JP7301281B2 - Gears, drive transmission devices and image forming devices - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear having a plurality of tooth rows with the same pitch and out of phase, and a drive transmission device and an image forming apparatus using the gear.

2. Description of the Related Art Conventionally, gears having a plurality of phased tooth rows have been used in drive transmission devices that require precise driving, such as photosensitive member driving in image forming apparatuses. It is possible to increase the meshing ratio with a plurality of phased tooth rows, disperse the load applied to each tooth, and improve durability (Patent Document 1: Japanese Patent No. 2710861, Patent Document 2: Japanese Patent No. 3387719).

On the other hand, as shown in FIGS. 4A to 4C, gears 100 and 200 formed with connecting rings 120 and 220 have been proposed in order to compensate for the strength of the face width that has become thinner due to the double-row tooth row (Patent Document 3: Japanese Patent No. 4508552). In the gears 100 and 200, a gap C is provided between a plurality of tooth rows in the axial direction as shown in FIG. 4B. , 220 projecting in the axial direction. By integrally connecting a plurality of tooth rows with the connecting rings 120 and 220, the lack of strength due to the thin tooth width is compensated for.

However, since the sliding surface S between the radial side surface 120b of one connecting ring 120 and the radial side surface 210b of the opposing tooth row 210 is wide, there is a problem of sliding friction resistance and noise and vibration due to sliding. was SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to reduce the sliding area between gears having a plurality of phased tooth rows, thereby reducing sliding frictional resistance and noise and vibration caused by sliding.

In order to solve the above-mentioned problems, the gear of the present invention has a plurality of tooth rows having the same pitch, the phases of adjacent tooth rows and teeth are shifted in the circumferential direction, and a gap is formed between each other in the axial direction, The plurality of tooth rows are integrally connected to each other by a connecting ring that protrudes in the axial direction toward the opposing tooth row on the tooth root side of each tooth row, and the connecting ring is a counterpart side that meshes with the plurality of tooth rows. A sliding surface is formed between the connecting ring of the plurality of tooth rows and is spaced apart from each tooth row in the axial direction and slides on each other, and the axial relative position of the plurality of tooth rows that mesh with each other by the sliding surface is regulated.

ADVANTAGE OF THE INVENTION According to this invention, the noise and vibration by sliding frictional resistance and sliding can be reduced.

1 is a cross-sectional view of meshing gears according to a first embodiment of the present invention; FIG. FIG. 10 is a cross-sectional view of meshing gears according to a second embodiment of the present invention; FIG. 10 is a cross-sectional view of meshing gears according to a third embodiment of the present invention; FIG. 11 is a cross-sectional view of meshing gears according to a fourth embodiment of the present invention; FIG. 11 is a cross-sectional view of engagement of gears according to a modification of the fourth embodiment; FIG. 11 is a cross-sectional view of meshing gears according to a fifth embodiment of the present invention; FIG. 11 is a cross-sectional view of engagement of gears according to a modification of the fifth embodiment; 1 is a perspective view of a gear according to a first embodiment; FIG. 1 is a schematic diagram of an image forming apparatus using gears according to an embodiment of the present invention; FIG. 1 is a perspective view of a conventional gear having multiple tooth rows; FIG. 1 is an enlarged perspective view of tooth portions of a conventional gear having a plurality of tooth rows; FIG. 1 is a meshing cross-sectional view of a conventional gear having multiple tooth rows; FIG.

A fixing device and an image forming apparatus (laser printer) according to embodiments of the present invention will be described below with reference to the drawings. A laser printer is an example of an image forming apparatus, and the image forming apparatus is not limited to a laser printer. That is, the image forming apparatus can be configured as a copier, a facsimile machine, a printer, a printing machine, or an inkjet recording apparatus, or a multifunction machine combining at least two of these.

The same or corresponding parts in each figure are denoted by the same reference numerals, and redundant description thereof will be appropriately simplified or omitted. Also, the dimensions, materials, shapes, relative positions, and the like in the description of each component are examples, and are not intended to limit the scope of the present invention unless otherwise specified.

In the following embodiments, the "recording medium" is described as "paper", but the "recording medium" is not limited to paper (paper). The "recording medium" includes not only paper but also OHP sheets, fabrics, metal sheets, plastic films, or prepreg sheets in which carbon fibers are previously impregnated with resin.

