Abstract:
A negative-pressure-type booster includes: a booster shell attached to a support member of a vehicle; a front shell and a rear shell which constitute the booster shell; and, at the four corners of a flat part of the rear shell, linking bolts having affixed thereto protruding parts that each protrude rearward from the flat part, the protruding parts being passed through continuous connecting holes in the support member, the negative-pressure-type booster characterized in that the linking bolts are composed of upper linking bolts arranged to the upper side of the center axis of the booster shell and lower linking bolts arranged to the lower side of the center axis of the booster shell, the protruding part of either of the upper linking bolts extending farther rearward than the protruding part of the other upper linking bolt and the respective protruding parts of the lower linking bolts.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a negative-pressure-type booster employed in a vehicle braking device. 
       BACKGROUND ART 
       [0002]    As one of negative-pressure-type boosters (boosters) of this type, a negative-pressure-type booster including a booster shell configured by a front shell and a rear shell and a diaphragm disposed between the front shell and the rear shell to partition the interior of the booster shell into a constant-pressure chamber (negative-pressure chamber) and a variable-pressure chamber, the constant-pressure chamber being configured to be formed between the front shell and the diaphragm and to be connected to a negative-pressure source, and the variable-pressure chamber being configured to be formed between the rear shell and the diaphragm and to be connected to the negative-pressure chamber or atmospheric air is known. For example, an example of the negative-pressure-type booster is described in the following Patent Literature 1. 
       CITATIONS LIST 
     Patent Literature 
       [0003]    Patent Literature 1: Japanese Unexamined Patent Publication No. 2012-250663 
         [0004]    On the rear shell side of the booster described in the Patent Literature 1, bolts having equal lengths are inserted into the four corners of the rear shell, and parts of the bolts protruding from the rear shell are inserted into connecting holes of a support member of a vehicle to attach the booster to the support member of the vehicle. Furthermore, threaded parts formed in the parts of the bolts protruding from the support member are meshed with nuts from the inside of the vehicle to attach the booster to the support member of the vehicle. 
       SUMMARY OF INVENTION 
     Technical Problems 
       [0005]    Generally, when a booster is to be attached to a vehicle, as described above, bolts protruding from a rear shell are inserted from an engine room side into connecting holes of a support member of a vehicle, and, thereafter, the bolts are meshed with nuts from a vehicle room side. In this manner, the booster is completely attached to the support member of the vehicle. 
         [0006]    However, in the configuration according to Patent Literature 1, after the bolts of the booster are inserted from the engine room side into the support member of the vehicle, the weight of the booster may allow the the bolts to fall out of the connecting holes of the support member of the vehicle so as to disadvantageously disengage the booster from the support member of the vehicle. In this manner, for example, the step of supporting the booster to prevent the booster from being disengaged after the booster is inserted into the support member of the vehicle is required to deteriorate the assembly workability of the booster to the support member of the vehicle. 
         [0007]    The present invention has been made in consideration of the above circumstances, and aims at providing a negative-pressure-type booster having good assembly workability when a booster is attached to a support member of a vehicle. 
       Solutions to Problems 
       [0008]    The present invention, in order to solve the above problems, provides a negative-pressure-type booster according to claim  1  including a booster shell attached to a support member of a vehicle, a front shell and a rear shell configuring the booster shell, and, at four corners of a flat part of the rear shell, and linking bolts to which protruding parts protruding rearward from the flat part are fixed, the protruding parts being inserted into connecting holes of the support member, wherein the linking bolts include upper linking bolts disposed on an upper side of a center axis of the booster shell and lower linking bolts disposed on a lower side of the center axis of the booster shell, the protruding part of any one of the upper linking bolts extends more rearward than the protruding part of the other upper linking bolt and the protruding parts of the lower linking bolts. 
         [0009]    The negative-pressure-type booster according to claim  2  wherein, in claim  1 , a lower linking bolt located on a diagonal line of one of the upper linking bolts is formed such that the lower linking bolt has a length equal to that of one of the upper linking bolts. 
         [0010]    The negative-pressure-type booster according to claim  3  wherein, in claim  1  or  2 , in one of the upper linking bolts, a cutout caught by the support member of the vehicle when the upper linking bolt is inserted into the support member is formed. 
