Abstract:
A vehicle safety restraint arrangement includes a retractable and extractable belt, a belt reel on which the belt is windable, a retraction mechanism adapted to retract the belt from an extracted position, and a belt retraction brake adapted to limit the retraction speed of the belt during retraction of the belt by imparting a braking force to the belt reel during retraction of the belt via inductance. The present disclosure also relates to a method for limiting the retraction speed of a belt arranged on a belt reel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to European patent application number EP 12175292.7, filed Jul. 6, 2012, which is incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a belt reel for a vehicle safety restraint arrangement, the belt reel is adapted to retract the belt from an extracted position using a retraction mechanism. The belt reel comprises a belt retraction brake adapted to limit the retraction speed during retraction of the belt. The present disclosure also relates to a method for limiting the retraction speed of a belt reel during retraction of a belt onto the belt reel. 
     BACKGROUND 
     Seat belts, sometimes referred to as safety belts, in vehicles have significantly reduced the probability of injuries during collisions or other incidents. The belt itself is generally wounded up about a reel, generally referred to as a belt reel. A belt reel of conventional type comprises a retraction mechanism to retract the belt from an extracted position. One extracted position is a buckled position, e.g., the position a driver of the vehicle has when being position behind the steering wheel and buckled up. 
     When the belt reel retracts the belt, the belt with its buckle runs the risk of either being retracted too slow or too fast. If retracted too slow, the belt can be caught between the vehicle body and its door which might damage the belt. If the buckle is caught between the door and the vehicle body, the buckle could break or damage the lacquer of the vehicle body. Should the belt reel retract the belt too fast, the buckle runs the risk of smashing into the interior panels of the vehicle and damage the interior panel. It has been noticed that a belt retraction speed approximately &gt;3.0 m/s can damage the interior panels of the vehicle if hit by the buckle. Even if the impact of the buckle on the interior panel does not destroy the interior panel, it leaves ugly marks which can reduce the value of the vehicle. Providing a controlled belt retraction is thus a problem which needs to be addressed. 
     In the published UK Patent Application No. GB 2,319,502 A, a retractor assembly is disclosed. The retractor assembly comprises a two curved brake shoes arranged at a distance. The belt travels between the two brake shoes during the extracting and retracting motion. The curved brake shoes comprise inductive material such that when current is passed through them they are attracted to each other imparting a brake force to the belt webbing. The rotatable spool, or belt reel, itself can also be provided with an eddy current brake to restrict the pay out of the belt during a crash or collision. The document is however silent as to how the belt can be retracted in a safe and secure manner without risking inflicting damages to the interior panel or the lacquer of the vehicle. 
     SUMMARY 
     It is an object of the present disclosure to at least partly solve the above mentioned drawbacks, at least provide for an improvement, or at least provide for a useful alternative to existing solutions. The objective is at least partly met by a belt reel for a vehicle safety restraint arrangement. The belt reel comprises a retractable and extractable belt, a retraction mechanism adapted to retract the belt from an extracted position, and a belt retraction brake adapted to limit the retraction speed of the belt by imparting a braking force to the belt reel during retraction of the belt. The braking force of the belt retraction brake is imparted to the belt reel via inductance. 
     The belt reel can be configured to have a retraction mechanism which can be adapted to retract the belt using a higher load than what would otherwise be suitable as during the retraction of the belt, the retraction speed of the belt can thus be kept from peaking. If the retraction mechanism is a pre tensioned biasing member, such as a pre tensioned spring, the belt retraction brake also compensates for tolerances of the pre tensioned spring of the belt reel. 
