| 摘要 |
A variable steering gear mechanism ( 9 ) is constructed of an external gear ( 15 ) connected to an input shaft ( 11 ), an internal gear ( 16 ) fixed to housing ( 10 ) and meshing with the external gear ( 15 ), an intermediate member ( 19 ) receiving a rotary force transmitted from the external gear ( 15 ), change means ( 18 a, 31, 33 a) capable of changing a rotation ratio of the output shaft ( 33 ) to a rotation of a guide member ( 18 ), and an Oldham coupling ( 17 ) connecting the intermediate member ( 19 ) to the guide member ( 18 ). When a speed reduction ratio thereof is set to, e.g., 6:1, it follows that the input member ( 18 ) of the change means makes a ¼ rotation (rotates through 90 degrees) during one-sided 1.5 rotations (540 degrees) of the input shaft ( 11 ), whereby a characteristic of the change means can be effectively utilized. A gear mechanism such as a hypocycloid mechanism has a characteristic capable of, though compact in configuration, obtaining a speed reduction ratio as large as 6:1, and also such a characteristic that the external gear ( 15 ), in addition to the self-rotation, revolves around the axis line of the internal gear ( 16 ), i.e., rotates while being eccentric. By contrast, according to the present invention, the use of the Oldham coupling ( 17 ) enables only the self-rotation to be extracted and transmitted by absorbing the eccentricity of the external gear ( 15 ). Additionally, a meshing length between the external gear ( 15 ) and the internal gear ( 16 ) becomes large, whereby smoother power transmission can be attained.
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