WHEEL DRIVE DEVICE

A wheel drive device that drives a wheel includes an output member, and a wheel member that is connected to the output member, in which the output member and the wheel member include a spigot fitting portion in which an outer peripheral spigot surface and an inner peripheral spigot surface are spigot-fitted, an anti-fretting agent is applied to the spigot fitting portion, and a seal member that prevents leakage of the anti-fretting agent is disposed between the output member and the wheel member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2022-110248, filed on Jul. 8, 2022, which is incorporated by reference herein in its entirety.

BACKGROUND

Technical Field

Certain embodiments of the present invention relate to a wheel drive device.

Description of Related Art

In the related art, a wheel drive device including an output member and a wheel member connected to the output member is disclosed. The output member and the wheel member include a spigot fitting portion in which an outer peripheral spigot surface and an inner peripheral spigot surface are spigot-fitted.

SUMMARY

According to an embodiment of the present invention, there is provided a wheel drive device that drives a wheel and including an output member and a wheel member that is connected to the output member, in which the output member and the wheel member include a spigot fitting portion in which an outer peripheral spigot surface, which is provided in one of the output member and the wheel member, and an inner peripheral spigot surface, which is provided in the other, are spigot-fitted, an anti-fretting agent is applied to the spigot fitting portion, and a seal member that prevents leakage of the anti-fretting agent is disposed between the output member and the wheel member.

DETAILED DESCRIPTION

Fretting wear is likely to occur at the spigot fitting portion between the output member and the wheel member. The inventors of the present application have found a new idea for suppressing the fretting wear at the spigot fitting portion.

It is desirable to provide a technique capable of suppressing fretting wear at a spigot fitting portion between an output member and a wheel member.

According to the present invention, it is possible to suppress the fretting wear at the spigot fitting portion between the output member and the wheel member. Hereinafter, embodiments will be described. The same reference numerals are added to the same components, and duplicated description will be omitted. In each drawing, components are omitted, enlarged, or reduced as appropriate for convenience of explanation. The drawings shall be viewed according to the orientation of the reference numerals.

One Embodiment

FIG.1is referred to. A wheel drive device10is attached to a vehicle body12such as a transport cart and is used to drive a wheel20. The transport cart is, for example, an automatic guided vehicle (AGV), an autonomous mobile robot (AMR), or the like. A use of the wheel drive device10of the present invention is not limited to the transport cart, and can be applied to various vehicles, such as a forklift and a self-propelled service robot.

The wheel drive device10includes a drive source16, a speed reducer18to which input rotation is input from an output shaft16aof the drive source16, and a wheel20to which output rotation is output from an output member42of the speed reducer18. For example, the drive source16is a motor, a gear motor, an engine, or the like. In addition to this, the wheel drive device10includes an attachment member21that is attached to the vehicle body12and supports each of the drive source16and the speed reducer18. Hereinafter, a direction along a rotation center line CL1of the output member42is referred to as an axial direction, and a radial direction and a circumferential direction having the rotation center line as the center of a circle are simply referred to as a radial direction and a circumferential direction.

FIG.2is referred to. The speed reducer18includes an input shaft22to which input rotation is input from the output shaft16aof the drive source16, a reduction mechanism24that decelerates the input rotation transmitted from the input shaft22and that converts the input rotation into output rotation, a casing26that accommodates the reduction mechanism24, and carriers28A and28B disposed inside the casing26in the radial direction are provided.

The speed reducer18in the present embodiment is an eccentric oscillation type speed reducer. The input shaft22of the speed reducer18is a crankshaft having at least one (here, two) eccentric body30. Eccentric phases of a plurality of eccentric bodies30are offset from each other. The input shaft22and the eccentric body30may be either separate or integral.

The reduction mechanism24of the eccentric oscillation type speed reducer18includes an external gear32that oscillates by the eccentric body30and an internal gear34that meshes with the external gear32. The external gear32is individually provided corresponding to each of the plurality of eccentric bodies30, and is supported by the eccentric body30to be relatively rotatable through an eccentric body bearing36. The internal gear34in the present embodiment includes an internal gear main body34aintegrated with the casing26, and an outer pin34bprovided on an inner peripheral portion of the internal gear main body34aand constituting internal teeth.

The carriers28A and28B are disposed on one side in the axial direction of the reduction mechanism24. The carriers28A and28B in the present embodiment include a first carrier28A disposed on one side in the axial direction and a second carrier28B disposed on the other side in the axial direction. The carriers28A and28B are connected through a connection member29such as a pin. The carriers28A and28B support the input shaft22through an input bearing38. A main bearing40is disposed between the casing26and the carriers28A and28B.

