Further features and details of the present invention will be apparent from the specific description hereinafter. In the drawing:
FIGS. 1 through 3 serve to describe an embodiment by way of example according to the invention in which the laser light is transmitted through the light deflection element,
FIGS. 4 and 5 serve to describe alternative configurations according to the invention of the embodiment of FIGS. 1 through 3, and
FIG. 6 serves to describe an embodiment in which the light deflection element operates with reflected laser light beams.
With all illustrated embodiments, there is proposed a respective apparatus according to the invention which in a continuously operating arrangement without involving a high level of additional complication and expenditure distributes laser radiation produced by a pump diode or pump diode arrangement or other suitable light source in a pulsed mode of operation on to a plurality of exit light waveguides which can transport the laser radiation in further succession to the laser resonators or laser amplifiers to be pumped—preferably of the cylinders. The proposed arrangements ensure sufficiently long optical superpositioning of the light source 3 or entry light waveguide 1 and the respective exit light waveguides 2 without interrupting the continuous movements involved. When using laser ignition arrangements for internal combustion engines, it is desirably provided in that respect that synchronisation devices are provided for synchronising the rotary movement of the light deflection element 4 with the rotary speed and the required ignition angle of the internal combustion engine. For that purpose, the apparatus shown in FIGS. 1 through 3 has the drive 15 for the light deflection element 4, the drive being described in greater detail hereinafter with reference to FIG. 2.
As shown in particular in FIG. 1, the laser light generated by the light source 3 which is in the form of a plurality of laser diodes is coupled into a focusing optical means 7 after collimation and operationally implemented re-stacking. The optical means 7 serves for generating the focus 17 of the laser light. Provided for distributing the laser light on to a plurality of exit light waveguides 2—here in the form of optical fibers—is the rotating light deflection element 4 which is displaced in a continuous rotary movement by way of the drive 15 which is described in greater detail hereinafter. In the illustrated embodiment the light deflection element 4 is in the form of a slightly wedge-shaped prism which rotates synchronously with the speed of rotation of the internal combustion engine about the focusing axis 22 and thereby causes a slight defined angular deflection of the focus 17 of the laser light with respect to the focusing axis 22. In that respect it is possible for the configuration to be based in particular on a slightly wedge-shaped prism if at least two of the wedge surfaces of the wedge-shaped prism include with each other an angle of a maximum of 10°, preferably a maximum of 5°. The slight angular deviations between the focus 17 and the focusing axis 22 are desirably in an angular range of between 0.5° and 5°, preferably in an angular range of between 1° and 2°. On the assumption of a focal length of the focusing optical means 7 of 30 mm and a spacing between the prism 4 and the beam entry surface 8 of 20 mm, with the data of the calculation example hereinafter, that affords a deflection angle in respect of the beam of 1.5° and a prism angle of 3° when using conventional kinds of glass with a refractive index of 1.5. By rotation of the prism and the angular deviation achieved in respect of the focus 17 the laser light generated by means of the light source 3 is successively deflected on to the individual light entry surfaces 8 of the exit light waveguides 2. In the preferred arrangement as shown in FIG. 3 the light entry surfaces 8 of the exit light waveguides 2 are arranged in mutually adjoining paired relationship on a closed line—here in the form of a circle 14. In that respect the rotationally symmetrical arrangement of FIG. 3 is preferred. That is afforded if the exit light waveguides 2 are wound around a common center 9 at least in the region of the apparatus. In principle however it is also possible to adopt arrangements differing from that rotational symmetry in respect of the laser light entry surfaces 8 of the exit light waveguides 2. In order not to have to interrupt the continuously rotating movement of the light deflection element 4 the exit light waveguides or the light entry surfaces 8 thereof should be of a suitably large cross-section dF so that sufficiently long superpositioning of the area of the focus 17 of the laser light with the respective light entry surface 8 is guaranteed. If required for that purpose the coating of the optical fibers can be removed.
In order to achieve maximum possible density in the arrangement of the light entry surfaces 8 the cross-section of the center 9 should be kept as small as possible. A dense arrangement of the laser light entry surfaces 8 contributes to the fact that, within the pump duration of the laser diodes forming the light source 3, the area of the focus 17 of the pump laser light overlaps the light entry surface 8 of the respective light exit waveguide 2 for a sufficiently long time. In general a number of exit light waveguides 2, corresponding to the number of cylinders of the internal combustion engine, is to be provided.
