Abstract:
The invention relates to a head-up display device, including a projector for generating a light beam carrying information to be displayed, a combiner having a display position for displaying the information in the field of vision of a user, and an optical system defining an optical path between the projector and the combiner when the latter is in the display position thereof, for directing the light beam onto the combiner. The optical system includes a first and a second deflecting mirror. The first mirror is arranged for receiving the light beam from the projector and for sending said light beam to the second mirror, the latter being arranged for sending the light beam over the optical path toward the combiner. An actuation system is provided for adjusting the length of the optical path between the projector and the combiner by positioning the first and second deflecting mirrors.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §371 of published PCT Patent Application Number PCT/EP 2011/061218, filed Jul. 4, 2011, claiming priority to French Patent Application Number FR1055779 filed on Jul. 16, 2010, and published as WO2012/007305 on Jan. 19, 2012, the entire contents of which is hereby incorporated by reference herein. 
     TECHNICAL FIELD OF INVENTION 
     The present invention relates to a head-up display device, in particular for motor vehicles, lorries, buses, trains, aircraft, etc. In particular, the invention relates to a head-up display device with a retractable combiner. 
     BACKGROUND OF INVENTION 
     A head-up display device typically includes a projection unit that produces a light beam intended to be directed towards a combiner in order to project images, in particular operating and driving information of a vehicle, in the form of a virtual image, in the field of view of a user, in particular a pilot or motor vehicle driver. 
     Designed originally for the display of information to pilots of combat aircraft, head-up display devices are increasingly used today in particular in the motor vehicle sector, more particularly in cars of medium and high range. Head-up display devices are reputed to contribute to road safety as they allow drivers to read the information without their eyes leaving the road in front of them. The virtual image containing the displayed information is moreover projected at a distance of a few meters in front of the driver, which allows him to read the information without modification of the accommodation of his eyes. 
     Head-up display devices exist which use a part of the windscreen as combiner, i.e. as the optical element which combines the light beam containing the information having to be presented to the user with the light coming from the environment. Other head-up display devices include a combiner independent of the windscreen. Such a combiner comprises a strip having the necessary optical properties to deviate at least a substantial part of the beam coming from the projection unit towards the user, while being sufficiently transparent to allow passage at the same time of a substantial part of the ambient light coming from the environment. 
     It has proved desirable to be able to protect the optical elements of the head-up display device, for example against dust and other detrimental influences, risking deterioration of the projection quality. 
     Another problem is the adjustment of the head-up display device to the needs of the driver. In particular, because the angle of view (the angle relative to the nominal direction up to which the image can be viewed with sufficient contrast) of a head-up display device is typically fairly small and the position of the eyes of the user can vary greatly from one user to the other, the head-up display device should be provided with means allowing the user to adjust the direction in which the beam carrying the information to be displayed at the height of his eyes is returned. 
     U.S. Pat. No. 5,394,203 describes a head-up display device comprising a combiner in the form of a reflective strip mounted tilting and acting as a lid that is closed when the device is not in use. However, given that the strip acts as a lid, one of its sides remains exposed to the detrimental influences. 
     Application WO 2007/057608 presents a head-up display device with a retractable combiner. The combiner is mounted on a movable support so as to be able to be displaced between a display position, in which the combiner is upright facing the driver, and a storage position, in which the combiner is returned back into the case which protects all of the optical and mechanical components of the head-up display device. The limit of travel of the movable support carrying the combiner can be adjusted to obtain adjustment of the angle of slope of the combiner and thus the angle of slope of the axis going from the eyes of the driver to the virtual image. 
     However, the head-up display device of application WO 2007/057608 does not allow adjustment of the distance at which the virtual image is displayed. Now the adjustment of the projection distance is very advantageous from the ergonomic point of view, as it allows the position of the virtual image to be suited relative to the mechanical architecture of the vehicle (in particular relative to the dimensions of the bonnet). Moreover, this type of adjustment allows the user to suit the display to his viewing conditions. 
