Ignition control system for marine engine

The present invention is an ignition control system for an engine having at least one combustion chamber and an ignition element for initiating combustion in the chamber. As one aspect of the ignition control, a switching circuit is provided for controlling the firing of the ignition element based upon either a signal received from a mechanism which detects and outputs a first firing timing signal or a computing mechanism which outputs a second firing timing signal based upon the first firing timing signal. As a second aspect of the ignition control, ignition elements are paired and fired together. In this arrangement, the ignition control includes a mechanism for counting outputted firing signals and assigning them values. These values are used to control the firing of the pairs of ignition elements, permitting the pairs of elements to be fired such that combustion initiation in individual combustion chambers corresponding is controllable.

FIELD OF THE INVENTION
 The present invention is an ignition control system for a marine engine.
 BACKGROUND OF THE INVENTION
 Watercraft powered by inboard or outboard motors typically include an
 electrical system. The motor includes a water propulsion device which is
 powered by an internal combustion engine. As is well known, an ignition
 system is utilized to fire one or more ignition elements corresponding to
 each combustion chamber of the engine, igniting the air and fuel mixture
 in each combustion chamber of the engine.
 It is very desirable to keep the engines used in these applications small
 and simple. To achieve this goal, use of a complex ignition system in
 which each ignition element is fired and controlled independently may be
 avoided. In particular, where the engine is of the four-cycle variety, a
 simple ignition system in which the ignition elements are paired is often
 used.
 In a four-cycle engine, pairs of cylinders are generally arranged so that
 their pistons are in the same position but out of phase in the operating
 cycle. In other words, when the pistons corresponding to one pair of
 cylinders are both at top dead center, one cylinder is in the combustion
 portion of the cycle, while the other cylinder is in the exhaust portion
 of the cycle.
 In the above-described arrangement where the ignition elements are paired,
 the ignition elements corresponding to a pair of cylinders are fired at
 the same time. To accomplish ignition in both cylinders, both ignition
 elements are fired every half-cycle. This arrangement permits the use of a
 single coil for both ignition elements, and eliminates the requirement
 that a separate firing timing signal be calculated and provided for the
 ignition element associated with each cylinder.
 In some situations, it is desirable to disable one or more of the cylinders
 of an engine without completely shutting down the engine. For example, it
 may be desirable to disable one or more cylinders to prevent excessive
 engine speed or reduce engine temperature.
 The above-stated ignition system, while being simple, has a drawback
 associated with a cylinder disabling function. Referring to FIG. 12(b),
 when it is desired to disable one cylinder, at least two cylinders must be
 disabled, since the ignition system permits only the turning on and off of
 the ignition signal associated with the pair of ignition element
 associated with two cylinders. In addition, if it is desirable to disable
 more than two cylinders, then four cylinders must be disabled. In the
 event the engine is of the four cylinder variety, the engine is shut down
 in this instance.
 In either event, the ability of the ignition system to disable cylinders in
 only pairs can be counterproductive in achieving the goals desired by
 disabling cylinders. For example, if a slight reduction in engine speed is
 desired to prevent high engine speed, disabling two cylinders (instead of
 just one) may cause such a drop in power that the engine stalls or the
 like. In that instance where the engine is powering a boat, then the user
 of the boat may be stranded on the water.
 An improved ignition system which overcomes the above-stated problems is
 desired.
 SUMMARY OF THE INVENTION
 The present invention is an ignition control system for an engine having at
 least one combustion chamber and an ignition element for initiating
 combustion in the chamber.
 As one aspect of the ignition control, a switching circuit is provided for
 controlling the firing of the ignition element based upon either a signal
 received from a mechanism which detects and outputs a first firing timing
 signal or a computing mechanism which outputs a second firing timing
 signal based upon the first firing timing signal.
 As a second aspect of the ignition control, ignition elements are paired
 and fired together. In this arrangement, the ignition control includes a
 mechanism for counting outputted firing signals and assigning them values.
 These values are used to control the firing of the pairs of ignition
 elements, permitting the pairs of elements to be fired such that
 combustion initiation in individual combustion chambers corresponding to
 the pair of ignition elements is controllable.
