JP2861760B2 - Mechanical fuse device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connection structure between a substantially round bar-shaped member and a member fitted to the same, and more particularly, to a mechanical fuse device for controlling a connection state of the two members. Related.

[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 apparatus 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 are provided. Are connected via a shear pin, and when an excessive load acts between the auxiliary member and the output gear, when a load of a predetermined value or more is applied to the shear pin, the shear pin is broken and the drive between the auxiliary member and the output gear is performed. A mechanical fuse device configured to release a connection state has been conventionally known.

According to such a mechanical fuse device,
For example, even when an abnormality such as a lock occurs in the motor and the motor cannot rotate at all, the driver of the vehicle operates the steering wheel to rotate the steering shaft to apply a high load to the shear pin, thereby breaking the shear pin, As a result, it is possible to reliably prevent the steering from being disabled due to the lock of the motor or the like.

[0004]

Conventionally, connecting members such as shear pins are generally made of metal or resin having excellent impact resistance. However, when a metal or resin is repeatedly subjected to a load, the strength of the metal or resin is relatively largely reduced due to fatigue. Therefore, in the conventional mechanical fuse device as described above, in the process in which the power steering device is used for a long time, the strength of the shear pin decreases due to fatigue,
As a result, the shear pin breaks even if the actual load acting on the shear pin is less than the designed breaking load, so that the electric power steering device is assisted in spite of the situation where it should maintain its original operating condition. 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.

Also, in order to prevent the shear pin from being broken in a situation where the actual load acting on the shear pin due to the strength reduction due to the fatigue of the shear pin is less than the set breaking load, the shear pin is reduced in consideration of the strength reduction due to the fatigue. If the set breaking load is set to be low, the set breaking load of the shear pin is lower than the load that the shear pin must withstand for the normal operation of the power steering device. In such a situation, if the transmission torque between the auxiliary member and the output gear increases, the shear pin breaks and the power steering device fails even though the power steering device should maintain its original operating state. Switch to a manual steering device if necessary.

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

However, when the connecting member is made of ceramics, the connecting member does not necessarily break cleanly into two parts even if a load of a predetermined value or more is applied to the connecting member. The two members may be broken due to bite of the fragments, thereby hindering the relative displacement of the two members with respect to each other, or scatter of the fragments may adversely affect the surroundings. In particular, such a problem is likely to occur when the connecting member is a half-moon-shaped flat key.

The present invention has been made in view of the above-mentioned problems in the conventional mechanical fuse device, and in consideration of the above-mentioned problems, even if the mechanical fuse device is used for a long period of time, the key as a connecting member is inferior due to a decrease in strength due to fatigue thereof. It does not break as necessary, so that it can operate normally for a long period of time, and when a load exceeding a predetermined value is applied to the key, the key breaks cleanly into two parts without substantial debris It is another object of the present invention to provide a mechanical fuse device improved so that the relative displacement of the two members with respect to each other is not hindered and the surroundings are not adversely affected.

[0009]

According to the present invention, there is provided, in accordance with the present invention, an arrangement according to claim 1, namely a first member substantially in the form of a round bar having a first keyway and the first member. A second member having a second key groove that is fitted to the member and is aligned with the first key groove, and loads the first and second members inserted into the first and second key grooves. A substantially semi-moon-shaped flat key that is communicatively coupled, wherein the key is made of ceramics, and a load transmitted between the first member and the second member is predetermined. In a mechanical fuse device configured to break and release the connection state of the first and second members when the value becomes equal to or more than the value, the key is provided on an opposing surface of a connection portion of the first and second members. A notch groove extending along the groove, and the notch groove gradually decreases toward the center in the extending direction. It is accomplished by a mechanical fuse device, characterized in that it comprises a set depth to.

According to the present invention, in the configuration of the first aspect, the notch grooves are provided on both side surfaces of the key, and the depth direction of each notch groove is substantially equal to the facing surface. (The configuration of claim 2).

[0011]

FIG. 11 shows the delayed fracture strength and fatigue strength of ceramics (silicon nitride) measured by metal (alloy steel, JIS standard SCM).
44 is a graph shown in comparison with the fatigue strength of (44). According to FIG. 11, the strength decrease due to metal fatigue is relatively large, whereas the fatigue strength of ceramics after 10 ⁸ times is about 80% of its initial strength, and the strength decrease due to ceramic fatigue is extremely small. I understand.

