DE112013005300T5 - transmission device - Google Patents

Abstract

A transmission device (1) includes an outer cylinder (2), a crankshaft (20), a support (4) rotatably supporting the crankshaft (20), and a spur gear (18) connected to the crankshaft (20) via a crankshaft (20) Serration is coupled. The serration (40) includes a protruding serration portion (41) formed on the crankshaft (20) and a recessed serration portion (42) formed in an inner peripheral surface of the spur gear (18) for defining an opening (18a) of the spur gear (18) is formed. The protruding serration portion (41) has inclined surfaces (41b) each of which is formed between adjacent ones of teeth (41a) of the protruded serration portion (41) at a proximal end of the protruded serration portion (41) and gradually toward an inner side of the protruded serration portion (41) inclines in a radially outward direction of the crankshaft (20). The spur gear (18) is held by the crankshaft (20) under the condition that webs are pressed against the inclined surfaces (41b), respectively.

Description

Technical area

The present invention relates to a transmission device.

Background of the invention

The transmission device described in Patent Document 1 is known as a small and light weight speed reducer designed to obtain a high speed reduction ratio. Such a transmission device is configured to transmit a rotational driving force of an engine to a crankshaft (eccentric shaft) and to rotate the crankshaft via a cylindrical input gear (intermediate gear) and a spur gear (transmission gear) meshing with the input gear.

The spur gear is coupled to one end of the crankshaft by serration. Specifically, the end of the crankshaft is formed with a protruded serration portion having teeth, whereas an inner peripheral surface surrounding an opening of the spur gear is provided with a recessed serration portion having recesses corresponding in shape to the teeth. When the crankshaft is inserted into the opening of the spur gear, the protruding and recessed serration portions mesh with each other. This engagement restricts the spur gear to the extent that there is no relative rotation between the spur gear and the crankshaft. A pair of retaining rings are attached to the crankshaft at both ends of the spur gear in the axial direction of the crankshaft. These restraint rings limit the spur gear to indicate that there is no relative movement between the spur gear and the crankshaft in the axial direction.

With regard to the transmission device described in Patent Document 1, the spur gear and the crankshaft are coupled to each other by the serration. The coupling section through the serration is configured such that the protruding and recessed serration portions mesh with each other when the crankshaft is inserted into the opening of the spur gear. For this purpose, in the coupling section by the serration, a small gap or play in the design or manufacturing tolerance is allowed. Therefore, wobbling of the spur gear in a rotational direction of the crankshaft is likely to occur when a large clearance occurs at the serration coupling section due to, for example, assembly or manufacturing accuracy of the spur gear and the crankshaft.

With respect to the gear device described in Patent Document 1, movement of the spur gear in the axial direction of the crankshaft is restricted by a pair of retaining rings. Therefore, wobbling of the spur gear in the axial direction is likely to occur due to design or assembly errors.

• Patentdruckschrift 1: JP 2010-286098 A

Wear on the spline coupling section while the transmission device is operated is likely to occur due to the influence of the wobble of the spur gear in the rotational and axial directions. It is also likely that vibrations will occur on the transmission device itself. It is also likely that the noise level is increasing.

• Patent Document 1: JP 2010-286098 A

Summary of the invention

An object of the present invention is to provide a transmission apparatus which is designed to reduce wear, vibration and noise in a coupling section between a spur gear and a crankshaft and to reduce the number of components.

According to one aspect of the present invention, a transmission apparatus for changing a rotational speed at a given rotational speed ratio for transmitting a driving force between a pair of complementary members includes an outer cylinder which is fixable to one of the complementary members; a crankshaft; a carrier fixable to another of the complementary members and received in the outer cylinder, the carrier supporting the crankshaft such that the carrier rotates relative to the outer cylinder in cooperation with the rotation of the crankshaft; and a spur gear coupled to one end of the crankshaft via serration. The serration includes a protruded serration portion formed at the end of the crankshaft and a recessed serration portion formed in an inner peripheral surface of the spur gear for defining an opening of the spur gear. The protruding serration portion includes teeth formed at intervals in a circumferential direction of the crankshaft and inclined surfaces each of which is formed between adjacent ones of the teeth at a proximal end of the protruded serration portion such that each of the inclined ones Surface gradually tends toward a proximal side of the protruding serration portion in a radially outward direction of the crankshaft. The recessed spline portion is provided with recesses formed along the inner peripheral surface of the spur gear for defining the opening, and lands each protruding between adjacent ones of the recesses between the adjacent teeth of the protruded spline portion. The spur gear is held by the crankshaft under the condition that webs are pressed against the inclined surfaces, respectively.

