JP2001187954A - Motion converting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the displacement of a moving shaft resulted from a radial load to satisfactorily keep the engagement state with a feed ring and to stably perform a motion conversion from rotating motion to linear motion or the reverse motion conversion. SOLUTION: Of four feed rings R1-R4 held within a rotating cylinder A and engaged with a screw shaft S, the engagement positions al and a2 of the two feed rings R1 and R2 are set to radially opposed positions, and the engagement positions a3 and a4 of the remaining two feed rings R3 and R4 are set to positions radially opposed to each other but shifted circumferentially by a prescribed angle to the engagement positions a1 and a2 of the first set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motion conversion device used for converting motion from rotary motion to linear motion or from linear motion to rotary motion.

[0002]

2. Description of the Related Art A motion conversion device for converting a rotary motion of a rotary drive source such as a motor into a linear motion, or a motion conversion device for performing a reverse motion conversion is used in various industrial fields. Have been. For example, in an electric power steering device configured to drive a steering assist motor in accordance with a steering operation and transmit the rotational force of the motor to a steering mechanism to perform steering assist, a steering wheel ( In general, the rotation of the motor is transmitted to a steering shaft (a rack shaft in a rack and pinion type steering mechanism) connected to the left and right front wheels, and the steering shaft is converted into a movement in the axial direction of the steering shaft. A motion conversion device is used.

[0003] As described above, the motion conversion device used in the power steering device may have a compact configuration so that a motor for assisting steering may be provided in a limited space around the steering mechanism. It is required to have high transmission efficiency so that a small motor can provide as large a steering assist force as possible.

[0004] As one of the motion converting devices having a simple configuration capable of meeting these demands, there is a motion converting device disclosed in Japanese Patent Application Laid-Open No. 59-9351. FIG. 7 is a perspective view schematically showing the configuration of the motion conversion device.

This motion conversion device has a screw shaft S having a thread groove formed on the outer periphery, a holding cylinder A coaxially surrounding the outside of the screw shaft S, and a shaft center inside the holding cylinder A. It comprises a plurality (three in the figure) of feed rings R _{1 to} R ₃ which are inclined and held eccentrically and are engaged with the thread groove on the outer periphery of the screw shaft S at one location in the circumferential direction. I have. In this figure, feed rings R _{1 to} R with respect to the axis of the screw shaft S are shown.
₃ is omitted, and the screw groove on the outer periphery of the screw shaft S is omitted. Rolling bearings such as ball bearings and roller bearings are used as the feed rings R _{1 to} R ₃ , and the engagement with the thread groove on the outer periphery of the screw shaft S is performed by an engagement projection provided on the inner peripheral surface of the inner ring. Has been made through.

[0006] screw axis S of the illustrated supported by bearings B _1, B ₂ and appropriate length spaced two places in the axial direction and is movably supported in the axial direction, also the feed ring R ₁ ~ The holding cylinder A holding R ₃ is rotatably supported coaxially with the screw shaft S. According to this configuration, the holding cylinder A
Is rotated around the axis, the three feed rings R _{1 to} R ₃ held by the holding cylinder A roll while maintaining engagement with the thread groove on the outer periphery of the screw shaft S, and S is pressed by the axial component of the frictional force acting on the engagement portion of each of the feed rings R _{1 to} R ₃ , and is moved in the axial direction,
The rotational movement of the holding cylinder A is converted into a linear movement of the screw shaft S.

On the other hand, when the screw shaft S moves in the axial direction, the holding cylinder A is rotated around the axis by the transmission in the opposite direction, and the linear movement of the screw shaft S is caused by the rotational movement of the holding cylinder A. Is converted to Further, in a configuration in which the holding cylinder A is supported movably in the axial direction and the screw shaft S is rotatably supported around the axis, the holding cylinder A is prevented from rotating by the screw shaft S.
Of the holding cylinder A to the rotational movement of the screw shaft S, respectively.

