Ignition timing control system for an engine

There is disclosed an ignition timing control system for an engine, capable of adjustably setting a timing for shifting from a fixed ignition timing after complete firing to an ordinary ignition timing. The control system comprises an ignition timing setting unit for setting an ignition timing from an ignition timing map using an engine load and the engine speed, a complete firing judgment unit for judging a complete combustion from conditions of the engine, and a delay setting element for setting a delay time for switching the fixed ignition timing to predetermined ignition timing at the time of starting in dependency on the engine temperature when the complete firing is judged.

BACKGROUND OF THE INVENTION 
The present invention relates to an ignition timing control system for an 
engine, and more particularly to the timing control system for shifting 
from a fixed ignition timing after complete firing to an ordinary ignition 
timing control in dependency on an engine temperature. 
Heretofore, for the ignition timing control system of this kind, there is 
an angular control method to detect projections or slits provided on a 
crank rotor rotating in synchronism with a crank shaft to messure an 
ignition timing as disclosed in e.g., Japanese Patent Application 
Laid-Open 61-96181. In addition, there is a time control method to detect 
passing time between the projections or slits provided on the crank rotor 
at predetermined intervals to measure an ignition timing as disclosed in 
Japanese Patent Laid-Open 60-47877, etc. 
Meanwhile, because an engine speed at the time of cranking is unstable, 
many systems have a measure to fix the ignition timing at position before 
top dead center (BTDC) 10.degree. at the time of cranking and then to 
advance an ignition angle after starting the engine to shift to an 
ordinary ignition timing. Generally, a timing for shifting to such an 
ordinary ignition timing is uniformly switched to the ordinary ignition 
timing when a starter switch is switched from an ON to an OFF state in 
dependency on the engine speed. 
In an ordinary operating state where the engine speed is stable, the time 
control method is more advantageous than the angle control method in 
various aspects, i.e. fast computing speed and simple structure. However, 
for an unstable initial or start-up time period immediately after 
starting, it is difficult to precisely detect changes in the engine speed. 
Namely, as shown by fixed ignition time period at the time of cranking in 
FIG. 1 and the ignition timing control immediately after starting in FIG. 
2, projections 1a and 1b are formed at an outer periphery of a crank rotor 
1, e.g., at positions of BTDC 10.degree. and BTDC 100.degree.. At the time 
of cranking, when a crank pulse produced in response to detection of the 
projection 1a is output for the fixed ignition timing, an ignition signal 
is output to an ignition drive means (not shown) to spark an ignition plug 
(state of FIG. 1). 
On the other hand, when the starter switch is turned OFF after complete 
firing, or when the engine speed rises to a predetermined value, the 
ignition timing control is switched to the ordinary ignition timing 
control. First, an angular velocity is calculated from a time period 
.alpha. from the time when the projection 1a is detected to the time when 
the projection 1b is detected to convert an ignition angle set depending 
upon the operating state to an ignition timing in accordance with a 
calculated angular velocity, thus to measure the ignition timing using the 
time when the projection 1b is detected as a reference time point. When 
the time reaches a predetermined ignition timing (BTDC 20.degree. in FIG. 
2), an ignition signal is output. 
However, the combustion characteristics generally vary in dependency on a 
combustion temperature. For example, firing at the initial time of 
complete firing at a high engine temperature is relatively stable. 
Accordingly, the shift of the ignition timing is relatively fast from the 
fixed position and to the ordinary ignition timing position and permits a 
smooth start-up characteristic. On the other hand, where the engine 
temperature is low such as in a cold starting, combustion becomes unstable 
also after complete firing. Particularly, in the case of an extremely low 
engine speed immediately after starting the engine, an interval of the 
time period .alpha. is prolonged. When the engine speed for this time 
period varies to much degree, even if the ignition timing is at BTDC 
20.degree. as shown in FIG. 2, an actual ignition angle may be excessively 
advanced to an extent of BTDC 30.degree.. 
As a result, when the ignition timing is suddenly advanced from the fixed 
ignition timing when starting the engine in the cold state, the engine 
speed is not smoothly increased. Consequently, engine stall would occur, 
thus making it difficult to obtain a satisfactory starting performance. 