     Furthermore, by using a retraction mechanism which retracts the belt using a higher load than what would otherwise be suitable, the risk of pinching the belt and possibly a belt buckle between a vehicle body and a door is reduced. 
     The belt retraction brake can be passive, passive in terms of that it requires no electricity to operate, i.e., no power source. Permanent magnets are advantageously used when the belt retraction brake is passive. In another embodiment it is conceivable that a power source is connected together with an electronic control unit (ECU), to better control the retraction brake properties of the belt reel. 
     According to an aspect, belt retraction brake comprises a coil portion adapted to cooperate with the belt reel, and at least one magnet arranged on the belt reel. The inductance is thus imparted during the retraction of the belt and as the belt reel rotates. A permanent magnet is advantageously used. 
     According to an aspect, the coil portion of the belt retraction brake comprises an inductor or coil, or optionally a copper cylinder. 
     According to an aspect, the belt reel can comprise a first end and a second end and a belt portion arranged between the first and the second ends of the belt reel. The belt can thus be wound up about the belt portion, at least after retraction of the belt. At least one end of the belt reel is adapted to form a part of the belt retraction brake, optionally both the first end and the second end of the belt reel are adapted to form a part of the belt retraction brake. 
     The first end and/or the second end of the belt reel can have different shapes and forms. For example, the first end and/or the second end of the belt reel can be; symmetric or non symmetric; have a polygonal form such as triangular (or trigon), quadrilateral (or quadrangle or tetragon), pentagon, hexagon, heptagon, octagon, enneagon or nonagon, decagon. It should be noted that from decagon and above, the periphery can be considered more or less circular. Advantageously, the first end and the second end comprise a substantially circular periphery, optionally a true circular periphery. It is possible that at least one end of the first end and the second end of the belt reel comprises a non circular periphery. 
     The coil, or copper cylinder, can be arranged in the proximity of the first end and/or the second end of the belt reel. 
     According to an aspect, at least one magnet is arranged on the first end and/or second end of the belt reel. The magnet can be a permanent magnet. At least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more magnets can be arranged on the first end and/or second end of the belt reel. A suitable number of magnets are between 6-20 magnets. The at least one magnet is advantageously arranged about the periphery of the first end and/or second end of the belt reel. 
     According to an aspect, the braking power of the belt retraction brake is about 1-30 Watts (W). 
     According to an aspect, the belt retraction brake comprises a disc shaped element, such as a copper disc, aluminum disc, or a disc a conductive material, and at least one permanent magnet. The disc shaped element can be arranged on the belt reel, and preferably on the first end and/or second end of the belt reel. The at least one permanent magnet can be arranged on a fixed position with respect to the disc shaped element, such as a belt reel housing. 
     According to an aspect, the retraction mechanism is adapted to impart a retraction force to the belt reel. The retraction force is rotating the belt reel so that the belt is retracted from an extracted position. The retraction force imparted to the belt reel by the retraction mechanism is larger than the braking force imparted to the belt reel via the belt retraction brake. 
     According to a second aspect, the present disclosure also relates to a method for limiting the retraction speed of a belt arranged on a belt reel. The belt reel is adapted for a vehicle safety restraint arrangement, the method comprising the steps of;
         retracting the belt onto a belt reel using a retraction mechanism;   limiting the maximum speed during the retraction by imparting a braking force to the belt reel using induction.       

