Speed reduction ratio automatic switching device

A speed reduction ratio automatic switching device includes a planetary gear mechanism. The planetary gear mechanism includes a sun gear provided for an input shaft, planetary gears in mesh with an outer circumferential side of the sun gear, an internal gear in mesh with an outer circumferential side of the planetary gears, and first and second carriers made of a semi-rigid magnetic material. The first and second carriers support the planetary gears in a rotatable manner, and rotate together with the planetary gears along with revolution of the planetary gears. Each of the sun gear, the planetary gears and the internal gear is a helical gear. First and second magnets for generating a thrust force in an axial direction are provided between the first and second carriers and the internal gear.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-178335 filed on Sep. 25, 2018, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a speed reduction ratio automatic switching device capable of, at the time of transmitting a driving force to an output shaft with speed reduction, automatically switching the speed reduction ratio.

Description of the Related Art

In Japanese Patent No. 4899082, the applicant of the present application proposes a speed reduction ratio automatic switching device having a planetary gear mechanism in a housing. This speed reduction ratio automatic switching device is provided between a rotary drive source and an actuator. An input shaft of the speed reduction ratio automatic switching device is coupled to the rotary drive source, and an output shaft of the speed reduction ratio automatic switching device is coupled to the actuator. A sun gear provided for the input shaft is in mesh with three planetary gears which are in mesh with an internal gear in the housing. Further, viscous resisting substance for generating a thrust force is provided between the internal gear and the planetary gears.

Then, a rotational force inputted from the rotary drive source to the input shaft is transmitted to the planetary gears through the sun gear, and the planetary gears revolve around the sun gear on the inner circumferential side of the internal gear. As a result, carriers provided with the planetary gears and having the output shaft are rotated. In this regard, since viscous resisting substance is provided between the planetary gears and the internal gear, viscous resistance is produced between the planetary gears and the internal gear. Therefore, in the case where a load in excess of a predetermined torque is applied to the carriers, based on the rotational speed difference between the internal gear and the carriers, the internal gear moves in the input shaft direction or the output shaft direction, and the speed reduction ratio outputted from the output shaft is switched automatically.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a speed reduction ratio automatic switching device capable of switching the speed reduction ratio of the outputted rotational driving force at a suitable switching point without any changes of the switching point regardless of the ambient environment or the number of driving rotations.

According aspect of the present invention, a speed reduction ratio automatic switching device capable of automatically switching a rotational driving force inputted to an input shaft at a predetermined speed reduction ratio to output the switched rotational driving force from an output shaft is provided. The speed reduction ratio automatic switching device includes a planetary gear mechanism, a resisting element, and a braking element, and the planetary gear mechanism includes a sun gear provided for the input shaft, a planetary gear in mesh with an outer circumferential side of the sun gear, an internal gear in mesh with an outer circumferential side of the planetary gear, and a carrier made of a hysteresis material, the carrier is coupled to the output shaft, configured to support the planetary gear in a rotatable manner, and rotate together with the planetary gear along with revolution of the planetary gear. The resisting element is configured to generate a thrust force in an axial direction between the internal gear and the carrier, and the braking element is configured to restrict rotation of the internal gear when the internal gear moves in the axial direction by the thrust force, as a result of a change of output load applied to the output shaft, wherein each of the sun gear, the planetary gear, and the internal gear comprises a helical gear, and the resisting element comprises a magnet provided between the internal gear and the carrier.

In the present invention, the planetary gear mechanism of the speed reduction ratio automatic switching device is made up of the sun gear provided for the input shaft, the planetary gear in mesh with the outer circumferential side of the sun gear, the internal gear in mesh with the outer circumferential side of the planetary gear, and the carrier coupled to the output shaft, configured to support the planetary gear in a rotatable manner, and rotate together with the planetary gear along with revolution of the planetary gear, wherein each of the sun gear, the planetary gear, and the internal gear is a helical gear, and the resisting element which generates a thrust force in the axial direction between the carrier made of a hysteresis material and the internal gear is provided. The resisting element is a magnet provided between the internal gear and the carrier made of a hysteresis material.

