Abstract:
The invention relates to a safety device for raising the bonnet of a motor vehicle in the event of a collision with a pedestrian. The safety device includes a pyrotechnic actuator provided with a thrust piston secured to a mechanism for raising the bonnet and able to deploy the said mechanism which is itself secured to the said bonnet, and a blocking device intended to block the said actuator in a given position. The main characteristic of this device is that it is made up of a shock-absorbing device employed when a pedestrian hits the bonnet which has been raised, so that the assembly consisting of the bonnet, the raising mechanism and the piston can move under the effect of the impact while at the same time being retarded.

Description:
[0001]    This is a Division of application Ser. No. 11/254,716 filed Oct. 21, 2008, which claims the benefit of French Patent Application No. 0412343 filed Nov. 22, 2004. The disclosure of the prior applications is hereby incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    The technical field of the invention is that of the devices used in the field of automotive safety to protect a pedestrian in the event of a frontal impact between the said pedestrian and a motor vehicle. 
         [0003]    When a pedestrian is struck by the front end of a motor vehicle, the pedestrian&#39;s head often comes into direct contact with the bonnet of the vehicle. The impact of the head on the bonnet causes the bonnet to deform. This deformation often occurs to such a point that the bonnet comes into contact with the engine block and any rigid parts such as suspension leg turrets, windscreen wiper mechanisms, etc. The movement of the pedestrian&#39;s head is then abruptly halted by the bonnet coming into contact with the engine block and therefore experiences a violent deceleration which may cause the pedestrian serious injury. 
         [0004]    The prior art already knows devices which, in the event of an impact between a pedestrian and a motor vehicle, allow the vehicle bonnet to be raised by a certain amount so as to prevent the pedestrian&#39;s limbs and especially his head from being stopped, in the impact against the bonnet, by the engine block situated just under the bonnet. In the devices of the prior art, the raising of the bonnet is performed at the rear end of the bonnet, that is to say at the windscreen end, which is the opposite end to the end used for opening or closing the bonnet in normal operation, the bonnet remaining fixed at the front end of the motor vehicle. 
         [0005]    Patent FR 2 848 947 relates to a safety device for raising the bonnet of a motor vehicle in the event of a collision, this device being situated under the said bonnet and comprising a mechanism for raising the said bonnet and an actuator, the said bonnet comprising a structure which, in normal operation, allows it to be opened or closed about an axis known as the pivot axis. 
         [0006]    The main characteristic of this device is that the raising mechanism first of all undergoes an unlocking phase by performing a first, translational, movement. 
         [0007]    The main characteristic of this device is that it undergoes an unlocking phase through a translational movement, followed by a deployment phase in a rotational movement. The safety device also foresees a later, shock-absorbing, phase allowing the bonnet to move with the struck pedestrian so as to lessen the effect of the said impact. However, no way of embodying such a shock-absorbing device is described. The safety devices according to the invention exhibit shock-absorbing devices the qualities of which are tailored to the requirements associated with the tight confines of motor vehicles and their low cost, namely, small size, simplicity of design and great reliability. Simplicity of design means that the shock-absorbing devices have not to require the addition of parts that need complex and costly machining. 
       SUMMARY 
       [0008]    The subject of the present invention is a safety device for raising the bonnet of a motor vehicle in the event of a collision with a pedestrian, comprising a pyrotechnic actuator provided with a thrust piston secured to a mechanism for raising the bonnet and able to deploy the said mechanism which is itself secured to the said bonnet, and a blocking device intended to block the said actuator in a given position, characterized in that it comprises a shock-absorbing device employed when a pedestrian hits the bonnet which has been raised, so that the assembly consisting of the bonnet, the raising mechanism and the piston can move under the effect of the impact while at the same time being retarded. More specifically, since the raising mechanism is blocked in a given position corresponding to a certain raising of the bonnet, the assembly consisting of the bonnet, the said mechanism and the piston can be likened to a single rigid component. The shock-absorbing device has to allow the said assembly to move under the effect of a pedestrian impact, in the opposite direction to the direction in which the bonnet is raised, so as to allow the bonnet to move with the said pedestrian in order to absorb the shock of the impact. For an understanding of the invention and, in particular, of claim  1 , the raising mechanism comprises a link rod and a raising lug. 
