Patent Publication Number: US-2007114774-A1

Title: Belt tension indicator

Description:
The present invention relates to a belt tension indicator for indicating tension in a belt for tethering a child safety seat for instance  
      The object of the present invention is to provide an improved belt tension indicator, in particular one in which provision is made for limiting the load applied by the belt to the child safety seat tethered by it.  
      According to the invention there is provided a belt tension indicator for indicating tension in a belt from a child safety seat to an anchorage, the indicator comprising: 
          a housing accommodating an end of the belt;     anchorage means extending from within the housing for securing the end of the belt to the anchorage;     an at least partially resilient connection of the belt in the housing to the securing means, the connection allowing resilient withdrawal of the belt from the housing at least to a predetermined tension associated with correct installation of the belt;     an indicator for indicating that the predetermined tension in the belt has been reached; 
 
 the resilient connection being adapted to allow further withdrawal of the belt at higher tension such as to limit deceleration of an occupant of the seat in an accident. 
       

      Preferably, the resilient connection is adapted to allow the further withdrawal in a resilient manner.  
      The resilient connection can be adapted to allow the further withdrawal at the same spring rate as that to the resilient withdrawal to the predetermined tension, in which case the resilient connection can include a single spring providing the resiliency to the predetermined tension and beyond.  
      Alternatively, the resilient connection can be adapted to allow the further withdrawal at a higher spring rate than that to the resilient withdrawal to the predetermined tension, in which case the resilient connection can include two different rate springs, the first providing for the resilience to the predetermined tension and the second providing for the high rate resilience, further withdrawal.  
      Again, wherein the resilient connection can be adapted to allow the further withdrawal at least partially at a steady tension, in which case, the resilient connection can include a member arranged to deform plastically to provide the steady tension.  
      The anchorage means can be a clip or a length of strap  
      In certain embodiments, the resilient means can include a shaft on which the strap is wound and resiliently urges the shaft in rotation to wind in the strap, at least when the strap is tensioned to the predetermined tension. Conveniently, the spring or plastically deformable member can be arranged within the shaft, being fast with the shaft at one end and with the housing at the other end; and a spring for indicating the predetermined tension is arranged in series with the said spring or deformable member. Further, the spring for indicating the predetermined tension can be arranged to become coil bound in the event of the predetermined tension being exceeded. Preferably, the indicator is a disc having indicating marks and arranged on the shaft with the indicating marks visible through a window in the housing according to the tension in the strap. Preferably the housing is of moulded plastics material, enclosing metallic members interconnecting anchorage means and the resilient connection.  
      In another embodiment, the resilient connection includes: 
          a central, transverse pin, the anchorage means being connected to the transverse pin;     over-ridable stops adjacent the ends of the pins;     a U member having the strap connected to the central limb of the U and spiral windings at the ends of the distal limbs, the ends of the transverse pin being received in the spiral windings terminating in fingers, with the terminal fingers engaging the over-ridable stops for resilient withdrawal of the strap up to at least the predetermined tension, 
 
 the arrangement being such that when the tension exceeds the predetermined tension, the terminal fingers over-ride the stops and windings un-wind with plastic deformation to provide the said limited deceleration. 
       

      Preferably, the indicating means is a flag carried on the U member and visible through a window in the housing. The indicating flag is crimped to the U member and able to slide along it when the tension exceeds the predetermined tension. Means can be included to limit the unwinding of the spiral windings, to provide a complete connection of the strap to the anchorage means in even of such unwinding. 
    
    
      To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:  
       FIG. 1  is a side view of a child safety seat secured onto an adult car seat with a top tether including a tension indicator according to the invention;  
       FIG. 2  is a perspective view of a first tension indicator of the invention;  
       FIG. 3  is a cross-sectional plan view of the tension indicator of  FIG. 2 ;  
       FIG. 4  is a cross-sectional side view of the tension indicator of  FIG. 2 ;  
       FIG. 5  is a view similar to  FIG. 3  of a variant, showing only certain components;  
       FIG. 6  is a cross-sectional side view on the line VI-VI in  FIG. 5 ;  
       FIG. 7  is a cross-sectional front view of another tension indicator of the invention;  
       FIG. 8  is a plan view of the tension indicator of  FIG. 7 ;  
       FIG. 9  is a side view of the tension indicator of  FIG. 7 ;  
       FIG. 10  is a partially sectioned perspective view of another embodiment of a tension indicator according to the invention;  
       FIG. 11  is a similar view of the indicator of  FIG. 10 , indicating predetermined tension;  
       FIG. 12  is a similar view of the indicator of  FIG. 10 , during plastic deformation during an accident; and  
       FIG. 13  is a view similar to  FIG. 10  showing a variant.  
    
