METHOD AND SYSTEM FOR CONTROLLING IGNITION COILS

Abstract

Method comprising: iterative estimation of an ignition coil temperature; Updating the iteratively estimated ignition coil temperature based on each of heat transfer from the engine to the ignition coil, internal resistance heating of the ignition coil, and heat transfer from the environment to the ignition coil; and Charging an ignition coil over a dwell time determined based on each of an engine temperature, an ambient temperature and a dwell time of a last spark ignition, wherein the internal resistance heating of the ignition coil is estimated based on a last determined residence time, an average residence time current and a primary coil resistance.

Description

AREA

[0001] The present description generally relates to methods and systems for controlling the current charging an ignition coil by determining a dwell time based on an estimate of the ignition coil temperature. GENERAL STATE OF THE ART / SUMMARY

[0002] Combustion in an internal combustion engine can be initiated by a spark generated by a spark plug. The spark can be triggered by charging an ignition coil with a low-voltage battery. The duration of the charge, or the dwell time, can determine the amplitude of the ignition coil current and thus the energy of the spark. The energy of the spark directly influences engine performance. For example, a spark with a lower than desired energy level can lead to unreliable combustion or misfire. On the other hand, a spark with a higher than desired energy level can increase wear on the ignition system.

[0003] Other attempts to address the problem of controlling ignition coils include controlling the ignition dwell time based on engine operating parameters. An exemplary approach is presented by Ruman et al. in US Pat. No. 5,913,302. In this approach, the ignition dwell time is determined based on engine speed and engine load.

[0004] However, the inventors have recognized potential problems with such systems. For example, the ignition coil temperature can affect the energy of the ignition spark. Varying ignition coil temperature can lead to fluctuations in the resistance of the electrical circuit, which in turn can affect the ignition coil current. Therefore, the dwell time to precisely control the ignition coil current can be determined based on the ignition coil temperature.

[0005] US 2005 / 0 045 165 A1 describes a device that performs the following method steps: iteratively estimating an ignition coil temperature and updating the iteratively estimated ignition coil temperature based on each of a heat transfer from the engine to the ignition coil, an internal resistance heating of the ignition coil and a heat transfer from the environment to the ignition coil.

[0006] Further relevant prior art documents are DE 10 2006 015 351 A1, DE 10 2005 019 352 A1, DE 199 06 391 A1, DE 100 12 956 A1 and DE 10 2005 008 458 A1.

[0007] According to the invention, the problems described above can be remedied by the features of the independent patent claims. Advantageous developments of the invention are described in the subclaims.

[0008] Accordingly, a method for charging an ignition coil determines a dwell time based on each of the engine temperature, the ambient temperature, and the dwell time of the last spark ignition. In this way, the ignition coil current can be precisely controlled by taking into account the variation in the ignition coil temperature.

[0009] As one example, the ignition coil is charged over a dwell time determined based on the ignition coil temperature, where the ignition coil temperature may be iteratively updated via an estimated rate of change in coil temperature (e.g., via a coil temperature change over time with a unit such as degrees per second). Because the ignition coil is mechanically coupled to the cylinder head and exposed to the ambient air, the rate of change in coil temperature depends on heat transfer from the engine and from the ambient air. Furthermore, current flow within the ignition coil may heat the ignition coil internally. Therefore, the rate of change in coil temperature may be calculated in real time by a controller based on each of an estimated heat transfer from the engine, internal resistive heating, and heat transfer from the ambient air.The internal resistance heating of the ignition coil can be calculated based on the ignition coil temperature from the last spark ignition event. The ignition coil temperature can be updated at time intervals shorter than the thermal time constant of the ignition coil, allowing the estimated ignition coil temperature to closely track the actual coil temperature. By accounting for heat transfer to and from the ignition coil, a variation in the ignition coil temperature can be precisely tracked at any time during engine operation without the need for additional equipment. Thus, the dwell time before each engine firing event can be determined based on the ignition coil temperature and the available battery voltage. This allows the charging current in the ignition coil to be precisely controlled.

