JPH07117690A - Mechanical fuse device - Google Patents

Abstract

PURPOSE:To permit the correct operation of a mechanical fuse device for a long time by preventing a connecting member from being broken over necessity due to the reduction of strength by fatigue, even if the mechanical fuse device is used for a long period. CONSTITUTION:A mechanical fuse device is constituted so that a steering shaft 10 and a driven gear 18 are connected through a key 32 inserted into each keyway formed on each member, and when a shearing load over a prescribed value acts between the steering shaft and the driven gear, the connection state of two members is released by the breakage of the key. The key is made of the ceramics having the very small reduction of strength due to fatigue.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connecting structure for two members, and more particularly to a mechanical fuse device for controlling the connecting state of two members.

[0002]

2. Description of the Related Art As one of mechanical fuse devices,
For example, as described in JP-A-61-220968, in an electric power steering device for a vehicle such as an automobile, an auxiliary member that rotates integrally with a steering shaft and an output gear driven by a motor Is connected via a shear pin, and an excessive load acts between the auxiliary member and the output gear, causing a shear pin to break when a load greater than a predetermined value is applied to the share pin and driving between the auxiliary member and the output gear. 2. Description of the Related Art A mechanical fuse device configured to release a connection state has been conventionally known.

According to such a mechanical fuse device,
For example, even if the motor becomes unusable due to an abnormality such as a lock, the vehicle driver operates the steering wheel to rotationally drive the steering shaft to apply a high load to the shear pin, causing the shear pin to break, As a result, it is possible to reliably prevent the steering from becoming impossible due to the motor being locked or the like.

[0004]

A connecting member such as a shear pin is generally made of a metal or resin having excellent impact resistance. However, the strength of metals and resins decreases comparatively significantly due to fatigue when repeatedly loaded. Therefore, in the conventional mechanical fuse device as described above, the strength of the shear pin decreases due to fatigue during the process in which the power steering device is used for a long period of time.
As a result, even if the actual load acting on the shear pin is less than the designed breaking load, the shear pin will be broken, which will assist the electric power steering device in the situation where it should maintain its original operating state. There is a problem that torque transmission is not performed between the member and the output gear, and the power steering device is unnecessarily switched to the manual steering device.

Further, in order to prevent the shear pin from being broken when the actual load acting on the shear pin due to the fatigue-induced strength reduction of the shear pin is less than the set breaking load, the shear pin is expected to be reduced in strength due to fatigue. Attempting to set a lower breaking load for the shear pin results in a lower breaking load on the shear pin than the load that the shear pin must withstand in order for the power steering system to operate properly, and so again in this case In such a situation, if the transmission torque between the auxiliary member and the output gear becomes high, the share pin will be broken and the power steering device will fail even though the power steering device should maintain its original operating state. If necessary, switch to a manual steering device.

On the other hand, since ceramics are inferior in impact resistance to metals and resins, it is conventionally considered unsuitable as a constituent material of a connecting member such as a key for connecting two members. Ceramics have an excellent feature that strength reduction due to fatigue is extremely small as compared with metals and resins.

In view of the above problems in the conventional mechanical fuse device, the present invention focuses on the fact that ceramics have an extremely small strength decrease due to fatigue. Even if the connecting member is used for a long period of time, the mechanical fuse device is improved so that the connecting member does not unnecessarily break due to the decrease in strength due to its fatigue, and thus can operate normally for a long period of time. It is intended to be provided.

[0008]

According to the present invention, the above-mentioned object is achieved by the structure of claim 1, that is, the first member and the second member are connected via a connecting member. In a mechanical fuse device that releases the connection state of the two members by breaking the connection member when a load of a predetermined value or more is applied between the members, the connection member is made of ceramics. Achieved by the featured mechanical fuse device.

According to the present invention, the mechanical fuse device further includes a steering shaft having a first key groove,
A driven gear having a second key groove that is fitted to the steering shaft and meshes with a drive gear that is driven by an electric motor and that is aligned with the first key groove, and is inserted into the first and second key grooves. A key that connects the steering shaft and the driven gear so that torque can be transmitted, the key is made of ceramics, and breaks when the transmission torque between the steering shaft and the driven gear exceeds a predetermined value. It is configured to release the connection between the steering shaft and the driven gear (Claim 2).