At this time, since the rolling of each of the feed rings R _{1 to} R ₃ occurs via a rolling element such as a ball or a roller interposed between the inner ring and the outer ring, the above-described motion conversion is performed with high transmission efficiency. been made in, also the holding tube a is a simple configuration in which only was holding the ring R ₁ to R ₃ is sent to the inside (bearing), which is assumed capable of meeting the requirements mentioned above.

[0009]

[SUMMARY OF THE INVENTION Now in the produced motion converter as described above, the on the peripheral surface of the screw shaft S 3 amino feed rings R ₁ to R ₃ in the engaged position a ₁ ~a ₃ Is
As shown, the engagement position a of the two feed rings R ₁ and R _3
1 , a ₃ and the engagement position a of the remaining one feed ring R _2
2 is set at a position facing the screw shaft S in the radial direction, and the screw shaft S is supported from a reverse position by a ₁ , a ₃ and a ₂ . According to this configuration, for example, when the feed rings R ₁ and R ₃ are pressed against the screw shaft S from the side of the respective engagement positions a ₁ and a ₃ in order to strengthen the engagement of the feed rings R ₁ and R ₃ , results deflection of the screw shaft S is restrained by the feed ring R ₂ to be engaged with the engagement position a _2, each feed rings R ₁ to R ₃ can be firmly engaged.

However, the engagement positions a ₁ to
When performing the setting of a _3, when the radial load is used under conditions that act on the screw shaft S, a stable transmission state there is a problem that can not be obtained.

FIG. 8 is an explanatory view of this problem. The engagement position a ₁ (and a ₃ ) of the feed ring R ₁ (and R ₃ ) is shown in FIG.
When the engaging position a ₂ of the feed ring R _2, is shown by respective triangles on axial section of the screw shaft S. With respect to such a screw shaft S, as shown by a white arrow in the drawing, the a ₁
When a pressing force P is applied in a direction orthogonal to a straight line (line a ₁ -a ₂ ) connecting the pressure force a and the line a ₂ , as shown by a two-dot chain line in FIG. feed rings R ₁ in the axial S bends displaced, the engagement position a _1, a _2,
And engagement of R ₂ is impaired there is a possibility that can not be performed stably transmission. The force in the direction perpendicular to the a ₁ -a ₂ line accompanied by the above displacement is a force that is constantly applied as a component of the radial load acting on the screw shaft S.
There is a possibility that it will always occur in a general use state.

The present invention has been made in view of such circumstances, and a radial load acting on a screw shaft in a use state is effectively supported by a plurality of feed rings engaged with a thread groove on the outer periphery of the screw shaft. It is possible to suppress the displacement of the screw shaft due to the radial load and maintain the engagement state in a favorable state,
It is an object of the present invention to provide a motion conversion device capable of stably performing a motion conversion from a rotary motion to a linear motion or a motion conversion reverse thereto.

[0013]

According to the present invention, there is provided a motion conversion device comprising: a screw shaft having a thread groove formed on an outer peripheral surface thereof; a holding cylinder disposed coaxially outside the screw shaft; A plurality of feed rings that are eccentrically held with an inclination corresponding to the lead angle of the screw groove and engage with the screw groove at one location in the circumferential direction. A first and a second ring set each including two or more feed rings, each of which is set at a position where an outer circumferential thread groove is opposed to a radial direction, and an engagement position of the first ring set And the second
And the engagement position of the ring set is shifted in the circumferential direction of the screw shaft.

In the present invention, for example, the four feed rings are divided into two sets of two, and the engagement positions between the two feed rings of the first set and the screw shafts are set at positions opposing each other in the radial direction. The engagement position between the two feed rings of the second set and the screw shaft is shifted by a predetermined angle in the circumferential direction of the screw shaft with respect to the two of the first set, and within the second set. Set at a position facing the radial direction. As a result, the screw shaft is supported at different positions in the circumferential direction by two ring sets each including two feed rings that are engaged with positions facing each other in the radial direction. Within, the pressing of one feed ring strengthens the engagement of the other feed ring,
Further, the displacement of the screw shaft due to the acting force in the direction orthogonal to the engagement position of one of the feed rings is suppressed by the other set of feed rings, and the engagement state of all the feed rings is maintained favorably.