     Document JP 10 333080 discloses a head-up display device with two deflection mirrors in the optical path between the projector and the combiner. The first of the two mirrors from the projector is mounted rotatable or displaceable in translation to be able to change the vertical position of the virtual image in the field of view of the user. 
     Document US 2005/0024490 describes a head-up display device, in which the last mirror, i.e. the one that is in the field of view of the user is retractable. In its storage position, the mirror forms the lid of the head-up display device. The rear face of this mirror (i.e. the upper face in the storage position) is provided with a foldable cover. This cover is deployed when the mirror is closed to give an appearance of quality to the device. The mirror can be formed as combiner; in this case, the cover is completely retracted when the mirror is in the display position. 
     Document U.S. Pat. No. 5,237,455 describes a head-up display device with a retractable combiner. The opening through which the combiner can be manually removed from and returned to the case is closable by a curtain. The opening and closing of this curtain is also performed manually. 
     SUMMARY OF THE INVENTION 
     A head-up display device comprises a projector to generate a light beam loaded with information to be displayed, a combiner having a display position to display the information in the field of view of a user and an optical system defining an optical path between the projector and the combiner when the latter is in its display position, to direct the light beam at the combiner. In accordance with the invention, the optical system comprises at least a first and a second deviation mirror in the optical path. The first mirror is arranged to receive the light beam from the projector and return it towards the second mirror, the latter being arranged to return the light beam on the optical path towards the combiner. The device also comprises an actuation system configured to adjust the length of the optical path between the projector and the combiner by positioning of the first and second deviation mirrors one relative to the other. By means of the arrangements of the invention, it is possible to adjust the distance at which the virtual image is situated from the combiner (projection distance). 
     The actuation system preferably comprises a mechanism coupled both to the first and to the second mirror. The mechanism could be manually driven by the user (e.g. by means of an adjustment lever connected to the mechanism). However, for more user comfort, the mechanism is preferably driven by an electric motor (e.g. a servomotor) which the user can control by means of a control button (e.g. on the dashboard). 
     In accordance with an advantageous embodiment of the invention, the second mirror is coupled to the mechanism so as to be displaceable in translation (preferably perpendicularly to its surface), and the first mirror is coupled to the mechanism to pivot by an angle determined as a function of the displacement of the second mirror. The angle of slope of the first mirror is in particular preferably given by a linear function of the displacement of the second mirror relative to a reference position. By this coupling of the first and second mirrors, it is ensured that the light beam arrives at the combiner whatever the position of the intermediate mirrors. In a way, by means of the first mirror, automatic aiming of the light beam at the second mirror and at the combiner is performed. On adjustment of the projection distance, the virtual image therefore remains substantially on the same axis passing through the eyes of the driver and the combiner. 
     The projector preferably comprises a spatial light modulator (in English: “spatial light modulator”), e.g. a holographic memory, in which the information to be displayed is stored in the form of holograms, or a backlit liquid crystal display. In this case, the projector advantageously comprises a backlighting light source (e.g. a laser source or one or more luminescent diodes) arranged to send through the liquid crystal display a light beam not yet loaded with the information to be displayed, and in which the liquid crystal display is mounted displaceable transversally to the direction of the light beam. In accordance with a first modification, the light beam can remain immobile when the spatial light modulator is displaced. In accordance with another modification, the projector is configured displaceable in translation in its entirety. It will be noted that the translation of the spatial light modulator transversally to the direction of the beam permits adjustment of the transversal position of the virtual image relative to the axis: eyes of the driver—combiner. The device preferably comprises a control lever mechanically coupled to the spatial light modulator, by means of which the user can adjust the transversal position of the virtual image. Alternatively, the spatial light modulator is displaceable by means of an electric motor (e.g. a servomotor) which the user can control by means of a button or a control knob. The button or the knob in this case transmit the adjustment instructions to the head-up display (e.g. via the communication network of the vehicle), which translates them into a mechanical movement. A modification of the invention in accordance with which the user can control the projection distance and the transversal position by a same button or control knob is considered as particularly ergonomic. 
