FIELD OF THE INVENTION

This invention relates to rotating beacons. This invention has particular application to rotating beacons for vehicular use, and for illustrative purposes the invention will be described with reference to this application. However, it is envisaged that this invention will find application in for example warning devices on fixed installations.

BACKGROUND OF THE INVENTION

Rotating beacons have been a mainstay of emergency service vehicles for many years. In its most fundamental a rotating beacon comprises a continuous light source that is focused into a beam and is either rotating or, more commonly, is located at the focus of a rotating reflector. The focussing element is most usually a parabolic reflector.

A rotating reflector may comprise the focussing element, but need not necessarily be so. For example, a parabolic focussing reflector may direct a beam into a rotating plane mirror. The optical parts are generally housed in an optically transparent dome closed over a base assembly including the motor components necessary to rotate the reflector and to lead in electrical power the motor and lamp.

One example of an incandescent-globe illuminated rotating beacon is that disclosed in DE 4304216 A1 published 18 August 1992. A beacon has a stationary halogen lamp (16) mounted on a bearing bracket (31 ), which is arranged on a lamp base (1 1 ). A vertical light beam is generated by the lamp (16) and parabolic reflector (17), and is turned into a substantially horizontal plane by a motor-driven plane mirror (24). The lamp (16) is mounted from below in the bracket.

The technology is constructed to accommodate the considerable heat generated by the QH globe. With a yield of 24 lumens/Watt and an overall thermodynamic efficiency of 3.5%, a 50W lamp beams at 1 200 lumens while generating 48.25W of heat. While most of the heat is radiated out with the light, the rotating beacon must deal with heat generated by conduction and convection heating of the beacon components.

With the advent of high intensity LEDs, there are examples of rotating beacons using this solid state technology. Typically, a polymer lower housing mounts an LED assembly including a heat sink, a driver circuit, and an electric motor driving a rotating parabolic reflector. The reflector is housed in a transparent polycarbonate upper housing. While the LEDs are more efficient at 14%, a 30 Watt LED array would generate about 26 Watts of heat, substantially all of which would be retained by the heat sink. In a closed system the heat build-up is such that high intensity LED beacons are not used beyond about 10 Watts. Even at this low power, the housing must be ventilated, exposing the electronics to the

environment. The light output of the diodes varies with temperature.

BRIEF SUMMARY OF THE INVENTION

In one aspect the present invention resides broadly in a rotating beacon including: a heat conducting mounting base having a ventilated lower chamber;

a substantially transparent housing secured to said mounting base and forming therewith a substantially closed upper chamber;

a reflector of at least part parabolic shape mounted for driven rotation about its focal point in said upper chamber; and

a light emitting diode assembly thermally coupled to said mounting base and emitting light substantially at said focal point.

The heat conducting mounting base may be formed from any suitable material including but not limited to metals such as aluminium or conductive composites such as carbon fibre. The heat conducting mounting base may be monolithic or may be fabricated. The mounting base may for example be cast in aluminium alloy.

The lower chamber may be defined by a side wall portion having a lower edge adapted to be mounted to a surface such as a vehicle roof, and an upper wall portion. The side wall portion may include openings in the form of one or more apertures or reliefs in the lower edge. The side wall portion and/or the upper wall portion may be provided with cooling surface-increasing devices such as integral cooling fins.

The mounting base may be integrally formed with a peripherally-threaded wall portion adapted to secure the substantially transparent housing to the mounting base. The assembly may be further sealed by a gasket or O-ring. Alternatively, the substantially transparent housing may be an interference fit, bayonet fit, and/or O-ring-sealed sliding fit to the mounting base.

The substantially transparent housing may be formed of any suitable material such as class or optically clear polymer. For example the substantially transparent housing may be formed of polycarbonate, acrylic or styrene polymer. The substantially transparent housing may be coloured. The substantially transparent housing may be formed with integral lensing components such as Fresnel lens components. The substantially transparent housing may be of any shape.

However, as the substantially transparent housing contains a rotating reflector it is envisaged that the shape will always be a shape of rotation such as a sphere or a cylinder.

