Abstract:
A rotational direction detecting switch detects a rotational direction of a shaft, preferably of a seat belt retractor. The detecting switch is formed of a switch plate having a support portion for pivotally supporting the switch plate and restricting members spaced apart from each other for restricting a rotating angle of the switch plate, a spring member attached to the switch plate between the restricting members for elastically contacting an outer circumference of the shaft, and a switch situated near the switch plate for detecting a rotating position of the switch plate. Since the spring member is used to contact the shaft, the elastic deformation is large. Therefore, tolerance in manufacturing the switch plate can be large, so that its assembling accuracy may not be so accurate. However, the rotating direction can be positively detected.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The invention relates to a switch to be used for detecting a rotational direction of a rotating member in a seat belt retractor to be mounted to a vehicle, such as an automobile, and a seat belt retractor using the same. 
     A seat belt winding device or retractor to be attached to an automobile has such a function that when a passenger takes a seat and pulls out a seat belt and a tongue is fastened to a buckle device, an extra withdrawing portion of the seat belt is absorbed or retracted. In order to provide the function, in a seat belt retractor of the prior art, a single return spring has been used. When a seat belt is put on a passenger&#39;s shoulder, the passenger pulls out the seat belt against an urging force of the return spring and leaves his hand from the seat belt after a tongue is engaged with a buckle, so that an extra withdrawing portion of the seat belt is wound up by a seat belt retractor until the seat belt fits the passenger&#39;s body. 
     As explained above, in the seat belt retractor, it is required to satisfy the following points at the same time: 
     (1) the excessively withdrawing portion of the seat belt is positively wound up until the seat belt fits the passenger&#39;s body, or when the passenger does not wear the seat belt, the withdrawn seat belt is positively stored in a storing portion; and 
     (2) an unnecessary pressing feeling is not given to a breast portion of the passenger in a normal wearing state. 
     However, in the seat belt retractor using an urging force of the single return spring, there have been such problems that in case a spring having a weak urging force is used to reduce the pressing feeling against the chest portion of the passenger, a winding force when the seat belt is wound up, i.e. at a storing time, becomes weak, so that an operating ability and storing ability are lowered. On the contrary, in case a spring having a strong urging force is used to obtain a sufficient winding force at the time of winding, the pressing feeding against the chest portion of the passenger at the normal wearing time becomes large. 
     Also, in a conventional seat belt retractor, there have been problems such that since the single return spring is built in, as a withdrawn amount or length of the seat belt is increased, the return spring is wound to thereby increase its urging force, and as the withdrawing amount of the seat belt is increased, the withdrawing force is increased. 
     As a device to solve the above problems, the present inventors invented a seat belt winding device or retractor for winding a seat belt by combining a return spring and a motor, and filed a patent application as Japanese Patent Application No. 11-10184 (hereinafter referred to as “former invention”, not prior art). In the seat belt retractor using the motor for winding the seat belt including the winding device of the former invention, generally, it is required that the motor is stopped when a passenger pulls out the seat belt to allow the seat belt to be pulled out with a small force. As a device for providing this mechanism, there has been proposed a device wherein a rotational direction of a shaft of a spool around which the seat belt is wound is detected, and in case the shaft is rotated in a seat-belt withdrawing direction, power supply to the motor is stopped. The device is also employed in the former invention. 
     FIG. 5 is a schematic view showing a rotational direction detecting switch used in the former invention. A base frame  21  is provided with a spool  22 , and a seat belt is wound around the spool  22 . When the spool  22  is driven in a winding or retracting direction, the seat belt is wound up. On the contrary, when the seat belt is pulled out manually, the spool  22  is rotated in a direction opposite to the winding direction. A spool shaft input gear directly connected to the spool shaft is provided with a ring-shape groove  23 . 
     The rotational direction detecting switch includes a switch plate  24  and a limit switch  25 , and the switch plate  24  is rotated around a rotating pin  26  as a shaft. Both ends of the switch plate  24  are provided with guides  24   a , and when the switch plate  24  is rotated for a predetermined region, the guide  24   a  hits the ring-shape groove  23  to thereby restrict its rotating region, i.e. angle. 