The following calculation formulae apply:
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Predetermined parameters:
Fiber diameter: df
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Rotary speed: n
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Number of cylinders: z
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Focal point diameter: dB
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That gives:
sector angle α = 360°/z
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The radius of the center point circle:
rM = df/(2 sin (α/2))
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The diameter of the central part:
d1 = 2(rM − df/2)
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The coupling-in internal of the focal point:
tE = [(df − dB)/(2rMΠ)]/(n/60)
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Applicant: deadline: (n/60) in the case of two-stroke operation, (2n/60) in the case of four-stroke operation and 2-times stepdown of the prism drive.
That coupling-in interval is to be longer than the pump duration of the laser medium. For that purpose it is necessary for the diameter of the focal point dB to be sufficiently small in relation to the diameter of the waveguide df.
FIG. 3 thus shows, on the basis of its eight exit light waveguides 2, an embodiment of a multiplexer for an eight-cylinder internal combustion engine. In the illustrated embodiment there is provided a fiber diameter df of the exit light waveguides 2 of 600 μm in each case. That results in a minimum diameter d1 of the center 9 of 968 μm. With a rotary speed of 6000 revolutions per minute a point on the center point circle 14 of the radius rM=783 μm, in the typical pump operating duration of 250 μs (microseconds), passes over a distance of 123 μm (micrometers) in the two-stroke mode and 61.5 μm in the four-stroke mode. In this example that means that, with a diameter in respect of the focus 17 of 400 μm, the laser light can still be coupled for a sufficiently long period into the respective exit light waveguides 2, with a sufficient safety margin.
FIG. 2 shows in an embodiment how the drive 15 for producing the rotary movement of the light deflection element can be designed. What is important for proper operability is a motor 5 which is accurate in terms of its position and which can be matched to the rotary speed and a rotary angle of the internal combustion engine to be ignited. Preferably electric motors and in particular synchronous motors are used for that purpose. In order to ensure a movement of the light deflection element 4, which is as continuous as possible, the arrangement comprises a step-down transmission or reduction gear unit 6—similarly to a clockwork mechanism. In the illustrated embodiment that transmits the rotary movement to a cylindrical receiving means 20 in which the prism forming the light deflection element 4 is held. The cylindrical receiving means 20 is supported in two bearings 21 and rotates together with the prism. The motor 5 is actuated by an electronic monitoring and control system 16 which determines the rotary speed of the motor 5 in dependence on the rotary speed presetting 18 of the internal combustion engine and the ignition angle presetting 19 which is preferably taken from a mapping. The advantages of the arrangements shown in FIGS. 1 through 3 are in particular that the beam path is only slightly deflected by the weakly optically deflecting light deflection element 4 but is otherwise not substantially changed. The precision demands on the mechanical components of the illustrated apparatus are low. The sole moving optical part is the deflection prism. The light source 3, the focusing optical means 7 and the exit light waveguides 2 are not moved. Errors in orientation—such as misalignment or out-of-true—have only a slight effect on the resultant beam deflection because of the small aperture angle necessary. The necessary aperture angle of the deflection prism can be easily achieved with the necessary degree of accuracy, in the state of the art. The necessary precision in respect of the arrangement of the light entry surfaces 8 of the exit light waveguides 2 can be maintained with a low level of complication and expenditure because of the reproducible and accurate diameter of the fibers and the static arrangement.
FIGS. 4 and 5 show two alternatives to the embodiment described hereinbefore. In FIG. 4 the rotating prism as the light deflection element 4 is disposed in front of the focusing lens 23 of the focusing optical means 7. That variant can be adopted if the space between the focusing lens 23 and the exit light waveguide 2 is small.
As shown in FIG. 5 the light deflection element 4 can also be embodied by suitable tilting of the focusing lens 23. In that case therefore the tilted focusing lens 23 is rotated as the light deflection element 4.
As already explained in the opening part of this specification, in contrast to the embodiments of FIGS. 1 through 5, FIG. 6 shows an arrangement according to the invention in which the light is deflected at the rotating light deflection element 4 by reflection, in respect of its direction of propagation. In the case of this group of embodiments it is preferably provided that the light deflection element 4 is of a substantially annular and/or disk-shaped configuration and has a reflection surface 10 at its inside face or surface. In that respect, in the case of the embodiments which can be particularly well governed in mechanical terms and which continuously rotate in one direction of rotation, it is preferable if the reflection surface 10 extends in at least one direction in space over an angular range of 360°. Both in the case of light deflection elements 4 which are of an annular configuration and also those which are of a disk-shaped configuration it is desirable if the reflection surface 10 has a sequence of mutually tilted, preferably immediately adjoining, curved surface segments, preferably spherical surface segments 11. The curved surface segments of the reflection surface 10 are in that case usually in the form of mirrors involving a different inclination. The rapidity of the switching-over operation depends on the periphery of the disk or ring forming the light deflection element 4—like on the speed of revolution and the laser beam diameter.