Therefore, in the case where a load in excess of a predetermined hysteresis torque is applied to the carrier made of a hysteresis material, the internal gear moves toward the input shaft or the output shaft based on the relative rotation difference between the internal gear and the carrier, and the internal gear is locked up, and fixed. In this manner, it is possible to automatically switch the speed reduction ratio of the rotational driving force.

As a result, in comparison with the conventional speed reduction ratio automatic switching device where the viscous resisting substance such as viscous oil or grease is used between the planetary gears and the carriers, and between the planetary gears and the internal gear, since the magnetic braking force between of the magnet and the carrier is utilized, changes of the temperature, etc. in the ambient environment and performance changes due to degradation over time, etc. do not occur. Accordingly, it becomes possible to perform switching of the speed reduction ratio over the years at the stable switching point.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A speed reduction ratio automatic switching device10shown inFIGS. 1 to 3includes first and second housings (housings)12,14which can be divided in axial directions (directions indicated by arrows A and B), and a planetary gear mechanism16stored in the first and second housings12,14.

For example, the first housing12is made of metal, and has a rectangular shape in cross section. A first shaft hole18is formed at the center of one end of the first housing12, and an input shaft30described later is inserted into the first shaft hole18. A first bearing20is provided in an inner circumferential surface of the first shaft hole18to support the input shaft30in a rotatable manner.

Further, a first lock (lock)22is formed inside the first housing12, in an inner wall surface of the first housing12facing the second housing14. The first lock22can be engaged with an internal gear lock receiver (internal gear clutch)56aof an internal gear36described later. The first lock22has a circular arc shape, and protrudes in a manner that the height of the first lock22is increased gradually toward the second housing14(in the direction indicated by the arrow A) (seeFIG. 4). It should be noted that, in the case where the internal gear36described later is translated toward one end in an axial direction (direction indicated by the arrow B, the direction of the input shaft30), the internal gear lock receiver56ais engaged with the first lock22.

As in the case of the first housing12, the second housing14has a rectangular shape in cross section. A second shaft hole24is formed at the center of the other end of the second housing14, and an output shaft44described later is inserted into the second shaft hole24. A second bearing26is provided in an inner circumferential surface of the second shaft hole24to support the output shaft44in a rotatable manner.

Further, a second lock (lock)28is formed inside the second housing14, in an inner wall surface of the second housing14facing the first housing12. The second lock28can be engaged with an internal gear lock receiver (internal gear clutch)56bof the internal gear36described later. In the same manner as in the case of the first lock22, the second lock28has a circular shape, and protrudes toward the first housing12(in the direction indicated by the arrow B) in a manner that the height of the second lock28is increased gradually. It should be noted that, in the case where the internal gear36described later is translated toward the other end (in the direction indicated by the arrow A, the direction of the output shaft44), the internal gear lock receiver56bis engaged with the second lock28.

As shown inFIGS. 1 to 3 and 5, the planetary gear mechanism16includes a sun gear32formed at an end of the input shaft30, three planetary gears34a,34b,34cprovided concentrically with the sun gear32, spaced from one another at an angle of about 120°, in mesh with the sun gear32to revolve around the sun gear32and rotate on their own axes, the internal gear36provided around the planetary gears34a,34b,34c, and a pair of first and second carriers (carriers)38,40holding the planetary gears34a,34b,34c.

The sun gear32is a helical gear formed at the other end of the input shaft30, and the input shaft30is coupled to a rotary drive shaft of a rotary drive source (not shown) through a coupling member (not shown).

