JP2012121437A - Free wheel hub - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of abnormal sound by collision of diaphragm side members when driving is changed, in a free wheel hub in which it is changed from four-wheel drive to two-wheel drive, or two-wheel drive to four-wheel drive.SOLUTION: An outer circumference part of a diaphragm 13, which divides the inside of a housing 6 into a two-wheel driving side negative pressure chamber 21 and a four-wheel driving side negative pressure chamber 22, is pinched from both sides by a sleeve 8 and a diaphragm cover 14. The center part of the diaphragm 13 is pinched from both sides by an outer reinforcement plate 15 and an inner reinforcement plate 16, and the outer reinforcement plate 15 and the inner reinforcement plate 16 are connected by caulking of a rivet 17, into the center part of which the outer reinforcement plate 15 and the inner reinforcement plate 16 are inserted. It is prevented that the rivet 17 shockingly contacts an end face of a front axle 1 by a rubber plate 31 provided at the end face of the front axle 1, when changing to the two-wheel drive. Moreover, it is prevented that the outer reinforcement plate 15 shockingly contacts a cylindrical part 14b by a rubber plate 30 of the end face of the cylindrical part 14b formed in the center part of the diaphragm cover 14, when changing to the four-wheel drive.

Description

  The present invention relates to a freewheel hub for a four-wheel drive vehicle.

  The FR-based four-wheel drive vehicle has a transfer that distributes power from the engine and the transmission to the front propeller shaft and the rear propeller shaft, and by the transfer, two-wheel drive (2WD) and four-wheel drive (4WD) To switch to.

  Here, when the driven side wheel and the driven side axle are in a coupled state during traveling by two-wheel drive, the driven side axle is rotated from the driven side wheel, so that the traveling resistance increases and energy is wasted. Will be consumed.

  In order to eliminate such inconvenience, in the four-wheel drive vehicle described in Patent Document 1, a free wheel hub is provided between the driven wheel and the driven axle, and the transfer is switched to the two-wheel drive. The driven wheel is disconnected from the driven axle and the driven wheel is set free to reduce wasteful running resistance. On the other hand, when the transfer is switched to four-wheel drive, the driven wheel and the driven axle are locked. Thus, the power from the engine is transmitted to the driven wheel.

  In order to switch between two-wheel drive and four-wheel drive, in the free wheel hub described in Patent Document 1, the wheel hub of the driven wheel is provided rotatably on the same axis as the driven axle. A two-wheel drive side negative pressure chamber and a four-wheel drive side negative pressure chamber are formed by incorporating a diaphragm into a hub housing connected to the side end face. It is deformed toward the wheel drive side negative pressure chamber, the slide gear connected to the diaphragm is slid on the driven side axle, the meshing of the slide gear and the outer gear fixed inside the hub housing is released, and the driven The wheel hub is free with respect to the side axle.

  Further, the diaphragm is deformed toward the four-wheel drive side negative pressure chamber by depressurization of the four-wheel drive side negative pressure chamber, and the wheel hub is moved to the driven side axle by meshing the slide gear and the outer gear moving toward the outer gear side. On the other hand, it is locked.

  Here, in order to maintain the two-wheel drive state (free state) or the four-wheel drive state (lock state), the pressure reduction of the two-wheel drive side negative pressure chamber or the four-wheel drive side negative pressure chamber is maintained for a long time. In this case, a large suction force is always applied to the seal member that seals each of the negative pressure chambers and the seal member that seals the negative pressure path communicating with each of the negative pressure chambers, thereby reducing the function of the seal member. , Will reduce durability.

  In order to eliminate such inconvenience, in the above freewheel hub, a magnet is attached to the inner surface of the diaphragm cover that holds the outer peripheral portion of the diaphragm, and the magnet includes a pair of reinforcing plates that sandwich the inner peripheral portion of the diaphragm from both sides. The two-wheel drive state is maintained by the action of adsorbing one outer reinforcing plate.

