Supporting structure of shaft of reduction gear

A first shaft at which a first gear is provided is supported by an angular roller bearing in which a pair of roller rows and which is rolling elements incorporated in a back-to-back combination, and a midpoint of a projection range of a range where the first gear and a second gear mesh with each other on the first shaft is made to exist in a span of a working point of the pair of roller rows of the angular roller bearing on the pinion shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a supporting structure of a shaft of a reduction gear.

Priority is claimed on Japanese Patent Application No. 2008-262117, filed Oct. 8, 2008, the content of which is incorporated herein by reference.

2. Description of Related Art

A structure, as shown inFIG. 4, which supports a pinion shaft14at the tip of which a bevel pinion12is formed in a reduction gear10is disclosed in Japanese Unexamined Patent Application Publication No. 2006-207828 (FIG. 2). The reduction gear10includes a speed reduction mechanism13(only a portion is shown) having the inscribed meshing planetary gear structure at its preceding stage, and the pinion shaft14is connected with a carrier16which is an output shaft of the speed reduction mechanism13at the preceding stage via a spline18. Further, the pinion shaft14is supported by a casing27by a tapered roller bearing24disposed almost at the center of the pinion shaft14, and a tapered roller bearing26disposed at a cylindrical portion16A of the carrier16via the carrier16. That is, the load in a radial direction and the load in a thrust direction applied to the pinion shaft24are shared and received by both the tapered roller bearings24and26.

On the other hand, a reduction gear28, as shown inFIG. 5, which supports a bevel pinion32integrated with a joint shaft30by one pair of ball bearings34and36is disclosed in Japanese Unexamined Patent Application Publication No. 2007-211920 (FIG. 1). The axial movement of one pair of ball bearings34and36is restrained by a stepped portion38A of the casing38, a stage portion30A of the joint shaft30, and a retaining ring40. In this reduction gear28, the thrust loads in an A direction and in a B direction generated in the bevel pinion32are received by one pair of ball bearings34and36whose axial movement have been restrained.

As such, when a shaft which generates a thrust load, especially during operation, like a shaft including a bevel pinion, is supported by the casing of the reduction gear, a supporting structure which can simultaneously cope with the load in the radial direction and the load in the thrust direction is required.

Therefore, a configuration in which the shaft is supported at both ends by one pair of bearings in order to receive the radial load and a configuration in which the axial movement of an inner ring or outer ring of a bearing is restrained in order to receive the thrust load are required, and it is necessary to increase the span of one pair of bearings in order to secure stable support. As a result, there is a problem in that axial length becomes large.

SUMMARY OF THE INVENTION

It is desirable to reduce the burden on a bearing even if a shaft of a reduction gear is, for example, a shaft to which both the loads in a radial direction and in a thrust direction are applied in supporting of the shaft, thereby enabling the shaft to be supported by a casing in a stable state without increasing the axial length of the reduction gear.

According to an embodiment of the invention, there is provided a supporting structure of a shaft of a reduction gear having within a casing a speed reduction mechanism formed by the meshing between a first gear provided at the tip of a first shaft and a second gear provided at a second shaft. The supporting structure includes an angular roller bearing which supports the first shaft provided with the first gear. The angular roller bearing has a pair of roller rows which is rolling elements incorporated in a back-to-back combination. The first shaft at which the first gear is provided is supported by an angular roller bearing in which a pair of roller rows which is rolling elements incorporated in a back-to-back combination. A midpoint of a projection range of a range where the first gear and the second gear mesh with each other on the first shaft is made to exist in a working point span of the pair of roller rows of the angular roller bearing on the first shaft.

The reduction gear of an embodiment of the invention has a speed reduction mechanism formed by the meshing between a first gear provided at the tip of a first shaft and a second gear provided at the second shaft. In the invention, the first shaft of the speed reduction mechanism is supported by an angular roller bearing in which “roller rows” which is rolling elements incorporated in a back-to-back combination. In addition, the angular roller bearing itself may be a single bearing having the pair of roller rows in a double row type, and may be two bearings which have the pair of roller rows separately. In the invention, a midpoint of a projection range of a range where the first gear and the second gear mesh with each other on the first shaft, in short, a “base point (working point)” where the load from the first gear is applied to the first shaft is made to exist in a working point span of the pair of roller rows of the angular roller bearing on the first shaft. Accordingly, the burden on the bearing can be lightened, and the first shaft can be supported in an extremely stable state (for example, even if the axial span of the pair of roller rows is small), by making the base point which the load from the first gear is applied fall within the span of the line of action of the pair of roller rows of the angular roller bearing.