         [0011]    After the linking bolts of the booster shell are inserted into the support members of the vehicle, the weight of the booster shell may allow the linking bolts to fall out of the support member of the vehicle. In contrast to this, according to the invention of claim  1 , one of the upper linking bolts is an extending bolt formed to have a length larger than that of the other upper linking bolt and the lower linking bolt located in a vertical direction of the upper linking bolt. In this manner, the extending bolt is formed to be longer as described above to make it difficult to allow the bolt to fall out of the connecting hole of the support member. Furthermore, when the linking bolts almost fall out of the support member, a contact portion between the lower linking bolts and the connecting holes of the support member acts as a supporting point to increase press force at a contact portion between the extending bolt and the connecting hole of the support member. Thus, in comparison with a case wherein the same bolts are used as upper linking bolts and lower linking bolts, the booster shell can be prevented from being disengaged from the support member of the vehicle. More specifically, since the step of preventing a booster sheel from being disengaged is not required, assembly workability of the booster shell to the support member of the vehicle can be improved. 
         [0012]    According to the invention of claim  2 , when the booster shell is almost disengaged, the lower linking bolts each having a length equal to that of the extending bolt are caught by upper ends of lower connecting holes of the support member. For this reason, in comparison with a case where an extending bolt is only caught by an upper connecting hole of the support member, the booster shell can be more preferably prevented from being disengaged. 
         [0013]    According to the invention of claim  3 , since the cutout is formed in an extending part of the extending bolt, when the booster is to be disengaged, the cutout of the extending bolt is caught by the upper end of the linking hole of the support member of the vehicle. In this manner, the booster can be more preferably prevented from being disengaged from the support member of the vehicle. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a sectional view showing an embodiment of a negative-pressure-type booster according to the present invention. 
           [0015]      FIG. 2  is a front view of a rear shell according to the present invention. 
           [0016]      FIG. 3  is an enlarged view of a periphery of an extending bolt according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0017]    Embodiments of the present invention will be described below in more detail. However, the present invention is not limited to the following embodiments as long as the present invention does not depart from the spirit and scope thereof. 
         [0018]    A first embodiment in a tie-rod negative-pressure-type booster serving as a negative-pressure-type booster (booster) according to the present invention will be described below with reference to the accompanying drawings. As shown in  FIG. 1 , a booster shell  1  includes a front shell  2  and a rear shell  3 , and a flexible diaphragm  4  is airtightly clamped between both the shells  2  and  3  with beads on the outer periphery of the diaphragm  4  to partition the interior of the booster shell into a constant-pressure chamber  5  and a variable-pressure chamber  6 . A disk-like plate  7  is superposed on the diaphragm  4  on the constant-pressure chamber  5  side, and the outer peripheral surface of a distal end of a piston is airtightly fixed to the diaphragm  4  and the plate  7 , and the front side of the piston  8  is exposed to the constant-pressure chamber  5 . A central part of the rear shell  3  is bent outward, a cylindrical protruding part  3   a  is extendedly provided rearward, and a through hole  3   b  is formed on an axial line. 
         [0019]    The piston  8  penetrates the through hole  3   b  and protrudes rearward from the protruding part  3   a  of the booster shell  1 , and a seal  9  is interposed between the inner peripheral surface of the through hole  3   b  and the outer peripheral surface of the piston  8  to block the variable-pressure chamber  6  from atmospheric air. Bellows  10  are fixed between the rear end edge of the piston  8  and the periphery of the through hole  3   b  to cover the outer periphery of the piston  8 . A negative-pressure applying pipe  11  is attached to the front shell  2 , and the constant-pressure chamber  5  communicates with an intake manifold (not shown) of an engine through the negative-pressure applying pipe  11  and kept at a negative pressure. 
         [0020]    Reference numeral  12  denotes a master cylinder. A distal end part  12   a  penetrates a central hole formed in the front shell  2  and airtightly protrudes into the constant-pressure chamber  5 , and a flange part  12   b  contacts with the rear surface of the front shell  2 . The front shell  2  and the rear shell  3  are coupled to each other with a tie-rod bolt  13  extending in parallel with an axial line of the booster shell  1  including both the shells at almost an intermediate position between the axial line and the outer periphery of the booster shell  1 , and fixed to the master cylinder  12 . More specifically, the tie-rod bolt  13  is fixed to the rear shell  3  such that a large-diameter attaching seat  13   a  is brought into airtight contact with the inner surface of the rear shall  3  in the variable-pressure chamber  6  and a rear end of the bolt  13  penetrating the rear shall  3  and extending rearward is caulked toward the outer surface of the rear shell  3 . An annular flange  13   b  is disposed on the tie-rod bolt  13  near the inner surface of the front shell  2 , a washer  14  being in contact with the flange  13   b  is fitted on a distal end part  13   c  extending more forward than the flange  13   b , a seal  15  tightly fitted on the distal end part  13   c  is pressed against the inner surface of the front shell  2  with the washer  14 , and the tie-rod bolt  13  airtightly penetrates the front shell  2  and protrudes forward. 