    
      Referring first to  FIG. 1 , there is shown a child safety seat  10  mounted on a vehicle seat  12  and secured in place by the lap strap  14  of a vehicle seat belt associated with the seat  12 . In addition, a top tether strap  16  extends from an upper part of the child seat  10  to an anchorage  18  on a parcel shelf  20  located behind the backrest  22  of the vehicle seat  12 . The tether strap  16  is connected to the anchorage  18  by a tension indicator  24  in accordance with the invention.  
      Referring now to FIGS.  2  to  4 , the tension indicator has a moulded plastics material casing  30  comprised of two inter-engaging halves  31 , 32 , clipped together along a median plane. An anchorage clip  33  extends from the rear of the casing. A window  34  in the top of the casing exposes an indicating disc  35 , and a front mouth  36  allows the strap to enter the casing. Internally, the indicator has two steel side plates  41 , 42 . They are interconnected by a thicker, load bearing rear pin  43 , on which the clip  33  is pivoted, and two thinner, front location pins  44 ,  45 , between which the strap passes. The pins have stepped down outer ends  46  which are peened into countersinks in the outside of apertures  47  in the plates. Thus the plates are secured at a determined spacing and the casing halves can be clipped and held to them by moulded formations  48 .  
      The plates are pressed and formed with dishes  49 , 50 , which face each other. The dishes have concentric apertures  51 , 52 . Received in the dishes are discs  53 , 54 , each stamped with a central square cut-out  55  and an offset bore  56 . A main shaft  57  of square tube is received in the discs and held in place by crimps  58 , with the discs at right angles to the tube. A rod  59  with turned down ends  60  is located between the discs at the bores  56 . This assembly  51 , 52 , 57 , 59  forms a spool for the end of the strap  16 , which is looped around the tube  57 , with a piece  161  turned back and stitched  162  in place. The loop is restrained from turning on the shaft by the rod  59 . It should be noted that the plates  41 , 42  are set apart with sufficient distance to avoid the strap fouling the plates when a few turns are wound around the tube.  
      The tube houses a wound wire torsion spring  61 . One end  62  of this—on the same side of the indicator as the indicating disc  35  and its window  34 —is engaged with the tubular shaft via a cross pin  63  engaging in a cross-bore at the end of the tube. The pin also holds the indicating disc onto the shaft, the disc having a square cut-out  65 , whereby it is rotationally fast with the shaft. End thrust on the tube from the spring is reacted by the disc to the outside of the dish  49  in the side plate  41 . The other end  66  of the spring engages with a U-shaped cross pin  67  whose ends  68  engage in one of a series of pairs of apertures  69  in the side plate  42 .  
      For use, the spring  61  is wound at its end  66  to wind the strap around the shaft, typically by 2½ turns. The winding is temporarily stopped with a green sector  70  of the rim  71  of the indicating disc  35  in the position of the window  34 . The turning is continued to bring a red sector  72  to the window&#39;s position. The device is then set by engaging the cross pin in the relevant ones of the apertures  69 . The rate of the spring is such that when the strap is drawn out to show the green sector at the window (after fitting the casing  30 ) the strap is tensioned to the desired strap tension.  
      For use, the top tether is adjusted at a clamp (not shown) in the child seat to the desired tension, typically 50 N. In an emergency, the top tether is pulled from the indicator in a load limiting manner until all the turns around the shaft are paid out. Then the tension in the strap is reacted directly via the shaft, the side plates and the clip to the anchorage.  
      Turning now to  FIGS. 5 and 6 , a variant is shown in which the spring  61  is replaced by a torsion bar  101  of soft or wrought iron. This material is able to withstand considerably more plastic deformation in twisting than mild steel and hence is well adapted to absorbing energy as it deforms to apply deceleration to an occupant of safety seat over an extended time interval. The central portion only of the load limiting tension indicator is shown in  FIGS. 5 and 6 , the peripheral components being as described in the preceding embodiment.  
      The torsion bar  101  at its indicator disc end is pinned  102  to the square tube shaft  103 . Its other end is pinned to a hub member  104 , having radial fingers  105 . These extend into voids  106  in a disc  107 , which is pinned  108  and clipped  109  to the side plate  110  at a position chosen in accordance with the length of strap wound onto the shaft  103 . Small compression springs  111  are accommodated in the voids and abutted by the sides of the voids in one direction and the fingers  105  in the other. Axially of the shaft, the springs are retained by the plate  110  on one side and a washer  112  on the other side. The washer is held in place by a pin  113  pinning the hub  104  to the torsion bar  101 .  