 Further objects, features, and advantages of the present invention over the
 prior art will become apparent from the detailed description of the
 drawings which follows, when considered with the attached figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
 The present invention relates to an ignition system of an engine.
 Preferably, the ignition system is associated with an engine used in a
 marine application, such as for powering an outboard motor. The invention
 comprises an ignition system control for such an ignition. Those of skill
 in the art will appreciate that the ignition system of the present
 invention may be used with engines adapted for use in other applications.
 Referring to FIG. 1, there is illustrated a watercraft 20. The watercraft
 20 illustrated is a power boat, may comprise any number of other types of
 crafts. The watercraft 20 has a hull 22 with a transom portion 24 to which
 is mounted an outboard motor 26. The outboard motor 26 is utilized to
 propel the watercraft 20. As known to those skilled in the art, the motor
 26 may also be of the inboard type.
 When of the outboard variety, the motor 26 is connected to the watercraft
 20 in a manner which allows it to pivot up and down in a vertical plane
 ("trimming") and rotate left and right in a horizontal plane ("steering")
 in a manner well known to those skilled in the art.
 The watercraft 20 illustrated includes a pair of seats 28. One of the seats
 28 is preferably positioned near a steering wheel 30. The steering wheel
 30 is connected remotely to the outboard motor 26 for effectuating
 movement of the motor left and right for steering the craft. Additionally,
 a throttle control such as a handle 32 is preferably positioned near the
 steering wheel 30 for use in controlling the speed of the watercraft 20 by
 changing the speed of the engine powering the motor 26. Preferably, this
 handle 32 simultaneously serves as a shift control lever for controlling
 the position of a transmission (not shown) associated with the motor 26.
 Such transmissions are well known, and generally permit the motor 26 to
 drive in forward, reverse and neutral states.
 A control panel 34 is preferably provided near the steering wheel 30, the
 control panel 34 having one or more gauges, meters or other displays for
 displaying various information to the user of the watercraft 20. These
 displays may display watercraft speed and the like. A switch panel 36 is
 also provided near the steering wheel 30. The switch panel 36 preferably
 includes one or more switches or controls, such as a main switch 38 and a
 kill switch 39.
 Referring still to FIG. 1, the motor 26 has a water propulsion device, such
 as a propeller (not shown) which is powered by an engine 40. The engine 40
 is preferably mounted within a cowling of the motor 26. The engine 40 may
 be arranged in a variety of configurations, such as in-line, "V" or
 opposed, may operate on a two or four-cycle principle, and be of the
 rotary, reciprocating piston or other type. Preferably, the engine 40 has
 four cylinders (and thus four combustion chambers) each having a piston
 reciprocally mounted therein and attached to a crankshaft and operates on
 a four cycle principle. The engine 40 is oriented within the cowling so
 that the crankshaft is generally vertically extending and in driving
 relation with the water propulsion apparatus of the motor 26.
 The details of the engine 40 are not described herein and are well known to
 those of skill in the art. In general, the engine 40 includes a fuel
 supply system for supplying fuel from a fuel source, such as a fuel tank
 42, to each combustion chamber of the engine 40. The engine 40 also
 includes an induction system for supplying air to each combustion chamber.
 An exhaust system routes exhaust of combustion from the engine 40 to a
 point external to the motor 26.
 The engine 40 includes an ignition system for initiating combustion of the
 air and fuel mixture supplied to each combustion chamber. This ignition
 system includes an ignition element associated with each cylinder of the
 engine. Preferably, and referring to FIG. 2, the ignition elements
 comprise at least one spark plug 44a-d associated with each cylinder
 (spark plug 44a corresponding to a first cylinder, spark plug 44b
 corresponding to a second cylinder, spark plug 44c corresponding to a
 third cylinder, and spark plug 44d corresponding to a fourth cylinder). As
 described in more detail below, a firing mechanism is associated with the
 spark plugs 44a-d for inducing a spark across a gap each spark plug 44a-d
 in order to initiate ignition of the fuel and air mixture within a
 combustion chamber or cylinder. In addition, and in accordance with the
 present invention, an ignition control system is provided for controlling
 the firing mechanism.
 FIG. 2 illustrates an electrical system 46 associated with the watercraft
 20. The electrical system 46 includes an ignition control circuit 48 of
 the ignition control of the present invention. In FIG. 2, area A denotes
 those components of the electrical system 46 which are positioned in the
 hull 22 of the watercraft 20, while area B denotes those components which
 are associated with the motor 26.