         [0021]    The distal end part  13   c  penetrates a linking hole formed in the flange part  12   b  of a master cylinder  12 , the front shell  2  and the flange part  12   b  are clamped between a nut  16  screwed on the distal end and the washer  14  to fix the master cylinder  12  to the booster shell  1  and to draw and couple the front shell  2  and the rear shell  3  to each other. Sliding holes of seal parts  4   a  disposed on the diaphragm  4  are airtightly fitted in the tie-rod bolts  13  such that the sliding holes can be slid on the tie-rod bolts  13  so as to keep the airtight partition between the constant-pressure chamber  5  and the variable-pressure chamber  6 . As shown in  FIG. 2 , in the embodiment, insertion holes  36  are formed at four corners of a flat part of the rear shell  3 . The insertion holes  36  are disposed such that, when the booster is attached to a support member  30  of a vehicle, a total of four linking bolts including two upper linking bolts  33  located on an upper side and two lower linking bolts  34  located on a lower side protrude (protruding parts  37 ). One (right side on the drawing) of the upper linking bolts  33  is the tie-rod bolt  13  described above, and the other (left side on the drawing) is a non-tie-rod bolt. The tie-rod bolt  13  is disposed as the lower linking bolt  34  located on a diagonal line of an extending bolt  35  of the upper linking bolt  33 , and, on the right of the tie-rod bolt  13 , a non-tie-rod bolt is disposed. The non-tie-rod bolts including the upper linking bolt  33  and the lower linking bolt  34  are the extending bolts  35  each having the protruding part  37  longer than that of the other (tie-rod bolt  13 ) of the upper linking bolts. Furthermore, as shown in  FIG. 1  and  FIG. 3 , a protruding part  38  of the extending bolt  35  has a cutout  39  formed by cutting out the protruding part  38 . 
         [0022]    Furthermore, the same linking bolts are disposed as each of the upper linking bolts  33  and each of the lower linking bolt  34  disposed on the diagonal line of the corresponding upper linking bolt  33  such that the upper linking bolt  33  and the lower linking bolt  34  have equal lengths. More specifically, the tie-rod bolt  13  serving as the lower linking bolt  34  is disposed on the lower side of the extending bolt  35  serving as the upper linking bolt  33 , and the other linking bolts are reversely disposed. The protruding parts  37  of the upper linking bolts  33  and the lower linking bolts  34  protruding from the rear shell are inserted into the connecting holes  38  (for example, a diameter of 10 mm) of the support member  30  of the vehicle. At this time, the length (for example, 30 mm) of the protruding part  37  of the extending bolt  35  is set on the basis of an intercentral distance (for example, 60 mm) of upper and lower connecting holes  38  of the support member  30 . A thread is formed on the protruding part  37 , and a nut  31  is screwed on the protruding part  37  from the vehicle inside of the support member  30  to attach the booster shell  1  to the vehicle. 
         [0023]    Reference numeral  17  denotes a master piston airtightly penetrating the front shell  2 . The master piston  17  is fitted in the master cylinder  12  such that the master piston  17  can be slid forward and rearward, and protrudes from a distal end part  12   a  of the master cylinder  12  into the constant-pressure chamber  5  to extend to almost the front-end surface of the piston  8 . An output rod  18  is interposed between the piston  8  and the master piston  17  such that the piston  8  transmits forward movement of the diaphragm  4  based on a difference between pressures in the constant-pressure chamber  5  and the variable-pressure chamber  6  to the master piston  17  through the output rod  18 . More specifically, a linking hole  17   a  is formed in the master piston  17  from a rear-end surface in an axial direction, and a bottom part of the linking hole  17   a  is formed to have a conical shape rounded at the top. At the conical bottom part of the linking hole  17   a , a distal end of a rod part  18   a  provided to extend toward the front of the output rod  18  is aligned and brought into contact with the bottom part such that the distal end can be relatively bent in the axial direction. An annular projection  18   b  formed at the rear end of the output rod  18  is fitted in an annular concave groove  8   a  formed rearward from the front-end surface in the piston  8  such that the annular projection  18   b  can relatively move in the axial direction. A return spring  19  is interposed between the front shell  2  and the front-end surface of the piston  8  to bias the piston  8  rearward. 
