Patent Publication Number: US-11378053-B2

Title: Engine ignition control unit for improved engine starting

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 62/728,996 filed on Sep. 10, 2018 the entire contents of which are incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to an engine ignition control unit for a combustion engine. 
     BACKGROUND 
     Capacitor discharge ignition (CDI) systems are widely used in spark-ignited internal combustion engines. Generally, CDI systems include a main capacitor that is charged by an associated generator or charge coil and is later discharged through a step-up transformer or ignition coil to fire a spark plug. CDI systems typically have a stator assembly and one or more magnets are typically mounted on an engine flywheel to generate current pulses within the charge coil as the magnets are rotated past the stator. The current pulses produced in the charge coil are used to charge the main capacitor which is subsequently discharged upon activation of a trigger signal. A microprocessor has inputs and outputs and is coupled to the ignition circuit by multiple wires which each separately provide signals to and from the microprocessor to control operation of the ignition system in accordance with various factors such as engine speed and desired ignition timing. 
     SUMMARY 
     In at least some implementations, a method of operating an ignition system for a combustion engine includes charging an energy storage device during at least a portion of the time when the engine is operating, permitting the level of energy stored on the charge storage device to decrease over time after the engine ceases to operate, determining the energy level on the energy storage device when the engine is restarted after having ceased operating, and setting at least one engine operational parameter as a function of the determined energy level. In at least some implementations, the at least one engine operational parameter may include one or more of: richness of a fuel and air mixture to be delivered to the engine, ignition timing, desired engine idle speed. 
     In at least some implementations, a switch is provided that has a first state in which charging of the energy storage device is not permitted and a second state in which charging of the energy storage device is permitted, and the switch is in the first state absent power being supplied to the switch, and the method includes the step of providing power to the switch when the engine is operating so that the switch is in the second state and charging of the energy storage device is permitted. In at least some implementations, power is not provided to the switch until the engine has been operating for a threshold time or threshold number of engine revolutions. In at least some implementations, power is not provided to the switch until the energy level on the energy storage device, when the engine is restarted after having ceased operating, has been determined. 
     In at least some implementations, the method also includes comparing the energy level on the energy storage device when the engine is restarted after having ceased operating with information relating to the rate at which energy in the energy storage device decays over time. When the energy level in the energy storage device corresponds to the engine having been not operating for between 5 minutes and 45 minutes, at least one of richness of a fuel and air mixture to be delivered to the engine, ignition timing, and desired engine idle speed is set to a level equal to such level used when starting a cold engine. The energy level that corresponds to the engine having been not operating for between 5 minutes and 45 minutes may be indirectly measured as zero volts or more than zero volts. 
     In at least some implementations, the method may include determining one or both of engine temperature and ambient temperature and wherein the at least one engine operational parameter is set based in part on one or both of the determined engine temperature and ambient temperature. One or both of the engine temperature and ambient temperature may be determined upon attempted restarting of the engine or when the engine has been restarted. 
     In at least some implementations, an engine control system includes a main energy storage device adapted to be communicated with an energy source, an ignition switch coupled to the main energy storage device to control discharge of energy from the main energy storage device, and a timing circuit including a second energy storage device, a second switch coupled to the second energy storage device and having a first state permitting current flow to the second energy storage device and a second state that does not permit current flow to the second energy storage device. 