The speed reducer18described above includes an output member42to which output rotation is transmitted from the reduction mechanism24and outputting the output rotation. The output member42in the present embodiment forms a tubular shape as a whole. The output member42in the present embodiment is the casing26, but the carriers28A and28B may be used in place of the casing26. Details of the output member42will be described later.

The wheel20travels on a traveling surface by being rotated by the output rotation output from the output member42. For example, the traveling surface is a floor surface of a building, a rail, or the like. The wheel20includes a wheel member44that is connected to the output member42, and a ground contact member46that is attached to an outer peripheral portion of the wheel member44. The wheel member44forms a tubular shape as a whole. Details of the wheel member44will be described later. The ground contact member46contacts the traveling surface when the wheel20travels. The ground contact member46in the present embodiment is a tire. Specific examples of the ground contact member46are not particularly limited, and in addition, a roller for an omni wheel, a roller for a mecanum wheel, or the like may be used.

An operation of the wheel drive device10described above will be described. In a case where the input rotation is input from the drive source16to the input shaft22of the speed reducer18, the reduction mechanism24operates. In a case where the reduction mechanism24operates, the output rotation decelerated with respect to the input rotation from the reduction mechanism24is transmitted to the output member42. In a case where the output rotation is transmitted to the output member42, the wheel20rotates together with the output member42, and the wheel20travels on the traveling surface.

In a case where the eccentric oscillation type speed reducer18is used as in the present embodiment, in a case where the input shaft22(crankshaft) rotates, the eccentric body30causes the external gear32to oscillate so that the center of the external gear32rotates around the rotation center line CL1of the output member42. In a case where the external gear32is oscillated, meshing positions of the external gear32and the internal gear34change in the circumferential direction. Accordingly, each time the input shaft22rotates once, one of the external gear32and the internal gear34(here, the internal gear34) rotates by a difference in the number of teeth between the external gear32and the internal gear34. The axial rotation component is transmitted to the output member42as output rotation.

FIG.3will be referred to. Hatching is omitted in the following drawings. One of the output member42and the wheel member44is an inner member50, and the other is an outer member52. In the present embodiment, the inner member50is the output member42, and the outer member52is the wheel member44. At least a part of the inner member50is disposed inward of the outer member52in the radial direction.

An insertion hole54into which the inner member is inserted toward one side in the axial direction (here, a counter motor side) is provided on an inner peripheral surface of the outer member52. The insertion hole54includes an opening portion54athat opens toward the other side in the axial direction (here, a motor side).

The inner member50and the outer member52respectively include axial abutment portions56A and56B that abut in the axial direction. The inner member50includes a first axial abutment portion56A, and the outer member52includes a second axial abutment portion56B that abuts against the first axial abutment portion56A in the axial direction. In the present embodiment, the first axial abutment portion56A is provided on a side surface portion of a first protrusion portion58A that protrudes outwardly in the radial direction on an outer peripheral surface of the inner member50. In addition, the second axial abutment portion56B is provided on a side surface portion of the second protrusion portion58B that protrudes inwardly in the radial direction on the inner peripheral surface of the outer member52.

The output member42and the wheel member44are connected by a connection member60. The output member42and the wheel member44in the present embodiment are connected by the connection member60at the respective axial abutment portions56A and56B. The connection member60in the present embodiment is a bolt, but may also be a rivet, a pin, or the like. A plurality of the connection members60are disposed with a space in the circumferential direction. The inner member50and the outer member52include an insertion hole61for inserting the connection member60. In the present embodiment, the insertion hole61of the inner member50is a female screw hole, and the insertion hole61of the outer member52is a non-screw hole. The connection member60is inserted into the insertion holes61of the inner member50and the outer member52in the axial direction, and connects the inner member50and the outer member52in a state in which the respective axial abutment portions56A and56B are abutted.

The inner member50and the outer member52include a spigot fitting portion66in which an outer peripheral spigot surface62and an inner peripheral spigot surface64are spigot-fitted. The outer peripheral spigot surface62is provided on an outer peripheral surface of the inner member50(here, the output member42), and the inner peripheral spigot surface64is provided on the inner peripheral surface of the outer member52(here, the wheel member44). The wheel member44is connected in a state in which the output member42and the wheel member44are spigot-fitted at the spigot fitting portion66.