According to the first aspect of the present invention, since the key for controlling the connection state of the first and second members is made of ceramics whose strength is hardly reduced due to fatigue, the mechanical fuse device is long. Even if it is used for a long period of time, the key does not break in a situation where the load acting on the key is significantly lower than the set load due to the decrease in strength due to the fatigue of the key. It will be possible to operate as intended.

Further, the key has a notch groove extending along the opposing surface of the connecting portion of the first and second members, and the notch groove is set so as to gradually decrease toward the center in the extending direction. The depth of the notch groove is constant over the entire extending direction of the notch groove due to the load acting between the first and second members. When the stress acting on the notch groove becomes uniform and the load acting on the key exceeds the set load, the key is broken into two pieces without any substantial debris.

According to the second aspect of the present invention, the notch grooves are provided on both side surfaces of the key, and the depth direction of each notch groove substantially connects the first and second members. When the load acting on the key exceeds the set load, the key is effectively divided into two parts along the opposing surface of the connecting part of the two members because it is inclined with respect to the side to match the opposing surface of the part. And the fracture surface of the key does not protrude more than the opposing surface of the connecting portion of the two members, so that the relative displacement of the first and second members with respect to each other is impeded by the key after the fracture. Never.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of the present invention.

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

In FIG. 1, reference numeral 10 denotes a steering shaft having a steering wheel 12 fixed to an upper end. The steering shaft 10 has a torque sensor 14 for detecting a steering torque on the way, and is connected at its lower end to a pinion shaft of a rack-and-pinion type steering device 16. Also, the steering shaft 12
A driven gear 18 is fixed between the torque sensor 14 and the lower end as described later, and the driven gear 18
And the driving gear 22 driven by the The rotation of the motor 20 is controlled by the electronic control unit 24 based on the detection results of the torque sensor 14 and other sensors not shown.
Thus, an 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 depression 28 as a first keyway along an axis 26 thereof. Further, the driven gear 18 is fitted to the steering shaft 10 at its boss 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. A semi-lunar plate-shaped ceramic key 32 is inserted into the recess 28 and the key groove 30, whereby the driven gear 18 is connected and fixed to the steering shaft 10 by the key 32.

In the illustrated embodiment, as shown in FIG. 4, the side surfaces 32A and 32B of the key 32 are provided with V-shaped notches 34 and 36, respectively, which are aligned with each other. . When the key 32 is properly inserted into the recess 28 and the key groove 30, the notch grooves 34 and 36 are provided on the opposing surfaces of the connecting portion of the steering shaft 10 and the driven gear 18.
That is, it extends parallel to the planar end surface 32C so as to extend in alignment with the surface 38 of the steering shaft and the inner surface 40 of the boss 18A of the driven gear.

Also, as shown in FIG.
4 and 36 have a width much greater than the spacing between the surface 38 of the steering shaft and the inner surface 40 of the boss 18A, thereby providing a differential thermal expansion between the steering shaft 10, the driven gear 18, and the key 32. Notches 34 and 3 for the steering shaft and the driven gear
6 is displaced in the left and right directions as viewed in FIG.
And, the inner surface 40 always falls within the range of the width of the notch groove.

FIG. 5 is a front view (A), a plan view (B) showing the first embodiment of the key shown in FIGS. 2 to 4, and the stress intensity at the bottom of the notch groove of this embodiment. FIG. 6 is a graph (C) showing a coefficient, and FIG. 6 is an enlarged partial longitudinal sectional view showing a cutout portion of the key of the first embodiment.

In the first embodiment, the notch 34
And 36 comprise a constant width portion and a wedge-shaped portion, and the central planes 34A and 36A of each notch groove extend in alignment with each other perpendicularly to the corresponding side surfaces 32A and 32B of the key 32, respectively. . Further, the depth of each notch groove is set so as to gradually become shallower toward the center in the extending direction of the notch groove, and the depth direction edge 34B of each notch groove is set.
And 36B have a smooth arc shape in a direction perpendicular to the center planes 34A and 36A.

Thus, for example, as shown in FIG.
The stress intensity factor at the bottom of the notch groove having a constant depth fluctuates greatly in the direction in which the notch groove extends, and gradually increases toward the center in the direction in which the notch groove extends. 5C, the stress intensity factor at the bottom of the notch groove in this embodiment is, as shown in FIG. 5C, the extension of the notch groove. It is substantially constant in the direction. Therefore, when the load acting on the key 32 exceeds the set load, the keys crack at the notch grooves 34 and 36 substantially simultaneously over the entire width in the extending direction thereof,
It breaks well in a substantially split state.