The motion converting device according to a second aspect of the present invention is characterized in that the screw shaft is movably supported in the axial direction, and the holding cylinder is rotatably supported around the axis. The rotation of the holding cylinder is converted into the movement of the screw shaft in the axial length direction by the rolling of the feed ring with the guide as a guide.

According to the present invention, a motion conversion device capable of maintaining good engagement of all feed rings is used for converting the rotational motion of a rotary drive source such as a motor into a movement in the axial direction of a screw shaft. Apply and make stable motion conversion.

Further, in the motion conversion device according to the third invention of the present invention, the two feed rings, each of which has an engagement position set on one side half in the axial cross section of the screw shaft, are provided between them. And at least one feed ring whose engagement position is set in the other half is sandwiched therebetween.

In the present invention, the feed ring engaging with one half and the feed ring also engaging with the other half in the axial cross section of the screw shaft are provided on the same side in the axial direction of the screw shaft. The arrangement is such that the rotational moment does not act in the axial direction of the screw shaft due to the pressing force applied to the respective engagement positions.

Further, in the motion converter according to a fourth aspect of the present invention, the feed ring is constituted by a rolling bearing having an outer ring fitted and fixed to the holding cylinder and an inner ring engaged with the screw groove. There is a feature.

According to the present invention, a rolling device such as a ball bearing or a roller bearing is used as a feed ring to be engaged with the screw shaft, and a motion converting device capable of quiet operation with low operation noise is simply constructed.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a perspective view schematically showing a configuration of a motion conversion device according to the present invention. The motion conversion device 1 according to the present invention includes two bearings B ₁ , B ₂ separated from each other by a suitable distance in the axial direction, similarly to the motion conversion device shown in FIG.
Screw shaft S supported by
And a plurality of eccentrically held inside a holding cylinder A rotatably supported coaxially with the screw shaft S and engaged with the outer periphery of the screw shaft S between the positions supported by the bearings B ₁ and B _2. (Four in the figure) feed rings R _{1 to} R _4, and the rotation of the feed rings R _{1 to} R ₄ accompanying the rotation of the holding cylinder A is converted into the movement of the screw shaft S in the axial direction, Further, a holding cylinder A for feeding the movement of the screw shaft S in the axial direction and holding the rings R _{1 to} R _4.
It is configured to convert to rotation.

A screw groove S ₁ (see FIG. 2) having a predetermined lead angle is formed on the outer periphery of the screw shaft S, and each of the feed rings R _{1 to} R ₄ is provided with the holding cylinder. A is held at an inclination corresponding to the lead angle inside A, and the screw groove S ₁ is provided at one position in the circumferential direction where the inclination angle matches.
Is engaged. A feature of the motion conversion device 1 according to the present invention is that the motion conversion device 1 is provided on the outer periphery of the screw shaft S, more specifically, the screw shaft S
In the setting mode of engagement position of the feed ring R ₁ to R ₄ on the peripheral of the screw groove formed on the outer circumference S _1. In FIG. 1, in order to demonstrate the relationship of the engagement position of the feed rings R ₁ to R _4, as in the FIG. 7, illustration of the screw groove S ₁ formed on the outer periphery of the screw shaft S, and Feed ring R
The illustration of the ₁ to R ₄ each tilted is omitted.

[0023] FIG. 2 is an explanatory view of the operation of the configured motion converter 1 as described above, engagement between the screw shaft S and one of the feed ring R ₁ is shown. The outer peripheral surface of the screw shaft S as shown in the figure, the screw groove S ₁ having a semicircular cross section is formed with a predetermined lead angle. Feed ring R
₁ is a ball bearing having a number of balls between the outer ring and the inner ring, a part of which is fitted with the outer ring in the illustrated holding cylinder A, and has a slope equal to the lead angle of the screw groove S _1. Is held. The inner peripheral surface of the inner ring of the feed ring R _1, are engaging projections circumferentially semicircular cross section corresponding to the screw groove S _1, the engagement projection is in a position (figure in which the tilt matches in a ₁₎ of are engaged with the screw groove S _1.

