Ignition apparatus for internal combustion engine

An ignition apparatus for an internal combustion engine includes means for generating signals indicating when the crankshaft and camshaft of the engine have respectively reached predetermined angular positions, a command circuit for initiating and terminating ignition operation in response to these position signals, and means for establishing a first operating condition, following each camshaft position pulse, in which the ignition operation is enabled and a second operating condition, following a subsequent crankshaft position pulse, in which ignition operation is inhibited, to thereby eliminate redundant ignition operation and the attendant power loss and heat generation. The apparatus also includes a timer circuit which act to enable resetting to the second operating condition by the crankshaft position pulses only during a fixed time interval following each cam shaft position pulse, in order to ensure stable operation when operating at very low engine speeds.

BACKGROUND OF THE INVENTION 
The present invention relates to an improved ignition apparatus for an 
internal combustion engine, of the type which does not employ a 
distributor. Various forms of ignition apparatus which do not incorporate 
a distributor are known in the prior art, e.g. as described in Japanese 
patents 58-19853 and 58-57631. Generally, to achieve a high degree of 
accuracy of ignition timing control with such prior art types of ignition 
apparatus, ignition signal pulses are generated by detecting when the 
crankshaft of the engine has reached specific angles of rotation, with 
this detection being performed by utilizing a pulse generating transducer 
(referred to in the following specification and claims by the term 
"pulser") having a rotor which is fixedly mounted directly on the 
crankshaft. Thus, for each cylinder of the engine, an ignition signal 
pulse will be generated once in each revolution of the crankshaft, with an 
ignition spark being thereby generated. As a result, for each desired 
ignition spark which is generated, one redundant ignition spark will be 
produced, i.e. occurring each time the piston is in the region of the top 
dead center position following an exhaust stroke. The generation of these 
redundant ignition sparks results in an increased level of power 
dissipation in the ignition coil, and increased heat dissipation by the 
coil. This is especially true when a "high energy" type of ignition coil 
is utilized. It therefore becomes necessary to use a larger size of 
ignition coil, in order to ensure that the rate of heat dissipation from 
the coil will be sufficient. This prevents the overall ignition system 
from being made lightweight and compact. 
SUMMARY OF THE INVENTION 
It is an objective of the present invention to provide an ignition 
apparatus for an internal combustion engine which will eliminate the 
disadvantage of prior art types of ignition apparatus which do not employ 
a distributor, i.e. the generation of redundant ignition sparks as 
described above, and in particular an ignition apparatus which will 
provide completely stable operation even when the crankshaft of the 
internal combustion engine is rotating at very low speed, such as at a 
time immediately following starting of the engine. In order to achieve 
this objective, such an apparatus basically comprises crankshaft position 
pulse generating means for detecting when the crankshaft of the internal 
combustion engine has rotated to a predetermined angular position and for 
generating corresponding crankshaft position pulses, camshaft position 
pulse generating means for detecting when the camshaft of the engine has 
rotated to a predetermined angular position and for generating 
corresponding camshaft position pulses, command signal generating means 
coupled to receive the crankshaft position pulses, for generating ignition 
command signals in response thereto, and an ignition circuit for passing a 
current through an ignition coil and interrupting this current to produce 
a high ignition voltage at timings determined by the ignition command 
signals. 
The apparatus also includes enabling means which are responsive to the 
camshaft position pulses and crankshaft position pulses for being set at 
appropriate timings to a first operating state in which operation of the 
ignition circuit in response to the ignition command signals is enabled, 
and a second operating state in which such ignition circuit operation is 
inhibited. The enabling means include timer means whereby setting to the 
latter sound operating state in response to the crankshaft position pulses 
is only enabled during periodic time intervals of fixed duration. 
More specifically, the enabling means comprise an enabling signal 
generating circuit for selectively inhibiting and enabling operation of 
the ignition circuit in response to the crankshaft position pulses and the 
camshaft position pulses. The enabling signal generating circuit is set to 
the first operating conditions in response to each camshaft position 
pulse, whereby the ignition circuit is enabled to generate high ignition 
voltages. When the succeeding crankshaft position pulse occurs, following 
an interval which is referred to in the specification as a first enabling 
interval, the enabling signal generating circuit is set in the second 
operating condition, in which generation of high ignition voltages by the 
ignition circuit is inhibited. This condition continues until the next 
first enabling interval begins. 
The apparatus also comprises a timer control circuit for controlling the 
transfer of the crankshaft position pulses to the enabling signal 
generating circuit, i.e. to selectively inhibit or enable the resetting of 
the enabling signal generating circuit by these pulses to the second 
operating condition mentioned above. The timer control circuit enables 
transfer of the crankshaft position pulses to the enabling signal 
generating circuit only during a time interval of fixed duration following 
each of the crankshaft position pulses, referred to in the specification 
as a second enabling interval.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, a circuit diagram is shown of an embodiment of 
an ignition apparatus according to the present invention. For simplicity 
of description, an ignition apparatus for a single-cylinder internal 
combustion engine (not shown in the drawings) is described. FIG. 2(a) to 
2(f) are waveform diagrams for illustrating the operation of the circuit 
of FIG. 1. Numeral 1 denotes the cam shaft of the internal combustion 
engine, having a cam shaft sprocket 5 fixedly mounted thereon. The cam 
shaft 1 is driven at 1/2 the speed of rotation of the crankshaft 12 of the 
internal combustion engine, by a sprocket chain 4 which couples the 
camshaft sprocket 5 to a crankshaft sprocket 6 mounted on crankshaft 12. 