 As the motor 26 is detachable from the watercraft 20, various electrical
 connectors 50 are included in the electrical system 46. These connectors
 50 permit separation and reconnection of those components in the two
 portions A and B of the electrical system.
 The electrical system 46 includes a base or primary power supply. This base
 power supply preferably comprises a battery 52. As illustrated in FIG. 1,
 the battery 52 may be conveniently mounted in the watercraft 20.
 The electrical system 46 also includes a secondary power supply. This power
 supply comprises a charging coil 54 associated with the engine 40. For
 example, the coil 54 may be associated with a flywheel mounted on the
 output or crankshaft of the engine 40, or be a separate generator, as is
 known to those of skill in the art. This coil 54 provides an electrical
 output when the engine 40 is running. The output passes through a
 rectifier 56.
 Either the battery 52 or charging coil 54 provides power through an
 ignition power circuit 58 to the ignition control circuit 48.
 As illustrated, power is provided through a watercraft power circuit 58
 when the main switch 38 is closed. A main fuse 62 is provided along a
 circuit connecting the rectified charging coil 54 output and the battery
 52 for preventing excessive current from flowing therethrough. Likewise, a
 similar fuse 64 is provided along the watercraft power circuit 58. During
 engine start-up, and before the charging coil 54 provides power, when the
 main switch 38 is closed, power is provided by the battery 52 through a
 back-up circuit 67. When the coil 54 is charging, power is provided
 therethrough to the ignition control circuit 48.
 As illustrated, power is provided to the various gauges and instruments
 associated with the control panel 34 through the watercraft power circuit
 58.
 The kill switch 39 is associated with a kill circuit 66. This circuit 66
 connects to the ignition control circuit 48 and grounds the system
 (stopping the firing of the spark plugs 44a-d and thus stopping the engine
 40) when closed.
 First and second pulser coils 70,72 are used to generate and output an
 ignition timing signal, as illustrated at the top of FIG. 3. In general,
 each pulser coil 70,72 provides an output signal or spike at a specific
 time, such as when a member mounted on a flywheel of the engine 40 passes
 by a pick-up element.
 In this arrangement, the first pulser coil 70 provides an ignition timing
 signal corresponding to the spark plugs 44a,44d corresponding to the first
 and fourth cylinders, while the second pulser coil 72 provides such a
 signal corresponding to the spark plugs 44b,44c corresponding to the
 second and third cylinders. The output of the pulser coils 70,72 is
 provided to a computer processing unit (CPU) 74 and an ignition switching
 circuit 76 of the ignition control circuit 48 through a respective input
 circuit 78,80.
 Power is provided to the CPU 74 through a non-contact type switch 82
 through an input circuit 84.
 A thermosensor 86 senses engine temperature. The thermosensor 86 may be
 arranged to monitor the engine temperature by measuring the temperature of
 the coolant associated with a cooling system of the engine 40. The output
 of the sensor 86 passes through an input circuit 88 to the CPU 74. As
 described in more detail below, the CPU 74 utilizes the output of this
 sensor 86 in an engine overheat control function.
 An oil pressure switch 90 is also provided. When this switch 90 closes, a
 signal is sent to the CPU 74 through an input circuit 92. At the same
 time, an alarm or lamp 94 is activated. A load or resistance 96 is
 associated with the alarm or lamp circuit, as is well known. The alarm or
 lamp 94 is preferably mounted at or near the control panel 34 of the
 watercraft 20.
 The ignition control circuit 48 includes a watchdog circuit 98. This
 circuit 98 monitors the condition of the CPU 74. As described in more
 detail below in conjunction with FIG. 3, the watchdog circuit 98 is
 arranged to reset the CPU 74 and the switching circuit 76 with an
 appropriate output signal.
 The ignition control circuit 48 also includes a capacitor-discharge
 ignition (CDI) circuit 100. This circuit 100 includes a control 102 which
 is powered and which is arranged to control the charging of a charging
 condenser 104.
 The spark plugs 44a,44d corresponding to the first and fourth cylinders are
 associated with a first ignition coil C1. The spark plugs 44b,44c
 corresponding to the second and third cylinders are associated with a
 second ignition coil C2.
