Laser spark plug and cleaning method for same

Abstract

A laser spark plug, in particular for an internal combustion engine, having a combustion chamber window through which laser radiation may be emitted from an interior of the laser spark plug toward an exterior, the laser spark plug having a component which surrounds at least part of the beam path of the laser radiation in the area of the exterior. In particular, the laser spark plug, in the area of the component, has at least one channel which has at least two orifice sections and which allows fluid communication between the orifice sections, a first orifice section being situated in the area of an outer surface of the combustion chamber window, and a second orifice section being situated in a radially outer area of the laser spark plug, in particular of the component.

Claims

1. A laser spark plug, for an internal combustion engine, having a combustion chamber window through which laser radiation is irradiatable from an interior of the laser spark plug toward an exterior, comprising: a component which surrounds at least part of a beam path of the laser radiation in an area of the exterior, the component including a first channel through which the laser radiation is directed; at least one second channel, in the area of the component, which includes at least two orifice sections and which allows fluid communication between the orifice sections; a first orifice section situated in the area of an outer surface of the combustion chamber window; and a second orifice section situated in a radially outer area of the laser spark plug, wherein: a longitudinal axis of the first orifice section and a longitudinal axis of the second orifice section are coaxial; the combustion chamber window delimits an interior side and an exterior side of the laser spark plug; a combustion chamber of the internal combustion engine is located in the exterior side of the laser spark plug; the entire first channel and the entire at least one second channel are located in the exterior side of the laser spark plug; the second channel is configured at least in sections as a stepped bore; the first channel has a first opening, a second opening, and an inner surface that delimits the first channel: the laser radiation passes through the first opening and the second opening of the first channel; the first orifice section of the second channel has a first orifice opening which allows fluid communication between the second channel and the first channel; and the first orifice opening is formed on the inner surface of the first channel between the first opening and the second opening of the first channel, wherein a longitudinal axis of at least one first longitudinal section of the second channel situated in the area of the first orifice section points at a radial inward lying area of an outer surface of the combustion chamber window.

2. The laser spark plug of claim 1, wherein the longitudinal axis of the first longitudinal section is oriented so that a point of intersection of the longitudinal axis with the outer surface of the combustion chamber window includes a distance relative to an optical axis of the laser spark plug which amounts to at least 20 percent of a radiation cross section of the laser radiation in the area of the outer surface.

3. The laser spark plug of claim 1, wherein at least one second longitudinal section of the second channel has a diameter of from 0.5 mm to 4.0 mm.

4. The laser spark plug of claim 1, wherein one or the first longitudinal section of the second channel situated in the area of the first orifice section has a diameter of from 0.1 mm to 2.0 mm.

5. The laser spark plug of claim 1, wherein the second channel has at least in sections an internal thread, for receiving a set screw.

6. The laser spark plug of claim 1, wherein the laser spark plug includes a fastening arrangement in a radially outer area for mechanically connecting to a target system, and wherein the second orifice section is situated in the area of the fastening arrangement.

7. The laser spark plug of claim 1, wherein the component includes at least one of a diaphragm and a prechamber.

8. A method for cleaning a laser spark plug, for an internal combustion engine, the method comprising: emitting, through a combustion chamber window, laser radiation from an interior of the laser spark plug toward an exterior, the laser spark plug having a component which surrounds at least part of the beam path of the laser radiation in an area of the exterior, the component including a first channel through which the laser radiation is directed, wherein the laser spark plug in an area of the component has at least one second channel which has at least two orifice sections and which allows fluid communication between the orifice sections, a first orifice section being situated in the area of an outer surface of the combustion chamber window, and a second orifice section being situated in a radially outer area of the component of the laser spark plug; and applying at least one of a cleaning fluid and an ultrasound to the second orifice section, wherein: a longitudinal axis of the first orifice section and a longitudinal axis of the second orifice section are coaxial; the combustion chamber window delimits an interior side and an exterior side of the laser spark plug; a combustion chamber of the internal combustion engine is located in the exterior side of the laser spark plug; the entire first channel and the entire at least one second channel are located in the exterior side of the laser spark plug; the second channel is configured at least in sections as a stepped bore; the first channel has a first opening, a second opening, and an inner surface that delimits the first channel; the laser radiation passes through the first opening and the second opening of the first channel; the first orifice section of the second channel has a first orifice opening which allows fluid communication between the second channel and the first channel; and the first orifice opening is formed on the inner surface of the first channel between the first opening and the second opening of the first channel, wherein a longitudinal axis of at least one first longitudinal section of the second channel situated in the area of the first orifice section points at a radial inward lying area of an outer surface of the combustion chamber window.

