Patent Publication Number: US-2004042696-A1

Title: Bearing structure and seat-weight measuring apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to bearing structures for use in a rotational structure of a mechanical structure and in an automobile cabin and further relates to a seat weight measuring apparatus having the bearing structures. In particular, it relates to a rotational structure and a bearing structure wherein discomfort of people therearound is eliminated by suppressing noise due to movement (rattle) of a member in a rotational supporting point within small clearance.  
       [0002] In an automobile cabin, various bearing structures are used, in which shaft members are inserted into bearing members. In these bearing structures, rattling of the shaft member may occur due to errors in size of the shaft member, the bearing member, and a sleeve member, or errors in size of a vehicle cabin and a seat. Although noise due to the chattering is very low, comfortableness in the automobile cabin may be reduced. Therefore, means for suppressing the rattle of the bearing structures is required.  
       [0003] The prior art will be described in detail below with reference to the bearing structure in the automobile cabin as an example, in which a seat belt and an airbag are equipped.  
       [0004] With regard to the current trend, in order to improve the performance of the seat belt and the airbag, operation of such safety equipment may be controlled in accordance with the weight of an occupant. For example, the gas quantity or gas rate for deploying the airbag may be adjusted, or the pre-tension of the seat belt may be adjusted according to the weight of an occupant. That requires detecting the weight of an occupant. As an example of such means, it is proposed to measure the seat-weight including the weight of an occupant by arranging load sensors (load cells) at four corners, back-and-forth and the right and left, under the seat so as to sum the loads applied to the load cells in the vertical direction.  
       [0005] An example of such a seat-weight measuring apparatus is disclosed in Japanese Unexamined Patent Application Publication No. 2000-258233 (incorporated by reference herein in its entirety). The seat-weight measuring apparatus in the Publication simply measures not only the weight of an occupant and a seat but also has a mechanism for absorbing displacement and/or deflection between the seat and a vehicle body for eliminating the load other than from the weight of the seat and an occupant (or goods) thereon as much as possible. In the seat-weight measuring apparatus having such a deflection absorbing mechanism, bearing structures are also used, so that means for suppressing rattle of bearing parts is also required.  
       [0006] Referring to FIGS.  9  to  12 , the seat-weight measuring apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2000-258233 will be further described below. First, structures around an vehicle seat will be described with reference to FIG. 12.  
       [0007]FIG. 12(A) is a front sectional view for schematically showing a structure of the seat attached to the vehicle body; and FIG. 12(B) is a side view thereof. In addition, arrows shown in the drawings indicate the following directions. UP: upward gravitational direction when the vehicle body is horizontal, DOWN: downward direction, FRONT: vehicle proceeding direction, REAR: reverse travel direction, LEFT: the left side facing in the vehicle proceeding direction, and RIGHT: the right side.  
       [0008] In FIG. 12, a seat  3  is shown. An occupant  1  sits on a seat cushion  3   a . The bottom surface of the seat cushion  3   a  is supported by a seat frame  5  made of a steel plate. The seat frame  5  comprises a bottom plate  5   a , side plates  5   c , vertical plates  5   e , and slide plates  5   g . The bottom plate  5   a  spreads out so as to cover the bottom surface of the seat cushion  3   a . The side plates  5   c  extend along the respective right and left sides of the bottom surface of the bottom plate  5   a . The vertical plate  5   e  hangs down from the bottom surface center of the side plate  5   c . The slide plate  5   g  protrudes to the right and left from the vertical plate  5   e  as blades, and end portions thereof are further bent upwardly.  
       [0009] Two seat rails  7  are arranged in parallel under the seat  3  in the right and left sides, extending in the back-and-forth direction. The cross-section of the seat rail  7  is U-shaped, a concave portion  7   c  exists inside thereof. The upper opening of the concave portion  7   c  is a groove  7   a  extending in the back-and-forth direction. Into the groove  7   a , the vertical plate  5   e  of the seat frame  5  is inserted. Into the concave portion  7   c  of the seat rail  7 , the slide plate  5   g  of the seat frame  5  is entered. The slide plate  5   g  is slidable within the seat rail  7  in the back-and-forth direction. To the bottom surface of the seat rail  7 , the seat-weight measuring apparatus  9  is connected. The seat-weight measuring apparatus  9  has an elongated box-like shape extending in the back-and-forth direction. Details of the seat-weight measuring apparatus  9  will be described later. At the front and rear ends of the bottom surface of the seat-weight measuring apparatus  9 , seat brackets  11  are attached. The seat bracket  11  is fixed to a seat fixing portion  13  of the vehicle body with bolts, etc.  
       [0010] Next, the structure of the seat-weight measuring apparatus is described.  
       [0011]FIG. 9(A) is a disassembled perspective view of the displacement and/or deflection absorbing mechanism of the seat-weight measuring apparatus  9 ; FIG. 9(B) is a front sectional view of a pin bracket.  
       [0012]FIG. 10(A) is a plan view of the entire structure of the seat-weight measuring apparatus; FIG. 10(B) is a side sectional view; FIGS.  10 (C) and (D) are front sectional views. In addition, in FIGS.  10 (A) and (B), substantially half of the rear part is not shown.  
       [0013]FIG. 11(A) is a plan view showing the relationship between a sensor plate and a half arm; FIG. 11(B) is a side view in a no-load state; FIG. 11(C) is a side view schematically showing a state in that a load is applied.  
       [0014] The seat-weight measuring apparatus  9  is constructed based on an elongated rail-like base (base frame)  21 . The base  21  extends in the back-and-forth direction when attached to the vehicle body and is a steel-plate pressed product having an upward U-shape front-section as shown in FIGS.  10 (C) and (D). The sectional bottom portion of the base  21  is called a bottom plate  21   c ; portions elevated at right angles from lateral ends of the bottom plate  21   c  are called side plates  21   a.    