  Also, a spring is incorporated between the diaphragm cover and the outer reinforcing plate, and the four-wheel drive state is maintained by the action of the spring pressing the diaphragm toward the four-wheel drive side negative pressure chamber. At this time, since the two-wheel drive state cannot be maintained if the magnetic attractive force by the magnet is smaller than the elastic force of the spring, the magnetic attractive force by the magnet is set to a value higher than the pressing force of the spring.

Japanese Patent Laid-Open No. 10-278621

  By the way, in the free wheel hub described in the above-mentioned Patent Document 1, when switching from two-wheel drive to four-wheel drive and the pressure due to the pressure reduction in the four-wheel drive side negative pressure chamber exceeds the magnetic force of the permanent magnet, The diaphragm is suddenly deformed toward the four-wheel drive-side negative pressure chamber by the elastic force, and a rivet that couples and integrates the pair of reinforcing plates impacts the shaft end surface of the driven-side axle. Since the collision is a collision between metal parts, a very loud impact sound is generated.

  Conversely, when switching from four-wheel drive to two-wheel drive, the diaphragm is deformed toward the two-wheel drive negative pressure chamber due to the pressure reduction of the two-wheel drive negative pressure chamber, and the outer reinforcing plate is located at the center of the diaphragm cover. When approaching the end surface of the formed cylindrical portion, the outer reinforcing plate is drawn at a stretch by the magnetic force of the permanent magnet, and the outer reinforcing plate impacts and collides with the end surface of the cylindrical portion. Also in this case, as described above, since the metal parts collide with each other, a very large impact sound is generated.

  As described above, in the conventional freewheel hub, a large impact sound is generated each time the drive is switched from the four-wheel drive to the two-wheel drive and the drive is switched from the two-wheel drive to the four-wheel drive. The point which should be improved in aiming at reduction of an impact sound was left.

  An object of the present invention is to provide a freewheel hub that can suppress the generation of impact sound due to a collision of a diaphragm side member when switching from four-wheel drive to two-wheel drive or from two-wheel drive to four-wheel drive. Is to provide.

  In order to solve the above problems, in the present invention, a wheel hub of a driven wheel is provided rotatably on the same axis as the driven axle, and the hub hub connected to the outer side end surface of the wheel hub is provided in the hub housing. An outer gear that rotates integrally with the hub housing and a sleeve on the outer side in the axial direction of the outer gear are provided, and a slide gear is slidably fitted to the end of the driven-side axle located inside the hub housing. The outer peripheral part of the diaphragm is clamped from both sides by an outer end face of the sleeve and a diaphragm cover having a cylindrical part press-fitted to the outer periphery of the outer end part. A wheel drive side negative pressure chamber and a four wheel drive side negative pressure chamber are provided on the inner side in the axial direction, and an outer reinforcing plate and an inner auxiliary member sandwiching the inner periphery of the diaphragm from both sides. The plate is joined by caulking a rivet inserted through the center thereof, the inner reinforcing plate is connected to the slide gear, and the slide gear is moved by elastic deformation of the diaphragm due to the pressure reduction of the two-wheel drive negative pressure chamber. The state is switched to two-wheel drive by moving in a direction to release the meshing with the outer gear, and the state of switching to two-wheel drive is maintained by the action of the permanent magnet attached to the inner surface of the diaphragm cover magnetically attracting the outer reinforcing plate. Due to the elastic deformation of the diaphragm due to the decompression of the wheel drive side negative pressure chamber, the slide gear is moved to the position where it is meshed with the outer gear to switch to the four-wheel drive, and the four-wheel is driven by the coil spring incorporated between the diaphragm cover and the outer reinforcing plate. In a freewheel hub that maintains the state of switching to driving, switching of driving due to deformation of the diaphragm Ryosuru elastically deformed by receiving the diaphragm member just before, it was adopted a structure in which a shock absorbing member that buffers an impact force due to the collision of the diaphragm member.

  In the free wheel hub having the above-described configuration, the diaphragm is elastically deformed toward the four-wheel drive side negative pressure chamber by depressurizing the four-wheel drive side negative pressure chamber, and the slide gear is moved in the direction of meshing with the outer gear. When the driving is switched, the diaphragm side member collides with the shock absorbing member immediately before the switching is completed, and the shock absorbing member is elastically deformed by the collision and the shock force is buffered.