According to the present invention, in the structure of claim 1, the connecting member has a notch groove extending along an opposing surface of the connecting portion of the two members, and the notch groove. Has a groove width that is set so that the facing surfaces of the two members fall within the width of the notch groove even if relative displacement of the notch groove with respect to the facing surfaces of the two members occurs. It is configured (configuration of claim 3).

[0011]

[Function] FIG. 18 shows delayed fracture strength and fatigue strength of ceramics (silicon nitride) as metal (alloy steel, JIS standard SCM).
415) is a graph showing comparison with the fatigue strength. From FIG. 18, the strength decrease due to metal fatigue is relatively large, whereas the fatigue strength after 10 ⁸ times of ceramics is about 80% of its initial strength, and the strength decrease due to fatigue of ceramics is extremely small. Understand.

According to the above-mentioned structure of claim 1, since the connecting member for controlling the connecting state of the first and second members is made of ceramics whose strength is not significantly reduced by fatigue, the mechanical fuse device is Even if it is used for a long period of time, the mechanical fuse device will not be destroyed in the situation where the load acting on it due to the strength decrease due to fatigue of the connecting member is significantly below the set load, and the mechanical fuse device will not be destroyed. It is possible to operate according to the intended design over a period of time.

Further, according to the above-mentioned structure of the second aspect, since the key is made of ceramics, the key is fractured in a situation where the set load is significantly reduced due to the strength decrease due to fatigue of the key. The connection between the steering shaft and the driven gear is not released, and therefore the power steering device is not unnecessarily switched to the manual steering device.

According to the above-mentioned structure of claim 3, the connecting member is relatively moved with respect to the first and second members due to the difference in thermal expansion between the first and second members and the connecting member. Even if the connecting member is displaced, the force applied to the connecting member by the first and second members is always the side edge of the notch groove, so the load when the connecting member breaks is set due to the relative displacement of the connecting member. It is surely prevented from deviating significantly from the load.

[0015]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic structural view showing an electric power steering device to which the mechanical fuse device according to the present invention is applied, and FIG. 2 is a first mechanical fuse device applied between the gear and the shaft of FIG. FIG. 3 is an enlarged partial vertical sectional view showing an embodiment, and FIG. 3 is a plan sectional view of the first embodiment shown in FIG.

In FIG. 1, reference numeral 10 denotes a steering shaft having a steering wheel 12 fixed to the upper end. The steering shaft 10 has a torque sensor 14 for detecting steering torque in the middle thereof, and is connected at its lower end to a pinion shaft of a rack-and-pinion steering device 16. In addition, the steering shaft 12
A driven gear 18 is fixed between the torque sensor 14 and the lower end of the motor 20 as will be described later.
It meshes with the drive gear 22 driven by. The rotation of the motor 20 is based on the detection result of the torque sensor 14 and other sensors not shown in the figure, and the electronic control unit 24
The auxiliary steering force is generated according to at least the steering torque.

As shown in FIGS. 2 and 3, the steering shaft 10 is provided with a half-moon shaped recess 28 as a first keyway along the axis 26 thereof. The driven gear 18 is fitted to the steering shaft 10 at its boss portion 18A, and a key groove 30 as a second key groove extending along the axis 26 is provided on the inner surface of the boss portion. A half-moon shaped ceramic key 32 as a connecting member is inserted in the recess 28 and the key groove 30,
Accordingly, the driven gear 18 is fixedly connected to the steering shaft 10 by the key 32.

In the illustrated embodiment, as shown in FIGS. 4 and 5, both sides 32A and 32B of the key 32 are provided with notched grooves 34 and 36 having V-shaped cross sections which are aligned with each other. Has been. Notch grooves 34 and 36 are for key 3
When 2 is properly inserted into the recess 28 and the keyway 30,
It extends parallel to the flat end surface 32C so as to extend in alignment with the opposing surface of the connecting portion of the steering shaft 10 and the driven gear 18, that is, the surface 38 of the steering shaft and the inner surface 40 of the boss portion 18A of the driven gear. There is.

