, the device works as follows. 
If a signal (SBI) from the needle-motion sensor 105 appears, then the 
switch 162 is situated in its position that is drawn in with a solid line. 
In this case, the system deviation SBD is applied to the output of the 
node 145. If there is no current signal from the needle-motion sensor 105, 
then the switch 162 is in its closed (drawn with a dotted line) position. 
In this case, the setpoint value SBS in the node 140 is compared to the 
output signal from the model 160 SBIM. 
Thus, the system deviation follows on the basis of the comparison between 
the setpoint value SBS and the output signal from the model 160, which 
specifies the simulated actual value SBIM. This system deviation D is then 
fed to the loop controller 130 and to the switching module 170 in place of 
the system deviation SBD. 
The system deviation D arrives via the fourth switch 175, in place of the 
system deviation SBD, at the switching module 170. For this purpose, the 
third switch 162 and the fourth switch 175 are switched in synchronism 
with the occurrence of the start-of-injection actual value SBI. 
In accordance with a still further embodiment of the present invention, the 
model simulates the system deviation, and not the actual value, and makes 
available a correction signal to correct the system deviation SBD. In this 
case, suitable means keep the output signal from the needle-motion sensor 
105 constant, at the last value. 
Thus, the signal SBD from the node 145 is constant between the individual 
measuring pulses and is then corrected accordingly in the summing point 
140 by means of the output signal from the model 160. For this purpose, 
the model 160 makes available a corresponding correction signal during 
those time intervals in which no current actual value SBI is present. 
The actual value of the needle-motion sensor is, therefore, only available 
at discrete instants and is only acquired at these instants. The system 
deviation between the discrete instants, in which the actual value is 
present, is calculated by means of the model 160. 
Various signals are plotted over the time t in FIG. 3. In the partial FIG. 
3a, the instants, in which the signals NBI from the needle-motion sensor 
105 occur, are marked with arrows. They occur at an interval of DNBI. This 
interval is dependent upon rotational speed. Since only one needle-motion 
sensor is generally provided, this signal occurs once per revolution of 
the engine. The time interval between two such signals amounts, for 
example, in FIG. 2, to approximately 37 msec. 
The individual program runs are executed with a fixed sampling time T. 
Thus, for example, the program run in accordance with FIG. 2 is executed 
approximately every 10 msec. These instants when the program runs start 
are marked by perpendicular lines. Generally, the pulses from the 
needle-motion sensor 105 do not occur simultaneously with the sampling 
instants T. The difference between the two pulses is denoted by DT. 
The manipulated variable P is plotted over time in the partial FIG. 3b. The 
setpoint value SBS is drawn in with a dot-dash line in the partial FIG. 
3c. A solid line marks the actual value SBI. The start of injection SBIM 
calculated by the model 160 is drawn in with a dotted line. Also plotted 
are the threshold values FEN+ and FEN-, which correspond to the range 
within which a closed-loop control takes place. 
At the beginning of the time interval being considered, the setpoint value 
SBS and the actual value SBI nearly conform with one another. After an 
abrupt change in the setpoint value SBS, as drawn in FIG. 3c, there is no 
change whatsoever in the manipulated variable or in the actual value 
within the time DT until the next sampling pulse. The system deviation is 
only recalculated at the next sampling interval. At this instant, the 
device recognizes that the system deviation is greater than the threshold 
value FEN+. The result is that the manipulated variable assumes its 
maximum value PMAX. 
The change in the manipulated variable P causes the actual value SBI to 
rise over time. The start of injection SBIM calculated by the model 160 
likewise rises over time. This signal is drawn in with a dotted line. If 
the next signal from the needle-motion sensor appears, then the model 160 
is adjusted in the next sampling interval. This means that the output 
signal SBIM from model 160 is corrected so as to allow the values of the 
output signal SBIM from model 160 and the measured actual value SBI to 
conform. The correction value is denoted by DFBD in the Figure. The value 
of the output signal SBIM starts, in turn, at the acquired value SBI of 
the actual value. 
This process is continued until the system deviation D is smaller than the 
range defined by the threshold values FEN+ and FEN. At this instant, the 
loop controller 130 is activated, and the output signal from the loop 
controller is set to a corresponding value. The loop controller 130 
defines the corresponding manipulated variable P in dependence upon the 
system deviation between the actual value SBIM determined by the model 160 
and the setpoint value SBS. 
In this specific embodiment, the same threshold values FEN+ and FEN can be 
retained for all operating ranges, in particular in all rotational-speed 
ranges. By this means, the degree of complexity required for the 
application is reduced.