An anti-fretting agent68is applied to the spigot fitting portion66. It can also be said that the anti-fretting agent68is applied to the outer peripheral spigot surface62and the inner peripheral spigot surface64. InFIG.3, hatching is applied to an application location of the anti-fretting agent68. The anti-fretting agent68has a function of preventing fretting wear caused by contact between the outer peripheral spigot surface62and the inner peripheral spigot surface64. Specific examples of the anti-fretting agent68are not particularly limited, and a liquid lubricant such as wax, oil, and fatty acid may be used in addition to a solid lubricant such as molybdenum disulfide and graphite, for example. In a case where the solid lubricant is used as the anti-fretting agent68, a mixture of the solid lubricant in a form of powder and a lubricating oil such as grease and oil may be used as the anti-fretting agent68.

A seal member70that prevents the anti-fretting agent68from leaking into an external space is disposed between the inner member50and the outer member52. For example, the seal member70is a contact type seal such as an O-ring and a lip seal, and here, the seal member70is the O-ring. The seal member70in the present embodiment is composed of an elastic body such as rubber. This seal member70is disposed between the inner member50and the outer member52with elastic deformation. The seal member70is disposed on one side in the axial direction with respect to the spigot fitting portion66, and prevents the anti-fretting agent68from leaking to the one side in the axial direction.

Each of the inner member50and the outer member52includes a pair of radial facing portions72facing each other in the radial direction. The spigot fitting portion66is provided on the pair of radial facing portions72. The seal member70is disposed between the pair of radial facing portions72. In the present embodiment, the radial facing portion72of the inner member50is provided on an outermost diameter portion73having the largest outer diameter in an axial range facing the inner peripheral surface of the outer member52in the radial direction. The radial facing portion72of the outer member52is provided at a position overlapping the radial facing portion72of the outermost diameter portion73in the radial direction.

At least one of the inner member50and the outer member52is provided with a recessed portion76that accommodates the seal member70. The recessed portion76is provided as an annularly continuous groove portion. Accordingly, by accommodating the seal member70in one recessed portion76of the inner member50and the outer member52, the seal member70can be mounted to the one recessed portion76. The recessed portion76in the present embodiment is provided on the outer peripheral surface of the inner member50(here, the output member42), and the seal member70can be mounted to the inner member50. Accordingly, when the wheel drive device10is assembled, the seal member70is less likely to come off than when the seal member70is accommodated in the recessed portion76of the outer member52, so that good workability can be obtained.

A radial gap74that is adjacent to the spigot fitting portion66in the axial direction is provided between the pair of radial facing portions72. A part of the radial gap74is closed by the seal member70. The radial gap74includes an opening end portion74athat is provided between end portions of the pair of radial facing portions72and opens in the axial direction. In a case where the inner member50and the outer member52are provided with the recessed portion76that accommodates the seal member70, the radial gap74is provided at a location excluding the recessed portion76. By providing the radial gap74between the pair of radial facing portions72, an axial dimension L1of the spigot fitting portion66, which causes fretting wear in the pair of radial facing portions72, can be shortened by the amount of an axial dimension L2of the radial gap74. As a result, the fretting wear can be suppressed as compared with a case where the radial gap74is not provided between the pair of radial facing portions72.

A gap between the pair of radial facing portions72in the radial gap74is wider than a gap between the pair of radial facing portions72in the spigot fitting portion66. The radial dimension R74of the radial gap74is smaller than a thickness dimension R70of the seal member70. Here, the thickness dimension R70refers to a radial dimension obtained by subtracting an inner diameter dimension from an outer diameter dimension of the seal member70.

The seal member70is provided at an intermediate position of the radial gap74in the axial direction. It can be said that the seal member70is not provided at the opening end portion74aof the radial gap74. Accordingly, the radial gap74can be widened with respect to the seal member70on the side opposite to the spigot fitting portion66in the axial direction, rather than the disposition position of the seal member70being the opening end portion74aof the radial gap74. As a result, it becomes difficult for only a foreign matter having a dimension smaller than the radial gap74to reach the seal member70from the external space, and the seal member70can be protected from contact with a foreign matter having a large dimension.

The axial abutment portions56A and56B of the output member42and the wheel member44are disposed on the side opposite to the seal member70in the axial direction with respect to the spigot fitting portion66. At least one of the first axial abutment portion56A and the second axial abutment portion56B (both in the present embodiment) may satisfy this condition. Accordingly, the axial abutment portions56A and56B abutting against each other can prevent the anti-fretting agent68from leaking to the spigot fitting portion66on the side opposite to the seal member70in the axial direction. As a result, other seal members for preventing leakage of the anti-fretting agent68can be omitted. In addition, by adopting the bolt as the connection member60, the axial abutment portions56A and56B can be brought into close contact with each other by tightening force of the bolt. As a result, the leakage of the anti-fretting agent68can be effectively suppressed by the axial abutment portions56A and56B abutting against each other.

