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BACKGROUND OF THE INVENTION
This invention relates to a control apparatus for an internal combustion
engine, and in particular to a control apparatus for an internal
combustion engine which is operable either with a low-octane rating fuel
or a high-octane rating fuel.
It is well known in the art that the octane rating of fuel gasoline is
greatly interrelated with a knock-resistibility in an internal combustion
engine. Namely, as the octane rating of gasoline becomes higher, the
knocking of an engine correspondingly decreases.
FIG. 1 shows an ignition timing vs output shaft torque characteristic in an
internal combustion engine in the case where a commercially available
low-octane gasoline (regular gasoline) and a commercially available high
octane gasoline (premium gasoline) of which the octane rating is higher
than that of the low-octane gasoline. In the figure, point A indicates a
knock limit for the low-octane gasoline while point B indicates a knock
limit for the high-octane gasoline, in which knock arises when the angle
of the ignition timing is advanced beyond these points. According to FIG.
1, it is possible to advance the angle of the ignition timing up to a
point B if the high-octane gasoline is used, where the output shaft torque
will be higher as compared with the use of the low-octane gasoline.
FIG. 2 shows a supercharging pressure vs output shaft torque characteristic
of an engine associated with a supercharger. Similar to FIG. 1, point A
represents a knock limit when using the regular low-octane gasoline and
point B represents a knock limit when using the premium high-octane
gasoline. It will be seen from FIG. 2 that the increase of a supercharging
pressure when the premium gasoline is used for the engine enables the
output shaft torque of the engine to be also increased as in FIG. 1.
Therefore, in an engine associated with such a characteristic
supercharger, if the ignition timing and the supercharging pressure are
advanced and increased respectively according to the mixing ratio of the
regular gasoline and the premium gasoline in the case where their mixture
is used or either one is used, the output of the engine can be enhanced.
However, in a conventinal ignition timing control apparatus for an internal
combustion engine, the reference ignition timing characteristic is preset
only for a predetermined gasoline, e.g. the low-octane rating gasoline.
Therefore when using the high-octane rating gasoline, an increase in the
output of the engine cannot be expected without any change or modification
of the reference ignition timing characteristic or the reference
supercharging characteristic, so that by some method, the presetting of
the reference ignition timing must be repeated towards the advance angle
or the presetting of the supercharging pressure must be repeated towards
the high pressure.
Particularly, such a repeated presetting of the reference ignition timing
is very hard when using the mixed fuel because, as shown in FIGS. 1 and 2
by point C, the knock limit exists between points A and B according to the
mixture ratio and so the possible advance limit or the possible increased
pressure limit is variable.
Even if the reference ignition timing or the supercharging pressure has
been again preset at the knock limits A and B, since the knock limits A
and B in FIG. 1 may vary with environmental conditions during the
operation of the engine such as temperature, humidity, etc., knocks easily
arise at the time of a transient operation such as an accelerated
operation of the engine, and accordingly it is quite difficult to avoid
the occurrence of engine knocks.
U.S. Pat. No. 3,822,583, titled "Method for Determining Octane Ratings of
Fuels under Road Conditions" issued on July 9, 1974 to B. D. Keller et al.
discloses a basic ignition timing control according to the octane rating
of gasoline by a knock detection.
SUMMARY OF THE INVENTION
It is a general object of the invention to provide a control apparatus for
an internal combustion engine wherein the occurrence of knocks is
detected, and a reference ignition timing displacement magnitude
indicating the mixture ratio of a high-octane rating fuel and a low-octane
rating fuel is determined according to the detected value, on the basis of
which the reference ignition timing is set in the advance angle or retard
angle direction and the reference operating parameter is set in the
increased value or reduced value, whereby the mixture ratio is determined
to continuously adjust the reference ignition timing and the reference
operating parameter value to an optimum angle. At the same time, the
occurrence of knock is immediately suppressed by controlling the ignition
timing in the direction of retard angle and the operating parameter value
on the real time basis when knock arises at the time of a rapid variation
of an environmental condition during the steady state engine operation or
at the time of a transient operation.
