Abstract:
A headlight for motor vehicles comprising a light-shield mechanism having at least first and second rotary light shields for producing respectively at least first and second different light beams, wherein the shield mechanism also comprises at least one means of mechanically locating the idle position of the shield mechanism, and an actuator able to make the first and second light shields, turn in two directions of rotation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention concerns in general terms a headlight for a motor vehicle comprising a light shield mechanism having at least two rotary light shields for producing respectively two different light beams. More particularly, the invention concerns a dual-function headlight capable of producing dipped/low beams and main light beams for both left-hand and right-hand traffic modes. 
         [0003]    2. Description of the Related Art 
         [0004]    A dual-function headlight comprising two rotary light shields is known from the inventive entity. The light shields make it possible to obtain a cutoff, so as to obtain, notably, dipped/low beam light beam for right-hand traffic and left-hand traffic modes. The rotation of the shields and their angular positioning are obtained by means of a control by stepping motor. This solution of control by stepping motor has drawbacks. 
         [0005]    A stepping motor is an actuator that remains relatively expensive and that requires adapted electronics, capable of generating the various pulsed signals necessary for its control. In addition, the problem of the loss of a step is liable to introduce imprecision in the angular positioning of the shields, which requires the implementation of particular provisions for periodically referencing the angular position of the axis of the stepping motor. 
         [0006]    There is, therefore, a need to provide an improved headlight that overcomes one or more of the problems of the prior art. 
       SUMMARY OF THE INVENTION 
       [0007]    The main objective of the invention is to provide a technical alternative to the use of a stepping motor in this type of headlight. 
         [0008]    The headlight for motor vehicles according to the invention comprises a light shield mechanism having at least a first rotary light shield and a second rotary light shield for producing respectively at least a first light beam and a second light beam wherein the first and second light beams are different light beams. 
         [0009]    In one aspect, the invention concerns a headlight for a motor vehicle comprising a light shield mechanism having at least first and second rotary light shields for producing respectively at least first and second light beams, such that the said shield mechanism also comprises: 
         [0010]    at least one means of mechanical location of the idle position of the shield mechanism; and 
         [0011]    an actuator able to make the first and second light shields turn in two directions of rotation. 
         [0012]    The mechanical location means is perfectly chosen from a retractable stop or other mechanical means of the roller, ball, spring or spring bolt type. “Idle position” means the position towards which the shield returns naturally, in particular in the case of failure of its actuation means. This is generally a position in which the beam emitted is a beam with cutoff (in contradistinction to a beam without cutoff of the main beam type). 
         [0013]    It should be noted that the term “headlight” used in the context of the present text concerns in fact, unless otherwise specified, the unit optical module able to be integrated subsequently in a complete headlight possessing other modules. 
         [0014]    In accordance with the invention, the shield mechanism also comprises, according to one embodiment, at least one first stop determining at least one first angular rotational stop position of the shield, the stop being retractable and able to allow the first angular rotational stop position of the shield to be passed by at least one of the first and second light shields when a lighting mode switching is demanded in the headlight; and an actuator able to make the first and second light shields turn in two rotation directions. 
         [0015]    According to another characteristic, the light shield mechanism also comprises elastic machines for bringing and holding a light shield in the first angular rotational stop position when the actuator is inactive. 
         [0016]    In a particular embodiment able to provide light beams with cutoff of the dipped type for right-hand and left-hand traffic modes, the light shield mechanism comprises first and second light shields having respective profiles able to produce the light beams with cutoff, like of the low beam/dipped type; and the first retractable stop determines angular positions of the first and second shields for producing light beams with cutoff. 
         [0017]    Preferably, the light shield mechanism also comprises at least one second stop of the fixed type determining at least one second angular rotational stop position of the shield for producing a light beam of the main beam type. 
         [0018]    According to another characteristic, the light shield mechanism comprises two second stops of the fixed type situated on each side of the retractable stop with predetermined angular offsets and preferably symmetrically, and each second stop of the fixed type determines a second respective angular rotational stop position for each of the first and second shields, for producing a light beam of the main beam type. 
