Abstract:
An automotive seat safety mechanism includes a seat back and a webbing arranged between the seat back and a vehicle roof. A retractor urges the webbing in a winding direction while simultaneously permitting the webbing to be drawn out in an unwinding direction when in a normal state and prevents the webbing from being drawn out when deceleration of the vehicle becomes greater than a predetermined value. A bypassing mechanism is arranged above the seat back. A pretensioner is included in the retractor. The retractor is arranged above and rearward from the seat back. The webbing extends between an upper position of the seat back and the retractor bypassing the bypassing mechanism. The webbing is disengaged from the bypassing mechanism when forward deceleration becomes greater than a predetermined value. The pretensioner is activated to quickly draw in the webbing in response to the forward deceleration.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an automotive seat safety mechanism that is installed in an automotive seat and functions when a collision occurs. 
     In the prior art, in addition to the employment of a three-point safety belt, which restrains a passenger to an automotive seat, mechanisms for increasing the strength of the seat itself has been proposed to resist impacts. For example, Japanese Laid-Open Patent Publication No. 2001-213211 describes a mechanism in which a webbing is arranged between a seat back and the roof of a vehicle. When an impact load is applied to the seat back, the webbing, which is drawn into a retractor, is locked. This securely supports the head rest and protects the head of the passenger. 
     In such case, the webbing functions as a reinforcing member and supports the seat back from the roof. However, such webbing has a shortcoming in that it reduces the interior space in the rear of the vehicle and interferes a passenger who gets into or out of the rear of the vehicle. Accordingly, it is preferable that the webbing be extended vertically upward from the seat back, as described in Japanese Laid-Open Patent Publication No. 2001-213211, so that the webbing does not extend in a rearward direction from the seat back. 
     However, since the seat back is normally inclined toward the rear when a passenger is sitting on the seat, the webbing described in the publication may not be able to efficiently support the seat back when an impact is applied to the seat back. 
     Referring to  FIGS. 18 and 19 , a webbing  100  functions to reinforce an automotive seat  101 . When an impact is applied to the rear of the vehicle (hereinafter, referred to as rear crash), a rotational moment acting to pivot the seat back  101  toward the rear (rearward pivoting) about basal portion O is applied to the seat back  101 . In such case, the rotational moment locks the webbing  100 . Thus, the locked webbing  100  supports the seat back  101  when the seat back  101  starts rearward pivoting. In other words, the webbing  100  directly counters the rotational moment, which is produced by the impact. 
     When an impact is applied to the front of the vehicle (hereinafter, referred to as front crash), a rotational moment acting to pivot the seat back  101  toward the front (forward pivoting) about basal portion O is applied to the seat back  101 . However, unlike during a rear crash, the forward pivoting of the seat back  101  first loosens the webbing  100 . Thus, the webbing  100  is not immediately locked. Theoretically, the webbing  100  is not locked until a force that pulls the webbing  100  is produced when the seat back  101  exceeds line P, which connects the basal portion Q of the webbing  100  and the pivoting center of the seat back  101 , as shown in FIG.  19 . 
     Therefore, during a front crash, the webbing  100  may not sufficiently absorb the impact and restrain the seat back  101 . 
     Further, the impact load applied to the seat back  101  may be stronger during a front crash than during a rear crash. For example, a passenger sitting in the rear seat may be thrown against the seat back  101  during a front crash. Additionally, when a rear passenger air bag is installed in the seat back  101 , the impact (reaction) resulting from the activation of the air bag may produce a rotational moment that results in forward pivoting of the seat back  101 . 
     Accordingly, there is a demand for a mechanism that functions to sufficiently support a seat back during a front crash. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an automotive seat safety mechanism that reinforces an automotive seat with a belt during a collision, especially during a front crash. 