In addition, when an embodiment of the invention is applied to the support of a shaft to which loads are applied in both the radial direction and the thrust direction like a shaft in which an orthogonal gear, such as a bevel pinion or a hypoid pinion, is incorporated, particularly remarkable effects are obtained. However, the shaft to which the invention is applied is not necessarily a shaft to which both loads are always applied.

According to an embodiment of the invention, it is possible to reduce the burden on a bearing even if the shaft of the reduction gear is, for example, a shaft to which the loads in the radial direction and the thrust direction are applied, thereby enabling the shaft to be supported by the casing in a stable state without increasing the axial length of the reduction gear.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the invention will be described in detail with reference to the drawings.

FIG. 1is a sectional view of a reduction gear to which an example of a supporting structure of a shaft of the reduction gear according to the invention has been applied, andFIG. 2is an enlarged view of essential parts ofFIG. 1.

A reduction gear GM1has a speed reducer G1and a motor M1connected with the speed reducer G1.

The speed reducer G1includes a speed reduction mechanism42of an inscribed meshing planetary gear structure at its preceding stage, and an orthogonal speed reduction mechanism44composed of a bevel gear set at its subsequent stage. Accordingly, the reduction gear GM1constitutes an orthogonal reduction gear in which the axis of an output shaft of the speed reducer G1is orthogonal to the axis of the motor M1.

The speed reduction mechanism42of the inscribed meshing planetary gear structure at the preceding stage includes eccentric bodies46and47incorporated into the outer periphery of a motor shaft43of the motor M1via a key45, external gears50and51rockably and rotatably incorporated into the outer peripheries of the eccentric bodies46and47via rollers48and49, and an internal gear52with which the external gears50and51internally mesh. The internal gear52is integrated with a casing54A at the preceding stage, and the internal teeth thereof are constituted by pins52A. The external gears50and51and the internal gear52have a slight difference in the number of teeth of, for example, about one to four. The speed reduction mechanism42of the inscribed meshing planetary gear structure outputs the relative rotation between the external gears50and51and the internal gear52to the orthogonal speed reduction mechanism44at the subsequent stage via a carrier56which is an output member via an inner pin55.

The orthogonal speed reduction mechanism44at the subsequent stage includes a pinion shaft (first shaft)60equivalent to the input shaft thereof. A bevel pinion (the first gear)62is directly formed at the tip of the pinion shaft60. The bevel pinion62meshes with a bevel gear (second gear)64. The bevel gear64is incorporated into an output shaft (second shaft)76.

The pinion shaft60is rotatably supported by the casing54(54C) by a double-row type angular roller bearing B1. The double-row type angular roller bearing B1is composed of an inner ring66, a first angular roller row68A and a second angular roller row68B disposed on the same plane, and an outer ring70.

The outer ring70of the angular roller bearing B1is fixed to the casing54C at the subsequent stage via a bolt71. Outer-ring-side first and second V-grooves (outer-ring-side first and second transfer surfaces)70A and70B of with an angle of 90° are bored at the inner periphery of the outer ring70. Inner-ring-side first and second V-grooves (inner-ring-side first and second transfer surfaces)66A and66B of with an angle of 90° are bored at the outer periphery of the inner ring66of the angular roller bearing B1. The first angular roller row (rolling element row)68A of the angular roller bearing B1is incorporated into a space on the first transfer surfaces66A and70A one by one via pockets72A provided in the outer ring70. The second angular roller row (rolling element row)68B of the angular roller bearing B1is incorporated into a space on the second transfer surfaces66B and70B one by one via pockets72B provided in the outer ring70. The incorporation aspect of the first and second angular roller rows68A and68B is so-called a back-to-back combination. In this embodiment, since the contact angles θ1and θ2of the first and second angular roller rows68A and68B are set to 45 degrees, respectively, as shown by a two-dot chain line inFIG. 1, lines of action Li1and Li2are formed at an angle of about 90 degrees from the first angular roller row68A (passing through the center of each roller), and lines of action Li3and Li4are formed at an angle of about 90 degrees from the second angular roller row68B (passing through the center of each roller). The reason why the contact angles θ1and θ2are set to 45 degrees is because it was considered that cross-rollers can be diverted, and stress balances in a radial direction and in a thrust direction are also good. Although every two lines of action Li1and Li2, and lines of action Li3and Li4are representatively depicted in the drawing, respectively, the lines of action exist about respective rollers of the first and second angular roller rows68A and68B. When the distance (span between working points P1and P2on the pinion shaft60) between points (working points) P1and P2where the lines of action Lit to Li4cross the axis O1of the pinion shaft60is set to L1, a midpoint (base point to which the load of meshing is applied) P3of a projection range R1of an meshing range E1between the bevel pinion62and the bevel gear64on the pinion shaft60is designed so as to exist within the distance L1. Since the first and second angular roller rows68A and68B are incorporated by a back-to-back combination, and the contact angles θ1and θ2thereof are set to 45°, the working points P1and P2are located at the other diagonal vertexes of a square having the position of the outer ring70of the angular roller bearing B1as diagonal vertexes. Reference numeral L1in the drawing is equivalent to the span between the working points P1and P2.