9. The method of claim 8, wherein a lance is inserted at least partly into the second orifice section to deliver the at least one of the cleaning fluid and the ultrasound.

10. The laser spark plug of claim 1, wherein the longitudinal axis of the first longitudinal section is oriented so that a point of intersection of the longitudinal axis with the outer surface of the combustion chamber window includes a distance relative to an optical axis of the laser spark plug which amounts to at least 40 percent of a radiation cross section of the laser radiation in the area of the outer surface.

11. The laser spark plug of claim 1, wherein at least one second longitudinal section of the second channel has a diameter of from 1.0 mm to 2.0 mm.

12. The laser spark plug of claim 1, wherein one or the first longitudinal section of the second channel situated in the area of the first orifice section has a diameter of from 0.2 mm to 1.0 mm.

13. The laser spark plug of claim 1, wherein the second channel is situated on a side of the combustion chamber window facing a combustion chamber of the internal combustion engine.

14. The method of claim 8, wherein the second channel is situated on a side of the combustion chamber window facing a combustion chamber of the internal combustion engine.

15. The laser spark plug of claim 13, wherein the second channel includes at least in sections an internal thread for receiving a set screw.

16. The method of claim 14, wherein the second channel includes at least in sections an internal thread for receiving a set screw.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a laser-based ignition system for an internal combustion engine having a laser spark plug which includes a prechamber.

(2) FIG. 2 schematically shows an end area of a first specific embodiment of a laser spark plug according to the present invention which faces the combustion chamber.

(3) FIG. 3 schematically shows a partial cross section of one further specific embodiment according to the present invention.

(4) FIG. 4 schematically shows a partial cross section of a laser spark plug according to the present invention to which a cleaning device is attached.

(5) FIG. 5 shows a detailed view of an end section of a laser spark plug according to the present invention which faces the combustion chamber, according to another specific embodiment. and

(6) FIG. 6 schematically shows a simplified flow chart of one specific embodiment of the method according to the present invention.

DETAILED DESCRIPTION

(7) FIG. 1 schematically shows a laser-based ignition system of an internal combustion engine, in which a laser spark plug 100 is situated in the area of a cylinder head of the internal combustion engine in such a way that an end section of laser spark plug 100 facing the combustion chamber protrudes in a manner known per se into combustion chamber 200 of the internal combustion engine.

(8) In the present case, laser spark plug 100 is supplied via a light guiding arrangement 22 with pump radiation which is provided by a pump light source 20. Laser spark plug 100 may, for example, include an integrated passive Q-switched solid state laser 102, which, when impacted by pump light from pump light source 20, generates high-energy laser ignition pulses in a manner known per se.

(9) Situated optically downstream from solid state laser 102 are focusing optics 104 which focus the generated laser radiation on an ignition point IP situated in prechamber 120a. In other embodiments (cf. for example, FIG. 3), the ignition point IP is situated directly in the combustion chamber. In the present case, an interior of laser spark plug 100 is delimited in the direction of prechamber 120a by a combustion chamber window 106 through which laser radiation L irradiates.

(10) FIG. 2 shows a detailed view of an end area of a laser spark plug facing the combustion chamber according to one specific embodiment of the present invention.

(11) The laser spark plug, similar to the schematic representation according to FIG. 1, includes a prechamber 120a into which laser radiation L may be irradiated through combustion chamber window 106 for igniting an air/fuel mixture contained in prechamber 120a.

(12) To protect outer surface 106a of combustion chamber window 106, the laser spark plug according to FIG. 2 has a diaphragm 120b, also referred to as a light path or light path element. Diaphragm 120b, in the present case by virtue of its somewhat truncated cone-shaped orifice, makes it possible on the one hand to apply laser radiation L to prechamber 120a from the interior area I of the laser spark plug situated on the left in FIG. 2, while at the same time protecting outer surface 106a of combustion chamber window 106 against dirt particles from prechamber 120a, because diaphragm 120b shields off at least areas of outer surface 106a of combustion chamber window 106.

(13) Prechamber 120a of the laser spark plug illustrated in FIG. 2 also includes so-called overflow channels 120a which allow fluid communication between prechamber 120a and space 200 surrounding it, for example, combustion chamber 200 of the internal combustion engine.

(14) In conventional laser spark plugs which have a prechamber, combustion chamber window 106, in particular outer surface 106a, may only be cleaned by introducing a cleaning fluid via overflow channels 120a into the interior of prechamber 120a, from where it contacts outer surface 106a of combustion chamber window 106 through the opening of diaphragm 120b. As a result, cleaning conventional laser spark plugs having a prechamber or diaphragm is costly and is only relatively minimally effective.