  For this reason, it is possible to prevent the diaphragm side member from abutting against the shaft end surface of the driven side axle.

  Conversely, when the diaphragm is elastically deformed toward the two-wheel drive-side negative pressure chamber by depressurizing the two-wheel drive-side negative pressure chamber, and the engagement of the slide gear with the outer gear is released to switch to two-wheel drive, the switching is completed. The diaphragm side member collides with the shock absorbing member immediately before the shock absorbing member, and the shock absorbing member is elastically deformed by the collision to buffer the shock force.

  For this reason, it is possible to prevent the diaphragm side member from abutting against the diaphragm cover.

  As described above, when the drive is switched from the four-wheel drive to the two-wheel drive or from the two-wheel drive to the four-wheel drive, the diaphragm side member is received by the shock absorbing member and the momentum is weakened before the switching is completed. The side member does not impactly contact the shaft end surface of the driven side axle or the diaphragm cover, and the generation of impact sound due to the collision of the diaphragm side member can be suppressed.

  Here, the diaphragm side member means a diaphragm, a pair of reinforcing plates that reinforce the diaphragm, and a rivet that combines and integrates the pair of reinforcing plates.

  In the freewheel hub according to the present invention, the impact absorbing member may be a rubber plate provided on the inner surface side of the diaphragm side member and the shaft end surface of the driven axle by bonding, or may be a soft synthetic resin plate. Also good. Further, it may be a rubber layer or a soft synthetic resin layer formed by coating.

  Further, the shock absorbing member comprises a coil spring incorporated between the axially facing surfaces of the end plate of the hub housing and the diaphragm side member and between the axially facing surfaces of the driven side axle and the diaphragm side member. Alternatively, it may be formed of a disc spring having a plurality of slits on the outer periphery and an elastic piece formed between adjacent slits.

  When a disc spring is employed as the impact absorbing member, the elastic piece is attached to the diaphragm side member so as to face the shaft end surface of the driven side axle. In this case, it is possible to employ attachment that is integrated with the diaphragm side member by caulking rivets.

  In the freewheel hub according to the present invention, as described above, when the drive is switched from the four-wheel drive to the two-wheel drive or from the two-wheel drive to the four-wheel drive, the diaphragm side member is the shock absorbing member before the switching is completed. Since the momentum is weakened by being received by the diaphragm side member, the diaphragm side member does not impactly contact the shaft end surface of the driven side axle or the diaphragm cover, and the generation of impact sound due to the collision of the diaphragm side member is suppressed. Can do.

A longitudinal sectional view showing an embodiment of a freewheel hub according to the present invention Sectional drawing which expands and shows the installation part of the diaphragm of FIG. FIG. 1 is a cross-sectional view of the freewheel hub shown in FIG. 1 in a four-wheel drive state. A longitudinal sectional view showing another embodiment of the freewheel hub according to the present invention 4 is a cross-sectional view of the freewheel hub shown in FIG. Longitudinal sectional view showing still another embodiment of the freewheel hub according to the present invention 6 is a cross-sectional view of the freewheel hub shown in FIG. 6 when switched to the four-wheel drive state. Longitudinal sectional view showing still another embodiment of the freewheel hub according to the present invention FIG. 8 is a cross-sectional view of the freewheel hub shown in FIG. 8 switched to the four-wheel drive state.

  Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a front axle 1 as a driven-side axle and a wheel hub 2 of a front wheel as a driven-side wheel provided outside thereof are arranged coaxially.

  A cylindrical spindle 3 is incorporated between the front axle 1 and the wheel hub 2, and the spindle 3 and the wheel hub 2 are relatively rotatably supported by a bearing 4.

  A hub housing 6 is coupled to the outer end surface of the wheel hub 2 by tightening bolts 5. An outer gear 7 is incorporated in the hub housing 6 and a sleeve 8 is incorporated on the outer side in the axial direction.