         [0019]    According to one particular embodiment, the retractable stop is elastic and flexes to enable the first angular position for a light shield to be passed when a mechanical torque greater than a maximum threshold torque is applied against the retractable stop. In addition, the actuator comprises a DC motor and an electronic control circuit able to control the motor in two directions of rotation. The electronic control circuit is advantageously equipped with electric current limitation means for limiting an electric current flowing in the motor when the latter is in a locked torque operating state. 
         [0020]    According to another aspect, the invention also concerns a motor vehicle equipped with at least one headlight (the unit optical module or complete headlight) according to the invention. 
         [0021]    According to embodiments of an optical module according to the invention the first and second beams with cutoff obtained with the shield mechanism are 
         [0022]    variant a: dipped/low beam beams for right-hand and left-hand traffics 
         [0023]    variant b: dipped/low beam (either right-hand traffic or left-hand traffic), and a beam in accordance with the new so-called AFS “Advanced Frontlighting Systems” regulations. This “AFS” beam is in particular chosen from the beam called a motorway beam (“motorway” in English), or a bad-weather beam (“adverse weather” in English), Those beams having in common notably the fact that they have a cut off. 
         [0024]    Variant c: a dipped/low beam (or AFS beam) and a beam with flat cutoff, like of the anti fog type. 
         [0025]    For each of these variants, a third beam of the main beam type is also proposed, so as to obtain a triple-function optical module, which will correspond to a position of the shield mechanism such that it does not obscure the rays emitted by the source directly or after reflection on the associated reflector. 
         [0026]    Other aspects and advantages of the present invention will emerge more clearly from a reading of the description of a particular embodiment that follows, this description being given by way of non-limiting example and made with reference to the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0027]      FIGS. 1A to 1C  show in a simplified fashion the general structure of a headlight according to the invention in various states of operation; 
           [0028]      FIG. 2  is an outline timing diagram of the control of a DC motor included in a shield mechanism of the headlight; and 
           [0029]      FIGS. 3A and 3B  show the shield mechanism in two states corresponding respectively to the production of a dipped beam for traffic on the right and a dipped beam for traffic on the left. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    With reference to  FIGS. 1A to 1B  and  2 , a description is now given of a particular embodiment of the invention in the form of a dual-function dipped/main beam headlight, referenced overall  1 , able to switch automatically between a right-hand traffic mode and a left-hand traffic mode. 
         [0031]    The headlight  1  described here is intentionally shown in a simplified manner in  FIGS. 1A to 1B  in order to facilitate understanding of the invention. 
         [0032]    The headlight  1  is of the elliptical type and is designed so as to emit a beam of illuminating light along an optical axis AA passing through foci F 1  and F 2 . The headlight  1  comprises essentially a light source  10  situated at a focus F 1  of the headlight  1 , an elliptical reflector  11 , a lens  12  and a light shield mechanism  13 . 
         [0033]    The light source  10 , the reflector  11  and the lens  12  are known elements, similar to those normally included in such a headlight for a motor vehicle. For this reason, these elements  10 ,  11  and  12  will not be detailed here. 
         [0034]    The shield mechanism  13  is situated substantially at the focus F 2  of the headlight  1 . 
         [0035]    As shown in more detail in  FIGS. 3A and 3B , the shield mechanism  13  comprises essentially two shields  130 D and  130 G formed in a single piece  130 , an actuator with motor  131 , a return spring  132  and three stops  133 ,  133 D and  133 G. In this particular embodiment, the stops  133 D and  133 G are situated on each side of the stop  133 , with given angular offsets, preferably symmetrically. 
         [0036]    The shield  130 D is provided with a profile suitable for introducing a cutoff of the dipped beam type in the traffic on the right mode TD. The shield  130 G for its part is provided with a profile able to introduce a cutoff of the dipped beam type in the traffic on the left mode TG. 
         [0037]    The actuator with motor  131  controls rotations of the shield piece  130  about an axis PP ( FIG. 3B ) perpendicular to the optical axis AA ( FIG. 1 ) of the headlight  1 . 