In addition, when switching timing of such an ignition timing is set in 
correspondence with the cold state, the ignition timing control at a low 
engine speed at a high engine temperature is not suitably conducted, 
resulting in the problem that a satisfactory starting or restarting 
performance cannot be obtained. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of the above circumstances. The 
object of the present invention is to provide an ignition timing control 
system for an engine for a time control, wherein the system is capable of 
adjustably setting the timing for switching from a fixed ignition timing 
to an ordinary ignition timing in dependency on an engine temperature, 
resulting in a satisfactory starting performance. 
The ignition timing control system for the engine according to the present 
invention comprises ignition timing setting means for setting an ignition 
timing from an ignition timing map using an engine load and an engine 
speed, respectively, complete firing judgement means for judging a 
complete firing from conditions of the engine, and delay setting means for 
setting a delay time for switching the fixed ignition timing to an 
ordinary ignition timing in dependency on a engine temperature when the 
engine is judged to be in a complete firing state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments according to the present invention will be described 
in detail with reference to the attached drawings. 
FIGS. 3 to 7 are views for explaining an embodiment according to the 
present invention. FIG. 3 shows a control unit 24 attached to an engine 10 
with horizontally opposed four cylinders. In this figure, the engine 10 
comprises a cylinder block 11, a cylinder head 12, an intake manifold 13 
and an exhaust manifold 14. The cylinder head 12 includes an intake port 
12a to which the intake manifold 13 is connected and an exhaust port 12b 
to which the exhaust manifold 14 is connected. Further, an ignition plug 
15 is secured on the head 12, and an igniting portion of the plug 15 is 
exposed to a combustion chamber 11a of the block 11. 
An air chamber 16 connects the intake manifold 13 with a throttle chamber 
17 having a throttle 17a. The throttle chamber 17 is connected to an 
intake pipe 18 connected to an air cleaner 19 upstream side thereof. 
Furthermore, an intake air flow sensor 20 is secured in the vicinity of 
the air cleaner 19 within the intake pipe 18. As shown in FIG. 3, a hot 
wire type air flow meter is used as a sensor 20. 
The intake manifold 13 includes a coolant passage (not shown). A coolant 
temperature sensor 21 is provided within the coolant passage. 
Furthermore, the cylinder block 11 also includes a crank shaft 11b. The 
crank shaft 11b includes a crank rotor 22 fixed on an end thereof. The 
rotor 22 includes projections 22a as a reference point for calculating an 
angular velocity, and projections 22b indicating reference crank angles of 
respective cylinders. One projection 22a indicates each reference point of 
cylinders of No. 1 and No. 2, and the other projection 22a leading by an 
angle of 180 degrees indicates each reference point of cylinders of No. 3 
and No. 4. One projection 22b that leads the projection 22a as the 
reference point of the cylinders No. 1 and No. 2 by an angle of 90 degrees 
indicates a crank angle of the cylinders of No. 1 and No. 2. The other 
projection 22b leading by an angle of 180 degrees from the projections of 
No. 1 and No. 2 cylinders indicates the crank angle of the cylinders of 
No. 3 and No. 4. These projections 22a and 22b are shown in detail in FIG. 
4. Namely, in this figure, a set angle .theta.1 of the projection 22a is 
BTDC 10.degree., and a set angle .theta.2 of the projection 22b is BTDC 
100.degree.. 
As shown in FIGS. 3 and 4, a crank angle sensor 23 comprising an 
electromagnetic pick-up is disposed at a position facing the outer 
periphery of the rotor 22. The sensor 23 includes a head for detecting 
change in the magnetic flux produced when the projections 22a and 22b pass 
through the sensor 23, and a signal generator for converting the change in 
magnetic flux detected to an a.c. voltage. The generator outputs a 
rotational angle signal Ne for detecting an engine speed and a crank 
angular velocity and a reference crank angle signal G for detecting a 
reference crank angle per each cylinder. 
The intake air flow sensor 20, the coolant temperature sensor 21, and the 
crank angle sensor 23 are connected to the ignition timing control unit 
24. The control unit 24 includes a central processing unit (CPU) 25 for 
performing a predetermined computation in dependency on various 
information sensed by the sensors 20, 21 and 23, a read only memory (ROM) 
26 for holding fixed data such as control programs for the CPU 25 and an 
ignition timing map MP.sub.IG, a random access memory (RAM) 27 for storing 
various data for data processing, an input/output (I/O) interface 28 
responsive to the sensors 20, 21 and 23, a bus line 29 interconnecting the 
CPU 25, the ROM 26, the RAM 27, and the I/O interface 28 each other and a 
drive circuit 31 connected to an output port of the I/O interface 28. The 
sensors 20, 21 and 23 constitute operating parameter sensing means 30 as 
shown in FIG. 5. The drive circuit 31 is connected to a distributor 32 
through an ignition coil 33, and the distributor 32 is connected to the 
ignition plug 15 (see FIG. 3). 
