Abstract:
A dual-mode retractor for an automotive seat belt webbing is configured to switch between a first mode and a second mode, the first mode being one of an ELR mode and an ALR mode, and the second mode being the other one of the ELR mode and the ALR mode. The retractor switches between the first mode and the second mode via a relative movement between a first part and a second part of the retractor. The magnetic field of a permanent magnet mounted on the first part is picked up by a Hall effect sensor. An interrupter plate is mounted on the second part in a position relative to the magnet, in which the interrupter plate, in which the interrupter plate exposes the HED to the original magnetic field in the first mode and to a modified magnetic field in the second mode.

Description:
TECHNICAL FIELD 
     The invention relates to a mode detection switch for a dual-mode self-locking automotive seat belt retractor operable both as an emergency locking retractor (ELR) and as an automatic locking retractor (ALR), where the seat belt retractor is part of a motor vehicle passive safety system comprising an additional associated restraint device, such as an inflatable airbag. 
     BACKGROUND 
     Motor vehicle seat belt retractors are usually one of three types, ALR, ELR, or dual-mode. An ALR includes a self-locking mechanism operating like a ratchet while a seat belt tongue is engaged with a seat belt buckle. The seat belt webbing is automatically tightened, while the ALR prevents extraction of the available belt webbing. The ALR racheting operation is cancelled when the webbing is fully retracted. An ELR includes a locking mechanism that is activated by vehicle acceleration (vehicle sensitive), webbing acceleration (webbing sensitive), or other crash sensing means to block webbing extension. Absent an activation of the ALR, seat belt webbing can be pulled out to lengthen the available seat belt webbing. Both an ALR and an ELR are configured to restrain a passenger during a frontal impact or vehicle rollover. A dual-mode retractor combines an ELR and an ALR, and a vehicle occupant chooses the desired mode. Typically, a dual-mode retractor is switched to the ALR mode by completely or nearly completely pulling out the seat belt webbing. The ELR can be converted to an ALR at the option of a vehicle occupant. While the ELR mode provides a comfortable adjustment for an occupant seated on a vehicle seat, infant carriers may be more safely secured in the ALR mode. An ALR has the advantage that is very easily used with child restraint systems, since the belt can be fastened and cinched down to secure the child restraint. However, an ELR is more acceptable for ordinary use since it provides enhanced comfort and convenience for the vehicle occupant. Dual-mode systems accommodate use with both child restraint systems and normal operation. 
     In a safety system that comprises at least one further restraint device, such as an airbag or a load limiter for the seat belt webbing, the currently selected mode of a dual-mode retractor constitutes a valuable piece of information for the operation of the additional restraint device. For example, it is generally not preferred to activate a frontal impact airbag for a seating position being used for securing a child restraint device. 
     Accordingly, some vehicle manufacturers are looking to verify the currently selected mode, i.e. ALR or ELR, so they can use this information to provide as an input to an electronic control unit (ECU) for controlling certain restraint system functions. Some current retractors use microswitches or simple contact switches as part of a detection circuit to comply with the seat belt use indicator requirement in FMVSS 408. These are simple switches and may not provide the proper information for use in a restraint system control algorithm included in an ECU. 
     SUMMARY 
     It is an objective of the present invention to provide a dual-mode retractor assembly capable of transmitting reliable information to an ECU on the currently selected mode of the dual-mode retractor. 
     According to the present invention, a dual-mode retractor for automotive seat belt webbing is configured to switch between an ELR mode and an ALR mode via a relative movement between a first part and a second part of the retractor. A permanent magnet mounted on the first part cooperates with a Hall Effect device (HED) positioned to detect the magnetic field. An interrupter plate is mounted on the second part in a position relative to the magnet, in which the interrupter plate allows the magnetic field to be detected by the Hall Effect sensor in the first mode and forms a shield between the magnet and the Hall Effect sensor in the second mode. The HED has the benefit over inductive sensors that it is an active sensor having its own power supply through electrical conduits. Accordingly, the HED is capable of detecting positions, not only movements that induce a change in magnetic flux. 
     Further details and benefits of the present invention become evident from the following description of the attached drawings illustrating a preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included for illustrative purposes only and are not intended to limit the scope of the invention. 
         FIG. 1  shows an axial side view of a dual-mode retractor according to one embodiment the present invention; 
         FIG. 2  shows an axial side view of the dual-mode retractor of  FIG. 1  operating in the ELR mode, with a partially removed cover; and 
         FIG. 3  shows an axial side view of the dual-mode retractor of  FIG. 1  operating in the ALR mode, with a partially removed cover. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 through 3  show an axial view onto a self-locking retractor  10  for a seat belt.  FIG. 1  shows the retractor  10  in a fully assembled state, while  FIGS. 2 and 3  show the retractor  10  without an outer cover  12 . 