According to this configuration, when the holding cylinder A rotates around the axis, the feed ring R held by the holding cylinder A
₁ rolls while maintaining engagement with the thread groove S _1, and this rolling causes the screw shaft S to have a frictional force F along the thread groove S _1.
And the screw shaft S becomes an axial component F of the frictional force F.
_As shown by a white arrow in the figure, the button is pushed by ₁ and moved in the direction of the pushing, that is, in the axial direction. The direction of this movement is determined according to the rotation direction of the holding cylinder A, and the rotational movement of the holding cylinder A is converted to the linear movement of the screw shaft S.

In order to stably perform the above-described motion conversion, it is important that the _four feed rings R _{1 to} R ₄ always maintain a good engagement state. In the present invention, the screw shaft S
Engaging position of the feed of the respective ring R ₁ ~R ₄ a ₁ ~a ₄ on the outer peripheral surface of the Yes and is set to as follows, and to keep a good engagement with the setting.

As shown in FIG. 1, four feed rings R ₁ -R
₄ is a first set of two feed rings R ₁ and R ₂ arranged on one side, and the other two feed rings R ₃ and R ₄ arranged on the other side.
As a second set, the engagement positions a ₁ , a ₂ of the first set of feed rings R ₁ , R ₂ are set so that they are opposed to each other in the radial direction of the screw shaft S. The engagement positions a ₃ , a ₄ of the second set of feed rings R ₃ , R ₄ are radially opposed to the screw shaft S between them, and the first set of feed rings R ₁ , R ₂ engagement position a ₁ ,
For a _2, it is set such that the position was shifted in the circumferential direction of the screw shaft S.

FIG. 3 is an explanatory diagram of the setting state of the engagement position as described above. In the drawing, the four feed rings R ₁ to R ₁ are shown.
The engagement positions a _{1 to} a _{4 of} R ₄ are shown by triangles on the circumference of the screw shaft S whose axial cross section is shown, respectively.
The engagement positions a ₁ and a ₂ of the feed rings R ₁ and R ₂ of
The engagement positions a ₃ , a _{4 of} the second set of feed rings R ₃ , R ₄ which are located at positions opposed to the screw shaft S in the radial direction and are set to be shifted by a predetermined angle θ therefrom are also in the radial direction. It is clear that the position is opposite to

By setting the engagement positions a _{1 to} a ₄ as described above, the screw shaft S is made to have the same radius as the first pair of feed rings R ₁ and R ₂ engaged at the positions opposed in the radial direction. A second set of feed rings R ₃ ,
With R _4, it is supported at four different positions in the circumferential direction. According to this configuration, in order to enhance one of the engagement of the feed ring R ₁ of the first set, when pressed against the said transmission Ri ring R ₁ from the side of the engagement position a ₁ to the screw shaft S, by this pressing The other feed ring R of the same set has a deflection of the screw shaft S.
₂ , the feed rings R ₁ and R ₂ can be firmly engaged. Such an engagement reinforcement is similarly applied to the second pair of feed rings R ₃ and R ₄ , so that all the feed rings R _{1 to} R ₄ can be firmly engaged.

On the other hand, in the state of use of the motion conversion device 1 in which the feed rings R _{1 to} R ₄ are engaged as described above, the screw shaft S is attached to the screw shaft S as shown by a white arrow in FIG. While feeding ring R ₁ set of 1, engaged position a ₁ of R _2, the pressing force P ₁ direction perpendicular to the straight line connecting the a ₂ is able to act, this time, the second set since the orientations facing the pressing force P ₁ (a ₃ in the figure) engaged position of one of the feed ring (R ₃ in the figure), the pressing force P ₁
Of the screw shaft S in the direction of action of the feed ring R ₃
And the engaged state of the first pair of feed rings R ₁ , R ₂ is maintained without being impaired. Incidentally, with respect to the pressing force acting from the pushing force P ₁ and the opposite direction, (in FIG R ₄₎ a second set of other feed ring without the effect of suppressing the deflection displacement of the screw shaft S, The engagement state can be maintained in exactly the same manner.