  The outer gear 7 has a ring shape, and spline teeth 9 as tooth portions are formed on the inner periphery thereof. Each of the outer gear 7 and the sleeve 8 is fixed to the inner diameter surface of the hub housing 6 by fitting with a spline, and rotates integrally with the hub housing 6. The outer gear 7 and the sleeve 8 are arranged in the axial direction. The opposing surfaces are sealed by incorporating a seal member 10.

  A slide gear 11 is fitted to the shaft end located inside the hub housing 6 of the front axle 1. The slide gear 11 is prevented from rotating around the front axle 1 by fitting of a spline or serration, and is movable in the axial direction. Spline teeth 12 that can mesh with the spline teeth 9 of the outer gear 7 are formed on the outer diameter surface thereof. Is provided.

  A diaphragm 13 is incorporated in the hub housing 6 outside the sleeve 8 in the axial direction. The outer peripheral portion of the diaphragm 13 is sandwiched from both sides by a diaphragm cover 14 having an outer end surface of the sleeve 8 and a cylindrical portion 14a press-fitted to the outer periphery of the outer end portion of the sleeve 8 on the outer periphery. A cylindrical portion 14 b is provided at the center portion of the diaphragm cover 14 toward the shaft end surface of the front axle 1.

  The central portion of the diaphragm 13 is sandwiched from both sides by an outer reinforcing plate 15 and an inner reinforcing plate 16, and the outer reinforcing plate 15 and the inner reinforcing plate 16 are coupled and integrated by caulking a rivet 17 that passes through the central portion. Has been.

  The outer reinforcing plate 15 and the inner reinforcing plate 16 are made of a press-formed product of a magnetic metal plate. A cylindrical portion 18 is provided on the outer peripheral portion of the inner reinforcing plate 16, and the opening end of the cylindrical portion 18 is bent inward. Thus, an inner cylinder portion 18a is formed, and the inner cylinder portion 18a is fitted to a cylindrical outer diameter surface 11a formed on the outer periphery of the outer side end portion of the slide gear 11, and is connected to the slide gear 11 in the axial direction. Has been.

  When the inner reinforcing plate 16 and the slide gear 11 are connected in the axial direction, here, a ring groove 19 is formed at the end of the cylindrical outer diameter surface 11 a of the slide gear 11, and a retaining ring 20 fitted in the ring groove 19. The end portion of the inner cylinder portion 18a is engaged.

  By incorporating the diaphragm 13, a two-wheel drive side negative pressure chamber 21 is formed inside the hub housing 6 in the axial direction outside of the diaphragm 13, and a four-wheel drive side negative pressure chamber 22 is formed in the axial direction inside of the diaphragm 13. When the two-wheel drive side negative pressure chamber 21 is depressurized, the diaphragm 13 is deformed toward the two-wheel drive side negative pressure chamber 21, and the slide gear 11 moves in a direction away from the outer gear 7, and the outer gear is moved. 7 is released, and the two-wheel drive state is set.

  Further, by depressurizing the four-wheel drive side negative pressure chamber 22, the diaphragm 13 is deformed toward the four-wheel drive side negative pressure chamber 22, and the slide gear 11 moves toward the outer gear 7 and meshes with the outer gear 7. The four-wheel drive state is set.

  A permanent magnet 23 is attached to the inner periphery of the inner surface of the diaphragm cover 14. The permanent magnet 23 may be annular or discontinuous in the circumferential direction. The permanent magnet 23 attracts the outer reinforcing plate 15 in a two-wheel drive state in which the slide gear 11 is disengaged from the outer gear 7 and maintains the two-wheel drive state.

  A coil spring 24 is incorporated between the diaphragm cover 14 and the outer reinforcing plate 15. The coil spring 24 urges the diaphragm 13 toward the four-wheel drive-side negative pressure chamber 22 to maintain a four-wheel drive state in which the slide gear 11 meshes with the outer gear 7. Is smaller than the magnetic force of the permanent magnet 23.

  In FIG. 1, reference numeral 25 denotes a suction path that communicates with the two-wheel drive side negative pressure chamber 21, and reference numeral 26 denotes a suction path that communicates with the four-wheel drive side negative pressure chamber 22. Further, reference numeral 27 denotes a seal member that seals between the suction path 25 communicating with the two-wheel drive side negative pressure chamber 21 and the suction path 26 communicating with the four-wheel drive side negative pressure chamber 22.

