Knocking detecting system and method for an internal combustion engine

A knocking detecting system comprising a microcomputer with an A/D converter, 4 which receives a frequency signal processed in accordance with the vibration signal of a knock sensor 1. The microcomputer 4 with the A/D converter operates including, at least, the A/D-conversion steps S.sub.1 -S.sub.4 of continuously sampling digital values, the steps S.sub.5 -S.sub.9 of integrating the differences between the digital values and a background level over a detecting period, and the steps S.sub.10 -S.sub.12 of comparing the integrated value with a judgement level, thereby to judge the presence of knocking and to evaluate a knocking level. The signal of the knock sensor 1 is converted into the digital values and is then arithmetically processed by the microcomputer 4. Thus, the knocking is detected, and the background level is calculated at high precision.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates, to a knocking detecting system for detecting 
the presence of knocking an automobile engines on the basis of the signal 
of a combustion vibration from a knocking sensor. More particularly, it 
relates to a system and a method in which a knocking signal is 
A/D-converted by a microcomputer for the detection of knocking and the 
calculation of a background level. 
2. Description of the Prior Art 
For the control of the ignition timing or supercharging pressure in an 
automobile engine, a judgement signal of a knocking detecting device for 
optimum control. The knocking detecting device in this case operates, for 
example, such that a signal from a knock sensor is amplified with an 
appropriate gain, a knocking component is extracted by a filter, and the 
waveform of the knocking component is rectified with respect to its 
central value. Subsequently, one of the rectified signals is used for 
evaluating a background level conforming to a noise level, and the other 
signal is compared with the background level, thereby to judge the 
presence of the knocking. Since means for creating the device are chiefly 
made up of analog circuits, the device has a large number of problems in 
circuit area, cost, the changes of detection characteristics attributed to 
the aging of analog elements, the number of stages of a matching 
operation, etc. Meanwhile, microcomputers with high-speed A/D converters 
have come into wide use in recent years, and it has been requested that 
the knocking detection based on the analog circuit processing should be 
performed by microcomputer processing. 
Heretofore, as to the knocking detecting device of this type, there has 
been a prior-art technique disclosed in Japanese Patent application 
Laid-open No. 193333/1984 by way of example. Here, the following is 
indicated: A pressure signal from an intracylindrical pressure sensor is 
input to an integrator through a charge amplifier, a BPF (band-pass 
filter) and a rectifier. Subsequently, the pressure signal having been 
input is integrated over a predetermined angular extent before a top dead 
center in the signal of a crank angle and over the predetermined angular 
extent after the to dead center, and the ratio of the respective integral 
values is computed. The computed value is compared with a reference value 
conforming to operating conditions, thereby to judge knocking. 
In addition, as to the setting of a background level, there is known a 
prior-art technique from Japanese Patent application Laid-open No. 
79320/1987 by way of example. In this prior-art technique, the background 
level is calculated in terms of the average value of the levels of the 
knocking signals of an intracylindrical pressure sensor, and, when the 
signal level is predetermined times the background value or above, the 
renewal of the background value is suspended. 
With the former of the prior-art techniques stated above, the pressure 
signal is integrated analogically, so that circuit arrangement and control 
become complicated. Besides, in such a case where the peak of combustion 
pressure is in the vicinity of the top dead center, it is sometimes 
impossible to detect the knocking precisely. With the latter of the 
prior-art techniques, the knocking signal of particularly high level is 
not referred to in the calculation of the background level. This such a 
problem that the level setting lacks preciseness. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of the drawbacks as stated 
above, and has for its object to provide a knocking detecting system and a 
knocking detecting method for an internal combustion engine in which the 
detection of knocking and the calculation of a background level are 
digitally processed by a microcomputer, thereby making it possible to 
simplify hardware and to enhance the precision etc. of control. 