         [0024]    A difference between pressures in both the chambers  5  and  6  is generated depending on stepping force acting on a brake pedal (not shown) by a driver. A reaction mechanism  20  which feeds back relative movement of the diaphragm  4 , consequently, the piston  8  with respect to the output rod  18  on the basis of the pressure difference is configured such that a disk-like reaction-force member  21  made of an elastic material is housed in a reaction-force chamber  18   c  surrounded by the annular projection  18   b  of the output rod  18 , the reaction-force member  21  is clamped between a reaction-force end face  8   b  surrounded by the annular concave groove  8   a  of the piston  8  and the bottom surface of the reaction-force chamber  18   c , and the piston  8  is compressively transformed depending on force pressing the output rod  18 , consequently, the master piston  17 . 
         [0025]    Reference numeral  22  denotes a valve mechanism which switches the variable-pressure chamber  6  to cause the variable-pressure chamber  6  to communicate with atmospheric air or the constant-pressure chamber  5  and which is built in the piston  8 . An annular control valve disk  23  is slidably fitted in a valve hole  8   c  formed at the central portion of the piston  8  in the axial direction. An annular negative-pressure valve opening/closing unit  23   a  disposed at the distal end of the control valve disk  23  detachably contacts with a negative-pressure valve  8   d  annularly extending from the bottom of the valve hole  8   c . A concave part formed inside the negative-pressure valve  8   d  communicates with the variable-pressure chamber  6  through a path  8   e  formed in the piston  8  in a radial direction and opened in the outer peripheral surface of the piston  8  in front of the seal  9 . A communication path  8   f  opening in a front end face of the piston  8  is formed in a portion where the outer periphery of the negative-pressure valve  8   d  is in contact with the negative-pressure valve opening/closing unit  23   a . When the negative-pressure valve opening/closing unit  23   a  comes away from the negative-pressure valve  8   d , a negative pressure is applied in the variable-pressure chamber  6 . 
         [0026]    An atmospheric-air valve opening/closing unit  23   b  is disposed on the control valve disk  23  at a position more rearward than the negative-pressure valve opening/closing unit  23   a  and detachably contacts with the rear-end face of an atmospheric-air valve disk  24 . When the atmospheric-air valve opening/closing unit  23   b  comes away from the atmospheric-air valve disk  24 , atmospheric air is fed into the variable-pressure chamber  6  through a center hole of the control valve disk  23 , the concave part formed inside the negative-pressure valve  8   d , and the path formed in the piston  8  in the radial direction. The rear end of the control valve disk  23  is coupled to an annular seal holder  25  with bellows  23   c  which allows the control valve disk  23  to move in the axial direction, the seal holder  25  is fitted in an inlet hole  8   g  extending from the valve hole  8   c  to the rear-end face of the piston  8  and pressed against a shoulder portion of the valve hole  8   c  by a compression spring  26 . An input rod  27  coupled to a brake pedal (not shown) is coupled to the atmospheric-air valve disk  24  through the inlet hole  8   g  on the inner side of the atmospheric-air valve  24 . The compression spring  26  is interposed between the rear-end face of the seal holder  25  and a spring bearing  28  being in contact with the shoulder portion of the input rod  27 . The compression spring  26  is interposed between the front-end face of the seal holder  25  and the rear-end face of the control valve disk  23  to bias the control valve disk  23  forward so as to bring the negative-pressure valve opening/closing unit  23   a  and the atmospheric-air valve opening/closing unit  23   b  into contact with the negative-pressure valve  8   d  and the atmospheric-air valve disk  24 . An air filter  29  which the input rod  27  airtightly penetrates is fixed to the opening of the inlet hole  8   g.    
