Internal combustion engine control system for use with turbo-charged engine, and method

To permit operation of engines, particularly turbo-charged engines, at the maximum power level just short of causing engine knocking, and preventing engine knocking, temperatures in the engine are sensed and, if an excessive temperature signal is detected, for example excessive engine temperature, exhaust gas temperature, turbo-charged air, or turbo charger temperature, a fuel supply system, for example a fuel injection system, is controlled to enrich the mixture, for example by multiplying the fuel injection time by a factor as commanded by an additional control stage (26, 27, 30) which stores in a memory, such as a ROM (27), engine operating characteristic curves. In addition, spark retardation by a retarding angle (.alpha.1) can be commanded, the spark retardation in combination with enriching of the fuel-air mixture being less than without such enrichment, thus permitting operation of the engine at appropriate power and efficiency level without noticeably increasing fuel consumption in the course of continued operation of the engine.

The present invention relates to a control system for internal combustion 
engines, and more particularly to internal combustion engines which 
include a turbo charger which so controls the engine that it operates at 
the most effective engine characteristics without, however, being 
subjected to overloading or excessive heating. 
BACKGROUND 
Internal combustion engines, for example of the gasoline type, with turbo 
supercharging, have the tendency to knock as the motor temperature 
increases. The tendency to knock is particularly serious upon substantial 
increase in engine operating temperature which, in turbo-charged engines, 
may readily occur due to the high degree of filling of the cylinders with 
combustible fuel-air mixture in accordance with the supercharging by the 
turbo charger. It has previously been proposed to prevent knocking of the 
engine by retarding the ignition timing (see, for example, German Patent 
Disclosure Document DE-OS No. 28 01 512 or DE-OS 26 59 239 to which U.S. 
Pat. No. 4,133,475 and 4,002,155 correspond). Many types of internal 
combustion (IC) engines, and particularly turbo-charged engines, then will 
have exhaust which is excessively hot, and cause excessive heating of the 
turbo charger. This is undesirable due to the resulting decrease in power 
and efficiency. It is also possible in turbo-charged motors to decrease 
the charge in pressure which, however, also decreases the power output. 
THE INVENTION 
It is an object to control the operating parameters of the engine such that 
the engine operates efficiently, yet does not overheat. 
Briefly, a control apparatus is provided which stores engine operating 
characteristics and has an engine operating temperature signal applied 
thereto, providing output signals to a fuel supply system, for example a 
fuel injection system, which, upon change of the temperature signal 
indicative of increased operating temperature and above a predetermined 
state represented by a point or level on a curve of the engine operating 
characteristics--which characteristics are stored in the control 
apparatus--controls the fuel supply to increase the proportion of fuel to 
air and to thereby enrich the fuel-air mixture being supplied to the 
engine. 
In accordance with a feature of the invention, a maximum limiting 
temperature is sensed which, when it is reached, inhibits flow of fuel to 
the engine. In addition to changing the fuel-air composition, the ignition 
timing can also be retarded. By enriching the fuel-air mixture, the degree 
of retardation of the spark can be substantially less, however, than in 
prior art systems, in which the fuel-air mixture was not interfered with. 
Both fuel enrichment as well as spark retardation can readily be set for 
specific engine types so that the engine will operate at its most 
efficient and power delivering characteristic operating point. 
The control system according to the present invention has the advantage 
that knocking of the IC engine can be prevented even at high engine 
temperatures without noticeable or substantial decrease in power output. 
Surprisingly, the increase in fuel use resulting from the increased fuel 
component in the fuel-air mixture is hardly noticeable, so that the 
average fuel consumption is hardly changed and can barely be measured. The 
reason appears to be that the increase in fuel occurs only if there is 
actual danger of engine knocking and is not continuously effective. 