For example, first and second carriers38,40are made of a semi-rigid magnetic material (hysteresis material), and dividable into two parts in axial directions (directions indicated by the arrows A and B). The first and second carrier38,40include a cylindrical inner part42having a large diameter, and the output shaft44protruding from the other end of the inner part42in the axial direction (indicated by the arrow A). The inner part42is provided to bridge between the first carrier38and the second carrier40. The output shaft44is formed in the second carrier40. It should be noted that, for example, the semi-rigid magnetic material has coercivity in the range of 10 to 100 Oe (800 to 8000 A/m).

Further, three gear storage holes46spaced from one another at equal angles of 120° along the circumferential direction are opened in the inner part42, and the planetary gears34a,34b,34care inserted into the gear storage holes46, respectively.

Further, the outer circumferential surface of the inner part42made up of the first and the second carrier38,40, has a substantially constant diameter in the axial directions (indicated by the arrows A and B).

The output shaft44is provided coaxially with the input shaft30at the center of the other end of the inner part42, and inserted into the second shaft hole24of the second housing14. In this manner, the output shaft44is supported in a rotatable manner by the second bearing26(seeFIG. 3).

For example, each of the planetary gears34a,34b,34chas a cylindrical shape having teeth of a helical gear in its outer circumferential surface. The planetary gears34a,34b,34care inserted into the gear storage holes46, respectively, in a manner that the axial lines of the planetary gears34a,34b,34care oriented substantially in parallel with the axial lines of the first and second carriers38,40, and the planetary gears34a,34b,34cpivotally supported by the first and second carriers38,40in a rotatable manner using pins48.

Further, the internal gear36having a large diameter is provided on the outer circumferential sides of the planetary gears34a,34b,34c, around the planetary gears34a,34b,34c. Inner teeth50of the internal gear36described later are in mesh with the planetary gears34a,34b,34c.

For example, the internal gear36has an annular shape, and the outer circumferential surface of the internal gear36faces the inner surfaces of the first and second housings12,14, and has inner teeth50formed at the center in the inner circumferential surface, and in mesh with the planetary gears34a,34b,34c. The inner teeth50are in the form of a helical gear, and protrude radially inward from the inner circumferential surface of the internal gear36. Front ends of the inner teeth50inserted into the gear storage holes46are in mesh with the planetary gears34a,34b,34c, respectively.

Further, a plurality of internal gear lock receivers56a,56bare curved and protrude from both ends of the internal gear36in the axial direction (indicated by the arrows A and B). The internal gear lock receivers56a,56bare protrusions curved in the circumferential direction corresponding to the first and second locks22,28of the first and second housings12,14. That is, the inner gear lock receivers56a,56b, and the first and second locks22,28function as inner gear lock elements.

Further, the torsion angle of the helical gears of the sun gear32, the planetary gears34a,34b,34c, and the internal gear36is not limited specially, but preferably in the range of 30° to 40°.

First and second magnets52,54are provided on both sides of the inner teeth50in the axial direction, in the inner circumferential surface of the internal gear36, and provided to face the outer circumferential surfaces of the first and second carriers38,40, respectively. As shown inFIG. 6, each of the first and second magnets52,54comprises a multipole permanent magnet including first magnet parts58each having an inner circumferential side magnetized to the south (S) pole and an outer circumferential side magnetized to the north (N) pole, and second magnet parts60each having an inner circumferential side magnetized to the N-pole and an outer circumferential side magnetized to the S-pole. The first magnet parts58and the second magnet parts60are provided alternately along a circumferential direction.

Each of the first and second magnets52,54has an annular shape formed by arranging the two first magnet parts58and the two second magnet parts60having a circular shape in cross section alternately adjacent to each other in the circumferential direction. The first and second magnets52,54are fixed to the inner circumferential surface of the internal gear36by an adhesive, etc. In this regard, the first and second magnets52,54are provided in the state where clearance having a predetermined interval is formed between the inner circumferential surfaces of the first and second magnets52,54and the outer circumferential surfaces of the first and second carriers38,40(seeFIG. 3).