As shown in FIG. 5, the ignition timing control unit 24 comprises crank 
pulse discrimination means 34, angular velocity calculating means 35, 
engine speed calculating means 36, intake air quantity calculation means 
37, coolant temperature calculation means 38, engine load calculator 39, 
ignition timing correction quantity calculator 40, ignition timing setting 
means 41, the ignition timing map MP.sub.IG, switching unit 44 as an 
ignition switching timing setting means, ignition time calculation means 
45, timer means 46 and ignition drive means 47. 
The crank pulse discrimination means 34 discriminates whether an output 
signal from the crank angle sensor 23 is the signal G produced in response 
to detection of the projection 22b of the crank rotor 22 or the signal Ne 
produced in response to detection of the projection 22a by a signal 
produced in response to detection of a projection of a cam rotor rotating 
in synchronism with a cam shaft (not shown). 
Thus, the cam rotor rotating in synchronism with the cam shaft makes 
one-half of the revolution during one revolution of the crank rotor 22. By 
detecting projections formed equiangularly every 90 degrees on an outer 
periphery of the cam rotor, it is possible to predict what signal is 
output from the crank angle sensor 23 after any projection of the cam 
rotor is detected. 
The angular velocity calculating means 35 calculates a time T.theta. from 
the time when the rotational angle signal Ne discriminated by the crank 
pulse discriminator 34 is detected to the time when next reference crank 
angle signal G is detected. Then, this calculating means 35 calculates an 
angular velocity .omega. of the crank shaft 11b from angular data between 
the projections 22a and 22b of the crank rotor 22 stored in advance in the 
ROM 26. 
The engine speed calculating means 36 calculates the engine speed N from 
the angular velocity .omega. calculated in the angular velocity calculator 
35. 
The intake air flow calculating means 37 calculates a volume of an intake 
air, i.e., an intake air quantity Q passing through the intake pipe 18 in 
dependency on an output signal from the intake air flow sensor 20. 
The coolant temperature calculating means 38 calculates a coolant 
temperature Tw from an output signal from the coolant temperature sensor 
21. 
The engine load calculation means 39 calculates a fundamental fuel 
injection quantity Tp (Tp=K.times.Q/N, K . . . constant) from the engine 
speed N calculated at the engine speed calculating means 36 and the intake 
air quantity Q calculated at the intake air quantity calculating means 37 
to output it. This fundamental fuel injection quantity Tp corresponds to 
an engine load. 
The ignition timing correction calculating means 40 calculates an ignition 
timing correction quantity X corresponding to data such as the coolant 
temperature Tw calculated at the coolant temperature calculation means 38. 
The ignition timing setting means 41 specifies an area of the ignition 
timing map MP.sub.IG stored in the ROM 26. As respective parameters, the 
engine speed N calculate at the engine speed calculating means 36 and the 
fundamental fuel injection quantity Tp as the engine load calculated at 
the engine load calculating means 39. The ignition timing setting means 41 
retrieves or searches an ignition timing (ignition angle) .theta.IG stored 
in this area and corrects the ignition timing .theta.IG by using the 
ignition timing correction quantity X calculated at the ignition timing 
correction quantity calculation means 40 to set a new ignition timing 
.theta.IG (.theta.IG.rarw..theta.IG+X). 
The switching unit 44 comprises complete firing judgment means 44a and 
delay setting means 44b. The complete firing judgment means 44a takes 
thereinto the engine speed N calculated at the engine speed calculation 
means 36 to make a comparison between the engine speed N and a reference 
engine speed NO (e.g., 500 r.p.m.) set in advance. When the engine speed N 
exceeds the reference engine speed NO (N.gtoreq.No), the complete firing 
judgment means 44a judges the engine 10 to be in a complete firing state. 
The delay setting means 44b is provided with the coolant temperature Tw 
calculated at the coolant temperature calculation mean 38 as an engine 
temperature when the engine 10 is judged to be in a complete firing state 
at the complete firing judgment means 44a. Then, the means 44b sets a 
delay time (delay timing), i.e., an ignition switching delay time for 
switching a fixed ignition timing SPKH to an ignition timing .theta.IG for 
an ordinary timing control after complete firing in dependency on the 
coolant temperature. 