     The belt reel can be a belt reel according to any of the appended claims. 
     The present disclosure relates to a belt reel for a vehicle safety restraint arrangement. The belt reel comprises a retractable and extractable belt, a retraction mechanism adapted to retract the belt from an extracted position, and a belt retraction brake adapted to limit the retraction speed of the belt by imparting a braking force to the belt reel during retraction of the belt. The braking force of the belt retraction brake is imparted to the belt reel via inductance. The present disclosure also relates to a method for limiting the retraction speed arranged on a belt reel. The present disclosure provides for a belt reel which reduces the risk for damage to the interior panel, lacquer or the vehicle body and/or door, and the belt itself. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non limiting embodiment of the present disclosure will be described in greater details with reference to the following figures in which; 
         FIG. 1  shows a driver of a car, the driver being buckled up using a belt, buckle and a belt reel according to an embodiment of the present disclosure; 
         FIG. 2  shows the belt reel of  FIG. 1  in greater detail; 
         FIG. 3  shows the belt reel of  FIG. 2  in a cross section; 
         FIG. 4  shows the belt reel of  FIG. 3  in a cross section; 
         FIG. 5  shows a belt reel according to the present disclosure in a cross section having an alternative belt retraction brake; 
         FIG. 6  shows the belt reel of  FIG. 5  in a cross section; 
         FIG. 7  shows a diagram of a the highest spot speed vs. number for; a belt reel without induction brake and; a belt reel comprising induction brake and a strengthened retraction mechanism in the form of a strengthened spring and; 
         FIGS. 8 a -8 b    show a schematic embodiment of a belt retraction brake in two different views. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a driver  10  of a vehicle  11 , in this case a car; the driver is positioned on the driver side of the vehicle in front of the steering wheel  12  on a driver seat  13 . To prevent the driver  10  from being injured in case of e.g., a collision, the driver  10  is buckled using a belt  14  comprising a buckle  15 . The belt  14  extends from a belt reel  20  according to an embodiment of the present disclosure, the belt reel being positioned on a pillar  25  of the vehicle. The pillar  25  is also referred to as the A-pillar  25  of the vehicle  11 . It should be noted that the belt reel  20  can be positioned in other positions in the vehicle  11 . The belt reel  20  forms a vehicle safety restraint arrangement together with the belt  14  and the buckle  15  after being assembled to the vehicle  11 . 
     Non limiting embodiments of the belt reel  20  will hereafter be described in greater detail.  FIG. 2  shows an embodiment of the belt reel  20  comprising a belt  14  wound up about the belt reel  20 . The belt  14  is transparently illustrated using dashed lines to better show the belt reel  20 . The belt reel  20  permits the belt  14  to be extracted and retracted, e.g., to fasten a driver as shown in  FIG. 1 . The belt reel  20  comprises a retraction mechanism in the form of a spring  19  (shown schematically in  FIG. 1 ) which is loaded as the belt  14  is retracted. If a user, such as a driver, buckles up, the spring is loaded so as to retract the belt  14  after being unbuckled back to a position which generally is in the proximity of the belt reel  20 . The belt reel  20  rotates about an axis of rotation A during the extraction or retraction of the belt  14 . The belt reel  20  comprises first and second ends  21 ,  22  and a belt section  23  extending between the first and second ends  21 ,  22 . The belt section  23  is that part of the belt reel  20  about which the belt  14  is wound up about. A shaft  24  extends from the first end and the second end  21 ,  22  of the belt reel  20 . Further shown in  FIG. 2  is a housing  26 , adapted to enclose the belt reel  20 , while permitting the belt  14  to extend through a slot or opening (not shown in  FIG. 2 ). For the sake of illustrating the belt reel  20 , the housing  26  is shown with portions partly transparent. The shafts  24  are rotationally attached to the housing  26 , which in turn is attached to the vehicle  11 , in  FIG. 1  in the proximity of the A-pillar  25  of the vehicle  11 . 
     The belt reel  20  comprises a retraction mechanism, retraction means, to retract the belt  14  from an extracted position, e.g., when a driver unbuckles the belt  14  from the position shown in  FIG. 1 . The retraction mechanism can be a spring which is pre tensioned, and loaded during the extraction of the belt  14  from the belt reel  20 . Other biasing members are possible, such as elastic polymer material, or an electric motor, or the like. The retraction mechanism can be configured to impart a torque to the belt reel of from 0.10-0.50 Nm, advantageously 0.10-0.3 Nm, preferably 0.12-0.25 Nm. 
     Arranged at the first end  21  of the belt reel  20  is a belt retraction brake  30 . It should be noted that the belt reel  20  can be arranged with one or more belt retraction brakes, e.g., two belt retraction brakes as shown in  FIG. 2 , however only one belt retraction brake  30  will be described herein. The retraction mechanism is adapted to impart a retraction force to the belt reel, however the retraction force imparted to the belt reel by the retraction mechanism is larger than the braking force imparted to the belt reel via the belt retraction brake. 
       FIG. 3  shows a cross section of the belt reel  20  shown in  FIG. 2  along the line I-I, the first and the second ends  21 ,  22 , the belt section  23 , and the belt  14 . The belt retraction brake  30  is arranged at the first end  21  of the belt reel  20 , and arranged to be in working cooperation with the first end  21  of the belt reel  20 . The belt retraction brake  30  is adapted to limit the speed of the belt  14  during retraction by reducing the angular velocity of the belt reel  20  during rotation, at least during the rotation which retracts the belt  14  back onto the belt reel  20 . 
       FIG. 4  shows a cross section of the belt reel  20  shown in  FIG. 3  and along the line II-II.  FIG. 4  shows the belt retraction brake  30  comprising a magnet portion  31 , in the embodiment comprising a plurality of poles indicated by N, for the north pole, and S, for the south pole. The magnet portion  31  can be formed by a plurality of magnets. An inductor or coil  32  comprising an iron core  33  and a copper wire  34  wrapped about a portion of the iron core  33  provides for the conductor. As the belt reel  20  rotates, eddy currents will be formed in the inductor  32  generating an electromagnetic force which imparts a braking force to the belt reel  20 , which in turn will limit the retraction speed of the belt  14  during belt retraction. 
     Some parameters which can be manipulated to increase the braking force imparted to the belt reel  20  are:
         Use stronger magnets—increases remanence T.   Change fields faster (rotate the belt reel  20  faster)—increases the frequency.   Use thicker materials of the conductive material, care have to be taken not to use too thick material as the distance between the magnets may be too far.   Lower resistivity materials—decreases ρ.       