Effects of the wheel drive device10described above will be described.

The anti-fretting agent68is applied to the spigot fitting portion66between the output member42and the wheel member44. Accordingly, the fretting wear at the spigot fitting portion66can be suppressed. As a result, durability of the wheel drive device10can be improved.

The seal member70that prevents the leakage of the anti-fretting agent68is disposed between the output member42and the wheel member44. Accordingly, the scattering of the anti-fretting agent68into an external space78can be suppressed. As a result, a state in which the anti-fretting agent68is applied to the spigot fitting portion66can be maintained for a long period of time, and the fretting wear suppression effect by the anti-fretting agent68can be exhibited for a long period of time. In addition, the seal member70can suppress intrusion of foreign matters from the external space78into the spigot fitting portion66.

Next, other features of the wheel drive device10will be described. Between the output member42and the wheel member44, a radial load is transmitted. In a case where a function of transmitting the radial load is exclusively exhibited in the spigot fitting portion66, it is preferable that the axial dimension L1of the spigot fitting portion66is made longer in order to reduce a contact pressure at the spigot fitting portion66. On the other hand, in the present embodiment, the function of transmitting the radial load between the output member42and the wheel member44is exclusively exhibited by a plurality of connection members60in place of the spigot fitting portion66. In addition, the spigot fitting portion66in the present embodiment is exclusively used to position the output member42and the wheel member44in the radial direction.

In exhibiting such positioning function, the axial dimension L1of the spigot fitting portion66may be short. Rather, as a countermeasure against fretting wear, it is preferable that the axial dimension L1of the spigot fitting portion66, which causes the fretting wear, is shortened. In addition, as the axial dimension L1of the spigot fitting portion66becomes shorter, frictional resistance is less likely to occur in a case where the inner member50is inserted into the insertion hole54of the outer member52.

From such a viewpoint, it is preferable that the axial dimension L1of the spigot fitting portion66is set to a size that is equal to or less than half the total dimension (=L1+L2) of the axial dimension L1of the spigot fitting portion66and the axial dimension L2of the radial gap74. Although a lower limit value is not particularly limited, for example, 4 mm or more may be a lower limit value, and preferably 5 mm or more may be a lower limit value. Accordingly, the axial dimension L1of the spigot fitting portion66can be shortened as compared with a case where the axial dimension L1of the spigot fitting portion66is set to a size that is more than half of the total dimension (=L1+L2). As a result, the occurrence of fretting wear can be suppressed as compared with such a case. In addition, as compared with such a case, the workability in a case where the inner member50is inserted into the insertion hole54of the outer member52can be improved. The axial dimension L1of the spigot fitting portion66may have a size that is more than half of the total dimension (=L1+L2).

As described above, the seal member70is mounted to the outer peripheral surface of the inner member50. To realize this, in the present embodiment, the seal member70is accommodated in the recessed portion76provided on the outer peripheral surface of the inner member50. Specific examples for mounting the seal member70is not particularly limited, and tightening, fitting, or the like may be used.

FIGS.3and4are referred to. In a case where the inner member50is inserted into the insertion hole54, the inner member50passes through the opening portion54aof the insertion hole54and then is moved until the first axial abutment portion56A abuts against the second axial abutment portion56B of the outer member52.

Here, a relief recessed portion80is provided on the inner peripheral surface of the outer member52to reduce the frictional resistance of the seal member70in a case where the inner member50is inserted into the insertion hole54. In a case where the relief recessed portion80is provided on the inner peripheral surface of the outer member52, the relief recessed portion80is provided between a contact location82of the seal member70with respect to the inner peripheral surface of the outer member52and the opening portion54aof the insertion hole54. In the present embodiment, the relief recessed portion80is provided between the radial facing portion72of the outer member52and the opening portion54aof the insertion hole54. The relief recessed portion80is provided to be recessed outwardly in the radial direction from the contact location82of the seal member70on the inner peripheral surface of the outer member52. An inner diameter R80aof the relief recessed portion80may be set to a size capable of avoiding contact with the seal member70mounted on the inner member50. For example, the axial dimension L80of the relief recessed portion80is larger than an axial dimension L70of the seal member70.