The reflector may be formed of metallized glass or plastic or coated or polished metal. The reflector may be a full parabola. However, in view of a configuration of most sources and in order to increase the reflective surface area, the reflector may have a reflective surface shaped as part of a much larger parabolic surface. To this end it may be preferred to use a substantially transparent housing of generally cylindrical shape, and to configure a substantially straight-edged, part parabolic reflector of size selected to rotate in close conformity to an inner cylindrical and/or upper circular surface of the substantially transparent housing. The reflector may be mounted for rotation in the upper chamber by any suitable means. For example, the reflector may be mounted to rotate or orbit about an axis that substantially contains the focal point of the reflector. Where the reflector is configured to sweep the reflected beacon around the horizon, the reflector may be mounted on rotating means associated with either the top of the substantially transparent housing or the mounting base. The rotating means typically includes a DC brushless "synchronous" electric motor driving a pinion or pulley which in turn reduction drives a gear or pulley supporting the reflector for rotation on a bush or bearing. Typical brushless DC motors use a rotating permanent magnet in the rotor, and stationary electrical current/coil magnets on the motor housing for the stator. A motor controller is required that converts DC to AC (with which the motor is synchronous); this may be inherent in the motor assembly or may be optimized on an external circuit board, typically mounted on the mounting base.

In the case of a moulded or cast mounting base, the motor and bearing may be precision-located in respective motor and bearing housings formed in the act of moulding or casting the mounting base. The gear or pulley may comprise a ring gear or pulley whereby the LED assembly may be direct mounted to the mounting base substantially at the centre of rotation of the ring gear or pulley.

The light emitting diode (LED) assembly may be a high power, multiple- semiconductor-device. For example, the LED assembly may be the metallic chassis, multiple-bead arrangements or LED arrays such as those marketed by CREE of North Carolina. For example, the CREE® XLamp® CXA1816 LED Array delivers high lumen output and high efficacy in a single package.

Size (mm x mm) 17.85 x 17.85

Maximum power (W) 38

Light output (Im) 1700 - 3800

The LED assembly may be associated with a driver circuit formed on a circuit board, which may also comprise a motor controller. In a specific embodiment, the printed circuit board may be formed from thermally conductive aluminium and is mounted to a heat sink comprising the mounting base with a heat conducting compound. In the case of substantially transparent housing top-mounting the means for rotating the reflector, electrical conductors may be secured to the substantially transparent housing. For example, the substantially transparent may be secured to the mounting base using a rotate and lock method and the electrical conductors may comprise two strands formed from electrically conductive aluminium. Each strand may be secured to the inside face of the substantially transparent housing and may provide an electrical connection from the base to a motor that is secured into the closed upper end of the substantially transparent housing.

In another aspect the present invention resides broadly in a rotating beacon including:

a mounting base;

a substantially transparent housing secured to said mounting base and forming therewith a chamber;

a part parabolic reflector mounted for driven rotation about its focal point in said chamber and being of a shape in elevation selected to substantially conform to said substantially transparent housing; and

a light emitting diode assembly emitting light substantially at said focal point.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view of a rotating beacon in accordance with an embodiment of the present invention;

Fig. 2 is a side view of the beacon of Fig. 1 ;

Fig. 3 is a front view of the beacon of Fig. 1 ;

Fig. 4 is a vertical section through the beacon of Fig. 1 ; Fig. 5 is a top perspective view of the cast base of the beacon of Fig. 1 ;

Fig. 6 is a bottom perspective view of the cast base of the beacon of Fig. 1 ;

Fig. 7 is an exploded perspective view of an alternative embodiment of a rotating beacon in accordance with an embodiment of the present invention; Fig. 8 is a side view of the apparatus of Fig. 7; Fig. 9 is an end view of the apparatus of Fig. 7; Fig. 10 is a vertical section view of the apparatus of Fig. 7; Fig. 1 1 is a top perspective view of the cast base of the apparatus of Fig. 7; and Fig. 12 is a bottom perspective view of the cast base of the apparatus of Fig. 7; DETAILED DESCRIPTION OF THE EMBODIMENTS

In the figures 1 to 6 there is provided a beacon assembly 10 including a mounting base 1 1 of cast aluminium alloy. The mounting base 1 1 is an integral, one-piece casting having formed therein a mounting flange 12 incorporating mounting pads 13 and bolt holes 14. The mounting flange is bounded at its inner periphery 15 by a side wall portion 16, which is closed over intermediate its height by an upper wall portion 17 to form a lower chamber 18. The side 16 and upper 17 wall portions support integrally formed cooling fins 20. The side wall portion 16 is relieved by eight ventilation ports 21 . The casting is provided with alternative threaded mounting bolt posts 19 for enabling the base 1 1 to be blind-fixed from below.