     In at least some implementations, the system includes one or more resistors coupled between the second switch and the second energy storage device to at least in part control the discharge rate of energy from the second energy storage device. In at least some implementations, a controller is coupled to the second switch and to the second energy storage device, and the controller is operable to control the state of the switch and to determine an energy level of the second energy storage device. In at least some implementations, the main energy storage device is a capacitor of a capacitive ignition discharge circuit. And in at least some implementations, the second energy storage device is coupled to ground and energy discharged from the second energy storage device is discharged to ground. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of certain embodiments and best mode will be set forth with reference to the accompanying drawings, in which: 
         FIG. 1  shows an example of a capacitor discharge ignition (CDI) system for a light-duty combustion engine; and 
         FIG. 2  is a schematic diagram of a circuit that may be used with the CDI system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The methods and systems described herein generally relate to combustion engines that include ignition systems with microcontroller circuitry, including but not limited to light-duty combustion engines. Typically, the light-duty combustion engine is a single cylinder two-stroke or four-stroke gasoline powered internal combustion engine. A piston is slidably received for reciprocation in an engine cylinder and is connected to a crank shaft that, in turn, is attached to a fly wheel. Such engines are often paired with a capacitive discharge ignition (CDI) system that utilizes a microcontroller to supply a high voltage ignition pulse to a spark plug for igniting an air-fuel mixture in the engine combustion chamber. The term “light-duty combustion engine” broadly includes all types of non-automotive combustion engines, including two and four-stroke engines typically used to power devices such as gasoline-powered hand-held power tools, lawn and garden equipment, lawnmowers, weed trimmers, edgers, chain saws, snowblowers, personal watercraft, boats, snowmobiles, motorcycles, all-terrain-vehicles, etc. It should be appreciated that while the following description is in the context of a capacitive discharge ignition (CDI) system, the control circuit and/or the power supply sub-circuit described herein may be used with any number of different ignition systems and are not limited to the particular one shown here. Further, while generally described with reference to a light-duty combustion engine, the methods and components described herein may be used with other types of engines including multi-cylinder engines, engines for automotive applications and other larger engines. 
     With reference to  FIG. 1 , there is shown a cut-away view of an exemplary capacitive discharge ignition (CDI) system  10  that interacts with a flywheel  12  and generally includes an ignition module  14 , an ignition lead  16  for electrically coupling the ignition module to a spark plug SP (shown in  FIG. 2 ), and electrical connections  5 ,  21  for coupling the ignition module to one or more auxiliary loads, such as a carburetor solenoid valve. The flywheel  12  shown here includes a pair of magnetic poles or elements  22  located towards an outer periphery of the flywheel. Once flywheel  12  is rotating, magnetic elements  22  spin past and electromagnetically interact with the different coils or windings in ignition module  14 . 
     Ignition module  14  can generate, store, and utilize the electrical energy that is induced by the rotating magnetic elements  22  in order to perform a variety of functions. According to one embodiment, ignition module  14  includes a lamstack  30 , a charge winding  32 , a primary winding  34  and a secondary winding  36  that together constitute a step-up transformer, a first auxiliary winding  38 , a second auxiliary winding  39 , a trigger winding  40 , an ignition module housing  42 , and a control circuit  50 . Lamstack  30  is preferably a ferromagnetic part that is comprised of a stack of flat, magnetically-permeable, laminate pieces typically made of steel or iron. The lamstack can assist in concentrating or focusing the changing magnetic flux created by the rotating magnetic elements  22  on the flywheel. According to the embodiment shown here, lamstack  30  has a generally U-shaped configuration that includes a pair of legs  60  and  62 . Leg  60  is aligned along the central axis of charge winding  32 , and leg  62  is aligned along the central axes of trigger winding  40  and the step-up transformer. The first auxiliary winding  38 , second auxiliary winding  39  and trigger winding  40  are shown on leg  60 , however, these windings or coils could be located elsewhere on the lamstack  30 . Magnetic elements  22  can be implemented as part of the same magnet or as separate magnetic components coupled together to provide a single flux path through flywheel  12 , to cite two of many possibilities. Additional magnetic elements can be added to flywheel  12  at other locations around its periphery to provide additional electromagnetic interaction with ignition module  14 . 
     Charge winding  32  generates electrical energy that can be used by ignition module  14  for a number of different purposes, including charging an ignition capacitor and powering an electronic processing device, to cite two of many examples. Charge winding  32  includes a bobbin  64  and a winding  66  and, according to one embodiment, is designed to have a relatively low inductance and a relatively low resistance, but this is not necessary. 
