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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention:
This invention relates to a control system for electronic engine control
for computing various controlled variables by a digital processor, and
more particularly to a system of reading the input signal from a
temperature sensor which detects the engine temperature.
2. Description of the Prior Art:
The input signal from a water temperature sensor for detecting cooling
water temperature (which is closely related to the engine temperature) is
an important factor in computing fuel injection amount during an engine
start period and during engine warming-up after the start period. An
analog sensor signal may be for example, A-D (Analog-Digital) converted
and read at predetermined intervals of time during operation of the
engine. In prior control systems for electronically controlled fuel
injection engines, frequency of reading the input signal from the water
temperature sensor during the start period is equal to that after the
start period (in this specification the start period means a period from
start and operation of a starting motor to occurrence of complete
explosion, and post-start period means a period during which the engine is
operated after the complete explosion, complete explosion being
self-sustained engine operation not requiring the starting motor
operation) and does not vary. The water temperature sensor generally
contains a thermistor to which voltage related to voltage of an
accumulator is applied. The voltage of the accumulator in the temperature
sensor varies (or fluctuates) greatly in the start period because current
is supplied to the starting motor, so that the input signal from the water
temperature sensor also fluctuates greatly. Thus, prior systems for
reading the input signal from the water temperature sensor during the
start period were subject to greatly deviating signals due to this
accumulator voltage variation so that fuel injection amount, for example,
are computed on the basis of that great deviation for a relatively long
time until the next reading, causing loss to accuracy in control. However,
after the start period the cooling water temperature has relatively small
time-based variation compared with other detected parameters, and any
reduction in the frequency of reading the cooling water temperature also
reduces the frequency of reading other parameters after the start period,
which is not advantageous for accuracy in engine control after the start
period.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a control system for
electronic engine control which reduces the degradation of accuracy in
control due to the variation of the output signal of a temperature sensor
during the start period without hindrance to reading the object to be
detected other than temperature after the start period.
According to the present invention achieving this object, in a control
system for electronic engine control for computing the controlled variable
object to be controlled by the digital processor on the basis of the input
signal from the temperature sensor detecting the engine temperature, the
frequency of reading the input signal from the temperature sensor before
the complete explosion of the engine (i.e., during starter motor
operation) is higher than that after the complete explosion of the engine
(i.e., after conclusion of the starter motor operation).
Thus, since the input signal from the temperature sensor is frequently read
during the start period when the input signal from the temperature sensor
greatly varies, the higher sampling rate reduces degradation of accuracy
in control due to the variation of the input (i.e., temperature feedback
signal).
The temperature sensor is generally a water temperature sensor for
determining the engine temperature from the temperature of the engine
cooling water.
An object to be controlled may be, for example, an electromagnetic fuel
injection valve system for supplying fuel to an intake system and
controlling opening time of the electromagnetic system fuel injection
valve, i.e. fuel injection amount control, as computted in relation to the
determined engine temperature.
In a preferred embodiment of the present invention, priority of reading the
input signal from the temperature sensor before the complete explosion of
the engine is higher than that after the complete explosion of the engine.
In the preferred embodiment, a schedule for determining the sequence of
reading inputs from various sensors before the complete explosion is
different from that after the complete explosion.
In the further preferred embodiment, the number of indications for reading
the input signal from the temperature sensor contained in the schedule
before the complete explosion is greater than that after the complete
explosion, meaning that such indications are more "densely packed" prior
to complete explosion than after.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of an electronically controlled engine
according to the present invention;
FIG. 2 is a block diagram of the FIG. 1 illustration;
FIG. 3 is a drawing showing the sequence of reading input signals during
and after the start period;
FIG. 4 is a drawing showing the relationship between cooling water
temperature and fuel injection pulse width; and
FIG. 5 is a drawing showing exemplary time-based variation of input voltage
from a water temperature sensor during the start period.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments of the present invention will be described with reference
to the drawings.
Referring to FIG. 1 showing generally the whole electronic control fuel
injection engine according to the present invention, air flow sucked from
an air cleaner 1 is controlled by a throttle valve 4 provided in a
throttle body 2 and interlocked with an accelerator pedal 3 inside a
vehicle. The air flow is then supplied to a combustion chamber 9 in an
engine body 8 through a surge tank 5, intake pipe 6 and intake valve 7.
Mixture burnt in the combustion chamber 9 is discharged as exhaust gas
through an exhaust valve 10 and exhaust manifold 11. An electromagnetic
fuel injection valve 14 is provided in the intake pipe 6 corresponding to
each combustion chamber 9. An electronic control system 15 may receive
input signals from a throttle switch 16 for detecting full closing of the
throttle valve 2, a water temperature sensor 18 mounted on a water jacket
17 of the engine body 8, a pressure sensor 19 provided in the surging tank
5 to detect intake pipe pressure related to the intake air flow rate, a
crank angle sensor 23 for detecting rotational angle of a distributor
shaft coupled to a crank shaft to detect rotational angle of the crank
shaft coupled to pistons 21 through connecting rods 22, an air fuel ratio
sensor 24 provided in the exhaust manifold 11 to detect oxygen
concentration in exhaust gas, and a vehicle speed sensor 25. The
rotational angle sensor 23 is provided with one portion 26 for producing
one pulse for two rotations of the crank shaft and another portion 27 for
producing one pulse for every predetermined crank angle, for example,
30.degree.. Fuel is forcibly sent from a fuel tank 30 through a fuel path
29 to the fuel injection valve 14 by a fuel pump 31.