Brief description of the drawing

1 Fig. 10 is a sectional view of a transmission apparatus according to the first embodiment of the present invention.

2 FIG. 10 is an enlarged sectional view of a coupling section between a spur gear and a crankshaft of the transmission device. FIG.

3 Fig. 10 is a sectional view of a transmission device according to a second embodiment of the present invention.

4 FIG. 10 is an enlarged sectional view of a coupling section between a spur gear and a crankshaft of the transmission device of FIG 3 ,

Description of exemplary embodiments

Embodiments of the present invention will be described below in detail with reference to the drawings.

First embodiment

A transmission device 1 According to the first embodiment of the present invention, it is designed as a speed reducer which can be used, for example, in rotary sections in a rotary body, an arm joint and the like of a robot and rotary sections of various machine tools. Will the transmission device 1 used in a rotary section of a robot, so is the transmission device 1 adapted to transmit a driving force between a base and a rotary body while changing a rotational speed at a given rotational speed ratio such that the rotary body is rotated relative to the base.

As in 1 is shown includes the transmission device 1 according to the first embodiment: an outer cylinder 2 ; an internal tooth pin 3 ; a carrier 4 ; a main camp 6 ; crankshafts 20 ; a crankshaft bearing 22 ; an oscillation gear 24 ; an input gear (not shown); Spur gears 18 , each with one of the crankshafts 20 is coupled; and retaining rings 43 for preventing falling, wherein each of the retaining rings 43 axially outside each of the spur gear wheels 18 is provided.

The outer cylinder 2 has a shape that can be fixed to one of two complementary elements (for example, the base of a robot), and acts as a housing of the transmission device 1 , The outer cylinder 2 is formed substantially in a cylindrical shape. The outer cylinder 2 is attached to the base of the robot by a bolt or the like. A majority of the interdental pins 3 is on the inner surface of the outer cylinder 2 at regular intervals in the circumferential direction of the inner surface. The internal teeth pins 3 act as internal teeth, with the Oszillationsgetrieberad 24 as an external toothed gear. The oscillation gear has a few teeth less than the internal teeth pins 3 on. In the first embodiment, two (several) Oszillationsgetrieberäder 24 used.

The carrier 4 has a shape that is fixable to the other complementary element (for example, rotary body of the robot). The carrier 4 turns relative to the outer cylinder 2 , The carrier 4 is in the outer cylinder 2 so absorbed that the carrier 4 coaxial with the outer cylinder 2 becomes. In the first embodiment, the carrier rotates 4 relative to the outer cylinder 2 about a common axis. The carrier 4 is fixed to a rotary body of the robot by a bolt or the like. Will the carrier 2 relative to the outer cylinder 2 rotated, the rotary body of the robot is rotated at the base.

The present embodiment shows an example in which the carrier 4 is attached to the rotary body and is rotated while the outer cylinder 2 immovably fixed to the base. However, the arrangement thereof may also be reversed. In short, the outer cylinder 2 may also be attached to the rotary body while the carrier 4 can be attached to the base.

The carrier 4 is from a couple of main bearings 6 supported, which are axially aligned with each other at a distance such that a relative rotation between the carrier 4 and the outer cylinder 2 allowed is. The carrier 4 includes a carrier base 32 and an end plate portion 34 , A recording room 33 is trained between them. The oscillation gears 24 acting as a transmission element for transmitting a rotational force between the outer cylinder 2 and the carrier 4 serve are in the reception room 33 added.

The carrier base 32 includes a base plate section 32a in the outer cylinder 2 close to one end of the outer cylinder 2 located, and wave sections 32b extending axially from the base plate section 32a out to the end plate section 34 extend. Each of the shaft sections 32b is through a pen 7 positioned at a given position in the end plate portion and then at the end plate portion 34 through a bolt 5 attached. Accordingly, the carrier base 32 with the end plate section 34 integrated. The carrier 4 includes a through hole 4a extending axially through a radially central region of the carrier 4 extends. The recording room 33 communicates with the appearance of the wearer 4 through the through hole 4a ,

It is a majority of crankshafts 20 (For example, three in the present embodiment). The crankshafts 20 are at regular intervals in the circumferential direction of the carrier 4 (at intervals of 120 °) arranged. Each of the crankshafts 20 is rotatable from the carrier 4 through a pair of crankshaft bearings 22 supported.