     Referring to  FIG. 1 , the outer cover  12  covers a switching mechanism  11  for switching the retractor between an automatic locking retractor mode (ALR mode) and an emergency locking retractor mode (ELR mode). The switching mechanism  11  will be explained in more detail in connection with the subsequent figures. 
     A Hall Effect device (HED)  14  is mounted on the cover  12  in a position opposite a magnet  16  located underneath the cover  12 . The HED  14  is connected to an electronic control unit (ECU)  20  via electric conduits  15 . 
     Referring now to  FIGS. 2 and 3 , the switching mechanism  11  is mounted on a base plate  22  forming a leg of a U-shaped housing in which a spool shaft  30  with a spool, not represented in the drawing, with the seat belt  24  wound on the spool is rotatably supported. A winding spring, not represented in the drawing, is also provided at the housing of the self-locking retractor  10 . The winding spring acts on the spool shaft  30  for winding the seat belt webbing  24 . At the other leg of the U-shaped housing, a blocking mechanism is located. 
     The spool shaft  30  extends through the base plate  22  for supporting, in a form-locking manner, a gear wheel  32  so that a fixed connection of the gear wheel  32  with the spool shaft  30  results. A rocker arm  34  is pivotably connected to the base plate  22  of the housing of the retractor and is provided with gear wheels  36  and  38  at both outer ends. The pivoting arrangement is designed such that the gear wheels  36  and  38  are constantly meshing with the gear wheel  32  fixedly connected to the spool shaft  30 . The gear wheels  32 ,  36 , and  38  are configured to mesh at all times, even during a movement of the rocker arm  34 . 
     A chevron-shaped guide slot  40  is arranged at a radially outer portion of the rocker arm  34 . The chevron-shaped guide slot  40  performs a circumferential movement when the rocker arm  34  pivots in direction  56  ( FIG. 2 ) or  66  ( FIG. 3 ). A spring arm  42  is supported at the base plate  22  of the housing of the retractor  10  which, due to a spring bias, is urged in the direction of engagement with the outer teeth  28  of the control disk  26 , as represented in  FIG. 3 . An elongated tab  43  formed on the spring arm  42  is held by the left half of the chevron-shaped guide slot  40  of the rocker arm  34  at such an angular position that, during normal operation of the retractor  10 , the spring arm  42  is radially removed from engagement with the outer teeth  28  of the control disk  26 . 
     The permanent magnet  16  is fixedly attached to the base plate  22  adjacent to an interrupter plate  18  fixedly mounted on the rocker arm  34 . The interrupter plate  18  is made of ferromagnetic material forming a magnetic shield and operates as a vane interrupter as will be explained in more detail below. The ferromagnetic material may be steel or any other material functioning as a magnetic shield. Interrupter plate  18  may act to shield and magnetic field from its influence on HED  14 , or change the direction or magnitude of the magnetic flux lines which interact with the HED. HED  14  produces an electrical output in response to a changed magnetic field. 
     The meshing gear wheels  32 ,  36 , and  38  are provided with switching lugs  44 ,  46 , and  48  in a plane outside of the plane of the gear teeth. The gear wheel  32  carries switching lug  44 , the gear wheel  36  switching lug  46 , and the gear wheel  38  carries switching lug  48 . 
     Based on the position shown in  FIG. 2 , the operation of the locking device will be described in the following. 
     In the position represented in  FIG. 2 , the self-locking retractor  10  functions as ELR with a vehicle-sensitive and belt-sensitive control of its blocking mechanism via control of the control disk  26 . In the position shown in  FIG. 2 , the magnet  16  generates a magnetic field that permeates the cover  12  and is picked up by the HED  14  attached to the cover  12 . The HED transmits the respective information to the ECU  20  that determines that the retractor  10  is in the ELR mode. 
     When, for example, for attaching a child seat, the seat belt  24  is removed from the spool in the direction of arrow  50 , the gear wheel  32  that is fixedly connected to the spool shaft  30  is rotated in the direction of arrow  52  whereby a load-free actuation of the gear wheels  36  and  38  in the direction of rotation of arrow  54  occurs. During this rotation of the gear wheels  32 ,  36 , and  38  the corresponding switching lugs  44 ,  46 , and  48  do not come into contact but are rotated past one another. 