In order to accomplish this object, the present invention, broadly in one
aspect, provides a control apparatus for an internal combustion engine
comprising: a sensing means for sensing vibrations including knocks in the
engine; a knock signal deriving means, responsive to the output of the
sensing means, for deriving the knock signals; means for generating
reference ignition timing signals; a correction magnitude determining
means for determining an ignition timing correction magnitude for
suppressing the occurrence of knock from the output of the knock signal
deriving means; a displacement magnitude determining means for determining
from the output of the knock signal deriving means or the output of the
correction magnitude determining means a displacement magnitude for the
reference ignition timing corresponding to the octane rating of a fuel
used in the engine; an ignition timing determining means responsive to the
outputs of the correction magnitude determining means and the displacement
magnitude determining means to determine an ignition timing of the engine;
and, operating parameter control means for controlling the operating
paramter in addition to the ignition timing of the engine in response to
the output of the correction magnitude determining means and the output of
the displacement magnitude determining means.
The operating paramters for the engine preferably comprises a supercharging
pressure, a compression ratio, and an air/fuel ratio.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an output shaft torque characteristic of an internal
combustion engine as a function of ignition timing;
FIG. 2 shows an output shaft torque characteristic as a function of
supercharging pressure;
FIG. 3 shows a block diagram of a first embodiment of a control apparatus
for an internal combustion engine in accordance with this invention;
FIGS. 4(A) and 4(B) show maps of ignition timing (supercharging pressure)
characteristics stored in a memory, depending on the octane rating of a
fuel;
FIGS. 5(a)-(c) show waveform graphs for explaining the operation of the
knock signal deriving portion in FIG. 3;
FIGS. 6(c)-(j) show waveform diagrams taken out of the various places of
the retard angle control magnitude determining portion and the reference
ignition timing displacement magnitude determining portion shown in FIG.
3;
FIG. 7 shows a block diagram of an arrangement of a second embodiment of a
control apparatus for an internal combustion engine in accordance with
this invention;
FIGS. 8(d), 8(k)-(n) and 8(p) show waveform diagrams taken out of the
various places of the reference ignition timing displacement magnitude
determining portion shown in FIG. 7; and,
FIG. 9 shows a diagram for explaining the output modes of the
retard/advance (reduced/increased pressure) mode decision unit shown in
FIG. 7.
Throughout the figures, the same reference numerals indicate identical or
corresponding portions and element.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in detail along the preferred
embodiments illustrated in the accompanying drawings.
FIG. 3 shows a circuit diagram of a first embodiment of a continuous
ignition timing control apparatus for an internal combustion engine in
accordance with this invention. In the figure, a knock sensor 1 is mounted
on an internal combustion engine (not shown) to sense knocks of the
engine. The output signal of the knock sensor 1 is received by a knock
signal deriving portion 2, enclosed with dotted lines, which is composed
of a bandpass filter 2a, a noise level detector 2b, and a comparator 2c.
The input of the bandpass filter 2a is connected to the knock sensor 1 and
the output thereof is connected to the noise level detector 2b and one
input of the comparator 2c. The output of the noise level detector 2b is
connected to the other input of the comparator 2c.
The comparator 2c of the knock signal deriving portion 2 is connected to a
retard angle control magnitude determining portion 50 and a reference
ignition timing displacement magnitude determining portion 52. The retard
angle control magnitude determining portion 50 includes an integrator 50a
and an analog to digital (A/D) converter 50b. The reference ignition
timing displacement magnitude determining portion 52 is formed of a pulse
generator 52a, a counter 52a, a timer 52c, an up/down counter 52d, a timer
52e, and a memory 52f. The input of the pulse generator 52a is connected
to the output of the comparator 2c and the output thereof is connected to
the input of the counter 52b. The timer 52c is connected to the reset
input of the counter 52b. The up-count input of the up/down counter 52d is
connected to the output of the counter 52b and the down-count input
thereof is connected to the timer 52e. The data input of the memory 52f is
connected to the output of the up/down counter 52d and the data output
thereof is connected to the preset input of the up/down counter 52d.
A first ignition timing computing unit 54 is formed of a proportion factor
calculator 54a, an interpolator 54b, and a subtractor 54c. The proportion
factor calculator 54a is connected to the output of the up/down counter
52d to convert the count of the up/down counter 52d into a proportion
factor. The interpolator 54b is connected to the output of ROM's 11 and 12
as well as the output of the calculator 54a so that an interpolation is
performed according to the proportion factor provided from the calculator
54a between the output data of the ROM's 11 and 12, thereby providing as
an output an ignition timing data determined by the interpolation. The
subtractor 54c has two inputs, one of which is connected to the output of
the interpolator 54b and the other of which is connected to the output of
the A/D converter 50b, and subtracts the output value of the A/D converter
50b from the ignition timing data from the interpolator 54b to provide an
ignition timing data output, which is shifted in the retard direction, to
a second ignition timing computing unit 18.
