JP3077481B2 - Gear with 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 gear, and more particularly, to a gear provided with a mechanical fuse device.

[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.

Further, when two members are connected by a key of a mechanical fuse device, a space for assembling the key is required at a connecting portion between the two members, so that the size and shape of the two members are changed. May have to be done, and when the two members cannot be changed in size or shape due to the relationship with other members,
It is not possible to provide a mechanical fuse device at a connection portion of those members.

In view of the above-mentioned problems in the conventional mechanical fuse device, the present invention incorporates a mechanical fuse device that normally operates for a long period of time, and incorporates the mechanical fuse device into a connection portion with other members. It is intended to provide an improved gear so that it is not necessary.

[0009]

According to the present invention, there is provided, in accordance with the present invention, an arrangement as set forth in claim 1, namely an inner gear member having an outer peripheral surface concentric with the axis and having a first keyway, An outer gear member having a second keyway that is fitted to the inner gear member and faces the outer peripheral surface at an inner peripheral surface concentric with the axis and aligned with the first keyway; and A plurality of teeth provided on at least one of an inner peripheral portion and an outer peripheral portion of the outer gear member and arranged around the axis; and the inner gear member and the inner gear member inserted into the first and second keyways. a key for connecting the outer gear member to be capable of transmitting torque, wherein the key is made of ceramics and the inner teeth are
The wheel member and the outer gear member are not in surface contact with each other.
The key is integrally connected by the key, and the key is broken when a load transmitted between the inner gear member and the outer gear member becomes a predetermined value or more, and the inner gear member and This is achieved by a gear configured to decouple the outer gear member.

According to the present invention, in the configuration of the first aspect, a relative displacement restricting means for restricting a relative displacement of the inner gear member and the outer gear member along the axis is provided.

[0011]

FIG. 8 shows the delayed fracture strength and fatigue strength of ceramics (silicon nitride) as measured by metal (alloy steel, JIS standard SCM4).
It is a graph shown in comparison with the fatigue strength of 15). According to FIG. 8, 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.

[0012] According to the former configuration (claim 1),
The key constitutes a mechanical fuse device that cooperates with the inner gear member and the outer gear member to control the connection state between them.The key is made of ceramics whose strength decrease due to fatigue is extremely small. even gear is used for a long time under the condition that act repeatedly relatively high loads, the keys will not break at a situation falls below greatly setting load load acting on it, also the inner gear member及
The outer and outer gear members are keyed without surface contact
Because they are integrally connected, the two members come into face contact
The fluctuation range of the frictional force between these members
Small, transmitted torque between two members when the key breaks
Does not deviate significantly from the specified value,
Is the load acting between the inner gear member and the outer gear member.
It breaks at the stage when the set load is accurately reached, so that the mechanical fuse device can be operated as intended for a long period of time.

Further, according to the former configuration, since the mechanical fuse device is provided at the connecting portion of the inner gear member and the outer gear member which cooperate with each other to form one gear, another mechanical fuse such as a shaft is provided. It is not necessary to change the size and shape of the gears and other members as in the case where a mechanical fuse device is incorporated in a connection portion with a member.

In particular, according to the latter configuration (claim 2), even when the key is broken due to the load acting on the key being equal to or greater than the set load, the inner gear member and the outer gear member are arranged along the axis. As a result, since the inner gear member or the outer gear member falls off and these gear members and other members are damaged, the possibility of damage is reduced.

[0015]

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

FIG. 1 is a schematic configuration diagram showing an electric power steering apparatus to which a gear device having a mechanical fuse device according to the present invention is applied, and FIG. 2 is a diagram showing a first embodiment of the driven gear shown in FIG. FIG. 3 is an enlarged partial longitudinal sectional view showing an essential part of the first 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 driven gear 18 includes a substantially disk-shaped inner gear member 26 and a substantially annular outer gear member 28 that are fitted together. ing. Although not shown in the figure, the inner gear member 26 is fixed at a central portion thereof to a shaft extending along the axis of the driven gear 18 or is formed integrally with the shaft. The face is provided with a plurality of teeth 30 arranged around the axis of the driven gear.
The inner gear member 26 has a substantially cylindrical outer peripheral surface 32 concentric with the axis of the driven gear 18, and the outer gear member 2
Numeral 8 is opposed to the outer peripheral surface 32 at an inner peripheral surface 34 concentric with the axis, and the outer peripheral surface 32 and the inner peripheral surface 34 are separated from each other by a very small clearance.

