Transmission device

A transmission device is provided in which a first speed change portion and a second speed change portion are formed. The first speed change portion includes an eccentric shaft having a main shaft portion on a first rotary axis and an eccentric shaft portion on a second rotary axis disposed eccentrically with respect to the first rotary axis; an eccentric unit that is rotatably supported on the eccentric shaft portion, and has external teeth formed on an outer peripheral portion thereof; and a housing having an axial center on the first rotary axis, and having internal teeth that mesh with the external teeth of the eccentric unit. The second speed change portion includes curved wave grooves respectively formed on the eccentric unit and a rotary unit; and rolling elements sandwiched between the curved wave grooves and moving along an orbit defined by the curved wave grooves.

TECHNICAL FIELD

The present invention relates to a transmission device mainly applied to a vehicle.

BACKGROUND ART

As disclosed in Patent Documents 1 and 2 below, a transmission device including an eccentric shaft, an eccentric unit and a rotary unit as follows is already known. The eccentric shaft includes a main shaft portion on a first rotary axis and an eccentric shaft portion on a second rotary axis disposed eccentrically with respect to the first rotary axis. The eccentric shaft portion is capable of revolving about the first rotary axis. The eccentric unit is rotatably supported on the eccentric shaft portion of the eccentric shaft and is capable of revolving about the first rotary axis, while rotating around the second rotary axis in a manner of being operatively associated with the rotation of the eccentric shaft about the first rotary axis. The rotary unit is capable of rotating about the first rotary axis, while being operatively associated with the axial rotation and the orbital revolution of the eccentric unit. In the transmission device, rotation of the main shaft portion of the eccentric shaft is transmitted to the rotary unit with speed reduced via a curved wave groove and a plurality of intermediate members having an orbit restricted by the curved wave groove.

Specifically, the arrangement disclosed in Patent Document 1 includes an eccentric rotary unit (eccentric unit)4rotatably supported on an eccentric shaft22of an eccentric shaft that includes an input shaft (main shaft portion)2extending along a first rotary axis and the eccentric shaft (eccentric shaft portion)22extending along a second rotary axis. The arrangement further includes a plurality of rolling balls (rolling elements)53that move along an orbit defined by an inner groove (curved wave groove)51in an outer periphery of the eccentric rotary unit4and an outer groove (curved wave groove)52in an inner periphery of a housing1. The movement of the rolling balls53along the orbit causes the eccentric rotary unit4to revolve about the first rotary axis, while rotating around the second rotary axis, in a manner of being operatively associated with rotation of the input shaft2. The arrangement further includes a driven disk (rotary unit)32that includes an adjustment mechanism40disposed on a side surface opposing one side surface of the eccentric rotary unit4. The driven disc32rotates about the first rotary axis on the basis of the axial rotation and the orbital revolution of the eccentric rotary unit4. (It is noted that the reference numerals and symbols used in the description of Patent Document 1 refer to those used in Patent Document 1.) Further, Patent Document 2 discloses an arrangement that includes an eccentric plate (eccentric unit)4rotatably supported on an eccentric shaft12that includes an input shaft portion (main shaft portion)12aextending along a first rotary axis and an eccentric portion (eccentric shaft portion)12dextending along a second rotary axis. The arrangement further includes a plurality of first rolling balls (rolling elements)10that move along an orbit defined by an epicycloidal groove portion (curved wave groove)7in one side surface of the eccentric plate4and a hypocycloidal groove (curved wave groove)6in a side surface of a stationary plate3that opposes the eccentric plate4. The movement of the first rolling balls10along the orbit causes the eccentric plate4to revolve about the first rotary axis, while rotating around the second rotary axis, in a manner of being operatively associated with rotation of the input shaft portion12a. The arrangement further includes a plurality of second rolling balls (rolling elements)11that move along an orbit defined by a hypocycloidal groove portion (curved wave groove)8in the other side surface of the eccentric plate4and a epicycloidal groove (curved wave groove)9in a side surface of an output plate (rotary unit)5that opposes the eccentric plate4, on the basis of the axial rotation and the orbital revolution of the eccentric plate4. The movement of the second rolling balls11along the orbit causes the output plate5to rotate about the first rotary axis in a manner of being operatively associated with the axial rotation and the orbital revolution of the eccentric plate4. (It is noted that the reference symbols used in the description of Patent Document 2 refer to the reference symbols used in Patent Document 2.)

