Patent Grant
9531165
This application claims priority to DE 10 2012 102 168.6, filed Mar. 14, 2012 and DE 10 2012 106 207.2, filed Jul. 10, 2012, which are hereby incorporated by reference in their entirety.
The invention relates to a method for actuating a spark gap in an internal combustion engine, in particular a spark plug, in which the spark gap is assigned a first ignition coil and a second ignition coil, each of which has a primary winding and a secondary winding that are inductively coupled to one another.
EP 2 325 476 A1 discloses a control unit for a spark plug in an internal combustion engine, said unit making it possible to increase the duration of the ignition spark. For this purpose, two ignition coils are assigned to the spark plug and are operated in a manner offset over time (controlled by a control device). The method starts in that a start signal for the ignition of the spark plug comes from an engine control unit, whereupon both primary coils are connected to the vehicle battery or to the dynamo of the vehicle and are charged. This occurs as long as the start signal coming from the engine control unit is present. When it disappears, the two primary windings are discharged by opening semiconductor switches that are arranged in the electrical circuit of the primary windings. As a result, a high voltage is induced in each of the secondary windings, which leads to a discharge between two electrodes of the spark plug. The two semiconductor switches are subsequently opened and closed alternately so that one of the two ignition coils always stores magnetic energy whilst the other delivers the stored energy to the spark plug. If the primary current exceeds a predefined limit value, it is restricted by opening a bypass so that the ignition coils do not reach magnetic saturation. The bypass continues to be opened and closed so as to thus keep constant the energy stored in the ignition coils. The semiconductor switches are switched over whenever the amperage of the secondary current falls below a predefined minimum. This minimum is determined newly in each cycle as a function of the maximum encountered primary current. A diode that blocks the secondary current whilst the primary winding is charged and allows the secondary current to pass whilst the primary winding is discharged is located in the electrical circuit of each secondary winding. To protect the diode against overload, the gradient over time of the secondary current, which is a measure for the magnitude of the secondary voltage, is monitored and is interrupted if a specific voltage level of the ignition process is exceeded. A disadvantage of this prior art is that, in spite of a considerable control effort, it is difficult to create stable conditions at the spark plug for a discharge process lasting for a predefined period of time.
The present invention creates, at low cost in an ignition system of the type mentioned in the introduction, stable conditions at the spark gap, in particular at a spark plug, for generating a discharge process lasting for a predefined period.
The method according to this disclosure for actuating a spark gap in an internal combustion engine, in which the spark gap is assigned a first ignition coil and a second ignition coil, each of which has a primary winding and a secondary winding that are inductively coupled to one another, may include the following steps:
(a) triggered by a start signal, the primary winding of the first ignition coil is charged, and with a delay D, for which 0≦D, the primary winding of the second ignition coil is charged by supplying direct current, wherein, whilst each primary winding is charged, the respective secondary winding is blocked. The start signal is given according to the desired ignition point (ignition timing).
(b) The total primary current flowing in the primary windings is preferably measured constantly.
(c) After a period T after the start signal, the end of said period marking the ignition time-point, the primary winding of the first ignition coil is abruptly discharged, and the primary winding of the second ignition coil is abruptly discharged with the delay D. Secondary currents are thus induced in the respective secondary windings and lead to an electrical discharge between two electrodes of the spark gap.
(d) The total secondary current flowing through the spark gap is preferably measured constantly.
(e) Thereafter the charging of the primary winding of the first ignition coil and of the primary winding of the second ignition coil are alternately started whenever the total secondary current falls below an upper threshold.
(f) The primary windings are then abruptly discharged whenever the total secondary current reaches a lower threshold or whenever the total primary current reaches an upper threshold.
(g) Steps (e) and (f) are repeated until the duration of the discharge process between two electrodes of the spark gap reaches a predefined value Z.
(h) Both primary windings then remain separated from the supply of direct current until there occurs a further start signal and the above sequence of steps is restarted with step (a).
In particular, a spark plug is a possible spark gap. However, instead of a spark plug, other ignition devices may also be used, with which ignition sparks can be generated in an internal combustion engine, for example an electrode, which is inserted through the cylinder head of an engine in an electrically insulated manner and which cooperates with a cylinder wall as a ground electrode so as to form a spark gap. This disclosure will be described hereinafter on the basis of spark plugs. The description is applicable to other spark gaps accordingly.