The outer peripheral surface 32 of the inner gear member 26 has a plurality of rectangular recesses 36 as a first keyway extending substantially radially and equally spaced from one another about an axis.
Are provided, and a recess 38 is provided around each recess 36. On the other hand, the inner peripheral surface 34 of the outer gear member 28 is provided with a plurality of rectangular cross-sectional key grooves 40 as second key grooves corresponding to the depressions 36. Each key groove is formed on the lower surface 28A of the outer gear member. Extends to

In each of the recesses 36 and the key grooves 40, a ceramic key 4 having a substantially rectangular cross section is formed.
2 is inserted, and the key 42 has the recess 36 and the keyway 4
The inner gear member 26 and the outer gear member 28 are integrally connected to each other by shrink fitting or press fitting in a resin-coated state, and the mechanical fuse device 44 is cooperated with these members. Make up.

FIGS. 4 to 6 are enlarged partial perspective views showing parts of the gears according to the second to fourth embodiments of the present invention, in which the keys are not provided. In FIGS. 4 to 6, parts corresponding to those in FIGS. 2 and 3 are denoted by the same reference numerals as those in FIGS.

In the second embodiment shown in FIG. 4, the inner peripheral surface 34 of the outer gear member 28 has a substantially cylindrical shape as in the first embodiment, while The outer peripheral surface 32 of the gear member 26 is formed of two conical surfaces inclined in opposite directions with respect to the axis of the driven gear, and the two conical surfaces cooperate with each other to define a convex portion 46 protruding radially outward. doing. The protruding portion 46 is lightly in contact with the inner peripheral surface 34 at its distal end in a substantially linear contact state.

In the third embodiment shown in FIG. 5, the outer peripheral surface 32 of the inner gear member 26 and the inner peripheral surface 34 of the outer gear member 28 correspond to the outer peripheral surface and the inner peripheral surface of the second embodiment, respectively. Surface and the lower surface 26A of the inner gear member.
And a plurality of tabs 4 on the upper surface 28B of the outer gear.
8 and 50 are fixed, for example, by welding. Tab 4
Numerals 8 and 50 are respectively spaced equidistantly around the axis of the driven gear and extend radially. Tab 48
And 50 are the lower surfaces 2 of the outer gear member 28 at the respective ends.
8A and the upper surface 26B of the inner gear member 26 at a distance slightly smaller than the upper surface 26B, thereby restricting the relative displacement of the inner gear member and the outer gear member along the axis of the driven gear. The displacement regulating means is defined.

[0024] Te is at the fourth embodiment shown in FIG. 6, but the outer peripheral surface 3 2 of the inner gear member 26 forms the same form and the outer peripheral surface of the second and third embodiment, Outer gear member 28
The inner peripheral surface of the 3 4 has become more and conical surface oblique to the cylindrical surface with the axis extending along the axis of the driven gear, the convex portion 4
Numeral 6 lightly abuts a portion where the cylindrical surface and the conical surface intersect in a substantially line contact state. Thus the conical surface of the projection 46 and the inner circumferential surface 3 4 mutually cooperate to the relative displacement regulating means for regulating that the outer gear member 28 displaced relative to the inner gear 26 downward in the figure along the axis Make up.

FIG. 7 is an enlarged partial longitudinal sectional view showing a main part of a fifth embodiment of the gear according to the present invention. In FIG. 7, portions corresponding to those in FIGS. 2 and 3 are denoted by the same reference numerals as those in FIGS.