         [0009]    Advantageously, the pyrotechnic actuator possesses a hollow cylindrical body containing the piston. 
         [0010]    According to a first preferred embodiment of the invention, the shock-absorbing device is located inside the pyrotechnic actuator. This embodiment encourages the shock-absorbing device to be of minimum bulk. 
         [0011]    As a preference, the shock-absorbing device consists structurally of the blocking device. In other words, the safety devices according to the invention have just one mechanical device which, depending on the applied stresses, may either block the raising mechanism or absorb the shock of the “bonnet+raising mechanism+piston” assembly. 
         [0012]    Advantageously, the hollow body exhibits a small-diameter upstream part and a larger-diameter downstream part which parts are connected to one another by a divergent passage, and the piston comprises a peripheral groove partially delimited by the internal wall of the said upstream part. Thus, the piston is positioned in the hollow body in such a way that the groove lies in the upstream part of the said body, the said piston being able to slide in the said upstream part. 
         [0013]    As a preference, the groove has a U-shaped cross section so that it exhibits two side walls facing one another and parallel to each other. 
         [0014]    Advantageously, a prestressed member is housed in the groove, bearing against the internal wall of the upstream part. 
         [0015]    In this way, withdrawal from the internal wall of the upstream part could cause the said member to relax. 
         [0016]    As a preference, the prestressed member consists of a snap ring which is an annular component having the shape of a ring provided with an opening. Thus, a radial pressure uniformly distributed over the said component allows the latter to deform elastically in such a way as to move the two ends that delimit the said opening closer together. 
         [0017]    According to an alternative form of the embodiment of the invention, the snap ring has a circular cross section. 
         [0018]    Advantageously, initiation of the actuator causes the piston to slide until the groove reaches the downstream part of the body, thus causing the snap ring to relax. 
         [0019]    In the absence of any particular stress, the snap ring, which is relaxed, prevents the piston from moving in the opposite direction. 
         [0020]    As a preference, the material of the upstream part of the body is deformable so as to allow the piston, following a pedestrian impact, to move in the opposite direction, carrying with it the snap ring which forcibly enters the said upstream part of the body which deforms. The length traveled by the snap ring in the upstream part corresponds to the shock-absorbing distance. 
         [0021]    According to another preferred embodiment of the invention, the shock-absorbing device consists of at least one weakening feature situated on the hollow body of the actuator. Advantageously, the said feature contributes towards reducing the total length of the said body in the event of a pedestrian impact. 
         [0022]    In other words, since the piston, which is secured to the raising mechanism and to the bonnet, is blocked, the hollow cylindrical body will tend to crumple on itself in the direction of its axis in the event of a pedestrian impact. 
         [0023]    The reduction in the length of the hollow body corresponds to the shock-absorbing distance. 
         [0024]    Advantageously, the blocking device is produced by means of a compressed snap ring situated in a peripheral groove of the piston and which relaxes when the said groove opens into a widened zone of the hollow body thus preventing the piston from moving in the opposite direction. As a preference, the said zones are separated from one another by an internal shoulder. Preferably, the snap ring has a rectangular cross section. 
         [0025]    Thus, the relaxed snap ring is blocked against the internal shoulder of the body, preventing the piston from moving in the opposite direction. 
         [0026]    According to a second preferred embodiment of the invention, the shock-absorbing device is external to the actuator. Advantageously, the actuator is mounted on a support piece secured to the vehicle and the shock-absorbing device is secured to the said piece. 
         [0027]    As a preference, the actuator is in contact with the support piece via a protrusion secured to the said actuator, the said protrusion being able to pivot in the said piece. 