     The ring-shape groove  23  contacts a circular arc edge  24   b  of the switch plate  24 . A circular arc groove  24   c  is formed on an inner side along the circular arc edge  24   b . Therefore, when the circular arc edge  24   b  abuts against the ring-shape groove  23 , the circular arc edge  24   b  is slightly bent to thereby provide a pressing force. Thus, the switch plate  24  is rotated without slipping according to the rotation of the ring-shape groove  23 . 
     FIG. 5 shows a state where the switch plate  24  located at an initial position, i.e. two dotted chain lines, has rotated in a counter-clockwise direction according to a rotation in a clockwise direction of the spool  22 , i.e. according to the withdrawal of the seat belt. Under the state, a contact arm  24   d  provided at a tail portion of the switch plate pushes a movable piece to turn on a limit switch  25 . Accordingly, the control device detects that the seat belt has been withdrawn. 
     In the rotating direction detecting switch according to the former invention as described above, the switch plate  24  is integrally molded of a material, such as a resin, having a certain elasticity. However, since a quantity of an elastic deformation of the circular arc edge  24   b  is small, in case the rotating shaft of the spool is de-centered or biased, a sufficient pressing force can not be obtained, so that the switch plate  24  is not rotated or, conversely, the pressing force is too strong to thereby damage or wear the circular arc edge  24   b . Also, there have been problems such that, by the same reason as mentioned above, a tolerance or manufacturing allowable error of the switch plate  24  becomes small, and a high assembling accuracy is required. Further, since a spool shaft input gear having the ring shape groove  23  and the switch plate  24  must be assembled separately, it is not easy to assemble the rotating direction detecting switch. 
     In view of the problems, the present invention has been made, and an object of the invention is to provide a rotational direction detecting switch, wherein even if a relative positional accuracy between a rotating member, a rotating direction of which is detected, and the switch plate is not so accurate, a relative positional relationship can be detected. 
     Another object of the present invention is to provide a rotational direction detecting switch as stated above, wherein an assembling can be easily carried out. 
     A further other object of the present invention is to provide a seat belt retractor, wherein the rotational direction detecting switch as stated above is employed. 
     Further objects and advantages of the invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     To attain the above objects, according to a first aspect of the invention, there is provided a rotational direction detecting switch including a spring member elastically contacting an outer circumference of a rotating member; a switch plate for supporting the spring member arranged to rotate around a supporting point and having members for restricting a rotating angle thereof; and a switch for detecting a rotational position of the switch plate. 
     In the rotational direction detecting switch, the spring member supported by the switch plate elastically contacts the outer circumference of the rotating member to thereby generate an elastic force, so that a friction force is generated between the rotating member and the spring member. Thus, the spring member is moved by the friction force according to rotation of the rotating member, and the switch plate supporting the spring member is rotated around the supporting point. The rotation of the switch plate is detected by the switch, such as a limit switch and a proximity switch, to thereby detect the rotational direction thereof. Incidentally, since the switch plate is provided with the members for restricting its rotating angle, the rotation of the switch plate is limited within a predetermined region. 
     In the rotational direction detecting switch according to the first aspect, since the spring member is used as a member to contact the rotating member, its possible deformation quantity is large, so that even if a rotating shaft of the rotating member is slightly biased, or relative attaching positions of the rotating member and the switch plate are changed, there is no risk that a sufficient force for rotating the switch plate can not be obtained, and that the spring member and the switch plate are damaged. Incidentally, the members for restricting the rotating angle of the switch plate may be integrally formed with the switch plate. 
     To attain the above objects, according to a second aspect of the invention, in the rotational direction detecting switch according to the first aspect, the members for restricting the rotating angle are projecting members formed on both sides of a forward edge of the switch plate. The projecting members abut against the rotating member to restrict the rotation of the switch plate. Forward edges of the projecting members are connected by a connecting member to thereby form a loop with the forward edge portion of the switch plate, the projecting members and the connecting member to surround the rotating member. 
     In the rotational direction detecting switch of the second aspect, when the switch plate is incorporated, the rotating member is inserted into the loop formed by the forward edge portion of the switch plate, the projecting members and the connecting member, and the rotating member and the switch plate are incorporated as a sub-unit. Thus, the rotational direction detecting switch can be easily assembled. Incidentally, the projecting members and the connecting member may be formed integrally. 
     To attain the above objects, according to a third aspect of the invention, there is provided a seat belt retractor having the rotational direction detecting switch of the first or second aspect. 
