Gear, and image forming apparatus provided with the same

A gear made of resin, comprising:

• a support cylindrical portion;
• a teeth-formed cylindrical portion arranged coaxially with the support cylindrical portion on a radially outer side of the support cylindrical portion and formed with a plurality of teeth in its outer periphery;
• and
• a web connecting an outer peripheral surface of the support cylindrical portion and an inner circumferential surface of the teeth-formed cylindrical portion, wherein
• the axial thickness of the web is constant from the outer peripheral surface of the support cylindrical portion until a radially intermediate position between the outer peripheral surface of the support cylindrical portion and the inner circumferential surface of the teeth-formed cylindrical portion, and becomes thinner gradually from the intermediate position until a position where the web is connected to the inner circumferential surface of the teeth-formed cylindrical portion.

A gear made of resin, comprising:

• a support cylindrical portion;
• a teeth-formed cylindrical portion arranged coaxially with the support cylindrical portion on a radially outer side of the support cylindrical portion and formed with a plurality of teeth in its outer periphery;
• a web connecting an outer peripheral surface of the support cylindrical portion and an inner circumferential surface of the teeth-formed cylindrical portion;
• and
• a plurality of radial ribs which connect the outer peripheral surface of the support cylindrical portion and the inner circumferential surface of the teeth-formed cylindrical portion, wherein
• an axial thickness of at least a part of the web becomes thinner gradually from the outer peripheral surface of the support cylindrical portion to the inner circumferential surface of the teeth-formed cylindrical portion, and
• the plurality of radial ribs are so provided as to be spaced apart from one another in a circumferential direction, and a circumferential thickness of each radial rib is constant from the outer peripheral surface of the support cylindrical portion until a radially intermediate position between the outer peripheral surface of the support cylindrical portion and the inner circumferential surface of the teeth-formed cylindrical portion, and becomes thinner gradually from the intermediate position until a position where the radial rib is connected to the inner circumferential surface of the teeth-formed cylindrical portion.

A gear made of resin, comprising:

• a support cylindrical portion;
• a teeth-formed cylindrical portion arranged coaxially with the support cylindrical portion on a radially outer side of the support cylindrical portion and formed with a plurality of teeth in its outer periphery;
• a web connecting an outer peripheral surface of the support cylindrical portion and an inner circumferential surface of the teeth-formed cylindrical portion;
• and
• an intermediate cylindrical portion arranged between the support cylindrical portion and the teeth-formed cylindrical portion coaxially with the support cylindrical portion, wherein
• the web includes:
• a first web which connects the outer peripheral surface of the support cylindrical portion and an inner circumferential surface of the intermediate cylindrical portion;
• and
• a second web which connects an outer peripheral surface of the intermediate cylindrical portion and the inner circumferential surface of the teeth-formed cylindrical portion, and
• an axial thickness of the second web becomes thinner gradually from the outer peripheral surface of the intermediate cylindrical portion to an inner circumferential surface of the teeth-formed cylindrical portion.

A gear made of resin, comprising:

• a support cylindrical portion;
• a teeth-formed cylindrical portion arranged coaxially with the support cylindrical portion on a radially outer side of the support cylindrical portion and formed with a plurality of teeth in its outer periphery;
• a web connecting an outer peripheral surface of the support cylindrical portion and an inner circumferential surface of the teeth-formed cylindrical portion;
• and
• an intermediate cylindrical portion arranged between the support cylindrical portion and the teeth-formed cylindrical portion coaxially with the support cylindrical portion, wherein
• the web includes:
• a first web which connects the outer peripheral surface of the support cylindrical portion and the inner circumferential surface of the intermediate cylindrical portion;
• and
• a second web which connects an outer peripheral surface of the intermediate cylindrical portion and the inner circumferential surface of the teeth-formed cylindrical portion, wherein
• an axial thickness of the second web is constant from the outer peripheral surface of the intermediate cylindrical portion to a radially intermediate position between the outer peripheral surface of the intermediate cylindrical portion and the inner circumferential surface of the teeth-formed cylindrical portion, and becomes thinner gradually from the intermediate position to the inner circumferential surface of the teeth-formed cylindrical portion.

A gear made of resin, comprising:

• a support cylindrical portion;
• a teeth-formed cylindrical portion arranged coaxially with the support cylindrical portion on a radially outer side of the support cylindrical portion and formed with a plurality of teeth in its outer periphery;
• and
• a web connecting an outer peripheral surface of the support cylindrical portion and an inner circumferential surface of the teeth-formed cylindrical portion, wherein
• an axial thickness of at least a part of the web becomes thinner gradually from the outer peripheral surface of the support cylindrical portion to the inner circumferential surface of the teeth-formed cylindrical portion, and the gear is formed by injection molding from a resin material.