A REAR VIEW SYSTEM FOR A VEHICLE

Abstract: An optical rear view system for a vehicle comprises a reflector mounted to receive light from objects to the rear of the vehicle and to reflect it towards an observer, provided with at least one further optical component between the reflector and the observer effective to direct towards the observer, by refraction or reflection, a portion of the light which upon reflection at the reflector is not directed towards the observer, whereby to provide a wider field of view than that obtainable from the reflector alone. The reflector is positioned forwardly of the observer so as to be in his field of view and the surface of the system on which light from an object behind the vehicle is first incident lies at an acute angle to the longitudinal axis of the vehicle and is inclined such that a forward part of the incident surface is further from the vehicle axis than a rearward part.

Description: A REAR VIEW SYSTEM FOR A VEHICLE This invention generally relates to a rear view system fo a vehicle, and particularly to such a system especially suitable for a road transport vehicle. Conventional rear view systems usually comprise a single interior mirror supplemented by two exterior mirrors. At one time exterior mirrors were mounted on the vehicle win over the front wheel but in more recent vehicles they are usually fitted on the doors at the front of the vehicle, which position represents the closest they can be brought to the driver whilst remaining forward of him. Exterior mirrors are becoming increasingly necessary as an aid to safe driving in today's traffic conditions. Dense traffic and multi-lane highways demand increasingly high standards of lane discipline and all-round awareness. The information necessary to maintain such high standards is achieved largely through the use of exterior rear view mirrors. In recognition of this evolving requirement, exterior mirrors have grown larger over recent years. So vital is the need for comprehensive visual information that this growth has even taken place against a background of 'intense efforts to reduce air drag. Conventional exterior mirrors, however, have been estimated to be responsible for the consumption of up to 1000 litres of fuel during the life of a car. Apart from this cost, exterior mirrors generate aerodynamic noise, are vulnerable to damage, can cause injury and, finally, look aesthetically displeasing on the smooth and rounded exterior surfaces which characterise modern car design. In recent years increasing emphasis has been placed on efficient use of non-renewable energy resources. Nowhere has this emphasis been more keenly applied than in the development of road transport vehicles. Although great progress has been made in the energy efficiency of engines and in reducing wastage of the mechanical energy thus generated primarily by improvements in vehicle weight reduction, tyre rolling loss reduction and vehicle aerodynamic drag reduction, there is one factor which still presents considerable problems. During medium and high speed cruising, the aerodynamic drag factor, which is the factor having the greatest effect at " higher speeds (where aerodynamic drag may account for up to 80% of the total mechanical energy loss) results in both drag and noise. For this reason, car manufacturers seek any practical means to reduce aerodynamic drag, but they also have many other requirements to fulfil in order to preserve the car as a convenient, comfortable and safe machine to use. As more and more exterior aerodynamic features become increasingly refined, the degrading effects of those which have largely resisted improvement are highlighted. The exterior mirror is one of these features. Furthermore, sited as they usually are in an area where the air speed can be somewhat greater than free stream speed, their degrading effect is magnified. Furthermore, although they are designed to yield under impact, exterior mirrors remain a traffic hazard. Mirror yield is of most benefit in very low speed impacts. In higher speed impacts, whether against another mirror or a pedestrian, mirror inertia plays an important role and considerable damage and/or injury can occur. The present invention seeks to provide a rear view system for a vehicle having substantially reduced protrusion beyond the exterior surface of the vehicle, as compared with existing exterior rear view mirrors, while retaining or improving the rearward and lateral fields of view. The present invention also seeks to provide a rear view system offering less resistance to vehicle motion and lower aerodynamic noise than conventional exterior mirrors whilst also being less of a hazard to other road users. According to one aspect of the invention, there is provided an optical rear view system for a vehicle, comprising a reflector mounted to receive light from objects to the rear of the vehicle and to reflect it towards an observer, characterised in that there is provided at least one further optical component between the reflector and the observer effective to direct towards the observer, by refraction or reflection, light which upon reflection at the reflector is not directed toward the observer, whereby to provide a wider field of view than that obtainable from the reflector alone. As will be appreciated, the rear view system of the invention is composed of passive optical elements, which present to the driver, optically and physically, largely the same view as that conventionally expected of a vehicle exterior mirror, while at the same time protruding beyond the local exterior surface of the vehicle by substantially less than the amount of an optically comparable conventional mirror, and is distinguished in this respect from rear view systems involving television cameras or other "video" arrangements which present the image of the rearward view on a screen. As used in this specification the term "observer" will be understood to mean the eye or eyes of an observer. In one embodiment the said further optical component is a second reflector and there is further provided a third reflector positioned to reflect light incident