       [0015] In the base side plate  21   a , pin holes  21   e  and  21   g  are formed two each on the front and rear portions. The respective holes  21   e  and  21   g  are formed on the right and left side plates  21   a  and  21   a ′ opposing each other.  
       [0016] The holes  21   e , which are closer to the end, are formed at positions approaching the center by approximately ⅛ of the entire length of the base  21  from the front and rear ends. The hole  21   e  is a hole much elongated in the vertical direction, as shown in FIG. 9(A). Within the elongated holes  21   e , end portions of a bracket pin (stopper pin)  27  are entered.  
       [0017] However, there are clearances between the bracket pin  27  and top/bottom and right/left ends of the elongated hole  21   e , so that the bracket pin  27  does not normally come into contact with internal edges of the elongated hole  21   e . When an excessive load is applied to the seat-weight measuring apparatus  9  (specifically, part of a pin bracket  25 ), however, the bracket pin  27  is lowered and abuts the bottom end of the elongated hole  21   e , so that the excessive load cannot be transmitted to a load sensor (a sensor plate  51 , details will be described). That is, the pin  27  and the elongated hole  21   e  form part of a mechanism for restricting the upper limit load applied to the sensor plate  51 . In addition, the principal function of the bracket pin  27  is to transmit the seat weight applied to the pin bracket  25  to a Z-arm (arm member)  23 .  
       [0018] At positions slightly closer to the center from the elongated holes  21   e  (approaching the center by approximately {fraction (1/10)} of the entire length of the base  21 ), the pin holes  21   g  are formed. Into the pin holes  21   g , a base pin (pivot pin)  31  is inserted. The base pin  31  exists so as to bridge between the right and left base side plates  21   a  and  21   a ′. At lateral ends of the pin  31 , retainers  33  are attached, so that the base pin  31  is fixed to the base  21 . In addition, the base pin  31  is a rotational central axis of the Z-arm  23 .  
       [0019] The Z-arm  23  is arranged inside the base  21 . The Z-arm  23  has a shape in plan view, in which one closer to the center of the base  21  is forked into two parts (forked parts  23   h ) while the other closer to the front or rear end is rectangular. The lateral ends of the half part closer to the front or rear end are elevated at right angles to form side plates  23   a . The forked part  23   h  is a simple flat plate. The side plate  23   a  is arranged along the inside of the side plate  21   a  in the base  21 ; however, there is a clearance between the both side plates  21   a  and  23   a.    
       [0020] The Z-arm  23  also has two pin holes  23   c  and  23   e  formed thereon. Into the pin hole  23   c  closer to the front or rear end, the bracket pin  27  is inserted. Into the pin hole  23   e  closer to the center, the base pin  31  is inserted. At the external periphery of the base pin  31  between the base side plate  21   a  and the Z-arm side plate  23   a , a perforated circular disk-like spacer  35  is fitted. The Z-arm  23  is rotated about the base pin  31 .  
       [0021] The forked part  23   h  of the Z-arm  23  has a length approximately half of the entire length of the Z-arm  23 . The forked parts  23   h  are laterally divided and extend toward the center in the front and rear direction, and are reduced in width at portions closer to the center. Application parts  23   j  at ends of the Z-arm forked parts  23   h  are sandwiched between blades  41   a  and  42   a  of the upper and lower half arms  41  and  42 .  
       [0022] When a load is applied to the pin bracket  25 , the load is transmitted to the Z-arm  23  via the bracket pin  27  so as to rotate the Z-arm  23  slightly (approximately 5° at most), which in turn is transmitted by the application parts  23   j  to the sensor plate  51  of the load sensor  50  via the half arms  41  and  42 .  
       [0023] The pin bracket  25 , as shown in FIG. 10(C), has a downward substantially U-shaped cross section. The length thereof in the front and rear direction is not so long, that is, {fraction (1/20)} of that of the base  21 . The top part  25   a  of the pin bracket  25  is flat, and the seat rail  7  shown in FIG. 12 is placed thereon. Both the parts are tightly fixed together with bolts, etc.  
       [0024] Lateral side plates  25   b  of the pin bracket  25  hang down from sides of the bracket  25 , and end portions of the side plates  25   b  are bent inwardly. The side plates  25   b  are arranged inside the Z-arm side plates  23   a  with clearances. On the side plates  25   b , pin holes  25   c  are formed. Into the pin holes  25   c , the bracket pin  27  is inserted. The pin holes  25   c  is larger in size than the diameter of the bracket pin  27 . Due to the clearance between them, errors in size of the seat and the vehicle body and accidental deformation are absorbed.  
       [0025] Between the respective lateral side plates  25   b  and the respective Z-arm side plates  23   a , a spring plate  29  is sandwiched. The spring plate  29  has perforated spring-washer portions which are fitted into outsides of the bracket pin  27  with clearances. The spring plate  29  serves as a centering mechanism for urging the pin bracket  25  toward the center.  
       [0026] Such a centering mechanism allows the pin bracket  25  to be positioned in the vicinity of the center of the slidable range as much as possible. Due to the operation of the centering mechanism, the movable ranges of the slide mechanism and the rotational mechanism can be ensured in the both directions (right/left, up/down, and front/rear) after the seat-weight measuring apparatus is equipped.  
       [0027] Next, structures around the sensor plate  51  are described.  
