The present invention relates to a method for operating an ignition system for an internal combustion engine, including a first voltage generator (also “primary voltage generator”) and a boost converter. The present invention relates, in particular, to an avoidance of an undesirable spark breakaway during operation.
Ignition systems are used in order to ignite an ignitable mixture in a combustion chamber of a spark ignited internal combustion engine. For this purpose, an ignition spark gap is acted on with electrical energy or a voltage, in response to which the forming ignition spark ignites the combustible mixture in the combustion chamber. The main requirements of modern ignition systems are an indirect result of required emissions and fuel reductions. Requirements of ignition systems are derived from corresponding engine-related approaches, such as supercharging and lean burn operation and shift operation (spray-guided direct injection) in combination with increased exhaust gas recirculation rates (EGR). The representation of increased ignition voltage requirements and energy requirements in conjunction with increased temperature requirements is necessary. In conventional inductive ignition systems, the entire energy required for ignition must be temporarily stored in the ignition coil. The stringent requirements with respect to ignition spark energy result in a large ignition coil design. This conflicts with the requirements for smaller installation spaces of modern engine concepts (“downsizing”). In an earlier application by the applicant, two main functions of the ignition system were assumed by different assembly units. A high voltage generator generates the high voltage necessary for the high voltage spark-over at the spark plug. A bypass, for example, in the form of a boost converter, provides energy for maintaining the ignition spark for continued mixture ignition. In this way, high spark energies may be provided at an optimized spark current profile despite a reduced ignition system design.
High spark currents are more robust in the combustion chamber as opposed to turbulent current, but they are known to result in stronger erosion of the spark plug electrodes. In contrast, small spark currents may result in a spark breakaway in the case of turbulent current in the combustion chamber, in the event the ignition spark energy or the spark current falls below a defined limit. The prior known systems do not satisfactorily exhaust the potential for spark stabilization in ignition systems.
In accordance with an example embodiment of the present invention, spark energy is provided according to demand so that the spark current may be set to a desired value. In this way a compromise may be achieved in a suitable manner between electrode erosion and the tendency toward spark breakaway. The example method according to the present invention for operating an ignition system is particularly suited for a gasoline-operated internal combustion engine, in which particular advantages in spray-guided direct injections and turbo-charged high load EGR are achieved. The ignition system, with which the method according to the present invention is carried out, includes a primary voltage generator and a boost converter, the boost converter being configured to maintain a spark generated with the aid of the primary voltage generator. Via the boost converter, it is possible to bring vehicle electrical system energy to a suitable voltage level and to guide it to the spark gap. The example method according to the present invention is distinguished by ascertaining a modified energy requirement for an ignition spark to be maintained with the aid of the boost converter. In other words, the energy requirement for the ignition spark may vary as a function of an instantaneous operating state and such a variation may be ascertained according to the present invention. In response thereto, the switch-on time of the boost converter, i.e., the point in time at which the boost converter is switched on, is modified in order to dose the ignition spark energy, or ignition spark current and ignition spark voltage according to need. In this way, the spark plug wear is reduced through the avoidance of high spark currents. A particularly severe electrode wear occurs in commercially available spark plugs, for example, at spark currents greater than 100 mA. On the other hand, a spark breakaway resulting from the increase in the power output of the boost converter is avoided by advancing the switch-on time of the boost converter and shifting the transient effect of the boost converter in the direction of “advance,” in particular, before the ignition time, when a lower spark current threshold value is undercut. Since the voltage generated by a boost converter, once switched on, increases over multiple operating cycles, the boost converter may therefore provide higher electrical energy upon ignition of the mixture. The reduction of heat loss in the boost converter by selecting its switch-on time according to need is also an advantage of the present invention. The load of the electrical components (for example, of a high voltage capacitor for intermediate storage of electrical energy) is reduced. The electrical components may therefore be selected more cost effectively when designing the ignition system according to the present invention. In the electrical (control) circuitry as well, less heat loss is generated when the working mode of the boost converter is adjusted to a modified energy requirement. On the whole, the present invention allows for a lower energy consumption and the reliable ignition of the mixture during demanding combustion processes of the ignition system from the vehicle electrical system (for example, of a motor vehicle or a passenger vehicle), as a result of which cable cross sections may be smaller dimensioned and consumption advantages may be achieved. Moreover, lower currents within the ignition system mean a reduction of electromagnetic emissions. In other words, the electromagnetic compatibility (EMC) is improved.