 The first ignition coil C1 is linked through a first circuit to the
 charging condenser 104, and the second ignition coil C2 is lined through a
 similar second circuit. The CDI circuit 100 includes a first thyristor 106
 positioned along the first circuit, and a second thyristor 108 is
 positioned along the second circuit. Both thyristors 106,108 are
 controlled by an output signal from the switching circuit 76. When the
 switching circuit 76 sends an appropriate signal to either of the
 thyristors 106,108, they open and current is allowed to flow from the
 condenser 104 through the first or second circuit to the first or second
 ignition coil C1,C2, at which time a spark is induced at the spark plugs
 corresponding thereto.
 Those of skill in the art will appreciate that in the four-cycle engine,
 each cycle comprises seven-hundred and twenty degrees of crankshaft
 rotation. In one three-hundred and sixty-degree rotation, each piston
 moves from top dead center downwardly to bottom dead center in an
 induction mode, then moves back to top dead center for combustion. In the
 next three-hundred and sixty degree cycle the piston moves downwardly as
 driven by the expanding combustion gasses, and then moves upwardly back to
 top dead center in an exhaust sequence.
 In the engine arranged as described above, the piston corresponding to a
 pair of cylinders (such as the first and fourth cylinders) are generally
 in the same position, but three-hundred and sixty degrees apart in the
 operating cycle. In other words, when the piston corresponding to the
 first cylinder is at top dead center for combustion, the piston
 corresponding to the fourth cylinder is also at top dead center but in the
 exhaust sequence. Likewise, the second and third cylinders are so
 interrelated.
 In the arrangement of the present invention, the spark plugs 44a,44d
 corresponding to the first and fourth cylinders are fired at the same
 time. As described in more detail below, the firing of the spark plug
 corresponding to cylinder which is in the combustion portion of the cycle
 is effective in initiating combustion, while the simultaneous firing of
 the spark plug corresponding to the other cylinder is ineffective since it
 is in exhaust mode. Thus, in each firing of both pairs of spark plugs
 44a/44d and 44b/44c only one of the firings is "effective" or "actual" in
 the sense that it initiates combustion.
 A first aspect of the ignition control of the present invention will be
 described with reference to FIG. 3. Once the engine 40 is started, the
 pulser coils 70,72 provide output signals and the CPU 74 begins
 processing. In the preferred arrangement, the CPU 74 does not begin to
 provide an ignition timing output signal for some time after the engine 40
 has been started. In the arrangement illustrated, this time constitutes
 two measuring cycles. These measuring cycles comprise a time between
 pulses or output spikes from the first and second pulser coils 70 and 72.
 Thereafter, the CPU 74 provides a second or "soft" ignition timing signal
 which is based on, but may vary from, the first signal from the pulser
 coils 70,72. The CPU 74 may alter the first signal based on a variety of
 factors to optimize ignition firing timing.
 During the time before the CPU 74 provides an ignition timing output
 signal, the spark plugs 44a-d are fired based on the output of the pulser
 coils 70,72. In particular, the output of the pulser coils 70,72 is
 provided to the switching circuit 76, which uses the signals directly as
 the ignition signals for the thyristors 106,108. After the CPU 74 begins
 providing an ignition firing signal, the switching circuit 76 is arranged
 to move to a "soft" mode in which it utilizes the ignition timing signal
 from the CPU 74 as the ignition firing timing signal (i.e. the signals
 from the pulser coils 70,72 are used unless the CPU 74 is providing a
 signal).
 This arrangement is advantageous since it provides time for the CPU 74 to
 calculate an accurate firing timing signal considering actual engine
 conditions.
 As also illustrated in this figure, in the event of engine shut-down or
 lack of power or the like, the watchdog circuit 98 is arranged to reset
 the CPU 74. Until the time for the CPU 74 to provide ignition timing
 signals has elapsed, the switching circuit 76 is arranged to utilize the
 hard ignition timing signals from the pulser coils 70,72, as described
 above.
 Additional aspects of the ignition control will be described with reference
 to FIG. 4. As illustrated, the CPU 74 preferably includes an overheat
 detection portion 110, an engine speed computation portion 112, a
 disabling cylinder determining portion 114, and an ignition signal output
 portion 117 which includes an ignition order counter portion 116.