thereon from the said reflector towards the said second reflector There is preferably further provided an "objective" refracting element effective to deflect onto the said reflector light from objects outside the observer's field of view through the reflector alone whereby further to extend the lateral field of view of the system. The said further optical component may be a refractive element. According to another aspect of the present invention an optical rear view system for a motor vehicle, comprising reflector positioned forwardly of the observer so as to b in his field of view, is characterised in that the surfac of the system on which light from an object behind the vehicle is first incident lies at an acute angle to the longitudinal axis of the vehicle and is inclined such that a forward part of the incident surface is further form the vehicle axis than a rearward part thereof. The said incident surface of the system may be a face of refractive element effective to deflect incident light towards the vehicle axis or an element having parallel faces the net refractive effect of which is to displace the' path of light passing through it without substantially changing its angle. The incident surface of the system may be continuous, that is having no discontinuities, or may be composed of a plurality of elementary prisms, and the angles of inclination of the incident surfaces of these may vary over the width of the optical element. This extends further the field of view through the system. There may also be further provided a refractive element in the path of light from the reflector to the observer. It is another fundamental characteristic feature of the present invention that at least a part of the reflector lies inside the boundary defined by the outer surface of the vehicle. In another aspect of the invention there is provided an optical rear view system for a motor vehicle, comprising a reflector mounted at least partly within the boundary of the vehicle defined by the surface of the vehicle door, the system being positioned at a height such that the image of objects to the rear of the vehicle formed by the system can be seen by observation of an optical component inboard of the vehicle at approximately the same horizontal level as the dashboard instruments. The present invention also comprehends a motor vehicle fitted with one or more rear view systems as herein defined. The present invention may be put into practice using only reflective elements or by using reflective and refractive elements. In embodiments using only reflective elements, reflection may take place at either silvered or, in the event of total internal reflection, non-silvered surfaces. In the case of refractive elements, these may be prisms either of the conventional, solid type or of the Fresnel type. In either case the surfaces may be planar, cylindrical, spherical, acylindric or aspheric, according to the specific requirements of the particular application. Various specific embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which Figure 1 is a schematic diagram of an embodiment using mirrors only; Figure 2 is a ray diagram illustrating the optical behaviour of the embodiment of Figure 1; Figure 3 is a schematic diagram of an embodiment using both reflecting and refracting surfaces; Figure 4 is a ray diagram which illustrates the optical behaviour of the embodiment shown in Figure 3; • Figure 5 is a diagram illustrating one practical form of the embodiment of Figure 3; Figure 6 is a ray diagram which illustrates the optical behaviour of the embodiment shown in Figure 5; Figure 7 is a diagram schematically illustrating another practical form of the embodiment of Figure 3, but incorporating Fresnel prisms; Figure 8 is a ray diagram which illustrates the optical behaviour of the embodiment shown in Figure 7; Figure 9 schematically illustrates an embodiment similar to that of Figure 7, but incorporating non-planar optical elements; Figure 10 is a ray diagram which illustrates the optical behaviour of the embodiment shown in Figure 9; Figure 11 is a schematic diagram of a further embodiment, in which the parts outside the vehicle may be physically separate from those inside; Figure 12 is a ray diagram which illustrates the optical behaviour of the arrangement shown in Figure 11; Figure 13 is a diagrammatic view illustrating in perspective a further embodiment of the invention seen from the outside of a vehicle; and Figure 14 is a perspective view from inside the vehicle of the embodiment of Figure 13. Referring first to Figure 1, planar surfaces 1,2 and 3 are silvered to act as mirror surfaces to light incident on the faces indicated by the arrows on the lead lines. Surfaces 2 and 3 are substantially parallel and surface 4 schematically represents the physical interconnection of surfaces 1 and 2. It does not form part of the optical system . The body line 10 in the drawings serves to identify the location of the mirror assembly with respect to the vehicle exterior; it may but does not necessarily coincid with a window of the vehicle. The broken line 9 illustrates the surface of an outer element, which may be a parallel face single sheet or a prismatic block filling the whole of the region bounded by the reflector 1, the body 10 and the line 9. Figure 2 illustrates the operation of the rear view syste by reference to a ray diagram. Light entering the rear view system from behind the vehicle, and from narrow lateral angles, enters the driver's eye via a single, conventional reflection at reflector 1. Other light, however, specifically that from wider angles, reaches the eye only after being reflected by a further two reflections. This light, while undergoing a first reflection in the same region of surface 1 as that for narrow angles, becomes shifted to the rear and appears to the eye to come from a region of surface 1 further outboard, a region which does not physically exist, as indicated by the broken lines. To Understand the function of the mirror assembly as described, it is necessary to appreciate that, for distant objects, it is only the ray angle which matters, not its