Each of the crankshafts 20 has a plurality of (in the first embodiment, two) eccentric portions 20a on. The eccentric sections 20a are axial between the crankshaft bearings 22 educated. Each of the eccentric sections 20a is formed in the form of a column whose axis with respect to the axis of the crankshaft 20 eccentric by a given eccentric amount. The eccentric sections 20a are in the crankshaft 20 formed with a phase difference of a given angle. It can also be an eccentric section 20a be used.

Each of the oscillation gears 24 is at each of the eccentric sections 20a the crankshaft 20 through a rolling bearing 28b appropriate. Each of the oscillation gears 24 is formed with a dimension slightly smaller than an inner diameter of the outer cylinder 2 is. Will each of the crankshafts 20 rotated, so occurs an oscillatory rotation of the Oszillationsgetrieberädern 24 in Kämm with the internal tooth pins 3 in cooperation with an eccentric rotation of the eccentric sections 20a on.

Each of the oscillation gears 24 includes a central through hole 24b , Eccentric section insertion holes 24c and shaft portion insertion holes 24d ,

The eccentric section insertion holes 24c are circumferentially around the central through hole 24b of the oscillation gear 24 provided around at regular intervals. Each of the eccentric sections 20a the crankshafts 20 is in each of the eccentric portion insertion holes 24c introduced, the rolling bearing 28a in between.

The shaft portion insertion holes 24d are circumferentially around the central through hole 24b of the oscillation gear 24 provided around at regular intervals. Each of the shaft portion insertion holes 24d is between circumferentially adjacent ones of the eccentric portion insertion holes 24c located. Each of the shaft sections 32b is in each of the shaft portion insertion holes 24d introduced with a gap.

An end of each of the crankshafts 20 is from the carrier 4 to the outside along the axial direction of the carrier 4 in front. Each of the front gears 18 is with the end of each of the crankshafts 4 that is outside the carrier 4 extends, coupled by a serration. The present invention is not limited to a configuration in which the spur gear 18 outside the carrier 4 is located. The transmission device may for example also be designed such that the carrier with a concave portion in which the Stirngetrieberad 18 is located, is provided.

The movement of the front gear 18 is on the crankshaft 20 in the rotational and axial directions by engaging in a coupling section of the serration 40 limited.

In particular, as in 2 shown is the serration 40 for coupling the spur gear 18 with the crankshaft 20 a protruding serration section 41 , which is at the end of the crankshaft 20 from the carrier 4 is formed projecting to the outside, and a recessed serration section 42 located in an inner circumferential surface of the spur gear 18 to set an opening 18a of the forehead gear 18 is trained.

The protruding serration section 41 includes teeth 41a at regular intervals in the circumferential direction of the crankshaft 20 are formed. It is not necessary, the teeth 41a at regular intervals in the circumferential direction. The teeth 41a may be formed at any intervals in the circumferential direction.

The protruding serration section 41 also includes inclined surfaces 41b each of which is between adjacent teeth 41a in the proximal end of the protruding serration section 41 is trained. Each of the inclined surfaces 41b is gradual toward the proximal end of the protruding serration section 41 in the radially outward direction of the crankshaft 20 inclined.

For example, a hobbed section may be used as a sloped surface 41b are used, wherein the high-heel increased section is produced when a cutting machine equipped with a serration machining hob, the protruding serration section 41 forms. The present invention is not specific to a method of forming the inclined surfaces 41b limited. The inclined surface 41b can be formed by any other suitable method.

The withdrawn serration section 42 includes recesses 42a along the inner circumferential surface of the spur gear 18 for fixing the opening 18a are formed. Each of the recesses 42a is at regular intervals in the circumferential direction of the spur gear 18 formed such that each of the recesses 42 has a shape which is an insertion of each of the teeth 41a the protruding serration section 41 allows. It is not necessary the recesses 42a train at regular intervals. The recesses 42 may be at any intervals corresponding to a distance between adjacent ones of the teeth 41a be educated.

The withdrawn serration section 42 also includes bars 42b each of which is between adjacent recesses 42a between the neighboring teeth 41a the crankshaft 20 is formed above.

At the in 2 shown embodiment, edges of the opening 18a of the forehead gear 10 (that is, edges of each of the webs 42b ) subjected to rejuvenation. However, the present invention is not limited to this, and tapering may be omitted.