Engines which operate with fuel injection can be controlled particularly 
easily, since characteristics which are stored in a computer controlling 
engine operation can be so arranged that fuel injection and ignition 
timing is set for optimum engine performance, for example for optimum 
minimum fuel consumption, without considering the results of such control 
with respect to the tendency to knock. By then increasing the fuel 
component of the fuel-air mixture, that is, by making the fuel-air mixture 
somewhat richer in order to prevent knocking, an additional control signal 
can be used which is derived as a modifying signal which can readily be 
introduced into a program controlled device as an additional modifying 
factor. Not only is knocking of the engine prevented but, simultaneously, 
excessive heating or boiling of the engine is reliably prevented. 
The temperature-dependent control which causes enrichment of the fuel-air 
mixture and/or changing of ignition timing, typically ignition 
retardation, can be derived from engine operating characteristic data 
stored in a suitable memory or storage device, for example a "read-only 
memory" (ROM). The point on the characteristic diagram at curve which 
causes change in the fuel-air composition, that is, enrichment of the 
mixture and/or change in ignition timing, can be selected based on 
temperatures measured at different points in the engine system, for 
example engine operating temperature, exhaust temperature, supercharging 
air temperature, or turbo supercharger apparatus, and, preferably, also 
based on speed and, if desired, additionally based on load placed on the 
engine, for example as sensed in the form of induction air absolute 
pressure, or a representative derived signal, which may for example be the 
timing signal in a fuel injection system.

Referring to FIG. 1: An electronic engine operation computer and engine 
characteristic memory 10 is controlled in dependence on engine operating 
parameters P, and provides output signals which control the dwell angle 
for the ignition, the ignition instant in form of an angle signal 
representative of an angle .alpha. with respect to the top dead center 
(TDC) position of a reference piston, as well as a basic fuel injection 
time ti of a fuel injection system. Such apparatus is known, see for 
example German Patent Disclosure Document DE-OS No. 28 50 534 or DE-OS No. 
30 00 562, to which U.S. applications Ser. No. 56,960, July 12, 1979, now 
U.S. Pat. No. 4,250,858, JEENICKE et. al., and Ser. No. 221,788, Dec. 31, 
1980, now U.S. Pat. No. 4,337,744, SEEGER et al., assigned to the assignee 
of this application, correspond; it is in public use, and installed in 
serially made motor vehicles, for example motor vehicles manufactured and 
sold by the German company BMW/(Bayerische Motoren Werke). The computer 10 
has a first control output terminal 11 providing an ignition control 
signal and a second control output 12 providing a fuel supply signal which 
is a time pulse to control opening of a fuel supply injection valve. The 
computer 10 includes a memory which provides the control outputs as a 
function of the engine parameters P in accordance with characteristic 
curves which are stored in the memory, for example in one or more ROMs, as 
described for example in the aforementioned publications, and in operating 
manuals, and as in actual public use. 
The ignition control signal output 11 is connected to an adder 13 which, in 
turn, is connected to an ignition system 14 which provides suitable spark 
energy, distributed to, for example, four spark plugs 15-18. The fuel 
supply signal output 12 is connected through a multiplier 19 to a fuel 
injection system 21 which, in the example shown, has four injection valves 
22 to 25, controlled thereby. Any desired number of fuel injection valves 
or spark plugs can be controlled by the system shown, and as modified in 
accordance with the present invention. 
A signal processing and analog/digital (A/D) conversion stage 26 has five 
temperature signals applied thereto. These five temperature signals, 
connected to inputs T1 to T5 are derived from suitable sensors, in which 
T1, for example, is engine temperature, T2 the exhaust gas temperature, T3 
induction or inlet air temperature, T4 charging air temperature derived 
from a turbo supercharger, and T5 the turbo charger temperature. 
Additionally, the stage 26 receives a signal representative of the speed n 
of the engine and a signal representative of the load L. The load signal L 
is preferably derived directly from the injection timing signal ti and 
representative of base fuel injection time. The two temperatures T4 and 
T5, of course, can be measured only at an engine having a turbo 
supercharger. In a simpler version, a lesser number of temperatures can be 
provided and evaluated, and in the simplest case, only a single 
temperature is necessary, for example engine temperature T1. In a simpler 
version, the input signal L representative of load and the speed signal n, 
or either of them, can also be omitted. 