(15) Hence, according to the present invention, the laser spark plug has at least one channel 122 which includes at least two orifice sections 122a, 122b and allows fluid communication between orifice sections 122a, 122b. According to the present invention, it is provided that a first orifice section 122a of channel 122 is situated in the area of outer surface 106a of combustion chamber window 106, and that a second orifice section 122b of channel 122 is situated in a radially outer area of laser spark plug 100, in particular of diaphragm 120b or prechamber 120a.

(16) In this way it is possible to introduce, particularly advantageously in the radially outward area of laser spark plug 100, a cleaning fluid from outside into channel 122 which is guided through channel 122 directly to surface area 106a to be cleaned of combustion chamber window 106.

(17) This means that during cleaning of laser spark plug 100 according to the present invention, a fluid transport of cleaning fluid takes place from exterior 200 or the radially outward area of prechamber 120a through channel 122 onto outer surface 106a of combustion chamber window 106. Cleaning fluid deflected from outer surface 106a may exit the laser spark plug or prechamber 120a advantageously through overflow channels 120a.

(18) In one further advantageous specific embodiment at least two channels 122 according to the present invention are provided, at least one first channel 122 capable of being used to deliver cleaning fluid to combustion chamber window 106, with at least one additional channel (not shown) being used to drain the delivered cleaning fluid from the area of prechamber 120a into exterior 200.

(19) Channel 122 according to the present invention may also have more than two orifice sections and thus, for example, may have a Y-shaped branching (not shown) and the like, at least two orifice openings 122a, 122b as described above to be arranged to allow easy cleaning of combustion chamber 106 from outside laser spark plug 100.

(20) In one further particular specific embodiment of the invention, see the detailed view in FIG. 5, it is provided that a longitudinal axis of at least one first longitudinal section LA1 of channel 122 situated in the area of first orifice section 122a points essentially at a radially inward lying area B1 of outer surface 106a of combustion chamber 106 so that it allows cleaning fluid to be efficiently applied to combustion chamber window 106.

(21) In one particular specific embodiment, it is provided that the longitudinal axis of first longitudinal section LA1 is oriented in such a way that a point of intersection of the longitudinal axis with outer surface 106a of combustion chamber window 106 includes a distance Y (FIG. 2) relative to optical axis OA of laser spark plug 100, which amounts to at least 20%, which may be at least 40%, of a radiation cross section of laser radiation L in the area of outer surface 106a. This essentially eccentric impact on combustion chamber window 106 results in a particularly good cleaning effect.

(22) In one further advantageous specific embodiment, see FIG. 5, it is provided that at least one second longitudinal section LA2 of channel 122 has a diameter Z2 of from approximately 0.5 mm to approximately 4.0 mm, in particular from approximately 1.0 mm to approximately 2.0 mm.

(23) In one further advantageous specific embodiment, it is provided that longitudinal section LA1 of channel 122 situated in the area of first orifice section 122a has a diameter Z1 of from approximately 0.1 mm to approximately 2.0 mm, in particular from approximately 0.2 mm to approximately 1.0 mm.

(24) FIG. 3 shows one further specific embodiment of the laser spark plug according to the present invention in which the laser spark plug is fitted not with a prechamber 120a (FIG. 2), but rather with a diaphragm 120b. Even in this invention variant at least one channel 122 may be provided for applying cleaning fluid to outer surface 106a of combustion chamber 106. As is apparent from FIG. 3, diaphragm 120b may also be configured as one piece with housing 100 of the laser spark plug.

(25) FIG. 4 shows a laser spark plug 100 according to the present invention having channel 122 according to the present invention, which, due to its suitability for cleaning laser spark plug 100 and its combustion chamber window 106, is also referred to as a flushing channel, and a cleaning device 300 situated around the end area of laser spark plug 100 which faces the combustion chamber. Cleaning device 300 includes an inlet Z for delivering cleaning fluid which is guided via inlet Z into an annular groove R. Cleaning device 300 may be mechanically connected to laser spark plug 100 in such a way that fluid communication is also established between annular groove R and flushing channel 122 according to the present invention, see FIG. 4. In this way the cleaning fluid delivered to cleaning device 300 passes from inlet Z via annular groove R into flushing channel 122 and thus onto the outer surface of combustion chamber window 106.

(26) A return flow of the cleaning fluid applied to combustion chamber window 106 to outlet A of cleaning device 300 may take place in the configuration illustrated in FIG. 4 via the overflow channels of the prechamber. The used fluid may be filtered, re-pressurized and delivered again to inlet Z, thereby advantageously resulting in a cleaning fluid circulation.