In the above-described embodiment, when the end of the crankshaft 20 in the opening 18a of the forehead gear 18 is introduced, the teeth 41a the protruding serration section 41 in the recesses 42a the withdrawn serration section 42 each introduced such that the withdrawn serration section 42 of the forehead gear 18 with the above serration section 41 the crankshaft 20 combs. During this process, the bridge becomes 42b between adjacent recesses 42a the withdrawn serration section 42 between adjacent teeth 41a the protruding serration section 41 introduced. The bridges 42a are then against the inclined surfaces 41b pressed, respectively in the proximal end of the protruding serration section 41 are formed. In this condition, the wedge effect of the inclined surfaces increases 41b in short, the compressive force with the action of the inclined surfaces 41b on the footbridges 42b in the radially outward direction of the crankshaft 20 , the frictional force in the interface between the inclined surfaces 41b and the jetties 42b , As a result, the spur gear is 18 with the crankshaft 20 engaged and held by this. Accordingly, the spur gear 10 firmly with the crankshaft 20 at the serration 40 for coupling the spur gear 10 with the crankshaft 20 connected without wobbling in any of the rotational and axial directions.

Each of the retaining rings 43 is on each of the crankshafts 20 on the distal end side of the crankshaft 20 for each of the front gears 10 assembled. The rear holder 43 is designed to prevent the spur gear 10 from the crankshaft 20 drops. The retaining ring 43 is formed of a C-shaped (that is, a partially discontinuous, non-closed, arcuate) member made of a metal material. After formation of the engagement of the spur gear 18 with the inclined surfaces 41b the protruding serration section 41 the crankshaft 20 the retaining ring expands 43 once and then on an annular groove 20b located in an outer circumferential surface of the crankshaft 20 is educated, watch out. The retaining ring 43 then contracts in a radially inward direction by its restoring force, so that the retaining ring 43 firmly at the end of the crankshaft 20 is attached.

A position of the crankshaft 20b is chosen such that the retaining ring 43 in contact with or adjacent a lateral surface of the spur gear 18 in the groove 20b is fitted when the webs 42a each against the inclined surfaces 41b be pressed, the Stirngetrieberad 18 at the end of the crankshaft 20 is mounted at a given position. The fact that the spur gear 18 at the end of the crankshaft 20 is mounted at an accurate position is therefore confirmed by the fact that the retaining ring 43 in the groove 20b is fitted.

The spur gear 18 as shown in 1 and 2 has teeth that extend parallel to the axial direction. Therefore, a force acting on the spur gear 18 acting in the axial direction, compared to a bevel gear during rotation of the Stirngetrieberades 18 that meshes with the input gear (not shown) is comparatively small. Corresponding There is no great force in the axial direction on the retaining ring 43 during operation of the transmission device.

Each of the front gears 18 meshes with the input gear (not shown). When a rotational drive force from a motor outside the transmission device acts on the input gear, the rotational drive force is applied to each of the spur gear wheels 18 transfer.

Next is the operation of the spur gear 1 described according to the first embodiment.

A rotational drive force from the engine outside the transmission device 1 gets on each of the front gears 18 transmitted via the input gear (not shown), so that each of the crankshafts 20 is rotated about the axis thereof.

The eccentric sections 20a become eccentric due to the rotation of the crankshaft 20 turned. An oscillatory rotation occurs on the oscillation gears 24 on that with the internal toothpicks 3 on the inner surface of the outer cylinder 2 in cooperation with the eccentric rotation of the eccentric sections 20a comb. The oscillatory rotation of the oscillation gears 24 gets on the carrier 4 over the crankshafts 20 transfer. In the present embodiment, the outer cylinder 2 immovable at the base 52 fixed, so the carrier 4 and the rotating body 50 relative to the outer cylinder 2 and the base 52 are rotated at a reduced rotational speed with respect to the input rotation.