PRIOR ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In the transmission device disclosed in Patent Document 1, however, the rotation of the input shaft2is converted into the axial rotation and the orbital revolution of the eccentric rotary unit4by the curved wave groove51formed in the outer periphery of the eccentric rotary unit4, the curved wave groove52formed in the inner periphery of the housing1so as to oppose the eccentric rotary unit4, and the rolling balls53that roll along the orbit defined by the two curved wave grooves51and52. The two curved wave grooves51and52thus increase a radial size of the transmission device. Additionally, the adjustment mechanism40is not to change speeds resulting in a single speed change stage and a high transmission ratio cannot be acquired from the single speed change stage.

With the transmission device disclosed in Patent Document 2, despite a plurality of speed change stages available, the curved wave grooves7and8formed in the opposite side surfaces of the eccentric plate4and the curved wave groove6formed in the side surface of the stationary plate3disable thinning of a wall thickness of the eccentric plate4and the stationary plate3. In addition, the rolling balls10and11disposed between the eccentric plate4and the stationary plate3, and between the eccentric plate4and the output plate5, inevitably increase an axial size of the transmission device. Furthermore, the use of the many rolling balls10and11increases not only the number of parts used, but also weight of the transmission device as a whole.

The present invention has been accomplished in light of such circumstances and it is an object thereof to provide a transmission device capable of having a speed change portion with a plurality of speed change stages without involving an increased size of the transmission device as a whole, while achieving reduction in the number of parts used and weight.

Means for Solving the Problems

In order to attain the above object, according to the present invention, there is provided a transmission device comprising: an eccentric shaft including a main shaft portion on a first rotary axis and an eccentric shaft portion on a second rotary axis disposed eccentrically with respect to the first rotary axis, the eccentric shaft portion being capable of revolving about the first rotary axis; an eccentric unit supported rotatably on the eccentric shaft portion and capable of revolving about the first rotary axis while rotating around the second rotary axis, the eccentric unit having external teeth formed on an outer peripheral portion thereof; a housing having an axial center on the first rotary axis and having internal teeth meshing with the external teeth of the eccentric unit on an inner peripheral wall thereof; a rotary unit capable of rotating about the first rotary axis and having one side surface opposed to one side surface of the eccentric unit; curved wave grooves formed in the one side surface of the eccentric unit and the one side surface of the rotary unit, respectively; and a plurality of rolling elements sandwiched between the curved wave grooves and moving along an orbit defined by the curved wave grooves, wherein at least the eccentric shaft, the eccentric unit and the housing form a first speed change portion and at least the eccentric unit, the rotary unit and the rolling elements form a second speed change portion, and the first and second speed change portions cause rotation of either one of the main shaft portion of the eccentric shaft or the rotary unit to be transmitted to the other of the main shaft portion of the eccentric shaft or the rotary unit with reduced or increased speed. (This is a first aspect.)

Further, preferably, the curved wave groove of the eccentric unit has waves that are greater in number than waves of the curved wave groove of the rotary unit. (This is a second aspect.)

Furthermore, preferably, the eccentric unit has a first thin-wall portion formed on the one side surface on an outer peripheral side with respect to the curved wave groove and a second thin-wall portion formed on the other side surface of the eccentric unit, and when viewed in a plane of projection perpendicular to the first rotary axis, the second thin-wall portion has an area greater than an area of the first thin-wall portion. (This is a third aspect.)