[0010] It should be understood that the foregoing summary is provided to introduce, in simplified form, a selection of concepts further described in the detailed description. It is not intended to identify important or essential features of the claimed subject matter, the scope of which is defined solely in the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that overcome any disadvantages noted above or in any part of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a schematic diagram of an exemplary cylinder of a multi-cylinder internal combustion engine. Fig. Figure 2 is a partial view of the engine cylinder showing an ignition system coupled to the engine. Fig. 3 shows a simplified electrical circuit of the ignition system. Fig. 4 illustrates an exemplary method for estimating an ignition coil temperature during engine operation. Fig. Figure 5 illustrates an exemplary method for determining the residence time. Fig. 6 illustrates an exemplary relationship between a primary coil resistance and the ignition coil temperature. Fig. Figure 7 presents timelines illustrating the variations of representative engine operating parameters over time during which the example methods are implemented. DETAILED DESCRIPTION

[0011] The following description relates to systems and methods for controlling the current used to charge an ignition coil coupled to an internal combustion engine system. An example of the internal combustion engine system is described in Fig. 1 shown. Fig. Figure 2 is a partial view of the engine system illustrating the location of an ignition system within the engine system. The ignition system may include an ignition coil and a spark plug. Fig. Figure 3 shows a simplified diagram of an electrical circuit of the ignition system. The electrical circuit includes a primary coil, a battery, and a secondary coil. By coupling the primary coil to the battery for a certain period of time, a charging current can build up and flow through the primary coil. The amplitude of the current depends on the ignition coil temperature. Fig. 4 illustrates an exemplary method for estimating the ignition coil temperature during engine operation. Fig. 5 further illustrates an exemplary method for determining the dwell time based on the estimated ignition coil temperature. The ignition coil temperature is estimated iteratively based on heat transfers between the ignition coil and the ambient environment. Heat may be generated during ignition coil charging through resistive heating. The resistive heating depends on the primary coil resistance, which in turn depends on the ignition coil temperatures. Fig. 6 shows an exemplary relationship between the ignition coil resistance and the ignition coil temperature. Fig. Figure 7 illustrates a variation of representative parameters over time, during which the Fig. 4-5 can be implemented using the exemplary procedures shown.

[0012] With reference to Fig. 1 is a schematic diagram depicting one cylinder of a multi-cylinder engine 10, which may be included in a propulsion system of a vehicle. The engine 10 may be controlled at least in part by a control system including a controller 12 and by input from a vehicle operator 132 via an input device 130. In this example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. A combustion chamber 30 (also referred to as cylinder 30) of the engine 10 may include combustion chamber walls 32 with a piston 36 positioned therein. The piston 36 may be coupled to a crankshaft 40 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. The crankshaft 40 may be coupled to at least one drive wheel of a vehicle through an intermediate gear system (not shown).Furthermore, a starter may be coupled to the crankshaft 40 via a flywheel (not shown) to enable a starting operation of the engine 10.

[0013] Combustion chamber 30 may receive intake air from an intake manifold 44 via an intake passage 42 and expel combustion exhaust gases via an exhaust manifold 48. Intake manifold 44 and exhaust manifold 48 may be selectively connected to combustion chamber 30 via the respective intake valve 52 and exhaust valve 54. In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.

[0014] A fuel injector 66 is shown disposed within intake manifold 44 in a configuration that provides so-called port injection of fuel into the intake port upstream of combustion chamber 30. Fuel injector 66 may inject fuel proportional to the pulse width of a signal FPW received from controller 12 via an electronic driver 68. Fuel may be delivered to fuel injector 66 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber 30 may alternatively or additionally include a fuel injector directly coupled to combustion chamber 30 for injecting fuel directly therein in a manner referred to as direct injection.

[0015] The intake passage 42 may include a throttle 62 with a throttle plate 64. In this particular example, the position of the throttle plate 64 may be varied by the controller 12 via a signal provided to an electric motor or actuator included in the throttle 62, a configuration commonly referred to as electronic throttle control (ETC). In this manner, the throttle 62 may be operated to vary the intake air provided to the combustion chamber 30, among other internal combustion engine cylinders. The position of the throttle plate 64 may be provided to the controller 12 by the throttle position signal TP. The intake passage 42 may include a mass air flow sensor 120 and a manifold air pressure sensor 122 for providing the corresponding MAF and MAP signals to the controller 12.

[0016] An ignition system 88 may provide an ignition spark to the combustion chamber 30 in response to a pre-ignition signal SA from the controller 12. The ignition system may include an ignition coil 90 and a spark plug 92. An ignition device (in Fig. 1 not shown) can be controlled by the controller 12 to adjust the ignition timing.