Features of the first embodiment

• (1) Looking at the transmission device 1 according to the first embodiment, the recessed serration section meshes 42 in the opening 18a of the forehead gear 18 is formed, with the protruding serration section 41 the crankshaft 20 , The inclined surfaces 41b located in the proximal region of the protruding serration section 41 are formed, respectively, against the webs 42b the withdrawn serration section 42 pressed. In this state, the inclined surfaces become 41b each firmly against the bars 42b to cause a large frictional force at the interface therebetween, resulting in a so-called "wedge effect". Therefore, the spur gear is 18 with the crankshaft 20 engaged and held by this. Accordingly, no wobbling occurs in any of the rotational and axial directions in the serration 40 as a coupling section between the spur gear 18 and the crankshaft 20 on. This makes it possible to reduce wear, vibration and noise in the serration coupling section. In addition, it is not necessary that a pair of retaining rings the Stirngetrieberad 18 stops to the axial movement of the spur gear 18 limit. Accordingly, a reduction in the number of components occurs.
• (2) Looking at the transmission device 1 According to the first embodiment, even if the wedge effect is weakened due to vibrations during running, the retaining ring 43 , on the crankshaft 20 on the end side of the crankshaft 20 for the spur gear 18 mounted, prevent the spur gear 18 from the crankshaft 20 drops. Therefore, it becomes possible to improve safety.
• (3) Looking at the transmission device 1 according to the first embodiment, the C-shaped retaining ring 43 made of a metal material, used as a stop on the crankshaft 20 on the end side of the crankshaft 20 for the spur gear 18 is mounted. This makes it possible, the Stirngetrieberad 18 at the end of the crankshaft 20 firmly attach, resulting in a further improved effect of preventing a fall of the spur gear 19 leads.

Modifications of the first embodiment

• (A) Looking at the transmission device 1 according to the first embodiment, the retaining ring 43 axially outside of the spur gear 18 assembled. However, the present invention is not limited thereto. The retaining ring 43 can also be omitted. Even if the retaining ring 43 is omitted, the transmission device 1 be used because of the withdrawn serration section 42 of the forehead gear 18 with the inclined surfaces 41b on the proximal side of the protruding serration section 41 the crankshaft 20 is engaged and held by them. It should be clear that the retaining rings 43 can be provided for improved security.
• (B) In the first embodiment, a retaining ring 43 for each of the crankshafts 18 provided to prevent the spur gear 18 falls. However, the present invention is not limited thereto. Two or more of the retaining rings 43 can for each of the crankshafts 18 be used. When using two or more retaining rings 43 for each of the crankshafts 18 can the two or more retaining rings 43 be used for an assumed width of the retaining rings 43 adjust when a spur gear 18 against another spur gear 18 is replaced with a different thickness, so that the occupied width for the other Stirngetrieberad 18 suitable is. Therefore, there is a very large fluctuation range from which the Stirngetrieberad 18 can be freely selected. Alternatively, a shim can be used in combination with a retaining ring 43 be used so that the thickness of the shim is used for width adjustment.
• (C) Although the transmission device according to the first embodiment is configured such that the crankshafts 20 around the central through hole 4a (please refer 1 ), the present invention is not limited thereto. For example, it is also possible to use a central crankshaft type, the central crankshaft type being a crankshaft 20 that in the radially central region of the carrier 4 is located.
• (D) In the first embodiment, the spur gear is 18 in the end of the crankshaft 20 from the side of the end plate section 34 of the carrier 4 introduced to the outside prominently. However, the present invention is not limited thereto. The transmission device may for example also be designed such that one end of the crankshaft 20 from the carrier base 32 of the carrier 4 protrudes outwards, so that the Stirngetrieberad 18 is mounted at this end.

Second embodiment

The transmission device 1 has been described as an example in connection with the first embodiment, wherein the transmission device 1 used the existing of a metal material C-shaped retaining ring as a stop on the crankshaft 20 on the distal end side of the crankshaft 20 for the spur gear 18 is mounted so this is not from the crankshaft 20 drops. However, the present invention is not limited thereto. Any other suitable stop, not the retaining ring 43 is, can also be used.

For example, an O-ring 45 in place of the metal material C-shaped retaining ring 43 at the in 3 and 4 shown transmission device 1 used. The rest is the same as in the first embodiment, so that a description thereof can be omitted.

The O-ring 45 is a continuous annular member made of an elastic material such as resin.

Like the retaining ring 43 is also the O-ring 45 on each of the crankshafts 20 on the distal end side of the crankshaft 20 for each of the front gears 18 fitted so that the O-ring 45 prevents the spur gear 18 from the crankshaft 20 drops. After the front gear 18 with the inclined surfaces 41b the protruding serration section 41 the crankshaft 20 engaged, the O-ring 45 on a groove 20b the crankshaft 20b paying attention. The groove 20b is in an outer peripheral surface of the crankshaft 20 formed in the form of a ring.

