Abstract:
Apparatus for maintaining a vehicle screen ( 12 ) supported with respect to a vehicle by a gasket ( 16, 24 ), said screen ( 12 ) comprising first ( 22 ) and second ( 27 ) edge regions wherein said gasket ( 16, 24 ) has a first conduit ( 20 ) means having an opening ( 21 ) proximate to said first edge region ( 22 ) and second conduit ( 25 ) means having an opening ( 26 ) proximate to said second edge region ( 27 ) and wherein the apparatus further comprises supply apparatus coupled to said first conduit means ( 20 ) for supplying a liquid thereto and collection apparatus coupled to said second conduit ( 25 ) means for collecting said liquid.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for maintaining a vehicle screen such as for example a vehicle headlamp. 
     2. Description of the Related Art 
     Vehicle screens such as headlamp lenses and windscreens require cleaning in order to retain their translucent properties. As dirt is deposited and collects on the surface of the screen the amount of light passing through the screen is diminished. In the case of a windscreen this reduces visibility. In headlamp applications deposited dirt on the lens can form a reflective layer as well as reducing light output. Light can therefore be reflected back towards the reflector and out of the headlamp in undetermined directions thereby causing glare. This problem is exacerbated by the heating effect caused by the light beam. As liquid contacts the headlamp lens, the beam tends to heat and thereby evaporate the liquid leaving any dirt previously suspended in the liquid on the surface of the headlamp. This so-called “burn-on” effect can increase the glare from a headlamp substantially. 
     Numerous techniques have been suggested in the past for overcoming these problems. Some of these solutions have used wipers to remove the dirt often requiring some form of water nozzle to spray water or cleaning liquid onto the screen surface prior to wiper action. 
     Problems are associated with many of these solutions. For example, they are prone to mechanical failure of the wiper components and to a cleaning liquid reservoir becoming empty since the liquid is not recycled but is lost as soon as it is sprayed. Furthermore, the driver is usually required to take positive action to clean the screen. 
     It is therefore an object of the present invention to at least partly mitigate the difficulties of the prior art. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a method of maintaining a surface of a translucent screen of a vehicle comprising the steps of providing a first edge region of said screen surface with liquid, causing the liquid to flow across the surface from the first edge region in the direction of a second edge region, and collecting said liquid in said second edge region, whereby said first edge region is selected from a top edge region and a bottom edge region, located below said top edge region, in response to said detected vehicle velocity. 
     According to a second aspect of the present invention there is provided apparatus for maintaining a vehicle screen supported with respect to a structure by a gasket, said screen having a first and second edge region, said gasket having first conduit means having an opening proximate to said first edge region and second conduit means having an opening proximate to said second edge region, wherein said structure is a vehicle and said screen is a headlamp screen and said first edge region is disposed below said second edge region, and wherein the system further comprises supply apparatus connectable to said first conduit means for supplying a liquid thereto and collection apparatus connectable to said second conduit means for collecting said liquid. 
    
    
     DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     An embodiment of the present invention will now be described hereinafter by way of example only with reference to the accompanying drawings in which: 
     FIG. 1 shows a cross-section to a vehicle headlamp for use in accordance with the present invention. 
     FIG. 2 shows a schematic layout including the vehicle head lamp and screen maintenance apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the Figures, like reference numerals refer to like parts. 
     Referring now to FIG. 1, a headlamp  10  comprises a translucent screen  12 , hereinafter referred to as a lens having an upper edge region  22  and a lower edge region  27 , a body portion  11  and gasket portions  16 ,  24 . The lens is secured around its periphery to the body portion  11  via the gasket portions. In the preferred embodiment the gasket may be formed by a tubular elastomeric moulding. The lens is of plastics, eg polycarbonate and has a generally convex cross-section. The upper edge region is disposed rearwardly of the lower edge region, to the left as seen in the Figure. The lower edge region is thus below the upper edge region. 
     The headlamp housing is secured to a first lower vehicle panel  14 , and a second upper vehicle panel  15  to which are fixed the gasket portions  24 ,  16  respectively surrounding the headlamp lens  12 . 
     A light bulb and reflector (not shown) are supported in the body portion  11  in a conventional manner to provide a beam of light from the headlamp. 
     A first vehicle panel  14  is generally disposed below the lower edge region  27  of the lens  12  and extends generally forward of the lens. A second vehicle panel  15  is disposed generally above the upper edge region  22  of the lens and extends generally rearwardly of the lens. The second panel  15  has a generally convex region proximate the lens  12  so as to provide a generally air-smoothed form. The shape of the panel  14 , lens  12  and panel  15  is such that as the vehicle moves forward in the direction of the arrow  18 , air flowing across the front of the vehicle flows generally upwardly across the outer surface of the lens  12  in the direction shown by the small arrows shown in FIG.  1 . 
     The portion  16  of the gasket to which is secured the upper edge of the lens  12  has a first conduit  20  running through it. A liquid may flow along the conduit, as will be described herein below. A first duct  21  leads from the first conduit  20  through the gasket wall to a region  22  at the top edge of the lens. 
     Likewise the portion  24  of the gasket which is secured to the lower edge of the lens has a second conduit  25  running through it along which a liquid can flow. A second duct  26  leads from the second conduit  25  to a region  27  at the bottom edge of the lens. 
     FIG. 2 shows liquid supply apparatus  30  which includes a first and second connecting pipe  31 ,  32 , a filter portion  34 , a liquid source  35  (for example a self-wetting formulation) and a pump  36 . The first connecting pipe  31  is connected to the first conduit  20  to allow liquid to flow through the pipe  31  into first conduit  20 . The connecting pipe  32  is connected to the second conduit  25 . The two connecting pipes  32 ,  31  are also connected to liquid control apparatus  33 . 