[0017] Fig. Figure 2 is a partial view of the engine system showing the location of the ignition system within the engine system. The ignition coil 90 is mechanically and electrically coupled to one end of the spark plug 92. The other end of the spark plug 92 is located within the cylinder chamber 30. The ignition system is mechanically coupled to the cylinder head 50. Thus, heat transfer can occur between the ignition coil and the cylinder head. In addition, since a portion of the ignition coil 90 is exposed to ambient air, heat transfer can also occur between the ignition coil and the ambient air. In addition, internal resistance heating can increase the ignition coil temperature when the coil is charged. Details on how the coil temperature is affected by heat transfer are discussed in detail in Fig. 4 revealed.

[0018] An exhaust gas sensor 126 is shown coupled to the exhaust passage 58 upstream of an emissions control device 70. The sensor 126 may be any suitable sensor for providing an indication of an exhaust air-fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a dual-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. The emissions control device 70 is shown located downstream of the exhaust gas sensor 126 along the exhaust passage 58. The device 70 may be a three-way catalyst (TWC), a NOx trap, various other emissions control devices, or combinations thereof.In some embodiments, the emissions control device 70 may be periodically reset by operating at least one cylinder of the engine within a particular air-fuel ratio during operation of the engine 10. A full-volume exhaust gas sensor 76 is shown coupled to the exhaust passage 58 downstream of the emissions control device 70. The sensor 76 may be any suitable sensor for providing an indication of an exhaust air-fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a dual-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. Additionally, a plurality of exhaust gas sensors may be located at partial-volume locations within the emissions control device.As an example, the embodiment may include a center bed sensor for sensing the air-fuel ratio in the center of the catalyst.

[0019] Other sensors 72, such as a mass air flow (AM) and / or a temperature sensor, may be located upstream of the emissions control device 70 to monitor the AM and the temperature of the exhaust gases flowing into the emissions control device. Fig. The sensor locations shown in Figure 1 are only an example of various possible configurations. For example, the emissions control device may include a partial volume setup with close-coupled catalysts.

[0020] The control 12 is in Fig. 1 as a microcomputer including a microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values, which in this specific example is shown as a read-only memory chip 106, a random access memory 108, a keep-alive memory 110 and a data bus.The controller 12 may receive various signals from sensors coupled to the engine 10, in addition to the signals previously discussed, including measurements of inducted mass air flow (MAF) from a mass air flow sensor 120; engine coolant temperature (ECT) from a temperature sensor 112 coupled to a cooling sleeve 114; a profile ignition pickup (PIP) signal from a Hall sensor 118 (or other type) coupled to the crankshaft 40; throttle position (TP) from a throttle position sensor; air mass and / or temperature of the exhaust gases flowing into the catalyst from sensor 72; an exhaust air-fuel ratio after the catalyst from sensor 76; and a manifold absolute pressure signal, MAP, from sensor 122. An engine speed signal, RPM, may be generated by controller 12 from the PIP signal.The manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold. It should be noted that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor may provide an indication of engine torque. Further, this sensor, along with the sensed engine speed, may provide an estimate of the charge (including air) being introduced into the cylinder. In one example, a sensor 118, also used as an engine speed sensor, may produce a predetermined number of evenly spaced pulses per revolution of the crankshaft. Additionally, the controller 12 may be in communication with a cluster display device, for example, to alert the driver to damage to the engine or exhaust aftertreatment system.

[0021] The controller 12 receives signals from the various sensors Fig. 1 and exposes the various actuators Fig. 1 to adjust engine operation based on the received signals and instructions stored in a non-transitory memory of the controller. For example, adjusting the ignition timing may include adjusting the ignition system's ignition device to adjust the timing for charging and discharging the ignition coil.

[0022] Fig. 3 illustrates an exemplary electrical circuit 300 of the ignition system. The ignition system may include an ignition coil and a spark plug. The ignition system may include a primary coil 312 and a secondary coil 314. The coils are magnetically coupled and arranged as a transformer, with the primary coil and the secondary coil sharing a common core 316. In some examples, the core 316 includes a ferromagnetic material, such as steel. In other examples, the core 316 includes a ferrimagnetic material, such as ceramic. The coils are magnetically coupled; a changing current in one coil electrodynamically induces current in the other coil. Additionally, the primary coil 312 has a first number of turns, and the secondary coil 314 has a second number of turns greater than the first number of turns, such that the voltage between the two coils is "boosted."