     The combiner can be formed as a semi-reflective mirror (flat or curved) or diffractive combiner (i.e. a combiner that deviates the light towards the user by means of an optical diffraction grating, optionally integrating an enlargement of the virtual image and/or a luminance level control.) The combiner is advantageously made of a plastics material. 
     In accordance with a very advantageous embodiment of the invention, the combiner is formed as a retractable combiner having a storage position in addition to its display position. The combiner is then preferably connected to an articulated mechanism configured to displace the combiner between the display position and the storage position. 
     In accordance with this embodiment of the invention, the head-up display device preferably comprises a case in which are arranged the projector, the optical system and the combiner, the case being provided with a first opening, through which the combiner can pass on its displacement between the storage and display positions, and a second opening, through which the light beam can pass from the optical system towards the combiner. 
     Preferably, the case also comprises a closure curtain to close the first opening when the combiner is in its storage position. 
     It will be appreciated that the movement which the combiner performs on its passage from the storage position to the display position can be so designed that the combiner and/or the mechanism to which the combiner is connected forces (e.g. by pushing) the curtain out of the path of the combiner to open the passage through the first opening. 
     The case preferably comprises a trapdoor closing the second opening when the combiner is in its storage position. Still more advantageously, the trapdoor is provided with a housing space to receive the curtain when this is forced out of the path of the combiner. 
     The opening and closing mechanism of the trapdoor is advantageously coupled to the mechanism intended to displace the combiner between the display position and the storage position. 
     The head-up display device preferably comprises a return means, e.g. a return spring, arranged to accumulate mechanical energy when the curtain is forced out of the path of the combiner and to use this energy to return the curtain into a closure position of the first opening when the combiner passes from its display position to its storage position. 
     The man skilled in the art will note that the system for retraction of the combiner and/or closure of the trapdoor can be formed independently of the system for adjustment of the projection distance described above. However, these two aspects of the invention are combined in particularly advantageous manner in the embodiment described by way of illustration below. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Other features and characteristics of the invention will become apparent from the detailed description of an advantageous embodiment presented below, by way of illustration, with reference to the attached drawings. These show: 
         FIG. 1 : a partial three-dimensional view of a head-up display device in accordance with a preferred embodiment of the invention; 
         FIG. 2 : a longitudinal section of the system for retraction of the combiner of the device of  FIG. 1 , with the combiner in its storage position; 
         FIG. 3 : a longitudinal section of the system of  FIG. 2 , the combiner being between its storage position and its display position; 
         FIG. 4 : a partial view of the system for opening and closing the curtain protecting the combiner in its storage position; 
         FIG. 5 : a partial view of the system of  FIG. 4 , with the combiner in its display position; 
         FIG. 6 : a basic diagram of the system for adjustment of the position of the virtual image; and 
         FIG. 7 : a partial view of the mechanism of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a perspective view of a head-up display device  10  for a motor vehicle, in accordance with a preferred embodiment of the invention. The device  10  comprises a system for retraction of the combiner, described in more detail with reference to  FIGS. 2 to 5 , as well as a system for adjustment of the position of the virtual image, described in more detail below with reference to  FIGS. 6 and 7 . 
     The device  10  firstly comprises a projector  12  to generate the light beam loaded with the image representing the information to be displayed to the driver of the vehicle. The projector  12  includes a liquid crystal display  14 , a light source  16  (coherent or non-coherent, depending on the type of the combiner, which can be diffractive or reflective producing a backlighting light beam and a mirror  18  returning the backlighting beam coming from the source  16  through the liquid crystal display  14 . The liquid crystal display functions as a spatial light modulator and produces the image that will be displayed to the driver. The optical path between the projector  12  and the display position of the combiner  20  is defined by an optical system. This comprises a first deviation mirror  22  and a second deviation mirror  24 . The first mirror  22  is arranged to receive the light beam from the projector  12  and return it towards the second mirror  24 , which is arranged to return the light beam to the combiner  20 , when this is in its display position (shown in  FIG. 1 ). 
