Rear-view system for vehicles
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention concerns improvements in or relating to rear view systems for vehicles and vehicles incorporating such systems. 
     In particular, although not exclusively, the present invention has reference to such a system suitable for use on motorised road vehicles. 
     2. Description of Related Art 
     Conventionally, a motorized road vehicle is provided with an internally mounted rear view mirror to give the driver a central vision through the rear window, and either wing or door mounted mirrors to give marginal vision to the rear and, in a narrow path, adjacent the side of the vehicle. For reasons of safety, it is desirable to afford the driver of the vehicle with as comprehensive as possible a view of the prevailing ambient driving conditions. It is known therefore to enhance the vision through the rear window by making the mirror convex to provide a panoramic view, but clearly the degree to which such can be achieved depends upon the vehicle body configuration and invariably the view is impaired by opaque parts of the body structure. Additionally, or in the alternative, it has been proposed to locate a prismatic lens at the rear of a vehicle, more especially a commercial vehicle, such that images of objects immediately to the rear of the vehicle are transmitted to the driver through the agency of a mirror. Similarly, endeavours have been made to improve the vision given by side mirrors, for example by adding a small convex mirror section in one corner in an attempt to give a wider viewing spectrum. However, the image is inevitably small which necessarily militates against the alleged advantage of providing a vision of greater breadth. 
     It is further known to provide side mirrors combined in close juxtaposition with prismatic arrangements for refracting light rays from objects to the rear of the vehicle, but the images of the mirrors necessitate diversion of the driver&#39;s eyes from the path ahead, and in any event tend not to widen the viewing scope. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to provide a rear view system for a vehicle having the capacity of facilitating inspection of the rear vista and for capturing a wider field of view than possible with conventional or known systems. 
     It is a further object of the invention to provide a vehicle incorporating such a rear view system. 
     According to a first aspect of the invention a rear view system for a vehicle includes in combination a light transmitting member and a light reflective medium spatially displaced from the member, the member presenting a first face for light emergence from which in use light rays are directed towards the medium and a second face for light incidence, each face being disposed on a respective side of a median plate, the member comprising a plurality of elemental prismatic sections, the prismatic angles of the elemental sections progressively changing along the length of the member whereby rays of refracted light emerging through the first face are in parallelism or substantial parallelism one with the other irrespective of the angles of incidence of the rays. 
     Advantageously, the member is so designed to ensure that the incident rays undergo essentially minimum deviation through the prismatic elemental sections. 
     Conveniently the shape of the first face of the member is generated by a locus of points calculated by the following formulae wherein the `y` axis is aligned along the median plane and the `x` axis extends orthogonally thereto: 
     
         x.sub.n =sin [(A.sub.n +d.sub.n)/2]·f.sub.n /cos (A.sub.n /2)+x.sub.n-1                                             ( 1) 
    
     
         y.sub.n =cos [(A.sub.n +d.sub.n)/2]·f.sub.n /cos (A.sub.n /2)+y.sub.n-1                                             ( 2) 
    
     Similarly the shape of the second face of the member is generated by a locus of points calculated by the following formulae wherein the `y` axis is aligned along the median plane and the `x` axis extends orthogonally thereto: 
     
         x.sub.n =[sin {(A.sub.n -d.sub.n)/2}]·[f.sub.n +sin {(d.sub.n -d.sub.n-1)/2}·W.sub.n-1 ]/cos (A.sub.n /2)+x.sub.n( 3) 
    
     
         y.sub.n =[cos {(A.sub.n -d.sub.n)/2}]·[f.sub.n +sin{(d.sub.n -d.sub.n-1)/2}·W.sub.n-1 ]/cos (A.sub.n /2)+y.sub.n( 4) 
    