The ROM's 11 and 12 which are first and second ignition timing
characteristic memory portions have stored therein ignition timing data at
corresponding memory addresses determined by an engine speed and a load
condition as illustrated in FIGS. 4(A) and 4(B). FIG. 4(A) shows data of
the ROM 11 set for the low-octane gasoline while FIG. 4(B) shows data of
the ROM 12, set for the high-octane gasoline, positioned in the side of
advance angle in relation to FIG. 4(A).
A crank angle sensor 16 detects the crank rotational angle of the engine,
and a pressure sensor 17 detects an intake air pressure of the engine. The
above noted ignition timing computing unit 18 computes the engine speed
from the output signal of the crank angle sensor 16, determines the load
condition of the engine from the output signal of the pressure sensor 17,
and converts the value determined by the engine speed and the load
condition into an address value, which is sent to the ROM's 11 and 12. The
ignition timing computing unit 18 also reads out the output data of the
subtractor 54c, computes the ignition timing from the output data of the
subtractor 54c on the basis of the output signal of the crank angle sensor
16, and sends the ignition signal to a switching circuit 7 and then an
ignition coil 8. The switching circuit 7 energizes or deenergizes an
ignition coil 8 in synchronization with the output signal of the computing
unit 18 to produce a high voltage necessary for the ignition of the
engine.
In addition to the above mentioned ignition timing control arrangement,
supercharging pressure is reduced to suppress the occurrence of knocks by
means of a supercharging pressure controller 70, ROM's 71 and 72, a driver
73, an actuator 74, and a waste gate valve 75.
The supercharging pressure controller 70 performs the same operation as the
first ignition timing computing unit 54, and comprises a proportion factor
calculator 70a, an interpolator 70b, and a subtractor 70c which
respectively perform the same function as the proportion factor calculator
54a, the interpolator 54b, and the subtractor 54c of the unit 54. The
input of the proportion factor calculator 70a is connected to the output
of the up/down counter 52d and the output thereof is connected to the
subtractor 70c through the interpolator 70b, which intern has two inputs,
one of which is connected to the ROM 71 and the other of which is
connected to the ROM 72. The inputs of the ROM's 71 and 72 are commonly
connected to the output of the second ignition timing computing unit 18.
The other input of the subtractor 70c is connected to the output of the
A/D converter 50b, and the output of the subtractor 70c is connected to
the driver 73.
The ROM's 71 and 72 have stored therein supercharging pressure
characteristic data, determined by engine speed and engine load, adapted
for the premium gasoline and the regular gasoline, respectively like FIGS.
4(A) and 4(B).
The input signal from the A/D converter 50b to the subtractor 70c serves
not only as a retard control angle signal but also as a control voltage
signal for the purpose of reducing the supercharging pressure, with an
ignition timing indicative signal corresponding to a certain supercharging
pressure indicative signal, and the input signal from the up/down counter
52d to the proportion factor calculator 70a serves not only as a
displacement magnitude for the reference ignition timing but also as a
displacement magnitude for reducing the reference supercharging pressure,
with an ignition timing indicative signal corresponding to a certain
supercharging pressure indicative signal.
The operation of each of the block portions will now be described with
reference to FIGS. 5 and 6. FIG. 5 shows waveforms indicating the
operation of each of the circuits in the knock signal deriving portion 2,
and FIG. 6 shows waveforms indicating the operation of each of the
circuits in the portions 50 and 52.
The knock sensor 1 is a vibration acceleration sensor generally well known
as being mounted on the cylinder block (not shown) etc., of an engine,
which converts the mechanical vibration into an electrical signal, and
generates a vibrating wave signal, as shown in FIG. 5(a), received by the
bandpass filter 2a. The bandpass filter 2a only passes therethrough a
frequency component inherent in knocks, from the output signal of the
knock sensor 1, thereby suppressing a noise component not relating to
knocks to provide an output good in S/N ratio as shown in FIG. 5(b) by
wave-form A.