     Trigger winding  40  provides ignition module  14  with an engine input signal that is generally representative of the position and/or speed of the engine. According to the particular embodiment shown here, trigger winding  40  is located towards the end of lamstack leg  62  and is adjacent to the step-up transformer. It could, however, be arranged at a different location on the lamstack. For example, it is possible to arrange both the trigger and charge windings on a single leg of the lamstack, as opposed to arrangement shown here. It is also possible for trigger winding  40  to be omitted and for ignition module  14  to receive an engine input signal from charge winding  32  or some other device. 
     Step-up transformer uses a pair of closely-coupled windings  34 ,  36  to create high voltage ignition pulses that are sent to a spark plug SP via ignition lead  16 . Like the charge and trigger windings described above, the primary and secondary windings  34 ,  36  surround one of the legs of lamstack  30 , in this case leg  62 . The primary winding  34  has fewer turns of wire than the secondary winding  36 , which has more turns of finer gauge wire. The turn ratio between the primary and secondary windings, as well as other characteristics of the transformer, affect the voltage and are typically selected based on the particular application in which it is used. 
     Ignition module housing  42  is preferably made from a plastic, metal, or some other material, and is designed to surround and protect the components of ignition module  14 . The ignition module housing has several openings to allow lamstack legs  60  and  62 , ignition lead  16 , and electrical connections  5 ,  21  to protrude, and preferably are sealed so that moisture and other contaminants are prevented from damaging the ignition module. It should be appreciated that ignition system  10  is just one example of a capacitive discharge ignition (CDI) system that can utilize ignition module  14 , and that numerous other ignition systems and components, in addition to those shown here, could also be used as well. 
     Control circuit  50  may be carried within the housing  42  or within a housing remote from the flywheel and lamstack and communicated with the ignition module  14  to receive energy from the module  14  and to control, at least in part, operation of the module. For example, a control module may be located on or adjacent to a throttle body, such as is shown and described in PCT patent application Ser. No. 17/028,913 filed Apr. 21, 2017 the disclosure of which is incorporated herein by reference in its entirety. Such a module may be responsive to a throttle valve position and/or other variables to control ignition timing, a fuel/air mixture content (such as by varying the amount of fuel or air with a valve), whether to cause an ignition event in a given engine cycle, engine speed control, among other things. The module could be located remotely from the engine and any throttle body, carburetor or other component associated with the engine, for example, in a handle, housing, cowling or other component of a vehicle or device that includes the engine. The control module may be coupled to portions of the ignition module  14  so that it can control, if desired, the energy that is induced, stored and discharged by the ignition system  10 . The term “coupled” broadly encompasses all ways in which two or more electrical components, devices, circuits, etc. can be in electrical communication with one another; this includes but is certainly not limited to, a direct electrical connection and a connection via intermediate components, devices, circuits, etc. The control circuit  50  may be provided according to the exemplary embodiment shown in  FIG. 2  where the control circuit is coupled to and interacts with charge winding  32 , primary ignition winding  34 , first auxiliary winding  38 , second auxiliary winding  39 , and trigger winding  40 . According to this particular example, the control circuit  50  includes an ignition discharge capacitor  52 , an ignition discharge switch  54 , a microcontroller  56 , a power supply sub-circuit  58 , as well as any number of other electrical elements, components, devices and/or sub-circuits that may be used with the control circuit and are known in the art (e.g., kill switches and kill switch circuitry). 
     The ignition discharge capacitor  52  acts as a main energy storage device for the ignition system  10 . According to the embodiment shown in  FIG. 2 , the ignition discharge capacitor  52  is coupled to the charge winding  32  and the ignition discharge switch  54  at a first terminal, and is coupled to the primary winding  34  at a second terminal. The ignition discharge capacitor  52  is configured to receive and store electrical energy from the charge winding  32  via diode  70  and to discharge the stored electrical energy through a path that includes the ignition discharge switch  54  and the primary winding  34 . Discharge of the electrical energy stored on the ignition discharge capacitor  52  is controlled by the state of the ignition discharge switch  54 , as is widely understood in the art. As these components are coupled to one or more coils in the ignition module  14 , these components may, if desired, be located within the ignition module on a circuit board  19  or otherwise arranged. 