Further, when the pressing force P ₂ in a direction perpendicular to the straight line connecting the second set of feed ring R _3, engagement of R ₄ position a _3, a ₄ are applied, the direction The deflection displacement of the screw shaft S is suppressed by one of the first set of feed rings (R _{1 in the} figure), and the second set of feed rings R ₂ , R
The engagement state of ₃ is maintained without being impaired. Also in this case, the other feed ring (R _{2 in the} figure) of the first set suppresses the bending displacement of the screw shaft S against the pressing force acting from the direction opposite to the pressing force P ₂ . The operation can be performed, and the engaged state can be maintained in the same manner.

As described above, in the motion converter 1 according to the present invention, the four feed rings R _{1 to} R with respect to the screw shaft S are provided.
_Since the engagement state of No. ₄ is maintained without being impaired by the pressing forces applied in various directions to the screw shaft S, the motion conversion from the rotational motion of the holding cylinder A to the linear motion of the screw shaft S is performed. Alternatively, the motion conversion from the linear motion of the screw shaft S to the rotational motion of the holding cylinder A can be performed stably.

In the configuration in which the screw shaft S is rotatably supported and the holding cylinder A is movably supported in the axial direction, the rotation of the screw shaft S is converted into the linear movement of the holding cylinder A. The conversion or the motion conversion for converting the linear motion of the holding cylinder A into the rotary motion of the screw shaft S can be performed in exactly the same manner.

As shown in FIG. 2, the feed rings R _{1 to} R ₄ are ball bearings having a large number of balls between an outer ring and an inner ring, and have a simple structure fixed by being fitted into a holding cylinder A. In addition, since each of the balls rolls without changing the position between them, there is no possibility of collision, so that the sound generated by the above-mentioned operation is small and a quiet operation is possible.

The deviation angle θ between the second set of engagement positions a ₃ and a ₄ with respect to the _first set of engagement positions a ₁ and a ₂ is 0.
The angle can be set as appropriate within the angle range of 90 ° to 90 °, but when θ = 0 °, the engagement positions of both sets are one in the circumferential direction as in the motion conversion device shown in FIGS. However, the displacement of the screw shaft with respect to the pressing force in the direction orthogonal to these cannot be suppressed, and when θ = 90 °, the acting force on the engagement position of one set causes the engagement of the other set to engage. Acts to weaken. Therefore, it is preferable that the deviation angle θ is set near 45 ° (about ± 10 °) which is an intermediate value between 0 ° and 90 °.

[0035] In the above embodiments, the feed rings R ₁ and R ₂ and the first set, there is a feed ring R ₃ and R ₄ as the second set, the feed ring R ₁ to R ₄ The grouping is not limited to this, and for example, the feed rings R ₁ and R
₄ may be changed to a first set, and the feed rings R ₂ and R ₃ may be changed to a second set.

However, even in this case, each feed ring R
_{1 to} R ₄ are two feed rings (the feed rings R ₁ and R ₄ in FIG. 1) each of which has an engagement position set at one half in the axial cross section of the screw shaft S. It is necessary to arrange at least one feed ring (the feed rings R ₂ and R ₃ in FIG. 1) between which the engagement position is set in the other half. This means that, in FIG. 1, when the feed rings R ₁ and R ₂ are engaged with one half of the screw shaft S and the feed rings R ₃ and R ₄ are engaged with the other half, the respective The pressing force applied to the engagement position of the feed rings R _{1 to} R ₄ generates a rotational moment in the same direction in the axial direction of the screw shaft S, so that the engagement state of each of the feed rings R _{1 to} R ₄ is well maintained. This is because there is a possibility that it will disappear.

Further, in the above embodiment, the configuration including the four feed rings R _{1 to} R ₄ has been described.
The motion conversion device 1 according to the present invention may be configured to include five or more feed rings. In this case, the feed rings provided in excess of four are assembled into one of the two sets, and the engagement position is set so as to be circumferentially aligned with one of the two feed rings in the set. And said 2
It does not belong to any of the sets, and the engagement position may be set separately from these.