         [0027]    An operation of the negative-pressure-type booster according to the embodiment described above will be described below. When the brake pedal (not shown) is stepped on to advance the atmospheric-air valve disk  24  through the input rod  27  against the spring force of the compression spring  26  with reference to the piston  8 , the atmospheric-air valve disk  24  is separated from the atmospheric-air valve opening/closing unit  23   b  of the control valve disk  23 , and atmospheric air filtered through the air filter  29  flows into the variable-pressure chamber  6  through the path  8   e . The difference between the pressures in the variable-pressure chamber  6  and the constant-pressure chamber  5  allows the diaphragm  4 , the plate  7 , and and the piston  8  to move forward, the output rod  18  is advanced by the piston  8  through the reaction-force member  21  of the reaction mechanism  20 , the master piston is pushed and moved by the output rod  18 , and a brake oil pressure depending on stepping force acting on the brake pedal is generated in the master cylinder  12 . 
         [0028]    The piston  8  elastically deforms the reaction-force member  21  by operating force applied to the diaphragm  4  and depending on the pressure difference in both the chambers to push and move the master piston  17  through the output rod  18  and relatively advances with reference to the atmospheric-air valve disk  24 , and the control valve disk  23  is biased forward by the compression spring  26  and advances together with the piston  8 . When the piston  8  presses the output rod  18  with operating force equivalent to the stepping force of the brake pedal, the atmospheric-air valve opening/closing unit  23   b  contacts with the atmospheric-air valve disk  24  to block the communication between the atmospheric air and the variable-pressure chamber  6  to hold a desired brake oil pressure. At this time, stepping force on the brake pedal is transmitted from a distal-end shaft of the atmospheric-air valve disk  24  through the input rod  27  to the reaction-force member  21 , and the reaction-force member  21  is elastically deformed depending on the stepping force. For this reason, the driver can feel reaction force. 
         [0029]    When the brake pedal (not shown) is released, the atmospheric-air valve disk  24  is moved rearward by the spring force of the compression spring  26  with reference to the piston  8 , and the atmospheric-air valve disk  24  presses the atmospheric-air valve opening/closing unit  23   b  to relatively move the control valve disk  23  rearward against the spring force of the compression spring  26  with reference to the piston  8 , and the annular negative-pressure valve opening/closing unit  23   a  is separated from the negative pressure valve  8   d . In this manner, the negative pressure in the constant-pressure chamber  5  is applied in the variable-pressure chamber  6  through the communication path  8   f  and the path  8   e  to eliminate the difference between the pressures in the constant-pressure chamber  5  and the variable-pressure chamber  6 , and the piston  8 , the plate  7 , and the diaphragm  4  are moved rearward by the spring force of the return spring  19  to eliminate an oil pressure in the master cylinder. The atmospheric-air valve disk  24  stops when a stop member  32  contacts with the periphery of a communication hole  3   b  of the rear shell  3  to stop, and the piston  8  contacts with the stop member  32  to stop. In this manner, the negative-pressure valve  8   d  contacts with the negative-pressure valve opening/closing unit  23   a  to block the communication between the constant-pressure chamber  5  and the variable-pressure chamber  6 . 
         [0030]    According to the above configuration, one of the upper linking bolts  33  corresponds to the extending bolt  35  which is formed to have a length larger than that of the other upper linking bolt  33  of the upper linking bolts and the lower linking bolt  34  located at a position vertical to the upper linking bolt  33 . In this manner, the extending bolt  35  is formed as described above to make it difficult to allow the bolt  35  to fall out of the connecting hole  38  of the support member  30 . Furthermore, when the linking bolts  33  and  34  almost fall out of the support member  30 , a contact portion between the lower linking bolt  34  and the connecting hole  38  of the support member  30  acts as a supporting point to increase press force at a contact portion between the extending bolt  35  and the connecting hole  38  of the support member  30 . Thus, in comparison with the case in which the same bolts are used as the upper linking bolts  33  and the lower linking bolts  34 , the booster shell  1  can be prevented from being disengaged from the support member  30  of the vehicle. More specifically, since the step of preventing the booster sheel  1  from being disengaged is not required, assembly workability of the booster shell  1  to the support member  30  of the vehicle can be improved. 
         [0031]    The embodiment has described a tie-rod booster. However, the present invention can also be applied to a negative-pressure-type booster except for the tie-rod booster, and the operating effect described above can be exerted.