     The ignition discharge switch  54  acts as a main switching device for the ignition system  10 . The ignition discharge switch  54  is coupled to the ignition discharge capacitor  52  at a first current carrying terminal, to ground at a second current carrying terminal, and to an output of the microcontroller  56  at its gate. As noted herein, the microcontroller  56  may be located remotely, if desired, which is to say not within the ignition module  14 . The ignition discharge switch  54  can be provided as a thyristor, for example, a silicon controller rectifier (SCR). An ignition trigger signal from an output of the microcontroller  56  activates the ignition discharge switch  54  so that the ignition discharge capacitor  52  can discharge its stored energy through the switch and thereby create a corresponding ignition pulse in the ignition coil. 
     The microcontroller  56  is an electronic processing device that executes electronic instructions in order to carry out functions pertaining to the operation of the light-duty combustion engine. This may include, for example, electronic instructions used to implement the methods described herein. In one example, the microcontroller  56  includes the 8-pin processor illustrated in  FIG. 2 , however, any other suitable controller, microcontroller, microprocessor and/or other electronic processing device may be used instead. Pins 1 and 8 are coupled to the power supply sub-circuit  58 , which provides the microcontroller with power that is somewhat regulated; pins 2 and 7 are coupled to trigger winding  40  and provide the microcontroller with an engine signal that is representative of the speed and/or position of the engine (e.g., position relative to top-dead-center); pins 3 and 5 are shown as being connected to a timing sub-circuit which will be described in more detail below; pin 4 is coupled to ground; and pin 6 is coupled to the gate of ignition discharge switch  54  so that the microcontroller can provide an ignition trigger signal, sometimes called a timing signal, for activating the switch. Some non-limiting examples of how microcontrollers can be implemented with ignition systems are provided in U.S. Pat. Nos. 7,546,836 and 7,448,358, the entire contents of which are hereby incorporated by reference. 
     The power supply sub-circuit  58  receives electrical energy from the charge winding  32 , stores the electrical energy, and provides the microcontroller  56  with regulated, or at least somewhat regulated, electrical power. The power supply sub-circuit  58  is coupled to the charge winding  32  at an input terminal  80  and to the microcontroller  56  at an output terminal  82  and, according to the example shown in  FIG. 2 , includes a first power supply switch  90 , a power supply capacitor  92 , a power supply zener  94 , a second power supply switch  96 , and one or more power supply resistors  98 . As will be explained below in more detail, the power supply sub-circuit  58  is designed and configured to reduce the portion of the charge winding load that is attributable to powering the microcontroller  56 , or other electrically powered devices, like a solenoid or the like. The components of the power supply sub-circuit  58  may be located in the ignition module, the control module that is separate from the ignition module, or a combination of the two, as desired. 
     The first power supply switch  90 , which can be any suitable type of switching device like a BJT or MOSFET, is coupled to the charge winding  32  at a first current carrying terminal, to the power supply capacitor  92  at a second current carrying terminal, and to the second power supply switch  96  at a base or gate terminal. When the first power supply switch  90  is activated or is in an ‘on’ state, current is allowed to flow from the charge winding  32  to the power supply capacitor  92 ; when the switch  90  is deactivated or is in an ‘off’ state, current is prevented from flowing from the charge winding  32  to the capacitor  92 . As mentioned above, any suitable type of switching device may be used for the first power supply switch  90 , but such a device should be able to handle a significant amount of voltage; for example between about 150 V and 450 V. 
     The power supply capacitor  92  is coupled to the first power supply switch  90 , the power supply zener  94  and the microcontroller  56  at a positive terminal, and is coupled to ground at a negative terminal. The power supply capacitor  92  receives and stores electrical energy from the charge winding  32  so that it may power the microcontroller  56  in a somewhat regulated and consistent manner. 