FIG. 4 is an explanatory diagram showing an example of the configuration of a motion conversion device including _six feed rings R _{1 to} R ₆ . In this figure, six feed rings R _{1 to} R ₆ are divided into two sets, and the first set of three R ₁ , R ₂ , R ₃ engagement positions a ₁ , R ₃ .
a ₂ and a ₃ are set such that a ₁ and a ₃ and a ₂ are radially opposed to each other, and a _second set of three R ₄ , R ₅ , R
₆ engaged position a ₄ of the a _5, a _6, a ₄ and a ₆ and a ₅
Are set so as to oppose each other in the radial direction, and the engagement positions a ₄ , a ₅ , and a _{6 correspond} to the engagement positions a of the first set.
_The position is set so as to be shifted in the circumferential direction with respect to ₁ , a ₂ and a ₃ . In this figure, the feed ring R
It is not shown of the holding tube which holds the ₁ to R _6.

FIG. 5 is a partially cutaway front view showing the structure of a main part of a power steering device provided with the motion conversion device according to the present invention. The rotation of the steering assist motor 3 is defined as a screw shaft S. The motion conversion device 1 according to the present invention is used to transmit the motion to the rack shaft 2 and move the rack shaft 2 in the axial direction.

The rack shaft 2 is supported inside a cylindrical rack housing 20 so as to be movable in the axial direction and extends in the left-right direction of the vehicle body (not shown). Both ends of the protruding rack shaft 2 are connected to unillustrated steering wheels (generally left and right front wheels) via respective tie rods. Rack housing
A pinion housing 21 is connected to an intermediate part of the pinion 20 at an axis thereof, and a pinion shaft 22 is supported inside the pinion housing 21 so as to be rotatable around the axis. In FIG. 5, the pinion shaft 22 has only a protruding end protruding upward from the pinion housing 21. The pinion shaft 22 is connected to a steering wheel (steering wheel) (not shown) via the protruding end, and is operated in accordance with the operation of the steering wheel for steering. It is designed to rotate around an axis.

A pinion (not shown) is integrally formed below a pinion shaft 22 extending inside the pinion housing 21. Further, rack teeth 23 are formed on the rack shaft 2 supported in the rack housing 20 over an appropriate length including a crossing position with the pinion housing 21, and mesh with the pinion below the pinion shaft 22. It is. Thus, the rotation of the pinion shaft 22 accompanying the operation of the steering wheel is converted into the movement of the rack shaft 2 in the axial length direction by the meshing of the pinion and the rack teeth 23, and the rotation of the rack shaft 2 in the rack housing 20 is further performed. The movement is transmitted to the left and right steering wheels via the tie rods, and a rack and pinion type steering mechanism is constructed in which these are steered according to the operation of the steering wheels.

The steering assist motor 3 for assisting the steering performed as described above has a cylindrical shape integrally formed by expanding the middle part of the rack housing 20 surrounding the rack shaft 2 over a suitable length. A motor housing 30 having a stator 31 fixed to the inner peripheral surface of the motor housing 30 and a rotor 32 coaxially arranged inside the stator 31;
It is configured as a phase brushless motor. Rotor 32
Is constituted by holding the magnetic poles 33 facing each other on the outer periphery of a cylindrical body having an inner diameter larger than the outer diameter of the rack shaft 2 with a slight gap on the inner surface of the stator 31. The ball bearings 34 and 35 are rotatably supported around the axis of the motor housing 30, and rotate in both forward and reverse directions in accordance with energization of the stator 31.

The rotation of the motor 3 generated as described above is converted into the movement of the rack shaft 2 in the axial direction by the operation of the motion converter 1 according to the present invention, which is provided on one side of the rotor 32 as a rotating member. It is made to be transmitted. FIG.
FIG. 2 is an enlarged sectional view of the vicinity of a component of the motion conversion device 1.

The motion converting device 1 is provided with the holding cylinder A and the four feed rings R _{1 to} R ₄ held inside the holding cylinder A as described above. The holding cylinder A is rotatably supported on an extension of the motor housing 30 on the same side by a four-point contact ball bearing 13 integrally formed with an intermediate part thereof as an inner ring. The motor 3 is coaxially connected via a connecting bracket 36 (see FIG. 1), and rotates coaxially with the rack shaft 2 according to the rotation of the motor 3. A screw groove S ₁ having a semicircular cross section is provided on the outer periphery of the rack shaft 2 as shown in FIG.
And is formed over a predetermined length range including the inside of the.