The ascertainment of the modified energy requirement preferably includes a measurement of an ignition spark current or an ignition spark voltage. This may take place using a shunt, for example, via which a current through the ignition spark gap of the ignition system is ascertained. The voltage may be ascertained, for example, with the aid of an electrical circuit, an analog circuit or a microcontroller, or by an ASIC within the ignition system. This requires fewer or no additional hardware outlays for implementing the method according to the present invention.
The ascertainment of the modified energy requirement also preferably includes a comparison of a measured electrical parameter of an ignition spark, or of a signal received by an electronic control unit, with an assigned reference. The reference may, for example, be retrieved from a memory medium.
This reference characterizes threshold values, for example, during the exceeding of which the ignition spark energy should be lowered to avoid erosion and during the undercutting of which the ignition spark energy should be increased to avoid an undesired spark breakaway. For example, threshold values in the form of ignition spark currents and/or ignition spark voltages may be saved as electrical parameters and compared with ascertained parameters. An engine control unit or an ignition control unit may be used as the electronic control unit, the evaluation electronics of which ascertains and provides signals for controlling the operation of the internal combustion engine. The comparison of measured values or control signals with individual threshold values represents a simple mathematical operation which, in terms of circuitry, is implementable in a cost-effective and space-saving manner.
The example method further preferably includes the step of classifying the electrical parameter by assigning a measuring value for the electrical parameter to a predefined parameter interval, for example, within a memory medium of the ignition system. Moreover, the switch-on time may be predefined by the control unit by taking into account the requirements of the combustion process. For example, engine operating states may be ascertained and taken into account. One example for one such state is an exhaust gas recirculation in partial load operation, which results in a relatively homogenous mixture state within the combustion chamber. In such a state, the boost converter is not required to be before the switch-off time of the primary voltage generator (ignition time). An overlap between the operation of the boost converter and the switch-off time (ignition timing) of the primary voltage generator) is advisable at an operating point with exhaust gas recirculation in high-load operation. In turn, an overlap between the operation of the boost converter and the switch-off time (ignition timing) of the primary voltage generator is not required in an operating state in which the catalytic converter is to be heated. In a shift operation, in turn, a non-homogenous mixture composition is present within the combustion chamber, in which an overlap between the operation of the boost converter and the switch-off time of the primary voltage generator is advantageous. The ignition system in this case may be configured to assign suitable switch-on times for the boost converter to respective parameter classes. The switch-on times may, for example, be assigned to the respective parameter class within a memory medium of the ignition system, and applied in response to a classification when determining the switch-on time of the boost converter. This operation is also a low-cost and, in terms of circuitry, simple and rapidly achievable option for implementing the present invention.
The parameter is further preferably ascertained within an FPGA and/or an ASIC of the ignition system. The aforementioned electronic components are situated, for example, within the ignition system, in particular, in the area of each spark plug for controlling the ignition process, the control of the ignition process being able to take place by way of contact with the spark plug. Thus, an implementation of the present invention is possible in this way without further hardware outlays.
The switch-on time is further preferably modified in response to a reduced energy requirement of the ignition system for a successful ignition. If the switch-on time of the boost converter is delayed as compared to the point in time of a switch-off of the primary voltage generator (so that it coincides, for example, with a point in time of a switch-off of the primary voltage generator), the current output and/or the voltage output and/or the power output of the boost converter is reduced at the switch-off time of the primary voltage generator, which results in a reduction of the corresponding electrical variable at the spark gap. In the reversed case, an advanced switching on of the boost converter in response to an increased energy requirement relative to the point in time of a switch-off of the primary voltage generator results in an increase in the current output and/or the voltage output and or the power output of the boost converter. In this way, a spark erosion as well as a breakaway of the ignition spark may be effectively avoided or reduced.
It may be very advantageous if the switch-on time is modified as a function of the operating state and/or as a function of the ascertained energy requirement. According to one exemplary embodiment, the switch-on time in a first ignition process is predefined as a function of the operating state, and for the following ignition processes determined as a function of the ascertained energy requirement. In this way, spark energy is provided according to demand.