Further, the first and second magnets52,54have substantially the same shape and structure, and are provided in a manner that the magnetic flux of the first and second magnets52,54is oriented in the radial direction. The four permanent magnets are provided in a manner that the S-pole and the N-pole are positioned adjacent to each other.

It should be noted that the first and second magnets52,54are not limited to the case where each of the first and second magnets52,54is made up of the two first magnet parts58and the two second magnet parts60(four magnet parts in total). The first and second magnets52,54may have a single annular structure magnetized to have different polarities in the circumferential direction, or may have structure where four or more divided magnet parts (the first and second magnet parts58,60) are arranged adjacent to each other in the circumferential direction.

The speed reduction ratio automatic switching device10according to the embodiment of the present invention basically has the above structure. Next, assembling of the speed reduction ratio automatic switching device10will be described briefly.

Firstly, in the state where the first and second carriers38,40are divided in the axial direction, after the three planetary gears34a,34b,34care inserted into the gear storage holes46, to support the planetary gears34a,34b,34cin a rotatable manner through the pins48, the first and second carriers38,40are moved closer to each other in the axial direction, and brought into contact with each other. The first and second carriers38,40are coupled together using tightening bolts (not shown).

Next, the sun gear32of the input shaft30is inserted into the center of the first carrier38, and brought into mesh with the planetary gears34a,34b,34c. In this state, the input shaft30is inserted into the first shaft hole18of the first housing12to support the input shaft30by the first bearing20. Further, the output shaft44is inserted into the second shaft hole24of the second housing14to support the output shaft44by the second bearing26. Then, the internal gear36is provided on the outer circumferential side of the first and second carriers38,40, and the inner teeth50of the first and second carriers38,40are brought into mesh with the planetary gears34a,34b,34c.

It should be noted that the first and second magnets52,54are attached to the inner circumferential surface of the internal gear36beforehand, and the first and second magnets52,54are positioned to face outer circumferential surfaces of the first and second carriers38,40with clearance having a predetermined interval in the radial direction.

Finally, in the state where the input shaft30is inserted into the first housing12and the output shaft44is inserted into the second housing14, the first housing12and the second housing14are moved closer to each other in the axial direction, and brought into contact each other, and then, coupled together by tightening bolts62(seeFIG. 1) to finish assembling of the speed reduction ratio automatic switching device10storing the planetary gear mechanism16in the first and second housings12,14.

Next, operation of the speed reduction ratio automatic switching device10assembled in the manner as described above will be described.

Firstly, a rotational driving force from a rotary drive source (not shown) is transmitted to the sun gear32through the input shaft30. In the case described below, when viewed in a direction from the input shaft30to the output shaft44in the direction indicated by the arrow A inFIG. 3, as shown inFIG. 5, the rotational driving force rotates the input shaft30and the sun gear32clockwise (in a direction indicated by an arrow C1).

When the rotational force at low load is transmitted to the input shaft30, by the rotational driving force transmitted from the sun gear32, the three planetary gears34a,34b,34crevolve around the sun gear32clockwise (in a direction indicated by an arrow D1) without rotating about their own axes. Accordingly, the internal gear36revolves clockwise (in a direction indicated by an arrow E1) as well. At this time, the magnetic flux guided from the first and second magnets52,54provided for the internal gear36to the first and second carriers38,40produce magnetic friction between the internal gear36and the first and second carriers38,40. By the magnetic braking force, the internal gear36and the first and second carriers38,40are combined together.

Therefore, by revolution of the internal gear36, the first and second carriers38,40rotate together, and the rotational driving force inputted from the input shaft30is outputted from the output shaft44to the outside.

That is, in the case where a low load which is the rotational driving force inputted from the input shaft30is not more than a predetermined hysteresis torque, the internal gear36and the first and second carriers38,40are coupled and rotate together by the magnetic braking force generated by the first and second magnets52,54.

