Reflective, road mounted studs, and road mounted studs with light-emitting diodes (LED's) have long been known, and have always had the attendant problem that they become dirty, with the result that the efficiency of reflectors and the output from LED's is impaired. Similar problems arise with traffic monitoring devices such as road mounted cameras, the efficiency of which are impaired if a stud lens becomes dirty.

The historic solution has been to mount reflectors and LED's in a socket with provision for vertical movement such that when struck by the wheels of a passing vehicle the reflectors/LED's are moved in and out of the socket, during which, the reflectors/LED's are wiped clean. During wet weather, cleaning in this way is considerably enhanced, by virtue of water gathering in the socket, this effectively washes the reflectors/LED's as they are wiped during their movement into the socket.

However, such techniques are not applicable to road studs with an upper domed lens on a socket, within which reflectors and/or LED's are housed.

The object of the invention seeks to provide a cleaning technique for domed road studs as mentioned above.

According to the present invention, a road stud comprises a lens mounted in a socket with provision for vertical movement, sealing means between the lens and the internal wall of the socket, an air passageway connecting the lower end of the socket interior to an air tank, and an outlet from the air tank directed at the outer surface of the lens.

Preferably, a compressed air storage tank is provided in the socket connected to an air compressor the air compressor being activated by the vertical movement of the lens. Further preferably, a water tank is also provided connected to the outlet from the air tank to allow water to be entrained in the air flow to the lens surface, and further preferably, a venturi is provided to maximise the amount of water entrained in the air supply.

Cleaning of the lens surface can be further enhanced if a cleaning medium is entrained in the water supply, for which purpose a block of cleaning agent can be positioned in the supply line from the water tank to the water connection to the air supply, or cleaning fluid can be added to the water in the water tank.

Thus, in its simplest form of construction and perhaps best suited to dry conditions, repeated impacting of the lens causes it to act as a piston to pressurise the air in the lower part of the socket, that is fed to the air tank, from where a pressure air stream is directed at the lens surface to blow away dust and other debris, or impacting the lens activates the compressor to provide a supply of compressed air directed at the lens surface.

In areas of poorer and wetter conditions, the provision of a water tank to allow water to be sprayed at the lens surface is highly desirable as is the provision of a cleansing agent, such as a solid block over which water flows as it progresses from the water tank to the outlet from the air tank, or cleaning fluid added to the water tank.

To prevent constant exhausting of the air tank, it may have a valved outlet to allow the tank to be pressurised over a period of time, by the compressor associated with the tank, to be operated periodically or as required to drive air to the outlet aimed at the lens, with entrained water and cleansing agent when they are provided.

The water tank may be such that it fills automatically with rain water, or may be such as requires to be filled periodically.

Several embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic part sectional side elevation of the inner components of a road stud according to the invention; Figures 2 & 3 are a schematic perspective view of the road stud of Figure 1 with a part of the wall of the socket removed for clarity ; Figure 4 is a schematic perspective view of the inner components of the socket; Figure 5 is a block diagram showing the interconnections of the components of the road stud of the invention; and Figures 6 to 9 are block diagrams showing alternative methods of control over pressure air and water.

In the drawings a road stud 1 has a socket 2 and a lens 3, the lens being slidably mounted towards the top of the socket.

Within the socket is an air compressor 4 within which is a piston having a plunger 5 emerging from the compressor, and which is in contact with the lower surface of the lens 3.

Also in the socket 2 is an air inlet 6 with a line connecting the inlet 6 an air inlet valve 7 connected to the air compressor 4.

The compressor 4 has an outlet connection 8 to a compressor outlet valve 9 that in turn is connected to a compressed air storage tank 10. Alongside the compressed air storage tank 10 is a water and cleaning fluid storage tank 11 connected by an air line 12 to the compressed air storage tank 10, and by an outlet pipe 13 to an air and water outlet block 14 with an associated solenoid valve 15.

As is indicated in Figure 5, the connection of the compressed air storage tank 10 to the outlet block 14 is preferably by way of a venturi 16 located within the water and cleaning fluid storage tank, and a filter 17 is preferably provided in the outlet pipe 13 from the water and cleaning fluid storage tank 11.

Thus, as vehicles repeatedly run over a road stud in accordance with the invention, the lens 3 is repeatedly depressed, as indicated in Figures 2 and 3, thereby activating the plunger 5 to reciprocate the piston in the air compressor 4, to draw air through the air inlet 6 and inlet valve 7, and to drive compressed air through the outlet valve 9 and to the compressed air storage tank 10, continuous exhaustion of the air in the storage tank 10 being prevented by the solenoid valve 15 associated with the outlet block 14.

When cleaning of the lens 3 outer surface is required, the solenoid valve is activated, to release compressed air from the storage tank 10, the surge of compressed air to the venturi in the water and cleaning fluid storage tank 11, causing water and cleaning fluid to be entrained in the compressed air to emerge through an air and water outlet feed tube 18 on the outlet block from where it is directed to the outer surface of the lens, the feed tube extending up through the wall of the socket and having an outlet associated with a cavity 19 on a securing ring 20 holding the lens in the socket, to direct air and water across the surface of the lens.

To ensure that the creation of a vacuum in the housing for the solenoid is avoided, the outlet block has an atmospheric air inlet21 connected within the block to housing for the solenoid The solenoid valve 15 may be activated periodically or may be activated by sensors on the lens 3 outer surface detecting a dirt build-up on the outer surface, and a charge to activate the solenoid can be from a capacitor via a switch, activated by a counter or by a signal from sensors on the lens. A charge on the capacitor can be from a solar cell.

Thus, as is illustrated in the block diagram of Figure 6, a solar cell 22 that is located below the lens 3 provides power to a capacitor 23 connected to a counter 24 that serves as a switch to connect the capacitor to the solenoid valve 15. Once the counter has reached a predetermined number, power is provided to the solenoid to cause the emission of water and cleaning fluid to the outer surface of the lens 3, until the capacitor is exhausted, when the solenoid valve switches off and the counter resets and the solar cell commences the recharging of the capacitor.

In the alternative and as is illustrated in the block diagram of Figure 7, the counter can be hard wired to a mains supply 25, to cause the emission of a water and cleaning fluid at predetermined intervals with the advantage the cleaning of the lens can take please during the hours of darkness and during inclement weather with poor visibility.

As is illustrated in the block diagram of Figure 8, in place of the counter 24, a switch 26 is provided connected to a sensor 27 attached to the surface of the lens 3. Here again, a solar cell 22 is provided to power a capacitor 23, connected by the switch 26 to the solenoid valve 15, the switch opening on receiving a signal from the sensors indicating a build-up of dirt on the lens surface, the emission of water and cleaning fluid continuing until the sensors cease to send a signal to the switch.

Figure 9 is a block diagram showing the switch 26 hard wire connected to a mains supply 25, the switch opening and closing as determined by the presence or absence of a signal from the sensor 27 on the lens surface.