The signal processing stage 26 processes the received input signals to 
change them to suitable processing levels, possibly passing them through 
wave-shaping or filtering networks to remove disturbances, and then, in an 
A/D stage, converts the received input signal into digital signal values. 
The digital signal values will be representative of addresses for the 
characteristic curves stored in an ROM 27 to which the processed signals 
are connected. The stored values read out from the ROM 27, in accordance 
with the addresses supplied by the stage 26, are then converted into 
analog values in D/A converter 28, deriving as the output from D/A 
converter 28 two control signals. The ROM 27 contains values relating the 
inputs to ignition angles .alpha.1 to provide appropriate output signals 
at output terminal 28', and two values F at output terminal 28" to modify 
the fuel supply signal from terminal 12 of computer 10. Providing control 
signals from characteristics stored in a memory, as such, is well known 
and can be carried out in accordance with any suitable method or system. 
The output from terminal 28' is applied as an adding input to terminal A 
of adder stage 13; the output from terminal 28" is supplied as a 
multiplying factor to terminal A of multiplier 19. A voltage value 
representative of engine temperature T1 additionally is supplied to a 
threshold stage 29, the output of which is connected through an OR-gate 32 
to a switching stage 20 to control a switch therein. 
A second threshold stage 30 is provided which receives a load signal which, 
like the load signal L applied to the stage 26, can be derived from the 
fuel supply signal ti. Further, the threshold stage 30 receives a speed 
signal n representative of engine output speed. The output from the 
threshold stage 30 is applied to the adder 13 and to the multiplier 19 in 
such a way that, if the output signal from the threshold stage 30 has a 
predetermined value, for example is a 1-signal, the inputs applied to the 
terminals A of the respective stages 13, 19 are no longer effective; the 
output from threshold stage 30, thus, is effective to disable modification 
of the signals derived from the computer 10 and applied to the respective 
ignition system 14 and the fuel injection system 21. In case of the adder 
13, the additional angle .alpha.1 will thus be set to zero; for the 
multiplier stage 19, the factor F will be 1.0. 
Operation, and method of control, with reference to FIGS. 2-6: Basically, 
the combustible fuel-air mixture is enriched when the engine, or one of 
its components, as determined by one or more of the temperatures T1, T2 . 
. . T5, reaches a value which might cause knocking. Enrichment lowers the 
combustion temperature, and thus decreases the tendency to knocking. 
Turbo-charged motors have the characteristic that enrichment must 
frequently go to substantially over the level necessary to achieve maximum 
power output, but only if high motor temperatures result due to stationary 
operation, that is, without moving cooling air flow. For optimum matching 
of the engine operation to these conditions, a graph as seen in FIG. 2 is 
derived relating enrichment to temperature. This graph can be derived 
theoretically or emperically by measurements. This graph, that is, the 
characteristic curve, is stored in the ROM 27. FIG. 2 illustrates a simple 
case, namely enrichment as a function of a single measured temperature. 
Enrichment is effected by multiplying the base fuel injection period ti by 
a multiplying factor F in the multiplying stage 19, that is, by modifying 
the base injection period so that it will be extended. The extended 
effective injection time then provides for the desired enrichment. This 
enrichment function, in the example shown, will become effective only 
starting from a temperature tx, and only in a region which is provided by 
the load, determined by the load signal L, and at a speed n. Only in the 
region where danger of knocking may result, that is, at a load higher than 
a base load Lo, and/or at a speed higher than a base speed no, is it 
desired to enrich the fuel-air mixture. If the values for L and n are 
below these base values, then, as above described, the multiplying factor 
F, applied to the multiplying stage 19, will be set to become 1.0 by 
operation of the threshold stage 30. 