Next, in the case where a high load which in excess of the predetermined hysteresis torque is applied to the second carrier40through the output shaft44, the planetary gears34a,34b,34cdo not revolve by rotation of the sun gear32, and the planetary gears34a,34b,34crotate about their own axes counterclockwise (in a direction indicated by an arrow D2) opposite to rotation of the sun gear32, and the internal gear36in mesh with the planetary gears34a,34b,34crotates counterclockwise (in a direction indicated by an arrow E2).

That is, when the load which exceeds the hysteresis torque of the first and second magnets52,54provided in the internal gear36and the first and second carriers38,40made of a hysteresis material, by the load applied to the output shaft44, the second carrier40formed integrally with the output shaft44and the first carrier38coupled to the second carrier40are decoupled from the internal gear36which has been coupled (joined) to the first and second carriers38,40by the magnetic braking force, and the planetary gears34a,34b,34cand the internal gear36in the form of helical gears generate a thrust force in a direction of the tooth trace formed helically, and the internal gear36moves toward the output shaft44in the axial direction (indicated by the arrow A).

As a result, the internal gear lock receiver56bof the internal gear36and the second lock28of the second housing14are engaged with each other. Accordingly, the internal gear36is locked, and further movement and rotation of the internal gear36are restricted. That is, the internal gear lock receiver56bof the internal gear36and the second lock28of the second housing14function as braking elements capable of restricting rotation of the internal gear36.

In this manner, since the internal gear36is locked, while the planetary gears34a,34b,34crotate on their own axes counterclockwise (in the direction indicated by the arrow D2) by rotation of the sun gear32on its own axis clockwise (in a direction indicated by an arrow C1), and the internal gear36, and the first and second carriers38,40revolve around the sun gear32clockwise (in the direction indicated by the arrow D1). As a result, the decelerated rotation speed and the increased torque are transmitted to the output shaft44of the second carrier40. It should be noted that the outputted torque is a force in correspondence with the gear ratio between the planetary gears34a,34b,34cand the internal gear36.

Next, in order to unlock the internal gear36, the input direction of the rotational driving force inputted from the input shaft30is reversed. That is, since the sun gear32is rotated counterclockwise (in the direction indicated by the arrow C2) through the input shaft30, while the planetary gears34a,34b,34crotate on their own axes clockwise (in the direction indicated by the arrow D1) by rotation of the sun gear32, the internal gear36and the first and second carriers38,40revolve on their own axes counterclockwise (in the direction indicated by the arrow E2). Then, when the sun gear32starts to rotate counterclockwise (in the direction indicated by the arrow C2), the internal gear36and the first and second carriers38,40rotate together by the magnetic braking force. As shown inFIG. 1, the lockup is released, and the internal gear36and the first and second carriers38,40return to their initial positions.

That is, after the internal gear36is unlocked, when the sun gear32is rotated counterclockwise (in the direction indicated by the arrow C2), the planetary gears34a,34b,34crotate counterclockwise (in the direction indicated by the arrow D2) without rotating on their own axes, and likewise, the internal gear36rotates counterclockwise on their own axes (in the direction indicated by the arrow E2).

Although the embodiment has been described in connection with the case where the input shaft30and the sun gear32rotates clockwise (in the direction indicated by the arrow C1), also in the case where the input shaft30and the sun gear32rotate counterclockwise (in the direction indicated by the arrow C2), the same operation and advantages are obtained.

That is, in the case where the input shaft30and the sun gear32rotate counterclockwise (in the direction indicated by the arrow C2), and in this state, a high load in excess of the predetermined hysteresis torque is applied to the first and second carriers38,40through the output shaft44, the internal gear lock receiver56aof the internal gear36and the first lock22are engaged with each other, and the internal gear36is locked. The internal gear lock receiver56aof the internal gear36and the first lock22of the first housing12function as braking elements capable of restricting rotation of the internal gear36.