     Only when a predetermined number of revolutions of the gear wheel  32  has been reached which corresponds to the predetermined unwinding state of the seat belt  24 , the switching lugs  44  and  46  of the gear wheels  32  and  36  abut one another such that upon a further loading of the gear wheel  32  in the direction of rotation  52  the rocker arm  34  is pivoted in the direction of arrow  56 . Due to this pivoting, the chevron-shaped guide slot  40  guides the tab  43  of the spring arm  42  into the right half of the chevron-shaped guide slot  40  so that, due to its spring action and the angular position of the tab  43 , the spring arm  42  is introduced in the direction of arrow  58  into the outer teeth  28  of the control disk  26 . 
     For example, the shown embodiment provides ten teeth on gear wheel  32  and  17  teeth on each of gear wheels  36  and  38 . Accordingly, the switching lug  44  on gear wheel  32  will mesh with each of the switching lugs  46  and  48  on gear wheels  36  and  38 , respectively, every  17  revolutions of the gear wheel  32 , corresponding to ten revolutions of the gear wheels  36  and  38 . 
     In this position, represented in  FIG. 3 , the control disk  26  is locked against further rotation of the spool shaft  30  in the direction of removal  50 , while it may rotate in the direction of winding up the seat belt (arrow  60 ). Accordingly, in the position represented in  FIG. 3 , the seat belt  24  may be wound onto the spool of the retractor  10  while even a slight removal of the seat belt  24  results in a blockage of this removable movement. Accordingly, the retractor  10  is in the ALR mode. The rocker arm  34  is not biased by a spring and remains in its respective position until a pair of switching lugs, consisting of switching lugs  44  and  46  or of switching lugs  44  and  48 , engages. 
     In the position shown in  FIG. 3 , the interrupter plate  18  covers the magnet  16  so that the magnetic field of the magnet  16  does not reach the HED  14  mounted on the cover  12 . The HED  14  transmits the respective information to the ECU  20  that determines that the retractor  10  is in the ALR mode. 
     As is evident from the described function of the HED  14 , it is sufficient that the HED  14  operates as a digital switch that distinguishes between the two modes, ALR and ELR. The HED  14  has the benefit over inductive sensors that it is an active sensor having its own power supply through conduits  15 . Accordingly, the information sent by the HED  14  is capable of detecting positions, not only movements that induce a change in magnetic flux. 
     When it is desired to release the constant activation of the locking mechanism during the subsequent winding of the seat belt  24 , the gear wheel  32  with the switching lug  46 , after rotating in the direction of arrow  62  for a predetermined number of revolutions, abuts the switching lug  48  of the gear wheel  38  which, during the winding movement of the seat belt  24  in direction of arrow  60 , is rotated in the direction of arrow  64 . In this position a further rotation of the gear wheel  32  results in a pivoting of the rocker arm  34  in direction of arrow  66 . The chevron-shaped guide slot  40  moves in the same direction. As a result, the spring arm  42  is guided by the left half of the chevron-shaped guide slot  40  so that the spring arm  42  is lifted in the direction of arrow  68  away from the outer teeth  28  of the control disk  26 . After completion of this movement, the switching position corresponds to the representation of  FIG. 2  again, in which a normal function of the vehicle-sensitive and the belt-sensitive control system of the retractor  10  is ensured. 
     As the magnet  16  is no longer covered by the interrupter plate  18 , the HED  14  picks up the magnetic field again and sends information to the ECU  20  that represents the ELR mode. 
     The present invention has the advantage of providing a highly reliable mode detection in a small integrated package size with a small number of additional components. A malfunction of the HED switch can be easily diagnosed, and the output of the HED can be directly processed in an ECU. 
     While the embodiment depicted in  FIGS. 1 through 3  operates with the chevron-shaped slot  40  engaging and disengaging the spring arm  42 , the invention is applicable to any dual-mode retractors that switch between the ELR mode and the ALR mode via a relative movement between two parts. The magnet  16  and the interrupter plate  18  can be mounted on any two parts of such a dual-mode retractor that move relative to each other during the switching operation. The interrupter plate  18  can be arranged relative to the magnet  16  in a position, in which the interrupter plate  18  covers the magnet in one of the two modes, ELR and ALR, and leaves the magnet  16  uncovered in the other one of the two modes. 
     Furthermore, the magnet  16  and the HED  14  may be combined into a subassembly that can be mounted to the cover  12  or to the base plate  22  as one unit. This may simplify the manufacturing process and provide better control of the air gap between the magnet and the HED  14 . 
     The foregoing description of an embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiment disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiment discussed was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.