     The power supply zener  94  is coupled to the power supply capacitor  92  at a cathode terminal and is coupled to second power supply switch  96  at an anode terminal. The power supply zener  94  is arranged to be non-conductive so as long as the voltage on the power supply capacitor  92  is less than the breakdown voltage of the zener diode and to be conductive when the capacitor voltage exceeds the breakdown voltage. A zener diode with a particular breakdown voltage may be selected based on the amount of electrical energy that is deemed necessary for the power supply sub-circuit  58  to properly power the microcontroller  56 . Any zener diode or other similar device may be used, including zener diodes having a breakdown voltage between about 3V and 20V. 
     The second power supply switch  96  is coupled to resistor  98  and the base of the first power supply switch  90  at a first current carrying terminal, to ground at a second current carrying terminal, and to the power supply zener diode  94  at a gate. As will be described below in more detail, the second power supply switch  96  is arranged so that when the voltage at the zener diode  94  is less than its breakdown voltage, the second power supply switch  96  is held in a deactivated or ‘off’ state; when the voltage at the zener diode exceeds the breakdown voltage, then the voltage at the gate of the second power supply switch  96  increases and activates that device so that it turns ‘on’. Again, any number of different types of switching devices may be used, including thyristors in the form of silicon controller rectifiers (SCRs). According to one non-limiting example, the second power supply switch is an SCR and has a gate current rate between about 2 μA and 3 mA. 
     The power supply resistor  98  is coupled at one terminal to charge winding  32  and one of the current carrying terminals of the first power supply switch  90 , and at another terminal to one of the current carrying terminals of the second power supply switch  96 . It is preferable that power supply resistor  98  have a sufficiently high resistance so that a high-resistance, low-current path is established through the resistor when the second power supply switch  96  is turned ‘on’. In one example, the power supply resistor  98  has a resistance between about 5 kΩ and 10 kΩ, however, other values may certainly be used instead. 
     During a charging cycle, electrical energy induced in the charge winding  32  may be used to charge, drive and/or otherwise power one or more devices around the engine. For example, as the flywheel  12  rotates past the ignition module  14 , the magnetic elements  22  carried by the flywheel induce an AC voltage in the charge winding  32 . A positive component of the AC voltage may be used to charge the ignition discharge capacitor  52 , while a negative component of the AC voltage may be provided to the power supply sub-circuit  58  which then powers the microcontroller  56  with regulated DC power. The power supply sub-circuit  58  may be designed to limit or reduce the amount of electrical energy taken from the negative component of the AC voltage to a level that is still able to sufficiently power the microcontroller  56 , yet saves energy for use elsewhere in the system, for example to drive a fuel injector in an electronic fuel injection system. Another example of a device that may benefit from this energy savings is a solenoid that is coupled to the windings  38  and  39  and is used to control the air/fuel ratio being provided to the combustion chamber. The power supply sub-circuit may be constructed and arranged as shown in  FIG. 2  and as described in PCT Application Publication WO 2017/015420. 
     Beginning with the positive portion of the AC voltage that is induced in the charge winding  32 , current flows through diode  70  and charges ignition discharge capacitor  52 . So long as the microcontroller  56  holds the ignition discharge switch  54  in an ‘off’ state, the current from the charge winding  32  is directed to the ignition discharge capacitor  52 . It is possible for the ignition discharge capacitor  52  to be charged throughout the entire positive portion of the AC voltage waveform, or at least for most of it. When it is time for the ignition system  10  to fire the spark plug SP (i.e., the ignition timing), the microcontroller  56  sends an ignition trigger signal to the ignition discharge switch  54  that turns the switch ‘on’ and creates a current path that includes the ignition discharge capacitor  52  and the primary ignition winding  34 . The electrical energy stored on the ignition discharge capacitor  52  rapidly discharges via the current path, which causes a surge in current through the primary ignition winding  34  and creates a fast-rising electro-magnetic field in the ignition coil. The fast-rising electro-magnetic field induces a high voltage ignition pulse in the secondary ignition winding  36  that travels to the spark plug SP and provides a combustion-initiating spark. Other sparking techniques, including flyback techniques, may be used instead. 