     The present invention provides an automotive seat safety mechanism including an automotive seat having a scat cushion and a seat back, which is arranged on a rear portion of the seat cushion, and a webbing arranged between the seat back and an upper portion of a vehicle. A retractor urges the webbing in a winding direction to draw in the webbing while strenuously permitting the webbing to be drawn out of the refractor in an unwinding direction when in a normal state and prevents the webbing from being drawn out when deceleration of the vehicle becomes greater than or equal to a predetermined value. The automotive seat safety mechanism includes a bypassing mechanism arranged above the seat back. A pretensioner is included in the retractor. The refractor is arranged rearward from the seat back in the upper portion of the vehicle. The webbing has an end secured to an upper position of the seat back and is extended through the bypassing mechanism to the retractor. The webbing is disengaged from the bypassing mechanism when forward deceleration of the vehicle becomes greater than or equal to a predetermined value. The pretensioner of the retractor is activated to quickly draw in the webbing in the winding direction in response to the forward deceleration. 
     A further aspect of the present invention is an automotive seat safety mechanism including an automotive seat having a seat cushion and a seat back, which is arranged on a rear portion of the seat cushion, and a webbing arranged between the seat back and an upper portion of a vehicle. A retractor urges the webbing in a winding direction to draw in the webbing while simultaneously permitting the webbing to be drawn out of the retractor in an unwinding direction when in a normal state and prevents the webbing from being drawn out when deceleration of the vehicle becomes greater than or equal to a predetermined value. The automotive seat safety mechanism includes a bypassing mechanism arranged above the seat back. A pretensioner is included in the retractor. The retractor is arranged in an upper portion of the seat back. The webbing has an end secured to the upper portion rearward from the seat back and is extended through the bypassing mechanism to the retractor. The webbing is disengaged from the bypassing mechanism when forward deceleration of the vehicle becomes greater than or equal to a predetermined value. The pretensioner of the retractor is activated to quickly draw in the webbing in response to the forward deceleration. 
     A further aspect of the present invention is an automotive seat safety mechanism including an automotive seat having a seat cushion and a seat back, which is arranged on a rear portion of the seat cushion, a child seat detachably installed on the automotive seat, and a webbing arranged between the seat back and an upper portion of a vehicle. A retractor urges the webbing in a winding direction to draw in the webbing while simultaneously permitting the webbing to be drawn out of the retractor in an unwinding direction when in a normal state and prevents the webbing from being drawn out when deceleration of the vehicle becomes greater than or equal to a predetermined value. The automotive seat safety mechanism includes a bypassing mechanism arranged above the scat back. A pretensioner is included in the retractor. The retractor is arranged rearward from the seat back in the upper portion of the vehicle. The webbing has an end secured to an upper position of the seal back and is extended through the bypassing mechanism to the retractor. The webbing is disengaged from the bypassing mechanism when forward deceleration of the vehicle becomes greater than or equal to a predetermined value. The pretensioner of the retractor is activated to quickly draw in the webbing in the winding direction in response to the forward deceleration. The child seat is fixed to the upper position of the seat back by a fastening belt. The fastening belt includes a load limiter. 
     Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
         FIG. 1  is a schematic side view showing an automotive seat safety mechanism according to a preferred embodiment of the present invention; 
         FIG. 2  is a schematic side view showing the automotive seat safety mechanism in an activated state; 
         FIG. 3  is a side view showing a lock mechanism in a normal driving state; 
         FIG. 4  is a side view showing the lock mechanism in a front crash state; 
         FIG. 5  is a side view showing the lock mechanism in a rear crash state; 
         FIG. 6  is a perspective view showing a guide hanger; 
       FIG.  7 ( a ) is a schematic view showing a pretensioner in a state prior to activation, and FIG.  7 ( b ) is a schematic view showing the pretensioner in a state subsequent to activation; 
         FIG. 8  is a schematic side view showing the state of a passenger compartment during normal driving; 
         FIG. 9  is a schematic side view showing the state of the passenger compartment during a front crash; 
         FIG. 10  is a schematic side view showing the state of the passenger compartment during a rear crash; 
         FIG. 11  is a perspective view showing a belt winding unit according to a further embodiment of the present invention; 
       FIG.  12 ( a ) is a cross-sectional side view showing a suspender and a guide hanger in an engaged state, and FIG.  12 ( b ) is a cross-sectional side view showing the suspender and the guide hanger in a disengaged state; 
         FIG. 13  is a schematic side view showing an automotive seat safety mechanism according to a further embodiment of the present invention; 
         FIG. 14  is a schematic side view showing a webbing in a state in which the belt is used as a screen; 
         FIG. 15  is a schematic side view showing the state of a passenger compartment in a further embodiment of the present invention in which a child seat is installed on the seat; 
         FIG. 16  is a schematic side view showing the state of the passenger compartment during a front crash; 
         FIG. 17  is an enlarged perspective view showing the vicinity of a belt, which fastens the child seat, and a load limiter; 
         FIG. 18  is a schematic side view showing a prior art seat back; and 
         FIG. 19  is a schematic side view illustrating rotational moment that is applied to the prior art seat back during a collision. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will now be discussed with reference to the drawings. 