For example, in this embodiment, as shown in FIG. 6, a range of the coolant 
temperature Tw is classified into five stages described below: 
______________________________________ 
(1) Tw .ltoreq. -20.degree. C. 
(2) -20.degree. C. &lt; Tw .ltoreq. 0.degree. C. 
(3) 0.degree. C. &lt; Tw .ltoreq. 30.degree. C. 
(4) 30.degree. C. &lt; Tw .ltoreq. 60.degree. C. 
(5) 60.degree. C. .ltoreq. Tw 
______________________________________ 
The ignition switching delay time is set to the following values in 
dependency on the coolant temperature Tw: 
______________________________________ 
(1) 5 sec. 
(2) 3 sec. 
(3) 2 sec. 
(4) 0.5 sec. 
(5) 0 sec. (switching immediately after complete firing) 
______________________________________ 
It is to be noted that each ignition switching delay time is set by 
calculating, the time from the complete firing to a stabilized combustion 
by an experiment in advance. The delay time is dependent upon the coolant 
temperature Tw. A set of such delay times are stored in advance in the ROM 
26 as a table of count values TIMDLY corresponding to respective ignition 
switching delay times using the cooling water temperature Tw as a 
parameter. 
The ignition switching timing setting unit 44 outputs the signal Ne in 
response to detection of the projection 22a (BTDC .theta.1) of the crank 
rotor 22 as a fixed ignition signal SPKH to the driver 47. The signal Ne 
is output from the crank pulse discriminator 34 during delay time period 
after complete firing. 
On the other hand, when a delay time .tau.0 elapses after the complete 
firing, the switching unit 44 outputs the ignition timing .theta.IG set at 
the ignition timing setting device 41 to the ignition time calculating 
means 45. 
The ignition time calculating means 45 divides the ignition timing 
.theta.IG output from the switching unit 44 by the angular velocity 
.omega. calculated at the angular velocity calculation means 35 to 
calculate an ignition timing TIG (TIG=.theta.IG/.omega.). 
The timer means 46 starts counting the ignition timing TIG calculated at 
the ignition time calculator 45 using a signal G output from the crank 
pulse discriminator 34 as a trigger signal. When the count value reaches 
the ignition time TIG. the timer 46 outputs an ignition signal SPK to the 
ignition driver 47. 
When the fixed ignition signal SPKH from the switching unit 44 or the 
ignition signal SPK from the timer 46 is input to the ignition drive means 
47, a current flowing in the primary winding of the ignition coil 33 is 
cut off. Thus, the ignition plug 15 of the corresponding cylinder is 
sparked. 
The operation of the embodiment will be now described in accordance with 
the flowchart shown in FIG. 7. This program is executed per each cycle. 
At the time of starting the engine, when the key switch is turned ON, the 
operation at a step S101 is first executed. Namely, the engine speed N is 
calculated in dependency on the output signal from the crank angle sensor 
23, and the coolant temperature Tw is calculated in dependency on an 
output signal from the coolant temperature sensor 21 is calculated. Then, 
the program execution proceeds to a step S102 to make a comparison between 
the engine speed N calculated at the step S101 and the reference engine 
revolution number NO. (e.g., 500 r.p.m.) set in advance as a revolution 
number of the complete firing. As a result, when N&lt;NO, it is judged that 
the engine does not reach the complete firing state. The program execution 
proceeds to a step S103. At this step, the count value TIMDLY 
corresponding to the ignition switching delay time .tau.0 in dependency on 
the coolant temperature Tw calculated at the step S101. Then, the program 
execution proceeds to a step S104 to output the fixed ignition signal SPKH 
in synchronism with the signal Ne produced in response to detection of 
BTDC .theta.1 (e.g., .theta. 1=10.degree.) output from the crank pulse 
discriminator 34. At a step S111, a current flowing in the primary winding 
of the ignition coil 33 through the ignition drive means 47 is cut off to 
spark the ignition plug 15 of the corresponding cylinder. The program of 
one cycle is thus completed. The program execution returns to the step 
S101. 