  In the free wheel hub configured as described above, the two-wheel drive-side negative pressure chamber 21 is depressurized when traveling by two-wheel drive. The diaphragm 13 is deformed toward the two-wheel drive negative pressure chamber 21 by the pressure reduction, and the slide gear 11 connected to the diaphragm 13 moves away from the outer gear 7, as shown in FIGS. 1 and 2. Further, the meshing with the outer gear 7 is released, the wheel hub 2 is disconnected from the front axle 1 and becomes free, and the rotation transmission from the wheel hub 2 to the front axle 1 is cut off.

  In the switching state to the two-wheel drive as described above, the permanent magnet 23 attracts the outer reinforcing plate 15. Even if decompression to the two-wheel drive side negative pressure chamber 21 is released by the adsorption, the freewheel hub is maintained in the two-wheel drive state.

  On the other hand, when traveling by four-wheel drive, the four-wheel drive negative pressure chamber 22 is decompressed. Due to the pressure reduction, the diaphragm 13 is deformed toward the four-wheel drive side negative pressure chamber 22, the slide gear 11 moves toward the outer gear 7, and meshes with the outer gear 7, as shown in FIG. The locked state is coupled to the front axle 1, and the rotation is transmitted from the front axle 1 to the wheel hub 2.

  At this time, since the coil spring 24 urges the diaphragm 13 toward the four-wheel drive side negative pressure chamber 22, the diaphragm 13 maintains a deformed state toward the four-wheel drive side negative pressure chamber 22. Even if the decompression to the wheel drive side negative pressure chamber 22 is released, the freewheel hub is maintained in the four-wheel drive state.

  In the switching to the two-wheel drive as described above, when the outer reinforcing plate 15 approaches the end surface of the cylindrical portion 14b formed at the center portion of the diaphragm cover 14, the outer reinforcing plate 15 is drawn at once by the magnetic force of the permanent magnet 23. As a result, the outer reinforcing plate 15 impacts and collides with the end surface of the cylindrical portion 14b, and a large collision noise is generated.

  Conversely, in switching to four-wheel drive, when the pressure due to the pressure reduction in the four-wheel drive side negative pressure chamber 22 exceeds the magnetic force of the permanent magnet 23, the diaphragm 13 is moved to the four-wheel drive side by the elastic force of the coil spring 24. The rivet 17 that deforms abruptly toward the negative pressure chamber 22 and couples and integrates the pair of reinforcing plates 15 and 16 impacts and collides with the shaft end surface of the front axle 1 to generate a large collision sound.

  In order to reduce the collision noise by switching the drive, in the embodiment shown in FIGS. 1 to 3, an impact absorbing member is provided on the end surface of the cylindrical portion 14 b formed in the center portion of the diaphragm cover 14 and the shaft end surface of the front axle 1. The rubber plates 30 and 31 are fixed by adhesion.

  As described above, the outer reinforcing plate 15 that reinforces the diaphragm 13 collides with the rubber plate 30 before the switching to the two-wheel drive is completed by attaching the rubber plate 30 to the end surface of the cylindrical portion 14b of the diaphragm cover 14. To do. Due to the collision, the rubber plate 30 is elastically deformed to absorb the collision force, and the momentum of the diaphragm 13 is weakened.

  For this reason, the outer reinforcing plate 15 does not come into impact contact with the cylindrical portion 14b of the diaphragm cover 14 and the generation of impact sound due to the collision can be effectively suppressed.

  Further, by providing the rubber plate 31 on the shaft end surface of the front axle 1, the rivet 17 collides with the rubber plate 31 before the switching to the four-wheel drive is completed. Due to the collision, the rubber plate 31 is elastically deformed to absorb the collision force, and the momentum of the rivet 17 that moves suddenly to the four-wheel drive negative pressure chamber 22 together with the diaphragm 13 is weakened.