When the depth of the notch groove is constant, the stress intensity factor fluctuates relatively largely because (1) the key has a half-moon shape, so that the broken line hatching in FIG. As shown in (2), when a higher load is applied to the key than the steering shaft and the driven gear, the contact surface between them is irregular, (2) the load is applied to the key from the steering shaft and the driven gear. This is because the distance (the arm length of the moment) between the contact point and the notch groove at the time of transmission and the secondary moment of area are not constant. According to the first embodiment, the notch groove It is considered that the stress intensity factor becomes substantially constant by canceling these effects by the setting of the depth.

FIG. 7 is a front view (A), a plan view (B) showing a second embodiment of the key shown in FIGS. 2 to 4, and the stress intensity at the bottom of the notch groove of this embodiment. FIG. 8 is a graph (C) showing coefficients, and FIG. 8 is an enlarged partial longitudinal sectional view showing a cutout portion of a key according to the second embodiment.

In the second embodiment, the notch 34
And 36 comprise a constant width portion and a wedge-shaped portion, and the central planes 34A and 36A of each notch groove extend in alignment with each other perpendicularly to the corresponding side surfaces 32A and 32B of the key 32, respectively. . The depth of each notch groove is set so as to gradually decrease as it goes toward the center in the extending direction of the notch groove.
B and 36B are linear.

Accordingly, as shown in FIG. 7C, the stress intensity factor at the bottom of the notch groove in this embodiment is not as uniform as in the first embodiment, The variation width of the stress intensity factor in the extending direction of the notch groove is much smaller than when the depth of the notch groove is constant. Particularly, as shown in the figure, when the curve of the stress intensity factor has a downwardly convex shape and the amount of curvature is small, the breaking of the key starts from both ends in the extending direction of the notch groove and is completed instantaneously. 10
As compared with the case where the stress intensity factor is largely curved upward as in (C), the key is more favorably broken into two parts.

FIG. 9 is an enlarged partial longitudinal sectional view showing a cutout portion of the key of the third embodiment of the key shown in FIGS.

In the third embodiment, the notch 34
And 36 have a constant width portion and a wedge-shaped portion, and each notch groove has a central plane 34A and 36A.
Are provided at the edges 34B and 36B in the depth direction of the notch groove, with the surface 38 of the steering shaft and the boss portion 18 of the driven gear.
A extends in alignment with each other at an angle to the corresponding side surfaces 32A and 32B of the key 32, respectively, so as to extend tangentially to an intermediate virtual cylindrical surface 42 between the inner surface 40 of A. . Although not shown in the drawings, the depth of each notch groove gradually increases toward the center in the extending direction of the notch groove in the same manner as in the above-described first or second embodiment. It is set to be shallow.

Therefore, according to the third embodiment, the variation range of the stress intensity factor in the extending direction of the notch groove is much smaller than when the depth of the notch groove is constant. Not only does the key break well into two halves without substantial fine debris, but the break of the key proceeds substantially along the imaginary cylindrical surface 42, thereby causing the key to break through the steering shaft. Surface 38 and driven gear boss 18
It does not protrude more than the inner surface 40 of A.

In the illustrated embodiments, the torque transmitted between the steering shaft 10 and the driven gear 18 is less than a predetermined value, so that the shear load applied to the key 32 by the steering shaft and the driven gear is reduced. When the load is less than the set breaking load determined by the type of ceramics constituting the key and the size and shape of the notch grooves 34 and 36, the key does not break, thereby keeping the driven gear united with the steering shaft. Is done.

On the other hand, when the transmission torque between the steering shaft 10 and the driven gear 18 exceeds a predetermined value, and the shear load applied to the key 32 exceeds the set breaking load, the key is notched. It breaks at the positions corresponding to 34 and 36, whereby the connection between the steering shaft and the driven gear is released, and the two members can freely rotate relative to each other about the axis 26.

In this case, the key breaks well into two parts without substantially generating small pieces, so that fine pieces enter between the two members and hinder relative rotation of the two members, The debris does not scatter around and have no adverse effect. In particular, according to the third embodiment, it is possible to reliably prevent the relative rotation of the two members from being hindered by the fracture surface of the key after the fracture.

The keyway 34 for the distance between the surface 38 of the steering shaft and the inner surface 40 of the boss 18A.
In the case where the width ratio of the notches is relatively small, when the relative displacement of the notch groove with respect to the steering shaft and the driven gear occurs due to a difference in thermal expansion of each member, etc., the key 32 by the steering shaft and the driven gear Is applied to a position other than the side edge of the notch groove, so that the key may not break even if a shearing load greater than the set breaking load is applied to the key.