In one aspect of performance of the present invention, there is provided a 
system for detecting knocking of an internal combustion engine having, a 
knock sensor mounted on said engine for detecting a vibration caused by an 
irregular combustion and for generating a knock signal, a crank angle 
sensor for detecting a crank angle and for producing a crank angle signal, 
an air flow meter provided in a throttle valve for detecting a volume of 
air induced into said engine and for producing an air mass signal, and a 
throttle sensor for sensing an opening degree of said throttle valve and 
for generating a degree signal, the improvement of the system which 
comprises control means responsive to said air mass signal and said degree 
signal for controlling said engine in optimum operating conditions and for 
generating a condition signal; A/D converting means responsive to said 
knock and crank angle signals and said condition signal for converting a 
frequency signal of said vibration into a digital value by continuously 
sampling said digital value and for producing a digital signal; 
integrating means responsive to said digital signal for integrating 
difference between said digital value and a background level and for 
generating an integrated signal; and deriving means responsive to said 
integrated signal for deriving a knock level by comparing said integrated 
signal with a judging level so as to simplify said system and to avoid 
characteristics deterioration due to aging by a long use. 
According to such a system, the signal of the knock sensor is converted 
into the digital value, which is arithmetically processed. Therefore, the 
detection of the knocking and the calculation of the background level are 
effected very precisely.

PREFERRED EMBODIMENTS OF THE INVENTION 
Now, embodiments of the present invention will be described in conjunction 
with the drawings. The control section of a knocking detecting system will 
be described with reference to FIG. 1. Numeral 1 designates a knock sensor 
which detects the vibration of an engine proper during combustion. The 
vibration signal of the knock sensor 1 is amplified at a predetermined 
gain by an amplifier 2, whereupon a necessary frequency component is 
extracted from the amplified signal and is input to a microcomputer with 
an A/D converter, 4 by a filter 3. Also, the crank angle signal of a crank 
angle sensor 5 is input to the microcomputer 4 with the A/D converter. The 
input signals are used for setting a knocking detecting period, judging 
engine operating conditions, and so forth. Besides, a knocking judgement 
signal and a knocking level which have been detected by the micro computer 
4 with the A/D converter are input to an engine controlling microcomputer 
6. They are used for controlling an ignition timing, and the ignition 
signal of the microcomputer 6 is applied to an ignition coil 7. The engine 
controlling microcomputer 6 can transfer data from and to the 
microcomputer 4 with the A/D converter. Further, it is supplied with 
signals from an air flow meter 8, a throttle sensor 9, etc., while it 
delivers a fuel injection signal to an injector 10. 
Next, the control of knocking detection will be described with reference to 
a flow chart in FIG. 2 and signal waveforms in FIG. 3. First, a 
predetermined knocking detecting period .theta. k (for example, 10-50 
degrees in terms of an ATDC angle) is set after ignition. When the period 
.theta. k has begun, the digital conversion of the knock signal by the A/D 
converter is started at step S1. Subsequently, data P is initialized at 
step S2, and the finishing time of the sampling period .theta. k is set at 
step S3. At step S4, in this way, the converted digital values KNADn (n=1, 
2, . . . ) are continuously input at high speed (for example, one samples 
value in 10-20 .mu.s) as shown in FIG. 3. At step S5, the absolute value 
of the difference between the digital value KNADn and the central voltage 
ADCNT of the input signals is compared with a background level BGL 
previously calculated depending upon the operating conditions of the 
engine, as shown in FIG. 3. In a case where the absolute value is not 
smaller, the value Kn of the difference between the two is calculated at 
step S6 as shown in FIG. 3. If the absolute value is smaller than the 
background level BGL, the next step is step S8. That is, the following is 
obtained: 
EQU Kn=.vertline.KNADn-ADCNT.vertline.-BGL 
Next, the difference value Kn is added to the data P at step S7. When the 
sampling period .theta. k has finished at step S8, the control flow 
proceeds to step S9, at which the integral value KNP of the difference 
values Kn is calculated as shown in FIG. 3. That is, the following is 
evaluated: 
EQU KNO=.intg.KN (1) 
Thereafter, at step S10, this integral value is compared with a comparison 
level KNLVL for a knocking judgement as set depending upon the operating 
conditions of the engine beforehand. In a case where the former is smaller 
than the latter, the control flow proceeds to step S11, at which a 
knocking judgement flag is cleared. To the contrary, in a case where the 
former is not smaller than the latter, the control flow proceeds to a step 
S12, at which the knocking judgement flag is set to judge the knocking. 