     In the above formulae, the symbols used except where indicated otherwise have the following meanings or values: ##EQU1## 
     In practice the member is of substantially concavo-convex form with the concave surface constituting the first face. The other surface constituting the second face has contiguous concave and convex parts extending in the direction of the median plane. The first and second faces progressively diverge from one another with the increasing prismatic angle of the elemental sections, W n  giving the varying width of the member. The first face may be angularly disposed in relation to the median plane in order in use to project emergent rays in any desired direction onto the light reflective medium. The ends of the member may be planar or of any convenient shape. 
     The length of the member from its smallest width to its largest width is chosen to give the broadest spectrum of image capture, and a particular and unique advantage of the present invention resides in the angular scope which the configuration of the member affords. The angular scope extends from 0° on a line perpendicular to the median plane to approximately 90° thereto. 
     The depth of the member may be costed dependent upon the individual requirements. 
     The light reflective medium may conveniently be a mirror of any suitable profile and shape, for example it may be plane, concave or convex, but the medium may in the alternative be prismatic and suitably oriented to reflect incident light towards a viewer. 
     According to a second aspect of the invention a vehicle including a driving position and a rear view system according to the first aspect wherein the light transmitting member is located to one side of the direct forward line of sight of the driving position, and the light reflective member is located in or adjacent the direct line of sight of the driving position. 
     The vehicle is preferable provided with means for positively directing or collimating the rays emerging from the first face of the light transmitting member onto the light reflective member. 
     The vehicle may be a road vehicle, motorised or manually powered, and more particularly, but not especially, is an automobile, in which case a light transmitting member is located on a respective front door in the manner of a conventional side mirror. 
     Alternatively, the light transmitting member may be located in a suitable position on the vehicle body. The member may be held within a housing and the housing may be integral with the door or mounted thereon, and may be streamlined. It is to be understood, however, that the light transmitting member is inherently streamlined and thus may be mounted on the vehicle in an appropriate manner without the need for a housing. 
     The light reflective member may conveniently be disposed on or in the dashboard of an automobile for ease of visibility, but any other suitable position may be selected to give the driver of the vehicle direct and unimpaired vision of the images transmitted by the member without the necessity of moving his head. 
     When located on a vehicle because of the angular scope of the light transmitting member, the sweep of vision given to the driver is from a point orthogonal to the driving position, which is normally a blind spot with conventional rear view systems, to a point directly to the rear of the vehicle. In this latter respect, the member may conveniently be disposed as to capture part of the vehicle body to provide a reference image for the driver to facilitate the judgement of distances and accordingly the proximity of other vehicles or objects. In view of the wide angular scope afforded by the rear view system, it can be a special feature of the invention that the light transmitting member may be of static form without the facility to change its orientation by the use of electronic components which make conventional mirrors expensive and troublesome to maintain. However, it is within the scope of this invention to provide means for changing the orientation of the member. 
     The light reflecting medium may be orientable to suit the needs of the individual driver or in the alternative it may be fixed in position. 
     Whilst the principal field of application of the present invention is for automobiles, it is to be understood that the expression `vehicle` is not to be limiting and accordingly will embrace any conveyance or mobile structure requiring a rear viewing facility. Thus for example the invention may also be utilised in aircraft or shipping where comprehensive vision of the ambient conditions is desirable, if not essential. 
     By way of example only, one form or rear view system according to the invention is illustrated in graphical form in the accompanying drawings, 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a plan view of the light transmitting member shown against an x,y plot; 
     FIG. 2 is a plan view corresponding to FIG. 1 and showing the light transmitting member in plan with the incident and emergent light paths; and 
     FIG. 3 is plan view of a part of a vehicle shown in diagrammatic form with the rear view system mounted thereon. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT(S) 
     With reference to FIGS. 1 and 2 of the drawings, a rear view system 1 includes a mirrorless light transmitting means 2 having a first face 4 through which refracted light emerges and a second face 6 for light incidence, the faces being disposed either side of a median plane 8. As can be seen from the illustrations, the member is substantially concavo-convex in form and its faces are generated as the loci of points calculated in accordance with the following formulae with the `y` axis coincident with the median plane. The first face 4 is substantially concave in shape whereas the face 6 presents a combined concave/convex profile in which a part of the face is concave and a contiguous part is convex. 
     For the first face 4: 
     
         x.sub.n =sin [(A.sub.n +d.sub.n)/2]·f.sub.n /cos (A.sub.n /2)+x.sub.n-1                                             (1) 
    
     
         y.sub.n =cos [(A.sub.n +d.sub.n)/2]·f.sub.n /cos (A.sub.n /2)+y.sub.n-1                                             (2) 
    