[0023] The primary coil 312 is electrically coupled to a voltage source, in this example, a battery 313. A resistance of the primary coil circuit is represented by a resistor 311. The resistor 311 may include a primary coil resistance and a wiring harness resistance. The primary coil 312 is also coupled to an igniter 322. The igniter 322 may be opened or closed by a signal received at terminal 330. When the igniter is closed, the battery 313 charges the primary coil 312, and a charging current builds up within the primary coil. The duration of the charging is referred to as the ignition coil dwell time. In response to the charging current reaching a desired value after the dwell time, the igniter 322 opens. Due to the sudden loss of current in the primary coil, a high voltage across the spark plug gap 342 induces an ignition spark.The current in the primary coil is also referred to as the ignition coil current. Charging current flowing through resistor 311 can generate heat and increase the ignition coil temperature. Furthermore, the ignition coil temperature can also be affected by heat transfer from the engine and the ambient air.

[0024] Fig. 4 illustrates an example method 400 for estimating ignition coil temperature. After triggering, the ignition coil temperature is iteratively updated based on heat transfer from the engine to the ignition coil, heat transfer from the ambient to the ignition coil, and internal resistive heating generated during ignition coil charging.

[0025] Instructions for performing method 400 and the other methods included herein may be executed by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the engine system, such as those described above with reference to Fig. 1. The controller may use motor actuators of the engine system to adjust engine operation according to the methods described below.

[0026] At 401, method 400 determines whether the vehicle is operating. For example, the vehicle may be considered operating in response to a key-on event. If the vehicle is OFF, method 400 continues monitoring the vehicle state at 402. Otherwise, method 400 proceeds to 403.

[0027] At 403, engine operating conditions may be determined by the controller when the vehicle is operating. The controller receives measurements from various sensors in the engine system and estimates operating conditions, such as engine temperature and ambient temperature.

[0028] At 404, method 400 determines a time interval for updating the ignition coil temperature T p As an example, the time interval for updating the ignition coil temperature can be shorter than the ignition coil's thermal time constant. In another example, the time interval for updating the ignition coil can be predetermined and stored in the controller's memory. The thermal time constant for the ignition coil can be in the range of seconds. As an example, a 100 ms task speed can be used as the update time interval.

[0029] At 405, an initial ignition coil temperature is estimated based on a predetermined calibration procedure. For example, the ignition coil temperature may be initialized based on the engine temperature and ambient temperature determined at 403. For example, the engine temperature may be estimated based on an engine coolant temperature. The ignition coil temperature may be calculated according to Equation 1: Tp(0)=C4+C5Ta+C6Te, where T p is the primary coil temperature, also referred to here as the ignition coil temperature; T a the ambient temperature; T e is the engine temperature; and C4, C5 and C6 are predetermined calibration coefficients.

[0030] At 406, procedure 400 is triggered and starts a counter from zero.

[0031] At 407, the controller checks whether the counter exceeds the update time interval of the T pexceeded. If the answer is YES, procedure 400 proceeds to 409. If the answer is NO, procedure 400 increments the counter at 408.

[0032] At 409, current engine operating conditions are estimated. The controller can estimate parameters including engine speed, engine temperature, vehicle speed, and ambient temperature from various sensors.

[0033] At 410, method 400 calculates a rate of change of the ignition coil temperature based on the engine temperature, the ambient temperature, and internal resistive heating. Method 400 also updates the ignition coil temperature based on the calculated rate of change. Because the ignition coil is mechanically coupled to the cylinder head and exposed to ambient air, the thermal energy in the primary coil may be affected by heat transfer from the engine and the environment. Additionally, the thermal energy in the primary coil may be affected by internal resistive heating during ignition coil charging. The rate of change of thermal energy may be expressed as: dQpdt=qe+qa+Pp, where Q p the heat energy in the primary coil, which is also referred to here as heat energy in the ignition coil; q e is the heat energy due to heat transfer from the engine; q ais the heat energy due to heat transfer from the environment; and P p is the heat energy due to internal heating. Based on Equation 2, the rate of change of the ignition coil temperature can be calculated as follows: dTdt=C0(Te−Tp)+C1(Ta−Tp)+C2Sv(Ta−Tp)+C3F(I¯pΔtN)2Rp, where T e and T a the engine temperature or ambient temperature estimated at 411; I p is an average residence time current in the primary coil; Δt is the residence time for the last ignition; N is the engine speed; R p is the primary coil resistance; S vis the vehicle speed; and C0, C1, C2, and C3 are predetermined calibration constants. The parameter F relates to the engine firing. When the engine is not firing, F = 0; when the engine is firing, F = 1. Thus, the rate of change of the ignition coil temperature (degrees per second) increases with an increase in the difference between the engine temperature and the ignition coil temperature, and increases with an increase in the difference between the ambient temperature and the ignition coil temperature. An increase in the vehicle speed can increase the rate of change of the ignition coil temperature due to increased convective heat transfer.