         [0038]    The actuator  131  comprises essentially an electric motor  1310  and an electronic control circuit  1311 . The motor  1310  is preferably a DC motor. The electronic circuit  1311  controls the functioning of the motor  1310  according to two input signals, namely a dipped/main beam mode control signal C/R and a signal controlling the traffic on the right/traffic on the left mode TD/TG. 
         [0039]    The circuit  1311  is supplied with a DC voltage V and delivers as an output a control voltage VM whose polarity is variable so as to control the direction of rotation of the motor  1310 . 
         [0040]    The functions of the stops  133 ,  133 D and  133 G and the functioning of the actuator with motor  131  will now be described in more detail. 
         [0041]      FIGS. 1A ,  1 B and  3 A show the headlight  1  in states corresponding to the traffic on the right mode TD. 
         [0042]    In  FIGS. 1A and 3A , the headlight  1  is in the dipped beam lighting mode, in TD traffic. This state corresponds to the time interval t 1  shown in  FIG. 2 . The control voltage VM is at 0 volts and the motor  1310  then exerts no rotation torque on the shield piece  130 . A return torque CR is on the other hand exerted by the spring  132  in the clockwise rotation direction SH so that the shield  130 D is held in abutment against the stop  133 . 
         [0043]    In accordance with the invention, the stop  133  is of the retractable type. In this particular embodiment, a property of elasticity is conferred on the stop  133  so as to make it retractable. Naturally the function of the stop  133  can be fulfilled in a different way by a person skilled in the art. For example, it can be in the form of a sliding stop actuated by an electromagnet. 
         [0044]    In this particular embodiment, the stop  133  no longer fulfils its function of rotational stopping of the shield piece  130  when the torque Cc applied to the shield piece  130  is greater than a maximum threshold torque Cm of given value. Thus, when the torque Cc applied to the shield piece  130  is greater than Cm, the mechanical force applied to the stop  133  by the shield  130 D or  130 G in abutment against it makes the stop  133  flex by elasticity. The flexion of the stop  133  is then sufficient to release the shield piece  130  and allow continuation of the rotation thereof after the stop  133  has been passed. 
         [0045]    In the state corresponding to  FIG. 1A , the return torque Cr due to the spring  132  is less than the maximum threshold torque Cm and the stop  133  then fully fulfils its function of rotational stoppage of the shield  130 , by contact of the shield  130 D against it (cf  FIG. 3A ). 
         [0046]      FIG. 1B  shows the headlight  1  in main-beam lighting mode, still in TD traffic. This state corresponds to the time interval t 2  shown in  FIG. 2 . 
         [0047]    The control voltage VM then has a value −Vm able to produce a rotation torque of the motor  1310  in the anticlockwise rotation direction Shi. When the shield  130 G comes into contact against the stop  133 D, the rotation of the shield piece  130  is interrupted. The voltage VM=−Vm is maintained so as to oppose the return torque Cr exerted by the spring  132  and to keep the shield piece  130  in the state shown in  FIG. 1B . 
         [0048]    In this particular embodiment of the invention, in order to avoid damage to the motor  1310  when the latter is in a locked torque state, a limitation of the current supply to the motor is provided. The locked torque state occurs when the shield piece  130  comes into contact against the stop  133 D in TD traffic mode or the stop  133 G in TG traffic mode. 
         [0049]    This limitation of the current of the motor  1310  is provided by the control circuit  1311 . A person skilled in the art will usefully refer to the patent application FR-2854941B, corresponding to U.S. Patent Application Publication Number 2004/0228137 which is incorporated herein by reference and made a part hereof, of the applicant in order to obtain details on the manner of achieving such a limitation of the current of the motor  1310 . 
         [0050]    With reference to  FIG. 2 , the time interval t 3  corresponds to the switching of the headlight  1  to traffic on the left mode TG. 