Numeral 2 denotes a pulser rotor of a camshaft pulser 3, while numeral 7 
denotes a pulser rotor of a crankshaft pulser 8, with pulser rotors 2 and 
7 being fixedly mounted directly on camshaft 1 and crankshaft 12 
respectively. The camshaft pulser 3 thereby generates camshaft position 
pulses in correspondence with angular positions of camshaft 1, and 
crankshaft pulser 8 similarly produces crankshaft position pulses in 
correspondence with angular positions of crankshaft 12. In the present 
embodiment, crankshaft pulser 8 produces a pair of pulses of mutually 
opposite polarity when the crankshaft reaches an initial ignition position 
and a position close to the maximum angle of advance, respectively. 
Numerals 9 and 10 denote waveform shaping circuits which perform waveform 
shaping and amplification of the pulses output from pulsers 3 and 8 
respectively. In addition, waveform shaping circuit 10 performs separation 
of "initial ignition position" pulses and "maximum angle of advance 
position" pulses from the pairs of pulses referred to above, and outputs 
these two trains of pulses on respectively different output signal lines, 
designated as 10a and 10b, which are coupled to inputs of an electronic 
advancement control circuit 11, which constitutes a command signal 
generating circuit for generating ignition command signals to control the 
initiation and termination of current flow in the ignition coil in order 
to execute each ignition operation and generate a high ignition voltage. 
The configuration and operation of electronic advancement control circuit 
11 can be similar to examples of such circuits which are well known in the 
art, e.g. as described in Japanese patents Nos. 58-19853 and 58-57631, and 
so no description of this circuit will be given herein. Control circuit 11 
is responsive to the "initial ignition position" and "maximum angle of 
advance position" pulse signals referred to above for producing an output 
signal which controls the initiation and termination of current flow in 
the primary of an ignition coil, as described hereinafter, to produce 
ignition. 
Numeral 12 denotes a vehicle battery which constitutes the power source for 
the ignition apparathus. The voltage of battery 12 is transferred through 
an ignition key switch 13 to a voltage stabilizer circuit 14 which 
supplies stabilized voltages to the circuits. 
Numeral 24 denotes an "engine start reset" circuit which produces an output 
signal, when the starter switch of the engine is actuated, that is 
transferred through an OR gate 25 to a reset input of a flip-flop 26, to 
thereby determine an initial status of flip-flop 26 as described 
hereinafter. The cam shaft position pulses which are output from camshaft 
pulser 3 as described hereinabove are applied to a set input of flip-flop 
26. 
The "initial ignition position" pulses from waveform shaping circuit 10 are 
also applied through OR gate 25 to the reset input of flip-flop 26. An 
output signal thereby produced from flip-flop 26 is inverted by an 
inverter 27, with the inverted signal being transferred through a diode 29 
to be combined with the output signal from angle of advance control 
circuit 11, which is transferred through diode 28. The combined signals 
thus produced are applied to the base of a driver transistor 31 which 
drives a power transistor 34. In the following, a time interval during 
which flip-flop 26 is in the set state, so that a high (positive) logic 
level output is produced therefrom, will be referred to as a first 
enabling interval. A resistor 30 serves to stabilize the current flow into 
the base of driver transistor 31, while resistors 32 and 33 serve to 
supply base current to transistor 34. The primary of an ignition coil 35 
is connected between the collector of transistor 34 and the output from 
key switch 13, while the secondary of ignition coil 35 is connected to a 
spark plug 36. 
During a first enabling interval, in which a high (positive) level output 
is produced from inverter 27 as illustrated in FIG. 2(c), driver 
transistor 31 is held in a saturated operating state, so that transistor 
34 will be held in the off state, and no current can flow through 
transistor 34 to produce ignition even if an output pulse is produced by 
control circuit 11. Thus, generation of ignition voltage by the ignition 
coil 35 can only occur during each first enabling interval. When the 
internal combustion engine is started, the speed of rotation of crankshaft 
12 will be reduced during each compression stroke, and the level of peak 
pulse output from pulser 8 will be accordingly decreased. Thus, the 
resultant level of pulses output from waveform shaping circuit 10 may not 
be sufficiently high for proper operation of the circuit. This condition 
may result in redundant ignition operation taking place during an exhaust 
stroke of the engine. In order to prevent such an occurrrence during 
low-speed rotation of the engine, a second enabling signal generating 
circuit 15 is provided, which operates on the basis of elapsed time. 
In circuit 15, a transistor 18 together with resistors 16 and 17 constitute 
a discharge circuit for discharging a capacitor 19 in response to each 
output pulse from waveform shaping circuit 9 of camshaft pulser 3. 