position in space. For closer objects a small compensation is needed, but this can be achieved by the driver moving his head. Only for very nearby objects, not applicable to vehicle exterior mirrors, is there significant ocular conflict over and above that which is accommodated in normal, everyday vision. The illustrated multiple reflection mirror system has a linear field, suffers no dispersion problems, and may be designed to produce a diminished image in the normal way, by making surface 1 appropriately convex. In this last mentioned case, though, it is necessary to set surfaces 2 and 3 out of parallel,at a relative angle according to the linear dimensions of the mirror system and the radius of curvature of surface 1. Light passing through the element 9 may be merely laterally deflected, if this element has parallel surfaces, or may be refracted towards the vehicle axis if the element 9 is a prism. The second embodiment of the invention, is generally illustrated in Figure 3. Planar surfaces 11 and 13 are refracting surfaces, while planar surface 12 is a reflector ( silvered, if necessary), acting to reflect light incident thereon. Figure 4 is a ray diagram constructed by assuming that the space between the three surfaces is filled with a homogeneous transparent medium, typically on acrylic, Plastics material. Such a system produces a non-linear, diminished field, with the image at object distance for all eye positions, together with some dispersion which might be expected to cause colour fringes on the image in certain conditions. The following design examples describe more practical forms of the basic arrangement, together with refinements which have the possibility favourably to modify certain optical or physical characteristics. Figures 5 and 6 show an arrangement using discrete prisms 14,15 and a separate reflector 12, and its ray diagram, respectively. By adopting different materials for the two prisms, in this case acrylic for prism 14 and acrylic/styrene copolymer for prism 15, dispersion may be effectively eliminated or at least reduced to an insignificant level. The angles of all four refracting surfaces, and the reflecting surface, as well as the optical properties of the prisms, are variables by which linearity, image size and dispersion may be developed to produce a desired, or acceptable optical performance. For example, all three aberrations are eliminated in a symmetrical design in which the prisms have equal apex angles, are in the same material, and form equal angles with the mirror. Unfortunately, in such a design the exit rays cannot readily be made to emerge towards the driver's eyes. However, by inserting one or more contact deviation achromatic prisms (not shown) in the light path from mirror assembly to eye this may be rectified. Alternatively, in some instances it may be possible to divert the light path by dual reflection from two additional mirrors (again not shown) . In some applications, for example passenger side mirrors, a diminished image may be desirable in order to widen the field of view. In this context it should be noted that the diminished image obtained by the optical system described is formed at the same distance as the object. This is preferred to the conventional convex mirror to diminish the image for which greater eye accommodation is needed. For reasons of packaging, weight and cost, practical designs incorporating Fresnel prisms are preferred. Figures 7 and 8 illustrate such a design, and its ray diagram, respectively. Preferably, the Fresnel mini- elements 16, 17 are formed only on the inside of each of two prisms 18, 19 as shown. The figures show the prismatic elements 16, 17 on a larger scale than would normally be used in practice, for the sake of clarity. Other possible advantages of the Fresnel type of design include reduced interference with window design and much reduced dispersion, although the discontinuities between individual prismatic mini-elements 16, 17 may constitute an optical disadvantage unless the image produced by each element can be appropriately overlapped. All of the foregoing examples of the prismatic type desig have used planar surfaces in order to keep the image at object distance for all light passing through the system. The introduction of non-planar surfaces tends to destroy this property, causing the image to move in a disconcerting way when the head is moved. Nevertheless, curved surfaces can be useful to change field linearity and image magnification, and may also permit lower protrusion designs. Figures 9 and 10 illustrate schematically such a design and its ray diagram, respectively, using cylindrically curved Fresnel prisms 20, 21. In order to highlight the need to keep the image at object distance, a parallel incident ray bundle 22 is shown in the Figure 10 ray diagram, which emerges from the system still parallel as ray bundle 23, as required. In order to achieve the necessary curvature, flat Fresnel prisms of plastics or other elastic material may be flexed into shape during installation into the mirror assembly housing. Figure 11 illustrates an embodiment in which protrusion is particularly low, and the exterior and interior parts are physically separate. Unlike the foregoing examples, this embodiment may have physically separated inner and outer parts on either side of a window, and may be considered more of a vehicle accessory than part of the door design. This particular embodiment, for which the ray diagram is shown in Figure 12, has been calculated using thin acrylic Fresnel prisms generally indicated by surfaces 24, 25, the outer one 24 of 15 deg prism angle and 1000 mm convex radius of curvature, and the inner one 25 of 35 deg prism angle and 350 mm concave radius of curvature. The reflector 12 has 3500 mm convex radius of curvature. Exterior protrusion is only 40 mm and optical aberrations are small over the practical working range of the design. Image size is diminished about 40%. Regarding installation of the described types of mirror assembly within the constraint of modern vehicle design and manufacture, except as mentioned for the example shown in Figure 