1. Field of the Invention
The present invention relates to a steering apparatus capable of improving operability of an operating lever in locking and unlocking.
2. Description of the Related Art
Conventionally, there have been developed various steering apparatuses each having tilting and telescoping functions. In particular, Japanese Patent Application Laid-open No. 2002-59851 discloses a steering apparatus equipped with a cam mechanism. The specific content of Japanese Patent Application Laid-open No. 2002-59851 is as follows. On an opposing surface 22a of a cam 22 that opposes a cam follower 21, there are provided a pair of first positioning portions 26 for positioning the cam follower 21 in unlocking and a pair of second positioning portions 27 for positioning the cam follower 21 in locking so as to oppose each other with the central axis line of the cam 22 (a central axis line C of a support shaft 15) interposed therebetween (see FIG. 3A in Japanese Patent Application Laid-open No. 2002-59851).
Between the first and second positioning portions 26 and 27, there are formed a flat surface with which the cam follower 21 is engaged when tilt lock is released, a flat surface with which the cam follower 21 is engaged when the tilt lock is established, and a cam surface 28 that connects the flat surfaces. On the other hand, on an opposing surface 21a of the cam follower 21 that opposes the cam 22, there are formed a pair of trapezoidal protrusions 31 that come slidably in contact with the positioning portions 26 and 27 and the cam surface 28 of the cam 22 (see FIG. 3B of Japanese Patent Application Laid-open No. 2002-59851).
The cam surface 28 includes a first inclined portion 29 having a relatively large inclination angle and a second inclined portion 30 having a relatively small inclination angle, and the second inclined portion 30 is positioned in a rear region of a stroke of an operating lever in fastening (see FIG. 4A of Japanese Patent Application Laid-open No. 2002-59851). Thus, by providing the inclined portions 29 and 30 on the cam surface 28, it is possible to reduce an operating force of an operating lever 16 without significantly increasing the range of an operation angle of the operating lever 16.
In particular, in order to cope with the rear region of the stroke in a fastening direction of the operating lever 16 where an operating torque tends to be large, the second inclined portion 30 having a relatively small inclination is provided on the cam surface 28. With the arrangement, the operating torque of the operating lever 16 in the rear region of the fastening stroke is reduced, and the operability of the operating lever 16 is improved.
Herein, the shape of a cam surface monotonically inclined from the beginning to the end that is widely used conventionally is defined as a virtual inclined line L constituted by a single straight line that connects the beginning of the cam surface 28 and the end thereof. In Japanese Patent Application Laid-open No. 2002-59851, the first inclined portion 29 and the second inclined portion 30 formed on the cam surface 28 are formed at positions (regions) above the virtual inclined line L at positions corresponding to the virtual inclined line L (see FIG. 4). The rotation amount of the cam follower 21 in the virtual inclined line L is the same as that in the cam surface 28 of Japanese Patent Application Laid-open No. 2002-59851, and the operation angle of the operating lever 16 in the virtual inclined line L is also the same as that in the cam surface 28 thereof.
In Japanese Patent Application Laid-open No. 2002-59851, in contrast to the virtual inclined line L monotonically inclined from the beginning to the end that is widely used conventionally, the inclined portions 29 and 30 are formed. The second inclined portion 30 in the rear region of the stroke of the operating lever 16 is a region where the operating force of the operating lever 16 is high as compared with that of the first inclined portion 29 in the front region of the stroke. The second inclined portion 30 having an inclination smaller than that of the virtual incline line L is provided in the rear region of the stroke, and the operating force of the operating lever 16 in the rear region of the fastening stroke is reduced without making the operation angle of the operating lever 16 larger than that of the virtual inclined line L (see FIG. 4).
However, the inclination formed in the cam surface 28 is formed at a position (region) above the virtual inclined line L in its entire region. When the cam surface 28 is compared with the virtual inclined line L at the point having the same rotation amount of the cam follower 21, a lift amount (an axial movement amount of the cam follower 21) of the cam surface 28 is larger and an axial force of the cam surface 28 is also larger than those of the virtual inclined line L. In the entire region from the beginning to the end of the cam surface 28, the operating force of the operating lever 16 is larger than that of the virtual inclined line L from the initial stage to the late phase stage (see FIG. 4).
In addition, when the tilt lock is established, in the initial stage of the operation, the cam follower 21 moves on the first inclined portion 29 steeper than the virtual inclined line L from the flat surface so that the operating force of the operating lever 16 in the initial phase of the tilt lock becomes large.
When the tilt lock is released, a force for movement from the rear region of the stroke where the operating force of the operating lever 16 is high to the front region where the operating force of the operating lever 16 is low is applied to the cam follower 21. In addition, the cam follower 21 moves from the second inclined portion 30 having a small inclination angle to the first inclined portion 29 having a large inclination angle and the flat surface so that there is a possibility that the operating lever 16 returns extremely quickly when the tilt lock is released.