As shown in FIGS. 4 and 6, the notches 34 and 36 are formed on the surface 38 of the steering shaft.
And the inner surface 40 of the boss portion 18A has a width much larger than that of the steering shaft 10, the driven gear 18, the key 32 due to a difference in thermal expansion between the steering shaft and the driven portion. Notch groove 3 for gear
Even if 4 and 36 are displaced relative to each other in the left and right directions as viewed in FIGS. 4 and 6, the surface 38 and the inner surface 40 are always within the width of the notch groove.

In the illustrated first embodiment, the torque transmitted between the steering shaft 10 and the driven gear 18 is less than a predetermined value, which causes the shear applied to the key 32 by the steering shaft and the driven gear. The type of ceramics whose load constitutes the key and the notch grooves 34, 3
When the load is less than the set breaking load determined by the size, shape, etc. of 6, the key does not break, so that the driven gear is maintained in an integrated state with the steering shaft.

On the other hand, when the transmission torque between the steering shaft 10 and the driven gear 18 becomes a predetermined value or more, and the shear load applied to the key 32 by them exceeds the set breaking load, the key is notched. Breakage occurs at positions corresponding to 34 and 36, which disconnects the steering shaft and driven gear, allowing the two members to freely rotate relative to each other about axis 26.

In this case, as shown in FIG. 7, when the ratio of the width of the keyways 34 and 36 to the distance between the surface 38 of the steering shaft and the inner surface 40 of the boss 18A is relatively small, When the relative displacement of the notch groove with respect to the steering shaft and the driven gear occurs due to the difference in thermal expansion of the members, the force applied to the key 32 by the steering shaft and the driven gear (indicated by a triangle in the figure). ) Is located at a position other than the side edge of the notch groove, and therefore the key may not break even if a shear load larger than the set breaking load acts on the key.

On the other hand, according to the illustrated embodiment, the surface 38 and the inner surface 40 fall within the width of the notch groove even if the notch grooves 34 and 36 are displaced relative to the steering shaft and the driven gear. The point of force applied to the key by the steering shaft and the driven gear always comes to the side edge of the notch groove, so that the key always breaks when the shear load applied thereto exceeds the set breaking load.

FIG. 8 is an enlarged partial sectional view showing a second embodiment of the mechanical fuse device applied between the rotary shaft of the motor and the gear shaft. In addition, in FIG. 8, the same reference numerals as those in FIG. 1 are attached to the portions corresponding to the portions shown in FIG.

In this embodiment, the rotating shaft 44 of the output gear 22 is connected to the rotating shaft 48 of the motor 20 via a strip-shaped ceramic torque limiter 46 as a connecting member. The rotating shafts 44 and 48 are bearings 50, respectively.
And 52 rotatably supported about an axis 54, their opposite end faces provided with grooves 56 and 58 aligned with the axis 54, the end of the torque limiter 46 being inserted into these grooves. Has been done.

In this second embodiment, the rotary shafts 44 and 4 are
8 is less than a predetermined value, the torsional load applied to the torque limiter 46 by the rotating shafts 44 and 48 is determined by the type of ceramics forming the key, the cross-sectional shape of the key, and the cross-sectional area. When the load is less than the set breaking load, the torque limiter does not break, so that the two rotary shafts are maintained in a state of being integrally connected.

On the other hand, when the transmission torque between the rotating shafts 44 and 48 exceeds a predetermined value and the torsional load applied to the torque limiter 46 by these rotating shafts exceeds the set breaking load, the torque limiter operates. It breaks, which releases the connection between the two rotary shafts and allows the two rotary shafts to freely rotate relative to each other about the axis 54.

FIG. 9 is a side view showing a column shaft support structure of a manual steering device to which the mechanical fuse device according to the present invention is applied, and FIG. 10 is a mechanical fuse device applied between the vehicle body and the column bracket of FIG. FIG. 11 is an enlarged partial perspective view showing a third embodiment, and FIG. 11 is an enlarged sectional view of the third embodiment shown in FIG.

In FIG. 9, 62 indicates a column shaft, and the column shaft 62 is the upper column tube 6
4 and a lower column tube 66 connected to the lower end of the upper column tube by press fitting. An upper steering shaft 70 and a lower steering shaft 72 having a steering wheel 68 fixed to the upper end.
Are rotatably inserted in the upper column tube 64 and the lower column tube 66, respectively, and are connected to each other by serration coupling.

