The present invention relates to a method for operating an ignition device for an internal combustion engine, particularly of a motor vehicle, having a laser device which has a laser-active solid having a passive Q-switch and generates a laser pulse for eradiating into a combustion chamber, and having a pumping light source which provides a pumping light for the laser-active solid of the laser device.
The present invention also relates to a control unit for such an ignition device, as well as a computer program for a control unit.
A method for operating an ignition device using a laser is described in DE 199 11 737.
Conventional operating methods for ignition devices of the type mentioned at the outset have the disadvantage that different interference effects, such as temperature changes and manufacturing tolerances in the properties of the components used have a negative effect on the exact maintaining of a desired point of ignition, and with that, they impair the combustion process, particularly with regard to having pollutant emissions that are as low as possible and with regard to the process having a high efficiency.
Example embodiments of the present invention provide a method, a control unit and a computer program of the type mentioned at the outset to the extent that, even under the influence of disturbance variables or manufacturing tolerances, the exact maintaining of a desired point of ignition is possible.
According to example embodiments of the present invention, in an operating method of the type mentioned at the outset, a point of ignition, at which the laser pulse is generated, is regulated to a setpoint value, by setting a radiation intensity of the pumping light and/or a pumping duration and/or a pumping starting point and/or a wavelength of the pumping light.
Because of the regulation of the point of ignition, it is advantageously possible to reduce the jitter in time during the generation of laser pulses to values which do not impair an orderly operation, and particularly one that is low in emissions, of the internal combustion engine. When using the regulating method, it is possible, for instance, to limit the jitter in time of laser pulses to values of less than about 10 μs, so that even at high rotational speeds of the internal combustion engine, such as 6,000 rpm, an interference-free operation is ensured.
Additional features, possible uses and advantages of example embodiments of the present invention are described in more detail below in the following description. All of the features described or illustrated constitute the subject matter hereof either alone or in any combination, regardless of the manner they are combined, and regardless of their representation in the description or their illustration in the drawings.
In
Fuel 22 injected into combustion chamber 14 is ignited using a laser pulse 24, which is eradiated into combustion chamber 14 by an ignition device 27 that includes a laser device 26. For this purpose, laser device 26 is fed, via a light guide device 28, with a pumping light that is provided by a pumping light source 30. Pumping light source 30 is controlled by a control and regulating device 32, which also activates injector 18.
Pumping light source 30 may be a semiconductor laser diode, for instance, which, as a function of a control current, emits an appropriate pumping light via light guide device 28 to laser device 26. Although semiconductor laser diodes, and other pumping light sources that take up little space, are preferred for use in the motor vehicle field, for the purpose of operating ignition device 27 according to example embodiments of the present invention, every type of pumping light source is usable, in principle.
As may be seen in
In the configuration of laser device 26 illustrated in
While passive Q-switch 46 is in its idle state, in that it manifests a comparatively low transmission coefficient, laser operation is avoided in laser-active solid 44, or rather, in solid 44, 46 that is bordered by coupling mirror 42 and output mirror 48. However, with increasing pumping duration, the radiation density in laser-oscillator 42, 44, 46, 48 increases, so that passive Q-switch 46 fades, that is, takes on a greater transmission coefficient, and the laser operation is able to begin.
In this manner, a laser pulse 24 is created that is also designated as a giant pulse, which has a relatively high peak power. Laser pulse 24 is coupled into combustion chamber 14 (
If necessary, an optical intensifier 70, for the optical intensification of laser pulse 24, may be assigned to laser-oscillator 42, 44, 46, 48, as shown in
Based on different interference effects such as temperature fluctuations, ageing effects and manufacturing tolerances in the material properties of laser-active solid 44, etc., since, in spite of invariable fire control, a jitter in time, that is, a fluctuation in time of the appearance of laser pulses 24 is able to come about, the point of ignition at which laser pulse 24 is actually generated is regulated to a specifiable setpoint value, according to example embodiments of the present invention.
On this matter,
Within pumping duration t_pump, on account of the irradiation of laser-active solid 44 with pumping light 60, as described before, an inversion of distribution is built up in it which, after the fading of passive Q-switch 46, finally leads to a laser operation, so that, at an actual point of ignition tZ, the laser pulse also designated by reference numeral 24 is emitted.
The actual occurrence of laser pulse 24 as well as corresponding point of ignition tZ are established, according to example embodiments of the present invention, by measuring means that are known per se and are not described in greater detail here, and are supplied to control device 32 for carrying out the regulating method according to example embodiments of the present invention. Since the actual point of ignition tZ is able to fluctuate, principally based on the interference effects described, pumping duration t_pump is advantageously selected such that it is greater than a specifiable time difference between the expected point of ignition and pumping starting time t1. This time difference is therefore designated also as safety time, and it is supposed to ensure that even when there is a delayed generation of laser pulse 24, the pumping light supply will not be interrupted prematurely.
With reference to the flow chart of
As input variable for the method according to example embodiments of the present invention, there is a setpoint value tZ_setpoint, which has been ascertained, for example, by control device 32 of internal combustion engine 10 as a function of other operating parameters, and which states when laser pulse 24 is to be eradiated into combustion chamber 14.
Setpoint value tZ_setpoint is supplied to a first characteristics curve KL1, which forms from this, for instance, a setpoint value I_setpoint for the radiation intensity emitted by pumping light source 30. Setpoint value I_setpoint is subsequently transformed to a corrected setpoint value I_setpoint′, by multiplication with a first correction factor KF1. After that, corrected setpoint value I_setpoint′ is transformed into a corrected setpoint value I_setpoint′, by a further multiplication by a second correction factor KF2.
First correction factor KF1 states a functional interrelationship between a temperature of internal combustion engine 10 and radiation intensity I_setpoint of pumping light source 30 that is actually to be set. In the process, according to example embodiments of the present invention, it is taken into account that laser device 26 has nearly the same temperature as internal combustion engine 10 itself, based on its spatial vicinity to internal combustion engine 10, in the direct environment of combustion chamber 14. Therefore, a temperature change in internal combustion engine 10 also effects a temperature change in laser device 26, and in components 44, 46 included in it.
Temperature changes in laser-active solid 44 also have an effect, for instance, on the generation of laser pulse 24 and the efficiency in the utilization of pumping light 60 that is irradiated into laser-active solid 44, and are accordingly taken into account by the power of correction factor KF1, in order always to ensure the setting of the required radiation intensity I_setpoint for pumping light 60, even at different temperatures of internal combustion engine 10 or of laser-active solid 44. Accordingly, corrected value I_setpoint′ represents a setpoint value for the radiation intensity of pumping light 60 that is cleaned up for the temperature of internal combustion engine 10.
Analogously to taking into account, as described above, the temperature of internal combustion engine 10, if a laser diode is used as pumping light source 30, one can also take into account the interrelationship between the temperature of the laser diode and the radiation intensity emitted by the laser diode and the emitted pumping wavelength of pumping light 60, which presently is indicated by correction factor KF2.
Both correction factors KF1, KF2 may be obtained as a function of the respective temperature and a corresponding characteristics curve, ascertained by measurements, for instance, in a conventional manner. The corresponding characteristics curves for ascertaining correction factors KF1, KF2, as well as characteristics curve KL1 may be stored, for instance, in a preferably nonvolatile memory of control unit 32 (
Corrected setpoint value I_setpoint″ for the radiation intensity, that was obtained in the manner described above, is subsequently compared in a limiter MX to a maximally admissible value for radiation intensity I_max, and, if necessary, it is limited to the latter. Corrected setpoint value I_setpoint′ is subsequently able to be recalculated into a corresponding control current for the laser diode of pumping light source 30, which may also be done via a characteristics curve (not shown).
The subsequent firing control of laser device 26 according to example embodiments of the present invention accordingly takes place by using radiation intensity I_setpoint′, ascertained as described above, for pumping light 60.
Radiation intensity I0 given in
Instead of setpoint value tZ_setpoint, the system deviation may be used directly as input variable in the flow chart as in
In the case of a laser pulse 24 that actually occurs too late, using the method illustrated in
Besides using a radiation intensity of pumping light 60 or a corresponding control current of a laser diode developed as a pumping light source 30, it is further possible to set pumping duration t_pump or pumping starting point t1, as well as a wavelength of pumping light 60, in order to influence the actual position in time of laser pulse 24.
The change in the wavelength of pumping light 60 may be made, for instance, using an active tempering of pumping light source 30 that is arranged as a laser diode.
In the case of influencing point of ignition tZ by a modification of pumping duration t_pump, a limitation of pumping duration t_pump to a maximally admissible pumping duration may advantageously be used in order to avoid thermal overloading of pumping light source 30.
In the method according to example embodiments of the present invention, it is particularly advantageously provided that the regulation of the point of ignition of laser pulse 24 takes place as a function of the rotational speed of internal combustion engine 10. Because of this, it is very advantageously possible to carry out especially precise regulation in particularly time-critical operating ranges, which correspond to comparatively high rotational speeds of internal combustion engine 10, for example, whereas, in other operating ranges having lower rotational speeds of internal combustion engine 10, a less accurate regulation of the point of ignition of laser pulse 24 needs to take place. Depending on the operating point of internal combustion engine 10 and the requirements on the maximum jitter in time of laser pulse 24, different control variables may also be modified in order to adjust the point of ignition.
The operating method for ignition device 27, according to example embodiments of the present invention, may be implemented in the form of a computer program, for instance, that is stored in an electronic memory of control unit 32, and that runs on control unit 32, or rather, on a computer (not shown) that is provided in the unit.
It is possible, quite generally, to influence the temporal position of laser pulse 24 simultaneously by a plurality of the influence variables named above. For example, pumping duration t_pump and radiation intensity IO of pumping light 60 may be modified at the same time, etc.
Slight corrections of the temporal position of laser pulse 24 are particularly able to be implemented by themselves, i.e. by a shifting of pumping starting time t1, whereas, for instance, the total omission of a laser pulse 24 is able to be corrected by a change in the influence variables controlling the laser operation, such as in radiation intensity IO as well as pumping duration t_pump or the wavelength of pumping light 60.
Because of the regulating method according to example embodiments of the present invention, described above, for the point of ignition of laser pulse 24, besides temperature fluctuations, other interference effects, such as different doping of laser-active solid 44 as well as different pumping volumes, may be compensated for, for example, as a function of a different pumping jet formation in the coupling region of pumping light 60 into laser-active solid 44, etc. In the same manner, different initial transmission values of passive Q-switch 46 and its influence on the temporal position of laser pulse 24 are able to be compensated for by the method described herein.
In the same manner, different reflection coefficients of coupling mirror 42 and output mirror 48 for pumping light 60 and laser pulse 24 may also be compensated for.
The principle described herein may also advantageously be used in stationary motors.
Number | Date | Country | Kind |
---|---|---|---|
10 2006 030 722.4 | Jul 2006 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP07/56080 | 6/19/2007 | WO | 00 | 4/13/2010 |