In the fifth embodiment, the outer peripheral surface 32 of the inner gear member 26 extends along the axis of the driven gear 18 and has two cylindrical surfaces spaced apart from each other in the radial direction. It consists of a plane that extends vertically and connects two cylindrical surfaces. Similarly, the inner circumferential surface 34 of the outer gear member 28 extends along the axis of the driven gear and is radially spaced apart from two cylindrical surfaces and extends perpendicular to the axis and connects the two cylindrical surfaces. It consists of a plane. The cylindrical surface and the flat surface of the outer peripheral surface 32 and the inner peripheral surface 34 face each other while being spaced from each other.

On the cylindrical surface on the side of the lower surface 26A of the outer peripheral surface 32, an annular convex portion 5 similar to the convex portion 46 protruding radially outward.
2 is provided, an annular protrusion 54 that protrudes toward the plane of the inner peripheral surface 34 extends annularly about the axis of the driven gear is provided on the plane of the outer circumferential surface 32. The protrusions 52 and 54 lightly abut substantially cylindrical contact with the corresponding cylindrical surface and the plane of the inner peripheral surface 34, respectively.

The mutually overlapping portions 26C and 28C in the axial direction of the inner as shown gear member 26 and the outer gear member 28 downward outer gear member 28 in cooperation with the convex portion 54 is in view against the inner gear member 26 It constitutes a relative displacement restricting means for restricting relative displacement. Also part 26C
And 28C are provided with a plurality of through holes 56 and 58 as first and second key grooves, respectively, which are aligned with each other in the axial direction. In each set of through-holes 56 and 58, a substantially round ceramic key 42 is inserted and fixed by shrink-fitting or press-fitting in a resin-coated state. 28
The mechanical fuse device 44 cooperates with C to integrally connect the inner gear member 26 and the outer gear member 28.

In each of the illustrated embodiments, the power steering device operates normally, and the torque transmitted between the inner gear member 26 and the outer gear member 28 of the driven gear 18 is less than a predetermined value. Accordingly, when the load applied to the key 42 by the inner gear member 26 and the outer gear member 28 is equal to or less than the maximum allowable load, the key does not break, whereby the inner gear member 26 and the outer gear member 28 are integrated with each other. The connected state is maintained, and the driving force of the motor 20 is reliably transmitted to the steering shaft 10 via the driving gear 22 and the driven gear 18.

On the other hand, an abnormality such as a motor lock occurs in the power steering device, the transmission torque between the inner gear member 26 and the outer gear member 28 of the driven gear 18 becomes a predetermined value or more, and the load on the key 42 is increased. Is greater than or equal to the set breaking load, the key is moved to the inner gear member 26 and the outer gear member 28.
And the inner gear member and the outer gear member are disconnected from each other, so that the two members can freely rotate relative to each other about the axis of the driven gear. As a result, the power steering device is switched to the manual steering device.

In this case, the key 42 is made of ceramics. Even if a relatively high load is repeatedly applied to the key 42, the strength decrease due to fatigue is extremely small. Therefore, the load acting on the key greatly reduces the set breaking load. It is possible to reliably prevent the key from breaking in a turning situation.

The inner gear member 26 and the outer gear member 28
Is transmitted as the sum of the load transmitted by the key 42 and the frictional force between the two members. In the first embodiment described above, the two members are
Not in contact, also Te is at the first Ni乃 optimum fifth embodiment,
The two members abut in substantially line contact,
Therefore, since the fluctuation range of the frictional force between the two members is smaller than that in the case where the two members are in surface contact, the transmission torque between the two members when the key 42 breaks is largely shifted from a predetermined value. This can be reliably prevented.

Further, according to the third to fifth embodiments, since the relative displacement regulating means for regulating the relative displacement between the inner gear member 26 and the outer gear member 28 is provided, the key 42 is broken. Also, it is possible to reliably prevent the outer gear member 28 from falling off from the inner gear member 26.

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, in the above embodiment, the key 42 is not provided with a notch groove, but in each of the above embodiments, the outer peripheral surface 32 of the inner gear member 26 and the inner peripheral surface of the outer gear member 28 are provided. A cutout groove may be provided in the key 42 corresponding to a portion between the surface 34.

Although the gear of the above embodiment is a helical gear, the gear of the present invention may be any external gear, and a plurality of teeth may be provided on the inner peripheral surface of the inner gear member. Any internal gear may be used.