         [0028]    Advantageously, the protrusion is of cylindrical shape. 
         [0029]    Preferably, the shock-absorbing device consists of a deformable piece borne by the support piece and situated in contact with the pyrotechnic actuator. Preferably, the protrusion is placed in a notch of the support piece, the said protrusion being in contact with the deformable piece. 
         [0030]    According to a second preferred embodiment of the invention, the deformable piece has at least one weakening feature able to encourage the said piece to deform following a pedestrian impact. 
         [0031]    It is necessary for the hollow body of the actuator to be in contact with the deformable piece because since the piston remains blocked in the said body following a pedestrian impact, it is the said body which will transmit the impact to the said deformable piece. 
         [0032]    According to another preferred embodiment of the invention, the deformable piece consists of a corrugated sheet, able to crumple on itself following a pedestrian impact transmitted by the body of the actuator to the said sheet. 
         [0033]    Preferably, the support piece has means for guiding the said protrusion, and the shock-absorbing device is included in the said guide means. 
         [0034]    Advantageously, the guide means are represented by two oblong openings through each of which the protrusion passes, the said protrusion being able to move in the said openings following a pedestrian impact with the bonnet. As a preference, the openings have, on their outline, a plurality of deformable teeth. The teeth thus increase the roughness of the outline of the said openings. Following the pedestrian impact, the body of the actuator moves, driving the protrusion in the direction dictated by the oblong openings. The movement of the said protrusion in the said openings causes the teeth to bend, thus retarding the said movement. 
         [0035]    According to another preferred embodiment of the invention, the width of the openings is smaller than the width of the said protrusion. In this way, under the effect of the impact of a pedestrian with the bonnet, the protrusion is moved forcibly along the said openings, widening them. 
         [0036]    The safety devices according to the invention have the advantage of having a well-controlled shock-absorbing function thanks to mechanical devices that are simple, perfectly suited to the small volumes available, conceded by motor vehicles. In addition, this shock-absorbing function can be tailored to a given configuration through a simple structural modification of the materials involved or simply by changing the material since the said materials are in commonplace use and have perfectly known mechanical properties. 
         [0037]    A detailed description of four preferred embodiments of a safety device according to the invention is given hereinafter with reference to  FIGS. 1 to 19 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]      FIG. 1  is a view in longitudinal section of a safety device according to the invention equipped with a shock-absorbing device involving a snap ring and which has not yet functioned. 
           [0039]      FIG. 2  depicts the device of  FIG. 1  once the shock-absorbing device has functioned. 
           [0040]      FIG. 3  is an enlarged view in longitudinal axial section of a shock-absorbing device involving a snap ring. 
           [0041]      FIG. 4  is an enlarged view in longitudinal axial section of the device of  FIG. 3 , following a pedestrian impact with the bonnet. 
           [0042]      FIG. 5  is a view in partial longitudinal section of a safety device according to the invention, having an actuator with a weakening feature. 
           [0043]      FIG. 6  depicts the device of  FIG. 5 , following a pedestrian impact with the bonnet. 
           [0044]      FIG. 7  is an enlarged view in longitudinal axial section of a pyrotechnic actuator of a safety device according to the invention, having a first variant of the weakening feature. 
           [0045]      FIG. 8  depicts the actuator of  FIG. 7  following the pedestrian impact with the bonnet. 
           [0046]      FIG. 9  is an enlarged view in longitudinal axial section of a pyrotechnic actuator of a safety device according to the invention, having a second variant of the weakening feature. 
           [0047]      FIG. 10  depicts the actuator of  FIG. 9  following the pedestrian impact with the bonnet. 
           [0048]      FIG. 11  is a side view of a safety device according to the invention equipped with an external shock-absorbing device comprising a piece with a weakening feature. 
           [0049]      FIG. 12  depicts the device of  FIG. 11  following a pedestrian impact with the bonnet. 