       [0028] The sensor plate (spring member)  51  which is a base material of the load sensor  50  is provided with a strain gauge formed thereon with a bridge circuit having strain resistances  54   a  to  54   d . The sensor plate  51 , as shown in FIGS.  10 (A) and (B) and FIG. 11, is tightly fixed to a column  63  in the central portion of the base bottom plate  21   c  with a washer  67 , a nut  68 , and a bolt  69 .  
       [0029] The half arms  41  and  42 , as shown in FIGS. 10 and 11, are components of a group of four, front/rear and up/down, and are assembled so as to sandwich the sensor plate  51  from the front/rear and up/down directions and fixed to sensor plate  51  with bolts  43 , etc.  
       [0030] Between both supporting points  41   b  and  42   b  of blades  41   a  and  42   a  extended from the upper/lower half arms  41  and  42 , the application part  23   j  of the Z-arm  23  is sandwiched. In addition, the supporting points are positioned at just the midpoint (a constricted part  51   c  of the sensor plate  51 ) of two strain gauges  54   a  and  54   c  or  54   d  and  54   b.    
       [0031] When a load is applied to the pin bracket  25  of the seat-weight measuring apparatus  9 , the Z-arm  23  is slightly rotated so as to raise the application part  23   j  thereof upwardly. It is FIG. 11(C) to show a state of the sensor plate and the half arm at this time schematically and exaggeratedly.  
       [0032] When the Z-arm application part  23   j  is raised, the supporting point  41   b  of the upper half arm  41  is elevated. A moment M is applied to end portions in the back and forth direction of the sensor plate  51 . Due to the moment M, the strain gauges  54   a  and  54   b  in the end portions in the back and forth direction are pulled while the strain gauges  54   c  and  54   d  in the central portion are compressed. Changes in resistance due to these actions of the respective strain gauges are converted to electrical signals so as to measure the strain of the sensor plate and the load applied to the pin bracket  25  by extension.  
       [0033] Next, the entire displacement/deflection absorbing mechanism of the seat-weight measuring apparatus will be described with reference to FIG. 10.  
       [0034] The pin bracket  25  is tightly fixed to the seat rail  7  with bolts, etc. In the vertical direction of the vehicle body, displacement is absorbed by the clearance between the pin hole  25   c  of the pin bracket  25  and the bracket pin  27 .  
       [0035] In the back and forth direction of the vehicle body, the pin hole  25   c  of the pin bracket  25  is elongated so as to absorb the displacement.  
       [0036] In the right and left direction of the vehicle body, displacement is absorbed by the clearance between the pin bracket side plate  25   b  and the Z-arm side plate  23   a . In addition, the centering mechanism by the spring plate  29  is provided in this part, as described above.  
       [0037] For the rotation about the vertical direction of the vehicle body as the axis, displacement is absorbed mainly by the clearance between the pin bracket side plate  25   b  and the Z-arm side plate  23   a.    
       [0038] For the rotation about the back and forth direction of the vehicle body as the axis, displacement is absorbed mainly by the clearance between the pin bracket side plate  25   b  and the Z-arm side plate  23   a , just like for about the vertical direction of the vehicle body.  
       [0039] For the rotation about the right and left direction of the vehicle body as the axis, displacement is absorbed mainly by the rotation of the pin bracket  25  about the bracket pin  27 .  
       [0040] In the seat-weight measuring apparatus  9  as constructed above, in order to adjust errors in size of each part and prevent strain from being generated, the diameter of the pin hole  23   c  is slightly larger than that of a bracket pin to be inserted (stopper pin)  27 . Therefore, the bracket pin  27  inserted into the pin hole  23   c  is not rigidly fixed relative to the Z-arm  23 . Accordingly, the bracket pin  27  is rattling within the pin hole  23   c , so that abnormal noise may be generated due to vibration by vehicle traveling, or the seat rail  7  supported by the bracket pin  27  via the pin bracket  25  may slightly vibrate. Thereby, an occupant sitting on the seat  3  may feel rattle.  
       [0041] The diameter of the pin hole  23   e  of the Z-arm side plate  23   a  is also slightly larger than that of the base pin  31  just like mentioned above, the base pin  31  is chattering within the pin hole  23   e , so that abnormal noise may be generated due to vibration by vehicle traveling, and comfortableness in a cabin may be damaged.  
       SUMMARY OF THE INVENTION  
       [0042] The present invention has been made in view of these problems, and it is an object of the present invention to provide a rotational structure and a bearing structure wherein discomfort of people therearound can be eliminated by suppressing noise due to movement (rattle) of a member in a rotational supporting point within small clearance. Furthermore, it is another object to provide a seat-weight measuring apparatus having such a rotational structure and a bearing structure.  
       [0043] In order to solve the aforementioned problems, a rotational structure according to the present invention comprises a center-of-rotation pin, two members relatively rotatable about the pin and having insertion holes for the pin, an internal sleeve lying between the insertion hole of one member (a first member) and the external periphery of the pin while extending into the insertion hole of the other member (a second member), and an external sleeve lying between the external periphery of the internal sleeve and the insertion hole of the second member, wherein the internal sleeve, while being press-fitted into the insertion hole of the first member, has a pressing section which is elastically pressed onto the external periphery of the pin so as to slidably and elastically keep the pin in contact with the internal sleeve, and wherein the external sleeve, while being press-fitted into the insertion hole of the second member, has a pressing section which is elastically pressed onto the external periphery of the internal sleeve so as to slidably and elastically keep the internal sleeve in contact with the external sleeve.  
       [0044] According to a rotational structure of the present invention, the free clearance in the radial direction is forced out due to the pressing sections of the external and internal sleeves, so that pins and the external and internal sleeves cannot rattle within insertion holes. Therefore, abnormal noise produced following the chattering of members can be suppressed.  