[0034] The internal resistance heating is the heat generated during the last ignition coil charging. Fig. 3, the primary coil current can be expressed by solving the circuit equation: RtIp+LpdIpdt=Vb, where Rt is the total circuit resistance; I p is the primary coil current, which is also referred to here as the ignition coil current; L p is the inductance of the primary coil; and V b the battery voltage. By releasing I p from equation 4, the following can be obtained: Ip(t)=VbRt(1−e−tRtLp).

[0035] The average residence time current during the last charge can be calculated using the following: Ip¯=VbRtΔt(Δt+LpRt(e−ΔtRtLp−1)).

[0036] The total circuit resistance R t depends on the ignition coil temperature. R t can be calculated as the sum of the primary coil resistance R p and the wiring harness resistance R h expressed as: Rt=Rp+Rh.

[0037] The wiring harness resistance does not change significantly with ignition coil temperature and can therefore be determined in advance during calibration. The primary coil resistance can be determined based on the estimated ignition coil temperature. For example, the controller can read the ignition coil temperature stored in memory and determine the primary coil resistance by checking a predefined lookup table. Fig. Figure 6 illustrates an exemplary relationship between primary coil resistance and ignition coil temperature. Primary coil resistance increases monotonically with increasing ignition coil temperature. Such a relationship may be provided by the ignition coil manufacturer.

[0038] Method 400 updates the ignition coil temperature based on the coil temperature estimated during the previous iteration and a time period from the last spark ignition to the current coil temperature update. As an example, the ignition coil temperature may be updated by weighting the rate of change of the ignition coil temperature by the time period since the last spark ignition: Tp(i+1)=Tp(i)+(dTpdt)iΔt(i), where i indicates the number of iterations; T p(i+1) displays the updated coil temperature; T p(i) indicates the coil temperature of the previous iteration; and Δt (i) indicates the time that has passed since the last ignition coil temperature assessment. As an example, Δt (i) at 404 as the update time interval of the estimated ignition coil temperature.

[0039] At 411, method 400 stores the updated ignition coil temperature in memory.

[0040] At 412, method 400 checks whether the vehicle is operating. If the vehicle stops operating, e.g., key off, method 400 ends. Otherwise, method 400 resets the counter to zero at 415 and continues estimating the ignition coil temperature.

[0041] Fig. 5 illustrates a method 500 for charging the ignition coil based on the estimated ignition coil temperature. Method 500 runs parallel to method 400 and uses the most recent ignition coil temperature estimate from method 400 to determine the dwell time.

[0042] At 501, method 500 determines whether the vehicle is operating. For example, in response to a key-on event, method 500 may determine that the vehicle is operating. If the vehicle is OFF, method 500 continues monitoring the vehicle state at 502. Otherwise, method 500 proceeds to 503.

[0043] At 503, a controller (such as controller 12 from Fig. 1) Engine operating conditions based on readings from various sensors in the engine system. Operating conditions may include engine speed, engine load, engine coolant temperature, available fuel quantity, and fuel composition.

[0044] At 504, control determines whether to initiate spark ignition. As one example, control may determine to start spark ignition once the engine begins running. As another example, control may determine to start spark ignition in response to an engine speed greater than a threshold. Control may determine to start spark ignition based on a spark delay. The spark delay may be determined based on engine operating conditions, including engine speed, engine load, engine temperature, and fuel conditions. If control determines not to initiate spark ignition, method 500 proceeds to 505, where control continues monitoring engine operating conditions. Otherwise, method 500 proceeds to 506.