Effects of the Invention

In accordance with the first aspect of the present invention, the first speed change portion includes: the eccentric shaft that includes the main shaft portion on the first rotary axis and the eccentric shaft portion on the second rotary axis disposed eccentrically with respect to the first rotary axis, the eccentric shaft portion being capable of revolving about the first rotary axis; the eccentric unit that is supported rotatably on the eccentric shaft portion and is capable of revolving about the first rotary axis while rotating around the second rotary axis, the eccentric unit having the external teeth formed on the outer peripheral portion thereof; and the housing having an axial center on the first rotary axis and having internal teeth meshing with the external teeth of the eccentric unit on the inner peripheral wall thereof; and the second speed change portion includes: the curved wave grooves each formed in the one side surface of the eccentric unit and the one side surface of the rotary unit, opposing the eccentric unit; and a plurality of the rolling elements that are sandwiched between the curved wave grooves and that move along the orbit defined by the curved wave grooves. Thus, despite the plurality of speed change stages formed from the first and second speed change portions, only the one side surface of the eccentric unit is required to have the curved wave groove of the eccentric unit and the housing is not required to have the curved wave groove. Thus, the eccentric unit and the housing can have a thin wall thickness, so that the transmission device can have a shorter axial length and reduced weight. In addition, the first speed change portion is formed such that the external teeth, protruding radially a short distance, of the eccentric unit and the internal teeth, protruding radially a short distance, of the housing engage each other and such that the curved wave grooves that extend to meander largely in the radial direction are not to engage each other across the rolling elements. The first speed change portion thus does not lead to a transmission device having an increased size in the radial direction. Additionally, the curved wave groove formed in the eccentric unit is formed utilizing a side surface as a dead material portion of the eccentric unit having the external teeth on the outer peripheral portion thereof. This arrangement makes effective use of the dead material portion and contributes to reduced weight of the eccentric unit.

In accordance with the second aspect of the present invention, the curved wave groove of the eccentric unit has waves that are greater in number than waves of the curved wave groove of the rotary unit. The number of waves of the curved wave groove formed in the one side surface requiring a predetermined area or greater for effecting axial rotation and orbital revolution of the eccentric unit can be made more than the number of waves of the curved wave groove of the rotary unit. This arrangement makes even more effective use of the one side surface of the eccentric unit and enables reduction in diameter and size of the rotary unit.

In accordance with the third aspect of the present invention, the eccentric unit has the first thin-wall portion formed on the one side surface on the outer peripheral side with respect to the curved wave groove and the second thin-wall portion formed on the other side surface of the eccentric unit. Thus, the first and second thin-wall portions achieve further reduction in weight of the eccentric unit. Additionally, when viewed in a plane of projection perpendicular to the first rotary axis, the second thin-wall portion has an area greater than the area of the first thin-wall portion. The area of the second thin-wall portion in the other side surface having no curved wave groove is further increased to achieve further reduction in weight.

EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS

1Housing1fInternal teeth2Eccentric shaft2aMain shaft portion2bEccentric shaft portion3Eccentric unit3aExternal teeth3bOne side surface of eccentric unit3cOther side surface of eccentric unit3dFirst thin-wall portion3eSecond thin-wall portion4Rotary unit4aOne side surface of rotary unit10Curved wave groove of eccentric unit11Curved wave groove of rotary unit13Rolling elementA First speed change portionB Second speed change portionX1First rotary axisX2Second rotary axis

MODE FOR CARRYING OUT THE INVENTION

Modes for carrying out the present invention are explained below by reference to the attached drawings.

First Embodiment

A transmission device according to a first embodiment of the present invention will be described below with reference toFIGS. 1 to 3.

InFIG. 1, a transmission device T according to the first embodiment includes a housing1, an eccentric shaft2, an eccentric unit3, and a rotary unit4. The housing1includes a short cylindrical portion1athat is integrated with a pair of left and right covering portions1band1cthat close open portions on axially opposite sides of the cylindrical portion1a. The eccentric shaft2, the eccentric unit3and the rotary unit4are housed in the housing1.

The eccentric shaft2includes a main shaft portion2aand an eccentric shaft portion2b. The main shaft portion2ais capable of rotating about a first rotary axis X1. The eccentric shaft portion2bis disposed on a second rotary axis X2that is eccentric with respect to the first rotary axis X1. The eccentric shaft portion2bis capable of revolving about the first rotary axis X1.