It may also be advantageous if the ascertainment of the modified energy requirement in a first step includes the ascertainment of an electrical parameter and/or a change of this parameter and/or a change speed of this parameter, whereby the electrical parameter may be, in particular, a current of the ignition spark and/or a voltage characterizing a voltage of the ignition spark. In a second step, it is checked whether an exceedance condition and/or undercut condition is met, by ascertaining whether a comparison variable exceeds a predetermined upper threshold value and/or undercuts a predetermined lower threshold value. The comparison value is, for example, the ascertained parameter or the change of this ascertained parameter or the change speed of this ascertained parameter. The switch-on time is modified by shifting the switch-on time to a later point in time relative to the switch-off time of the primary voltage generator if the exceedance condition is met, or by shifting the switch-on time to an earlier point in time relative to the switch-off time of the primary voltage generator when the undercut condition is met. In this way, the spark current is adjusted to a value so that neither a spark breakaway is imminent, nor a strong erosion of the spark plug electrode occurs.
The ignition system designed for an internal combustion engine, with the aid of which the example method according to the present invention is carried out, includes a boost converter for maintaining a spark generated with the aid of a primary voltage generator. The ignition system is characterized by an element for ascertaining a modified energy requirement for an ignition spark to be maintained with the aid of the boost converter. In other words, the element is able to ascertain an operating state change of the ignition system or the internal combustion engine, in response to which the spark plug is to be supplied with a modified electrical energy or a modified electrical output in order to avoid both a spark breakaway and excessive wear of the ignition system. In addition, the manipulated variable may be predefined via the control unit as a function of the combustion process. The ignition system according to the present invention also includes an element for modifying a switch-on time of the boost converter in response to an ascertained energy requirement change. This element is configured in accordance with the modified energy requirement to adjust the switch-on time of the boost converter, for example, relative to the crank angle of the internal combustion engine of a speed-dependent variable or relative to the switch-off time of the primary voltage generator in order to feed a modified output to the spark gap. The features, feature combinations and the resulting advantages correspond essentially to those explained in conjunction with the first named inventive aspect, so that in order to avoid repetitions, reference is made to the above explanations.
For example, the ignition system includes a shunt, with the aid of which it is configured to carry out an ignition spark current measurement, in order to ascertain a modified energy requirement. Alternatively, an inference may be made via a voltage measurement about the level of the spark current. A defined output is delivered by the operation of the boost converter. Thus, current and voltage have a fixed relationship to one another. The voltage measurement via the shunt may take place, for example, via an FPGA and/or an ASIC of the ignition system. In addition, an ignition spark voltage ascertained without the use of a shunt may also be used by the aforementioned integrated circuitry for ascertaining a changed energy requirement of the ignition spark gap. In this case, the electrical parameter to be ascertained also includes currents, voltages and/or outputs. Since present ignition systems sometimes include an ASIC at each combustion chamber or at each spark plug, the ignition system may be implemented with minimal hardware outlays or with no additional hardware outlays at all.
In addition, the ignition system also includes memory media, for example, with the aid of which it is configured to classify the instantaneous energy requirement. In other words, the energy requirement measured in the instantaneous operating state may be compared to energy requirement classes within the memory media. In addition, the memory media may hold predefined switch-on times for the boost converter in store, which have proven suitable for the respective energy requirement classes. In this way, a simple and cost-effective implementation in terms of circuitry of the ignition system is possible.
Exemplary embodiments of the present invention are described in detail below with reference to the figures.
Diode 16 is oriented conductively in the direction of capacitance 10. Due to the transfer ratio, a switching operation by switch 27 in the branch of primary side 15_1 also acts on secondary side 15_2. However, since current and voltage according to the transformation ratio are higher or lower on the one side than on the other side of the transformer, more favorable dimensionings for switch 27 for switching operations may be found. For example, lower switching voltages may be implemented, as a result of which the dimensioning of switch 27 is potentially simpler and more cost-effective. Switch 27 is controlled via a control 24, which is connected via a driver 25 to switch 27. Shunt 19 is provided as a current measuring element or voltage measuring element between capacitance 10 and secondary coil 9, the measuring signal of which is fed to switch 27. In this way, switch 27 is configured to react to a defined range of current intensity i2 through secondary coil 9. A Zener diode is connected in the reverse direction in parallel to capacitance 10 for securing capacitance 10. Furthermore, control 24 receives a control signal SHSS. Via this signal, the feed of energy or power output via bypass 7 into the secondary side may be switched on and off. In the process, the output of the electrical variable introduced by the boost converter and into