 The output of the thermosensor 86 is provided to the overheat detection
 portion 110. In the event an engine overheat situation is detected, an
 engine overheat protection function is employed by the CPU 74, as
 described in more detail below in conjunction with FIGS. 9 and 10.
 The output of the pulser coils 70,72 is provided to the engine speed
 computation portion 112, which determines the engine speed from the output
 of the pulser coils 70,72. As described in more detail below, the CPU 74
 employs an engine speed reduction or overrev prevention function in the
 event the engine speed exceeds a predetermined speed.
 The output of the pulser coils 70,72 is also provided to the ignition order
 counter portion 116 of the CPU 74. This portion of the CPU 74 is arranged
 to utilize the pulser coil 70,72 signal output to count and assign a count
 value to these signals.
 FIG. 5 is a table which correlates the pulser coil 70,72 outputs to a
 variety of cylinder firing data. When the first pulser coil 70 provides a
 first signal, the ignition order counter 116 gives the signal a value of
 1. In the arrangement where the firing order for the cylinders is arranged
 to be 1, 3, 4, 2, the first signal is assumed to correspond to cylinder 1
 In other words, an imaginary ignited cylinder value of 1 is assigned,
 since it is assumed the first cylinder fired. Since the first pulser coil
 70 corresponds to the spark plugs 44a,44d corresponding to the first or
 fourth spark plugs, the fired cylinders associated with this signal number
 are 1 or 4. In actuality, because only one of those two cylinders is in
 the combustion portion of the cycle (the other being in the exhaust cycle)
 the cylinder in which ignition actually occurs is either cylinder 1 or
 cylinder 4.
 The next signal received by the ignition order counter 116 is from the
 second pulser coil 72. When this signal is received, it is given a value
 of 2. The cylinder which is imagined to have fired is cylinder 3 (i.e. the
 second of the cylinders to fire in the firing order), and the actually
 fired cylinders must be 2 or 3, since the two spark plugs corresponding
 thereto fire together. Since only one of the cylinders is then in the
 combustion cycle, in either only cylinder 2 or 3 does ignition actually
 occur.
 The next signal received by the ignition order counter 116 is from the
 first pulser coil 70. When this signal is received, it is given a value of
 3. The imaginary cylinder firing corresponding to this value is 4, both
 cylinders 1 and 4 are actually fired, but combustion is only initiated in
 either cylinder 1 or 4.
 The next signal received by the ignition order counter 116 is from the
 second pulser coil 70. When this signal is received, it is given a value
 of 4. The imaginary cylinder firing corresponding to this value is 2, the
 actually fired cylinders are 2 or 3, with combustion initiated in only
 cylinder 2 or 3. The data then repeats.
 FIG. 6 is a flowchart illustrating a cylinder disabling function of the CPU
 74 as accomplished with the cylinder disabling portion 114 and counter
 116. Once the engine 40 is started, and in a step S1, the ignition order
 counter 116 begins to function. In a step S2, an input signal is received
 from one of the pulser coils 70,72. In a step S3, the ignition order
 counter 116 assigns the signal an imaginary cylinder count number or
 value, as described above.
 In a step S4, the CPU 74 determines if a disabling signal (as described
 below) has been received. If not, an ignition signal is output from the
 ignition signal output portion 117 of the CPU 74 to the switching circuit
 76 in a step S5. If a disabling signal has been received, the cylinder
 disabling portion 114 of the CPU 74 is arranged to set up an imaginary
 disabled cylinder in a step S6. If in a step S7, if the imaginary disabled
 cylinder matches the imaginary ignited cylinder, then no ignition signal
 is provided and the process repeats. In that event, the lack of an
 ignition signal prevents the firing of a cylinder which is otherwise in
 the combustion portion of the operating cycle. If the imaginary disabled
 cylinder does not match the imaginary ignited cylinder, then an ignition
 signal is output in step 5 and then the process repeats.
 FIG. 7 illustrates a cylinder disabling arrangement employed by the CPU 74.