The column shaft 62 is fixed to the vehicle body 76 via a column bracket 74 at the center of the upper column tube 64, and is fixed to the vehicle body at the lower end of the lower column tube 66 via a jacket bracket 78. ing. As shown in FIG. 10, the column bracket 74 includes a main body portion 74A that supports the upper column tube 64 and a base portion 74B that is integral with the main body portion. The base portion 74B has a steering wheel 68. A pair of notches 80 that open toward the side are provided.

A support member 82 having a substantially hexagonal block shape is fitted in each notch 80. As shown in FIG. 11, the support member 82 has a bolt insertion hole 83 provided in the center and grooves 84 provided on the outer edges of both side portions. The bolt 86 is inserted into the bolt insertion hole 83,
The support member 82 is fixed to the vehicle body by fixing the bolt to the vehicle body 76 with the nut 88. Groove 84
Is a notch 8 in the base portion 74B of the column bracket 74.
0 peripheral edge portion is inserted, and cylindrical shear pins 94 made of a ceramic as a connecting member are inserted into four holes 90 and 92 provided in the supporting member 82 and the base portion 74B so as to be aligned with each other. As a result, the support member and the column bracket are integrally connected to each other.

In the third embodiment, the load acting between the column shaft 64 and the bracket 74 and the vehicle body 76 is less than a predetermined value, so that the bracket and vehicle body share pin 94 via the support member 82. If the shear load applied to the shear pin is less than the set breaking load determined by the type of ceramics forming the shear pin, the cross-sectional shape of the shear pin, and the cross-sectional area, the shear pin does not break, and thus the bracket 74 is integrated with the vehicle body 76. It remains fixed.

On the other hand, when the load acting between the column shaft 64 and the bracket 74 and the vehicle body 76 becomes a predetermined value or more, and the shear load applied to the shear pin 94 by these exceeds the set breaking load, the shear pin moves to the bracket. The base portion 74B is broken at a position corresponding to the upper and lower surfaces of the base portion 74B, whereby the connection state between the bracket and the vehicle body is released, and the column shaft 64 and the bracket can be freely displaced relative to the vehicle body.

FIG. 12 is a perspective view showing the lower surface of an electric vehicle to which the mechanical fuse device according to the present invention is applied.
3 is a perspective view showing the battery carrier shown in FIG. 12,
14 is an enlarged partial perspective view showing a fourth embodiment of the mechanical fuse device applied between the battery carrier and the vehicle body of FIG. 13, and FIG. 15 is a front and rear view of the vehicle of the fourth embodiment shown in FIG. FIG. 16 is an enlarged sectional view of the fourth embodiment shown in FIG. 14 as seen in the lateral direction of the vehicle.

In these drawings, reference numeral 110 denotes a power supply battery housed in a battery carrier 112 fixed to the lower part of the vehicle body 100. As shown in FIG. 13, a plurality of brackets 114 having a horizontal portion 116 extending in the vehicle lateral direction are fixed to the side surface 112A of the battery carrier 112. Each of the horizontal portions 116 is provided with a notch 118 that is opened to the rear of the vehicle.

As shown in FIG. 14, the horizontal portion 116
A peripheral portion of the notch 118 is engaged with a groove 122 formed on a lateral side surface of the support member 120 having a substantially rectangular parallelepiped shape. The groove 122 is formed along the longitudinal direction of the vehicle, whereby the bracket 114 is formed.
Can be pulled out from the support member 20 toward the front of the vehicle (in the direction of arrow A in FIG. 14). Notch 11
Through holes 124 and 126 which are aligned with each other are provided in the peripheral portion of 8 and both ends of the support member 120, respectively. A cylindrical ceramic char pin 128 is inserted into the through holes 124 and 126, and the support member 120 and the bracket 114 are integrally connected to each other by a shear pin.

A bolt insertion hole 130 is provided at the center of the support member 120. As shown in FIGS. 14 and 15, a bolt 132 is inserted into the bolt insertion hole 130 from below the vehicle body. The bolt 132 is a weld nut 136 fixed to an inner plate 134A of a rocker 134 forming a part of the vehicle body. It is fastened and fixed to. Thus, the battery carrier 112 is fixed to the rocker 134 via the support member 120 and the bracket 114. The bolt 132 is also inserted through a hole 139 provided at the end of the plastically deformable thin plate-shaped energy absorbing belt 138, whereby the end of the energy absorbing belt 138 is fixed to the rocker 134 together with the support member 120 and the like. Has been done.