     The structure of a passenger compartment related with the present invention will first be discussed. Referring to  FIGS. 8  to  10 , a front seat  11  includes a seat back  12  and a seat cushion  13 . The seat cushion  13  is fixed on a base  14 . A reclining mechanism (not shown) enables the seat back  12  to be reclined. Further, a slide mechanism (not shown) enables the seat  11  to move forward and rearward relative to the base  14 . 
     A three-point belt  16  is attached to the seat  11 . The belt  16  is fastened to a holder  17 , which is attached to the base  14 . In the preferred embodiment, an air bag  18  is installed in the rear of the seat back  12 . A further air bag  18  is installed in a steering wheel  19 . 
     A head rest  20  is arranged above the seat back  12 . In the preferred embodiment, the head rest  20  is fixed to a projecting portion  21   a  of a support frame  21 , which is the frame of the seat back  12 . 
     The distal end of a webbing  25  is connected to the projecting portion  21   a  by means of a holder  23 . The basal portion of the webbing  25  extends upward and leads into a roof  27  of the vehicle. A guide hanger  28 , which serves as a guide, is arranged in the roof  27 . As shown in  FIGS. 1 and 2 , a belt winding unit  30  is arranged above the guide hanger  28  (in the roof  27 ). The guide hanger  28  and the belt winding unit  30  will now be discussed in detail. 
     Referring to  FIGS. 1 and 2 , the roof  27  has an opening  31 . The opening  31  extends rearward from a position corresponding to the normal position of the seat back  12 . The guide hanger  28  is arranged at a position corresponding to the opening  31 . Referring to  FIG. 6 , the guide hanger  28  includes left and right hockey stick-like base frames  32  and front and rear connecting frames  33 , which connect the base frames  32 . Thus, the guide hanger  28  defines a rather flat square frame. 
     An engaging frame  35  is arranged on the front connecting frame  33 . Upper and lower engaging bars  36 ,  37  extend parallel to each other in the horizontal direction in the engaging frame  35 . The lower engaging bar  37 , which engages the webbing  25 , functions to change the direction of the webbing  25  when the webbing  25  is extended in a bypassed manner by the guide hanger  28 . The surface of the lower engaging bar  37  is curved to define a guide surface that smoothly guides the webbing  25 . 
     Bearings  34  are formed in the rearward portion of the base frame  32 . A support shaft  38  is received in the bearings  34  to support the guide hanger  28  in a cantilevered manner. The guide hanger  28  pivots about the support shaft  38  between a normal position, in which the guide hanger  28  closes the opening  31 , and a drop position, in which the guide hanger  28  is dropped from the normal position. 
     The belt winding unit  30  includes a lock mechanism  39 , which is located in the front portion of the belt winding unit  30 , and a retractor  55 , which is located in the rear portion of the belt winding unit  30 . The lock mechanism  39  will now be discussed. 