the spark gap, in particular via the frequency and/or pulse-pause ratio, may also be controlled via a suitable control signal SHSS. In addition, according to the present invention, a switch-on time may be shifted via control signal SHSS if the energy requirement of the ignition spark gap changes. A switching signal 32 is also indicated, with the aid of which switch 27 may be activated via driver 25. When switch 27 is closed, inductance 15 is supplied with a current via electrical energy source 5, which flows directly to electrical ground 14 when switch 27 is closed. When switch 27 is open, the current is directed through inductance 15 via diode 16 to capacitor 10. The voltage occurring in response to the current in capacitor 10 is added to the voltage dropping across second coil 9 of step-up transformer 2, thereby supporting the electric arc at spark gap 6. In the process, however, capacitor 10 is discharged, so that by closing switch 27, energy may be brought into the magnetic field of inductance 15, in order to charge capacitor 10 with this energy again when switch 27 is re-opened. It is apparent that control 31 of switch 30 provided in primary side 3 is kept significantly shorter than is the case with switching signal 32 for switch 27. Optionally, a non-linear two-terminal circuit, symbolized by a high voltage diode 33 depicted with dashed lines, of coil 9 of boost converter 7 on the secondary side, may be connected in parallel. This high voltage diode 33 bridges high voltage generator 2 on the secondary side, as a result of which the energy delivered by boost converter 7 is guided directly to spark gap 6, without being guided through secondary coil 9 of high voltage generator 2. No losses across secondary coil 9 occur as a result and the degree of efficiency is increased. An ascertainment according to the present invention of a modified energy requirement for the spark gap is possible through an information technology linking of engine control unit 40, which receives a first signal S40 for setting an operating point of an internal combustion engine and outputs a corresponding second signal S40′ to a microcontroller 42. ASIC 42 is further connected to a memory 41, from which references in the form of limiting values for classes of energy for the instantaneous or future required electrical energy for maintaining the spark gap may be read. ASIC 42 is configured to influence the working mode of boost converter 7, to supply controller 24 with a control signal SHSS modified according to need or temporally shifted, in response to which driver 25 supplies switch 27 with a modified or temporally shifted switching signal 32. For example, boost converter 7 may be switched on sooner or later in response to the receipt of changed switching signal 32, so that the voltage across diode 10 is lower or higher at the switch-off time of switch 30.
According to one exemplary embodiment, switch-on time te is modified in step 300 as a function of the ascertained operating state and/or as a function of the ascertained energy requirement. Switch-on time te may, in particular, be predefined in a first ignition process as a function of the operating state and be determined for the following ignition processes as a function of the ascertained energy requirement.
According to one exemplary embodiment, the ascertainment of the modified energy requirement includes three steps, the ascertainment of an electrical parameter and/or a change of this parameter and or a change speed of this parameter taking place in step 100. The electrical parameter may, for example, be a current of the ignition spark and/or a voltage characterizing a voltage of the ignition spark. In step 200, it is checked whether an exceedance condition and/or an undercut condition is met by ascertaining whether a comparison variable exceeds a predetermined upper threshold value and/or undercuts a predetermined lower threshold value. The exceedance condition is met if the comparison variable exceeds the predetermined upper threshold value. The undercut condition is met if the comparison variable undercuts the predetermined lower threshold value. The comparison variable is, for example, the ascertained parameter or the change of this ascertained parameter or the change speed of this ascertained parameter. Switch-on time te is modified in step 300, for example, by shifting switch-on time te to a later point in time relative to switch-off time ta of primary voltage regulator 2 if the exceedance condition is met, or by shifting switch-on time te to an earlier point in time relative to the switch-off time ta of primary voltage generator 2 if the undercut condition is met. In this way, the spark current is adjusted to a value so that neither a spark breakaway is imminent nor a severe erosion of the spark plug electrode occurs. The shifting according to the present invention of switch-on time te in step 300 may take place in predefinable steps or continuously.
A computer program may be provided, which is configured to carry out all described steps of the method according to the present invention. The computer program in this case is stored on a memory medium. As an alternative to the computer program, the method according to the present invention may be controlled by an electrical circuit provided in the ignition system, an analog circuit, an ASIC or a microcontroller, which is configured to carry out all described steps of the method according to the present invention.
Even though the aspects and advantageous specific embodiments according to the present invention have been described in detail with reference to exemplary embodiments explained in conjunction with the figures, modifications and combinations of features of the depicted exemplary embodiments are possible for those skilled in the art, without departing from the scope of the present invention.
Number | Date | Country | Kind |
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10 2013 223 195.4 | Nov 2013 | DE | national |
10 2014 216 040.5 | Aug 2014 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/072216 | 10/16/2014 | WO | 00 |