The electronic system 15 computes fuel injection amount and fuel injection
period on the basis of various input signals so as to send fuel injection
pulses to the fuel injection valve 14 while computing ignition timing to
send ignition signals to ignition coil 32. The secondary current in the
ignition coil 32 is sent to a distributor 33. Further, the injection valve
14 is maintained in an opened condition only when it receives pulses from
the electronic control system 15.
FIG. 2 is a block diagram of the interior of the electronic control system
15. CPU (Central Processing Unit) 35 as a digital processor, ROM
(Read-Only Memory) 36, RAM (Random Access Memory) 37, C-RAMs (Complement
type RAM) 38, input interface 39 and input/output interface 40 are all
connected to each other through bus 41. One C-RAM 38 can be supplied with
predetermined power so as to hold memory even during stoppage of the
engine. The input interface 39 has a built-in A/D (Analog/Digital)
converter, and analog outputs of the water temperature sensor 18 and
pressure sensor 19 are sent to the input interface 39. The outputs of the
throttle switch 16, crank angle sensor 23, air fuel ratio sensor 24 and
vehicle speed sensor 25 are sent to the input/output interface 40, and
electric signals to the fuel injection valve 14 and ignition coil 32 are
sent from the input/output interface 40.
FIG. 3 shows the sequence of A/D conversion in the input interface 39,
i.e., the sequence of reading the input signals. In FIG. 3, the input
signals are assumed to be of three types, A, B and water temperature. Step
36 determining whether it is the start period, and if so judged the
sequences of A/D conversion of the input signals is selected, and if it is
judged to be after the start period the sequence T of A/D conversion of
the input signal is selected. Step 36 may be based on, for example, the
time taken for rotation of a predetermined angle of the engine crank
shaft. When the complete explosion is produced (i.e., after the start
period) the required time for the predetermined rotation is less than a
predetermined value. The sequence S A/D conversions are signal A (step S
37), signal B (step S38), water temperature signal (step S39), signal B
(step S40), signal A (step S41), signal B (step S42), water temperature
signal (step S43), . . . in that order. The sequence T steps are signal A
(step T37), signal B (step T38), signal A (step T39), signal B (step T40),
signal A (step T41), signal B (step T42), signal A (step T43), . . . water
temperature signal (step T50), . . . in that order. The frequency of A/D
conversion of the water temperature signal (i.e., frequency of reading
water temperature during the start period) is selected higher than that
after the start period.
FIG. 4 shows the relationship between cooling water temperature and pulse
width of fuel injection (i.e., input pulse width of the electromagnetic
system fuel injection valve 14) during the start period. The fuel
injection pulse width is a function of cooling water temperature. FIG. 5
shows time-based variation of input voltage from the water temperature
sensor 18 during the start period. During the start period, voltage of the
accumulator is varied by operation of the starting motor so that the input
voltage from the water temperature sensor 18 is also greatly varied.
Hence, when the frequency of reading the input from the water temperature
sensor 18 is small relative to a large input deviation per time reading,
difficulties are encountered in computing a controlled variable, for
example, fuel injection pulse width shown in FIG. 4. Since the frequency
of reading during the start period according to the present invention is
large, the changing input can be read immediately. Even though the input
greatly deviates, the previous difficulties in computing the controlled
variable can be remarkably reduced. Since the voltage variation of the
accumulator is slight after the start period and the time-based variation
of water temperature is small compared with that of the other objects to
be detected, the frequency of reading the input from the water temperature
sensor 18 is reduced after the start period, as shown by T in FIG. 3.
It is assumed, for example, that the time intervals between reading the
inputs from the water temperature sensor 18 during the start period are 20
m sec. and the time intervals between readings of the input from the water
temperature sensor 18 after the start period is 1 sec.
In a first embodiment where the frequency of reading the cooling water
temperature during the start period differs from that after the start
period, the priority of reading the cooling water temperature before the
complete explosion may also differ from that after the complete explosion.
For example, the priority of reading the cooling water temperature after
the start period is lower than the priority of the other detecting
amounts, and the priority of reading the cooling water temperature during
the start period is higher than the reading priority for the other
detections. Further, in a second embodiment, two schedules for determining
the sequence of reading the inputs from various sensors are provided for
the start period and the post-start period, and the number of reading of
the cooling water temperature in the schedule table for the start period
is higher than for the post-start period schedule.
Thus, according to the present invention, the frequency of reading the
input signal from the temperature sensor during the start period is higher
than that after the start period, so that the input read from the
temperature sensor when the input greatly deviates during the start period
affects such input only for a very short period to thereby improve the
accuracy in controlling the electronically controlled engine.
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