     The lock mechanism  39 , which functions as a bypassing mechanism, includes a cam mechanism having a cam  41 , a first lever  42 , a second lever  43 , and a ratchet lever  44 . The cam  41  is generally oval and rotates about a rotational shaft  41   a . A first engaging notch  45  is formed in the front portion of the cam  41 . An engaging projection  46  projects from the cam  41  on the substantially opposite side of the first engaging notch  45 . A second engaging notch  47  is formed at an upper position of the cam  41  between the first engaging notch  45  and the engaging projection  45 . The weight distribution of the cam  41  is such that the left side of the rotational shaft  41   a  (the side of the first engaging notch  45 ) is heavier than the right side of the rotational shaft  41   a  (the side of the second engaging notch  46 ), as viewed in FIG.  3 . As a result, when the cam  41  is free in the state of  FIG. 3 , the cam  41  rotates in a counterclockwise direction. 
     The first lever  42  is located above the cam  41 . The first lever  42  is supported pivotally about a pivot shaft  42   a . An engaging projection  48  projects from the distal end of the first lever  42 . The engaging projection  48  engages the second engaging notch  47 . The first lever  42  is curved at the vicinity of the engaging projection  48  in correspondence with the curve of the cam  41  in the vicinity of the second engaging notch  47 . Thus, the distal portion of the first lever  42  comes into close contact with the peripheral surface of the cam  41  when the engaging projection  48  engages the second engaging notch  47 . 
     Part of the second lever  43  overlaps the first lever  42 . The second lever  43  is pivotally supported about a pivot shaft  43   a , the axis of which is the same as the pivot shaft  42   a  of the first lever  42 . A spring (not shown) constantly urges the second lever  43  in a clockwise direction about the pivot shaft  43   a . The distal end of the second lever  43  defines an engaging end  49 , which engages the engaging projection  46 . An engaging recess  50  is defined adjacent to the engaging end  49 . The ratchet lever  44  is arranged rearward from the cam  41 . The ratchet lever  44  is pivotally supported about a pivot shaft  44   a . A ratchet  51  projecting forward from the ratchet lever  44  engages the engaging recess  50 . An arm  52  extends downward from the ratchet lever  44 . The arm  52  is connected to an output shaft  54  of a solenoid  53 , which is fixed to a base plate  40 . 
     The lock mechanism  39  is shown in three states in  FIGS. 3  to  5 . Normally, as shown in the state of  FIG. 3 , the pivoting of the cam  41  is restricted due to the engagement between the engaging projection  48  of the first lever  42  and the second engaging notch  47  of the cam  41 . Further, the upper engaging bar  36  of the guide hanger  28  is engaged with the first engaging notch  45  of the cam  41 . In this state, the guide hanger  28  is arranged in the roof  27  at a normal position. The other two states of the lock mechanism  39  will be discussed later. 
     The retractor  55  is supported by a holding frame  57 , which is secured to a reinforcement pipe frame  56  arranged in the roof  27 . A spring (not shown) constantly urges the retractor  55  to wind the webbing  25 . The retractor  55  includes a pretensioner  58 . Referring to FIGS.  7 ( a ) and  7 ( b ), the pretensioner  58  includes a piston  61 , a cylinder  62 , a propulsion agent  63 , an ignitor  64 , a wire  65 , and a rotor  66 . The ignitor  64  ignites the propulsion agent  63  to generate combustion pressure, which is applied to the piston  61 . This pushes the piston  61  and pulls the wire  65 . Thus, the wire  65  rotates the rotor  66  and instantaneously draws the webbing  25  into the retractor  55 . 
     Referring to  FIGS. 1 ,  2 ,  7 ( a ), and  7 ( b ), the solenoid  53  and the pretensioner  58  are connected to and controlled by an electronic control unit (ECU)  71 . The ECU  71  includes a central processing unit (CPU), a memory, and an input/output interface (none shown). 
     The ECU  71  is connected to an acceleration (G) sensor  72 . The acceleration sensor  72  sends a detection signal to the ECU  71  when detecting predetermined acceleration or deceleration. 
     The operation of the preferred embodiment will now be discussed. 