The term "recording medium" also includes media to which developer and ink can be applied, recording paper, and recording sheets. In addition to plain paper, "paper" includes thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

In addition, the term "image formation" used in the following description refers not only to imparting meaningful images, such as characters and figures, to a medium, but also to imparting meaningless images, such as patterns, to a medium. also means

In the image forming apparatus shown in FIG. 3, a large number of gears are used to transmit driving force from a motor, which is a power source, to rotating bodies such as rollers and shafts. The image forming apparatus will be described later. First, referring to five embodiments of gears 100 and 200 used in the image forming apparatus shown in FIGS. 1A to 1G and FIG. 2 which is a perspective view of the first embodiment. explain. However, it goes without saying that the gear or drive transmission device of the present invention can be used in other than the image forming apparatus.

(First embodiment)
FIG. 1A is a cross-sectional view of a state in which gears 100 and 200 of the first embodiment are in mesh with each other. That is, the gears 100 and 200 of the same shape each have two tooth rows 110 and 210 with the same pitch circle (pitch line P), and the tooth tip 110a of the tooth row 110 of one gear 100 is the same as that of the other gear. 200 tooth rows 210 are meshed with each other between tooth tips 210a.

The gears 100 and 200 are of the same module and integrally formed of two spur gears phased at a 1/2 pitch. One gear 200 will be described with reference to the perspective view of FIG. 2. Two tooth rows 210, 210 having the same pitch circle are formed with a predetermined gap C in the axial direction. The two tooth rows 210, 210 are circumferentially out of phase with each other by a half pitch. A connecting ring 220 having an outer diameter slightly larger than the diameter of the pitch line P is formed between the two tooth rows 210 , 210 .

A connecting ring 220 integrally connects the two tooth rows 210 , 210 in the axial direction. That is, the two tooth rows 210 , 210 whose phases of the teeth are shifted by half a pitch are laminated together in the axial direction via the disk-shaped portion of the connecting ring 220 . The connecting ring 220 has a small-diameter narrow first portion 221 that is continuous in the circumferential direction, and a large-diameter portion 221 that is intermittently formed at equal intervals in the circumferential direction and forms part of the tooth roots of the two tooth rows 210 , 210 . and a wide second portion 222 .

The small-diameter first portion 221 is connected to the root side of one tooth row 210 via the large-diameter second portion 222 , while the first portion 221 is connected to the second portion 222 of the other tooth row 210 . It is When the gears 100 and 200 are meshed with each other as shown in FIG. 1A, a predetermined gap is provided between the outer peripheral surfaces 121a and 221a of the first portions 121 and 221 and the outer peripheral surfaces 122a and 222a of the second portions 122 and 222. are intermittently formed at regular intervals in the circumferential direction.

The side surfaces 122b, 222b of the second portions 122, 222, which extend radially outward from the first portions 121, 221, overlap each other on the sliding surface S. This sliding surface S is included in the shaded portion in FIG. The size of the sliding surface S is almost halved compared to FIG. 4C showing the conventional sliding surface S, and the position of the sliding surface S includes the pitch line P, that is, the pitch circle in the radial direction. It can be seen that it is formed across the

That is, the sliding surface S in FIG. 1A is formed in a narrow range that traverses the pitch line P (pitch circle) radially inward and outward. As a result, when the gears 100 and 200 mesh and rotate, the linear velocity difference between the radial side surfaces 122b and 222b constituting the sliding surface S becomes almost zero, thereby reducing sliding friction resistance, sliding noise, and vibration accompanying sliding. can do.

Furthermore, in manufacturing the molds for the gears 100 and 200, the mold surface for forming the sliding surface S is a flat surface that can be easily manufactured in one step using a milling machine or the like. For this reason, the gears 100 and 200 obtained by mold molding are less likely to cause variation in the position of each sliding surface S, and it is easy to reduce sliding frictional resistance, sliding noise, and vibration associated with sliding. Further, increasing the precision of the sliding surface S is also beneficial for improving the relative positioning precision between the gears 100 and 200 in the rotation axis direction.

(Second embodiment)
FIG. 1B is a cross-sectional view showing a state in which gears of the second embodiment of the present invention are meshed. In this second embodiment, two sliding surfaces S1 and S2 are formed between connecting rings 120 and 220. As shown in FIG. One sliding surface S1 is formed between the radial side surface 121b of the first portion 121 of the connecting ring 120 of the gear 100 and the radial side surface 222b of the second portion 222 of the connecting ring 220 of the gear 200. .