The noise level detector 2b may be composed of, e.g. a half-wave rectifying
circuit, an averaging circuit, and an amplifying circuit etc. The noise
level detector 2b converts the output of the bandpass filter 2a (FIG.
5(b), wave-form A) into a DC voltage by the half-wave rectification and
the averaging operations, the DC voltage being amplified with a
predetermined amplification to have a level, as shown in FIG. 5(b) by a
wave-form B, higher than the noise component of the output signal of the
bandpass filter 2a (FIG. 5(b), wave-form A) but lower than the knock
component of the same.
The comparator 2c compares the output signal of the noise level detector 2b
(FIG. 5(b), wave-form B) with the output of the bandpass filter 2a (FIG.
5(b), wave-form A). In the case where no knock occurs (FIG. 5, section C),
since the output signal of the bandpass filter 2a (FIG. 5(b), wave-form A)
is not greater than the output signal of the noise level detector 2b (FIG.
5(b), wave-form B), the comparator 2c provides no output, while in the
case where knocks occur (FIG. 5(b), section D), since the former signal is
greater than the latter signal, the comparator 2c provides as an output a
pulse train as shown in FIG. 5(c). Accordingly, the output pulse train
from the comparator 2c can be used for determining whether or not knocks
have occurred.
When the knock signal deriving portion 2 derives knock signals as shown in
FIG. 5(c), the comparator 2c provides as an output a pulse train as shown
in FIG. 6(c). As shown in FIG. 6(d), the pulse train shown in FIG. 6(c) is
integrated by the integrator 50a to provide as an output therefrom an
integrated voltage. The output voltage of the integrator 50a through the
A/D converter 50b serves as a control voltage to retard the angle of the
ignition timing by means of the first and second ignition timing computing
unit 54 and 18 and to reduce the supercharging pressure by means of the
supercharging control portion 70. Namely, upon the occurrence of knocks
the pulse train output of the compartor 2c causes the output voltage of
the integrator 50a to be increased to retard the ignition timing and to
reduce the supercharging pressure, thereby suppressing the occurrence of
knocks on the real time basis. On the other hand, when knock ceases, the
output voltage of the integrator 50a decreases to return the ignition
timing toward the advance angle and increase the supercharging pressure.
Therefore, the retard angle control magnitude determining portion 50, as
shown in FIG. 6(d) by the output of the integrator 50a, forms a closed
loop control system for retarding the angle of the ignition timing up to
the knock limit point on the real time basis in response to the occurrence
of knocks. While the rising rate or the falling rate of the output voltage
of the integrator 50a is dependent upon the responsiveness in the
retardation of the ignition timing and the reduction of the supercharging
pressure or the stability of the closed loop control, it is set at a
relatively high responsiveness because of the requirements of immediate
response to knocks.
The displacement magnitude determining portion 52 serves to determine a
displacement magnitude from the reference ignition timing and the
reference supercharging pressure according to the occurrence rate of
knocks. The pulse generator 52a receives as an input the pulse train
output (FIG. 6(c) from the comparator 2c and then provides output pulses
(FIG. 6(e)). That is to say, the pulse generator 52a provides one output
pulse in response to a knock which occurs during one ignition. The output
pulses of the pulse generator 52a are counted by the counter 52b, the
count value being shown in FIG. 6(f). The timer 52c provides one output
pulse (FIG. 6(g)) per a predetermined time interval to the counter 52b
whose count is reset to zero by the output pulse of the timer 52c. The
output of the counter 52b becomes a logic high level when the count value
of the counter 52b exceeds a predetermined value which is "count 3" in
this case, as shown in FIG. 6(h). This means that when a predetermined
number of knocks have occurred within a predetermined time interval, i.e.
the occurrence rate of knocks has exceeded a predetermined value, the
counter 52b provides a high level output signal.
The up/down counter 52d counts up by one when the output of the counter 52b
has a logical transition from the low level "0" to the high level "1". The
timer 52e provides one output pulse per a predetermined time interval as
shown in FIG. 6(j) to the up/down counter 52d which is counted-down by one
by the output of the timer 52e. The count of the up/down counter 52d is
shown in FIG. 6(i).
The memory 52f stores the count of the up/down counter 52d at the time of
the ignition switch being turned off or at the time of a reduction in the
power source voltage, while presetting the stored count as the count of
the up/down counter 52d. Namely, even if the engine is stopped, the memory
52f enables a displacement magnitude of the reference ignition timing and
the reference supercharging pressure to be retained.