Feature of the second embodiment

• (1) Looking at the transmission device 1 According to the second embodiment, even if the above-described wedge effect is weakened by vibrations during running, the O-ring 45 , on the crankshaft 20 on the distal end side of the crankshaft 20 for the spur gear 18 mounted, prevent the spur gear 18 from the crankshaft 20 drops. Therefore, safety can be improved.
• (2) The transmission device 1 according to the second embodiment uses the O-ring 45 made of an elastic material, as a stop, so that it is easy, the stop on the crankshaft 20 to assemble. This facilitates the automation of the assembly of the transmission device 1 ,

Modification of the second embodiment

Looking at the transmission device 1 according to the second embodiment, the O-ring 45 to prevent falling off the front gear 18 located. However, the present invention is not limited thereto, and therefore, the O-ring 45 can also be omitted. Even if the O-ring 45 is omitted, the transmission device 1 be used because of the withdrawn serration section 42 of the forehead gear 18 with the inclined surfaces 41b on the proximal side of the protruding serration section 41 the crankshaft 20 is engaged and held by it. It should be clear that the O-rings 45 can be provided for improved safety.

Summary of the embodiments

The above-described embodiments will be summarized below.

In the above-described embodiments, the recessed serration portion formed inside the opening of the spur gear meshes with the protruding serration portion of the crankshaft. The inclined surfaces formed in the proximal portion of the protruded serration portion are respectively pressed against the ribs of the recessed serration portion. In this state, the inclined surfaces are respectively pressed firmly against the ridges to cause a large frictional force at the interface therebetween and to obtain a so-called "wedge effect". Therefore, the spur gear is engaged with the crankshaft so that the spur gear is held by the crankshaft. Accordingly, no wobble occurs in any of the rotational and axial directions in a coupling section between the spur gear and the crankshaft. This makes it possible to reduce wear, vibration and noise in the coupling section. Moreover, it is not necessary to hold the spur gear by using a pair of retaining rings that restrict the axial movement of the spur gear. This leads to a reduced number of components.

The transmission device may further include a stopper mounted on the crankshaft on the distal end side of the crankshaft for the spur gear to prevent the spur gear from falling off the crankshaft.

With regard to the spur gear having this feature, even if the wedge effect is weakened by vibrations during running, the retaining ring mounted on the crankshaft on the distal end side of the crankshaft for the spur gear can prevent the spur gear from the crankshaft drops. Therefore, the security is improved.

The stopper may be a C-shaped retaining ring made of a metal material.

According to the above-described configuration, the retaining ring is fixedly secured to the end of the crankshaft, resulting in a very effective prevention of dropping.

Alternatively, the stopper may be an O-ring made of an elastic material.

According to the above-described embodiment, it becomes easy to mount the stopper on the crankshaft. This simplifies the automation of the assembly of the transmission device.

As described above, in the above-described embodiments, it becomes possible to reduce wear, vibration, and noise in the coupling section between the spur gear and the crankshaft. Moreover, it is not necessary to hold the spur gear using a pair of retaining rings that restrict the axial movement of the spur gear. This requires a reduced number of components.

Claims (4)

A transmission device for changing a rotational speed at a given rotational speed ratio for transmitting a driving force between a pair of complementary elements, comprising: an outer cylinder which is fixable to one of the complementary elements; a crankshaft; a carrier which is fixable to another of the complementary elements and received in the outer cylinder, wherein the carrier supports the crankshaft so that the carrier rotates relative to the outer cylinder in cooperation with the rotation of the crankshaft; and a spur gear coupled to one end of the crankshaft via serration, wherein the serration includes a protruded serration portion formed at the end of the crankshaft and a recessed serration portion formed in an inner peripheral surface of the spur gear for defining an opening of the spur gear; wherein the protruded spline portion includes teeth formed at intervals in a circumferential direction of the crankshaft and inclined surfaces each of which is formed between adjacent ones of the teeth at a proximal end of the protruded serration portion such that each of the inclined surfaces gradually approaches one proximal side of the protruding serration section in a radially outward direction of the crankshaft; and wherein the recessed serrated portion is provided with recesses formed along the inner circumferential surface of the end gear for defining the opening, and lands each of which is protruded between adjacent ones of the recesses between the adjacent teeth of the protruded serration portion, and wherein the spur gear is held by the crankshaft under the condition that the ridges are respectively pressed against the inclined surfaces. The transmission apparatus according to claim 1, further comprising a stopper mounted on the crankshaft at an end-side position for the spur gear, the stopper preventing the spur gear from falling off the crankshaft. Transmission device according to claim 2, wherein the stopper is a C-shaped retaining ring, which consists of a metal material. Transmission device according to claim 2, wherein the stopper is a C-shaped retaining ring, which consists of an elastic material.

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