On the other hand, when it is judged at the step S102 that N.gtoreq.NO, the 
engine 10 is judged to be in a complete firing state. The program 
execution advances to a step S105. At this step, a judgement is made as to 
whether a count value TIMDLY is equal to 0 (zero) or not. As a result, 
when the count value TIMDLY is not equal to 0, the program execution 
advances to a step S106. At this step, the current count value TIMDLY 
obtained by subtracting one (1) from the previous count value TIMDLY is 
set. Then, the program execution proceeds to the step S104 to perform an 
ignition timing control based on the fixed ignition timing. Until the 
count value TIMDLY becomes zero (0), the above-described routine is 
repeatedly executed. 
Thus, immediately after the complete firing of the engine 10, the fixed 
ignition timing is conducted up to the count value set in dependency on 
the coolant temperature Tw immediately before the complete firing of the 
engine 10 at the step S103, in other words, during a period of the 
ignition switching delay time .tau.0. 
When the count value TIMDLY is judged to be equal to zero at the step S105 
and the ignition switching delay time .tau.0 elapses, it is judged that 
the combustion after complete firing becomes stable. Then, the program 
execution proceeds to the step S107. At this step, the control is switched 
to an ordinary ignition timing control. Thus, the fundamental fuel 
injection quantity (load data) Tp is determined by the intake air quantity 
Q based on the output signal from the intake air flow sensor 20 and the 
engine speed calculated at the step S101. Then, the program execution 
proceeds to a step S108. At this step, the ignition timing (ignition 
angle) .theta.IG is calculated directly or by the calculation from the 
ignition timing map MP.sub.IG for the load data Tp and the engine speed N 
as parameters, respectively. A corrective operation 
(.theta.IG.rarw..theta.IG+X) is applied to the ignition timing .theta.IG 
thus calculated by using the ignition timing correction quantity X based 
on the coolant temperature Tw calculated at the step S101. 
Then, at a step S109, the ignition time TIG suitable for a current 
operating state is calculated from the angular velocity .omega. calculated 
in dependency on the output signal from the crank angle sensor 23 and the 
ignition timing .theta.IG calculated at the step S108 
(TIG=.theta.IG/.omega.). At a step S110, the ignition time TIG calculated 
at the step S109 is set at the timer 46. Counting is initiated by using 
the signal G indicating the reference crank angle as the trigger signal. 
When the count value reaches the ignition time TIG, the ignition signal 
SPK is output. The current flowing in the primary winding of the ignition 
coil is cut off through the ignition drive means 47 to spark the ignition 
plug 15 of the corresponding cylinder through the distributor 32 (step 
S112). The program execution per cycle is thus completed and returns to 
the step S101. 
As described above, the time at which switching from the fixed ignition 
timing immediately after complete firing to an ordinary ignition timing 
control is carried out is adjustably set in dependency on the coolant 
temperature Tw at the time of complete firing. Accordingly, at the low 
temperature, there is no possibility that switching from the unstable 
combustion state to the ordinary ignition timing control is suddenly 
conducted, thus making it possible to effectively prevent an engine stall, 
etc. Further, at the high temperature, switching to an ordinary ignition 
timing control can be conducted immediately after complete firing, leading 
to elimination of slow or insufficient operation. Consequently, the 
start-up of the engine is smoothly conducted, resulting in improved 
starting performance. 
It is to be noted that while the engine temperature including the coolant 
temperature is sensed by a thermosensor secured at the cylinder block, it 
may be sensed directly by a temperature sensor within the cylinder. 
Further, while the complete firing state is determined by the engine speed, 
it may be determined under the condition where the key switch is switched 
from ON to OFF, and another condition may be added thereto. 
Furthermore, the delay time after complete firing may be set by counting 
the number of ignitions (five, ten, fifteen, and twenty times, etc.) set 
in dependency on the coolant temperature Tw as shown in FIG. 8 after 
complete firing. 
It is further to be noted that while the fundamental fuel injection 
quantity Tp is used as load data in this embodiment, an intake pipe 
pressure or a throttle opening degree may be used as load data in place of 
such a fundamental fuel injection quantity. 
Accordingly, even in an ignition timing control having the time control 
system, timing for switching from the fixed ignition timing to the 
ordinary ignition timing control side may be adjustably set in dependency 
on the engine temperature. Thus, the ignition timing control system can 
advantageously not only provide a satisfactory starting performance, but 
also smoothly increase the engine speed after the complete firing. 
While the presently preferred embodiments of the present invention have 
been shown and described, it is to be understood that these disclosures 
are for the purpose of illustration and that various changes and 
modification may be made without departing from the scope of the invention 
as set forth in the appended claims.