     Turning now to the negative component or portion of the AC voltage that is induced in the charge winding  32 , current initially flows through the first power supply switch  90  and charges power supply capacitor  92 . So long as second power supply switch  96  is turned ‘off’, there is current flow through power supply resistor  98  so that the voltage at the base of the first power supply switch  90  biases the switch in an ‘on’ state. Charging of the power supply capacitor  92  continues until a certain charge threshold is met; that is, until the accumulated charge on capacitor  92  exceeds the breakdown voltage of the power supply zener  94 . As mentioned above, zener diode  94  is preferably selected to have a certain breakdown voltage that corresponds to a desired charge level for the power supply sub-circuit  58 . Some initial testing has indicated that a breakdown voltage of approximately 6 V may be suitable in some light-duty engine applications, although other values may be used. The power supply capacitor  92  uses the accumulated charge to provide the microcontroller  56  with regulated DC power. Of course, additional circuitry like the secondary stage circuitry  86  may be employed for reducing ripples and/or further filtering, smoothing and/or otherwise regulating the DC power. 
     Once the stored charge on the power supply capacitor  92  exceeds the breakdown voltage of the power supply zener  94 , the zener diode becomes conductive in the reverse bias direction so that the voltage seen at the gate of the second power supply switch  96  increases. This turns the second power supply switch  96  ‘on’, which creates a low current path  84  that flows through resistor  98  and switch  96  and lowers the voltage at the base of the first power supply switch  90  to a point where it turns that switch ‘off’. With first power supply switch  90  deactivated or in an ‘off’ state, additional charging of the power supply capacitor  92  is prevented. Moreover, power supply resistor  98  preferably exhibits a relatively high resistance so that the amount of current that flows through the low current path  84  during this period of the negative portion of the AC cycle is minimal (e.g., on the order of 50 μA) and, thus, limits the amount of wasted electrical energy. The first power supply switch  90  will remain ‘off’ until the microcontroller  56  pulls enough electrical energy from power supply capacitor  92  to drop its voltage below the breakdown voltage of the power supply zener  94 , at which time the second power supply switch  96  turns ‘off’ so that the cycle can repeat itself. This arrangement may somewhat simulate a low cost hysteresis approach. 
     Accordingly, instead of charging the power supply capacitor  92  during the entire negative portion of the AC voltage waveform, the power supply sub-circuit  58  only charges capacitor  92  for a first segment of the negative portion of the AC voltage waveform; during a second segment, the capacitor  92  is not being charged. Put differently, the power supply sub-circuit  58  only charges the power supply capacitor  92  until a certain charge threshold is reached, after which additional charging of capacitor  92  is cut off. Because less electrical current is flowing from the charge winding  32  to the power supply sub-circuit  58 , the electromagnetic load on the winding and/or the circuit is reduced, thereby making more electrical energy available for other windings and/or other devices. If the electrical energy in the ignition system  10  is managed efficiently, it may possible for the system to support both an ignition load and external loads (e.g., an air/fuel ratio regulating solenoid) on the same magnetic circuit. 
     This arrangement and approach is different than simply utilizing a simple current limiting circuit to clip the amount of current that is allowed into the power supply sub-circuit  58  at any given time. Such an approach may result in undesirable effects, in that it may be slow to reach a working voltage due to the limited current available, thus, causing unwanted delays in the functionality of the ignition system. The power supply sub-circuit  58  is designed to allow higher amounts of current to quickly flow into the power supply capacitor  92 , which charges the power supply more rapidly and brings it to a sufficient DC operating level in a shorter amount of time than is experienced with a simple current limiting circuit. 
     As mentioned above, the electrical energy that is saved or not used by power supply sub-circuit  58  may be applied to any number of different devices around the engine. One example of such a device is a solenoid that controls the air/fuel ratio of the gas mixture supplied from a carburetor to a combustion chamber. Referring back to  FIG. 2 , the first auxiliary winding  38  and the second auxiliary winding  39  could be coupled to a device  88 , such as a solenoid, an additional microcontroller or any other device requiring electrical energy. The first and second auxiliary windings  38  and  39  may be connected in parallel with each other and may each have one terminal coupled to the solenoid via intervening diodes  100  and  102 , respectively and their other terminals coupled to ground. A zener diode  104  may be connected in parallel between the solenoid and coils  38  and  39  to protect the solenoid from a voltage greater than the zener diode breakdown voltage (excess current flows through the zener diode to ground). 