The other sliding surface S2 is formed between the radial side surface 122b of the second portion 122 of the connecting ring 120 of the gear 100 and the radial side surface 221b of the first portion 221 of the connecting ring 220 of the gear 200. . The two sliding surfaces S1 and S2 are smaller in area than the sliding surface S of the first embodiment described above. The first portions 121, 221 are wider than the second portions 122, 222, but otherwise the same as in the first embodiment.

When the gears 100, 200 are in mesh with each other, the coupling rings 120, 220 contact each other on the sliding surfaces S1, S2, thereby regulating the relative positions of the gears 100, 200 in the rotation axis direction. In addition, by arranging two sliding surfaces S1 and S2 which are closer to the pitch line P and have a smaller area than the sliding surface S of the first embodiment on the inside and outside of the pitch line P in the radial direction, the sliding friction resistance and the sliding It is possible to further reduce dynamic noise and vibration accompanying sliding.

Further, as in the first embodiment, variations in the positions of the sliding surfaces S1 and S2 are less likely to occur, and sliding frictional resistance, sliding noise, and vibration accompanying sliding can be easily reduced. Further, increasing the precision of the sliding surfaces S1 and S2 is also beneficial for improving the relative positioning precision between the gears 100 and 200 in the rotation axis direction.

(Third embodiment)
FIG. 1C is a cross-sectional view showing a state in which the gears 100 and 200 of the third embodiment of the present invention are meshed with each other. extends obliquely across the pitch line P at . That is, the shape of the sliding surface S is not limited to the axial direction or the shape perpendicular to the pitch line P, and may intersect the pitch line P at an angle (approximately 30° in the illustrated example) as shown in FIG. 1C. .

Connection rings 120 and 220 having an outer diameter including the pitch line P are formed between the two rows of teeth 110 and 210 of the gears 100 and 200, respectively. Each two rows of tooth rows 110 and 210 are integrally connected in the axial direction by the connecting rings 120 and 220 .

The connecting rings 120, 220 are composed of first portions 121, 221 of small diameter and wide width which are continuous in the circumferential direction, and large diameter and narrow first portions 121, 221 which are intermittently formed in the circumferential direction and form part of the root of each tooth row 110, 210. It consists of second parts 122 , 222 . When the gears 100 and 200 are meshed with each other as shown in FIG. 1C, the inclined surfaces 121c and 221c of the first portions 121 and 221 overlap each other to form the sliding surface S. As shown in FIG.

When the gears 100 and 200 mesh and rotate, the difference in linear velocity between the inclined surfaces 121c and 221c forming the sliding surface S becomes almost zero, so that sliding friction resistance, sliding noise, and vibration accompanying sliding can be reduced. . Advantages in mold manufacturing, relative positioning accuracy between gears 100 and 200, and the like are the same as in the first and second embodiments described above.

As a function and effect unique to the inclination of the sliding surface S, an effect that the contact of the sliding surface S in the meshing rotation of the gears 100 and 200 becomes smooth in the circumferential direction can be expected, and noise and sliding are further reduced. Effective for reduction. Of course, the sliding surfaces S, S1, and S2 shown in FIGS. 1A and 1B may also be inclined with respect to the pitch line P as in the third embodiment shown in FIG. 1C.

(Fourth embodiment)
1D and 1E are cross-sectional views showing a state in which gears of a fourth embodiment of the present invention are meshed with each other. In this embodiment, the connecting rings 120, 220 have a constant outer diameter and are not divided into a first portion and a second portion as in FIGS. 1A and 1B. Instead, a convex portion 210c is formed on the radial side surface 210b of one tooth row 210. As shown in FIG. Compared with the conventional FIG. 4C, the only difference between the two is the presence or absence of the convex portion 210c.

A sliding surface S is formed by overlapping the tip of the convex portion 210c and the radial side surface 120b of the connecting ring 120 of the mating gear 100. As shown in FIG. The size of this sliding surface S can be reduced to a fraction of the size of the conventional sliding surface S shown in FIG. 4C. The shape of the protrusions 210c is arbitrary, and one or a plurality of protrusions 210c can be formed in a dot shape for each tooth, or can be formed as streaky protrusions extending in the circumferential direction.