  For this reason, the rivet 17 does not come into impact contact with the shaft end surface of the front axle 1 and the generation of impact sound due to the collision can be effectively suppressed.

  2 and 3, the rubber plates 30 and 31 are attached to the end surface of the cylindrical portion 14b of the diaphragm cover 14 and the shaft end surface of the front axle 1 by bonding, but the end surface of the cylindrical portion 14b of the diaphragm cover 14 and the front axle are also shown. A rubber layer may be coated on the end face of one shaft.

  Further, instead of the rubber plates 30 and 31, a soft synthetic resin plate may be attached by adhesion or a soft synthetic resin layer may be provided by coating.

  2 and 3, the rubber plate 30 is provided on the end face of the cylindrical portion 14b of the diaphragm cover 14, but the rubber plate 30 is provided on the attracting surface of the permanent magnet 23 as shown in FIG. May be. Instead of the rubber plate 30, a soft synthetic resin plate may be provided, or a rubber layer or a soft synthetic resin layer may be provided by coating.

  FIG. 5 shows a state where the two-wheel drive state shown in FIG. 4 is switched to the four-wheel drive state.

  2 to 5 show the rubber plates 30 and 31 as the shock absorbing member, the shock absorbing member is not limited to the rubber plate, and a coil spring or a disc spring may be used as the shock absorbing member. Good. Further, the position where the impact absorbing member is assembled is not limited to that shown in FIGS.

  6 and 7, a coil spring 32 is incorporated between the opposed end plate of the hub housing 6 and the outer reinforcing plate 15, and the closed end of the recess 33 formed on the shaft end surface of the front axle 1 and the rivet 17. A coil spring 34 is incorporated between the opposed parts.

  Here, as shown in FIG. 7, the coil spring 32 incorporated between the closed end plate of the hub housing 6 and the opposing portion of the outer reinforcing plate 15 is naturally supported at one end by the closed end plate of the hub housing 6. In this state, the other end has a length positioned on the diaphragm 13 side from the end face of the cylindrical portion 14b, and the outer reinforcing plate 15 receives the outer reinforcing plate 15 immediately before the completion of switching to the two-wheel drive to weaken the momentum. This prevents contact with the cylindrical portion 14b in an impact.

  Further, as shown in FIG. 6, the coil spring 34 incorporated between the closed end of the recessed portion 33 and the opposed portion of the rivet 17 is a natural state in which one end is supported by the closed end of the recessed portion 33 and the other end is recessed. 33 has a length located outside the opening end of 33 and receives the rivet 17 immediately before the completion of switching to the four-wheel drive to weaken the momentum and prevent the rivet 17 from impactingly contacting the shaft end surface of the front axle 1. ing.

  8 and 9 show that a disc spring 35 is used as an impact absorbing member for preventing the rivet 17 from impactingly contacting the shaft end surface of the front axle 1 when switching to four-wheel drive, and the outer reinforcing plate 15 is used when switching to two-wheel drive. As in the case shown in FIGS. 2 and 3, a rubber plate 30 is used as an impact absorbing member for preventing the shock absorbing member from impactingly contacting the end face of the cylindrical portion 14 b of the diaphragm cover 14.

  Here, the disc spring 35 has a plurality of slits 36 provided at equal intervals in the circumferential direction on the outer peripheral portion, and an elastic piece 37 is provided between adjacent slits 36. The disc spring 35 is attached so as to overlap the inner surface of the inner reinforcing plate 16 by caulking the rivet 17. In this case, the disc spring 35 is attached such that a plurality of elastic pieces 37 are opposed to the shaft end surface of the front axle 1, and in the two-wheel drive state, as shown in FIG. It is located inside and immediately abuts against the shaft end surface of the front axle 1 just before the completion of switching to four-wheel drive, and is elastically deformed to prevent the rivet 17 from impactingly contacting the shaft end surface of the front axle 1.