As shown in FIG. 13, a substantially U-shaped belt guide 140 is fixed to the side surface 112A of the battery carrier 112 on the vehicle front side from the fixing position of the energy absorbing belt 138. As shown in FIG. 14, the belt guides 140 are parallel to each other in the support portions 14
0A and 140B, and the upper support 140A is located on the vehicle rear side of the lower support 140B. The energy absorbing belt 1 is provided between the supporting portions 140A and 140B.
38 is inserted in a state of being in contact with the outer surface of the support portion.

As shown in FIG. 13, a plurality of pins 142 are formed on the side surface 112A of the battery carrier 112.
Is fixed. The pin 142 is inserted into an elongated hole 146 provided at the lower end of the link 144, whereby the lower end of the link 144 is pivotally supported by the pin 142, and the upper end of the link 144 is shown in the figure. Although not shown, it is pivotally supported by the rocker 134.

In the fourth embodiment, the load acting between the battery carrier 112 and the bracket 114 and the vehicle body 100 is less than a predetermined value, and thus the support member 1
When the shear load applied to the shear pin 128 by the bracket and rocker 134 via 20 is less than the set breaking load determined by the type of ceramics forming the shear pin, the cross-sectional shape of the shear pin, and the cross-sectional area, the shear pin does not break, This allows the bracket 11
4 is kept fixed to the rocker 134 integrally.

On the other hand, when the load acting between the bracket 114 and the rocker 134 becomes a predetermined value or more, and the shear load applied to the shear pin 128 becomes the set breaking load or more, as in the case of a collision of an electric vehicle, The share pin is broken at a position corresponding to the upper and lower surfaces of the horizontal portion 16 of the bracket, whereby the connection state between the bracket and the rocker is released, and the battery carrier 112 and the bracket 114 can be displaced relative to the rocker 134 forward of the vehicle. Like

Therefore, at the time of a collision of an electric vehicle, the battery carrier 112 is displaced relatively to the front side with respect to the vehicle body, and the belt guide 140 is supported with its supporting portions 140A and 140B sliding on both sides of the energy absorbing belt 138. While moving in sequence, the kinetic energy of the battery 110 and the battery carrier 112 is absorbed, and the impact at the time of a collision given to the vehicle body and the occupants of the vehicle is mitigated. Further, in this case, the battery carrier 112 is maintained in a state of being suspended and supported by the rocker 134 via the link 144, so that it does not drop to the ground. Further, the pin 142 fixed to the battery carrier 112 is a long hole 14 provided at the lower end of the link 144.
Since it is inserted through the connector 6, the link does not hinder the forward movement of the battery carrier 112 at the beginning of the collision of the vehicle.

Although the present invention has been described in detail above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments, and various other embodiments are also possible within the scope of the present invention. It will be apparent to those skilled in the art that

For example, the cutout grooves 34 and 36 provided in the key 32 of the first embodiment have a V-shaped cross section, but the cutout groove provided in the connecting member has the double V-shape shown in FIG.
It may be of any cross-sectional shape, including shape. Further, although the shear pins 94 and 128 in the third and fourth embodiments have a cylindrical shape, the shear pins may have an arbitrary cross-sectional shape, and these shear pins have the same shape as in the first embodiment. The share pin may also be provided with a notch groove in alignment with the facing surface of the connecting portion of the two members to which they are connected. Even if the notch groove is displaced relative to the two members in the axial direction of the share pin due to, for example, the facing surface of the connecting portion of the two members is set to always fit within the width of the notch groove. It is preferable.

[0046]

As is apparent from the above description, according to the constitution of claim 1 of the present invention, the strength of the connecting member for controlling the connecting state of the first and second members is extremely small due to fatigue. Since it is made of ceramics, even if the mechanical fuse device is used for a long period of time, the load acting on the connecting member due to the strength decrease due to fatigue of the connecting member is significantly lower than the set load. Therefore, the mechanical fuse device can be operated as designed for a long period of time.