     Because the magnets  22  are fixed to the flywheel  12 , the position of the magnets relative to one or more coils of the ignition circuit may be used to determine the position of the flywheel and thus, the position of the crankshaft and piston. This information may also be used to determine the engine speed (e.g. the time from a certain engine position in one revolution to the same engine position in the next revolution may be used to determine the engine speed during that revolution). Use of multiple magnets spaced about the periphery of the flywheel can enhance the resolution of this determination by providing more data points in a revolution. Engine speed may also be determined by a sensor that is responsive to the position of the flywheel. Representative sensors including magnetically responsive sensors like hall-effect sensors or variable reluctance sensors. The flywheel may have teeth and the sensors may be responsive to the passing by of one or more teeth to determine flywheel position and hence, crankshaft position. The trigger coil  40  or a different coil in the ignition module may be used as a VR sensor as noted above. 
     Also shown in  FIG. 2  is a timing sub-circuit  110  that permits a determination of the time since an engine was last operating, within a first threshold. The timing sub-circuit  110  includes an energy storage device  112  that is charged during operation of the engine to a threshold charge level which may be the maximum charge that can be stored on the device. The charge stored/energy level on the device  112  decays over time at a known rate when the engine is no longer operating. Thus, determination of the charge remaining on the device  112  at some time after the engine stopped operating permits determination of the time that has passed since the engine stopped operating. 
     This determined engine off time (i.e. the time since the engine stopped operating) along with one or more other factors may be used to determine an appropriate engine operating scheme that may include various engine operational control parameters, including but not limited to, one or more of richness of a fuel and air mixture to be delivered to the engine, ignition timing, desired engine idle speed among other engine operating conditions. Representative other factors that may be used in combination with the determined engine off time to refine the engine operating scheme/parameters to be used include, but are not limited to, one or both of the engine temperature and the ambient temperature. Such temperatures and the engine off time may be determined when the engine is restarted, or during attempted restarting of the engine. Different engine operational parameters may be used when the engine/ambient temperature is lower than when either or both temperatures are higher. Further, certain engine control parameters may be used when the engine has been stopped for greater than the first threshold time, as well as for different lengths of time within the first threshold time. In at least some implementations, an engine stopped for greater than the first threshold time may be operated as if the engine is being started from a cold or not recently operated condition. Conversely, an engine that very recently stopped operating, for example within a minute, may be restarted with the same engine operational control parameters that were used before the engine operation terminated, or with minimal change to one or more of such parameters. 
     In at least some implementations, the energy storage device is a capacitor  112  that is coupled to a regulated power supply such as the output  82  of the power supply sub-circuit  58 , or Vcc/other supply voltage. To permit greater control over the charging of the capacitor  112 , a switch  114  may be interposed in the circuit  110  including the capacitor and the capacitor may be charged when the switch is in a first state and is not charged when the switch is in a second state. Among other possibilities, the switch  114  may be in the second state when the engine is not operating, or otherwise when power is not provided to the switch, and may remain in the second state until after some threshold of engine operation is achieved and power is supplied to the switch. Thus, in at least some implementations, not all flywheel rotation results in charging of the capacitor  112 . For example, initial rotation(s) of the flywheel/engine during attempted but failed starting attempts, or rotation of the engine during initial starting that is quickly followed by an engine stall, might not result in charging of the capacitor  112 . Thus, such failed engine operating events do not add charge to the capacitor  112  which would interfere with or render inaccurate subsequent determination of the charge on the capacitor and subsequent determination of the time since the engine was last operated. That is, if all flywheel rotation resulted in charging of the capacitor  112 , then repeated attempts to start the engine or the like would increase the charge on the capacitor  112  and make it seem as though the engine was running more recently than it actually was. By delaying charging of the capacitor  112  by leaving the switch  114  in its second state, the charge on the capacitor when the engine initially begins steady operation can be determined before additional charge is added to the capacitor to permit more accurate determination of the time since the engine was last operated, at least within the first threshold. 