     The liquid control apparatus  33  includes the filter portion  34 , liquid source  35  and the pump  36 . The filter portion  34  is connected to the other end of each of the connecting pipes  31 ,  32 . Liquid  35  is stored in a container (not shown) to provide. a source of the liquid. The liquid is pumped to and from the container along the connecting pipes  31 ,  32  by a pump  36 . 
     Liquid control apparatus  30  is connected to receive control signals from control circuitry  37  along control signal line  38 . The control circuitry  37  is connected to vehicle sensor apparatus  40 . The vehicle sensor apparatus includes a velocity sensor  41  for detecting the vehicle velocity and a headlamp condition sensor  42  for controlling cleaning of the headlamp. The headlamp condition sensor  42  may be any type of sensor capable of detecting the quantity of dirt or contaminant on the surface of the screen. For example such a sensor may be a surface resistivity sensor or a temperature detector or a scattered light detector. 
     The headlamp condition sensor  42  is connected to control circuitry  37  by a first signal line  43 . The sensor outputs a condition control signal C on signal line  43  which is input to the control circuitry  37  for controlling liquid supply to the screen. The vehicle velocity sensor  41  is connected to the control circuitry  37  by a second signal line  44  and outputs a signal V VEH  on said signal line  44  indicating the detected velocity of the vehicle. 
     In response to the signals from the velocity sensor  41  and headlamp condition sensor  42  the control circuitry  37  outputs a control signal P on control signal line  38  which controls operation of the liquid supply apparatus  30 . The condition control signal C causes the control circuitry to supply liquid to the screen whilst the vehicle velocity signal V VEH  selects the mode in which liquid is supplied. 
     When liquid supply is initiated the cleaning apparatus can operate in two modes as will be described hereinbelow. 
     In a first mode the vehicle velocity is below a threshold velocity and liquid flows generally downwardly across the lens surface under the force of gravity. In this mode the control signal P from control circuitry  37  controls pump  36  to apply a positive pressure to supply liquid by pumping liquid from the liquid source  35  along first connecting pipe  31  to the first conduit  20  in gasket portion  16 . Liquid from the gasket flows through the first duct  21  to the upper edge region  22  at the upper edge of the lens. The liquid in region  22  flows downwards across the lens surface under the force of gravity where it is collected in lower edge region  27  at the lower edge of the lens. The collected liquid flows through the second duct  26  under negative pressure (caused by sucking) from the pump and into the second conduit  25  running through the portion  24  of the gasket. The liquid flows from the second conduit  25  along the second connecting pipe  32  through the filter portion  34  and returns to the liquid source  35  thereby recycling the liquid. 
     In the second mode of operation the vehicle velocity is above a threshold velocity such that the air flow shown by the small arrows in FIG. 1 across the surface of the lens is sufficient to cause liquid provided by the second duct  26  into the lower edge region  27  to flow generally upwardly across the surface of the lens where it collects in upper edge region  22  at the upper edge of the lens. In this second mode control signal P on control signal line  38  controls the pump  36  to supply liquid from the liquid source  35  along the second connecting pipe  32  to the second conduit  25  running through the lower portion  24  of the gasket. Liquid in the gasket conduit  25  flows through second duct  26  to the lower edge region  27  at the lower edge of the lens. The liquid in region  27  is induced to flow upwardly by the movement of air caused by the vehicle motion and collects in the upper edge region  22  at the upper edge of the lens. The collected liquid flows through the first duct  21  into the first conduit  20  running through the gasket portion  16 . The liquid flows from the conduit  20  along the first connecting pipe  31  through the filter portion  34  and returns to the liquid source  35  thereby recycling the liquid. 
     In both the situation where fluid flows downwards under gravity and upwards as a result of air flow due to vehicle motion the result is that the fluid  17  spreads thinly across the part of the surface of the lens where cleaning is desired. The fluid is provided at one edge region of the screen and collected in another edge region depending upon the velocity of the vehicle. As a result any dirt which would otherwise have settled and accumulated on the headlamp lens thereby causing a deterioration in the translucency of the lens is instead entrained in the fluid film flowing over the screen. The fluid, after flowing across the screen, is filtered in the filtering apparatus to keep the fluid clean prior to recycling. 
     It will be appreciated that fluid flow is also to some extent dependent on the lens geometry and that instead of fluid flow being generally upwardly and/or downwardly configurations of lens or the surrounding airflow inducing structure could cause liquid to flow to collecting regions in the side edges of the screen where ducts and conduits in the gasket could be provided to enable to liquid to be recycled. 
     In this way the present invention provides a method and apparatus for keeping the lens or screen of a vehicle headlamp clean whilst recycling the cleaning fluid used, thereby reducing the maintenance required to keep the cleaning fluid “topped-up”. 
     It will also be appreciated that as the liquid is recycled some regeneration of the liquid may be required to maintain the liquid at a desired composition. For example under precipitous weather conditions the liquid may tend to become more dilute as some water falling on the screen may be collected with the liquid and be recycled. Likewise under high temperature conditions the concentration of the liquid may be affected. In order to overcome these problems it is envisaged that an adjustable dosing tank  100  could be provided to supply doses of concentrate to the liquid source in order to maintain the liquid within a desired range of concentration. 
     Although the present invention has been described in respect of vehicle headlamps it will be understood that the invention could be adapted to provide cleaning for any screen where cleaning is desired for example trains, aircraft and the like. 
     It will also be understood that the invention may be adapted for use in only one of the two described modes of operation. In applications for vehicles which are only capable of slow motion or where the vehicle configuration does not allow sufficient upward air flow across the screen, the invention only operates in the first mode of operation where liquid flows downwards across the lens due to gravity. Alternatively the invention may operate only when the vehicle is travelling at relatively high velocities when only the second mode of operation will be required.