 The disabling cylinder portion 114 of the CPU 74 is arranged to employ one
 or more disabling patterns for disabling one cylinder of the engine 40. In
 a first pattern, the imaginary disabled cylinder is given a value of one
 and each time the imaginary ignited cylinder value is one, no firing
 signal is sent by the CPU 74 to the switching circuit 76, and the spark
 plugs 44a,44d corresponding to the first and fourth cylinders are not
 fired. This means that either the first or fourth cylinder, which would
 otherwise be set to fire, does not fire. On the other hand, when the
 imaginary ignited cylinder 4 is counted, a firing signal is provided, so
 that either the other of the first or fourth cylinders are actually fired
 each cycle. Of course, a firing signal is provided at both the imaginary
 ignited cylinder values of 2 and 3. In this manner, three of the four
 cylinders are fired each cycle.
 As illustrated by patterns 2-4, a similar arrangement may be employed with
 imaginary disabled cylinder values of 2, 3 or 4, whereby three of the four
 cylinders are fired.
 The cylinder disabling portion 114 is also arranged to disable two of the
 four cylinders. With reference to pattern number 5, the imaginary
 disabling cylinder values are set as both 1 and 4, whereby the CPU 74 does
 not send a firing signal when the imaginary ignited cylinder values are 1
 and 4. In this arrangement, both the first and fourth cylinders are
 prevented from firing, while cylinders 2 and 3 are both fired.
 As illustrated, the CPU 74 may be arranged to prevent the firing of any
 pair of two cylinders in similar fashion. It is generally desirable to
 fire the cylinders in evenly spaced patterns to promote smooth running of
 the engine.
 Though not illustrated, the cylinder disabling portion 114 includes one or
 more patterns for disabling three of the four cylinders in similar fashion
 to that described above. In addition, the cylinder disabling portion 114
 includes a pattern for disabling all cylinders in which no firing signal
 is provided at any time.
 FIG. 12(a) illustrates graphically the cylinder disabling function of the
 ignition control of the present invention. As illustrated, and as
 described above, the ignition control is arranged such that the cylinders
 may be disabled one by one. In this arrangement, even though the spark
 plugs 44a-d corresponding to the cylinders are paired, the ignition
 control permits the effective disabling of each cylinder. The ignition
 control can thus be used to disabled none, one, two, three or all of the
 cylinders. This is in sharp contrast to the arrangement of the prior art
 illustrated in FIG. 12(b) where the cylinders can only be disabled in
 pairs.
 FIG. 8 illustrates an engine speed disabling or overrev protection function
 of the ignition control. As illustrated, in a first step S1, the CPU 74
 determines if the oil pressure switch is on. If so (indicating a lack of
 oil pressure), then the cylinder disabling portion 116 of the CPU 74 is
 arranged to disable all of the cylinders in a step S10. When all of the
 cylinders are prevented from running, the engine 40 stops and the user may
 check the lubricating system.
 If the oil pressure switch is not on, in a step S2 the CPU 74 checks to
 determine if an engine overheat signal is received from the overheat
 detection portion 110. If so, an engine overheat disabling mode associated
 with an engine temperature control function, as described in more detail
 below, is instituted.
 If not, in a step S3, the CPU 74 checks the engine speed as calculated by
 the engine speed computation portion 112. If the engine speed is less than
 a predetermine high engine speed, such as 6000 rpm, then in a step S3 then
 the process repeats itself.
 If the engine speed is equal to or greater than this high speed, then in
 another step S4, the CPU 74 checks to see if the engine speed has become
 equal to or higher than a higher speed, such as 6100 rpm. If not (i.e. the
 engine speed is between 6000 and 6100 rpm), then in a step S5, the CPU 74
 is arranged to disable one cylinder and the process repeats. This
 instruction is preferably input into the disabling function illustrated in
 FIG. 6 at step S4, wherein the cylinder disabling portion 114 employs one
 of the "one cylinder disabled" patterns described in conjunction with FIG.
 7 to prevent the appropriate firing signal for disabling one cylinder.
 If the engine speed is equal to or greater than this higher speed, then in
 a step S6, the CPU 74 checks to see if the engine speed has risen to or is
 above a higher speed, such as 6200 rpm. If not, in a step S7, the CPU 74
 disables two cylinders. If so, then in a step S8, the CPU 74 checks to
 determine if the engine speed is at or above a still higher speed, such as
 6300 rpm. If not, then the CPU 74 disables three cylinders in a step S9,
 and if so, then all cylinders are disabled in step S10 and the engine is
 completely shut down.