         [0051]    During the time interval t 3 , the control voltage VM is reversed in polarity and becomes VM=+Vm. The motor  1310  then supplies a mechanical torque in the clockwise rotation direction SH that is added to the torque Cr exerted by the spring. The torque Cc applied to the shield piece  130  then takes a value that is greater than the torque Cm so that the retractable stop  133  flexes sufficiently and no longer forms an obstacle to the rotation of the shield piece  130 , which comes into the state shown in  FIG. 1C . Naturally, to have correct functioning of this switching to TG traffic mode, the voltage VM must keep the value +Vm for a sufficient period to enable the stop  133  to be passed by the two screens  130 D and  130 G, as shown in  FIG. 1C . After the stop  133  is passed by the shield  130 G, the voltage VM can be returned to 0 volts in order to come into the TG traffic dipped lighting mode or maintained at +Vm in order to come into TG traffic main-beam lighting mode. 
         [0052]    In  FIGS. 1C and 3B , the headlight  1  is shown in dipped lighting mode in TG traffic. This state corresponds to the time interval t 4  shown in  FIG. 2 . The control voltage VM is at 0 volts and the motor  1310  then exerts no rotation torque on the shield piece  130 . The return torque Cr is on the other hand exerted by the spring  132  in the anticlockwise rotation direction SHi so that the shield  130 G is kept in abutment against the stop  133 , or more precisely against a contact face of the stop  133  that is opposite to that serving as an abutment for the shield  130 D in TD traffic mode 
         [0053]    The stop  133  here operates in the same way as described above in relation to the TD traffic mode and can be retracted also for switching from TG traffic mode to TD traffic mode. 
         [0054]    In the state corresponding to  FIG. 1C , the return torque Cr due to the spring  132  is therefore less than the maximum threshold torque Cm and the stop  133  fully fulfils its function of rotational stoppage of the shield piece  130  by contact of the shield  130 G against the stop  133  (cf  FIG. 3B ). 
         [0055]      FIG. 1D  shows the headlight  1  in main-beam lighting mode, still in TG traffic. This state corresponds to the time interval t 5  shown in  FIG. 2 . The control voltage VM then has a value +Vm shown in  FIG. 2 . 
         [0056]    The control voltage VM then has a value +Vm able to produce a rotation torque of the motor  1310  in the clockwise rotation direction SH. When the shield  130 D comes into contact against the stop  133 G, the rotation of the shield piece  130  is interrupted. The voltage VM=+Vm is maintained so as to oppose the return torque Cr exerted by the spring  132  and to keep the shield piece  130  in the state shown in  FIG. 1D . The limitation of the current of the motor  1310  is here also provided in order to prevent damage to it in locked torque. 
         [0057]    The time interval t 6  shown in  FIG. 2  corresponds to the switching of the headlight  1  to traffic on the right mode TD, in order to return to the state of the time interval t 1  or t 2 . The functioning of this switching is similar to that described above for passage from TD mode to TG mode and will not be detailed here. 
         [0058]    As appears clearly in the light of the above description of this first embodiment of the invention the stops  133 ,  133 D and  133 G determine various angular positions of rotational stoppage of the shields. 
         [0059]    The retractable stop  133  with its opposing contact faces determine two angular positions, a first one for the shield  130 D and another for the shield  130 D, these angular positions corresponding to TD traffic mode dipped lighting and TG traffic mode dipped lighting. 
         [0060]    The fixed stops  133 D and  133 G determine two angular main-beam lighting positions for the shields  130 D and  130 G, one for TD traffic mode and the other for TG traffic mode. 
         [0061]    Naturally the present invention is not limited to the details of the particular embodiment described here by way of example, but on the contrary, extends to any modifications within the capability of a person skilled in the art without departing from the scope of the invention. 
         [0062]    Thus a person skilled in the art may not use a DC motor for the rotation of the shield piece  130  but use for example other types of actuator such as a stepping motor or an electromagnet. In the case of the use of a stepping motor, the presence of stops in accordance with the invention will afford greater robustness of the angular positioning of the shield piece, for example by allowing a referencing in the event of loss of step. 
         [0063]    While the form of apparatus herein described constitutes a preferred embodiment of this invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.