Patent ID: 8064802

Claim:
A driving-force transmission device comprising: a driving-force transmitting member that includes a rotary shaft unit including a large-diameter portion at a first end and a small-diameter portion at a second end, a driving-force input unit that is engaged with a driving unit that is connected to a driving source to receive a rotary driving force, and a driving-force output unit that is engaged with a drive target to output the rotary driving force to the drive target, which are integrally formed, one of the driving-force input unit and the driving-force output unit being formed at the first end and is engaged with an engaging target arranged concentrically on the rotary shaft unit, other one of the driving-force input unit and the driving-force output unit being formed on an outer circumference of the rotary shaft unit; a support member that rotatably supports the rotary shaft unit at a first support portion of the large-diameter portion and at a second support portion of the small-diameter portion; and a sleeve bearing that is arranged between the first support portion and the support member such that rotation of the driving-force transmitting member in a rotational direction relative to the support member is restricted by friction between the sleeve bearing and the first support portion of the large-diameter portion, wherein the driving-force transmitting member is formed of a material having a linear expansion coefficient larger than that of the sleeve bearing, and Δx 1 >r 1 ×Δt×a−R 1 ×Δt×b is satisfied, where R 1 is inner radius of the sleeve bearing, r 1 is outer radius of the rotary shaft unit, Δx 1 is difference between the inner radius R 1 and the outer radius r 1 at a reference temperature, Δt is maximum amount of temperature change of the driving-force transmitting member relative to the reference temperature, a is linear expansion coefficient of the sleeve bearing, and b is linear expansion coefficient of the driving-force transmitting member.