     For the second face 6: 
     
         x.sub.n =[sin {(A.sub.n -d.sub.n)/2}]·[f.sub.n +sin {(d.sub.n -d.sub.n-1)/2}·W.sub.n-1 ]/cos (A.sub.n /2)+x.sub.n(3) 
    
     
         y.sub.n =[cos{(A.sub.n -d.sub.n)/2}]·[f.sub.n +sin {(d.sub.n -d.sub.n-1)/2}·W.sub.n-1 ]/cos (A.sub.n /2)+y.sub.n(4) 
    
     In the above formulae, the symbols used except where indicated other wise have the following meanings of values: ##EQU2## 
     In this example, values for the x,y coordinates for both faces have been calculated over a full range of prismatic angles from 0° to 82° at 2° intervals and the results are shown in the accompanying table for which the key is provided at its foot. Additionally, the material from which the member is formed is crown glass having a refractive index of 1.523. 
     As will more particularly be seen from FIG. 2, the angles of incidence of rays on face 6 vary from 10° to 80° as shown; the rays are refracted by the member undergoing minimum deviation to emerge through face 4 in substantial parallelism to give an image. The emergent rays are directed towards a light reflecting medium (not shown) which in this example is a plane mirror spatially displaced from face 4 of the member. 
     Referring not to FIG. 3, when the rear view system 1 is employed on an automobile generally depicted at 10, the member 2 is mounted on the door 12 adjacent a driving position 14, and a mirror 16 is located on or in the dashboard 15 directly in front of the driving position as shown. A further member 2 (not shown) is mounted on the passenger door (not shown) and is disposed so as to direct rays emerging from its face 4 to a further mirror 18 located adjacent mirror 16 thereby to provide the driver with a comprehensive view from both sides of the automobile 10 which does not require lateral movement of the head, whilst providing a wider image capture than that hitherto available with conventional side mirrors. 
     The principal advantage of the present invention is that the driver of a vehicle is provided with a more comprehensive picture of the ambient conditions than is possible with conventional mirrors or known devices, and thus the safety of driving is considerably enhanced, particularly by removing blind spots normally associated with existing systems. 
     Whilst the present invention has been specifically described in relation to a mirrorless light transmitting means manufactured from crown glass, it is to be understood that other materials or media may be used therefor and the refractive index will vary accordingly. 
     It is also to be understood that the invention can be made in kit form for retrofitting to existing vehicles. 
     