     The combiner  20  is retractable by means of a retraction system shown in more detail in  FIGS. 2 to 5 . In addition to its display position, the combiner  20  has a storage position essentially flattened inside the case  25  of the head-up display device  10 . The combiner  20  is fixed to an articulated mechanism which displaces it between the display and storage positions. More precisely, the articulated mechanism comprises, on either side of the combiner  20 , a first connecting rod  26  and a second connecting rod  28  which are joined by an articulation  30  at one of their ends. The other end of the first connecting rod  26  is housed movable in rotation on a first bearing  32  displaceable in translation by an electric motor  34 , while the other end of the second connecting rod  28  is housed movable in rotation on a second bearing  36  fixed relative to the case  25 . The combiner  20  is attached to the first connecting rod  26 . To bring the combiner from its storage position (shown in  FIG. 2 ) to its display position, the motor  34  turns a pinion  38 , which drives the displacement of the first bearing  32  on a rack  40  and therefore the shortening of the base of the triangle the vertices of which are formed by the bearings  32  and  36  and by the articulation  30 . As a result the combiner  20  rises progressively as the first and second bearings  32 ,  36  approach each other. When the combiner  20  is completely upright, the motor  34  stops and locks the articulated mechanism in the bent position. Preferably, the limit of travel of the pinion  38  on the rack  40  is adjustable by the driver, who can thus adjust the slope of the combiner  20  in the display position. 
     The case  25  of the device  10  comprises a first opening, through which the combiner  20  passes on its displacement between the storage and display positions, and of a second opening, through which the light beam passes from the optical system towards the display position of the combiner  20 . A closure curtain  42  is provided to close the first opening and protect the combiner  20  against dust when the combiner  20  is in its storage position. 
     As shown in  FIGS. 4 and 5 , the movement performed by the combiner  20  on its passage from the storage position to the display position is so designed that the combiner pushes the curtain  42  out of its path to open the passage through the first opening. When the combiner  20  pushes back the curtain  42 , this is displaced in slideways  44  provided on the side walls of the case  25  (see  FIG. 1 ) and on the trapdoor  46  provided to close the second opening when the combiner is in its storage position. On the lower side of the trapdoor  46 , the grooves  48  define a housing receiving the curtain  42  when this is displaced out of the path of the combiner  20 . When the curtain  42  is displaced by the combiner  20 , it pushes against a fixing piece  50 , fixed to a return spring  52  that stretches and accumulates mechanical energy. In the display position of the combiner, the curtain  42  remains in abutment against the combiner  20 . The mechanical energy accumulated in the return spring  52  is used to return the curtain  42  into the closure position of the first opening when the motor  34  operates in the opposite direction and the combiner  20  passes from its display position to its storage position 
     To open and close the trapdoor  46 , the head-up display device comprises a trapdoor opening and closing mechanism coupled to the mechanism intended to displace the combiner  20  between the display position and the storage position. The mechanism for opening and closing the trapdoor comprises a spring  54 , a driving element  56 , slideways  58  and a pivoting element  60  attached to the trapdoor  46 . When the combiner  20  is in its storage position, the motor  34  and the bearing  32  abut against the driving element which is at its limit of travel and holds the trapdoor  46  closed by means of the pivoting element  60 . In this position, the spring  54  is compressed. When the motor  34  and the bearing  32  are displaced in the direction of the second bearing  36  following a command for turning on the head-up display device  10 , the spring  54  is decompressed and displaces the driving element  56  in the slideways  58 . This displacement turns the pivoting element  60  about its axis  62  and the trapdoor passes into the open position, thus permitting the passage of the light beam coming from the projector  12 . 
     The head-up display device  10  also includes a system for adjustment of the position of the virtual image ( FIGS. 6 and 7 ). The projection distance of the virtual image is adjustable by means of a system for actuation of the deviation mirrors  22  and  24 . The vertical position of the virtual image can moreover be adjusted by a system for translation of the liquid crystal display  14 . 
     The principal of the adjustment of the projection distance around a nominal distance is explained with reference to  FIG. 6 . The image comprising the information to be displayed is generated by the projector  12 . The length p of the optical path between the projector and the combiner (in the display position) is given by
 