           [0050]      FIG. 13  is a perspective view of the relative arrangement of the deformable piece and of the pyrotechnic actuator. 
           [0051]      FIG. 14  is a perspective view of a concertina piece acting as a shock-absorbing device for a safety device according to the invention. 
           [0052]      FIG. 15  depicts the piece of  FIG. 14  following a pedestrian impact with the bonnet. 
           [0053]      FIG. 16  is a side view of part of the support piece for the pyrotechnic actuator, the said piece being equipped with two toothed side openings. 
           [0054]      FIG. 17  depicts the part of the support piece of  FIG. 16  following a pedestrian impact with the bonnet. 
           [0055]      FIG. 18  is a side view of part of the support piece for the pyrotechnic actuator and the said piece being equipped with two narrow side openings. 
           [0056]      FIG. 19  depicts the part of the support piece of  FIG. 18  following a pedestrian impact with the bonnet. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]    With reference to  FIGS. 1 and 2 , a first preferred embodiment of a safety device  1  according to the invention comprises a pyrotechnic actuator  2 , a link rod  3 , a raising lug  4  and a locking hook  5 . The link rod  3  has the shape of an elongate part with a variable U-shaped cross section so that it has two mutually parallel faces. The said link rod  3  has an upstream part  6  able to pivot about a pivot pin  7  passing through its two parallel faces, and a downstream part  8  able to be raised when the upstream part  6  pivots about its pin  7 . 
         [0058]    The said downstream part  8  comprises, on each of these faces, an elongate opening  9 , each opening having, passing through it, a pivot pin  10  secured to the raising lug  4 , the said lug  4  itself being secured to the bonnet  11 . The link rod  3  has, on one of its faces, a fixed protrusion  12  equipped with a flat  13 . The pyrotechnic actuator  2  comprises a cranked rear part  14  in which a pyrotechnic charge  15  is housed and a front part in the form of a straight hollow cylindrical body  16  in which a piston  17  is housed. The said straight hollow body  16  has a small-diameter upstream part  18  and a larger-diameter downstream part  19  which parts are connected to one another by a divergent passage  20 , the said upstream part  18  being in contact with the cranked rear part  14 . The piston  17  is made up of a widened body  21  extended by a cylindrical rod  22  comprising a shoulder  25 . In this way, the rod  22  exhibits a widened part in contact with the widened body  21  of the piston  17  and a smaller-diameter part. The said widened body  21  of the piston  17  has a peripheral groove  23  and exhibits an outside diameter slightly smaller than the inside diameter of the upstream part  18  of the hollow cylindrical body  16  of the actuator  2 . The piston  17  is placed in the actuator  2  in such a way that its widened body  21  is housed in the upstream part  18  of the straight hollow body  16  and can slide therein hermetically. Thus, the peripheral groove  23  is partially delimited by the internal wall of the said upstream part  18  of the hollow body  16 . The actuator  2  is able to pivot at the same time as the link rod  3  about a pivot pin not depicted in the figures and which is parallel to the pivot pin  7  of the said link rod  3 . With reference to  FIGS. 3 and 4 , the groove  23  has a shoulder  26  to distinguish a smaller-diameter part  27  corresponding to the deepest part of the said groove  23  from a larger-diameter part  28 . A prestressed snap ring  24 , of circular cross section, bearing against the internal wall of the upstream part  18  of the hollow cylindrical body  16  is housed in the said groove  23  at its deepest part. An electro-pyrotechnic initiation system is positioned near the pyrotechnic charge  15  to initiate its combustion. The hook  5  is mounted to pivot on the vehicle and can effect a rotary movement about a pivot pin  29 . 
         [0059]    The way in which this first preferred embodiment of the safety device  1  according to the invention works is as follows. 
         [0060]    An electrical impulse device sets off the electro-pyrotechnic ignition system which initiates the combustion of the pyrotechnic charge  15 . 