Charging of capacitor 19 takes place through a resistor 20, so that a 
sawtooth waveform appears across capacitor 19, which is applied to the 
inverting input of a comparator 23. A voltage detection threshold level is 
established at the junction of two resistors 21 and 22, which is applied 
to the non-inverting input of comparator 23. Comparator 23 is selected to 
be of a type whereby the output terminal of the comparator is held in an 
effectively open-circuit condition so long as the potential applied to the 
non-inverting input of the comparator is lower than that applied to the 
inverting input, and whereby the comparator output terminal is 
short-circuited to ground potential (which in this embodiment corresponds 
to the low logic level potential) when the potential of the non-inverting 
input becomes higher than that of the inverting input. It can thus be 
understood that after each camshaft position pulse is input to circuit 15 
from waveform shaping circuit 9, output line 10b of waveform shaping 
circuit 10 will be connected to ground potential (thereby inhibiting input 
of the "initial ignition position" pulse signal to the reset terminal of 
flip-flop 26 through OR gate 25) and will remain in that condition until a 
fixed time interval has elapsed, i.e. until the voltage on capacitor 19 
rises to the threshold level. In this way, ignition operation is enabled 
only during a fixed time interval following each output pulse from 
camshaft pulser 3. Such a fixed time interval will be referred to in the 
following as a second enabling interval. 
The operation of the circuit of FIG. 1 will now be described in greater 
detail, referring to the waveform diagrams of FIG. 2(a) to 2(d). FIG. 2(a) 
shows the crankshaft position pulses produced by crankshaft pulser 8. The 
positive-going pulses of this signal correspond to the initial ignition 
positions, while the negative-going pulses correspond to the positions of 
maximum angle of advance. FIG. 2(b) shows the output pulses from camshaft 
pulser 3, with each of these pulses being produced during an intake stroke 
of the internal combustion engine. The point at which each of these pulses 
is generated must be between a position which is prior to that at which 
conduction by transistor 34 must be initiated to begin an ignition 
operation when the engine is operating at a high speed of rotation and 
subsequent to that at which the immediately preceding initial ignition 
position pulse is produced by crankshaft pulser 8. FIG. 2(c) shows the 
output signal from flip-flop 26. This signal can only be set at the high 
logic level (i.e. to establish a first enabling interval) during a second 
enabling interval, which is determined by circuit 15 as described 
hereinabove, that is to say while the output of comparator 23 is in the 
open-circuit, i.e. floating, state which is maintained for a fixed time 
interval following each output pulse from the camshaft pulser 3. 
FIG. 2(f) shows the flow of current in the primary of ignition coil 36, 
which is initiated and terminated by an output signal from advancement 
control circuit 11, i.e. a low-logic level state of the output from 
control circuit 11 during which drive transistor 31 is set in the 
open-circuit state so that output transistor 34 is set in the on, i.e. 
conducting, state. It will be apparent that this can only occur during an 
interval in which the output from flip-flop 26 is at the high logic level, 
i.e. during a first enabling interval which occurs within a second 
enabling interval. Such a condition can only occur at an appropriate 
timing for ignition to be initiated, i.e. during a compression stroke of 
the engine. 
If the speed of rotation of the engine is so low that the level of an 
output pulse from crankshaft pulser 8 is insufficient to cause reset of 
flip-flop 26 after this has been set by the preceding camshaft pulser 
output pulse, flip-flop 26 will remain in the set state (with a high logic 
level output being produced thereby) until the next output pulse from 
crankshaft pulser 8 occurs which is of sufficiently high level to cause 
reset of flip-flop 26. However in such a case, any redundant output 
signals produced by control circuit 11 in response to a camshaft pulser 
output pulse will not result in an ignition operation being initiated, 
since at such a time, comparator 23 will function as described to inhibit 
transfer of a reset pulse from waveform shaping circuit 10 to flip-flop 
26, i.e. such a redundant output signal would not be produced during a 
second enabling interval. Thus no redundant ignition current flow will 
take place in output transistor 34 (i.e. during an exhaust stroke) in such 
a case. This will be true even if the engine starter switch is momentarily 
actuated and and then released, so that the engine speed attains a very 
low value. 
From the above description it can be understood that a ignition apparatus 
according to the present invention provides very stable operation, with 
freedom from unnecessary power dissipation and resultant heating of the 
ignition coil due to generation of spurious ignition sparks during exhaust 
strokes, even when the engine is rotating at low speed, and during the 
time immediately after starting of the engine has been executed. It can 
also be understood that such a ignition apparatus can have a very simple 
configuration. 
It will be apparent that various other specific circuit arrangements could 
be utilized to perform the functions of an ignition apparatus according to 
the present invention as described above. Thus, although the present 
invention has been described in the above with reference to a specific 
embodiment, various changes and modifications to the embodiment may be 
envisaged, which fall within the scope claimed for the invention as set 
out in the appended claims. The above specification should therefore be 
interpreted in a descriptive and not in a limiting sense.