      In normal use, tension of the strap (not shown in  FIG. 5 ) turns the spool assembly including the shaft  103 . This movement is conveyed to the torsion bar via the pin  102 . The action is transferred to the hub  104 , which compresses the springs  111 . When the predetermined tension in the strap has been applied, in effect assuring that there is no slack in it, the springs have been compressed. They react the tension and the consequent rotation of the shaft is indicated by the indicator disc  114 .  
      In an accident, the strap tension increases. The shaft is held from rotation by the springs being coil bound. The torsion bar then twists, dissipating energy as described.  
      In a non-illustrated alternative, the torsion bar can be replaced by a spring such as  61 , but having a stiffer rate. It in effect is in series with the springs  111  as regards its torsional effect, in the same way as the torsion bar is. It dissipates energy also in an accident, with the added advantage to being able to rewind the strap on rebound. Further the spring could be arranged to dissipate energy plastically. For this it may be preferable to place a torsion bar in series with a spring both within the shaft  103 .  
      Turning on to  FIGS. 7, 8  and  9 , the indicator thereshown is housed in a short length of rectangular steel tube  201 , with plastic material end caps  202 , themselves having openings (not shown) for a strap and an anchor clip. A torsion bar  203  extends across the tube and has a plain end  204  in a plain bore  205 —on the right hand side in  FIG. 7 . The bar has a square section end  206  at its other end, engaging in a contoured aperture  207 , allowing limited rotation. Journalled immediately inside the end  206  is an indicator disc  208 . This is rotationally engaged by a strap tube  209 , itself rotationally fast with the torsion bar at a second square section  210 . The strap has a central loop  211  extending through a longitudinal slit (not shown) in the tube. The strap is wound  212  around the outside of the tube. At the square  210 , the tube has an end with a square aperture  213  for engaging the torsion bar. It also has a lug  214  with an aperture engaging a small torsion spring  215 , the other end of which is engaged in the side wall  216  of the tube  201 . The tube has a window for viewing the indicator disc  208 .  
      In normal use, the torsion bar, strap tube and indicator disc rotate as a unit, under the influence of the strap in one direction and the spring  215  in the other. The square  206  of the bar and the contoured aperture  213  limit the rotational movement under normal use. In an accident, with more strap being pulled out, the spring  215  is wrenched from its engagement apertures and the rotation of the strap tube is resisted by the torsion bar. This twists plastically, dissipating energy.  
      Turning now to  FIGS. 10, 11  and  12 ,  FIG. 10  illustrates an alternative tension detector in which the hook  330  is replaced by a second flexible strap  350  having its end stitched into a loop  352  that wraps round a central shaft  354 . A U-shaped one-piece coil spring has two coiled end portions  356  and  358  wrapped round the shaft  354 . The end portions  356  and  58  are inter-connected by a central stirrup  360 . The tether strap  316  has a loop  362  sewn into its end which engages round the stirrup  360 . The ends of the shaft  354  are journalled in side walls of a housing  366 . Each side wall has an inwardly direct abutment projection  368 , one of which is visible in  FIGS. 11 and 12 .  
      The upper surface of the housing  366  includes a window  370  through which an arcuate indicator  372  is visible. The indicator  372  has side legs  374  and  376  that are slidably mounted on the stirrup  360 .  
      When the strap  316  is relaxed, the left hand end of the arcuate indicator  372  is visible through the window  370 , as shown in  FIG. 12 . When the strap  316  is tightened, the arcuate indicator  372  pivots to the position shown in  FIG. 11  in which its right hand end, which is of a different colour to its left hand end, is visible through the window  370 , indicating that the strap  316  has been tightened adequately.  
      In the event of a crash, the coiled end portions  356  and  358  of the spring over-ride the abutment projections  368  and partially unwrap from the shaft  354  so that an extended stirrup portion  360  projects from the housing  366  as shown in  FIG. 12 .  
       FIG. 13  shows another form of tension detector which is identical to the tension detector shown in FIGS.  10  to  12 , except that the second strap  50  is replaced by a hook  378 , similar to the hook  33  of FIGS.  1  to  4 . Additionally the free ends of the coiled end portions  356 , 358  are looped together to avoid the possibility of them unwinding completely off the shaft  354 .