                                           TABLE                                   
__________________________________________________________________________
A                Devn.               First side Second side               
Ref. ind = 1.2                                                            
        r   i    o    ldg. edge                                           
                           tr. edge                                       
                                W    x     y    x    y                    
__________________________________________________________________________
0.0     0.0 0.000                                                         
                 0.000                                                    
                      0.000                                               
                           0.000                                          
                                2.000                                     
                                     -1.000                               
                                           0.000                          
                                                1.000                     
                                                     0.000                
2.0     1.0 1.523                                                         
                 1.046                                                    
                      0.477                                               
                           1.523                                          
                                2.035                                     
                                     -1.027                               
                                           1.000                          
                                                1.008                     
                                                     1.018                
4.0     2.0 3.047                                                         
                 2.094                                                    
                      0.953                                               
                           3.047                                          
                                2.107                                     
                                     -1.081                               
                                           2.018                          
                                                1.026                     
                                                     2.055                
6.0     3.0 4.572                                                         
                 3.144                                                    
                      1.428                                               
                           4.572                                          
                                2.214                                     
                                     -1.162                               
                                           3.036                          
                                                1.052                     
                                                     3.092                
8.0     4.0 6.099                                                         
                 4.197                                                    
                      1.901                                               
                           6.099                                          
                                2.358                                     
                                     -1.271                               
                                           4.054                          
                                                1.086                     
                                                     4.131                
10.0    5.0 7.628                                                         
                 5.256                                                    
                      2.372                                               
                           7.628                                          
                                2.539                                     
                                     -1.406                               
                                           5.073                          
                                                1.129                     
                                                     5.172                
12.0    6.0 9.160                                                         
                 6.321                                                    
                      2.840                                               
                           9.160                                          
                                2.756                                     
                                     -1.570                               
                                           6.093                          
                                                1.181                     
                                                     6.217                
14.0    7.0 10.697                                                        
                 7.393                                                    
                      3.303                                               
                           10.697                                         
                                3.010                                     
                                     -1.761                               
                                           7.115                          
                                                1.241                     
                                                     7.264                
16.0    8.0 12.237                                                        
                 8.475                                                    
                      3.763                                               
                           12.237                                         
                                3.302                                     
                                     -1.981                               
                                           8.138                          
                                                1.311                     
                                                     8.317                
18.0    9.0 13.783                                                        
                 9.567                                                    
                      4.217                                               
                           13.783                                         
                                3.633                                     
                                     -2.229                               
                                           9.163                          
                                                1.389                     
                                                     9.374                
20.0    10.0                                                              
            15.335                                                        
                 10.670                                                   
                      4.665                                               
                           15.335                                         
                                4.003                                     
                                     -2.506                               
                                           10.190                         
                                                1.475                     
                                                     10.438               
22.0    11.0                                                              
            16.894                                                        
                 11.788                                                   
                      5.106                                               
                           16.894                                         
                                4.413                                     
                                     -2.813                               
                                           11.220                         
                                                1.571                     
                                                     11.509               
24.0    12.0                                                              
            18.460                                                        
                 12.921                                                   
                      5.540                                               
                           18.460                                         
                                4.864                                     
                                     -3.149                               
                                           12.254                         
                                                1.676                     
                                                     12.589               
26.0    13.0                                                              
            20.035                                                        
                 14.071                                                   
                      5.965                                               
                           20.035                                         
                                5.357                                     
                                     -3.517                               
                                           13.290                         
                                                1.790                     
                                                     13.677               
28.0    14.0                                                              
            21.620                                                        
                 15.240                                                   
                      6.380                                               
                           21.620                                         
                                5.894                                     
                                     -3.915                               
                                           14.332                         
                                                1.913                     
                                                     14.777               
30.0    15.0                                                              
            23.215                                                        
                 16.430                                                   
                      6.785                                               
                           23.215                                         
                                6.476                                     
                                     -4.346                               
                                           15.377                         
                                                2.045                     
                                                     15.888               
32.0    16.0                                                              
            24.822                                                        
                 17.643                                                   
                      7.178                                               
                           24.822                                         
                                7.105                                     
                                     -4.810                               
                                           16.429                         
                                                2.186                     
                                                     17.013               
34.0    17.0                                                              
            26.441                                                        
                 18.883                                                   
                      7.559                                               
                           26.441                                         
                                7.783                                     
                                     -5.309                               
                                           17.486                         
                                                2.338                     
                                                     18.154               
36.0    18.0                                                              
            28.075                                                        
                 20.151                                                   
                      7.925                                               
                           28.075                                         
                                8.511                                     
                                     -5.843                               
                                           18.551                         
                                                2.499                     
                                                     19.312               
38.0    19.0                                                              
            29.725                                                        
                 21.450                                                   
                      8.275                                               
                           29.725                                         
                                9.293                                     
                                     -6.413                               
                                           19.623                         
                                                2.670                     
                                                     20.490               
40.0    20.0                                                              
            31.392                                                        
                 22.785                                                   
                      8.608                                               
                           31.392                                         
                                10.132                                    
                                     -7.022                               
                                           20.704                         
                                                2.852                     
                                                     21.690               
42.0    21.0                                                              
            33.079                                                        
                 24.158                                                   
                      8.921                                               