         [0061]    The gases delivered move the piston  17  which, in a first phase, unlocks the safety device  1  by exerting thrust on the hook  5  and which, in a second phase, comes to bear against the flat  13  of the protrusion  12  of the link rod  3  via the shoulder  25  of its rod  22 , so as to cause the said link rod  3  to rotate about its pin  7 . The rotation of the said link rod  3  leads to the raising of the bonnet  11  by virtue of the raising lug  4 , the pivot pin  10  of which can move in the elongate openings  9  of the downstream part  8  of the link rod  3 . Thus, the piston  17  slides in the straight hollow cylindrical body  16  until the peripheral groove  23  reaches the divergent passage  20  and the snap ring  24  relaxes to occupy the shallower part  28  of the said groove  23 . In this final position which corresponds to the one depicted in  FIGS. 1 and 3 , the snap ring  24  prevents any movement of the piston  17  in the opposite direction, unless external stress is exerted. Thus, the assembly represented by the bonnet  11 , the raising lug  4 , the link rod  3  and the piston  17  constitutes a rigid component. All of this first phase corresponds to a phase of arming the safety device  1 . 
         [0062]    With reference to  FIG. 4 , in the event of a pedestrian impact with the bonnet  11  in the direction shown by the arrow in  FIG. 1 , the impact thus generated is transmitted to the piston  17 , and its intensity is such that the said piston  17  will begin to move in the opposite direction, carrying with it the snap ring  24  which is relaxed. During this movement in the opposite direction, the said snap ring  24  forcibly enters the small-diameter upstream part  18  of the hollow cylindrical body  16  which deforms. This phase of deforming the hollow cylindrical body  16  corresponds to a phase of absorbing the shock of the bonnet  11  because the said bonnet  11  can move under the effect of the pedestrian impact while at the same time being retarded. With reference to  FIG. 4 , the movement of the bonnet  11  halts when the safety device  1  returns to the re-engagement position. In this embodiment the snap ring  24  has had the dual function of acting as a blocking device and of acting as a shock-absorbing device. 
         [0063]    With reference to  FIGS. 5 and 6 , a second preferred embodiment of a safety device  101  according to the invention comprises a pyrotechnic actuator  102 , a link rod  103 , a raising lug  104  and a locking hook  105 . The link rod  103  has the shape of an elongate piece of variable. U-shaped cross section so that it exhibits two mutually parallel faces. The said link rod  103  has an upstream part  106  able to pivot about a pivot pin  107  passing through its two parallel faces and a downstream part  108  able to be raised when the upstream part pivots about its pin  107 . 
         [0064]    The said downstream part  108  comprises, on each of its faces, an elongate opening  109 , each one having, passing through it, a pivot pin  110  secured to the raising lug  104 , the said lug  104  itself being secured to the bonnet  111 . 
         [0065]    On one of its faces, the link rod  103  has a fixed protrusion  112  equipped with a flat  113 . The pyrotechnic actuator  102  comprises a cranked rear part  114  in which a pyrotechnic charge  115  is housed and a front part in the form of a straight hollow cylindrical body  116  in which a piston  117  is housed. 
         [0066]    The piston  117  is made up of a widened body  121  extended by a cylindrical rod  122  comprising a shoulder  125 . In this way, the rod  122  has a widened part  130  in contact with the widened body  121  of the piston  117  and a smaller-diameter part  121 , the said widened part  130  having a peripheral groove  123 . The straight hollow cylindrical body  116  has one end in contact with the cranked rear part  114  and a free end equipped with an opening to allow the widened part  130  of the rod  122  to pass, the said opening having a diameter greater than that of the said widened part  130 . A cylindrical piece  132  provided with a passage, the diameter of which is appreciably greater than the diameter of the said widened part  130  of the rod  122  but smaller than the diameter of the opening, is fixed inside the straight hollow cylindrical body  116 , near its free end. Thus, the widened part  130  of the rod  122  can slide hermetically in the said piece  132  because the opening of the hollow cylindrical body  116 , which is too wide, does not permit it. The piston  117  is placed in the actuator  102  in such a way that the peripheral groove  123  is partially delimited by the internal wall of the hollow cylindrical piece  132 . A prestressed snap ring  124 , of rectangular cross section, is housed in the said groove  123 , bearing against the said internal wall. The actuator  102  is able to pivot at the same time as the link rod  103  about a pivot pin not depicted in the figures and which is parallel to the pivot pin  107  of the said link rod  103 . With reference to  FIGS. 7 and 9 , the straight hollow cylindrical body  116  has a weakening feature  133 ,  134  either in the form of a narrow bulging  133  of the said body  116  or in the form of two successive restrictions  134  of the said body  116 . 