The integral value KNP on this occasion is detected as the level of the 
knocking. 
Owing to this embodiment, in the knocking detecting period of the 
combustion cycle of the engine, the frequency signal of the vibration 
detect ed by the knock sensor 1 is input to the microcomputer 4 and is 
continuously converted into the digital values KNADn, which are used for 
the processing. That is, the increment of the plus or minus digital value 
KNADn relative to the background level BGL is added, and such incremental 
values Kn are integrated. Accordingly, the integral value KNP in this case 
conforms to the magnitude of the knocking, and the presence of the 
knocking and the knocking level are appropriately detected using the 
integral value KNP. 
Now, an embodiment in which the background level is similarly calculated by 
an A/D conversion and processed by the microcomputer 4 will be described 
with reference to a flow chart in FIG. 4. First, also in this case, a 
background level detecting period .theta. B as predetermined (for example, 
10-50 degrees in terms of an ATDC angle) is set within the cycle of the 
engine, and it sometimes overlaps the knocking detecting period .theta. k 
stated before. Herein, when the period .theta. B has begun, the A/D 
conversion of the knock signal is started at step S21, and data P and the 
number N of data items are initialized at step S22. Subsequently, the 
finishing time of the detecting period .theta. B is set at a step S23, and 
A/D-converted digital values BGADn (n=1, 2, . . . ) are continuously 
obtained at high speed at step S24. At steps S25, S26 and S27, the average 
amplitude value BGAVE of the digital values BGADn in one combustion cycle 
of the engine is calculated on the basis of the digital values BGADn, and 
the number N of the data items and the central voltage ADCNT of the input 
signals which have been obtained in the detecting Period, as follows: 
##EQU1## 
Besides, in order to absorb the fluctuation of the average amplitude value 
BGAVE between fueling cycles, the average amplitude value BGAVE obtained 
every cycle is subjected to weighted averaging at steps S28 and S29, so as 
to be renewed. That is, the new average amplitude value BGAVE.sub.new is 
obtained on the basis of the calculated average amplitude value BGAVE, an 
old average amplitude value BGAVE.sub.old and a weighted averaging rate X, 
as follows: 
EQU BGAVE.sub.new =(1/X) {BGAVE+(X-1)BGAVE.sub.old } 
Thereafter, at step S30, the background level BGL is calculated using a 
background coefficient KBG previously set in accordance with the operating 
conditions of the engine, as follows: 
EQU BGL=KBG BGAVE.sub.new 
Owing to this embodiment, the background level is also calculated in such a 
way that the digital values generated by the A/D conversion of the signal 
of the knock sensor 1 are processed by the microcomputer 4 with the A/D 
converter. In addition, since the average amplitude value is subjected to 
the weighted averaging every cycle, the background level becomes the 
optimum one which fluctuates little between the cycles, and it is used as 
the threshold value of the knocking detection described before. 
Although, in the above, the embodiments of the present invention have been 
described, the invention is not restricted only to them. 
As set forth above, according to the present invention, the detection of 
knocking and the calculation of a background level based on the signal of 
a knock sensor are done by converting the signal into digital values and 
arithmetically processing the digital values by means of a microcomputer 
with an A/D converter. Therefore, the invention can simplify hardware as 
compared with an analog system, and it has a great effect especially in 
case of coping with a plurality of knock sensors. Moreover, 
characteristics deteriorate little due to aging. The number of stages of a 
matching operation is small. Further, the characteristics of the knocking 
detection and the background level calculation are set with high 
versatilities.