The position of the convex portion 210c may be formed close to the tooth tip 210a of the tooth row 210 as shown in FIG. may be formed by As a result, the linear velocity difference on the sliding surface S becomes almost zero, and sliding frictional resistance, sliding noise, and vibration accompanying sliding can be further reduced.

(Fifth embodiment)

1F and 1G are cross-sectional views showing a state in which the gears of the fifth embodiment of the present invention are in mesh with each other. In this embodiment, a connecting ring 120 of the gear 100 has a radial side surface 120b formed with a protrusion 120c.

The convex portion 120c may be formed close to the tip of the tooth row 210 as shown in FIG. 1F, or may be formed away from the tip of the tooth row 210 and close to the pitch line P as shown in FIG. 1G. You may As a result, the linear velocity difference on the sliding surface S becomes almost zero, and sliding frictional resistance, sliding noise, and vibration accompanying sliding can be further reduced.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are possible based on the technical concept of the scope of claims. For example, the gears of the above-described embodiments are described assuming that two spur gears of the same module are integrally formed with the phases of the teeth shifted by 1/2 pitch, but the gears are not necessarily limited to this. isn't it. For example, it is possible to use two integrally molded gears whose modules differ by an integral multiple. It is also possible to use two helical gears of the same module with the same helix angle and opposite helix directions that are integrally molded out of phase, that is, a gear shaped like a helical gear. It is possible.

Furthermore, the amount of phase shift is not limited to 1/2 pitch, and it is possible to arbitrarily change the amount of shift as required. For example, in an embodiment with three rows of teeth, a "1/3 pitch offset" is also possible in addition to a half pitch offset. In addition, chamfers may be formed at the ends of the sliding surfaces S, S1, and S2 in the circumferential direction so as to smoothen the overlapping of the opposing surfaces that constitute the sliding surfaces.

(laser printer)
An embodiment in which the gear or drive transmission device of the above-described embodiment of the present invention is applied to the copying machine shown in FIG. 3 as an image forming apparatus will be described below. This copying machine functions as a so-called digital color copying machine, which digitizes image information obtained by scanning and reading an original and uses it for image formation. This copying machine also has a facsimile function for exchanging image information of a document with a remote location, and a so-called printer function for printing image information handled by a computer on paper.

In FIG. 3, the copying machine forms an image on paper by an intermediate transfer method using an intermediate transfer belt 11, and is a tandem-type electronic printer that forms toner images of each color with dedicated process cartridges. A photographic device. A multi-tiered sheet feeding section 2 is provided at the lowermost portion of the copier in the vertical direction.

An image forming section 1 is provided above it, and a scanner section 3 is provided above it. At each stage of the paper feed unit 2, a paper feed tray 21 is provided for accommodating a sheet bundle including plain paper as a recording member, OHP sheets, second original drawings, and the like.

Approximately in the center of the image forming section 1, a transfer device 10 is provided, on which an endless intermediate transfer belt 11 is stretched by a plurality of rollers provided inside a belt loop. The intermediate transfer belt 11 rotates (surface moves) clockwise in the figure. Four process cartridges 40Y, 40M, 40C, and 40K for forming yellow, magenta, cyan, and black toner images are arranged above the intermediate transfer belt 11 along the surface movement direction of the intermediate transfer belt 11. is set.

Hereinafter, Y, M, C, and K, which are color codes, will be omitted as appropriate. Above the four process cartridges 40, two optical writing units 20a and 20b are provided as latent image writing means.

Each process cartridge 40 is provided with a drum-shaped photosensitive member 41 as a latent image carrier. Each photoreceptor 41 is rotatable counterclockwise in the drawing, and is surrounded by a known charging device 42, developing device 43, photoreceptor cleaning device 44, and lubricant coating device 45. is provided. The gears 100 and 200 and the drive transmission device according to the embodiment of the present invention described above are used at least for rotationally driving the photoreceptor 41, but can also be used for rotationally driving rollers and belts other than the photoreceptor 41. Of course.

