Rotary shafts – gudgeons – housings – and flexible couplings for ro – Overload release coupling – Torque transmitted via frictional engagement of planar...
Reexamination Certificate
1998-05-12
2001-05-15
Browne, Lynne H. (Department: 3629)
Rotary shafts, gudgeons, housings, and flexible couplings for ro
Overload release coupling
Torque transmitted via frictional engagement of planar...
Reexamination Certificate
active
06231448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power steering system for generating an auxiliary steering force for the steering of a vehicle such as a four-wheel-drive car or the like.
2. Description of the Related Art
FIG. 16
shows an example of a power steering system. The power steering system as shown in
FIG. 16
is disclosed in Japanese Patent Application, First Publication, No. Hei 9-84300, in which output shaft
2
of driving unit (i.e., motor)
1
for generating the above auxiliary steering force and input shaft
3
coupled to the steering unit of a vehicle are coupled via torque limiter
4
. This torque limiter
4
comprises cylindrical limiter cover (or case)
5
having a bottom, fixed in a manner such that the cover is rotationally driven together with the output shaft
2
, similar cylindrical cover
6
having a bottom, which covers from the opening side to the outer surface of the limiter cover
5
, limiter plate (or boss)
7
which is arranged to be relatively rotatable with respect to limiter cover
5
and is coupled to the input shaft
3
, and friction plate
9
which is arranged between cover
6
and limiter plate
7
via forcing member (or spring member)
8
so as to be driven together with the limiter cover
5
and which is relatively rotatable with respect to the limiter plate
7
.
The above cover
6
is attached on limiter cover
5
after limiter plate
7
, forcing member
8
, and friction plate
9
are set in the limiter cover
5
. The cover
6
is fixed by folding down and clamping the peripheral edge of its opening side, and forcing member
8
comes in contact with the bottom of the cover
6
, by which pressing force by this forcing member
8
is supported. In the power steering system having the above-described structure, during ordinary steering, auxiliary steering force generated from driving unit
1
is properly transmitted from output shaft
2
via torque limiter
4
to input shaft
3
by frictional force generated between limiter cover
5
, friction plate
9
, and limiter plate
7
caused by pressing force of forcing member
8
. In a case in which impact force is transmitted from the wheel side of the steering unit, a slip is generated between limiter cover
5
, friction plate
9
, and limiter plate
7
of torque limiter
4
, and impact torque is absorbed; thus, it is possible to prevent excessive torque from acting on output shaft
2
of driving unit
1
.
In torque limiter
4
in such a power steering system, a predetermined frictional force is generated between limiter cover
5
, friction plate
9
, and limiter plate
7
, as described above; thus, it is necessary to ensure sufficient contact areas between these members. Accordingly, it is inevitable that the outer diameter of torque limiter
4
is considerably large. However, in a torque limiter having such a large outer diameter, which is rotated together with output shaft
2
and input shaft
3
, the moment of inertia of this torque limiter
4
also becomes large, and there occur problems in that the driving force necessary for rotationally driving output and input shafts
2
and
3
is increased, and follow-up capability between rotation of input shaft
3
and rotation of output shaft
2
is degraded. In particular, in the above conventional power steering system, cover
6
is arranged to cover the outer surface of limiter cover
5
. Therefore, the outer diameter of torque limiter
4
is further increased and the moment of inertia is also increased; thus, the above-mentioned problems are assumed to be very substantial.
Also in torque limiter
4
in the above power steering system, it is required that during ordinary steering, auxiliary steering force be properly transmitted from output shaft
2
to input shaft
3
, while when impact force acts thereon, impact torque is securely absorbed, as described above. Therefore, pressing force caused by the forcing member
8
must be strictly controlled so as to set the friction force between limiter cover
5
, friction plate
9
, and limiter plate
7
to be in a predetermined range. However, in the above conventional power steering system, the pressing force caused by the forcing member
8
is supported by cover
6
which covers limiter cover
5
, and the opening of this cover
6
is simply clamped and fixed to limiter cover
5
. Therefore, the support position of forcing member
8
is liable to change according to clamping conditions, and there is also a possibility that cover
6
will shift due to spring-back and deformation of the clamped opening of cover
6
, by which support of forcing member
8
becomes unstable. According to the above possibilities, there occurs another problem in that predetermined frictional force is not provided between limiter cover
5
, friction plate
9
, and limiter plate
7
.
SUMMARY OF THE INVENTION
In consideration of the above circumstances, the present invention provides a power steering system based on a first objective to reduce the moment of inertia of the torque limiter, and on a second objective to accurately determine pressing force by a forcing member.
In addition, the present invention has a further objective to improve efficiency of forming a limiter plate as a constituent of the torque limiter of the power steering system.
In order to realize the above objectives, the present invention provides a power steering system in which an output shaft of a driving unit and an input shaft of a steering unit are coupled via a torque limiter, the torque limiter comprising: a substantially-cylindrical rotating member which is rotatable together with one of the output shaft and the input shaft; and a rotated member which is rotatable together with the other of the output shaft and the input shaft, and which is forced toward the rotating member side by a forcing member supported by the rotating member.
Regarding the above basic structure, a typical example is such that the rotating member is a substantially-cylindrical limiter cover with a bottom, and the rotated member is a limiter plate contained in the limiter cover.
In the above typical example, it is possible for the forcing member to be supported by a concave portion formed in an inner-peripheral area of the limiter cover.
According to such a structure, the forcing member is supported by a concave portion formed in an inner-peripheral area of the limiter cover; thus, in contrast to the above-mentioned conventional power steering system, it is unnecessary to provide a cover (
6
) for supporting the forcing member (
8
). In this case, it is possible to prevent the outer diameter of the torque limiter from exceeding the outer diameter of the limiter cover and to regard the outer diameter as that of the torque limiter. Therefore, the moment of inertia of the torque limiter can be reduced. Accordingly, the driving force of the driving unit can be reduced and rapid follow-up between rotation of the input shaft and rotation of the output shaft can be realized, and good steering response can be obtained.
In the conventional structure which includes a cover (
6
) attached to the limiter cover (
5
) by clamping the opening portion of the cover (
6
), the position where the forcing member is supported may be shifted depending on clamping conditions, or due to deformation by spring-back, by which support of the forcing member becomes unstable. In contrast, according to the support by providing the concave portion formed in the limiter cover as described above, the above problems can be prevented, and it is possible to accurately position the forcing member in the limiter cover and to easily and accurately set the relevant force to be a predetermined size. Consequently, during ordinary steering, the output shaft and the input shaft can be stably rotated integrally, while if an impact force acts on the steering unit side, it is possible to more reliably generate sliding and to prevent excessive torque from being transmitted.
In the concave portion, a ring-shaped member having an inner-diameter smaller than the diameter of the inner-per
Abe Hideaki
Aoki Susumu
Furuuchi Hideki
Binda Greg
Browne Lynne H.
Darby & Darby
Mitsuba Corporation
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