 FIGS. 9 and 10 illustrate an engine overheat protection function associated
 with the overheat detection portion 110 of the ignition control. As
 illustrated in FIG. 9, after the engine 40 is started the CPU 74 is
 arranged to determine if an engine temperature Ts is equal to or greater
 than a predetermine high temperature Tmax (step S1). If so, then in a step
 S2, the CPU 74 checks to determine if the engine temperature Ts has fallen
 to a level equal to or below a predetermined low temperature Tmin after a
 time t1. If the temperature Ts has not fallen, then in step S3, an engine
 overheat signal is outputted.
 If the temperature Ts is less than Tmax in step S1, then in a step S4, it
 is determined whether the temperature Ts has increased at a faster rate of
 speed than a predetermined rate of speed. If so, then the overheat signal
 is outputted in step S3. If not, then the CPU 74 rechecks the rate of
 increased in the temperature Ts.
 If the temperature Ts is greater than Tmin in step S2, then the rate of
 increase in the temperature Ts is checked in step S4, as described above.
 FIG. 10 is a graph illustrating this overheat detection function. As
 illustrated, the engine 40 is preferably of the type having a coolant
 system in which when the engine is not running, there is no coolant in the
 water jackets. Coolant fills the water jackets and other passages some
 time after the engine 40 is started.
 In this graph, the line for step S2 illustrates the condition when the
 temperature exceeds Tmax after a time t1 and an overheat condition is
 determined. Likewise, if the rate of increase in temperature as evident by
 line S4 exceeds a predetermined rate of increase .DELTA.Ta/.DELTA.ta, then
 an overheat condition is determined.
 FIG. 11 is a flowchart illustrating an engine temperature reduction
 function of the ignition control associated with the present invention.
 After the engine starts, in a step S1, it is determined if there is an
 engine overheat detection signal. If not, then the CPU 74 is arranged to
 check for excessive engine speed (see flowchart illustrated in FIG. 8 and
 described above). If an engine overheat detection signal is received, then
 in a step S2, it is determined if the engine speed E/N is equal to or
 greater than a predetermine low speed, such as 2000 rpm. If not (i.e. the
 engine speed is less than 2000 rpm) then in a step S10, it is determined
 if there are any disabled cylinders. If not, the process returns to step
 S1, and if so, then these cylinders are not disabled to bring up the
 engine speed, and the process returns to step S1.
 If the engine speed is equal to or greater than 2000 rpm, then in a step S3
 it is determined if there are any cylinders disabled. If not, then in a
 step S4, an instruction to disable one cylinder of the engine is output
 (such as in step S4 of the flowchart illustrated in FIG. 6 and associated
 with the patterns illustrated in FIG. 7). The process then returns to the
 first step S1.
 If there is already one disabled cylinder, then in step S5, it is
 determined if there are two cylinders disabled already. If not, then in
 step S6 an instruction to disable two cylinders is output and the process
 returns to step S1.
 If so, then in step S7 it is determined if there are three cylinders
 disabled. If not, then in a step S8 an instruction to disable three
 cylinders is output and the process returns to step S1. If so, then in a
 step S9 an instruction to disable all cylinders is output.
 FIG. 13 is a flowchart illustrating a second embodiment cylinder disabling
 function in accordance with the present invention for use in controlling
 the engine speed of the engine. FIG. 8 illustrates an engine overrev
 function associated with the ignition control in which the decision to
 disable each additional cylinder is determined based upon whether higher
 engine speeds occur.
 In accordance with the function illustrated in FIG. 13, if it is determined
 that the engine speed equals or exceeds a predetermined speed, such as
 6000 rpm, then it is determined if there is already one cylinder disabled.
 If not, then one cylinder is disabled and the engine speed is checked to
 see if it still equals or exceeds this predetermined high speed. If so,
 then an additional cylinder is disabled, and so on until all cylinders are
 disabled.
 Of course, the foregoing description is that of preferred embodiments of
 the invention, and various changes and modifications may be made without
 departing from the spirit and scope of the invention, as defined by the
 appended claims.