[0037]

As is apparent from the above description, according to the structure of the first aspect of the present invention, the key cooperates with the inner gear member and the outer gear member to control the connection between them. The key is made of ceramics whose strength decrease due to fatigue is extremely small, so even if the gear is used for a long time in a situation where a relatively high load is repeatedly applied to the key, the key will not It does not break when the load acting on it falls significantly below the set load, and the inner and outer gear members
They are integrally connected by a key without surface contact
Therefore, compared to when two members are in surface contact,
Key fluctuates due to the small fluctuation range of frictional force between members
The transmission torque between the two members greatly deviates from the specified value
Key, which allows the key to
At the stage when the load acting on the vehicle member reaches the set load exactly, the mechanical fuse device can be operated as intended for a long period of time.

According to the first aspect of the present invention, the mechanical fuse device is provided at the connecting portion of the inner gear member and the outer gear member which cooperate with each other to form one gear, and is incorporated in the gear itself. Therefore, it is possible to eliminate the necessity of incorporating a mechanical fuse device in a connection portion between a gear and a shaft or another member such as a shaft. Also, it is possible to eliminate the need for incorporating a mechanical fuse device in a connection portion between a gear and another member. It is possible to eliminate the need to change the size and shape of the member.

According to the second aspect of the present invention, even when the key is broken due to the load acting on the key being equal to or greater than the set load, the inner gear member and the outer gear member are mutually separated along the axis. , The inner gear member or the outer gear member falls off, and the possibility that these gear members and other members are damaged can be reliably reduced.

[Brief description of the drawings]

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

FIG. 2 is an enlarged partial perspective view showing a main part of the driven gear shown in FIG.

FIG. 3 is an enlarged partial longitudinal sectional view showing a main part of the first embodiment shown in FIG. 2;

FIG. 4 is an enlarged partial perspective view showing a portion of the gear according to the second embodiment of the present invention where a key is not provided;

FIG. 5 is an enlarged partial perspective view showing a part of the third embodiment of the gear according to the present invention, in which a key is not provided, in a partially broken manner.

FIG. 6 is an enlarged partial perspective view showing a part of the gear according to the fourth embodiment of the present invention, in which a key is not provided;

FIG. 7 is an enlarged partial longitudinal sectional view showing a main part of a fifth embodiment of the gear according to the present invention.

FIG. 8 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 26 ... Inner gear member 28 ... Outer gear member 36 ... Depression 40 ... Key groove 42 ... Key 48, 50 ... Tab 56, 58 … Through hole

Continuation of the front page (56) References JP-A-59-69538 (JP, A) JP-A-1-188727 (JP, A) JP-A-2-309008 (JP, A) Jpn. , U) Fully open 1988-33709 (JP, U) Fully open 1988-6,525 (JP, U) Fully open 1-60027 (JP, U) Fully open, 3-103 (JP, U) Fully open 3-7559 (JP, U) U.S. Pat. No. 5,873,784 (US, A) West German Patent Application No. 4437452 (DE, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F16H 35 / 10,55 / 17 B62D 5/04

Claims (2)

(57) [Claims] An inner gear member having an outer peripheral surface concentric with the axis and having a first keyway; and an inner peripheral surface fitted to the inner gear member and concentric with the axis and opposed to the outer peripheral surface. An outer gear member having a second keyway aligned with the first keyway, and at least one of an inner peripheral portion of the inner gear member and an outer peripheral portion of the outer gear member provided around the axis. a plurality of teeth arranged, it is inserted into the first and second keyway and a key for connecting the inner gear member and said outer gear member to transmit the torque, constituted by the key ceramics The inner gear member and the outer gear
The members are integrated by the key without surface contact with each other
It is connected to said key releases the connected state of the inner gear member and said outer gear member load transmitted is broken and becomes greater than a predetermined value between the outer gear member and the inner gear member Gears configured as follows. 2. The gear according to claim 1, further comprising a relative displacement regulating means for regulating a relative displacement of said inner gear member and said outer gear member along said axis. gear.