Thus, the reference ignition timing displacement magnitude determining
portion 52 determines the occurrence rate of knocks and then produces a
displacement magnitude to retard the reference ignition timing and to
reduce the reference supercharging pressure by the output of the up/down
counter 52d if the occurrence rate of knocks exceeds a predetermined value
while the displacement magnitude is shifted toward the advance angle and
the increased supecharging pressure if the displacement magnitude is not
shifted toward the retard angle and the reduced supercharging pressure
respectively within a predetermined time interval.
Therefore, the displacement magnitude determining portion 52, similar to
the retard angle control magnitude determining portion 50, also forms a
closed loop control system for retarding/advancing the ignition timing and
reducing/increasing the supercharging pressure according to the occurrence
of knocks, through the first and second ignition timing computing units 54
and 18. However, both portions are different in that the portion 50
controls the ignition timing in the direction of retard angle and the
supercharging pressure in the direction of reduction on a real time basis
in order to suppress the occurrence of knocks by the detection thereof
whereas the portion 52 operates the occurrence rate of knocks by the
detection thereof and then displaces the reference ignition timing in the
direction of retard angle or advance angle and the reference supercharging
pressure in the direction of a reduced or increased pressure thereby to
provide a reference ignition timing and a reference supercharging pressure
adapted for the octane rating of a fuel used for the engine. Therefore,
the responsiveness in displacement of the determining portion 52 toward
the advance angle or the retard angle and the reduced pressure or the
increased pressure is set more slowly than that of the determining portion
50.
Now the first ignition timing computing unit 54 will be described.
The proportion factor calculator 54a changes the output count of the
up/down counter 52d into a proportion factor. Assuming that the proportion
factor calculator 54a receives as an input an output count N of the
up/down counter 52d, this count N is divided by a maximum preset count
value Nmax from the up/down counter 52d, the result being assumed to be a
proportion factor k (=N/Nmax). Therefore, in the case where the premium
gasoline is used, the knock limit point is relatively positioned in the
direction of advance angle, and accordingly the count N of the up/down
counter 52d will be substantially zero so that the proportion factor k
becomes equal to zero. On the other hand, in the case where the regular
gasoline is used, the knock limit point is relatively positioned in the
direction of retard angle, and accordingly the count N of the up/down
counter 52d will be substantially Nmax so that the proportion factor k
becomes equal to 1. Further in the case where mixed gasoline of premium
and regular gasolines is used, as shown in FIG. 2 by the characteristic
curve C, the knock limit characteristic exists between those in the case
where premium gasoline is used and in the case where regular gasoline is
used so that the count N of the up/down counter 52d assumes a value
between zero and Nmax, i.e. 0<N<Nmax, thereby 0<k<1. Therefore, it can be
seen that the proportion factor k indicates the mixture ratio of premium
gasoline and regular gasoline.
Meanwhile, the ROM's 11 and 12 receive as inputs an address value
corresponding to the engine speed and the engine load from the second
ignition timing computing unit 18 and then provides as an output the
ignition timing data stored in that address to the interpolator 54b.
Assuming that the ignition timing characteristic stored in the ROM 11 be
set for the premium gasoline and that the ignition timing data in that
address be .theta..sub.B, and that the ignition timing characteristic
stored in the ROM 12 be set for the regular gasoline and that the ignition
timing data in that address be .theta..sub.A, the ignition timing
characteristic of the ROM 11 is set at the same timing as that of the ROM
12 or toward the advance angle beyond the latter so that .theta..sub.A
<.theta..sub.B. Hence the interpolator 54b performs the interpolating
operation according to the proportion factor k between .theta..sub.A and
.theta..sub.B. Namely, the operation of .theta..sub.B -k(.theta..sub.B
-.theta..sub.A) is performed, the resultant value .theta. .sub.C as
assumed, having a value divided proportionally by a ratio of k:(1-k)
between .theta..sub.B and .theta..sub.A. Therefore, it will be found that
when premium gasoline is used, .theta..sub.C =.theta..sub.B because k=0,
when regular gasoline is used, .theta..sub.C =.theta..sub.A because k=1,
and when a mixture of premium and regular gasolines is used, .theta..sub.A
<.theta..sub.C <.theta..sub.B because 0<k<1. Therefore, .theta..sub.C has
a value proportionally divided between .theta..sub.A and .theta..sub.B on
the basis of a proportion factor k indicating the mixture ratio of premium
and regular gasolines so that even though a mixture of premium and regular
gasolines is used, an optimum reference ignition timing can be provided
according to the mixture ratio of premium high-octane gasoline and regular
low-octane gasoline, by means of the above interpolation.
