1 AUSTRALIA Patents Act 1990 WEIDMULLER PTY LTD COMPLETE SPECIFICATION INNOVATION PATENT Invention Title: Headlight assembly The following statement is a full description of this invention including the best method of performing it known to us:- 2 Headlight assembly Field This disclosure relates, generally, to a headlight assembly and, more particularly but not necessarily exclusively, to a headlight assembly for a vehicle such as a locomotive. 5 Background Headlights are fitted to the front of vehicles such as locomotives to light the way ahead. At present, the illumination source of such a headlight is usually an incandescent light bulb. Incandescent light bulbs have a relatively short life 10 necessitating regular replacement which increases maintenance costs and downtime of the locomotive. They also use a large amount of power. Further, if the headlight fails during use, there is a total cessation of illumination which could have very severe consequences. In addition, an incandescent light bulb generates a large amount of heat and 15 therefore there is a risk that someone can burn themselves on such a headlight. Summary In one aspect, there is provided a headlight assembly which includes a housing defining a recess in which a solid state illumination source is received, 20 the housing being shaped and dimensioned for retrofitting in a receiving formation of a mounting member without requiring modification either of the housing or of the mounting member; a substantially transparent cover member for closing off the recess; a sealing arrangement interposed between the housing and the cover member for 25 inhibiting ingress of moisture and foreign material into the recess of the housing; a heat dissipation arrangement arranged on the housing for dissipating heat generated by the illumination source; and illumination source comprises an array of light emitting diodes (LEDs) connected in a plurality of groups of LEDs, the LEDs in each group and the groups 30 being interconnected so as to provide redundancy. The array may, for example, comprise 36 LEDs arranged in six groups and the groups may be positioned to form a hexagonal array which fits within the recess of the housing, the recess typically being circular to be able to be retrofitted in the mounting member. The LEDs in each group 35 1666893_.doc 3 may be interconnected so that up to 12 LEDs (maximum of two per group) may be able to fail open circuit while still providing 90% light output from the array as a whole. The housing may be of spun aluminium. The cover member may be received in a rim portion of the housing and the 5 sealing arrangement may comprise a first elastomeric sealing member interposed between a lip of the rim portion of the housing and the cover member and at least one further elastomeric sealing member interposed between the cover member and a spacer member which spaces the cover member from a carrier of the illumination source. A further elastomeric sealing member may be interposed between the spacer 10 member and the carrier. It will be appreciated that the carrier is a printed circuit board (PCB) and the spacer member is a spacer ring, the recess of the housing being circular. The sealing members may each be of a light, closed cell foam material. In combination the sealing members may provide sealing against ingress of moisture and foreign matter to the required international standard. For example, the sealing arrangement 15 may provide sealing to IP66 ingress protection level. The cover member may be of a synthetic plastics material such as an engineering plastics material. As an example, the cover member may be a polycarbonate. The heat dissipation arrangement may comprise a heat sink assembly mounted 20 to an operatively rear surface of the housing, the heat sink comprising a plurality of fins with the fins containing fluting to increase their surface areas. The heat sink may comprise a plurality of discrete elements arranged in a cruciform pattern on the rear surface of the housing with the fins of the elements being parallel to one another to facilitate air flow through the fins to effect cooling. 25 Brief description of drawings In the drawings, Fig. I shows a plan view of an embodiment of a headlight assembly with the illumination source omitted for the sake of clarity; 30 Fig. 2 shows a rear view of the headlight assembly; Fig. 3 shows a side view of the headlight assembly; Fig. 4 shows a sectional side view of the headlight assembly taken along line IV-IV in Fig. 1; and Fig. 5 shows a plan view of the headlight assembly including the illumination 35 source and showing the interconnection of elements of the illumination source.
4 Detailed description of exemplary embodiments In the drawings, reference numeral 10 generally designates an embodiment of headlight assembly. The headlight assembly 10 is particularly intended for use on a locomotive. Such locomotives have one or two headlights arranged above the cabin 5 and the headlights are mounted above the cabin via a mounting member in the form of a mounting plate (not shown). Often such headlights are arranged in pairs in the mounting plate. The headlight assembly 10 is intended to be retrofitted in the mounting plate to replace an existing incandescent headlight in the mounting plate without requiring 10 modification of the mounting plate or the headlight assembly 10 itself. The headlight assembly 10 comprises a housing 12. The housing 12 defines a recess 14 within which a solid state illumination source 16 (Fig 5) is receivable. The housing 12 is a circular housing and is of spun aluminium. The assembly 10 includes a cover member 18. The cover member 18 is of a 15 transparent material so that light can be emitted through it and is of a synthetic plastics material. More particularly, the cover member 18 is of an engineering plastics material such as a suitable polycarbonate that is dimensioned and configured to meet the relevant international standards relating to vibration, impact and shock resistance. The housing 12 is similarly designed to meet the relevant international standards. More 20 particularly, the housing 12 and cover member 18 are designed to comply with international standards IEC61373. As indicated above, the illumination source 16 is a solid state illumination source and is mounted on a printed circuit board (PCB) 20 received between the housing 12 and a carrier plate 22 defining a rear of the housing 12. The printed circuit 25 board 20 supports an array of light emitting diodes (LEDs) 24. Each LED 24 is a lensed LED having a lens component 26 for focusing light emitted by the LED itself. In the embodiment illustrated, the LEDs 24 are arranged in a hexagonal array to be received in the circular recess 14 of the housing 12. The hexagonal array comprises four LEDs 24 per side and the LEDs are arranged in six triangular groups, one of the 30 groups being demarcated by the dotted line 28 in Fig 5 of the drawings. Further, as shown by the tracks 30 on the printed circuit board 20 of the illumination source 16, within each group 28, the LEDs 24 are parallel and serially interconnected as follows: three LEDs being serially interconnected, two LEDs serially interconnected with each other and being connected in parallel with the three serially interconnected LEDs, and a 35 further single LED connected in parallel with the group of two LEDs and the group of three LEDs.