Accordingly, the frictional resistance of the seal member70can be reduced as compared with a case where the relief recessed portion80is not provided on the inner peripheral surface of the outer member52. As a result, it becomes easier to insert the inner member50into the insertion hole54of the outer member52, and good workability can be obtained.

Another Embodiment

FIGS.5and6are referred to. The seal member in the present embodiment is mounted on the inner peripheral surface of the outer member52in place of the outer peripheral surface of the inner member50. To realize this, the recessed portion76that accommodates the seal member70is provided on the inner peripheral surface of the outer member52.

The relief recessed portion80is provided on the outer peripheral surface of the inner member50in place of the inner peripheral surface of the outer member52. In a case where the relief recessed portion80is provided on the outer peripheral surface of the inner member50, the relief recessed portion80is provided between the contact location82of the seal member70with respect to the outer peripheral surface of the inner member50and the spigot fitting portion66. The relief recessed portion80is provided to be recessed inwardly in the radial direction from the contact location82of the seal member70on the outer peripheral surface of the inner member50. An outer diameter R80bof the relief recessed portion80may be set to a size capable of avoiding contact with the seal member70mounted on the outer member52. For example, the axial dimension L80of the relief recessed portion80is larger than the axial dimension L70of the seal member70.

Accordingly, as compared with a case where the relief recessed portion80is not provided on the outer peripheral surface of the inner member50, the frictional resistance of the seal member70can be reduced as in the one embodiment. In relation to such an effect, the seal member may be mounted to one of the inner peripheral surface of the outer member52and the outer peripheral surface of the inner member50, and the relief recessed portion80may be provided on the other.

Next, modification examples of each component described so far will be described.

Specific examples of the speed reducer18are not particularly limited, and various reduction mechanisms can be applied, such as a bending meshing type speed reducer, a simple planetary gear type speed reducer, a traction drive, or the like, in addition to the eccentric oscillation type speed reducer. The type of the eccentric oscillation type speed reducer is not particularly limited. As an example of this, the center crank type in which the crankshaft (input shaft22) is disposed on the rotation center line of the output member42has been described in the embodiment. In addition to this, it may be a distribution type in which a plurality of crankshafts are disposed at positions offset in the radial direction from the rotation center line of the output member42. The type of the bending meshing type speed reducer is not particularly limited, and may be, for example, a cup type having one internal gear, a silk hat type, or the like in addition to a tubular type having two internal gears.

One of the output member42and the wheel member44may be the inner member50having the outer peripheral spigot surface62, and the other may be the outer member52having the inner peripheral spigot surface64. To realize this, unlike the embodiment, the wheel member44may be the inner member50, and the output member42may be the outer member52.

The radial gap74that is adjacent to the spigot fitting portion66in the axial direction may not be provided between the pair of radial facing portions72. It can also be said that the axial range of the spigot fitting portion66may be adjacent to a range overlapping the seal member70in the radial direction.

The seal member70may be provided at the opening end portion74aof the radial gap74.

The recessed portion76may be provided on at least one of the output member42and the wheel member44. The recessed portion76may be provided on both the inner peripheral surface of the outer member52and the outer peripheral surface of the inner member50unlike the embodiment. In addition, neither the output member42nor the wheel member44may have the recessed portion76that accommodates the seal member70.

The seal member70may be disposed individually on both sides in the axial direction with respect to the spigot fitting portion66. The seal member70may be disposed only on the side of the axial abutment portions56A and56B with respect to the spigot fitting portion66unlike the embodiment. Each of the output member42and the wheel member44may not include the axial abutment portions56A and56B.

Neither the inner member50nor the outer member52may be provided with the relief recessed portion80.

The above-described embodiments and modification examples are examples. The technical ideas that abstract the embodiments and modification examples should not be construed as being limited to the contents of the embodiments and modification examples. Many design changes such as the change, addition, and deletion of components can be made with respect to the contents of the embodiments and modification examples. In the above-described embodiments, the contents for which such design changes are possible are emphasized by adding the notation “embodiment”. However, design changes are allowed even in the contents in which there is no such notation. Hatching applied to the cross section of the drawing does not limit the material of the hatched object. Structures and numerical values as mentioned in the embodiments and modification examples naturally include those that can be regarded as the same when manufacturing errors and the like are taken into consideration.

Any combination of the above components is also valid. For example, any description of other embodiments may be combined with the embodiment, or the modification examples may be combined with any description of the embodiments and modification examples.

A component composed of a single member in an embodiment may be composed of a plurality of members.

Similarly, a component composed of a plurality of members in an embodiment may be composed of a single member.