The side wall portion 16 extends above the upper wall portion 17 to provide a substantially cylindrical mounting spigot 22 on which is supported a polycarbonate transparent housing 23 and which forms, with the mounting base 1 1 , an upper chamber 24. The mounting spigot 22 is threaded to engage a corresponding threaded portion 25 of the transparent housing 23, the upper chamber 24 being environmentally sealed by O-ring 26.

The upper wall portion 17 is integrally formed with, on its upper surface, a bearing stop land 27, inner bearing race mount 28, LED assembly thermal mount 30, circuit board mounting posts 31 , motor housing portion 32, anti-torque lug recess 33, motor retainer plate posts 34 and electrical cable lead-out 35.

A synchronous DC motor 36 is located in the motor housing portion 32 and is secured against counter rotation by an anti-torque lug 37 adapted to engage the lug recess 33. The motor 36 is retained in the motor housing portion 32 by apertured retainer plate 40 and machine screws 41 . The motor shaft 42 passes through the aperture 43 in the retainer plate 40 and is terminated by an input spur gear 44.

A bearing housing 45 has a gear mounting flange 46 and a sleeve portion into which the outer race of a bearing assembly 47 is pressed. The inner race of the bearing assembly 47 is pressed onto the inner bearing race mount 28 until it contacts the bearing stop land 27. A bearing retainer plate 50 is secured to the top 51 of the inner bearing race mount 28 by machine screws 52.

An annular output spur gear 53 is mounted to the gear mounting flange 46 by machine screws 54, and in turn mounts a metallized polymer parabolic reflector 56 by machine screws 57. The reflector 56 is maximized for height and width in the upper chamber. The output spur gear 53 meshes with the input spur gear 44 to provide a reduction drive between the motor 36 and the reflector 56.

A CREE® XLamp® CXA1816 LED Array 60 is installed to the LED assembly thermal mount 30 using thermal paste and machine screws 61 , the contact tails (not shown) being led out through respective milled cut-outs 62 which are sealed from below the upper wall portion 17.

The motor 36 and LED array 60 are controlled by a circuit board 63 connected via DC leads (not shown) passing through the electrical cable lead-out 35. The contact tails (not shown) led out through respective milled cut-outs 62 are also terminated on the circuit board 63. The circuit board 63 is physically supported on the mounting base by circuit board mounting posts 31 .

In the embodiment of figures 7 to 12, like components have like numerals with the embodiment of figures 1 to 6. In the second embodiment, the reflector 56 and annular gear 53 are integrally formed of a metallized polymer material to simplify the construction. The bearing housing 45 receives a bearing or a low friction thrust bush 70 is retained to the integral annular gear 53 by set screws 71 . A corresponding land 72 is formed about the LED thermal mount 30 to form a thrust face for the bearing or bush 70.

In this embodiment the synchronous DC motor 36 is mounted directly to the circuit board 63, simplifying the wiring arrangement. Apparatus in accordance with both of the above embodiment is substantially hermetically sealed, reducing condensation within the upper chamber. The implications for management of heat from the high power LED module are dealt with by the use of an integrally cast aluminium alloy base including integral ventilation ports and multiple cooling fins while providing a sturdy and stable base for mounting the beacon. The reflector elevation area is maximized.

In the second embodiment these advantages are yet further enhanced by moving the motor to the circuit board, liberating space for the inclusion of integrally cast, concentric cooling fins 73. While the air within the cover 23 is heated by the electronic components, the rotation of the reflector creates a circulation passing air over the cooling fins 73, which are integral with the heat sink provided by the cast base 1 1 . In this embodiment the circuit board is limited to a part circular shape in order to expose the cooling fins 73.

The above embodiments of the present invention are illustrative and not limiting. Various alternatives and equivalents are possible. Other additions, subtractions or modifications are obvious in view of the present disclosure and are intended to fall within the scope of the appended claims.