       [0045] In addition, in the present invention, by contrast to the above description, the bore of the sleeve may be press-fitted so that the pressing section of the sleeve may be elastically urged in the external diameter side, and this case is also within the scope of the present invention.  
       [0046] In a rotational structure according to the present invention, the pressing section may be a tapered end portion of the sleeve.  
       [0047] In this case, the pressing section can be readily fabricated. Moreover, the tapered pressing section fits perfectly on the entire external periphery of the pin or the internal sleeve, the pressing can be performed with a uniform elastic force in the radial direction.  
       [0048] In a rotational structure according to the present invention, the sleeve may have a flange section which lies between side surfaces of the first and second members. In this case, the flange section of the sleeve serves as a plane bearing between the first and second members.  
       [0049] In a rotational structure according to the present invention, a surface of the sleeve may be coated with a material having a low coefficient of friction. In this case, there is an advantage that the sleeve slides more smoothly.  
       [0050] A bearing structure for use in an automobile cabin according to the present invention comprises a bearing member, a sleeve member fitted into an insertion hole of the bearing member, and a shaft member fitted into an insertion hole of the sleeve member, wherein the sleeve member is formed so that any of part of the insertion hole of the sleeve member always comes into contact with the shaft member so as not to allow the shaft member to run freely within the insertion hole of the sleeve member when the shaft member moves.  
       [0051] In the bearing structure according to the present invention, the sleeve member is formed so that any of part of the insertion hole of the sleeve member always comes into contact with the shaft member. Accordingly, the shaft member does not rattle within holes of the sleeve members even when the shaft member moves due to vibration during vehicle traveling, so that noise and vibration are transmitted to the arm member and the sleeve member from the contact portion so as to be damped. Therefore, abnormal noise generated in a cabin during vehicle traveling following the chattering of the shaft member can be suppressed, eliminating uncomfortable feeling of an occupant sitting on the seat.  
       [0052] The bearing structure according to the present invention may also be applied to a seat-weight measuring apparatus. That is, in an apparatus for measuring the seat weight including the weight of an occupant sitting on an automobile seat, the apparatus comprising a rail-like base frame fixed to a vehicle body or part of the seat, an arm member supported to the base frame rotatably in the vertical direction by a pivot member, a stopper pin attached to the arm member and being movably brought into engagement with an opening of the base frame so as to restrict the rotational range of the arm member, and a bracket pivotably attached to the arm member by the stopper ping so as to transmit the seat weight to the stopper pin, wherein the load applied to the stopper pin allows the arm member to rotate about the pivot member so as to produce displacement in a sensor, a bearing structure comprises sleeve members wherein the pivot member is inserted into the arm member via one of the sleeve members while the stopper pin is also inserted into the bracket via the other sleeve member, so that any of part of the insertion holes of the respective sleeve members always comes into contact with the pivot member and the stopper pin, so as not to allow the pivot member and the stopper pin to run freely within the insertion holes when the pivot member and the stopper pin move.  
       [0053] In the bearing structure according to the present invention, part or the entirety of the sleeve member may be tapered so that the sleeve member always comes into contact with the shaft member. Furthermore, part or the entire of the sleeve member may be slit in an axial direction.  
       [0054] Also, in order to cause any of part of the insertion hole of the sleeve member to always come into contact with the shaft member, part or the entirety of the sleeve member may be formed to be bellow-shaped, or part or the entire radial section of the sleeve member may be formed to be polygonal.  
       [0055] In the bearing structure according to the present invention, it is preferable to circumferentially cover a pipe on the shaft member so as to stick on the external surface of the shaft member. In this case, the sleeve member is circumferentially covered on the pipe. Thereby, the clearance between the shaft member and the sleeve member is further reduced, so that abnormal noise due to the rattle of the shaft member during vehicle traveling is further suppressed.  
       [0056] In the bearing structure according to the present invention, the sleeve member may have a double structure comprising an internal sleeve inserted into the insertion hole of the bearing member while being inserted to the shaft member from outside and an external sleeve inserted into the insertion hole of the bearing member while being inserted to the internal sleeve from outside.  
       [0057] A seat-weight measuring apparatus according to the present invention for measuring the seat-weight including the weight of an occupant sitting on a vehicle seat, the seat-weight measuring apparatus comprises a base frame extending in a longitudinal direction of a vehicle, rail brackets respectively arranged toward back and forth ends of the base frame and lying between the base frame and a seat rail which slides in the longitudinal direction of the vehicle, and a sensor section mounted on the base frame and comprising a strain sensor fixed to a central portion of the base frame in a longitudinal direction and arms respectively arranged at back and forth ends of the base frame and extending in the longitudinal direction, the arm having a pressing part for transmitting a force to the strain sensor at one end (a central end) and a connecting part to the rail bracket at the other end (one of the front end and the rear end), wherein the arm and the rail bracket are provided with insertion holes for center-of-rotation pins formed thereon, and the arm and the rail bracket are connected to each other so as to be relatively rotatable about the pin, wherein the seat-weight measuring apparatus further comprises an internal sleeve lying between the insertion hole of the arm and the external periphery of the pin while extending into the insertion hole of the rail bracket, and an external sleeve lying between the external periphery of the internal sleeve and the insertion hole of the rail bracket, and wherein the internal sleeve, while being press-fitted into the insertion hole of the arm, has a pressing section which is elastically pressed onto the external periphery of the pin so as to slidably and elastically keep the pin in contact with the internal sleeve, and wherein the external sleeve, while being press-fitted into the insertion hole of the rail bracket, has a pressing section which is elastically pressed onto the external periphery of the internal sleeve so as to slidably and elastically keep the internal sleeve in contact with the pin.  