         [0067]    The way in which this second preferred embodiment of a safety device  101  according to the invention works is as follows. 
         [0068]    An electrical impulse sets off the electropyrotechnic ignition system which initiates the combustion of the pyrotechnic charge  115 . The gases delivered move the piston  117  which, in a first phase, unlock the safety device  101  by exerting thrust on the hook  105  and which, in the second phase, comes to bear against the flat  113  of the protrusion  112  of the link rod  103  via the shoulder  125  of its rod  122  to cause the said link rod  103  to rotate about its pin  107 . The rotation of the said link rod  103  leads to the raising of the bonnet  111  by virtue of the raising lug  104 , the pivot pin  110  of which can move in the elongate openings  109  of the downstream part  108  of the link rod  103 . Thus, with reference to the  FIGS. 7 and 9 , the piston  117  slides in the straight hollow cylindrical body  116  until the peripheral groove  113  reaches the opening at the end of the straight hollow cylindrical body  116  and the snap ring  124  relaxes. In this position, the relaxed snap ring  124  acts as a blocking device, preventing, inter alia, any movement of the piston  117  in the opposite direction. In this way, the assembly represented by the bonnet  111 , the raising lug  104 , the link rod  103  and the piston  117  constitutes a rigid component. All of this first phase corresponds to a phase of arming the safety device  101  which is identical to the phase described in respect of the first preferred embodiment of the invention. 
         [0069]    Upon pedestrian impact with the bonnet  111  in the direction shown by the arrow in  FIG. 5 , the impact thus generated is transmitted to the piston  117 , solidly blocked by the snap ring  124 . With reference to  FIGS. 8 and 10 , the forces will then be transferred to the weakening features  133 ,  134  of the hollow cylindrical body  116  which will react by crumpling on itself, thus leading to a reduction in its length. This crumpling allows the bonnet  111  to move under the effect of the pedestrian impact, while at the same time being retarded. 
         [0070]    With reference to  FIG. 6 , the movement of the bonnet  111  halts when the safety device  1  returns to the re-5 engaged position. 
         [0071]    With reference to  FIGS. 11 and 12 , a third preferred embodiment of a safety device  201  according to the invention differs from the second preferred embodiment described hereinabove in that the weakening features are no longer produced on the body of the pyrotechnic actuator  202  but are produced on a deformable piece  240  placed in contact with the said actuator  202 , on the same side as the pyrotechnic charge, not depicted in  FIGS. 11 and 12 . The safety device  201  is fixed to the vehicle by means of an elongate support piece  241  having a variable U-shaped cross section, the said piece  241  having, on each of these two parallel edges, an elongate notch  242  each facing the other. The cranked rear part of the pyrotechnic actuator  202  comprises a cylindrical lateral protrusion  243 , the diameter of which is appreciably smaller than the width of the notch  242 , and the actuator  202  is positioned with respect to the support piece  241  in such a way that the said protrusion  243  lies in the closed end of the said notch  242 . During the phase of arming the safety device  201 , the protrusion  243 , the axis of which is parallel to the pin  207  of the link rod  203 , will constitute the axis of rotation of the actuator  202 . 
