Machine element or mechanism – Gearing – Follow-up mechanism
Reexamination Certificate
2002-01-18
2004-08-31
Williams, Thomas (Department: 3683)
Machine element or mechanism
Gearing
Follow-up mechanism
C180S444000, C464S047000
Reexamination Certificate
active
06782771
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a joint for interconnecting an output shaft of an electric motor and a rotating shaft, and to a steering assist system using the same.
Heretofore, there have been proposed devices as automotive steering assist system which provides an auxiliary force to manual steering force by way of an electric motor.
FIG. 8
illustrates an example of a steering assist system of this type, which is arranged as follows. A first steering shaft
102
with a steering wheel (handle)
101
attached thereto is connected in series with a second steering shaft
104
disposed therebelow via a torsion bar
103
. A torque sensor
105
detects a steering torque based on a quantity of relative rotational displacement between the first steering shaft
102
and the second steering shaft
104
. On the other hand, an electric assist motor
106
is driven based on the detection result while the rotation of the electric motor
106
is transmitted to the second steering shaft
104
as reduced by a deceleration mechanism
109
whereby the auxiliary force is added to the manual steering force applied by means of the steering wheel
101
.
The deceleration mechanism
109
consists of a worm shaft
107
formed with a worm, and a synthetic-resin worm wheel
108
integrally rotatably mounted to the second steering shaft
104
as meshed with the worm. The worm shaft
107
is integrally rotatably connected with an output shaft of the electric motor
106
via a joint. The worm shaft
107
and the second steering shaft
104
are each supported by bearings at opposite ends thereof, so as to be prohibited from moving radially or longitudinally.
The prior-art steering assist system has the following problem. If backlash occurs at a meshing engagement area between the worm of the worm shaft
107
and the worm wheel
108
, the backlash causes so-called rattling noises, which may be conveyed to a passenger compartment to annoy a vehicle operator or passenger. Therefore, it is a general practice in the fabrication of the system to combine the worm shaft
107
and worm wheel
108
of suitably selected sizes such that the backlash may be avoided. However, it is quite difficult to avoid the occurrence of backlash no matter how the adjustment is made in the fabrication of the system as a countermeasure against the backlash, because the teeth of the worm shaft
107
and worm wheel
108
are worn through the operations of the steering assist system. There is another fear that the synthetic-resin worm wheel
108
may expand due to water absorption, heat or the like resulting in the increase of rotational torque (rotational resistance).
In this connection, there is proposed a steering assist system arranged such that the worm shaft
107
is supported in a manner to be biased toward the worm wheel
108
and is spring biased toward the worm wheel thereby preventing the occurrence of backlash or the increase of the rotational torque (see, for example, Japanese Unexamined Patent Publication No.2000-43739).
However, this steering assist system must allow for the eccentricity and inclination of the worm shaft
107
relative to the output shaft of the electric motor
106
. Accordingly, an elongate joint such as a universal joint is required for interconnecting these shafts. Thus, the system requires a larger space for the interconnection of the shafts, resulting in the increase of size and costs.
Furthermore, the worm shaft
107
is prone to vibrate during the rotation of the electric motor
106
. This leads to a fear that the vibration is transmitted to the steering wheel
101
which, in turn, may provide an impaired steering feeling.
In the event of a failure of the electric motor
106
which involves an abnormal increase of the rotational resistance of the output shaft thereof, there will be required a significant increase of steering effort on the steering wheel.
OBJECT OF THE INVENTION
It is an object of the invention to provide a joint which provides a compact, low-cost connection between the output shaft of the electric motor and the rotating shaft driven into rotation by the output shaft and which is capable of damping the vibration of the rotating shaft.
It is another object of the invention to provide a joint adapted to permit relative rotation between the output shaft and the rotating shaft when the rotational resistance of the output shaft or rotating shaft is increased abnormally.
It is still another object of the invention to provide a steering assist system which provides a compact, low-cost connection between the output shaft of the electric motor and the rotating shaft driven into rotation by the output shaft and which is capable of damping the vibration of the worm shaft.
It is yet another object of the invention to provide a steering assist system adapted to permit relative rotation between the output shaft and the rotating shaft when the rotational resistance of the output shaft or rotating shaft is increased abnormally.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, a joint for integrally rotatably connecting a rotating shaft to an output shaft of an electric motor comprises: a first transmission member integrally rotatably mounted on the output shaft; a second transmission member enclosing the first transmission member via a gap therebetween and providing integrally rotatable connection of the rotating shaft; and an elastic body interposed between the first transmission member and the second transmission member for transmission of the rotation of the first transmission member to the second transmission member.
The joint of this construction transmits the rotation of the output shaft of the electric motor to the rotating shaft via the elastic body interposed between the first and second transmission members. In this process, the elastic body is capable of accommodating or allowing for the eccentricity and inclination between the output shaft of the electric motor and the rotating shaft. This negates the need for establishing alignment between the output shaft of the electric motor and the rotating shaft so that the connection of these shafts is facilitated. If the rotating shaft vibrates, the elastic body damps the vibration thereby suppressing the noises. The joint has a simple construction and is designed to be reduced in the axial length thereof, requiring a smaller space for interconnection between the output shaft of the electric motor and the rotating shaft. Thus, the joint contributes to the reduction of size and costs of various apparatuses including the electric motor and rotating shaft.
It is preferred in the above joint that the first transmission member, second transmission member and elastic body comprise cylindrical bodies. In this case, the structure of the joint may be much more simplified.
The joint may have an arrangement wherein flat faces in opposed relation are formed at an outer periphery of the first transmission member and an inner periphery of the second transmission member. In this case, the relative rotation between the first and second transmission members is restrained by the flat faces. Therefore, the rotation of the electric motor can be easily and assuredly transmitted to the rotating shaft via the elastic body. Besides, the structure of the joint may be even more simplified. Where the rotating shaft is subjected to an excessive load, the flat faces of the transmission members receive the load thereby to protect the elastic body from the excessive load. Thus, the elastic body is prevented from being fractured by the excessive load, so that the joint is increased in durability and reliability.
The joint according to the first aspect of the invention may be used in a steering assist system for interconnecting an output shaft of an electric motor and a worm shaft, the steering assist system providing steering assist by transmitting the rotation of the electric motor to a steering shaft via the worm shaft, as the rotating shaft formed with a worm, and a worm wheel meshed with the worm of the worm shaft.
T
Iino Takeo
Kinme Shigetaka
Kobayashi Masanori
Oka Kunihiro
Sano Osamu
Koyo Seiko Co. Ltd.
Smith , Gambrell & Russell, LLP
Williams Thomas
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