                           33.079                                         
                                11.030                                    
                                     -7.671                               
                                           21.794                         
                                                3.044                     
                                                     22.915               
44.0    22.0                                                              
            34.787                                                        
                 25.574                                                   
                      9.213                                               
                           34.787                                         
                                11.992                                    
                                     -8.362                               
                                           22.896                         
                                                3148 24.169               
46.0    23.0                                                              
            36.519                                                        
                 27.037                                                   
                      9.481                                               
                           36.519                                         
                                13.021                                    
                                     -9.098                               
                                           24.011                         
                                                3.463                     
                                                     25.455               
48.0    24.0                                                              
            38.277                                                        
                 28.553                                                   
                      9.723                                               
                           38.277                                         
                                14.125                                    
                                     -9.880                               
                                           25.140                         
                                                3.689                     
                                                     26.779               
50.0    25.0                                                              
            40.064                                                        
                 30.129                                                   
                      9.936                                               
                           40.064                                         
                                15.307                                    
                                     -10.713                              
                                           26.285                         
                                                3.928                     
                                                     28.144               
52.0    26.0                                                              
            41.885                                                        
                 31.770                                                   
                      10.115                                              
                           41.885                                         
                                16.575                                    
                                     -11.598                              
                                           27.449                         
                                                4.181                     
                                                     29.558               
54.0    27.0                                                              
            43.743                                                        
                 33.486                                                   
                      10.257                                              
                           43.743                                         
                                17.938                                    
                                     -12.542                              
                                           23.633                         
                                                4.447                     
                                                     31.028               
56.0    28.0                                                              
            45.644                                                        
                 35.287                                                   
                      10.356                                              
                           45.644                                         
                                19.406                                    
                                     -13.547                              
                                           29.841                         
                                                4.727                     
                                                     32.563               
58.0    29.0                                                              
            47.592                                                        
                 37.185                                                   
                      10.408                                              
                           47.592                                         
                                20.990                                    
                                     -14.619                              
                                           31.077                         
                                                5.023                     
                                                     34.174               
60.0    30.0                                                              
            49.597                                                        
                 39.193                                                   
                      10.403                                              
                           49.597                                         
                                22.705                                    
                                     -15.766                              
                                           32.344                         
                                                5.335                     
                                                     35.874               
62.0    31.0                                                              
            51.665                                                        
                 41.331                                                   
                      10.335                                              
                           51.665                                         
                                24.568                                    
                                     -16.994                              
                                           33.647                         
                                                5.665                     
                                                     37.681               
64.0    32.0                                                              
            53.810                                                        
                 43.621                                                   
                      10.190                                              
                           53.810                                         
                                26.602                                    
                                     -18.313                              
                                           34.992                         
                                                6.012                     
                                                     39.615               
66.0    33.0                                                              
            56.046                                                        
                 46.092                                                   
                      9.954                                               
                           56.046                                         
                                28.836                                    
                                     -19.735                              
                                           36.387                         
                                                6.379                     
                                                     41.704               
68.0    34.0                                                              
            58.392                                                        
                 48.783                                                   
                      9.608                                               
                           58.392                                         
                                31.305                                    
                                     -21.274                              
                                           37.842                         
                                                6.765                     
                                                     43.987               
70.0    35.0                                                              
            60.875                                                        
                 51.749                                                   
                      9.125                                               
                           60.875                                         
                                34.060                                    
                                     -22.947                              
                                           39.367                         
                                                7.171                     
                                                     46.513               
72.0    36.0                                                              
            63.534                                                        
                 55.067                                                   
                      8.466                                               
                           63.534                                         
                                37.169                                    
                                     -24.780                              
                                           40.979                         
                                                7.594                     
                                                     49.357               
74.0    37.0                                                              
            66.429                                                        
                 58.858                                                   
                      7.571                                               
                           66.429                                         
                                40.733                                    
                                     -26.805                              
                                           42.700                         
                                                8.030                     
                                                     52.631               
76.0    38.0                                                              
            69.661                                                        
                 63.322                                                   
                      6.339                                               
                           69.661                                         
                                44.914                                    
                                     -29.068                              
                                           44.563                         
                                                8.462                     
                                                     56.523               
78.0    39.0                                                              
            73.427                                                        
                 68.853                                                   
                      4.573                                               
                           73.427                                         
                                50.000                                    
                                     -31.644                              
                                           46.621                         
                                                8.851                     
                                                     61.384               
80.0    40.0                                                              
            78.228                                                        
                 76.455                                                   
                      1.772                                               
                           78.228                                         
                                56.636                                    
                                     -34.664                              
                                           48.970                         
                                                9.058                     
                                                     68.071               
82.0    41.0                                                              
            87.677                                                        
                 93.353                                                   
                      -5.677                                              
                           87.677                                         
                                68.204                                    
                                     -38.432                              
                                           51.865                         
                                                7.686                     
                                                     81.875               
__________________________________________________________________________
 Key to table of figures:                                                 
 Col. 1 A = angle of prism                                                
 Col. 2 r = angle of refraction (= 0.5 A)                                 
 Col. 3 i = angle of incidence (i = arcsin (Ref ind. sinr))               
 Col. 4 devn. = o = 2i-2r                                                 
 Col. 5 ldg. edge = 0.5 (A - o)                                           
 Col. 6 tr. edge = 0.5 (A + o)