 p=L 0 +L 1 +L 2  Eq. 1,
 
in which L 0  designates the distance between the projector and the mirror  22  (also M 1  in  FIG. 6 ), L 1  the distance between the mirror  22  and the mirror  24  (also M 2 ), and L 2  the distance between the mirror  24  and the combiner  20 .
 
     The distance of the virtual image from the combiner D iv  can be approximated with sufficient accuracy by the product of the length of the optical path between the projector and the combiner p and the enlargement factor g of the combiner (Eq. 2).
 
 D   iv   =p·g   Eq. 2.
 
     To adjust the projection distance, the length of the optical path between the projector  12  and the combiner  20  can therefore be adjusted. In the device  10 , the length of the optical path p is adjusted by positioning of the first and second deviation mirrors  22  and  24  one relative to the other. 
     Two cases can be distinguished. When it is required to reduce the projection distance (relative to the nominal projection distance), the mirror  24  is displaced upwardly in  FIG. 6  (perpendicularly to its surface) and the mirror  22  is simultaneously turned anticlockwise. When it is required to increase the projection distance (relative to the nominal projection distance) the mirror  24  is displaced downwardly in  FIG. 6  (perpendicularly to its surface) and the mirror  22  is simultaneously turned clockwise. 
     In this way, the projection distance can be varied between a minimum value D iv     —     min  and a maximum value D iv     —     max , defined respectively by Eq. 3 and Eq. 4
 
 D   iv     —     min   =g ·( L 0 +L 1 min   +L 2 min ) and  Eq. 3
 
 D   iv     —     min   =g ·( L 0 +L 1 max   +L 2 max )  Eq. 4.
 
The extreme positions of the mirrors  22  and  24  are shown by broken lines in  FIG. 6 .
 
     The mirrors  22  and  24  are positioned by means of a mechanism coupled both to the first and to the second mirror (see  FIG. 7 ). The mechanism is driven by an electric motor  64  which the user can control by means of a control button (e.g. on the dashboard). 
     The second mirror  24  is coupled to the mechanism so as to be displaceable in translation perpendicularly to its reflective surface. The first mirror  22  is coupled to the mechanism to pivot by an angle θ determined as a function of the displacement of the second mirror  24 . As shown in  FIG. 7 , the mirror  24  is fixed on a movable support which can slide perpendicularly to the reflective surface of the mirror  24 . The mirror  24  is positioned by means of an electric motor  64  that drives a pinion  66  meshing in a rack  68  fixed on the movable support carrying the mirror  24 . When the motor  64  turns, it causes the simultaneous turning of the first mirror  22 , by means of a gear and belt mechanism  70 . The transmission ratios between the motor  64  and the second mirror  22 , on the one hand, and between the motor  64  and the mirror  22 , on the other, are so selected that automatic aiming is effected of the light beam at the second mirror  24  and at the combiner  20  and it is therefore ensured that the light beam arrives substantially at the same place on the combiner  20  whatever the position of the intermediate mirrors  22  and  24 . On adjustment of the projection distance, the driver does not therefore see the virtual image to be displaced vertically or laterally. 
     To position the virtual image vertically, the liquid crystal display  14  can be displaced transversally relative to the direction of the backlighting light beam coming from the light source  16 . ( FIG. 7  does not show the deviation mirror  18  between the light source  16  and the liquid crystal display  14 .) The displacement of the liquid crystal display  14  is effected by means of an electric motor  72 , which drives a pinion  74 , and rack  76  system. As the displacement of the liquid crystal display  14  is in a plane perpendicular to the light beam, there is no notable resulting variation in the projection distance of the virtual image. 
     The driver can therefore adjust the projection distance and the vertical position of the virtual image independently. 
     To control the different electric motors (which can be servomotors), the head-up display device  10  comprises a control unit (not shown in the figures) having one or more interfaces for interaction with the user (e.g. control buttons). In the example shown in the figures, the user can in particular adjust the slope of the combiner (determined by the limit of travel of the pinion  38  on the rack  40 ), which allows him to adjust the display to his height (or, more precisely, the height of his eyes); The projection distance (determined by the position of the mirrors  22  and  24 ); and the vertical position of the virtual image (determined by the position of the liquid crystal display  14 ). 
     It will be appreciated that the head-up display device  10  is in a compact, easily integrated form, while offering the facility of adjustment to the individual needs of the user. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow. 
     Key: 
     
         
           10  head-up display device 
           12  projector 
           14  liquid-crystal display 
           16  light source 
           18  mirror 
           20  combiner 
           22  first deviation mirror 
           24  second deviation mirror 
           25  case 
           26  first connecting rod 
           28  second connecting rod 
           30  articulation 
           32  first bearing 
           34  electric motor 
           36  second bearing 
           38  pinion 
           40  rack 
           42  closure curtain 
           44  slideway 
           46  trapdoor 
           48  groove 
           50  fixing piece 
           52  return spring 
           54  spring 
           56  driving element 
           58  slideway 
           60  pivoting element 
           62  pivoting axis 
           64  electric motor 
           66  pinion 
           68  rack