One covering portion1bof the housing1includes a cylindrical first boss portion1dthat has its axial center on the first rotary axis X1. The other covering portion1cof the housing1includes a cylindrical second boss portion1ethat has its axial center on the first rotary axis X1. The main shaft portion2aof the eccentric shaft2is rotatably supported on the inside of the first boss portion1dvia a first bearing5. The rotary unit4is rotatably supported on the inside of the second boss portion1e. Additionally, a thrust washer6is disposed between the other covering portion1cand the rotary unit4.

The eccentric unit3having external teeth3aformed on an outer peripheral portion thereof is rotatably supported on the eccentric shaft portion2bvia a second bearing7. Additionally, the cylindrical portion1ahaving its axial center on the first rotary axis X1has internal teeth1fformed on an inner peripheral wall thereof. The internal teeth1fmesh with the external teeth3aof the eccentric unit3. Thus, rotating the eccentric shaft2about the first rotary axis X1causes the eccentric unit3having the external teeth3ain mesh with the internal teeth1fof the cylindrical portion1ato revolve about the first rotary axis X1, while rotating around the second rotary axis X2. In contrast, revolving the eccentric unit3about the first rotary axis X1, while allowing the eccentric unit3to rotate around the second rotary axis X2, causes the eccentric shaft2to rotate about the first rotary axis X1.

A first rotary shaft8is spline-connected to the main shaft portion2aof the eccentric shaft2. A second rotary shaft9is spline-connected to the rotary unit4. Thus, rotation from an outside is transmitted from one of the first and second rotary shafts8and9to the main shaft portion2aof the eccentric shaft2and the rotary unit4, and rotation of the main shaft portion2aof the eccentric shaft2and the rotary unit4is transmitted to the outside from the other of the first and second rotary shafts8and9.

Reference is also made toFIG. 2as a schematic view andFIG. 3as a cross-sectional view from arrowed line A3-A3inFIG. 1. The rotary unit4has one side surface4aopposing one side surface3bof the eccentric unit3. The one side surface3bof the eccentric unit3and the one side surface4aof the rotary unit4have a curved wave groove10and a curved wave groove11formed therein, respectively. The curved wave groove10and the curved wave groove11each extend in a peripheral direction along a trochoidal curve. A plurality of ball-shaped rolling elements13held in a race member12are disposed between the two curved wave grooves10and11so as to move along the orbit sandwiched between, and defined by, the two curved wave grooves10and11.

Thus, when the eccentric unit3revolves about the first rotary axis X1while rotating around the second rotary axis X2, a position at which the two curved wave grooves10and11face each other moves. Then, the rolling elements13sandwiched between the two curved wave grooves10and11move and rotate as the position at which the two curved wave grooves10and11face each other moves. This action causes the rotary unit4to rotate about the first rotary axis X1. In contrast, when the rotary unit4is rotated about the first rotary axis X1, the eccentric unit3revolves about the first rotary axis X1while rotating around the second rotary axis X2.

Additionally, a first thin-wall portion3dis formed on the one side surface3bof the eccentric unit3on an outer peripheral side with respect to the curved wave groove10. A second thin-wall portion3eis formed on the other side surface3cof the eccentric unit3. When viewed in a plane of projection perpendicular to the first rotary axis X1, the second thin-wall portion3ehas an area greater than an area of the first thin-wall portion3d.

In the first embodiment, the number of internal teeth1fformed on the inner peripheral wall of the cylindrical portion1ais 80, the number of external teeth3athat are formed on the outer peripheral portion of the eccentric unit3and that are in mesh with the internal teeth1fis 70, the curved wave groove10formed in the one side surface3bof the eccentric unit3forms a hypotrochoid wave groove having six waves, the curved wave groove11formed in the one side surface4aof the rotary unit4forms an epitrochoid wave groove having four waves, and the number of rolling elements13held between the two curved wave grooves10and11is 5. Thus, as will be described later, rotation input from the first rotary shaft8is subjected to speed reduction to 5/7 and the rotation is reversed and output from the second rotary shaft9.

