Angular position prediction for engine ignition control

An engine ignition control system includes a device adapted to receive the ignition timing signal which is generated by the engine original ignition pulse generator. The device derives a pulse sequence synchronous with the rotation of the engine from the original ignition timing signal. The device then generates a precision ignition signal from the synchronous sequence pulse at the optimum ignition angle. The precision ignition signal is supplied back to the original ignition system of the engine for the generation of the ignition sparks. The synchronous pulse sequence represents the angular position of the rotation of the engine in higher accuracy then the original ignition timing signal. In preferred embodiments, the synchronous pulse sequence represents the angular position of the engine up to 1 degree making high accuracy ignition advance control for most old engines that can produce only the ignition timing signal from its original ignition pulse generator possible.

FIELD OF THE INVENTION 
The present invention relates to an engine ignition control system and more 
specifically to an engine ignition control system which predicts the 
engine angular position for optimum ignition basing on the original 
ignition timing signal. 
BACKGROUND OF THE INVENTION 
A spark-ignition internal combustion engine is powered by the ignition of 
combustion mixture which develops pressure to pistons driving the crank 
shaft. The power delivered to the piston will be maximum if it is driven 
at the time when the piston is positioned at the top dead center. Ignition 
of fuel in the combustion chamber occurs when a spark is generated across 
the spark plug at a specific time controlled by the ignition system. Since 
the pressure of the combustion need some times to develop after the 
ignition. To maximize the power, the ignition should occur before the 
piston reaching the top dead center. 
The ignition control system is responsible for the generation of ignition; 
the determination of the exact timing for the ignition and the management 
required for the related devices such that they can work efficiently. 
There are two common ignition generation methods. 
The first type of the ignition generation system is the contact-breaker 
system in which timing pulses are generated by a contact-breaker 
mechanically coupled to the crank shaft of the engine, normally the 
contact is closed to allow current to flow through the ignition coil. 
Reaching the right time for ignition, the contact is broken, magnetic 
field in the coil collapses suddenly, a high voltage needed for the 
ignition is induced in the secondary winding of the ignition coil. Some 
systems employ beaker-less electronic devices to substitute for the 
contacts which may wear out, these electronic devices include magnetic 
induction; hall effect; optical pickup devices which practically have no 
wear out. The problem of this type of ignition system being extra measures 
has to be taken to handle the dwell angle since current has to remain 
flowing through the ignition coil in order to maintain the magnetic field. 
Dwell angle control is employed to determine the optimum time when to 
switch on the current before the next ignition otherwise the power 
dissipation of the ignition coil is accountable. 
The second type of the ignition generation system is the capacitor 
discharge system in which the spark for ignition are generated by the 
rapid discharge of a charged capacitor through the ignition coil. The 
advantage of such system being, no power dissipation after the capacitor 
is fully charged because the charging current ceases, and the energy 
stored in a capacitor is the energy for sparking. It remains relatively 
constant until it reaches the high engine speed, at which the charging 
time for the capacitor is not enough. 
Such ignition systems described above offer only the high energy sparks for 
ignition, the time at which such sparks should occur has to be precisely 
controlled in order to achieve high engine efficiency. Assuming that the 
time required for the pressure of the ignited mixture to develop is 
constant, the higher the engine speed, the position of the piston should 
be further away before reaching the top dead center. This position is 
normally interpreted as angular position and is commonly called the 
ignition advance angle or simply ignition advance. 
Actually, many factors affect the time required for the combustion to 
deliver its maximum power, and the ignition advance should change 
according to the rotational speed of the engine, normally the ignition 
advance increases with a steeper slope at the lower speed and gradually 
become less steep at the higher speed. 
Motor cars are spacious enough to handle such advance mechanically, they 
have the centrifugal ignition advance control to compensate for speed 
changes and the vacuum ignition advance control to compensate for air fuel 
ratio. However, those devices are either not accuracy enough or they 
cannot respond to rapid changes at which states the fuel wastage are 
obvious. 
