Device for correcting functional, quantities in an internal combustion engine

This invention relates to a device for correcting functional quantities of an internal combustion engine in accordance with detonation. The correction is made by comparing the amplitude of a vibratory signal indicative of detonation with a reference signal. In order to cause the correction to take place, a sensitivity factor is used multiplied by a correcting constant which depends on the value of the reference signal or on the ratio of the reference signal to the reference signal in the absence of detonation, this being an index of the basic characteristics and operating state of the engine and transducer.

This invention relates to a device for correcting, in accordance with 
detonation, functional parameters such as spark advance and supercharging 
pressure in a controlled ignition internal combustion engine. 
The thermal efficiency of internal combustion engines can be improved by 
using explosion chambers of grouped arrangement and increasing the 
compression ratio. This leads to a reduction in fuel consumption and an 
increase in specific power. 
However, as the compression ratio increases, so does the tendency of the 
engine to detonate because the maximum pressure and temperature of the 
cycle increase. On the other hand, the anti-detonating power of fuels is 
gradually falling because of the reduction in the allowable lead additives 
content. 
A method commonly used for preventing detonation is to delay the ignition, 
so as to regain an adequate margin over the spark advance values at the 
limit of detonation. 
This however penalises the engine, which suffers a reduction in power and 
efficiency. 
It is therefore advisable, in order to improve thermal efficiency during 
engine partial load operation, to increase the compression ratio by either 
using supercharging or reducing the explosion chamber volume, whereas if 
good performance during acceleration is required then it is necessary to 
avoid penalising the engine during the transient state, and the engine can 
be prevented from causing detonation during full-throttle operation by 
using suitable means. 
Electronically controlled ignition systems for regulating the spark advance 
in accordance with engine parameters are known. Some of these systems 
already control the detonation by varying the spark advance. In 
supercharged engines, supercharger pressure control means are provided 
which control the opening of a bleed valve downstream of the blower, or of 
a turbine bypass valve, where supercharging is by means of a 
turbocompressor. 
The detonation transducers used are generally of two types, namely 
ionisation sensors and piezoelectric sensors or accelerometers. The former 
are located directly in the explosion chamber, whereas the latter are 
generally arranged on the cylinder head, on the cylinder block or on the 
engine intake manifold. 
The detonation, which can be produced in each engine cylinder each time 
combustion occurs, is characterised by an increase in engine vibration 
generally in the frequency ranges of between 4 and 6 kHz and between 9 and 
11 kHz. The transducers must therefore be able to sense vibrations of 
these frequencies. 
The amplitude of a detonation pulse produced by the transducer can be as 
much as 20 times greater than the vibratory signal due to the background 
noise generated by the engine during normal operation without detonation. 
Devices have therefore been proposed for correcting the spark advance and 
supercharging pressure in accordance with the detonation, in which the 
vibratory signal provided by the accelerometer within a prechosen angular 
range including the top dead centre, after passing through a band-pass 
filter, it is processed in order to obtain the mean value of the amplitude 
for a predetermined number of cycles; this value constitutes the reference 
signal with which the amplitude of the single pulse emitted during the 
next cycle by the accelerometer is compared. 
If the ratio of the single pulse amplitude to the reference signal is 
greater than a predetermined detonation sensitivity value, the control 
device acts on the ignition system in order to delay the striking of the 
spark, in order to reduce the cycle pressure and temperature and restore 
normal combustion conditions. 
The detonation sensitivity value varies with the engine operating 
conditions, and can for example be a function of the engine r.p.m. Our 
research on these devices has shown that they have certain limitations 
when used on series-produced engines in that they neglect certain factors 
which influence the construction and operation of such engines. These 
factors are mainly the constructional tolerances, which are inevitable 
even on engines of one and the same type, the state of engine aging, and 
the constructional tolerances of the detonation transducers themselves. 
We have therefore improved the existing correction devices by introducing 
certain modifications which make them particularly suitable for solving 
the problems deriving from their use on series-produced engines. 