The feed rings R _{1 to} R held by the holding cylinder A
Reference numeral ₄ denotes a ball bearing which holds a number of balls between the outer ring and the inner ring and has an inner diameter sufficiently larger than the outer diameter of the rack shaft 2 inserted therein. And is held with an axis inclined with respect to. The inner peripheral surface of the inner ring of each feed rings R ₁ to R _4, semicircular engaging protrusion is circumferentially provided corresponding to the cross section of the screw groove S ₁ of the rack shaft 2 periphery.

The angle of inclination of the axis of the feed ring R ₁ to R ₄ are equal to the lead angle of the thread groove S _1, in the circumferential position where the inclination of each coincides with the inclination of the thread groove S _1, each of are engaged with the screw groove S ₁ through the engaging projection provided around the inner ring. The engagement positions of these feed rings R _{1 to} R ₄ are such that two (R ₁ , R ₂ ) on one side are a first set and two (R ₃ , R ₄ ) on the other side are a second set. As a set, it is set on the circumference of the rack shaft 2 as the screw shaft S as described in FIGS. 1 and 3.

In FIG. 6, the engagement positions a _{1 to} a ₄ of the feed rings R _{1 to} R ₄ are indicated by circles on the front side of the drawing.
Those on the back side are indicated by ●, respectively, and the engagement positions a ₁ , a 1 of the first set of feed rings R ₁ , R ₂ as shown in the figure.
_2, one front side, the other is set at a position opposed to radially In the rear side, a second set of feed ring R _3, R ₄ engaged position a _3, a ₄ also Similarly, one is on the front side, the other is on the back side, and is set at a position facing the radial direction. Further, the engagement positions a ₃ and a ₄ of the second set are the same as those of the first set. For the engagement positions a ₁ and a ₂ ,
It is clear that the offset is set in the circumferential direction.

In the motion conversion device 1 configured as described above, the holding cylinder A rotates around the axis in accordance with the rotation of the steering assist motor 3, and is held inside the holding cylinder A with this rotation. The four feed rings R _{1 to} R ₄ roll along the thread groove S ₁ on the outer periphery of the rack shaft 2 with which the respective inner rings are engaged. Due to this rolling, the engagement positions a ₁ -a of the feed rings R ₁ -R ₄ are applied to the rack shaft 2 as shown in FIG.
_{In 4} , a frictional force F is applied along the thread groove S ₁ ,
The screw axis S is moved by the axial component force F ₁ to the press has been axial direction of the frictional force F.

By the operation of the motion conversion device 1 as described above,
The rotation of the steering assisting motor 3 is converted into a movement in the axial direction of the rack shaft 2 inside the rack housing 20, and this movement is transmitted to left and right steering wheels via a tie rod (not shown). That is, the steering performed as described above in accordance with the operation of the steering wheel is assisted by the generated force of the motor 3.

At this time, radial loads are applied to the rack shaft 2 in various directions by the action of an external force such as a road surface reaction force applied to the steering wheel. In the motion conversion device 1 according to the present invention, the four Engagement position a ₁ of the feed rings R _{1 to} R ₄
By ~a ₄ has been set as described above, engagement of the feed rings R ₁ to R ₄ is the is satisfactorily maintained without also impaired under the action of the radial load, the motion converting the aforementioned It can be performed reliably.

FIGS. 5 and 6 show an example of application to a rack-and-pinion type power steering apparatus in which the rotation of a steering assist motor 3 is transmitted to a rack shaft 2 serving as a screw shaft S. However, the motion conversion device 1 according to the present invention is not limited to this, and various types of power are configured to transmit the rotation of the steering assist motor to the steering shaft that performs steering by moving in the axial direction. Applicable to steering devices,
Furthermore, it is needless to say that the present invention can be applied not only to the power steering apparatus but also to any power transmission system that requires a conversion of motion from rotary motion to linear motion or from linear motion to rotary motion.

