Machine element or mechanism – Gearing – Follow-up mechanism
Reexamination Certificate
2000-11-28
2003-02-11
Joyce, William C (Department: 3682)
Machine element or mechanism
Gearing
Follow-up mechanism
C074S089420, C074S424720, C074S424810, C074S424950
Reexamination Certificate
active
06516680
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a power steering apparatus comprising a motor as a power-source of the steering assisting force.
DESCRIPTION OF RELATED ART
Power steering apparatus is to alleviate the labor burden required for steering by rotating a steering wheel and to receive favorable steering feeling such apparatus is equipped in many automobiles. Furthermore, in recent years there has been practically employed an electric power steering apparatus utilizing an electric motor which is driven according to the operation of the steering wheel, instead of the hydraulic actuator extensively used conventionally.
Such power steering apparatus has a merit of elastically meeting to the change of the properties of the assisting force according to the operating conditions such as HI/LOW of the vehicle speed, LARGE/SMALL of the steering angle, and the like by control of motor driving for steering assistance, however, in realization of such control, a transmission system for transmitting the rotation of the motor for steering assistance to the steering mechanism is essential.
The motor for steering assistance is provided in linkage with the steering wheel. The motor are connected with the middle portion of a steering column which rotates according to steering of the steering wheel or provided at the middle portion of the steering shaft, both ends of which is connected with traveling wheels (in general, right and left front traveling wheels), for steering by shifting in the axial direction (e.g., a rack shaft in the rack-pinion type steering mechanism). In the former, however the rotation of the motor for steering assisting is to be transmitted to the steering column which is a rotary member, and while there is a benefit that the above transmission system can be simply constituted by a general gearwheel reduction mechanism, the portion of the steering column outside the saloon is small, so that it is difficult to secure a installation position for the transmission system including said motor, and there is an inconvenience that the application range could be limited.
Against the above, however the latter has complicated constitution of the transmission system for converting the rotation of the motor for steering assistance into the shift of the steering shaft in the axial direction, it has large freedom for arranging positions of the transmission system including the motor over the axial length of the steering shaft arranged to the right and left in the bow of the vehicle, and has an advantage of applicability to extensive kinds of vehicles. However, even in this constitution, curtailment of the space for arranging the transmission system including the motor as above is an important task. For example, as disclosed in Japanese Patent Laid-open Publication No. S61-191468, a power steering apparatus aiming at curtailing the installation space by using a ball screw mechanism for the above transmission system has so far been proposed.
This power steering apparatus employs a portion of the steering shaft as a male screw member on the outer periphery of which a thread of the ball screw is formed, and on the outside of the male screw member, there are arranged the nut members which are screw connected through a large number of balls with restraint given to the movement in the axial direction in the housing for supporting the steering shaft, and the rotation force from the motor for steering assisting is transmitted to the nut member, so that according to the rotation the steering shaft is shifted to the axial direction by utilizing the screw advance of the ball screw. By this, it is possible to constitute the transmission mechanism that gives the large reduction ratio inside said housing compact, and by mounting the miniaturized motor near the housing of the steering shaft, the requirements for reducing the layout space as described above can be met.
However, in the conventional constitution as above, there is required high precision for forming the ball screw thread in the outer periphery of the steering shaft, for which a large number of steps are required for processing; moreover, great amount of labor is required for adjusting screw engagements between the ball screw threaded male screw member and the nut member.
Though the balls which are filled in the ball screw thread in the nut member move in rotation in the screw groove according to the screw advance of the balls screw to smooth the movement of the steering shaft, but at the same time the balls deflect by their rotational movement in the direction of movement of the steering shaft. In order to prevent this deflection, there are provided bypass mechanisms for moving the balls in circulation at the right and left ends in the nut member, thereby supporting smooth movement in rotation of the balls. However, the bypass mechanisms constituted in the nut member are extremely complicated, involving the problems that due to a large number of portions constituting the said mechanisms increases are caused in the number of steps for assembly and cost.
Furthermore, there is another problem that in the above bypass mechanism and ball screw thread, because there is no retaining member to keep the distance between the balls constant, the balls collide against one another and the noise generated thereby is large.
The present invention has been made in reflection of the situation as above. An object of the invention is to provide a power steering apparatus which generates low noise and which can securely convert the rotation of the motor for steering assistance to the movement of the steering shaft in the axial direction by the transmission system having a simple constitution to take the place of the ball screw mechanism, thereby it is possible to meet the requirements for curtailing the installation space of the transmission system including the steering assistance motor and simplifying the adjustment work at the assembly.
DISCLOSURE OF THE INVENTION
A power steering apparatus of the present invention has a constitution to assist steering by transmitting rotational force of a motor driven according to steering to a steering shaft supported in a housing with its rotary movement restrained and by moving said steering shaft in the axial direction, comprising a rotary cylinder supported in said housing with its movement in the axial direction restrained and rotated coaxially with said steering shaft by the rotational force transmitted from the motor, a plurality of feed rings fit and held in said rotary cylinder, made eccentric in different directions with respect to the axial center of the rotary cylinder, being rotatable on the axis that is parallel with said axial center, a spiral groove provided on the outer circumference of the steering shaft to be engaged at one position in a circumferential direction with a projection provided around the inner surface of the feed ring, and adjusting means for adjusting the eccentricity amount of the plural feed rings by the operation from the outside of the rotary cylinder.
FIG. 1
shows an explanatory view for illustrating the principle of converting the rotation of the feed ring of the present invention to the movement in axial direction of the steering shaft. The steering shaft
101
is supported under allowance of shift in the axial direction only. The feed ring
163
has a steering shaft
101
inserted through its inner circumferential portion, the inner diameter is larger than the outer diameter of the steering shaft
101
, and the feed ring
163
is disposed eccentrically to the axial center of the steering shaft
101
so as to come into contact with the outer circumferential surface of the steering shaft
101
at one place of the inner circumferential surface of the feed ring
163
. Further, the axial center of the feed ring
163
is provided with inclination by an angle &thgr; to the axial center of the steering shaft
101
.
When the feed ring
163
having such constitution rotates around the axial center of the steering shaft
101
; for example, in the white base arrow mark directio
Nakamura Kensaku
Nakamura Masahide
Sano Osamu
Joyce William C
Koyo Seiko Co. Ltd.
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