Most of the motorcycle ignition advance are fixed values, for example 18 
degrees before top dead center BTDC at idle speed and remains unchanged 
though out the operating range. This simple fact indicates that most of 
the motorcycle are not working in the optimum performance. 
Ignition advance control is to compensate the time required for the 
ignition of fuel to reach its maximum pressure; dwell angle is to control 
the time before supplying current to the ignition coil so that the power 
dissipation in the coil is minimized. Both are functions of time. In the 
traditional engines, time T can only be represented by an angle D (degree) 
while the engine is running at the rotational speed R.P.M.(revolution per 
minute) 
EQU D=[T.times.R.P.M..times.360/60] 
for example if the time required for the combustion pressure to develop is 
4 milliseconds, then at 1000 R.P.M., by advancing the ignition by 4 
milliseconds means the ignition should occur while the crank shaft is 
positioned at 24 degrees before reaching the top dead center. Ignition 
advance angle and dwell angle should be defined together with the R.P.M. 
the engine is running at. These values are commonly represented by curves 
with ignition advance angle and dwell angle vs. The engine rotational 
speed. 
If there exist a set of optimum ignition advance angles for various 
operation conditions represented as curves, then if the ignition system is 
triggered at the angle as indicated in the curves, the ignition of the 
engine are said to be optimized. Practically curves for various operation 
conditions such as temperature, humidity, octane value, etc. can be 
obtained from tables stored in read only memory device, or they can be 
determined by computing devices which connect directly to sensors tracing 
the related physical quantities. An angular position reference precise 
enough to indicate the angle for the ignition is needed. 
For every ignition coil, there exist a best charging time for the magnet 
field at different supply voltage. If these values are transformed to 
angle C at different engine rotational speeds, thus by storing 
P=90.degree.-C (4 cylinders) or P=60.degree.-C (6 cylinders) in the read 
only memory device, by converting the analog values of the supply voltage 
to digital values, then by looking up tables that contain the values for 
the angle P for different supply voltages and engine rotational speeds, 
Dwell angle can be controlled if a precise enough angular position 
reference is available. 
Improving the efficiency of engines is the modern trend, it helps to 
preserve energy and to protect the environment. Other than changing the 
compression ratio; adding valves etc. mechanically, modern engine design 
uses two major approaches to achieve engine improvement. 
Firstly, high precision ignition control is employed. The modern ignition 
control system requires that the accuracy of such reference to within 1 
degree. The control unit can that compute or lookup tables to determine 
the optimum ignition angle. 
Secondly, high precision fuel control is employed. The best fuel to air 
ratio; injection, etc., are controlled by the computer according to the 
operating conditions. 
Both measures required entirely new devices. Commonly, the ignition timing 
signal is not coming from the distributor but a new crank shaft position 
detector; the fuel is not supplying from the carburetor but the fuel 
injection devices. These new measures are not for traditional engine which 
can only be working inefficiently, polluting the environment until they 
extinct. 
An object of the invention is therefore to provide an angular position 
prediction device which derives a pulse sequence synchronous with the 
rotation of the engine from the original ignition timing signal such that 
optimum ignition for any engine is possible. 
SUMMARY OF THE INVENTION 
The invention provides an ignition control system for internal combustion 
engine including an ignition control device adapted to receive the 
ignition timing signal which is generated by the engine original ignition 
pulse generator, wherein the engine rotation angular position predictor in 
the said device derives a pulse sequence synchronous with the rotation of 
the said engine from the said original ignition timing signal, the said 
device then generates a precision ignition signal from the said 
synchronous sequence pulse at the optimum ignition angle, the said 
ignition signal is supplied back to the said original ignition system of 
the said engine for the generation of the ignition sparks, and the said 
optimum ignition angle may either be stored in memory devices or be 
determined by computing device which connects to sensors which traces the 
related physical quantities. 
The said engine rotation angular position predictor is a computation system 
which calculates and predicts the angular position of the said engine 
basing on the said original ignition timing signal containing 
instantaneous engine position, angular speed and acceleration information. 