11, it is envisaged that the system will generally be housed in the door structure as shown in Figure 13 and 14. In this case it. is anticipated that the majority of the mirror system will be concealed within the interior of a door 27, and that the parts of the system which protrude into the vehicle interior will be conceale by appropriate design of the area surrounding the viewing aperture, and a suitable outer cowling 26 (Figure 13). Adjustment of the system, cleaning and sealing from the outside environment may take several forms. Wherever possible the outermost optical element should form, or be enclosed by, a continuous part of the vehicle's exterior skin (such as the cowling 26), so that the remainder of the mirror system may be designed without the requirement of sealing, thereby facilitating the overall design task. As mentioned, the body line 10 illustrated in the Figures is shown for location purposes only. In most cases it is anticipated that the door dropping glass will finish short of the mirror assembly, and that the remainder of the window aperture visibility requirement will be fulfilled by a fixed quarter light above the mirror assembly, as illustrated in Figures 13 and 14 by the quarter light 30. The key features of the invention as disclosed herein are the dividing and individual routing of incoming light beams, and the displacing of light rays, exploited either separately or together by use of passive optical reflecting and/or refracting elements, to produce a vehicle exterior mirror system in which the exterior protrusion of the system is substantially less than that of an equivalent conventional mirror. Although the invention is illustrated by examples using these principles separately, combinations of the principles ar not excluded Furthermore, the invention also applies to optical systems in which the incoming light beam is brok up into more than two packets of rays which transit the mirror system independently, and which are subsequently reformed for presentation to the eyes. Included in this category are systems in which fragmentation of the light beam causes some parts of the incoming field to be lost one eye, but which are nevertheless effective because th part of the incoming field is accessible to the other eye. Although described hereinbefore in relation to embodimen in which the light rays are all substantially in the sam plane it will nevertheless be appreciated that the chang in direction upon reflection or refraction may also be o of the common plane, allowing greater freedom in positioning the various elements of the system. It will be further appreciated that any of the optical surfaces of any of the optical elements including the reflector, 'may be composed of substantially planar surfa elements inclined to the general plane of the surface at the point where they are located.

Claims: CLAIMS 1. An optical rear view system for a vehicle, comprising a reflector mounted to receive light from objects to the rear of the vehicle and to reflect it towards an observer, characterised in that there is provided at least one further optical component between the reflector and the observer effective to direct towards the observer, by refraction or reflection, a portion of the light which upon reflection at the reflector is not directed towards the observer, whereby to provide a wider field of view then that obtainable from the reflector alone. 2. An optical rear view system according to Claim 1, characterised in that the said further optical component is a second reflector and there is further provided a third reflector positioned to reflect light incident thereon from the said reflector towards the said second reflector. 3. An optical rear view system according to Claim 1, characterised in that there is further provided an "objective" refracting element effective to deflect onto the said reflector light from objects outside the observer's field of view through the reflector alone whereby further to extend the lateral field of view of the system. 4. An optical rear view system according to Claim 1 characterised in that the said further optical component is a refractive element. 5. An optical rear view system for a motor vehicle, comprising a reflector positioned forwardly of the observer so as to be in his field of view and at least one other optical component, characterised in that the surface of the system on which light from an object behind the vehicle is first incident lies at an acute angle to the longitudinal axis of the vehicle and inclined such that a forward part of the incident surface is further from the vehicle axis than a rearward part thereof. 6. An optical rear view system according to Claim 5, characterised in that the said incident surface of the system is a face of a refractive element effective to deflect incident light towards the vehicle axis. 7. An optical rear view system as claimed in Claim 5, characterised in that at least one surface of at least one optical element is composed of a plurality of planar surface elements inclined to the general plane of the said surface. 8. An optical rear view system according to Claim 5 characterised in that the incident surface of the system is composed of a plurality of elementary prisms. 9. An optical rear view system according to Claim 8 characterised in that the angle of inclination of the incident surfaces of the said elementary prisms varies across the width of the said incident surface. 10. An optical rear view system according to Claim 5, characterised in that there is further provided a refractive element in the path of light from the reflecto to the observer. 11. An optical rear view system according to Claim 5, characterised in that at least a part of the reflector lies inside the boundary defined by the outer surface of the vehicle. 12. A motor vehicle having at least one optical rear vie system according to any preceding claims mounted in a position along one side or in the door of the vehicle.

Inventors: MILNER PETER JAMES, MILNER, PETER, JAMES
Applicants: MILNER PETER J, MILNER, PETER, JAMES
Application year: 1989
Main classification: B60R1
IPC codes: B60R1