[0045] At 506, method 500 determines a dwell time of the ignition coil based on the ignition coil temperature. As an example, the controller may load a current estimate of the ignition coil temperature from memory. The controller may also determine an available battery voltage. The dwell time may then be determined based on the loaded ignition coil temperature and the battery voltage via a pre-calibrated lookup table.

[0046] Alternatively, the controller can determine the dwell time each time the ignition coil temperature is estimated. When the ignition spark needs to be generated, the controller charges the primary coil for the specified dwell time.

[0047] At 507, the primary coil may be charged over the dwell time. As an example, an ignition device (such as the ignition device 322 of Fig. 3) be closed for a period equal to the dwell time. After the primary coil charging is completed and the primary coil circuit is interrupted at 508, an ignition spark is generated in the combustion chamber.

[0048] At 509, control detects whether the vehicle has ended operation. Vehicle operation may be determined to have ended in response to a key-off event. If the vehicle is operating, method 500 proceeds to 504. Otherwise, method 500 ends.

[0049] With reference to Fig.7 illustrates variations in engine operating conditions during implementation of methods 400 and 500. The x-axes represent time and increase from left to right, as indicated by the arrows. The first graph from the top represents an ambient temperature. The ambient temperature may be measured by a temperature sensor. The ambient temperature is increasing, as indicated by the y-axis. The second graph from the top represents a vehicle status. The status of the vehicle may be ON or OFF. As an example, the vehicle status may be determined in response to a key-on or key-off event. The third graph from the top represents a vehicle speed. The vehicle speed is increasing, as indicated by the y-axis. The fourth graph from the top represents an engine coolant temperature (ECT). The ECT may be measured by a temperature sensor coupled to the cooling circuit.The ECT increases, as indicated by the y-axis. The ECT can be used to estimate engine temperature. The fifth graph from the top plots the estimated ignition coil temperature over time. A cross indicates the time at which the ignition coil temperature is estimated. The sixth graph from the top illustrates the dwell time, which was calculated based on the ignition coil temperature and the battery voltage. The dwell time is calculated here in response to the respective estimate of the ignition coil temperature. Alternatively, the dwell time can be calculated before each spark ignition. The seventh graph from the top plots an engine ignition or engine firing event in a cylinder. An asterisk indicates the generation of an ignition spark.

[0050] At T0, the vehicle begins operation. For example, in response to a key-on event, the crankshaft begins to crank and the vehicle speed increases from zero. The engine coolant temperature may also increase over time. In response to the vehicle starting, the controller begins estimating the ignition coil temperature and dwell time. The initial ignition coil temperature T p(0)741 can be estimated based on the measured engine temperature and ambient temperature 701 according to Equation 1. The first dwell time 751 is determined based on the first ignition coil temperature 741 and the battery voltage via a lookup table. The coil temperature and dwell time are estimated at an ambient temperature 701, as shown at 746 and 757. The coil temperature and dwell time are estimated at an ambient temperature 702, as shown at 747 and 756. As the ambient temperature decreases, the estimated coil temperature 746 decreases and the dwell time 756 increases.

[0051] At T1, after a period of time P1 from T0, the ignition coil temperature becomes T p(1)742. The time interval P1 is chosen to be shorter than a thermal time constant of the ignition coil. Since there is no engine firing due to engine start-up at T0, the rate of change of the ignition coil temperature can be updated based on equation 3 with F=0. Alternatively, the initial ignition coil temperature can be kept constant at T p(0) The dwell time 752 is calculated based on the coil temperature 402 and the battery voltage.

[0052] At T2, the engine begins firing. As an example, the engine may begin firing in response to an engine speed higher than a threshold. The controller may initiate the first engine firing by charging the ignition coil for a dwell time of 752 seconds.

[0053] At T3, after the time interval P1 from the last assessment of the coil temperature 742, the rate of change of the ignition coil temperature is calculated. The rate of change of the ignition coil temperature can be calculated based on the dwell time of the last firing (i.e., dwell time 752) and the coil temperature 742 according to Equation 3 with F=1. In other words, the rate of change of the ignition coil temperature is calculated based on the last determined dwell time 752. Then, the third coil temperature T p(2) 743 is determined based on the rate of change of the ignition coil temperature according to Equation 8. The dwell time 753 is calculated based on the coil temperature 743 and the battery voltage.