[0052]

As described above in detail, in the motion converting apparatus according to the present invention, the feed ring held by the holding cylinder and engaged with the thread groove on the outer periphery of the screw shaft is assembled into two sets each including two or more feed rings. Since the engagement positions of these feed rings are set at positions facing each other in the radial direction in each set, and are set so as to be shifted in the circumferential direction of the screw shaft between the two sets, various positions are set with respect to the screw shaft. Under the action of the radial load applied in the direction of, it is possible to keep the engagement state of all the feed rings in good condition, and to stably perform the motion conversion from rotary motion to linear motion or vice versa. Becomes possible.

In the motion converter according to the second aspect of the present invention, the screw shaft is movably supported in the axial direction, and the holding cylinder is supported so as to be rotatable around the axis. It is necessary to convert the rotational motion into linear motion, such as a power steering device that converts the rotation of the steering assist motor into the axial length of the steering shaft. It can be conveniently used for various applications.

In the motion converter according to the third aspect of the present invention, at least an engagement position is set on the other half of the screw shaft between two feed rings whose engagement positions are set on one half of the screw shaft. Since one feed ring is sandwiched and the feed ring engaged with one half and the feed ring engaged with the other half are not concentrated on the same side in the axial direction, each feed ring is provided. The rotational force does not act in the axial direction of the screw shaft due to the pressing force applied to the engaging position, and the good engagement state is maintained without being impaired.

Further, in the motion conversion device according to the fourth aspect of the present invention, since the rolling bearing is used as the feed ring, the motion conversion device capable of quiet operation with low operation noise can be simply constructed. It has excellent effects.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a configuration of a motion conversion device according to the present invention.

FIG. 2 is an operation explanatory diagram of the motion conversion device according to the present invention.

FIG. 3 is an explanatory diagram of an engagement position of a feed ring in the motion conversion device according to the present invention.

FIG. 4 is an explanatory diagram showing a configuration example of a motion conversion device according to the present invention including six feed rings.

FIG. 5 is a partially cutaway front view showing a configuration of a main part of a power steering device provided with the motion conversion device according to the present invention.

6 is an enlarged sectional view of the vicinity of a component of a motion conversion device in the power steering device shown in FIG. 5;

FIG. 7 is a perspective view schematically showing a configuration of a conventional motion conversion device.

FIG. 8 is an explanatory diagram of a problem of the conventional motion conversion device.

[Explanation of symbols]

1 motion converter 2 rack shaft 3 motor A holding cylinder a ₁ ~a ₆ engaged position R ₁ to R ₆ feed ring S screw shaft S ₁ thread groove

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Osamu Sano 3-5-8 Minamisenba, Chuo-ku, Osaka-shi, Osaka F-term (reference) 3D033 CA04

Claims (4)

[Claims] 1. A screw shaft having a screw groove formed on an outer peripheral surface thereof,
A holding cylinder coaxially disposed outside the screw shaft, and eccentrically held in the holding cylinder with an inclination corresponding to a lead angle of the screw groove, and the screw groove is provided at one location in a circumferential direction. A plurality of feed rings, each of which includes two or more feed rings each of which is set at a position at which an engagement position with the thread groove on the outer periphery of the thread groove is set at a position facing radially. 1, a second ring set, wherein the engagement position of the first ring set and the engagement position of the second ring set are set to be shifted in the circumferential direction of the screw shaft. Motion conversion device. 2. The screw shaft is movably supported in the axial direction, and the holding cylinder is rotatably supported around the axis. The motion conversion device according to claim 1, wherein the rotation of the holding cylinder is converted into a movement of the screw shaft in an axial direction. 3. Two feed rings, each having an engagement position set on one side half in the axial cross section of the screw shaft, and an engagement position being set on the other half between them. 3. The motion conversion device according to claim 1, wherein the at least one feed ring is disposed between the motion conversion devices. 4. The rolling ring according to claim 1, wherein the feed ring includes a rolling bearing having an outer ring fitted and fixed to the holding cylinder and an inner ring engaged with the screw groove. The motion conversion device according to the above.