The said computation system may includes analog or digital system which 
employs computing algorithms that can calculate, predict and perform error 
correcting such that a high precision synchronous pulse sequence 
representing the angular position of the rotation of the said engine can 
be generated. 
The said synchronous pulse sequence is a sequence that each pulse 
represents the said engine rotation angular position predictor resolution 
M, if the said engine rotation angular position predictor resolution is 2 
degrees, thus each said pulse corresponds to the rotation of the said 
engine by 2 degrees. By Counting the number of said pulse elapsed from a 
reference point of know angular position, the angle position of the engine 
can be determined. The said reference point of know angular position may 
be the original ignition pulse which occur at the original known angle, 
however any other suitable means of obtaining reference point of know 
angular position may be used. 
The ignition control system may be suitable for adapting existing ignition 
system electronic ignition or conventional ignition. The ignition control 
system is placed between the original ignition pulse generator and the 
ignition system, such timing pulse generator includes contact-breaker, 
magnetic induction pickup, hall effect, optical pickup. Such ignition 
system includes capacitor discharge ignition system, contact breaker 
system and engine management system. 
The ignition control system may have multiple ignition advance curves 
stored as tables in the device, these curves may include economical curve 
that ignition advance are set for most economical combustion; curve for 
high engine speed in which ignition advance are set for faster pick up and 
efficiency at high speed; high pay load curve in which ignition advance 
are optimized for high power. In some embodiments, more curves can be 
stored; curve value can be tailor-made to individual engine. 
The ignition control system may have manual or automatic curves selection. 
In some embodiments, curves can be selected anytime by manual switches or 
automatically by the device computation algorithm. 
The ignition control system may have a computing device which can determine 
the optimum ignition angle directly from the data obtained by the sensors 
tracing the related physical quantities. 
The ignition control system may have a switch to provide angular offset to 
the produced precision ignition signal such that it is shifted in advance 
or retard from the original ignition timing signal to compensate the 
mechanical error in the idle ignition advance setting which otherwise can 
only be adjusted mechanically. 
The ignition control system may have a maximum engine speed setting which 
limits the engine from running at the speed higher that the setting. 
The ignition control system may have a handset which transmits a device 
identification code. On comparison of the code with the stored value, the 
generated precision ignition signal can be disabled if the codes do not 
match. 
The ignition control system may be installed in a detachable unit, by 
removing the unit from the housing, the ignition may either be disabled or 
switched back to its uncontrolled operation. 
The operation of the ignition control system may be overridden by an 
external interface which may include parallel, serial or wireless links to 
control the operation of the device such as monitoring the engine speed, 
curve selected and the engine instantaneous advance, overriding the 
advance directly or changing the curve contents. 
The said external interface may be connected to an external control unit or 
a computer system which provides the management function.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the first embodiment, a block diagram of the connection of the 
ignition control system and the motorcycle employing the present 
invention. The original ignition pulse which is generated by a magneto 101 
coupling directly to the crank shaft of the engine is connected to the 
ignition control device 103, the produced precision ignition signal is fed 
to the original capacitor discharge ignition system 102 which drives the 
ignition coil 104 to generate the sparks. 
The original ignition pulse is generated by a magneto 101, however it may 
be generated by any device which generates pulse whose position and 
frequency are fixed in relation to the position and speed of the rotation 
of the engine. 
The original capacitor discharge ignition system 102 generated the 
high-voltage for ignition after receiving the precision ignition pulse, 
however any suitable device that can generate the high-voltage for 
ignition after receiving the precision ignition pulse may be used. 
FIG. 2 shows a block diagram of the motorcycle after employing the present 
invention. 
The original ignition timing signal which is generated by the magneto is 
conditioned by the pulse shaper 201, it is then used by the engine 
rotation angular position predictor 202 to derive a synchronous pulse 
sequence 203 which represents the angular position of the rotation of the 
engine. 
In this embodiment, the reference point of know angular position is the 
original ignition pulse which occurs at every half cycle 180.degree. of 
the engine rotation. However the absolute TDC position has to be offset 
since the pulse is fixed at a certain angle F before top dead center BTDC. 