The start signal, which triggers the sequence of steps according to this disclosure, determines the ignition point for the spark plug and can be emitted for example by an engine control device or by a sensor, which is responsive to the position of a camshaft of the internal combustion engine. Triggered by the start signal, the primary winding of the first ignition coil is charged by supplying direct current. So that no secondary current flows in the respective secondary winding during this process, the secondary winding is blocked, preferably by a diode arranged in the electrical circuit of the secondary winding, whilst the respective primary winding is charged. Instead of a diode, a semiconductor switch located in the electrical circuit of the secondary winding could also be used to block said secondary winding and is controlled by the primary current, such that the semiconductor switch performs a blocking function as long as the primary current flows.
At the start of the method according to this disclosure, the primary winding of the second ignition coil is charged with a delay D compared to the primary winding of the first ignition coil, for which 0≦D. The greater the overlap between the first charging process of the first ignition coil and the first charging process of the second ignition coil, the stronger the total primary current, which is given by adding the currents flowing through the two primary windings. The delay is preferably D≠0, that is to say the two first charging processes do not overlap completely, but only in part. The delay should not be selected to be so great, however, that the two first charging processes taking place at the start of the method according to this disclosure do no longer overlap at all, rather the overlap should lead to an increase in the strength of the first pulse of the total primary current.
In accordance with this disclosure, the total primary current supplied to the primary windings is measured. This measurement is expediently taken in the line coming from the direct current source at a point before this line branches to the two primary windings. If the internal combustion engine drives a vehicle, as is preferred, a vehicle battery or a direct current generator, for example the dynamo of the vehicle, are possible direct current sources. The amperage is measured for example such that a resistor is arranged in the line coming from the direct current source and the voltage drop caused by the direct current is measured at said resistor.
The primary windings are charged in that the current from the positive pole of a direct current source flows through the device for measuring the strength of the primary current, through the first primary winding to the ground pole of the direct current source and also through the second primary winding to the ground pole of the direct current source. The direction of current “from the positive pole of the direct current source to the ground pole” is to be understood in the sense of standard technical language; the electrons flow in the opposite direction. The charging processes of the primary winding of the first ignition coil and of the primary winding of the second ignition coil are to be interrupted before the ignition coil reaches saturation. A considerable distance should be maintained from the state of saturation. It is thus recommended to interrupt the charging processes at the latest when 95% of the saturation amperage has been reached in the primary windings. In a particularly advantageous embodiment of the method, the charging processes are interrupted whilst the amperage in the primary windings still rises approximately linearly. By charging of the primary windings, however, an amount of energy that is sufficient to generate a spark as a result of the subsequent discharge of the ignition coil between two electrodes of the spark plug and sufficient to maintain the discharge thus ignited must be stored in any case for a certain period.
A semiconductor switch is preferably provided in the line from each of the primary windings to the ground pole and is controlled by a control device. The respective semiconductor switch is closed whilst a primary winding is charged. The primary current flowing through the primary winding, the increase of said current being slowed by self-induction, leads to a growth of the energy that is stored in the magnetic circuit of the ignition coil and that energy is released when the primary current is interrupted by opening the semiconductor switch, thus terminating the charging process. Due to the abrupt change of current in the primary winding, a high secondary voltage is induced in the respective secondary winding and results in a secondary current, causing the desired electrical discharge between two electrodes of the spark plug, specifically between a central electrode and a ground electrode arranged at a distance therefrom.
If T is the duration of the first charging process of the primary windings, the offset D over time between these two charging processes should be 0≦D<T. D is preferably approximately half as long as T.
The two ignition coils are discharged in a manner offset over time by the control unit according to this disclosure dependent on the amperages. As a result, the secondary currents in the two secondary windings accordingly occur offset over time. The offset over time is to be selected such that the two secondary currents occurring in different secondary windings do not only overlap in the event of the first discharge of the two primary windings occurring after a start signal, but also with the following discharge processes, so that there are no gaps in the total secondary current supplied to the spark gap or spark plug, respectively. The “total secondary current” is understood to mean the sum of secondary currents, which flow into the two individual secondary windings, formed by superimposing the secondary currents. The total secondary current should not fall below a lower threshold, which is to be selected so as to be so high that the discharge burning between the electrodes of the spark plug does not extinguish if the total secondary current reaches this lower threshold. A switchover, on the primary side of the ignition coil of which the primary winding has just been charged, from charging to discharging is therefore implemented at the latest once this lower threshold of the total secondary current has been reached, and the total secondary current is thus abruptly increased again.
So that the total secondary current can be monitored, it has to be measured. It is expediently measured by providing an ammeter, in particular a resistor, in a line that connects both the secondary winding of the first ignition coil and the secondary winding of the second ignition coil to a ground pole, the drop in voltage being measured at said ammeter as a measure for the amperage of the total secondary current. The measured total primary current and the measured total secondary current are expediently conveyed to a control device, which controls, for both ignition coils, the moment for switching from charging to discharging of the primary winding and the moment for switching from discharging to charging of the primary winding.
After, as a result of the first charging and discharging of the primary winding of the first ignition coil and as a result of the first charging and discharging of the primary winding of the second ignition coil, a discharge has been started between the electrodes of the spark plug, the primary winding of the first ignition coil and the primary winding of the second ignition coil then start to be charged alternately whenever the total secondary current falls below an upper threshold. It can thus be ensured that there is sufficient time available during the current discharge of either of the two primary windings to charge the other primary winding to such an extent that the discharge burning between the electrodes of the spark plug will continue without interruption. The charging of the primary windings ends each time the primary current reaches an upper threshold, which is selected such that sufficient magnetic energy has been stored up to that point in the relevant ignition coil so as to continue without interruption the discharge burning between the electrodes of the spark plug when the ignition coil is discharged. At the latest, the charging of the primary windings thus ends each time the total secondary current coming from above reaches a lower threshold, which is selected such that the amperage of the total secondary current is still sufficient to maintain the discharge burning between the electrodes of the spark plug. The primary winding that has just been charged is switched from charging to discharging at the latest when this lower threshold of the total secondary current is reached, whereby the total secondary current increases abruptly again until above its upper predefined threshold.
The described interaction between the two ignition coils is continued until a preselected duration, during which the discharge is to burn between the electrodes of the spark plug, has elapsed. This duration is referred to in this instance as the ignition period. The two ignition coils are then separated from the direct current supply so that the discharge burning between the electrodes of the spark plug extinguishes. The method according to this disclosure is run through again with the occurrence of the next start signal, which may come from an engine control unit. The method according to this disclosure is run through in full for each spark plug in each operating cycle of the internal combustion engine. The operating cycle consists in a four-stroke engine of four successive strokes, and in a two-stroke engine of two successive strokes.
The threshold values for the primary current and for the secondary current may remain the same or may be changed for each run of the method according to this disclosure. The lower threshold of the secondary current may remain the same for each run of the method according to this disclosure, this being the preferred scenario.
In an advantageous development of the method the upper threshold for the primary current may vary. It may be predefined in a variable manner by an engine control unit according to the operating mode of the internal combustion engine. The fuel consumption of the engine and the pollutant emission of the engine can thus be optimised, for example depending on the engine load and/or on the engine speed and/or on the cooling water temperature and/or on the composition of the exhaust gas, for which the starting signal of a lambda sensor in the exhaust gas system is a useful parameter.
The upper threshold of the total primary current may be changed incrementally or continuously within a run of the method according to this disclosure, provided a discharge burns between the electrodes of the spark plug; if the upper threshold of the total primary current is to be changed, the threshold is preferably changed between two successive runs of the method according to this disclosure.
The upper threshold of the total secondary current can be changed to optimise the fuel consumption and the pollutant emission of the engine in accordance with the manner in which the upper threshold of the primary current is changed.
This disclosure provides considerable advantages:
Another exemplary method differs from the method described above in that, instead of the total primary current and the total secondary current, components thereof, namely the currents flowing into the two individual primary windings and the currents flowing into the two individual secondary windings, are monitored in terms of the moment at which threshold values are reached and are used to help to control the ignition processes. Practically the same ignition current profile and practically the same advantages as in the case of the method described above are achieved.
It also possible to combine the two methods just mentioned by monitoring either the total primary current and the individual secondary currents or the individual primary currents and the total secondary current.
These teachings can be applied to a situation in which more than two ignition coils per spark plug are operated in a coordinated manner and provide their contribution to an ignition current in a cyclically swapped manner, said ignition current flowing without interruption during the desired ignition period.
In an advantageous development of this disclosure, two ignition coils control not only one, but two spark plugs and ignite them simultaneously or approximately simultaneously. The two spark plugs are selected such that they belong to a pair of two cylinders of a spark ignition engine having an even number of cylinders. The cylinders of the spark ignition engine are assigned in pairs to a pair of ignition coils, such that, of the two cylinders forming a pair, one cylinder is always located in the exhaust stroke when the other cylinder of the pair is located in its compression stroke. The two spark plugs are arranged in parallel. If one spark plug ignites in the compression stroke, the other spark plug then ignites in the exhaust stroke, and the situation is reversed in the next engine cycle.
This development is particularly suitable for four-stroke engines. It has the advantage that it is implemented with half the number of ignition coils.
In some embodiments, the charging of the primary winding of the first ignition coil and the charging of the primary winding of the second ignition coil are not started when the strength of the total secondary current falls below an upper threshold, but instead are started when a given time interval t1 or t2, respectively, ends, which begins whenever the strength of the total secondary current falls to a lower threshold or when the strength of the total primary current raises to an upper threshold.
In other embodiments, the charging of the primary winding of the first ignition coil and the charging of the primary winding of the second ignition coil are not started when the strength of the secondary current flowing through the first or second ignition coil, respectively, falls below a threshold. Instead the charging of the primary winding of the first ignition coil is started whenever a given time interval t1 ends, which begins whenever the strength of the secondary current flowing through the first ignition coil falls to a lower threshold or whenever the primary current flowing through the second ignition coil raises to an upper threshold. Likewise, the charging of the primary winding of the second ignition coil is started whenever a given time interval t2 ends which begins whenever the strength of the secondary current flowing through the second ignition coil falls to a lower threshold or whenever the primary current flowing through the first ignition coil raises to an upper threshold.
The time intervals t1 and t2 can be selected to be zero. If they are not selected to be zero, then they are anyway selected so short that the pulse-shaped secondary currents, which flow through the second ignition coil, follow without interruption in time the pulse-shaped secondary currents which flow through the first ignition coil. The pulse-shaped secondary currents can alternately overlap each other in time, instead of follow each other without interruption.
Preferably the time intervals t1 and t2 are so selected, that 0≦t1≦500 μs and 0≦t2≦500 μs. More preferably the time intervals t1 and t2 are so selected, that 0≦t1≦100 μs and 0≦t2≦100 μs.
The time intervals t1 and t2 can be changed, particularly corresponding to settings of an engine control unit. Preferably t1 and t2 are not changed during a run of the method from step (a) to step (b). Preferably t1 equals t2
The methods may be further combined by replacing (i) the feature that charging the primary winding of the first ignition coil and charging of the primary winding of the second ignition coil are alternately started whenever a given time interval t1 or t2 respectively ends with (ii) the feature that charging the primary winding of the first ignition coil is started whenever a given time interval t1 ends, which is started whenever the strength of the secondary current flowing through the first ignition coil falls below a threshold or whenever the primary current flowing through the second ignition coil rises to an upper threshold. Other combinations of the methods described above are also possible and examples are provided below.
The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:
The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.
The circuit arrangement illustrated in
The two primary windings 6 and 7 are connected in parallel to a direct current source Vcc. A device 10 for measuring the strength of the total primary current, that is to say the strength of the current that flows collectively through the two primary windings 6 and 7, is located in the supply line, which connects the direct current source Vcc to both primary windings 6 and 7. The measuring device 10 is connected via a line 13 to the control device 15. A measuring signal is conveyed to the control device 15 via the line 13 and is a measure for the strength of the total primary current.
A controllable switch, in particular a semiconductor switch 8 and a semiconductor switch 9, is arranged in each of the two primary electrical circuits connected in parallel. The semiconductor switch 8 is connected to the control device 15 by a control line 11. The semiconductor switch 9 is connected to the control device 15 by a control line 12.
At the start of the method, the primary windings 6 and 7 are charged with direct current from the direct current source Vcc with closed semiconductor switches 8 and 9. The diodes 2 are connected such that the secondary windings 4 and 5 are blocked during charging of the primary windings 6 and 7. If the semiconductor switch 8 is opened, a very high voltage is produced in the secondary winding 4 due to an abrupt change of current in the primary winding 6 and results in a secondary direct current that flows in the forward direction of the diode 2 in the secondary electrical circuit. As soon as the high voltage exceeds the dielectric strength of the air/fuel mixture between the spark plug electrodes 1a and 1b, a discharge takes place therebetween. The two ignition coils 42 and 43 are controlled such that they operate in push-pull mode, so that a spark does not just flash over temporarily between the electrodes 1a and 1b. Before the discharge between the electrodes 1a and 1b caused by opening the semiconductor switch 8 extinguishes, the semiconductor switch 9 is opened and the semiconductor switch 8 is closed, such that the spark plug is supplied with further energy from the ignition coil 43, whilst a further charging process takes place at the same time in the ignition coil 42. This interaction is continued until the discharge between the electrodes 1a ends with opening of both semiconductor switches 8 and 9.
The method performed in this instance will be described in more detail on the basis of
The method according to this disclosure is initiated by a start signal 24. The start signal 24 may be a rectangular pulse lasting for a period T, of which the rising flank prompts the control device 15 to close the semiconductor switch 8. See the first graph in
With a time delay D after closing the semiconductor switch 8, which preferably corresponds approximately to half the period T, the semiconductor switch 9 is closed, so that a current 27 of increasing amperage starts to flow in the primary winding 7, as illustrated in the third graph in
The primary currents 26 and 27 flowing through the two primary windings 6 and 7 add each other by superimposition in the supply line, in which the ammeter 10 is arranged, to give a total primary current 28, the profile of which is illustrated in the fourth graph in
If the upper threshold 34 of the total primary current 28 is only reached once the period T has elapsed, a control signal is conveyed from the control device 15 to the semiconductor switch 9 and opens said switch, whereupon a high voltage is induced in the secondary winding 5 and allows the total secondary current 31 to rise above a predefined upper threshold 35. See the bottom graph in
If, for any reason, the strength of the total secondary current 31 should reach the lower threshold 36 before the strength of the total primary current 28 has reached the upper threshold 34, the previously closed semiconductor switch is opened in any case and the spark plug is thus supplied with a further current impulse so that the discharge burning between the electrodes 1a and 1b does not extinguish.
The interaction is continued until the discharge burning between the electrodes 1a and 1b has reached a predefined period, the ignition period Z. Once this is the case, both semiconductor switches 8 and 9 are held open by the control device 15 so that the two ignition coils 42 and 43 can discharge completely and the discharge between the two spark plug electrodes 1a and 1b extinguishes.
The described course of the method is performed once in each cycle of the internal combustion engine once it has been started by a start signal 24, which is normally supplied by an engine control unit and determines the ignition point for the spark plug 1.
The sequence of steps summarised in the box to the right in
The method described with reference to
Whereas, in the exemplary embodiment according to
The modified method leads to the same result as the method in the first exemplary embodiment, which can be seen in the bottom graph in
The method performed in the circuit arrangement according to
If
The thresholds 38 and 45 as well as the thresholds 39 and 44 can be used alternatively or jointly. If they are jointly used, then the threshold which is reached first causes the opening of the semiconductor switch 8 or the semiconductor switch 9, respectively. To use the thresholds 38 and 45 as well as the thresholds 39 and 44 gives a greater safety to the method.
The method described with reference to
The exemplary embodiment illustrated in
With the circuit arrangement illustrated in
The primary windings 6 and 7 with closed switches 8 and 9 are first charged with direct current from the direct current source Vcc. The diodes 2 are switched so that the secondary windings 4 and 5 are blocked as the primary windings 6 and 7 are charged. If the switch 8 is then opened, a very high voltage is produced in the secondary winding 4 due to the abrupt change of current in the primary winding 6 and results in a secondary direct current that flows in the secondary circuit of the ignition coil 42 in the forward direction of the diode 2.
Since the two cylinders of the spark-ignition engine in which the sparks plugs 1 and 25 are located are selected such that, when one of the cylinders is in the compression stroke the other cylinder is in the exhaust stroke, only one discharge process of the two discharge processes simultaneously taking place at the two spark plugs 1 and 25 is then used to ignite a compressed fuel/air mixture.
Whilst a spark discharge takes place in the cylinder with the spark plug 1 in the compression stroke and leads to ignition of the fuel/air mixture, the other cylinder with the spark plug 25 is in its exhaust stroke; the exhaust gas provided during the exhaust stroke in the cylinder with the spark plug 25 is subject to a much lower pressure than the fuel/air mixture in the compression stroke. Since the ignition voltage is pressure-dependent, a much lower ignition voltage falls at the spark plug at which a discharge takes place in the exhaust stroke than at the spark plug in the cylinder currently in its compression stroke. As a result, much less energy is consumed for the ignition sparks igniting in the exhaust gas than for the ignition sparks produced in the compressed, as yet unburned fuel/air mixture. The majority of the ignition energy supplied by the two ignition coils 42 and 43 of a cylinder pair is therefore available for the ignition of the fuel/air mixture that is as yet unburned, this being advantageous.
Although in the ignition system according to
Due to the alternating discharge of the two ignition coils 42 and 43, a continuous ignition spark is generated at the spark plugs 1 and 25 in the method explained on the basis of
The circuit arrangement shown in
The circuit arrangement shown in
While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 102 168 | Mar 2012 | DE | national |
| 10 2012 106 207 | Jul 2012 | DE | national |
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| Number | Date | Country | |
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| 20130241429 A1 | Sep 2013 | US |