The device according to the invention, for correcting functional quantities 
of an engine, comprises transducers for prechosen engine parameters, at 
least one engine vibratory signal transducer for sensing detonation, 
band-pass filter means for the vibratory signal, a microprocessor provided 
with a processing stage for calculating the functional quantities produced 
as a function of the prechosen engine parameters, with a processing stage 
for withdrawing the vibratory signal within a predetermined angular range 
of each engine cycle and for calculating a reference signal constituted by 
the mean value of the amplitude of the vibratory signal for a 
predetermined number of engine cycles, with memory locations containing 
predetermined detonation sensitivity factors as a function of a prechosen 
engine parameter, and with a processing stage for comparing the reference 
signal with the amplitude of a pulse of the vibratory signal emitted 
within a cycle subsequent to those of the predetermined number and for 
correcting the calculated functional quantities when the result of the 
comparison is greater than a predetermined sensitivity factor, and 
actuator means, operationally connected to the microprocessor, for causing 
the variation in the functional quantities to take place in accordance 
with the calculated and generally corrected values, the device being 
characterized in that the microprocessor also comprises further memory 
locations containing predetermined constants for correcting the 
sensitivity factors in accordance with the reference signal, and a 
processing stage for identifying the corresponding correcting constant in 
the further memory locations and for manipulating by means of the constant 
the sensitivity factor used in the comparison. 
According to a further embodiment, the device is characterized in that the 
further memory locations contain predetermined constants for correcting 
the sensitivity factors in accordance with the ratio of the reference 
signal to a basic reference signal, the microprocessor comprising a 
processing stage for calculating, on initialisation of the microprocessor, 
the basic reference signal as the mean value of the amplitude of the 
vibratory signal originating from the transducer within a predetermined 
angular range of each engine cycle for a predetermined number of cycles, 
and a processing stage for calculating the ratio of reference signal to 
basic reference signal, for identifying the corresponding correcting 
constant in the further memory locations and for manipulating by means of 
the constant the sensitivity factor used in the comparison. 
In this embodiment, the sensitivity factor varies with the engine operating 
conditions, and is in addition adjusted to the characteristics and state 
of the individual engine and transducer.

In the FIGURE, the reference numeral 10 indicates overall a microcomputer 
constituted by a microprocessor (CPU) 11, a random access memory (RAM) 12, 
a read-only memory (ROM) 13 containing the data tables and operational 
programs of the microprocessor, and an input/output unit 14. 
The microprocessor, memory and input/output unit are connected together by 
a parallel bus 15 for the data, a parallel bus 16 for the addresses, and a 
parallel bus 17 for the internal control signals. 
The input/output unit 14 receives, by way of the line 18, a signal emitted 
by a sensor which senses the angular position of the engine feed throttle 
valve, receives by way of the line 19 a signal emitted by a sensor which 
senses the temperature of the engine cooling water, receives by way of the 
line 20 a signal emitted by a sensor which senses the temperature of the 
engine feed air, receives by way of the line 21 a signal emitted by an 
engine detonation transducer indicated by 22, and finally receives by way 
of the line 39 a signal emitted by a sensor which senses the engine 
supercharging pressure. 
The transducer 22 is in this case a piezoelectric accelerometer fixed to 
the internal combustion engine cylinder head. The transducer is connected 
to an amplifier 23 connected to a band-pass filter 24, which allows 
passage of the engine vibratory signal lying for example within a 
frequency band of between 6 and 9 kHz. 
The input/output unit 14 also receives, by way of the line 25, a pulse 
signal generated by the magnetic sensor 26 on passage of the notches 27 of 
the wheel 28, which is connected to the drive shaft. 
In the case under examination, as the engine is a four cylinder, 
four-stroke engine supercharged by means of a turbocompressor, ignition 
must occur twice for each engine revolution. Thus the wheel 28, which can 
be the engine flywheel, is provided with two notches 27 disposed 
180.degree. apart and suitably phased with respect to the cylinder top 
dead center. As these two notches pass in front of the sensor 26, they 
generate two reference pulses for each engine revolution. Each of these 
pulses corresponds to the ignition advance calculated by the 
microprocessor. 
The pulse signal generated by the sensor 26 is also used by the 
microprocessor for calculating the engine r.p.m. 
The unit 14 receives through the line 29 a second pulse signal emitted by 
the magnetic sensor 30 on passage of the notch 31 of the wheel 32, 
connected to a shaft which rotates at one half of the engine speed. 
The notch 31 is also suitably phased with respect to the cylinder top dead 
center, and the pulse signal which it generates for every two engine 
revolutions is used for counting the engine cycles, the engine being of 
the four-stroke type. 
