Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1999-08-19
2001-06-12
Dickson, Paul N. (Department: 3618)
Motor vehicles
Steering gear
With electric power assist
C180S400000, C180S443000, C180S444000
Reexamination Certificate
active
06244374
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-235942 filed on Aug. 21, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrically operated power steering device that is employed in a vehicle such as an automobile or the like.
2. Description of the Related Art
In an electrically operated power steering device of a certain type, a rotational shaft of an electric motor is rotationally driven so as to apply a steering assist force to a steering shaft. The electrically operated power steering device of this type is disclosed, for example, in Japanese Patent Publication Laid-Open No. HEI 8-163889.
However, according to the electrically operated power steering device of the aforementioned type, a stator of the electric motor is provided with a yoke portion with which teeth portions are integrated, and coils are wound around the teeth portions. Besides, the stator is securely fixed within a housing. Thus, the yoke portion and the housing have a double structure, and the overall diameter is comparatively large. On the contrary, if an attempt is made to reduce the size of the electric motor without changing the above-described structure, it is necessary to make the teeth portions and the yoke portion compact. In this case, it is impossible to ensure sufficient output torque of the electric motor. In other words, the aforementioned electrically operated power steering device makes it difficult to ensure sufficient output torque of the electric motor and to reduce the size of the electric motor.
SUMMARY OF THE INVENTION
The present invention has been conceived in consideration of the above-described problem. It is thus an object of the present invention to provide an electrically operated power steering device of a simple and compact structure.
According to a first aspect of the present invention, there is provided an electrically operated power steering device that is composed of an electric motor generating a steering assist force that assists a steering force and a steering shaft to which the steering assist force is applied. The electrically operated power steering device has the following features. That is, the electric motor has a stator and a rotational shaft that is rotationally driven within the stator so as to apply a steering assist force to the steering shaft. The stator has teeth portions composed of electromagnetic steel plates, coils wound around the teeth portions, and a yoke portion made of a magnetic substance that accommodates the coils and the teeth portions and that can be utilized as a housing.
In this case, the yoke portion may be made of a steel pipe, or the yoke portion may be made of an iron type magnetic material with a low percentage of carbon contents. Further, the steering shaft may be a rack bar that is arranged coaxially within the rotational shaft of the electric motor and that penetrates the rotational shaft, or the yoke portion may partially serve as part of housing that accommodates part of the rotational shaft and part of the rack bar.
In the electrically operated power steering device of the present invention, the yoke portion can be utilized also as part of the housing of the electrically operated power steering device. Thus, the electrically operated power steering device can be made simple and compact. Furthermore, steering preload torque (loads) can be generated by means of an iron loss at the yoke portion. Hence, it is possible to ensure running stability of the vehicle appropriately (i.e., to prevent swinging motions in response to a force (reverse input) inputted from the steering wheels via the steering shaft).
Still further, according to the present invention, in the case where the yoke portion is made of a steel pipe that is less expensive than electromagnetic steel plates, the amount of expensive electromagnetic steel plates used for the stator can be reduced. Also, the yoke portion can be constructed at low costs, and the electrically operated power steering device can be manufactured at low costs. In the case where the yoke portion is made of an iron type magnetic material with a low percentage of carbon contents, the steering preload torque can be set optimally in accordance with the type of the vehicle by suitably selecting the material of the yoke portion among iron type magnetic materials with a low percentage of carbon contents.
Still further, according to the present invention, in the case where the steering shaft is a rack bar that is arranged coaxially within the rotational shaft of the electric motor and that penetrates the rotational shaft, the electric motor can be arranged around the rack bar in a compact manner, whereby it becomes possible to reduce the overall diameter and to reduce the size of the electrically operated power steering device. Furthermore, in the case where the yoke portion partially serves as part of the housing that accommodates part of the rotational shaft and part of the rack bar, the number of components of the electrically operated power steering device can be reduced, and the manufacturing costs can also be reduced.
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Mizutani Ryoji
Tomita Masaaki
Dickson Paul N.
Draper Deanna
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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