[0054] At T4, the vehicle speed and the engine firing frequency increase. The coil temperature and dwell time are still updated at time interval P1. Thus, the coil temperature and dwell time are updated at a constant frequency, independent of the engine firing frequency. The coil temperature may decrease in response to high vehicle speed due to increasing convective cooling.

[0055] At T5, engine firing is stopped and the vehicle is stopped. In other words, the engine has stopped rotating and the vehicle speed is zero. The controller continues to estimate the coil temperature and dwell time. This way, the estimated dwell time is available when the engine is restarted.

[0056] At T6, the vehicle stops operating. The control system stops estimating the coil temperature and dwell time.

[0057] In this way, the ignition coil temperature can be precisely estimated based on heat transfer from the engine, the ambient air, and internal resistance heating. The ignition coil dwell time can be updated in parallel with the ignition coil temperature estimate. This allows the charging current and the corresponding spark power to be precisely controlled.

[0058] The technical effect of estimating the ignition coil temperature based on heat transfer is that a temperature sensor is not required. The technical effect of estimating the rate of change of the ignition coil temperature based on heat transfer from the engine, the ambient air, and internal resistance heating is that the ignition coil temperature can be estimated accurately. The technical effect of updating the ignition coil temperature at a frequency higher than a minimum frequency is that a deviation between the estimated and the actual ignition coil temperature can be avoided. The minimum frequency is the inverse of the thermal time constant of the ignition coil.The technical effect of updating the ignition coil temperature at a frequency higher than the engine firing frequency is that the heat transfer from the resistive heating generated by the respective engine firing to the ignition coil can be taken into account.

[0059] As one embodiment, a method includes charging an ignition coil for a dwell time determined based on each of an engine temperature, an ambient temperature, and a dwell time for a most recent spark ignition. In a first example of the method, wherein the dwell time is further determined based on a primary coil resistance. A second example of the method optionally includes the first example and further includes estimating the primary coil resistance based on a temperature of the ignition coil. A third example of the method optionally includes one or more of the first and second examples and further includes updating the temperature of the ignition coil at a frequency higher than an engine firing frequency.A fourth example of the method optionally includes one or more of the first through third examples, and further includes determining the dwell time based on vehicle speed. A fifth example of the method optionally includes one or more of the first through fourth examples, and further includes increasing the dwell time as the difference between the engine temperature and an ignition coil temperature increases. A sixth example of the method optionally includes one or more of the first through fifth examples, and further includes increasing the dwell time as the difference between the ambient temperature and an ignition coil temperature increases.

[0060] As another embodiment, the method comprises: estimating an ignition coil temperature; updating the ignition coil temperature based on each of a heat transfer from the engine to the ignition coil, an internal resistance heating of the ignition coil, and a heat transfer from the ambient to the ignition coil; and charging the ignition coil over a dwell time determined based on the updated ignition coil temperature. In a first example of the method, wherein the internal resistance heating of the ignition coil is estimated based on a last determined dwell time, an average dwell time current, and a primary coil resistance. A second example of the method optionally includes the first example and further includes determining an initial ignition coil temperature based on each of an engine temperature and an ambient temperature in response to a key-on event.A third example of the method optionally includes one or more of the first and second examples, and further includes further comprising updating the ignition coil temperature in response to a key-off event. A fourth example of the method optionally includes one or more of the first through third examples, and further includes updating the ignition coil temperature at a frequency independent of an engine firing frequency. A fifth example of the method optionally includes one or more of the first through fourth examples, and further includes estimating heat transfer from the engine to the ignition coil based on an engine temperature and the most recently updated ignition coil temperature.A sixth example of the method optionally includes one or more of the first through fifth examples and further includes estimating heat transfer from the ambient to the ignition coil based on an ambient temperature and the most recently updated ignition coil temperature.