         [0072]    With reference to  FIG. 13 , the deformable piece  240  is fixed to the support piece  241  by means of a peg  244  secured to the deformable piece  240  and which becomes inserted in a notch of the said support piece  241 . The deformable piece  240  comprises a body  246  which on the whole has a U-shaped cross section and is extended by two parallel lugs  245  each having, at its end, a notch intended to house the protrusion  243 . 
         [0073]    The support piece  241 , the deformable piece  240  and the pyrotechnic actuator  202  are arranged in such a way that the protrusion  243  finds itself blocked in the closed end of the elongate notch  242  of the support piece  241  by the notches of the two lugs  245  of the deformable piece  240 . The body  246  of the deformable piece  240  comprises a weakening feature  247  in the form of a narrow restriction. 
         [0074]    The way in which this third preferred embodiment of a safety device  201  according to the invention works is as follows. 
         [0075]    The phase of arming the safety device  201  is in every respect identical to the equivalent phase described for the first and second preferred embodiments of the invention. 
         [0076]    Upon pedestrian impact with the bonnet  211  in the direction shown by the arrow in  FIG. 11 , since the piston  217  is solidly blocked in the actuator  202  by the blocking device involving the snap ring of rectangular cross section, the impact is transmitted to the protrusion  243  having passed through the raising lug  204  and the link rod  203 . The intensity of the said impact is such that the actuator  202  will exert thrust on the deformable piece  240  via the protrusion  243 , the said piece  240  then crumpling on itself at its weakening feature  247 . This deformation of the piece  240  allows the bonnet  111  to move under the effect of the pedestrian impact, while at the same time being retarded. According to  FIG. 12 , the movement of the bonnet  211  halts when the safety device  201  has returned to the re-engaged position. It should be noted that, during the arming phase, the piece  240  is sized in such a way as to counter the thrust forces of the actuator  202  without experiencing plastic deformation. 
         [0077]    With reference to  FIG. 14 , the deformable piece may consist of a corrugated sheet  250  placed in contact with the pyrotechnic actuator. With reference to  FIG. 15 , in the event of a pedestrian impact, the said actuator exerts thrust in the direction shown by the arrow on the said sheet which will crumple, allowing the bonnet to move while at the same time being retarded. 
         [0078]    With reference to  FIGS. 16 and 17 , a fourth preferred embodiment of a safety device according to the invention differs from the third preferred embodiment described above in that the deformable piece has been removed and in that the protrusion  343  passes through two oblong openings  344  facing one another and placed on the two parallel edges of a support piece  345  secured to the vehicle and having a variable U-shaped cross section. The axis of the protrusion  343  is parallel to the pivot pin  307  of the link rod. Each of the two openings  344  comprises a plurality of triangular and deformable teeth  346 , situated along their outline. 
         [0079]    The way in which this fourth preferred embodiment of a  25  safety device according to the invention works is as follows. 
         [0080]    The phase of arming the safety device is in every respect identical to the equivalent phase described for the first three embodiments of the invention described hereinabove. 
         [0081]    Upon pedestrian impact with the bonnet, the impact is transmitted to the protrusion  343 . The intensity of the said impact is such that the actuator  302  will move in the direction shown by the arrow in  FIG. 13 , carrying along the protrusion  343  which itself moves in the openings  344  crumpling the teeth  346  as it passes. The openings  344  encourage the movement of the bonnet following a pedestrian impact with the bonnet, and the teeth  346 , which crumple, retard the said movement. 
         [0082]    With reference to  FIGS. 18 and 19 , the two oblong  5  openings  354  are smaller in width than the diameter of the protrusion  353 . 
         [0083]    Following the pedestrian impact with the bonnet, the actuator  302  moves in the direction shown by the arrow in  FIG. 18  carrying along the protrusion  353  which itself moves forcibly in the openings  354 . The openings, which widen as they deform as the said protrusion  353  passes, contribute to retarding the movement of the bonnet.