     Using a belt retraction brake  30  during the retraction of the belt  14  is very advantageous, in practice; if the angular velocity of the belt reel  20  is increased the braking force of the belt retraction brake  30  will be significantly improved. 
       FIG. 5  shows another embodiment of a belt reel  20 .  FIG. 6  shows a cross section of the belt reel  20  shown in  FIG. 5  along the line III-III. With reference to  FIGS. 5 and 6 , the belt reel  20  comprises a belt  14 , first and second ends  21 ,  22  with a belt section  23  arranged therebetween. At the first end  21  of the belt reel  20  is arranged an alternative belt retraction brake  30 . The belt retraction brake  30  comprises in this case a circular copper ring  35  arranged about a magnet portion  31 , in the form of a plurality of magnets, to create the braking force imparted to the belt reel  20 , instead of a coil as described above. 
       FIG. 7  shows a diagram comprising first and second graphs A, B which represent the relation between the belt retraction brake  30  of the belt reel  20 , described above using non limiting embodiments, and different types of damages which may occur during as a consequence of the retraction speed of the belt reel. The belt reel being positioned in a car as seen in  FIG. 1 . The first axis is the highest spot speed (m/s) (highest speed at a point in time) and the second axis is the number of retractions (dimensionless). 
     The diagram of  FIG. 7  is further partitioned in three areas: 
     the first area represents damage to pillars and doors, and primarily the A-pillar of the car; 
     the second area represents a state at which no damage occurs, i.e., the belt is retracted without any damages or negative consequences; and 
     the third area represents damage to the belt web, buckle, door seal, or the lacquer in the door area of the car. 
     The first graph A shows the normal distribution for a normal belt reel having a standardized retraction mechanism. As can be seen in  FIG. 7 , using a normal belt reel without a belt retraction brake, a percentage of the retractions inflict damage to the pillars or side panels of the car. Another percentage can inflict damage to the belt web, or door seal, due to being retracted to slow, i.e., the retraction mechanism is too weak. 
     The damages mentioned above can be costly and renders ugly and unaesthetic marks on the interior of the car, or on the belt or its buckle. There is also a risk that the belt itself, sometimes referred to as the belt web, can be damaged, which can have dramatic consequences during a collision. 
     Using a belt reel comprising a belt retraction brake, according to embodiments of the present disclosure, the normal distribution can be better fitted to the safe zone, i.e., the second area shown in  FIG. 7 . The belt retraction brake permits the retraction mechanism to be stronger than what is otherwise suitable, while at the same time prevent the belt from acquiring an excessive speed during the retraction of the belt. 
     It has been noticed that as the belt reaches a retraction speed of more than &gt;3.0 m/s, the buckle  15  of the belt  14  can damage the interior panels of the car. The magnet portion  31  should thus be selected so that the retraction speed of the buckle is kept below 3.0 m/s, or preferably below 2.5 m/s. Optionally, as mentioned above, other parameters can be varied to limit the retraction speed. 
     Suitable force of the magnets used in the magnet portion  31  are; 0.5-3 T, preferably about 0.75-2 T. 
       FIGS. 8 a -8 b    show a schematic embodiment of a magnetic brake which can be used for the purpose of the disclosure.  FIG. 8 a -8 b    show a disc shaped element in the form of a copper disc  40  with an aperture  41 . The copper disc  40  is connected to the belt reel  20  and has the same axis of rotation A, as shown in  FIG. 2 , and rotates with the rotation vector {right arrow over (ω)}=ω about the axis A. Total diameter is D y . On each of the opposite sides of the copper disc are two button shaped permanent magnets  43 ,  44  arranged, totally four permanent magnets, with a radii of rmag a height of I mag  and with a distance of t gap  away from the copper disc  40 . The permanent magnets are arranged as close together as possible, which determines the angle Φ in  FIG. 8 a   . The permanent magnets  43 ,  44  have been magnetized with a remanence Br. A couple of the permanent magnets have a unidirected remanence, so that there are magnetic fields parallel with the rotation axis A of the copper disc  40 . 
     The following references and values are used with respect to  FIGS. 8 a -8 b   . 
     