In FIG. 3, the transfer device 10 has an intermediate transfer belt 11, a belt cleaning device 17, four primary transfer rollers 46, and the like. The intermediate transfer belt 11 is tensioned by a plurality of rollers including a tension roller 14 , a drive roller 15 and a secondary transfer counter roller 16 . Then, it is endlessly moved clockwise in the figure by the rotation of the drive roller 15 driven by the belt drive motor.

The four primary transfer rollers 46 are arranged so as to be in contact with the inner peripheral surface of the intermediate transfer belt 11, respectively, and receive application of a primary transfer bias from a power source. Further, the intermediate transfer belt 11 is pressed from its inner circumferential surface toward the photosensitive member 41 to form a primary transfer nip.

At each primary transfer nip, a primary transfer electric field is formed between the photoreceptor and the primary transfer roller under the influence of the primary transfer bias. The toner image on the photoreceptor 41 is primarily transferred onto the intermediate transfer belt 11 under the influence of this primary transfer electric field and nip pressure.

The transfer device 10 also has a secondary transfer roller 22 that constitutes a secondary transfer unit below the intermediate transfer belt 11 . The secondary transfer roller 22 is pressed against the secondary transfer opposing roller 16 with the intermediate transfer belt 11 therebetween.

Then, the secondary transfer roller 22 collectively secondary-transfers the toner image on the intermediate transfer belt 11 onto the paper fed between itself and the intermediate transfer belt 11 . A belt cleaning device 17 is provided downstream of the secondary transfer opposing roller 16 in the direction of surface movement of the intermediate transfer belt 11. The belt cleaning device 17 cleans residual toner remaining on the surface of the intermediate transfer belt 11 after image transfer. is removed. Further, the belt cleaning device 17 has a lubricant application mechanism, and applies lubricant to the surface of the intermediate transfer belt 11 .

A fixing device 25 for fixing the toner image formed on the paper onto the surface of the paper is provided on the downstream side of the secondary transfer roller 22 in the paper conveying direction. A fixing pressure roller 27 is pressed against the endless fixing belt 26 .

After the image has been transferred, the paper is transported to the fixing device 25 by an endless transport belt 24 stretched between a pair of rollers 23 . A sheet reversing device 28 is provided below the secondary transfer roller 22 to reverse the sheet when forming images on both the front and back surfaces of the sheet.

When a copy of a color original is made by the copier having the above configuration, the scanner section 3 reads the image of the original set on the contact glass. Also, the intermediate transfer belt 11 is rotated to form a toner image on each photoreceptor 41 by a known image forming process. Next, the toner images formed on the photoreceptors are successively superimposed and primarily transferred onto the intermediate transfer belt 11 to form a four-color superimposed toner image on the intermediate transfer belt 11 .

On the other hand, in parallel with the image forming operation of the four-color superimposed toner image on the intermediate transfer belt 11 , the paper is separated and fed one by one from the selected paper feeding tray 21 of the paper feeding section 2 and fed to the registration roller 29 . transport towards. The separated and conveyed paper collides with the nip of the registration roller 29 to temporarily stop the conveyance and wait.

The registration rollers 29 are started to rotate at appropriate timing so that the positional relationship between the four-color superimposed toner image formed on the intermediate transfer belt 11 and the leading edge of the paper is at a predetermined position. Due to the rotation of the registration roller 29, the waiting sheet is fed again. As a result, the four-color superimposed toner image on the intermediate transfer belt 11 is secondarily transferred to a predetermined position on the paper by the secondary transfer roller 22 to form a full-color toner image on the paper.

The sheet on which the full-color toner image is thus formed is sent to the fixing device 25 located downstream of the secondary transfer roller 22 in the conveying path. The fixing device 25 fixes the full-color toner image secondarily transferred by the secondary transfer roller 22 onto the paper. The sheet on which the full-color toner image is fixed is discharged to the outside of the apparatus by the discharge rollers 30 .

In a duplex print mode in which images are formed on both sides of a sheet of paper, when a sheet of paper with a full-color toner image fixed only on the first side is ejected from the fixing device 25, the sheet is not ejected by the ejection rollers 30, but is reversed. It is sent to device 28 . Then, after the front and rear surfaces of the sheet are reversed by the sheet reversing device 28 , the sheet is transported again to the registration rollers 29 . After that, a full-color image is formed also on the second side by passing through the secondary transfer roller 22 and the fixing device 25 .