In the embodiment shown in FIG. 6 the light deflection element 4 is of an annular configuration. It rotates about the axis of rotation 12. The entry light waveguides 1 and the exit light waveguides 2 as well as the associated laser light exit surfaces 13 and laser light entry surfaces 8 in this embodiment are arranged stationarily centrally within the light deflection element 4 of an annular configuration. The illustrated embodiment has two entry light waveguides 1, the laser light of which is respectively distributed on to a plurality of exit light waveguides 2. For distribution of the laser light the annular rotating light deflection element 4 has a reflection surface 11 formed from a succession of differently inclined spherical surface segments 11. The spherical surface segments 11 are each of the same spherical radius and are in directly adjoining relationship. The reflecting surfaces are respectively in the form of mirrors. The mirrors forming the spherical surface segments 11 are each curved in such a way that the center of the curvature is the center of rotation of the ring. That is achieved by the center points of at least two and preferably all spherical surface segments 11 being disposed on the axis of rotation 12 of the annular light deflection element 4. That ensures that the laser beam is constantly coupled into one of the exit light waveguides 2 when passing through a sector or a spherical surface segment 11. The curvature of the mirrors or spherical surface segments 11 is so selected that the focusing of the laser beam is the same at each mirror and the laser beam is not distorted thereby. In order to achieve the necessary tilt angle between the individual spherical surface segments 11 the center points of each two adjacent spherical surface segments 11 are disposed in mutually displaced relationship in the direction of the axis of rotation 12 of the annular light deflection element 4. They are therefore displaced relative to each other in their vertical height. The angular deviation of the laser beams should be as small as possible so that the beam is distorted as little as possible. It is desirable in that respect if the magnitude of the angle between a laser light beam issuing from the light source 3 and/or the entry light waveguide 1 and the laser light beam reflected at the light deflection element 4 is at most 45°, preferably at most 20°, in which respect negative as well as positive angles are possible. The path between the laser light exit surface 13 of the entry light waveguide 1 and the point of impingement on the mirror and the distance between that point of impingement and the light entry surface 8 of the respective exit light waveguide 2 should be approximately the same for each spherical surface segment 11. That spacing, by virtue of the focusing properties of the curved spherical surface segments 11, should correspond approximately to half the radius thereof. The greater that radius is, the correspondingly smaller must the tilt angle be, with the same spacing in respect of the beam being coupled in. Slight distortion phenomena which the angular deviation causes can possibly be compensated again by an aspherical curvature if the construction requires a greater tilt angle. With a high degree of beam divergence a respective collimator can be arranged in the laser exit surfaces 13 of the entry light waveguide 1.
In the variant shown in FIG. 6 the laser light is divided by two entry light waveguides 1 on to respective pluralities of exit light waveguides 2. That is an attractive proposition in particular when laser ignition arrangements are to be provided for V-engines as here the laser beam must be divided in phase-displaced relationship for each bank of cylinders, for which purpose two multiplexers would otherwise be required. By a suitable increase in the number of entry light waveguides 1 and exit light waveguides 2 it is also possible to replace more than two multiplexers by means of an apparatus according to the invention. That is always desirable in order to keep the reflection angles low if as shown in FIG. 6 the entry light waveguide or waveguides 1 is or are arranged centrally between the exit light waveguides 2 associated with it or them. The variant shown in FIG. 6 permits a rapid switching-over action. The distance in which the laser light beam can freely propagate in air can be kept small. Furthermore the distance in which the laser beam propagates freely in air also remains constant over the entire spherical surface segment 11. In addition a focusing effect occurs with the spherically curved mirrors 11. That means that it is possible to dispense with an additional focusing lens. The curvature of the mirrors or spherical surface segments 11 can be so selected that an astigmatic beam acquires a symmetrical intensity profile. The laser light beam, on passing through a spherical surface segment 11, is deflected in a stable condition on to only one respective light entry surface 5 of an exit light waveguide. The rotation of the light deflection element 4 means that there is a low level of loading on the reflection surface 10 as the laser light constantly impinges on a different location of the reflection surface 10 by virtue of the rotation of the laser light. The drive for rotation of the annular light deflection element 4 as shown in FIG. 6 can also be effected as shown in FIGS. 1 through 5 by way of a motor and a step-down transmission. The latter can for example engage the ring 4 from the exterior by way of a tooth arrangement. The apparatus according to the invention can be in the form of a compact, self-contained structural unit with connections which are known in the state of the art, in particular for the exit light waveguides and optionally the entry light waveguide or waveguides.
Patent Application
20080037089