       
         
               
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                   
               
             
             
               
                 d y   
                 total diameter 
                 70 
                 mm 
               
               
                 d cu   
                 width of copper disc 
                 14 
                 mm 
               
               
                 t cu   
                 thickness of copper disc 
                 2 
                 mm 
               
               
                 σ cu   
                 conductivity of copper disc 
                 5.998 * 10 7   
                 S/m 
               
               
                 t gap   
                 air gap 
                 1 
                 mm 
               
               
                 r mag   
                 radii of permanent magnet 
                 4 
                 mm 
               
               
                 l mag   
                 height of permanent magnet 
                 3 
                 mm 
               
               
                 d off   
                 position radially of permanent magnet 
                 1 
                 mm 
               
             
          
           
               
                 φ 
                 angular distance between the permanent 
                 As small as possible 
               
               
                   
                 magnets 
               
             
          
           
               
                 Br 
                 remanence of the permanent magnets 
                 1 
                 T 
               
               
                 n mag   
                 Number of magnets (on each side) 
                 2 
               
               
                   
               
             
          
         
       
     
     Metals other than copper could be used for the copper disc  40 , such as aluminum for example. The thickness t cu  of the copper disc can be between 0.5-5 mm, preferably 2.0-3.5 mm. The position radially of permanent magnet d off  can be −1 to 3 mm, preferably 0.5-1.5 mm. The angular distance between the permanent magnets Φ can be 5-25 degrees, but as close as possible is advantageous. Preferably the magnets are positioned adjacent each other. The radii of permanent magnet r mag  can be between 2-15 mm, 2-8 mm or advantageously 3-6 mm. The height of permanent magnet I mag  can be 0.5-10 mm, 2-8 mm, advantageously 3-6 mm. Optionally the number of magnets on each side can be 1, 2, 4, 6, 8, 10 or more, preferably 2-10 magnets on each side. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.