[0061] As yet another embodiment, a system comprises: an engine, a spark plug coupled to the engine, an ignition coil coupled to the spark plug, and a controller configured, using computer-readable instructions stored in non-transitory memory, to: regularly update an estimated ignition coil temperature based on a rate of change of the ignition coil temperature, wherein the rate of change of the ignition coil temperature is a mathematical function of each of an engine temperature, an ambient temperature, and a first dwell time for a most recent spark ignition; charge the ignition coil over a second dwell time determined based on the updated estimated ignition coil temperature.In a first example of the system, the controller is further configured to update the estimated ignition coil temperature based on an average residence time current of the ignition coil. A second example of the system optionally includes the first example and further includes the controller being further configured to update the estimated ignition coil temperature at a frequency determined based on a thermal time constant of the ignition coil. A third example of the system optionally includes one or more of the first and second examples and further includes the controller being further configured to update the estimated ignition coil temperature at a frequency determined based on a vehicle speed.A fourth example of the system optionally includes one or more of the first through third examples, and further includes that the controller is further configured to update the estimated ignition coil temperature by weighting the rate of change of the ignition coil temperature by a time period since the last spark ignition. A fifth example of the system optionally includes one or more of the first through fourth examples, and further includes that the dwell time is further determined based on a battery voltage.

[0062] It is understood that the configurations and routines disclosed herein are exemplary in nature, and these specific embodiments are not to be considered limiting, as numerous variations are possible. For example, the above technique may be applied to V-6, I-4, I-6, V-12, horizontally opposed 4-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various systems and configurations, and other features, functions, and / or characteristics disclosed herein.

[0063] The following claims particularly set forth certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims are to be construed as including the inclusion of one or more such elements and neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application. Such claims, whether broader, narrower, the same, or different in scope than the original claims, are also to be considered included within the subject matter of the present disclosure.

Claims

[1] Method comprising: iterative estimation of an ignition coil temperature; Updating the iteratively estimated ignition coil temperature based on each of heat transfer from the engine to the ignition coil, internal resistance heating of the ignition coil, and heat transfer from the environment to the ignition coil; and Charging an ignition coil over a dwell time determined based on each of an engine temperature, an ambient temperature and a dwell time of a last spark ignition, wherein the internal resistance heating of the ignition coil is estimated based on a last determined residence time, an average residence time current and a primary coil resistance. [2] The method of claim 1, wherein the primary coil resistance is further determined based on each of an engine temperature and an ambient temperature in response to a key-on event. [3] The method of claim 1, further comprising terminating the ignition coil temperature update in response to a key-off event. [4] The method of claim 1, further comprising updating the ignition coil temperature at a constant frequency independent of an engine firing frequency. [5] The method of claim 1, wherein the heat transfer from the engine to the ignition coil is estimated based on an engine temperature and the last determined ignition coil temperature. [6] The method of claim 1, wherein the heat transfer from the ambient to the ignition coil is estimated based on the ambient temperature and the last determined ignition coil temperature. [7] The method of claim 1, wherein the ignition coil temperature is further based on the last determined ignition coil residence current. [8] The method of claim 1, further comprising updating the iteratively estimated ignition coil temperature at a frequency determined based on a thermal time constant of the ignition coil. [9] The method of claim 1, further comprising updating the iteratively estimated ignition coil temperature based on a vehicle speed. [10] The method of claim 1, further comprising updating the iteratively estimated ignition coil temperature by weighting a rate of change of the ignition coil temperature with a time duration from the last iteratively estimated ignition coil temperature. [11] The method of claim 1, further comprising determining the residence time based on a battery voltage. [12] The method of claim 1, further comprising determining the dwell time based on a vehicle speed. [13] System comprising: an engine, a spark plug coupled to the engine, an ignition coil coupled to the spark plug and a controller configured, using computer-readable instructions stored on non-volatile memory, to: periodically update an estimated ignition coil temperature based on a rate of change of the ignition coil temperature, wherein the rate of change of the ignition coil temperature is a mathematical function of each of an engine temperature, an ambient temperature, and a first residence time for a last spark ignition; charge the ignition coil for a second dwell time determined based on the updated estimated ignition coil temperature; wherein the controller is further configured to update the estimated ignition coil temperature based on each of heat transfer from the engine to the ignition coil, internal resistance heating of the ignition coil, and heat transfer from the environment to the ignition coil, where the controller is further configured to update the estimated ignition coil temperature based on an average residence time current of the ignition coil. [14] The system of claim 13, wherein the controller is further configured to update the estimated ignition coil temperature at a frequency determined based on a thermal time constant of the ignition coil. [15] The system of claim 13 or 14, wherein the controller is further configured to update the estimated ignition coil temperature based on a vehicle speed.

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