Further, according to the above-mentioned structure of claim 2, since the key is made of ceramics, the key is fractured in a situation where the set load is significantly reduced due to the strength decrease due to fatigue of the key. The connected state of the steering shaft and the driven gear is not released, and therefore it is possible to reliably prevent the power steering device from being switched to the manual steering device unnecessarily, and the steering shaft and the driven gear can be reliably prevented. There is no need to significantly change the structure of the connecting portion or add any part.

According to the third aspect of the invention, the connecting member is relatively moved with respect to the first and second members due to the difference in thermal expansion between the first and second members and the connecting member. Even if the connecting member is displaced, it is possible to ensure that the force applied to the connecting member by the first and second members is always the side edge portion of the cutout groove, and thus the load when the connecting member breaks It is possible to reliably prevent a large deviation from the set load due to the relative displacement of.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an electric power steering device to which a mechanical fuse device according to the present invention is applied.

FIG. 2 is an enlarged partial vertical cross-sectional view showing a first embodiment of the mechanical fuse device applied between the gear and the shaft of FIG.

FIG. 3 is a plan sectional view of the first embodiment shown in FIG.

FIG. 4 is an enlarged partial plan sectional view showing a main part of FIG.

FIG. 5 is a front view showing a key of the first embodiment.

FIG. 6 is an explanatory diagram showing a force applied to a key when a displacement occurs in the mechanical fuse device of the first embodiment.

FIG. 7 is an explanatory diagram showing a force applied to a key when a displacement occurs in a mechanical fuse device of a comparative example.

FIG. 8 is an enlarged partial sectional view showing a second embodiment of the mechanical fuse device applied between the rotary shaft of the motor and the gear shaft.

FIG. 9 is a side view showing a column shaft support structure of a manual steering device to which the mechanical fuse device according to the present invention is applied.

10 is an enlarged partial perspective view showing a third embodiment of the mechanical fuse device applied between the vehicle body and the column bracket of FIG. 9. FIG.

FIG. 11 is an enlarged sectional view of the third embodiment shown in FIG.

FIG. 12 is a perspective view showing a lower surface of an electric vehicle to which the mechanical fuse device according to the present invention is applied.

13 is a perspective view showing the battery carrier shown in FIG. 12. FIG.

FIG. 14 is an enlarged partial perspective view showing a fourth embodiment of the mechanical fuse device applied between the battery carrier and the vehicle body of FIG.

FIG. 15 is a sectional view of the fourth embodiment shown in FIG. 14 as seen in the vehicle front-rear direction.

16 is an enlarged cross-sectional view of the fourth embodiment shown in FIG. 14 as seen in the vehicle lateral direction.

FIG. 17 is an enlarged partial sectional view showing another embodiment of the cutout groove provided in the key of the first embodiment.

FIG. 18 is a graph showing the fatigue strength of ceramics in comparison with the fatigue strength of metals.

[Explanation of symbols]

 10 ... Steering shaft 16 ... Rack and pinion type steering device 18 ... Driven gear 22 ... Drive gear 32 ... Keys 44, 48 ... Rotation shaft 46 ... Torque limiter 62 ... Column shaft 74 ... Column bracket 82 ... Support member 94 ... Share pin 112 ... Battery carrier 114 ... Bracket 120 ... Supporting member 128 ... Share pin

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Hasegawa 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Kazunori Kagawa 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation

Claims (3)

[Claims] 1. A first member and a second member are connected via a connecting member, and when a load of a predetermined value or more acts between the two members, the connecting member is broken and the two members are connected. A mechanical fuse device for releasing the connected state of members, wherein the connecting member is made of ceramics. 2. A steering shaft having a first key groove, and a second key groove which is fitted to the steering shaft and meshes with a drive gear driven by an electric motor to be aligned with the first key groove. A driven gear and a key that is inserted into the first and second key grooves and connects the steering shaft and the driven gear to each other so that torque can be transmitted. The key is made of ceramics, and the steering shaft and the driven gear are connected to each other. A mechanical fuse device configured to break when the transmission torque between the gear and the gear exceeds a predetermined value and release the connection between the steering shaft and the driven gear. 3. The mechanical fuse device according to claim 1, wherein the connecting member has a notch groove extending along a facing surface of a connecting portion of the two members, and the notch groove is The facing surface of the two members has a groove width set so as to be within the width of the notch groove even if relative displacement of the notch groove with respect to the facing surface of the two members occurs. Mechanical fuse device characterized by