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

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

For example, the cross-sectional shapes of the notches 34 and 36 provided in the key 32 of each of the illustrated embodiments are V-shaped or a combination of a rectangle and a V-shaped. Any cross-sectional shape may be used, including a double V-shape consisting of a large angle root and a small groove angle tip.

[0038]

As is apparent from the above description, according to the structure of the first aspect of the present invention, the key is made of ceramics whose strength is hardly reduced due to fatigue. Even if the mechanical fuse device is used for a long time, the key does not break in a situation where the load acting on the key is significantly lower than the set load due to the decrease in strength due to the fatigue of the key. The notch groove has a depth set to gradually decrease toward the center in the extending direction, and the depth of the notch groove is Since the stress acting on the notch groove becomes uniform due to the load acting between the first and second members as compared with the case where it is constant over the entire direction, the load acting on the key is reduced. Over the set load The key and the key are broken into two parts without any substantial debris, so that the breaking of the key prevents the first and second members from being displaced relative to each other and adversely affects the surroundings. The fear can be greatly reduced.

According to the second aspect of the present invention, the notch grooves are provided on both side surfaces of the key, and the depth direction of each notch groove substantially connects the first and second members. When the load acting on the key exceeds the set load, the key is effectively divided into two parts along the opposing surface of the connecting part of the two members because it is inclined with respect to the side to match the opposing surface of the part. And the fracture surface of the key does not protrude more than the opposing surface of the connecting portion of the two members, so that the relative displacement of the first and second members with respect to each other is impeded by the key after the fracture. Thus, the relative displacement between the two members can be smoothly performed.

[Brief description of the 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 longitudinal sectional view showing one embodiment of a mechanical fuse device applied between the gear and the shaft of FIG. 1;

FIG. 3 is a plan sectional view of the embodiment shown in FIG. 2;

FIG. 4 is an enlarged partial plan sectional view showing a main part of FIG. 3;

FIG. 5 is a front view (A), a plan view (B) showing the first embodiment of the key shown in FIGS. 2 to 4, and a stress intensity at the bottom of the notch groove of the first embodiment; It is a graph (C) which shows a coefficient.

FIG. 6 is an enlarged partial longitudinal sectional view showing a cutout portion of the key according to the first embodiment.

FIG. 7A is a front view showing a second embodiment of the key shown in FIGS. 2 to 4, FIG. 7B is a plan view thereof, and FIG. 7B shows the stress intensity at the bottom of the notch groove of the second embodiment. It is a graph (C) which shows a coefficient.

FIG. 8 is an enlarged partial longitudinal sectional view showing a cutout portion of a key according to a second embodiment.

FIG. 9 is an enlarged partial longitudinal sectional view showing a cutout portion of a key according to a third embodiment of the key shown in FIGS. 2 to 4;

FIG. 10 is a front view (A) showing a key having a constant depth;
It is a plan view (B) and a graph (C) showing the stress intensity factor at the bottom of the notch groove of this key.

FIG. 11 is a graph showing the fatigue strength of ceramics in comparison with the fatigue strength of metal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Steering shaft 16 ... Rack and pinion type steering device 18 ... Driven gear 22 ... Drive gear 28 ... Depression 30 ... Key groove 32 ... Key 34, 36 ... Notch groove

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Iwasaki 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Kazunori Kagawa 1 Toyota Town Toyota City, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation ( 58) Surveyed field (Int.Cl. ⁶ , DB name) B62D 5/04 F16C 35/10

Claims (2)

(57) [Claims] A first member having a substantially round bar shape having a first keyway, and a second member having a second keyway fitted to the first member and aligned with the first keyway. A key having a substantially half-moon shape and being inserted into the first and second keyways and connecting the first and second members so as to transmit a load, wherein the key is It is made of ceramics, and is configured to break when the load transmitted between the first member and the second member is equal to or more than a predetermined value and release the connection state of the first and second members. In the mechanical fuse device described above, the key has a notch groove extending along a facing surface of a connecting portion of the first and second members, and the notch groove has a central portion in an extending direction thereof. A mechanical fuse device having a depth set so as to gradually decrease as it goes toward 2. The mechanical fuse device according to claim 1, wherein the notch grooves are provided on both side surfaces of the key, and the depth direction of each notch groove is substantially the opposite surface. A mechanical fuse device characterized by being inclined with respect to the side surface so as to match with the side surface.