Therefore the TDC can be determined by F/M number of synchronous pulses 
elapsed before reaching the reference point of know angular position where 
M is the resolution of the angular position predictor and F is the angle 
offset of the reference point of know angle position from the TDC. 
Consequently, if the optimum ignition angle is N degrees BTDC, then the 
number of synchronous pulses before reaching the reference position of 
know angular position can be determined by (N-F)/M. where M is the 
resolution of the angular position predictor, F is the angle offset of the 
reference point of know angular position from the BTDC and N is the 
optimum ignition angle. 
The idle ignition advance adjustment switch 207 provides a means to 
calibrate the idle advance without actually adjusting it mechanically. 
This setting can also be used to compensate for different octane value; 
change of spark plus type, etc. By converting the value of the adjustment 
switch to number of synchronous pulse W, then by advancing or retarding 
the precision ignition pulse by W pulses effectively adjusts the angle 
according to the switch setting. 
FIG. 5 shows the optimum ignition advance curve for a typical 4 strokes 
motorcycle engine. 
The curves for different operation conditions are stored in the EEPROM 208. 
Three curves are stored in this embodiment, the economical curve provides 
the most energy saving and less polluted ignition advance timing; the high 
speed curve provides best pick up and high engine speed ignition advance 
timing; the high payload curve provides ignition advance timing for high 
fuel to air ratio combustion. These curves can be selected by the curve 
selection switch setting 206 anytime even while the engine is running. 
The external interface 205 provides a mean to monitor the performance of 
the engine, to control the system via the external device attached and to 
set the curve data stored in the memory. The external device 211 connected 
to the external interface 205 may be computer running software for the 
monitoring, controlling and setting of the curves, or it may be any 
external device providing these functions partially or completely. 
The maximum speed limit can be set by an external device 211 to protect the 
engine from running out of its safety working range. The device 
identification code can also be set by the external device 211 to enforce 
the security. Once the speed limit is set, the precision ignition pulse 
generator 204 will cease to operate if the engine speed reaches the limit 
or the precision ignition signal generator 204 will generates the ignition 
pulse according to all settings. The generated precision ignition pulse is 
then fed to the ignition pulse driver 210 to trigger the original 
capacitor discharge ignition system that produce the sparks. 
A block diagram show a motorcar employing the present invention according 
to a second embodiment is shown in FIG. 3. As in the first embodiment, the 
original ignition timing signal which is generated by the magnetic pickup 
device in the distributor 301 is connected to the ignition control device 
303, the produced precision ignition signal is fed to the ignition coil 
302 of original electronic ignition system, the generated high voltage is 
distributed in turn to sparks plugs through the distributor 304 to 
generate the sparks. 
FIG. 4 shows the functions of the motorcar after employing the present 
invention. All functions as in the first embodiment are provided, together 
with the following features. 
As in the first embodiment, the original ignition timing signal from the 
pulse generator in the distributor is conditioned by the pulse shaper 401, 
it is used by the engine rotation angular position predictor 402 to derive 
a synchronous pulse sequence 403 which represents the angular position of 
the rotation of the engine. 
The dwell angle controller 413 provides the control by looking up table in 
the EEPROM 409. The supply voltage value is measured by the Analog to 
Digital converter 412, the digital voltage value and the engine speed is 
used to address the equivalent dwell angle P in the table stored in the 
EEPROM 409. Current is allowed to flow through the ignition coil P degrees 
after each ignition, using the synchronous pulse sequence as the angular 
position reference. By providing the dwell angle control, the ignition 
coil works more efficiently through out the operating range. 
The original centrifugal advance device are disabled to allow the device to 
provide ignition advance electronically. If the vacuum advance gain is 
accurate then only the economical curve is used as the fundamental, 
otherwise, the vacuum advance is disabled, more curves are stored for 
better control and the curve selection is done by computing algorithm. 
Other embodiments and variations within the spirit and scope of the 
invention are anticipated.