The threshold stage 29 will respond if the engine temperature rises over a 
maximum permissible limiting value tm. Response of the threshold stage 29 
cuts off fuel injection by opening the switch 20. This will either cause 
drop-out of the load signal below Lo, or the speed below no. If either one 
of these signals drops below the base value, a timing delay stage 31 is 
triggered, the timing delay stage 31 being connected through OR-gate to 
switch 20 so that, after the delay set into the timing unit, the switch 20 
will again close, thus permitting injection of fuel to resume. It is, of 
course, also possible to omit the timing stage 31 and to initiate new 
injection of fuel directly by the output from threshold stage 29, and 
introducing some hysteresis into the switching characteristics of the 
threshold stage 29 so that, after engine temperature drops, switch 20 is 
commanded to change back to connected condition. Smoothness of operation 
of the vehicle can be improved by avoiding a reconnection jolt, upon 
sudden re-supply of fuel, as known from prior publications--see, for 
example, German Patent Disclosure Document DE-OS 28 34 638, to which U.S. 
application Ser. No. 52,342, June 27, 1979, now U.S. Pat. No. 4,285,314, 
KIENCKE et al., assigned to the assignee of the present application, 
corresponds--which discloses automatic spark retardation upon resumption 
of fuel supply after an interruption, and gradual change of the spark to 
the commanded value to thereby gradually supply power to the engine, 
rather than suddenly. 
The knocking limit, that is, the limit of engine operation before the 
engine will knock, can be additionally controlled by also controlling the 
ignition timing in dependence on one or more temperatures, as sensed. ROM 
27, or a portion thereof, can retain characteristics in which an 
additional ignition timing angle .alpha.1 is added to the ignition timing 
angle .alpha. in the adding stage 13. The ignition timing signal .alpha.1 
changes the ignition timing angle .alpha. commanded for example by the 
ignition control signal 11 in retarding direction, so that, consequently, 
retardation of the spark by the angle .alpha.1 will result in dependence 
on temperature. Again, this change is suppressed if the threshold stage 30 
has responded, that is, below load limits of the base load Lo and the base 
speed no set into the threshold stage. 
Additional parameters can be used in order to control the temperature 
dependent enrichment of the fuel-air mixture and/or temperature dependent 
ignition timing adjustment; various temperatures or several temperatures 
can be used as control parameters in addition to the additional 
parameters. Preferably, such additional parameters or additional 
temperature control is effected in accordance with well known computer 
control of engine operating characteristics, and stored within the memory 
of unit 10. FIGS. 3 to 6 illustrate control in accordance with 
characteristic diagrams in dependence on engine temperature T1 and exhaust 
temperature T2, the load signal L, and the speed n. The first two 
parameters, temperatures T1 and T2, form a single function with respect to 
knocking limits which, in case of the ignition, results in a correction 
ignition angle Z1 (FIG. 3) and, for fuel injection, in a correction factor 
F1. The two further parameters, load and speed, together form a further 
function which, in case of ignition, results in a correction factor Z2 
with respect to the correction angle Z1 and, in case of fuel injection, in 
a further correction factor F2. The four parameters can be combined with 
respect to their various functions, leading to characteristic fields or 
curves which are stored in the ROM 27. Specific points of these 
characteristics, in case of ignition Z1.times.Z2, and in case of fuel 
injection F1.times.F2, can be selected according to any desired 
combination of the four parameters. A corrected ignition angle will then 
result: .alpha.+.alpha.1, in which .alpha.1=Z1 .times.Z2. A corrected fuel 
injection time is determined by ti F, in which F=F1.times.F2. 
The functions and characteristics can be introduced, of course, as 
additional characteristic functions included in the engine operation 
computer and engine characteristic memory, and integrated therewith. The 
characteristics for the temperature dependent correction of the ignition 
timing--in direction of ignition retardation, and of injection time--in 
the direction of making the fuel-air mixture richer, that is, more fuel 
per quantity of air, can be superimposed over, or modulated on, the basic 
engine operating characteristics stored in the stage 10. The output from 
threshold stage 30 should then, suitable, be connected to stage 10 or an 
equivalent recognition stage be included in the operating computer 10. 
Various changes and modifications may be made within the scope of the 
inventive concept.