In addition, the axial movement of the pinion shaft60of the orthogonal speed reduction mechanism44at the subsequent stage toward the bevel pinion62is regulated by a groove60A formed at an outer periphery of the pinion shaft60, and a retaining ring74fitted into the groove60A. As the retaining ring74is pinched between the inner ring66and the carrier56, the axial movement thereof is regulated. In addition, the axial movement of the pinion shaft60towards the side opposite to the pinion is regulated as an end62A of the bevel pinion62abuts on the inner ring66. Further, the bidirectional axial movement may be regulated only by the retaining ring74as long as a gap can be filled up with high precision.

The pinion shaft60has a knurled portion60B on the side of the preceding stage speed reduction mechanism, and the knurled portion60B is press-fitted into the inner periphery of a cylindrical portion56A of the carrier56at the preceding stage. The carrier56is a rotational member (output member of the preceding stage speed reduction mechanism) which rotates at the same rotating speed coaxially with the pinion shaft (first shaft)60, and the inner ring66of the angular roller bearing B1is directly fixed via a bolt72. In addition, a portion of the carrier56is supported by the motor shaft43via a bearing69. In this embodiment, as mentioned above, the pinion shaft60is press-fitted into the inner ring66of the angular roller bearing B1. Therefore, the carrier56, the pinion shaft60, and the inner ring66are eventually integrated as a large rotational member as a whole. In addition, if priority is given to ease of assembling, transmission of power is sufficiently allowed only by the knurled portion60B. Therefore, the fitting between the pinion shaft60and the inner ring66may not be necessarily press fitting. In this case, the radial load and thrust load applied to the pinion shaft60are transmitted to the inner ring66of the angular roller bearing B1in the path of the knurled portion60B→carrier56→bolt72, and are received by the inner ring66. Accordingly, the precision of the portion of the pinion shaft60which faces the inner ring can be relaxed, and machining cost can be reduced.

An output shaft76of the orthogonal speed reduction mechanism44is supported by a cross-roller bearing B2. The cross-roller bearing B2is mainly composed of an inner ring80, an outer ring82, and cross-rollers (rolling elements)84disposed between the inner ring80and the outer ring82.

The bevel gear64is connected with an axial end80A of the inner ring80of the cross-roller bearing B2via a bolt86, and the output shaft76is fixed to an opposite axial end80B via a bolt88. The outer ring82of the cross-roller bearing B2is connected with and supported by the casing54(54C) via a bolt90. The cross-rollers (rolling elements)84of the cross-roller bearing B2are incorporated in a state where the rotational axis thereof is alternately changed 90° via pockets92provided in the radial direction of the outer ring82.

In addition, reference numerals93A and93B of the drawing represent oil seals, and reference numerals94A and94B represent O rings.

Next, the operation of the reduction gear GM1according to this embodiment will be described.

When the eccentric bodies46and47are rotated by the rotation of the motor shaft M1, the external gears50and51are guided by the outer peripheries of the eccentric bodies46and47(via the rollers48and49), and rockingly rotate while being inscribed in the internal gear52. In this embodiment, since the internal gear52is fixed to the casing54(54A), the free rotation of the external gears50and51is restrained, and only almost rocking is performed inside the internal gear52. As a result, the relative rotation resulting from a difference in the number of teeth occurs between the internal gear52and the external gears50and51. This relative rotation component is transmitted to the carrier56, which is equivalent to the output shaft of the speed reduction mechanism42, via the inner pin55.

When the carrier56rotates, the carrier56, the inner ring66, and the pinion shaft60integrally rotate as a large lump by the press fitting between the knurled portion60B of the pinion shaft60, and the inner periphery of the cylindrical portion56A of the carrier56, the connection between the carrier56, and the inner ring66of the angular roller bearing B1via the bolt72, and the press fitting between the inner ring66and the pinion shaft60. Accordingly, when the pinion shaft60rotates, the bevel pinion62directly formed at the tip of the pinion shaft60rotates, and the bevel gear64which meshes with the bevel pinion62rotates.