1: Image forming section 2: Paper feeding section 3: Scanner section 10: Transfer device 11: Intermediate transfer belt 14: Tension roller 15: Drive roller 16: Secondary transfer counter roller 17: Belt cleaning device 20a, 20b: Optical writer Loading unit 21: Paper feed tray 22: Secondary transfer roller 23: Roller 24: Conveyor belt 25: Fixing device 26: Fixing belt 27: Fixing pressure roller 28: Sheet reversing device 29: Registration roller 30: Paper discharge roller
40Y, 40M, 40C, 40K: Process cartridge 41: Photoreceptor 42: Charging device 43: Developing device 44: Photoreceptor cleaning device 45: Lubricant application device 46: Primary transfer roller 100, 200: Gears 110, 210: Tooth row 120, 220: connecting rings 110a, 210a: addendum 120b, 121b: radial side surfaces 120c, 210c: convex portions 121, 221: first portions of connecting rings 122, 222: second portions of connecting rings 121a, 221a: outer periphery Surfaces 121c, 221c: inclined surfaces 122a, 222a: outer peripheral surfaces 122b, 222b: radial side surfaces 210b, 221b, 222b: radial side surfaces C: clearance P: pitch lines S, S1, S2: sliding surfaces

Japanese Patent No. 2710861 Japanese Patent No. 3387719 Japanese Patent No. 4508552

Claims (9)

A plurality of tooth rows having the same pitch are formed such that the phases of adjacent tooth rows and teeth are shifted in the circumferential direction and are spaced apart from each other in the axial direction, and the plurality of tooth rows are formed at the root of each tooth row. are integrally connected by a connecting ring protruding in the axial direction toward the tooth row facing each other on the side,
The connecting ring forms a sliding surface spaced apart from each tooth row in an axial direction between the connecting ring of the plurality of mating tooth rows that mesh with the plurality of tooth rows and slides on each other. 1. A gear, characterized in that the axial relative positions of a plurality of tooth rows that mesh with each other are regulated by a moving surface. A plurality of tooth rows having the same pitch are formed such that the phases of adjacent tooth rows and teeth are shifted in the circumferential direction and are spaced apart from each other in the axial direction, and the plurality of tooth rows are formed at the root of each tooth row. are integrally connected by a connecting ring protruding in the axial direction toward the tooth row facing each other on the side,
The connecting ring is axially spaced apart from each of the tooth rows and is spaced apart from each other in the axial direction between the plurality of tooth rows and the projections formed to protrude toward the connecting ring from the plurality of mating tooth rows that mesh with each other. What is claimed is: 1. A gear, comprising: a sliding surface that slides against each other; and the sliding surface regulates relative axial positions of a plurality of tooth rows that mesh with each other. A plurality of tooth rows having the same pitch are formed such that the phases of adjacent tooth rows and teeth are shifted in the circumferential direction and are spaced apart from each other in the axial direction, and the plurality of tooth rows are formed at the root of each tooth row. are integrally connected by a connecting ring protruding in the axial direction toward the tooth row facing each other on the side,
The connecting ring has a convex portion that protrudes in an axial direction from the connecting ring toward a plurality of mating tooth rows that mesh with the plurality of tooth rows. A sliding surface is formed between the radial side surface of the tooth row and axially spaced apart from each tooth row to slide against each other, and the axial relative position of the plurality of tooth rows that mesh with each other is regulated by the sliding surface. A gear characterized by: 2. The gear of claim 1, wherein said sliding surface extends across the pitch circle of said plurality of teeth and in a direction perpendicular to the axial direction of said plurality of teeth. 2. A gear according to claim 1, wherein said sliding surface extends across the pitch circle of said plurality of teeth in a direction oblique to the axial direction of said plurality of teeth. The connecting ring is composed of a small-diameter first portion axially spaced apart from the plurality of teeth and a large-diameter second portion axially adjacent to the plurality of teeth. 2. A gear as claimed in claim 1, wherein a sliding surface is formed. The connecting ring comprises a small diameter first portion axially spaced from the plurality of teeth and a large diameter second portion axially adjacent to the plurality of teeth, wherein the first portion and the 2. A gear according to claim 1, wherein said sliding surfaces are formed on both said second portions. A drive transmission device comprising the gear according to any one of claims 1 to 7. An image forming apparatus comprising the gear according to any one of claims 1 to 7 or the drive transmission device according to claim 8.

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