       [0058] In addition, by contrast to the above description, the internal sleeve may arranged in the rail bracket side while the external sleeve in the arm side, and this case is also within the scope of the present invention.  
       [0059] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0060] These and other features, aspects and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.  
     [0061]FIG. 1 is a disassembled perspective view of an essential part of a seat-weight measuring apparatus having a bearing structure according to the present invention applied thereto.  
     [0062]FIG. 2 is a plan view of the seat-weight measuring apparatus in one end side having a bearing structure according to the present invention applied thereto.  
     [0063]FIG. 3 includes sectional views of the seat-weight measuring apparatus of FIG. 2: (a) is a sectional view at the line IIIa-IIIa of FIG. 2, and (b) is a sectional view at the line IIIb-IIIb of FIG. 2.  
     [0064]FIG. 4( a ) is a front view a sleeve member used in a bearing structure according to the present invention; FIG. 4( b ) is a side view of FIG. 4( a ).  
     [0065] FIGS.  5 ( a ) to ( d ) are front views of respective sleeve members used in the bearing structure according to the present invention.  
     [0066] FIGS.  6 ( a ) to ( d ) are perspective views of respective sleeve members used in the bearing structure according to the present invention.  
     [0067]FIG. 7 is a perspective view of a pipe circumferentially covered on a shaft member in the bearing structure according to the present invention.  
     [0068]FIG. 8( a ) is a schematic illustration for showing operation of a conventional bearing structure; FIG. 8( b ) is a schematic illustration for showing operation of the bearing structure according to the present invention.  
     [0069]FIG. 9 includes drawings for illustrating a conventional example: FIG. 9(A) is a disassembled perspective view of a displacement/deflection absorbing mechanism of a seat-weight measuring apparatus, and FIG. 9(B) is a front sectional view of a pin bracket.  
     [0070]FIG. 10 includes drawings for illustrating a conventional example: FIG. 10(A) is a plan view showing the entire structure of the seat-weight measuring apparatus, FIG. 10(B) is a side sectional view, and FIGS.  10 (C) and (D) are front sectional views.  
     [0071]FIG. 11 includes drawings for illustrating a conventional example: FIG. 11(A) is a plan view showing the relationship between a sensor plate and a half arm, FIG. 11(B) is a side view in a no-load state, and FIG. 11(C) is a side view schematically showing a state in that a load is applied.  
     [0072]FIG. 12 includes drawings for illustrating a conventional example: FIG. 12(A) is a front sectional view schematically showing a structure of a part in that a seat is attached to a vehicle body, and FIG. 12(B) is a side view.  
     [0073]FIG. 13 is a perspective view of a double sleeve according to the present invention.  
     [0074]FIG. 14 is an enlarged front sectional view of a stopper pin along an axis of a seat-weight measuring apparatus having the double sleeve.  
     [0075]FIG. 15 is an enlarged sectional view for schematically and exaggeratedly showing the vicinity of the double sleeve. 
    
    
     DETAILED DESCRIPTION  
     [0076] Preferred embodiments will be described below; however, the present invention is not limited to these.  
     [0077] In FIGS.  1  to  3 , a seat-weight measuring apparatus  100  has the following elements: a rail-like base frame  102  fixed to a vehicle body; an arm member (a bearing member)  104  vertically rotatably supported by a pivot pin (shaft member)  106  relative to the base frame  102 ; a stopper pin (shaft member)  108  for restricting the rotational range of the arm member  104 ; a bracket (bearing member)  160  pivotablly connected to the stopper pin  108  relative to the arm member  104 ; the bracket  160  transmits the weight of a seat including that of an occupant to the stopper pin  108 ; and sleeve members  116  and  164  interposed between the pivot pin  106  and the arm member  104 , and between the stopper pin  108  and the bracket  160 , respectively.  
     [0078] A sleeve member, which is a feature of the present invention, will be described below. The sleeve members  116  and  164  shown in FIGS.  1  to  3  use any one of sleeve members shown FIGS.  4  to  6 . The sleeve members shown FIGS.  4  to  6  have a shape that any of part of an insertion hole of the sleeve member abuts a peripheral surface of the pin  106  or  108 , even when the pivot pin  106  or the stopper pin  108 , both of which are inserted into the sleeve members, is moved due to vibration by vehicle traveling.  
     [0079]FIG. 4( a ) is a front view of a sleeve member  200 ; and FIG. 4( b ) is a side view thereof. In FIG. 4, in the sleeve member  200 , a tubular section  200   b  is linked to the flange section  200   a , and an end portion  200   c  of the tubular section  200   b  is formed. When the pivot pin  106  or the stopper pin  108  is inserted into the tubular section  200   b , the end portion  200   c  comes into contact with a peripheral surface of the pin  106  or  108 .  
     [0080] Next, modifications of the sleeve member will be described. Each of FIGS.  5 ( a ) to ( d ) are front views of different sleeve members. In a sleeve member shown in FIG. 5( a ), a tubular section  202   b  is linked to an annular flange section  202   a , and an end portion  202   c  of the tubular section  202   b  is formed to be substantially square by drawing. In a sleeve member shown in FIG. 5( b ), a tubular section  204   b  is linked to an annular flange section  204   a , and an end portion  204   c  of the tubular section  204   b  is finely corrugated by drawing. In a sleeve member shown in FIG. 5( c ), a tubular section  206   b  is linked to an annular flange section  206   a , and an end portion  206   c  of the tubular section  206   b  is formed to be elliptic by drawing. In a sleeve member shown in FIG. 5( d ), a tubular section  208   b  is linked to an annular flange section  208   a , and an end portion  208   c  of the tubular section  208   b  is formed to be substantially triangular by drawing.  