It should, however, be noted that the numbers of external teeth, internal teeth and curved wave grooves are not limited in the first embodiment. For example, the number of internal teeth1fformed on the inner peripheral wall of the cylindrical portion1aand the number of external teeth3aformed on the outer peripheral portion of the eccentric unit3may be set to any number. In addition, the numbers of the curved wave grooves10and11may be set to any number if a difference in the number of waves between the curved wave grooves10and11is set to 2. Alternatively, the number of waves of the curved wave groove11formed in the one side surface4aof the rotary unit4may be greater than the number of waves of the curved wave groove10formed in the one side surface3bof the eccentric unit3as in the second embodiment to be described later.

When the number of internal teeth on the inner peripheral wall of the cylindrical portion is Z1, the number of external teeth on the outer peripheral portion of the eccentric unit is Z2, the curved wave groove formed in the one side surface of the eccentric unit is Z3and the curved wave groove formed in the one side surface of the rotary unit is Z4, a transmission ratio between the main shaft portion of the eccentric shaft and the rotary unit in the mechanism as described above is given by the following expression: [1−{(Z1×Z3)/(Z2×Z4)}]. In the first embodiment, Z1=80, Z2=70, Z3=6 and Z4=4, and a reduction ratio when the first rotary shaft8is an input shaft is −5/7. Thus, the rotation input from the first rotary shaft8is transmitted from the main shaft portion2ato the rotary unit4as a reversed rotation having speed reduced to 5/7 and output from the second rotary shaft9.

Operation of the first embodiment will be described below.

A first speed change portion A includes at least the eccentric shaft2, the eccentric unit3and the housing1. The eccentric shaft2includes the main shaft portion2aon the first rotary axis X1and the eccentric shaft portion2bon the second rotary axis X2disposed eccentrically with respect to the first rotary axis X1. The eccentric shaft portion2bis capable of revolving about the first rotary axis X1. The eccentric unit3is supported rotatably on the eccentric shaft portion2band is capable of revolving about the first rotary axis X1while rotating around the second rotary axis X2. The eccentric unit3has the external teeth3aformed on the outer peripheral portion thereof. The housing1has the internal teeth1fmeshing with the external teeth3aof the eccentric unit3, formed on the inner peripheral wall of the cylindrical portion1athat has its axial center on the first rotary axis X1. A second speed change portion B includes at least the curved wave groove10, the curved wave groove11and the rolling elements13. The curved wave groove10includes a hypotrochoidal curve formed on the one side surface3bof the eccentric unit3. The curved wave groove11includes an epitrochoidal curve formed on the one side surface4aof the rotary unit4, opposing the one side surface3bof the eccentric unit3. The rolling elements13move along the orbit sandwiched between, and defined by, the two curved wave grooves10and11. Thus, despite the plurality of speed change stages of the first and second speed change portions A and B, only the one side surface3bof the eccentric unit3is required to have the curved wave groove10of the eccentric unit3, and the covering portion1bas one of the covering portions of the housing1is not required to have the curved wave groove, so that the eccentric unit3and the covering portion1bcan have a thin wall thickness. Thus, the transmission device can have a short axial length and reduced weight. In addition, the first speed change portion A is formed such that the external teeth3a, protruding radially a short distance, of the eccentric unit3and the internal teeth1f, protruding radially a short distance, of the cylindrical portion1aof the housing1engage each other and such that the curved wave grooves that extend to meander largely in the radial direction are not to engage each other across the rolling elements. The first speed change portion A thus does not lead to a transmission device having an increased size in the radial direction. Additionally, the curved wave groove10formed of the hypotrochoidal curve and formed in the eccentric unit3is formed utilizing a side surface as a dead material portion of the eccentric unit3having the external teeth3aon the outer peripheral portion thereof. This arrangement makes effective use of the dead material portion and contributes to reduced weight of the eccentric unit.