     In at least some implementations, the switch  114  is coupled to the controller  56  and the controller provides power to the switch or otherwise actuates the switch from its second state to its first state. The controller  56  may require a certain energy level in the system before it is woken up and able to command the switch  114  and ignition circuit in general. Initial attempts to start the engine might not provide sufficient power to the controller  56  to render the controller operational, in which case, the controller cannot change the state of the switch  114 . Thus, energy from the power supply coupled to the capacitor  112  is not automatically (that is, without intervention or control from the controller) communicated with the capacitor  112  during the initial attempts to start the engine. When the engine is operating and the controller  56  is sufficiently powered, the controller may determine the charge level of the capacitor  112  before changing the state of the switch  114  and allowing further charging of the capacitor. In this way, the charge on the capacitor  112  when determined by the controller  56  is representative of the time since the engine was last operating sufficiently to power the controller and permit charging of the capacitor  112 . 
     In the implementation shown, the switch  114  is a MOSFET arranged between the power source and the capacitor  112 ; a diode  116  is coupled between the switch and capacitor to prevent reverse current flow from the capacitor through the switch, one or more resistors  118 ,  120 ,  122  may control the capacitor discharge rate and otherwise smooth out charging and discharging of the capacitor; and the timing sub-circuit  110  is coupled to the controller at pins 3 and 5 to permit actuation of the switch (e.g. via power provided from pin 5) and determination of the charge on the capacitor  112  (e.g. at pin 3) when desired. Other switches and control schemes may be used. 
     The first threshold may be set to a desired level for a particular engine and/or engine application. In at least some implementations, the first threshold may be between 5 minutes and 45 minutes, although any limit within the determinable decay period for a capacitor or other energy storage device may be used. When the engine is off for a time greater than the first threshold, the engine may be operated as if the engine is cold/has not been operated recently, and may then be operated in accordance with any other desired factors, such as the engine temperature or ambient temperature without consideration for the time since the engine was last started. When the engine has been off for less than the first threshold amount of time, the time since the engine was last started may be included in process of selecting a desired engine control scheme or at least one engine operational parameter. While the operation is noted in terms of time, no actual “time” needs to be calculated. Instead, the decisions may be made as a function of the energy detected on the capacitor without correlating that energy level to a unit of time. The first threshold may then be a level of charge on the capacitor down to and including zero volts. That is, the first threshold need not be set to correspond to total discharge of the capacitor and could be set at a level between full charge and full discharge. 
     Thus, a method of operating an ignition system for a combustion engine may include a) charging an energy storage device during at least a portion of the time when the engine is operating, b) permitting the level of energy stored on the charge storage device to decrease over time after the engine ceases to operate, c) determining the energy level on the energy storage device when the engine is restarted after having ceased operating, and d) setting at least one engine operational parameter as a function of the determined energy level. A switch may be provided to control charging of the energy storage device. The switch has a first state in which charging of the energy storage device is not permitted and a second state in which charging of the energy storage device is permitted, and the switch is in the first state absent power being supplied to the switch. With such a switch, the method may include the step of providing power to the switch when the engine is operating so that the switch is in the second state and charging of the energy storage device is permitted. Then, charging of the energy storage device can be delayed until after the energy level on the device is determined. In at least some implementations, power is not provided to the switch until the engine has been operating for a threshold time or threshold number of engine revolutions. 
     It is to be understood that the foregoing description is not a definition of the invention, but is a description of one or more preferred embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. For example, a method having greater, fewer, or different steps than those shown could be used instead. All such embodiments, changes, and modifications are intended to come within the scope of the appended claims. 
     As used in this specification and claims, the terms “for example,” “for instance,” “e.g.,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.