The bevel gear64is directly fixed via the bolt86to the axial inside of the inner ring80of the cross-roller bearing B2. For this reason, the inner ring80rotates at the same rotating speed as the bevel gear64. On the other hand, since the inner ring80is fixed to the output shaft76via the bolt88, the rotation of the bevel gear64is transmitted to the output shaft76as it is.

Here, the pinion shaft60at the subsequent stage is supported by the angular roller bearing B1which is combined back to back such that the contact angles θ1and θ2are 45°, and the midpoint P3of the projection range R1of the range E1where the bevel gear64meshes with the bevel pinion62on the pinion shaft60exists within the span L1of the working points P1and P2of the angular roller bearing B1which is combined back to back. Further, the angular roller bearing B1has a distance Ls1in the axial direction, and has the first transfer surfaces66A and70A of the first angular roller row68A, and the second transfer surfaces66B and70B of the second angular roller row68B (double-row type). Accordingly, although a bearing itself is one, the loads in the radial direction and the thrust direction, which are applied to the pinion shaft60with the midpoint P3as a base point can be stably received by the angular roller bearing B1.

Moreover, in this embodiment, (A) the carrier56which is an output shaft at the preceding stage is directly fixed to the inner ring66of the angular roller bearing B1via the bolt72, (B) a portion of the carrier56is supported by the motor shaft43via the bearing69, (C) the knurled portion60B of the pinion shaft60is press-fitted into the inner periphery of the cylindrical portion56A of the carrier56, and (D) the pinion shaft60is press-fitted into the inner ring66of the angular roller bearing B1. For this reason, the carrier56, the pinion shaft60, and the inner ring66of the angular roller bearing B1stably rotate as a large lump as a whole, so that the pinion shaft60can be rotated in a significantly stable state.

Another embodiment of the invention is shown inFIG. 3.

In the reduction gear GM2according to this embodiment, a spur pinion96is formed at the tip of a pinion shaft95, and the spur pinion96meshes with a spur gear98.

Even in this embodiment, the pinion shaft95equivalent to an input shaft at the subsequent stage is supported by the angular roller bearing B1in a back-to-back combination having a contact angle of 45° which has already been described. The configuration of the angular roller bearing B1itself is the same as that of the earlier embodiment. In this embodiment, a midpoint P4of a projection range R2of an meshing range E2between the spur pinion96and the spur gear98on the pinion shaft95exists within the span L1of the working points P1and P2of the angular roller bearing B1which is combined back to back.

Therefore, even if a large radial load is applied from the spur pinion96side, or even if a thrust load is applied to the pinion shaft95for some reason, the loads in the radial direction and the thrust direction can be received by the angular roller bearing B1, and the pinion shaft95can be rotated in a significantly stable state. In addition, the configuration in which the inscribed meshing planetary gear mechanism42at the preceding stage of the speed reducer G1and the pinion shaft60are supported, and the construction in which the output shaft99of the speed reduction mechanism44at the subsequent stage is supported are fundamentally the same as those of the earlier embodiment. Accordingly, main constituent parts in the drawing are denoted by the same reference numerals as those of the earlier embodiment, and duplicate description thereof is omitted.

In addition, the contact angle of the angular roller bearing according to the invention is not limited to 45°. The contact angle may be set in consideration of the balance between a radial road and a thrust load, the distance from the angular roller bearing to the meshing point between the first and second gears, etc. For example, when the ratio at which a radial road is applied is high, it is possible to set the contact angle to be smaller than 45°, and on the contrary, when the ratio at which a thrust load is applied is high, it is also possible to set a contact angle to 45° or more. However, the midpoint of the projection range of the range where the first and second gear mesh with each other on the first shaft needs to exist within the span of a line of action on the first shaft.

Further, although the double-row type single angular roller bearing has been adopted in the above embodiment, the angular roller bearing in the invention has only to be a bearing in which a pair of roller rows are incorporated (combined back to back), and is not necessarily a double-row type single bearing. Even if the number of bearings is two, the burden on each bearing can be made small by the invention. Thus, the span of bearing can be made small, and the effect that the axial length of the speed reducer can be shortened can be properly obtained.

A predetermined shaft in a speed reducer can be rotated and supported in a stable state while the loads in the radial direction and the thrust direction applied to the shaft are received by one bearing.