     As shown in  FIG. 8 , a driver normally sits on the front seat  11  and fastens the three-point belt  16  to drive the vehicle. The driver adjusts the seat  11 , or the position of the seat  11  relative to the base  14 , to where the driver feels comfortable driving. The driver also adjusts the seat back  12  to an angle at which the driver feels comfortable. The webbing  25  is drawn out of or drawn into the retractor  55  in accordance with the position and angle of the seat back  12 . In this state, the retractor  55  constantly applies a predetermined tension to the webbing  25 , which extends toward the roof  27 . In the normal driving state, the guide hanger  28  is located at a position where it closes the opening  31 , as shown in the state of  FIGS. 1 and 8 . That is, in the lock mechanism  39 , the engaging projection  48  of the first lever  42  is engaged with the second engaging notch  47  of the cam  41 , and the upper engaging bar  36  of the guide hanger  28  is engaged with the first engaging notch  45  of the cam  41 . 
     When a front crash occurs and an impact having a predetermined force or greater is applied to the vehicle, the vibration caused by the impact separates (disengages) the engaging projection  48  of the first lever  42  from the second engaging notch  47  of the cam  41 . This rotates the cam  41  in the counterclockwise direction (the state of FIG.  4 ). Simultaneously, the upper engaging bar  36  of the guide hanger  28  is separated (disengaged) from the cam  41 . Thus, the guide hanger  28  pivots downward about the bearings  34 . In other words, the guide hanger  28  drops into the passenger compartment as shown in the states of  FIGS. 2 and 9 . 
     Further, the acceleration sensor  72  detects sudden deceleration and sends a detection signal to the ECU  71 . In response to the detection signal, the ECU  71  heats the ignitor  64  of the pretensioner  58 . This burns the propulsion agent  63  and generates combustion pressure, which instantaneously draws the webbing  25  into the retractor  55 . As a result, as shown in the state of  FIG. 2 , the webbing  25 , which extends straight and directly from the retractor  55 , supports the upper portion of the seat back  12 . In this state, the tension applied to the webbing  25  is strong. This counters the rotational moment acting to pivot the seat back  12  forward. 
     The front crash also activates the air bags  18  in response to the detection of acceleration sensors, which are incorporated in the air bags  18 , and inflates bags G. 
     When a rear crash occurs and an impact having a predetermined force or greater is applied to the vehicle, a rotational moment acting to pivot the seat back  12  rearward is produced. The seat back  12  is supported from an upper rearward position when a front crash occurs. However, when a rear crash occurs, it is preferred that the seat back  12  be supported from above. Thus, the lock mechanism  39  remains locked so that the guide hanger  28  is not dropped. That is, the acceleration sensor  72  detects sudden acceleration due to the rear crash and sends a detection signal to the ECU  71 . In response to the detection signal, to the ECU  71 . In response to the detection signal, the ECU  71  drives the solenoid  53  (i.e., moves the output shaft  54  to the rear) and rotates the ratchet lever  44  in the counterclockwise direction, as viewed in FIG.  3 . This separates (disengages) the ratchet  51  from the engaging recess  50 , rotates the second lever  43  in the clockwise direction, and engages (locks) the engaging projection  46  of the cam  41  with the second lever  43 . As a result, the second lever  43  restricts counterclockwise rotation of the cam  41 . Thus, the upper engaging bar  36  of the guide hanger  28  is not separated from the first engaging notch  45  (as shown in the state of FIG.  10 ). Further, the retractor  55  locks the belt  25 . Thus, the seat back  12  counters rotational moment acting to pivot the seat back  12  rearward. 
     The preferred embodiments has the advantages described below. 
     (1) During a front crash, the guide hanger  28  is dropped to support the seat back  12  from a direction that is close to the vector component of a reaction direction of the rotational moment applied to the seat back  12 . Thus, the seat back  12  resists a strong rotational moment. Further, during a rear crash, the guide hanger  28  is not dropped and the webbing  25  is locked in a state extended in an upward direction. Thus, the seat back  12  is supported in an optimal manner during both front and rear crashes. 
     (2) The dropping of the guide hanger  28  would momentarily loosen the tension applied to the webbing  25 . However, the webbing  25  is drawn into the retractor  55  simultaneously with the front crash. Thus, the seat back  12  is supported without any time lag. 
     (3) When a rear crash occurs, the cam  41  is locked so that it does not rotate. This guarantees that the guide hanger  28  will not be dropped. 