The hypotrochoid wave groove10formed in the one side surface3bof the eccentric unit3has the number of waves greater than the number of waves of the epitrochoid wave groove11formed in the one side surface4aof the rotary unit4. The number of waves of the hypotrochoid wave groove10formed in the one side surface3bof the eccentric unit3, requiring an area equal to or greater than a predetermined area for effecting axial rotation and orbital revolution of the eccentric unit3, can be made more than the number of waves of the epitrochoid wave groove11of the rotary unit4. This arrangement makes even more effective use of the one side surface3bof the eccentric unit3having a wide area and enables reduction in diameter and size of the rotary unit4.

Additionally, the first thin-wall portion3dis formed on the one side surface3bof the eccentric unit3on an outer peripheral side with respect to the curved wave groove10and the second thin-wall portion3eis formed on the other side surface3cof the eccentric unit3. Thus, the first and second thin-wall portions3dand3eachieve further reduction in weight of the eccentric unit3. When viewed in a plane of projection perpendicular to the first rotary axis X1, the second thin-wall portion3ehas an area greater than the area of the first thin-wall portion3d. The area of the second thin-wall portion3ein the other side surface3chaving no curved wave groove of the eccentric unit3is further increased to achieve further reduction in weight.

Second Embodiment

A transmission device according to a second embodiment of the present invention will be described below.

In the second embodiment, the number of the curved wave grooves11formed in the one side surface4aof the rotary unit4is greater by 2 than the number of the curved wave grooves10formed in the one side surface3bof the eccentric unit3. Specifically, the curved wave groove10formed in the one side surface3bof the eccentric unit3is the epitrochoid wave groove having four waves and the curved wave groove11formed in the one side surface4aof the rotary unit4is the hypotrochoid wave groove having six waves, with the number of internal teeth1fon the inner peripheral wall of the cylindrical portion1aand the number of external teeth3aon the outer peripheral portion of the eccentric unit3in the first embodiment remaining unchanged.

In the second embodiment, Z1=80, Z2=70, Z3=4, and Z4=6 and thus the reduction ratio with the first rotary shaft8as the input shaft is 5/21. Rotation input from the first rotary shaft8is subjected to speed reduction to 5/21 and is output from the second rotary shaft9.

Third Embodiment

A transmission device according to a third embodiment of the present invention will be described below with reference toFIG. 4.

The third embodiment differs from the first embodiment in the following points. Specifically, a casing (housing)1covers a motor M as a drive unit. The one covering portion1bof the housing1is formed as a bulkhead1bthat separates a transmission portion including a first speed change portion A and a second speed change portion B from the motor M. In addition, the first rotary shaft is formed as a rotary shaft8of the motor M. The third embodiment has an arrangement similar to the first embodiment in other respects.

In the third embodiment, the transmission device including the drive unit can be made as one assembly so as to be formed compactly.

The first to third embodiments of the present invention have been explained above, but the present invention is not limited to the above embodiments and may be modified in a variety of ways as long as the modifications do not depart from the spirit and scope thereof.

For example, in the first to third embodiments, rotation input from the first rotary shaft8is to be output from the second rotary shaft9. An arrangement may be possible in which rotation input from the second rotary shaft9is output from the first rotary shaft8.

Additionally, in the first to third embodiments, the rolling elements13are each formed into a ball shape. The rolling elements13may each nonetheless be a roller shape or a pin shape.

The cylindrical portion1aof the housing1is required only to allow the internal teeth1fmeshing with the external teeth3aof the eccentric unit3to be formed on the inner peripheral wall thereof, and does not necessarily have to have a cylindrical shape.

Additionally, in the first to third embodiments, the curved wave groove10formed in the one side surface3bof the eccentric unit3and the curved wave groove11formed in the one side surface4aof the rotary unit4are the hypotrochoid wave groove and the epitrochoid wave groove. The present invention is not, however, limited to the foregoing arrangement. For example, one of the curved wave grooves may be a hypocycloid wave groove, while the other of the curved wave grooves may be an epicycloid wave groove.