Moreover, by reversing the orientation of the rotational driving force to rotate the sun gear32clockwise (in the direction indicated by the arrow C1) through the input shaft30, the internal gear36is unlocked, and returns to the initial position shown inFIG. 1.

On the other hand, when the internal gear36is locked, by decreasing the load applied to the output shaft44, it is possible to unlock the internal gear36. That is, in the state where the load applied to the output shaft44is decreased, by clockwise rotation of the sun gear32(in the direction indicated by the arrow C1), the planetary gears34a,34b,34crotate counterclockwise (in the direction indicated by the arrow D2) on their own axes, and at the same time, the internal gear36, and the first and second carriers38,40revolve together clockwise (in the direction indicated by the arrow E1), and the internal gear36in mesh with the planetary gears34a,34b,34crotate clockwise (in the direction indicated by the arrow E1).

Since the magnetic braking force is generated between the internal gear36and the first and second carriers38,40, and the planetary gears34a,34b,34cand the internal gear36are helical gears, a thrust force is generated in the direction of the tooth trace formed helically on the gear cylindrical surface.

Further, as shown inFIG. 4, since the internal gear lock receiver56aand the first lock22have a shape of a curve drawn in the circumferential direction, when the internal gear36rotates clockwise (in the direction indicated by the arrow E1), a force is applied in addition to the thrust force, in a direction opposite to the direction indicated by the arrow A, and the internal gear36is translated. Specifically, the internal gear36rotates clockwise (in the direction indicated by the arrow E1), and at the same time, the internal gear36is translated toward the input shaft30. The internal gear lock receiver56bis spaced from the second lock28, and the internal gear36is unlocked.

As described above, in the embodiment of the present invention, in the planetary gear mechanism16of the speed reduction ratio automatic switching device10, helical gears are used as the sun gear32, the planetary gears34a,34b,34cand the internal gear36, and the first and second magnets52,54are provided between the first and second carriers38,40and the internal gear36. The first and second carriers38,40are made of a magnetic material (hysteresis material) and hold the planetary gears34a,34b,34c.

In the structure, in the case where a high load in excess of the predetermined hysteresis torque is applied to the first and second carriers38,40through the output shaft44, the first and second carriers38,40which have been coupled to the internal gear36by the magnetic braking force is decoupled from the internal gear36, the planetary gears34a,34b,34cand the internal gear36comprising helical gears generate the thrust force in the direction of the tooth trace formed helically, and the internal gear36is translated toward the input shaft30or the output shaft44in the axial direction. In this manner, it is possible to automatically switch the speed reduction ratio of the rotational driving force outputted from the output shaft44.

As a result, in comparison with the conventional reduction ratio automatic switching device where viscous resisting substance such as viscous oil or grease is provided between the planetary gears and the carriers, and between the planetary gears and the internal gear, since the magnetic braking force generated by the first and second magnets52,54provided between the first and second carriers38,40and the internal gear36is utilized, changes of the ambient environment such as temperature, humidity, etc. and performance changes due to degradation over time, etc. do not occur. Accordingly, it becomes possible to stably perform switching of the speed reduction ratio over the years at the desired switching point regardless of the ambient environment and/or the number of driving rotations of the speed reduction ratio automatic switching device10.

Further, even in the case where the load applied to the output shaft44is changed, it becomes possible to unlock the internal gear36from the first housing12or the second housing14, and switch the speed reduction ratio automatically. Thus, it is possible to output the driving force at low torque and at high speed.

The above planetary gear mechanism16has structure where the first and second magnets52,54are provided on both sides in the axial direction, for the inner teeth50of the internal gear36. However, the present invention is not limited in this respect. For example, only one of the first magnet52or the second magnet54may be provided. It may be possible to design the first magnet52and the second magnet54to have different magnetic characteristics.

The speed reduction ratio automatic switching device according to the present invention is not limited to the above embodiment. It is a matter of course that various structures may be adopted without departing from the gist of the present invention.