     In the seat belt retractor of the invention, the rotational direction detecting switch according to the first or second aspect is used, the rotational direction of the spool can be positively detected to thereby provide the seat belt rector performing a reliable operation. Also, in case the rotational direction detecting switch according to the second aspect is employed, an assembling work can be easily carried out. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a seat belt retractor of an embodiment according to the present invention; 
     FIG.  2 ( a ) is an enlarged view of a rotational direction detecting portion of a rotational direction detecting switch of an embodiment according to the present invention; 
     FIG.  2 ( b ) is a sectional view taken along line  2 ( b )— 2 ( b ) in FIG.  2 ( a ); 
     FIG. 3 is a perspective view of the rotational direction detecting portion shown in FIG.  2 ( a ); 
     FIG. 4 is a schematic view showing another embodiment of the rotational direction detecting portion; and 
     FIG. 5 is a schematic view showing a rotational direction detecting switch used in the former invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereunder, an embodiment according to the present invention is explained with reference to the accompanying drawings. FIG. 1 is an exploded perspective view of a seat belt winding device or retractor of an embodiment according to the present invention. In FIG. 1, reference numeral  1  is a retainer;  2  is a motor;  3  is a motor gear;  4  is an L-gear;  5  is an S-gear;  6  is a holding member;  7  is a roller;  8  is a connect gear;  9  is a bush gear;  9   a  is a sliding portion;  9   b  is a spline portion;  10  is a return spring;  11  is a spring cover;  12  is a rotating direction detecting device;  12   a  is a switch plate;  12   b  is a switch spring;  13  is a limit switch; and  14  is a cover. 
     A driving force of the motor  2  attached to the retainer  1  is transmitted to the L-gear  4  through the motor gear  3 ; then, transmitted to the S-gear  5  through a clutch mechanism structured by the S-gear  5 , the holding member  6  and rollers  7 ; and then, transmitted to the bush gear  9  through the connect gear  8  from the S-gear  5 . A rotating shaft of the bush gear  9  is coupled with the return spring  10  to urge rotation of the bush gear  9  toward the seat belt winding direction. Incidentally, in an actual seat belt retractor, while a spool for winding a seat belt therearound is coupled with the spline portion  9   b  of the bush gear  9 , the portion is omitted in FIG.  1 . Further, the L-gear  4 , S-gear  5  and holding portion  6  are coaxially held by a rotating shaft provided at the retainer  1 , and the connect gear  8  is held by another rotating shaft provided at the retainer  1 . The bush gear  9  is supported by a rotating shaft provided at the cover  14 . 
     The bush gear  9  includes the sliding portion  9   a , an outer peripheral portion of which elastically contacts the switch spring  12   b  of the rotational direction detecting portion  12 . Thus, the switch plate  12   a  rotates clockwise or counter-clockwise according to a rotational direction of the bush gear  9 . When the bush gear  9  rotates in a seat belt withdrawing direction, a striker portion of the switch plate  12   a  pushes a movable piece of the limit switch  13  to turn on. The limit switch  13  and switch plate  12   a  are also supported by the retainer  1 . 
     The motor  2  is a one-way rotating motor, and is driven in a seat belt winding direction, i.e. in the same direction as an urging direction of the return spring  10 . 
     The S-gear  5 , hold block  6  and rollers  7  incorporated into the L-gear  4  constitute the clutch mechanism. When the bush gear  9  is rotated in the seat belt withdrawing direction by an outer force, a mechanical power transmission of the L-gear  4  and the S-gear  5  is disconnected, so that when the seat beat is withdrawn, the motor  2  does not become a load. Also, when the motor  2  is not rotated, in the same manner, the mechanical power transmission of the L-gear  4  and the S-gear  5  is disconnected, so that the motor  2  does not become a load of the winding force of the return spring  10 . On the contrary, when the motor  2  is rotated, a driving force is transmitted from the L-gear  4  to S-gear  5  through the clutch mechanism and, finally, winding of the seat belt through the bush gear  9  is carried out by the driving force of the motor  2  and an urging force of the return spring. Detailed explanations of the clutch mechanism are omitted since it is not related to the present invention. 
     In the seat belt retractor of the present embodiment, it is important that the rotational direction detecting switch includes the rotational direction detecting portion  12  and the limit switch  13 . The rotational direction detecting switch is used such that when the bush gear  9  is rotated in the seat belt withdrawing direction, the limit switch  13  is turned on, and driving of the motor  2  is stopped by the output of the limit switch  13 . 