     (4) The seat back  12  of the seat  11  is supported by the webbing  25  during a collision. Thus, the seat  11  resists strong rotational moments during a collision. As a result, the three-point belt  16  may be employed for the seat  11  without a special reinforcement structure. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms. 
     The present invention is applied to the driver&#39;s seat in the preferred embodiment. However, the present invention may also be applied to a passenger seat. Additionally, the present invention may also be applied to a seat included in a seat row other than the front row in a vehicle having three or more seat rows. 
     As shown in  FIG. 13 , the retractor  55  may be fixed to the support frame  21  and accommodated in the head rest  20 . In this case, the distal end of the webbing  25  is connected to a holding frame  75 , which is attached to the reinforcement pipe frame  56  in the roof  27 . 
     As shown in  FIG. 14 , a projector  76  may be arranged above the seat  11 . The projector  76  uses the webbing  25  as a screen to project an image. 
     As shown in  FIGS. 15 and 16 , when installing a child seat  91  on the seat  11 , a load limiter  92  may be arranged between the child seat  91  and the seat  11 . As shown in  FIG. 17 , the distal portion of a webbing  93  is attached to the load limiter  92 . The load limiter  92  is torque controlled so that an initial stroke amount with respect to an applied load is small. Thus, the load limiter  92  locks the webbing  93  when a sudden impact is produced. Then, as time elapses, the webbing  93  may gradually be drawn out of the load limiter  92 . The distal end of the webbing  93  is connected to a holder (not shown) located in a lower portion of the seat  11 . The load limiter  92  includes a hook  94 . The hook  94  is engaged with a holder  95 , which is arranged on the rear surface of the seat  11 . 
     The lower portion of the child seat  91  is fixed to the seat  11  with the three-point belt  16 . The upper portion of the child seat  91  is fixed to the seat  11  by extending the webbing  93  through the child seat  91  and fastening the hook  94  of the load limiter  92  with the holder  95 . The relationship of the holder  95  and the hook  94  may be reversed. 
     In such structure, the child seat  91  moves integrally with the seat  11  at the moment a front crash occurs. However, the load limiter  92  is instantaneously activated and gradually releases the forward torque applied to the child seat  91 . Thus, the load limiter  92  gradually absorbs the impact force. When installing the child seat  91  on the front seat, safety is further improved by employing the safety mechanism of the present invention. 
     In the preferred embodiment, the form and material of the webbing  25  is not limited. It is only required that the webbing  25  be flexible and have sufficient strength so that it can be drawn into and out of the retractor  55 . 
     In the preferred embodiment, the pretensioner  58  is activated only during a front crash. However, the pretensioner  58  may also be activated during a rear crash. The air bag  18  may also be activated during a rear crash. 
     The bypassing mechanism is not limited to the structure of the preferred embodiment. For example, as shown in  FIGS. 11 ,  12 ( a ), and  12 ( b ), suspenders  81 , which function as guides, may be fixed to the roof. The suspenders  81  engage a guide hanger  82 . As shown in FIGS.  12 ( a ) and  12 ( b ), each suspender  81  has a sleeve  83 . Pins  85  extend through and out of opposites sides of the sleeve  83 . The pins  85  are urged outward by a spring  84 . The guide hanger  82  includes boxes  87 , which are arranged at positions corresponding to the suspenders  81  to receive the sleeves  83 . Referring to FIG.  12 ( a ), the sleeves  83  are normally received in the boxes  87 , and the pins  87  are engaged with through holes  88 , which extend through the boxes  87 . However, the vibration produced by a collision disengages the pins  87  from the through holes  88  and drops the guide hanger  82 . This extends the webbing  25  directly between the retractor  55  and the seat back  12 . 
     The lock mechanism  39  is an illustrative example and other structures may be employed. 
     The position where the webbing  25  is secured to the seat back  12  is not limited to the position of the preferred embodiment. 
     The webbing  25  may be detachably secured to the seat back  12 . 
     The rear seat air bag  18  may be eliminated. 
     The three-point belt  16  may be attached to a center pillar  15 . 
     The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.