     [0081] Each of FIGS.  6 ( a ) to ( c ) are perspective views of different sleeve members. In a sleeve member shown in FIG. 6( a ), a tubular section  212   b  is linked to an annular flange section  212   a , and an intermediate portion  212   c  is constricted so as to form the tubular section  212   b  to be bellow-shaped, so that the intermediate portion  212   c  comes into contact with a peripheral surface of the pivot pin  106  or the stopper pin  108 . In a sleeve member shown in FIG. 6( b ), a tubular section  214   b  is linked to an annular flange section  214   a , and an end portion  214   c  of the tubular section  214   b  is constricted while slits  214   d  are cut therein. In a sleeve member shown in FIG. 6( c ), a tubular section  216   b  is linked to an annular flange section  216   a , and spiral grooves  216   c  are formed on the tubular section  216   b.    
     [0082] Next, the structure of the seat-weight measuring apparatus will be described. As shown in FIGS.  1  to  3 , the base frame  102  of the seat-weight measuring apparatus has a substantially U-shape with a missing top surface in a direction perpendicular to a longitudinal direction (the longitudinal direction is referred to as a back-and-forth direction below). The base frame  102  comprises a bottom plate  102   a  and side plates  102   b  vertically elevated from the right and left both sides in the longitudinal direction of the bottom plate  102   a . In each vicinity of both ends of the base frame  102  in the back-and-forth direction, a pair of pivot-pin insertion holes  110  are formed so as to penetrate the side plates  102   b  coaxially in the direction perpendicular to the longitudinal direction.  
     [0083] The arm member  104  is an elongated plate-like member having the substantially half of the length of the base frame  102  in the longitudinal direction, and one arm member  104  is arranged in one half section of the base frame  102  in the longitudinal direction while the other one arm member  104  in the other half section. One half section of the arm member  104  is an application part  112  forked laterally, which applies a load on a sensor plate  150  by vertical movement of the end portion thereof in accordance with the rotation of the arm member  104  about the pivot pin  106 , as will be described later. Each one of the arm members  104  extends between the right and left side plates  102   b  toward the central portion of the base frame  102  in the longitudinal direction so that the application part  112  faces that of the other arm member  104 .  
     [0084] In the other half section of the arm member  104 , a pair of side plates  104   a  are elevated along the right and left sides of the arm member  104  in the longitudinal direction. On the side plates  104   a , pivot insertion holes  114  are formed so as to overlap coaxially with the insertion holes  110  formed on both the right and left side plates  102   b . Into the pivot insertion holes  114 , the respective sleeve members  116  are inserted. The arm member  104  is held to the base frame  102  by the pivot pin  106  which is inserted into and penetrates the insertion holes  114 , into which the sleeve members  116  are inserted, and the insertion holes  110  of the base frame  102 , and moreover, the arm member  104  is rotatable vertically about the pivot pin  106 . Both ends of the pivot pin  106  extend outside the right and left sides of the base frame  102 , and the pivot pin  106  is fixed not to come out with a nut  156  screwed on one end.  
     [0085] Since this sleeve member  116  uses any one of the aforementioned members shown in FIGS.  4  to  6 , even when the pivot pin  106  is moved due to vehicle vibration, etc., the contact between the tubular section of the sleeve member  116  and the peripheral surface of the pivot pin  106  is always maintained. Thereby, the bracket  160  can be held without rattling while abnormal noise can be suppressed.  
     [0086] On the side plates  104   a  of the arm member  104 , stopper-pin insertion holes  122  are formed in the vicinity of an end portion separating from the application part  112  across the pivot pin insertion holes  114 . The stopper-pin insertion holes  122  are formed so as to penetrate the right and left side plates  104   a  coaxially in the direction perpendicular to the longitudinal direction. The stopper pin  108  is inserted into the insertion holes  122  and assembled into the arm member  104  while extending in parallel with the pivot pin  106  (see FIG. 2). Both ends of the stopper pin  108  inserted into the insertion holes  122  are inserted into respective guide holes  124  which are formed on the both side plates  102   b  of the base frame  102  and elongated in the vertical direction. The stopper pin  108  is movable in the vertical direction within the guide holes  124 . Both ends of the stopper pin  108  extend outside the sides of the base frame  102  via the guide holes  124 , and the stopper pin  108  is fixed not to come out with a nut  154  screwed on one end.  
     [0087] Referring now to FIG. 7, a pipe to be inserted into a shaft of the stopper pin  108  will be described. Although omitted in FIGS. 1 and 2, it is preferable that the shaft of the stopper pin  108  be provided with a pipe shown in FIG. 3 as numeral  130  circumferentially covered thereon. FIG. 7( a ) is a perspective view of an example of such a pipe.  
     [0088] In the pipe  130 , intermediate portions are constricted to form small-diameter portions  130   b , and slits  130   c  are opened so as to extend in the axial direction. When the stopper pin  108  is inserted into the pipe  130 , the small-diameter portions  130   b  stick to the shaft of the stopper pin  108 . When inserting the stopper pin  108  into the pipe  130 , the pipe  130  deforms appropriately at portions of the slits  130   c , enabling the stopper pin  108  to be easily inserted. By circumferentially covering the stopper pin  108  with such a pipe  130 , clearances between the stopper pin  108 , the sleeve members  164 , and the arm member  104  are further reduced, so that abnormal noise due to the rattle of the stopper pin  108  during vehicle traveling is further suppressed.  