5 With this configuration, redundancy is provided so that, if any one LED 24 fails in the group 28 in an open circuit manner, the remaining LEDs 24 in the group 28 remain connected and one group 28 is not affected by any failed LEDs in another group. 5 In addition, the LEDs 24 are driven by an external, remotely mounted driver (not shown) via a cable connection 31 having a cable 32 connected, at a first end, to a cable gland 34 connected to the PCB 20 and a second end of the cable 32 connected to a connector 36 for connection to the driver. The driver drives the LEDs 24 so that, if one LED fails, current is increased to 10 the remaining LEDs so that the intensity of the illumination of the headlight assembly 10 as a whole remains substantially the same. The applicants have found that up to two LEDs per group 28 can fail without significant degradation of the intensity of the illumination output from the LEDs 24. With the arrangement of the LEDs 24, the luminous intensity of the LEDs 24 is 15 of the order of 300,000 Cd and provides an illuminance of 5.25 lux at 240m as required by the relevant standards. These figures are achieved by using a pair of headlight assemblies 10 in the mounting plate. It will be appreciated that, because the headlight assembly 10 is mounted externally on the locomotive, it is exposed to the elements. Thus, the assembly 10 20 includes a sealing arrangement 38 received in a recess 14 of the housing 12 and interposed between at least the cover member 18 and the housing 12. In this regard, the housing 12 comprises a rim portion 40 having an inwardly turned lip 42. The sealing arrangement 38 comprises a first sealing gasket 44 interposed between the lip 42 of the housing 12 and an external surface of the cover 25 member 18. A second sealing gasket 46 of the sealing arrangement 38 is interposed between an internal surface of the cover member 18 and a spacer ring 48. A third sealing gasket 50 of the sealing arrangement is interposed between the spacer ring 48 and the PCB 20. Still further, the housing 12 includes a radially outwardly extending flange 30 portion 52. This flange portion 52 bears against a shoulder (not shown) on a operatively inner surface of the mounting plate. A further, elastomeric sealing ring (also not shown) bears against the flange 52 further to seal the assembly 10 relative to the mounting plate. The gaskets 44, 46 and 50 are of an elastomeric material and, more particularly, 35 a light, closed cell foam material to provide protection against ingress of moisture and 6 foreign matter, such as dust, to the required standard. In particular, the sealing arrangement 38 provides a protection level complying with the IP66 standard. The LEDs 24 of the array generate substantial heat. Thus, the headlight assembly 10 includes a heat dissipation arrangement 52 carried on the carrier plate 22 5 of the housing 12. The heat dissipation arrangement 52 comprises a heat sink. More particularly, the heat dissipation arrangement 52 comprises a plurality of discrete heat sink elements 54 which are custom engineered of aluminium and are extruded to dissipate the heat generated by the illumination source 16. Each heat sink 54 comprises a plurality of fins 58. Although not illustrated, 10 surfaces of the fins 58 are, further, fluted or grooved to provide increased surface area to facilitate heat dissipation. As illustrated most clearly in Fig 2 of the drawings, the heat sink elements 54 are arranged in a cruciform pattern on the mounting plate 22 with the fins 58 extending parallel to one another to facilitate air flow through the heat dissipation arrangement 15 52. In use, the headlight assembly 10 is able to be retrofitted in the mounting plate without modification of the mounting plate or of the housing 12 of the assembly 10. To facilitate mounting, the housing 12 has a plurality of radially outwardly extending mounting lugs 60 mounted to the housing 12. As illustrated in Figs 1-4 of the 20 drawings, at least two such lugs are provided but, optionally, four such lugs 60 may be provided as shown in Fig 5 of the drawings. As indicated above, the illumination source 16, via the LEDs 24, provides the required illumination to comply with the necessary standards. The assembly 10 has the benefit that the power consumption of the assembly 10 is substantially lower than the 25 equivalent incandescent headlight. More particularly, the power consumption of the headlight assembly 10 is less than about 20% of the power consumption of the equivalent incandescent headlight. For example, the power consumption of the headlight assembly 10 is less than 70W whereas the power consumption for the equivalent incandescent headlight is of the order of 350W. 30 In addition, the headlight assembly 10 is ruggedised and is able to withstand far greater impacts than the equivalent incandescent headlight. The headlight assembly 10 has been tested to withstand an impact of over 75J, whereas the standard incandescent headlight failed at less 20J. Still further, as described above, due to circuit redundancies, if one of more 35 LEDs 24 of the array fail, the light output is not adversely affected to any significant 7 extent. The circuit redundancies also provide that upto 80% light output is available even after an impact of greater than 200J. A further benefit of the headlight assembly 10 in comparison with a standard incandescent headlight is the much longer life of the headlight assembly 10. The 5 headlight assembly 10 has a life of the order of 30,000 to 50,000 hours in comparison with a life of 300 to 1,000 hours for a standard incandescent headlight. It is also possible to flash the headlight assembly 10 without adversely affecting the life of the headlight assembly 10. Another benefit of the headlight assembly 10 is that, even if one or more of the 10 LEDs 24 fails, the assembly 10 is still fully functional, as described above. In contrast, should a globe of an incandescent headlight fail, the incandescent headlight itself becomes inoperative which could have severe, adverse consequences. In addition, the lighting assembly 10 has very low temperature and is safe to touch. A maximum surface temperature of the lighting assembly 10 is of the order 15 65 0 C which is considerably lower than the equivalent incandescent light. It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not 20 restrictive.