(27) Cleaning device 300 may advantageously also include an arrangement for tempering, in particular heating, of the cleaning fluid, which may result in the shortening of a cleaning period. The heater may be advantageously configured in such a way that the cleaning fluid is heated to below boiling point or also at most up to a predefinable limit of approximately 50 C. in order to prevent burns when handling device 300.

(28) As previously mentioned, FIG. 5 shows a detailed view of an end area of laser spark plug 100 according to the present invention which faces the combustion chamber. A first longitudinal section LA1 of channel 122 according to the present invention is, as is apparent from FIG. 5, oriented in such a way that it points essentially at a radially inward center area of outer surface 106a of combustion chamber window 106, making possible a precise application of cleaning fluid to the optically active outer surface of combustion chamber window 106. If first longitudinal section LA1 has a smaller diameter than at least one further second longitudinal section LA2 connected thereto in the axial direction of channel 122, a jet effect for fluid flowing through channel 122 may be caused in a manner known per se so that it may influence a flow rate of cleaning fluid streaming onto combustion chamber window 106. In the present case, first longitudinal section LA1 has a first diameter Z1, and second longitudinal section LA2 has a second diameter Z2>Z1. The configuration of channel 122 illustrated in FIG. 5 may be advantageously configured as a stepped bore, making it possible to produce the laser spark plug according to the present invention and its housing 100 particularly economically.

(29) The outer orifice or outer orifice section 122b of channel 122 is particularly advantageously situated in the area of an external thread 108, with which laser spark plug 100 may be screwed into a cylinder head. This advantageously ensures that channel 122 is sealed off from its surroundings while laser spark plug 100 is screwed into the cylinder head.

(30) Alternatively or in addition, an internal thread 122c may also be provided in channel 122, into which a set screw may be screwed in order to seal off channel 122.

(31) Angle of channel 122 or at least its end section facing combustion chamber window 106 or its longitudinal axis LA1 is, in one further specific embodiment, advantageously selected in such a way that a point of intersection of the corresponding longitudinal axis with outer surface 106a of combustion chamber window 106 extends a distance Y relative to optical axis OA or beam path S of laser spark plug 100, which amounts to at least approximately 20%, which may be at least approximately 40%, of a beam cross section of laser radiation L in the area of outer surface 106a, see reference symbol S in FIG. 5, resulting in a particularly efficient cleaning.

(32) Alternatively, the degree of distance between a point of intersection of the outer edge of channel 122 in area 122a with combustion chamber window 106 and optical axis OA or beam path S may be selected to be so large that it corresponds to the laser beam radius on outer surface 106a or to at least approximately 75% thereof, see reference symbol Y in FIG. 5.

(33) According to the present invention, the cleaning fluid may be introduced with a tube or a lance which may be screwed directly or with a flange in an internal thread of flushing channel 122. Thereafter, the cleaning fluid may, as previously described, exit the laser spark plug or its prechamber via light path-element 120b or overflow channels 120a.

(34) In the design of channel 122 having at least two different cross sections, it may be advantageously ensured that when using a lance which is inserted from the outside into channel 122, the lance may not be inserted so deeply into channel 122 that it comes into contact with combustion chamber window 106. In addition, this allows the position of the lance to be precisely determined.

(35) A weak, aqueous acid may be provided as a cleaning fluid for use with the at least one channel 122 according to the present invention, for example, an aqueous solution of acetic acid, in particular a 30% acetic acid solution. Alternatively, the cleaning fluid may also contain between approximately 10% and approximately 80%, which may be between 15% and approximately 50% acetic acid (C.sub.2H.sub.4O.sub.2) diluted in water (H.sub.2O).

(36) All other aqueous acids which are weakened or diluted to the point that they do not attack the laser spark plug or combustion chamber window 106 itself may likewise be considered, in particular if they are able to dissolve oil ash such as, for example, calcium sulphate (anhydride) or calcium phosphate compounds.

(37) FIG. 6 shows a simplified flow chart of one specific embodiment of the method according to the present invention. In a first step 400 a lance (not shown) is inserted from the outside into channel 122 (FIG. 1) in order to supply channel 122 with a cleaning fluid.

(38) In a subsequent step 410 the cleaning fluid is injected under pressure from the lance into channel 122 and finally onto combustion chamber window 106, then drained through the conical aperture of diaphragm 120b (FIG. 5) or overflow channels 120a out of laser spark plug 100 or interior I of prechamber 120a.

(39) In one further specific embodiment at least one further step may also advantageously follow after step 410, for example, rinsing with a neutral liquid, for example, purified water, ethyl alcohol (ethanol), isopropanol, in order to protect the spark plug from corrosion. A quick drying liquid that evaporates without residue is advantageous.