     [0089] FIGS.  7 ( b ) and ( c ) are drawings showing other examples of pipes for circumferentially covering the stopper pin  108 . In a pipe  132  shown in FIG. 7( b ), spiral concave grooves  132   b  are formed on a peripheral surface  132   a  so as to stick on the peripheral surface of the stopper pin  108 .  
     [0090] A pipe  134  shown in FIG. 7( c ) is a bellow-type pipe having small-diameter portions  134   b  constricted in the radial direction at predetermined intervals. In the pipe  134 , the small-diameter portions  134   b  come into contact with the peripheral surface of the stopper pin  108 . In addition, each pipe shown in FIGS.  7 ( a ) to ( c ) can be used for the pivot pin  106  just like for the stopper pin  108 .  
     [0091] The structure of the seat-weight measuring apparatus will be described in succession. As is most clearly shown in FIG. 1, the guide hole  124  formed in the base frame  102  is an elongated hole having a predetermined length in the vertical direction and has a width sufficiently larger than the diameter of the stopper pin  108 . Both ends of the stopper pin  108  are inserted into the guide holes  124 . The both ends of the stopper pin  108  are movable in the vertical direction by the length of the guide hole  124  in the vertical direction. In addition, when the arm member  104  is rotated about the pivot pin  106 , the arm member  104  vertically moves integrally with the stopper pin  108 ; at this time, the rotational range of the arm member  104  is restricted by the stopper pin  108  which is limited in the vertical-movement stroke by the guide holes  124 .  
     [0092] To the stopper pin  108 , the bracket  160  is attached. The bracket  160  is connected to a seat rail (not shown in FIGS.  1  to  3 ) which is extendedly arranged under each of the right and left side faces of a seat (not shown in FIGS.  1  to  3 ) via a bolt and nut or a rivet. The bracket  160  connects the seat rail to the seat-weight measuring apparatus  100  while transmitting the seat weight including the weight of a person sitting thereon to the stopper pin  108 .  
     [0093] In the bracket  160 , the stopper-pin insertion holes  162  are formed. Into the stopper-pin insertion holes  162 , the sleeve members  164  are inserted, so that the bracket  160  is held to the stopper pin  108  rotatably about the axis of the stopper pin  108 . The sleeve member  164  uses any one of aforementioned members shown in FIGS.  4  to  6 . Therefore, just like mentioned above, even when the stopper pin  108  is moved due to vehicle vibration, etc., the contact between the tubular section of the sleeve member  116  and the peripheral surface of the stopper pin  108  is always maintained, so that the bracket  160  can be held without rattling while abnormal noise can be suppressed.  
     [0094] In addition, other structures of the seat-weight measuring apparatus  100  may be the same as those of the seat-weight measuring apparatus  9  disclosed in the aforementioned Japanese Unexamined Patent Application Publication No. 2000-258233. That is, although not shown in FIGS.  1  to  3 , in the central portion of the base frame  102  in the longitudinal direction, a load sensor having a sensor plate just like the aforementioned sensor  50  is arranged, and to the sensor plate, ends of the application part  112  of the arm member  104  is connected via half arms. The sensor plate is fixed to a column elevated from the central portion of the base frame  102  with bolts and nuts. When a load is applied to the stopper pin  108  in the vertical direction, each of the arm members  104  is rotated about the pivot pin  106  so that the ends of the application part  112  are moved in the vertical direction. At this time, in the sensor plate connected to the ends of the application part  112 , strain is generated, and the sensor detects the load applied to the stopper pin  108  based on the strain.  
     [0095] The seat-weight measuring apparatus  100 , just like the seat-weight measuring apparatus  9 , is arranged so as to support a pair of seat rails which are extendedly arranged under the right and left side-faces of a vehicle seat from the under side, and is fixed to a vehicle body floor via a seat bracket (not shown) disposed under the base frame  102  (see FIG. 12). The seat rails and the seat-weight measuring apparatus  100  are connected to each other via the bracket  160  as described above. Thereby, the weight of a seat and an occupant sitting on the seat is applied to the stopper pin  108  via the bracket  160 , so that the load sensor detects the weight by the aforementioned mechanism.  
     [0096] Next, the operation of a bearing structure according to the present invention will be described with reference to FIGS.  8 ( a ) to ( c ). FIG. 8( a ) is a schematic view for exaggeratedly showing the operation of a conventional bearing structure. In a sleeve member  222 , a tubular section  222   b  is conventionally formed to have the same diameter in the axial direction. When such a sleeve member  222  is inserted into an insertion hole of a bearing member  240  and then, a shaft member  220  such as a pivot pin is inserted into the sleeve member  222  so as to form a bearing structure, the structure may be assembled in a state that a part of the shaft member  220  is separated from the internal surface of the sleeve member  222  due to dimensional difference in design.  
     [0097] In such a bearing structure, when a vehicle is traveling or an occupant on a seat moves, the shaft member  220  may be rattling (dancing) within the hole of the sleeve member  222 . At this time, the shaft member  220  is brought into contact with an internal surface of the hole in the sleeve member  222 , thereby generating abnormal noise (contact noise between metals).  
     [0098] In contrast, as shown in FIGS.  8 ( b ) and ( c ), such abnormal noise cannot be generated in a bearing structure according to the present invention. FIGS.  8 ( b ) and ( c ) are schematic views for exaggeratedly showing the operation of the bearing structure according to the present invention. In a sleeve member  230  in the drawing, just like the sleeve member shown in FIG. 4, the end  230   c  of a tubular section  230   b  is constricted. The sleeve member  230  is inserted into an insertion hole of the bearing member  240 , and the shaft member  220  (a pivot pin  106  and a stopper pin  108 ) is inserted into the sleeve member  230 .  