Furthermore, in the first ignition timing computing unit 54, the subtractor
54c subtracts from the output value .theta..sub.C of the interpolator 54b
the output value .theta..sub.D of the A/D converter 50b in the retard
angle control magnitude determining portion 50 to provide as an output
therefrom the ignition timing data of .theta..sub.E (=.theta..sub.C
-.theta..sub.D) to the second ignition timing computing unit 18. Namely,
the subtractor 54c performs a retard angle correction for the reference
ignition timing by subtracting the retard angle control magnitude from the
optimum reference ignition timing obtained by the interpolator 54b in
order to suppress knocks occurring during a transient operation of the
engine or at a time of rapid transition of the environmental condition.
The second ignition timing computing unit 54 computes an ignition timing
from the ignition timing data (the output value of the subtractor 54c) on
the basis of the output of the crank angle sensor 16 to provide as an
output therefrom an ignition signal. This art is well known in the art of
an ignition timing control so that the description thereof will not be
repeated.
On the other hand, the supercharging pressure control portion 70 performs
the same operation as the ignition timing computing unit 54 as set forth
above. Therefore, the proportion factor calculator 70a provides as an
output therefrom the same proportion factor k as the proportion factor
calculator 54a.
Now assuming that input supercharging pressure data into the interpolator
70b from the ROM's 71 (low-octane) and 72 (high-octane) be P.sub.B and
P.sub.A respectively, since the supercharging pressure characteristic
stored in the ROM 71 is preset to be the same as or to be higher than that
stored in the ROM 72, it is given that P.sub.A .ltoreq.P.sub.B. The
interpolator 70b performs the interpolation operation of the equation:
P.sub.C =P.sub.B -k(P.sub.B -P.sub.A), P.sub.C being provided as an
output. The subtractor 70c subtracts, from the output value P.sub.C of the
interpolator 70b, the output supercharging pressure value P.sub.D, which
corresponds to the ignition timing data .theta..sub.D as described above,
of the A/D converter 50b of the retard control angle determining portion
50 to provide as an output the resultant supercharging pressure data
P.sub.E (=P.sub.C -P.sub.D) to the driver 73 which actuates the actuator
74 which further control the waste gate valve 75 as shown in FIG. 3.
Thus, from the optimum reference supercharging pressure provided by the
interpolator 70b, is subtracted a reduction magnitude of supercharging
pressure for suppressing knocks occurring during a transient operation of
engine or at a time of rapid transition of environmental condition,
thereby correcting the reference supercharging pressure.
In this embodiment, the proportion factor calculator 70a may be omitted and
instead the output of the proportion factor calculator 54a may be
connected to the interpolator 70b.
Next, a second embodiment of this invention will now be described with
reference to FIGS. 7 and 8.
This second embodiment shown in FIG. 7 is different from the first
embodiment in the arrangement of the reference ignition timing
displacement magnitude determining portion, and of the first ignition
timing computing unit as well as of the supercharging pressure control
portion, and in connection with the retard angle control magnitude
determining portion, the reference ignition timing displacement magnitude
determining portion, and of the first ignition timing computing unit.
Therefore, the description of the portions or elements denoted by the same
reference numerals in both embodiments will not be repeated.
In FIG. 7, the reference ignition timing displacement magnitude determining
portion 53 is formed of a retard/advance mode decision unit 53a, a first
timer 53b, a second timer 53c, an up/down counter 53d which may be the
same as the up/down counter 52d, and a memory 53e which may be the same as
the memory 52f; and the first ignition timing computing unit 55 is formed
of an adder 55a, a proportion factor calculator 55b which may be the same
as the calculator 54a, and an interpolator 55c which may be the same as
the interpolator 54b.
The retard/advance mode decision unit 53a has one input terminal connected
to the output terminal of the retard angle control magnitude determining
portion 50 to receive the output of the A/D converter 50b and has two
output terminals one of which is, as a retard mode output (reduced
supercharging pressure), connected to the first timer 53b and the other of
which is, as an advance mode output (increased supercharging pressure),
connected to the second timer 53c, thereby comparing the output value of
the A/D converter 50b with a predetermined value and consequently
providing the retard (reduced) mode output or the advance (increased) mode
output.
The output terminals of the timers 53b and 53c are respectively connected
to the up-count input terminal and the down-count input terminal of the
up/down counter 53d. The input terminal of the memory 53e is connected to
the output terminal of the up/down counter 53d while the output terminal
of the memory 53e is connected to the preset input terminal.
The adder 55a has two input terminals one of which is connected to the
output terminal of the reference ignition timing displacement magnitude
determining portion 53, namely, the output terminal of the up/down counter
53d and the other of which is connected to the output terminal of the
retard angle control magnitude determining portion 50, namely, or the
output terminal of the A/D converter 50b. The output terminal of the adder
55a is connected to the input terminal of the proportion factor calculator
55b. The interpolator 55c receives as inputs thereto output data of the
ROM's 11 and 12 as well as the output value of the proportion factor
calculator 55b while providing as an output therefrom the calculated
result to the second ignition timing computing unit 18.
It will be seen from FIGS. 3 and 7 that while in the first embodiment the
output of the comparator 2c is connected to the inputs of the integrator
50 as well as the pulse generator 52a, in the second embodiment the output
of the comparator is only connected to the input of the integrator 50a.
Also in this embodiment of this invention, in addition to the ignition
timing control the supercharging pressure is reduced to suppress the
occurrence of knocks by means of a supercharging pressure controller 77,
ROM's 71 and 72, a driver 73, an actuator 74, and a waste gate valve 75
which are the same as the corresponding elements denoted by the same
reference numerals in the first embodiment shown in FIG. 3 so that the
description of the corresponding portions and elements denoted by the same
reference numerals will not be repeated.
FIG. 8 shows various waveforms in the operation of the reference ignition
timing (supercharging pressure) displacement magnitude determining portion
53 shown in FIG. 7. FIG. 8(d) shows the output voltage of the integrator
50a which is converted into a digital value by the A/D converter 50b. The
retard/advance (reduced/increased pressure) mode decision unit 53a has two
reference values to be compared with its input value, one of which is a
retard (reduced pressure) mode decision reference (V1) and the other of
which is an advance (increased) mode decision reference (V2), whereby the
output value of the A/D converter 50b is compared with the retard
(reduced) mode decision reference and the advance (increased) mode
decision reference.
FIG. 9 shows the output modes of the decision unit 53a. Now, when the
output value V of the A/D converter 50b is above the retard (reduced) mode
decision reference V1, the decision unit 53a assumes the retard angle
(reduced pressure) mode, thereby rendering the retard (reduced) mode
output thereof at a high logic level as shown in FIG. 8(k) while when the
output value of the A/D converter 50b is below the advance (increased)
mode decision reference V2, the decision unit 53a assumes the advance
angle mode, thereby rendering the advance (increased) mode output thereof
at the high level as shown in FIG. 8(l). When the output value of the A/D
converter 50b is intermediate between the references V1 and V2, the
decision unit 53a assumes a stop mode where the retard (reduced) mode
output and the advance (increased) mode output are at a low logic level.
While the retard (reduced) mode output of the decision unit 53a is at the
high level, the timer 53b provides as an output therefrom one pulse per a
predetermined time interval as shown in FIG. 8(m). While the advance
(increased) mode output of the decision unit 53a is at the high level, the
timer 53c provides as an output therefrom one pulse per a predetermined
time interval as shown in FIG. 8(n).
FIG. 8(p) shows the count of the up/down counter 53d which up-counts the
output pulses of the timer 53b and down-counts the output pulses of the
timer 53c. Therefore, when the output value of the A/D converter 50b is
greater than the retard (reduced) mode decision reference V1, the retard
angle (reduced pressure) mode appears, thereby up-counting the count of
the up/down counter 53d, when the output value of the A/D converter 50b is
smaller than the advance angle (increased pressure) reference V2, the
advance angle (increased pressure) mode appears, thereby down-counting the
count of the up/down counter 53d, and when the output value of the A/D
converter 50b is intermediate between the references V1 and V2, the stop
mode appears, thereby retaining the current count of the up/down counter
53d.
As to the operation of the first ignition timi | | |