     FIGS.  2 ( a ) and  2 ( b ) show detailed structure of the rotational direction detecting portion  12 , and FIG. 3 shows a perspective view thereof. FIG.  2 ( a ) is a plan view, and FIG.  2 ( b ) is a sectional view taken along line  2 ( b )— 2 ( b ) in FIG.  2 ( a ). In the following drawings including FIGS.  2 ( a ),  2 ( b ) and FIG. 3, the same constitutional elements as those shown in FIG. 1 are represented by the same reference symbols and their explanations are omitted. In FIGS.  2 ( a ) and  2 ( b ), reference numeral  12   c  is a pressing portion;  12   d  is a striker;  12   e  is a rotating shaft hole; and  12   f  is rotating angle restricting portions, i.e. projecting members;  12   f ′ is an edge portion. 
     The switch spring  12   b  is embedded in the switch plate  12   a , sandwiched between portions a and b at curved ends  12   b ′, pressed by the pressing portion  12   c , and held by the switch plate  12   a  with its own elastic force thereby not to be dislocated or separated. The switch spring  12   b , as described before, elastically contacts the sliding portion  9   a  of the bush gear  9  to thereby transmit the rotation of the sliding portion  9   a  to the switch plate  12   a  through a friction with the sliding portion  9   a . The switch spring  12   b  may be a wire spring. 
     When switch plate  12   a  is rotated around a rotating shaft fitted into the rotating shaft hole  12   e , the striker  12   d  pushes the movable piece of the limit switch  13 . A forward end of the switch plate  12   a  is provided with the rotational angle restricting portions  12   f . When the switch plate  12   a  is rotated by a predetermined angle, one of the rotational angle restricting portions  12   f  contacts the sliding portion  9   a  of the bush bear  9  to thereby stop rotation of the switch plate  12   a . Thereafter, though the switch spring  12   b  slides along the sliding portion  9   a , since the friction therebetween is not so large, the switch spring  12   b  and the sliding portion  9   a  do not wear. 
     In the embodiment according to the present invention, different from the switch plate of the former invention, since the switch spring  12   b  is used as a member for contacting the sliding portion  9   a , a deformation quantity by which the switch spring  12   b  can be elastically deformed is large. Therefore, even if the rotating shaft of the spool is de-centered or biased, a sufficient pressing force can be obtained and the pressing force does not become too strong. Thus, there are no such occasions that the switch plate does not rotate and parts wear. Also, tolerance or a manufacturing allowable error of the switch plate becomes large, so that its assembling accuracy may not be so strict. 
     FIG. 4 shows a detailed drawing of a rotational direction detecting portion  12  of another embodiment. In the embodiment, forward ends of the two rotating angle restricting portions  12   f  are connected by a connecting member  12   g  so that a loop portion is formed by the forward edge  12   h  of the switch plate, rotational angle restricting portions  12   f  and the connecting member  12   g . The switch plate is operated in the same manner as in the switch plate shown in FIGS.  2 ( a ) and  2 ( b ). 
     In the embodiment, the sliding portion  9   a  of the bush gear  9  is fitted into the loop portion. Thus, when the seat belt retractor shown in FIG. 1 is assembled, the loop portion of the rotational direction detecting portion  12  is hooked over the sliding portion  9   a  of the bush gear  9  to be a sub-unit, so that when the bush gear  9  is incorporated, the switch plate  12   a  is simultaneously incorporated. Thereafter, the rotating shaft is inserted into the rotating shaft hole  12   e  of the switch plate  12   a  to thereby easily carry out its assembly. 
     As described hereinabove, according to the first aspect of the invention, since the spring member is used as a member to contact the rotating member, its possible deformation quantity is large, so that even if the rotating shaft of the rotating member is slightly de-centered or a relative attaching position of the rotating member and the switch plate is changed, there are no such risks that a sufficient power to rotate the switch plate can not be obtained, and that the spring member and switch plate are damaged. Also, its assembling accuracy may not be so accurate. 
     According to the second aspect of the invention, in addition to the advantages as mentioned in the first aspect, the rotating member and the switch plate can be incorporated as a sub-unit. 
     According to the third aspect of the invention, there can be obtained a reliably operating seat belt retractor wherein the rotational direction of the spool can be positively detected. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.