The unit 14 is connected by the lines 42 and 33 to the final stage 34 of 
the engine ignition system. This final stage comprises a power transistor 
34 connected to the electricity supply, the ignition coil to which the 
transistor is also connected, and a distributor for distributing high 
voltage to the spark plugs, indicated in FIG. 1 by 35, 36, 37, 38. The 
unit 14 is also connected by the line 40 to the block 41 which 
diagrammatically represents a valve in the supercharger turbine bypass. 
The values of the detonation sensitivity factors S as a function of 
prechosen engine parameter, for example the engine r.p.m., are tabulated 
in the memory 13. 
The same memory also contains the tabulation of the values of the 
sensitivity factor correcting constants K as a function of a reference 
signal R or as a function of the ratio of a reference signal R to a basic 
reference signal Ro, where the reference signal R is constituted by the 
mean value of the amplitude of the vibratory signal originating from the 
transducer 22 calculated for a predetermined number of engine cycles 
during the engine operation, and the basic reference signal Ro is 
constituted by the mean value of the amplitude of the vibratory signal 
originating from the transducer 22 calculated for a predetermined number 
of engine cycles on initialisation of the microprocessor. 
The described device operates in the following manner. 
If the values of the correcting constant K are tabulated in the memory as a 
function of the ratio, at the moment of its initialisation the 
microprocessor calculates the value of the basic reference signal Ro as 
the mean value of the amplitude of the vibratory signal originating from 
the transducer 22 under these conditions, i.e. in the absence of 
detonation. 
The mean value is calculated for a predetermined number of engine cycles by 
withdrawing the vibratory signal of the transducer 22 within a 
predetermined angular range of each engine cycle. This mean value 
constitutes the basic reference signal Ro and is memorised in the RAM 12. 
In contrast, if the values of the correcting constant K are tabulated in 
the memory as a function of the reference signal, the microprocessor does 
not calculate the basic reference signal Ro. 
The microprocessor 11 then continues by executing the calculation programs 
and uses the tables of data contained in the read-only memory 13 to 
process the signals, indicative of the engine operating conditions, which 
enter the unit 14 and to calculate as a function of these signals the most 
suitable spark advance angle with respect to the top dead center. The 
microprocessor then converts the calculated spark advance angle into a 
delay time t.sub.r, with respect to a base reference, which in this 
particular case is the pulse generated by the notch 27 which precedes the 
top dead centre of the cylinder in the compression stage. 
If the engine is subject to detonation, the microprocessor is able to make 
a correction to the calculated spark advance angle, to the corresponding 
delay time and to the supercharging pressure, by processing the vibratory 
signal originating from the transducer 22. 
The microprocessor withdraws said vibratory signal within a predetermined 
angular range of each engine cycle and calculates the mean value of the 
amplitude for a predetermined number of engine cycles. This mean value 
constitutes the reference signal R with which the microprocessor compares 
the amplitude of a pulse of the vibratory signal emitted by the transducer 
22 in a cycle subsequent to those of said predetermined number. In making 
the comparison, the microprocessor uses a detonation sensitivity factor 
which it takes from the tabulated values in the ROM 13 on the basis of the 
effective engine r.p.m. The microprocessor also uses a sensitivity factor 
correcting constant K which it takes from the values tabulated in the ROM 
13 on the basis either of the calculated value of the reference signal R 
or of the ratio of the reference signal R to the basic reference signal 
Ro. 
The microprocessor multiplies the sensitivity factor by the correcting 
constant determined in this manner, and checks whether the ratio of the 
amplitude of said vibratory signal pulse to the reference signal is 
greater or less than the sensitivity factor corrected as stated 
heretofore. 
If the ratio is greater, the microprocessor is able to correct the 
supercharging pressure in the sense of reducing it, by opening the valve 
41 in the turbine bypass, and also corrects the calculated spark advance 
angle in the sense of retarding it until the detonation disappears and 
said ratio is less than the corrected sensitivity factor. 
On arrival of the pulse generated by the notch 27 corresponding to the 
cylinder in the compression stage, the microprocessor triggers the 
counting of the calculated delay time, possibly corrected in the presence 
of detonation, and at the end of the count causes inhibition of the power 
transistor 34 of the final stage, to interrupt the charge on the engine 
ignition coil, which thus results in the striking of the spark at the 
spark plug of the cylinder in the compression stage. 
The correction signal indicative of detonation, as calculated by the 
microprocessor by the procedure heretofore described, can thus be used not 
only for correcting the spark advance but also for regulating the 
supercharging pressure in the sense of reducing it, where the engine is of 
the supercharged type.