1 Front axle (driven axle)
2 Wheel hub 6 Hub housing 7 Outer gear 11 Slide gear 13 Diaphragm 14 Diaphragm cover 14a Cylindrical portion 14b Cylindrical portion 15 Outer reinforcing plate 16 Inner reinforcing plate 17 Rivet 18 Cylindrical portion 21 Two-wheel drive side negative pressure chamber 22 Four-wheel drive side negative pressure Chamber 23 Permanent magnet 24 Coil spring 30 Rubber plate (impact absorbing member)
31 Rubber plate (shock absorbing member)
32 Coil spring (impact absorbing member)
34 Coil spring (shock absorbing member)
35 Disc spring (shock absorbing member)
36 slit 37 elastic piece

Claims (8)

A wheel hub of a driven wheel is provided rotatably on the same axis as the driven axle, and an outer gear that rotates integrally with the hub housing is connected to an outer end surface of the wheel hub, and the outer gear A sleeve is provided on the outer side in the axial direction, and a slide gear is slidably fitted to an end portion of the driven side axle located inside the hub housing and is prevented from rotating, and an outer side end surface of the sleeve and its outer side The outer periphery of the diaphragm is sandwiched from both sides by a diaphragm cover having a cylindrical portion that is press-fitted into the outer periphery of the end, and the two-wheel drive-side negative pressure chamber is formed on the outer side in the axial direction of the diaphragm, and 4 A negative pressure chamber is provided on the wheel drive side, and an outer reinforcing plate and an inner reinforcing plate that sandwich the inner peripheral portion of the diaphragm from both sides are clamped with a rivet inserted through the center portion thereof. The inner reinforcing plate is connected to the slide gear, and the two-wheel drive is performed by moving the slide gear in a direction to release the meshing with the outer gear by elastic deformation of the diaphragm due to the pressure reduction of the two-wheel drive side negative pressure chamber. The permanent magnet attached to the inner surface of the diaphragm cover maintains the switching state to the two-wheel drive by the action of magnetically attracting the outer reinforcing plate, and slides by the elastic deformation of the diaphragm due to the decompression of the negative pressure chamber on the four-wheel drive side In a freewheel hub in which the gear is moved to a position meshing with the outer gear and switched to four-wheel drive, and the state of switching to four-wheel drive is maintained by a coil spring incorporated between the diaphragm cover and the outer reinforcing plate.
A freewheel hub comprising an impact absorbing member that is elastically deformed by receiving a diaphragm side member immediately before completion of switching of driving due to the deformation of the diaphragm and cushions an impact force caused by the collision of the diaphragm side member .   The freewheel hub according to claim 1, wherein the shock absorbing member is made of a rubber plate bonded to the inner surface side of the diaphragm side member and the shaft end surface of the driven side axle.   2. The freewheel hub according to claim 1, wherein the shock absorbing member includes a rubber layer coated on an inner surface side of a diaphragm side member and a shaft end surface of a driven side axle.   2. The freewheel hub according to claim 1, wherein the shock absorbing member is made of a soft synthetic resin plate bonded to the inner surface side of the diaphragm side member and the shaft end surface of the driven side axle.   The freewheel hub according to claim 1, wherein the impact absorbing member is formed of a soft synthetic resin layer coated on an inner surface side of the diaphragm side member and a shaft end surface of the driven side axle.   2. The shock absorbing member comprises a coil spring incorporated between an axially opposed surface of the hub housing end plate and the diaphragm side member and between an axially opposed surface of the driven side axle and the diaphragm side member. The freewheel hub described.   The shock absorbing member is provided between the axially facing surfaces of the diaphragm cover and the diaphragm side member and between the driven side axle and the axially facing surface of the diaphragm side member, and is provided on the diaphragm cover and the diaphragm side member. The shock absorbing member is made of a rubber plate, a rubber layer, a soft synthetic resin plate, and a soft synthetic resin layer, and the shock absorbing member provided between the opposing surfaces of the driven side axle and the diaphragm side member has a plurality of slits. 2. A disc spring having an outer periphery and having an elastic piece formed between adjacent slits, wherein the disc spring is attached to a diaphragm side member so that the elastic piece faces the shaft end surface of the driven axle. The freewheel hub described.   The free wheel hub according to claim 7, wherein the disc spring is integrated with a diaphragm side member by caulking the rivet.

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