     [0099] In the bearing structure according to the present invention, when the vibration due to vehicle traveling is transmitted thereto, even when the shaft member  220  moves in the direction of arrows F in FIGS.  8 ( b ) and ( c ), the end  230   c  of the sleeve member  230  always comes into contact with the peripheral surface of the shaft member  220  by following the movement of the shaft member  220 . Accordingly, the shaft member  220  does not rattle within holes of the sleeve members  116  and  164 , so that even when the shaft member  220  is rattling due to vibration, the abnormal noise and vibration are transmitted to the bearing members such as the arm member  104  and the bracket  160  via the sleeve members  116  and  164  so as to be damped. Therefore, abnormal noise generated in a cabin during vehicle traveling due to the rattle of the shaft member  220  can be suppressed, eliminating uncomfortable feeling of an occupant sitting on the seat.  
     [0100] Next, referring to FIGS.  13  to  15 , a rotational structure (double sleeve example) according to the present invention will be described. FIG. 13 is a perspective view of a double sleeve example according to the present invention. FIG. 14 is an enlarged front sectional view along a stopper pin axis for showing a seat-weight measuring apparatus having the double sleeve. FIG. 15 is an enlarged sectional view for exaggeratedly and schematically showing the vicinity of the double sleeve.  
     [0101] As shown in FIG. 14, double sleeves  300  fit a peripheral surface of a tubular section of a stopper pin  108  from outside. The double sleeve  300 , as plainly shown in FIG. 13, comprises a long internal sleeve  301  and a short external sleeve  302  fitting the internal sleeve  301  from outside. The sleeves  301  and  302  are drawing products from steel plates and have flange sections  301   a  and  302   a  at each one of ends and tapered draw sections (pressing sections)  301   b  and  302   b  at the other ends. Internal surfaces of the sleeves  301  and  302  and end-faces of the flange sections  301   a  and  302   a  are coated with a material with a low coefficient of friction such as Teflon. Due to the Teflon coating, the members can be smoothly slid therebetween. In addition, in FIGS. 13 and 15, inclinations of the draw sections  301   b  and  302   b  are exaggeratedly illustrated.  
     [0102] As shown in FIG. 14, the internal sleeve  301  of the double sleeve  300  is fitted between the shaft of the stopper pin (center-of-rotation pin)  108 , the hole  114  of the arm (first member) side-plate  104   a , and the hole  162  of the bracket (second member)  160 . The external sleeve  302  is pressed within the hole  162  of the bracket  160 . The flange section  302   a  of the external sleeve  302  lies between the arm side-plate  104   a  and the bracket  160 . The flange section  302   a  serves as a plane bearing between the arm side-plate  104   a  and the bracket  160 . The flange section  301   a  of the internal sleeve  301  lies along the outside of the arm side-plate  104   a.    
     [0103] The relationship between the double sleeve  300  and peripheral members and operation thereof will be described. First, the external periphery of the internal sleeve  301  is pressed into the hole  114  of the arm side-plate  104   a , so that the internal sleeve  301  cannot rattle within the hole  114 . Since as for between the internal sleeve  301  and the stopper pin  108  fitting the internal hole of the internal sleeve  301 , although there are clearances between the stopper pin  108  and the internal sleeve  301  other than the draw section  301   b , the draw section  301   b  of the internal sleeve  301  abuts and holds the external peripheral surface of the stopper pin  108  elastically, the stopper pin  108  cannot rattle within the internal hole of the internal sleeve  301 . The tapered draw section  301   b  comes into contact with the entire external periphery of the stopper pin  108  with an appropriate elastic force in the radial direction.  
     [0104] Next, as for the external sleeve  302 , between the external sleeve  302  and the internal sleeve  301  fitting the internal hole of the external sleeve  302 , the draw section  302   b  of the external sleeve  302  abuts and holds the external peripheral surface of the internal sleeve  301  elastically. Therefore, although there are clearances between the internal sleeve  301  and the external sleeve  302  other than the draw section  302   b , the internal sleeve  301  cannot rattle within the internal hole of the external sleeve  302 . The tapered draw section  302   b  comes into contact with the entire external periphery of the internal sleeve  301  with an appropriate elastic force in the radial direction. Furthermore, the external periphery of the external sleeve  302  is pressed into the hole  162  of the bracket  160 , so that the external sleeve cannot rattle within the hole  162 .  
     [0105] Accordingly, there is no clearance between the arm side-plate  104   a  of the bracket  160  and the stopper pin  108 , in which each member rattles, when the weight applied to the seat is changed, noise generated by the rattling of the members (i.e., noise generated by contact between metals) can be suppressed.  
     [0106] As described above in detail, in the rotational structure according to the present invention, the free clearance in the radial direction is forced out due to the pressing parts of the external and internal sleeves, so that pins and the external and internal sleeves cannot rattle within insertion holes. Therefore, abnormal noise produced following the chattering of members can be suppressed.  
     [0107] Since the bearing structure according to the present invention uses the sleeve member formed so that any of part of the insertion hole of the sleeve member always comes into contact with the shaft member, the shaft member does not run freely within the insertion hole of the sleeve member and vibration and noise are transmitted to the arm member and the sleeve member from the contact portion so as to be damped. Also, noise generated by the contact between members (contact noise between metals) can be suppressed, thereby eliminating uncomfortable feeling of an occupant sitting on the seat.  
     [0108] The priority applications, Japanese Patent Application Nos. 2001-011865 and 2001-379905 filed on Jan. 19, 2001 and Dec. 13, 2001, respectively, are hereby incorporated by reference herein in their entirety.  
     [0109] Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims.