Electric power steering apparatus for vehicle

Disclosed is an electric power steering apparatus for a vehicle. The electric power steering apparatus for a vehicle has a structure in which a motor shaft, an input shaft, a pinion shaft, and the like are coaxially disposed to improve a structure of a conventional art in which an electric motor is essentially exposed, so as to prevent interference with other structures, thereby forming a layout of the steering apparatus to be compact.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority under 35 U.S.C. §119(a) to Korean Application Serial No. 10-2013-0061777, which was filed in the Korean Intellectual Property Office on May 30, 2013, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric power steering apparatus for a vehicle, and more particularly to an electric power steering apparatus for a vehicle, which has a structure in which a motor shaft, an input shaft, a pinion shaft, and the like are coaxially disposed and improves a structure of a conventional art in which an electric motor is essentially exposed to prevent interference with other structures, thereby forming a layout structure of the steering apparatus to be compact.

2. Description of the Related Art

FIG. 1is a view illustrating a structure of a conventional electric power steering apparatus.

As shown inFIG. 1, the conventional electric power steering apparatus100for a vehicle includes a steering system extending from a steering wheel101to both wheels108, and an auxiliary power mechanism120for supplying an auxiliary steering force to the steering system.

The steering system includes a steering shaft102having one end thereof connected to the steering wheel101and the other end thereof connected to a driving shaft by means of a universal joint103.

The driving shaft includes an input shaft104connected to the steering shaft102, and a pinion shaft106which is connected to the input shaft104by means of a torsion bar (not shown) and has a pinion gear111mounted on a lower end thereof.

The pinion gear111mounted on the pinion shaft106is tooth-engaged with a rack gear112formed on an outer peripheral surface of a rack bar109, and the rack bar109has both ends connected to wheels108of the vehicle through tie rods151and knuckle arms153, respectively.

The auxiliary power mechanism120includes a torque sensor125for detecting a torque generated at the input shaft104and outputting an electric signal proportional to the detected torque as a driver rotates the steering wheel101, an electric control unit123for generating a control signal based on the electric signal transmitted from the torque sensor125, an electric motor130for generating an auxiliary power based on the control signal transferred from the electric control unit123, and worm141and worm wheel143for transferring an auxiliary power from the electric motor130to the pinion shaft106.

However, in the conventional electric power steering apparatus for the vehicle, the electric motor, the worm, the worm wheel, and the like are used to construct a reducer of the auxiliary power mechanism120. In this structure, the electric motor is essentially exposed when they are mounted on the vehicle, and causes interference with other structures. Accordingly, there is a disadvantageous in the layout.

SUMMARY OF THE INVENTION

The present invention has been developed to solve the above-mentioned problems in the conventional art, and an aspect of the present invention is to provide an electric power steering apparatus for a vehicle, which has a structure in that a motor shaft, an input shaft, a pinion shaft, and the like are coaxially disposed to improve a structure of a conventional art in which an electric motor is essentially exposed, so as to prevent interference with other structures, thereby forming a layout structure of the steering apparatus to be compact.

The aspect of the present invention is not limited thereto, and other aspects of the present invention will be apparently understood by those skilled in the art through the below description.

In accordance with an aspect of the present invention, an electric power steering apparatus is provided. The electric power steering apparatus includes: an electric motor supported on an inner peripheral surface of a housing, having a hollow shape, and including a sun gear mounted on an outer peripheral surface of one end; a planetary gear assembly which includes a plurality of first planetary gears internally engaged with a first ring gear fitted in the housing, a plurality of second planetary gears connected to the plurality of first planetary gears by a connection shaft respectively, and internally engaged with a second ring gear, and a carrier to which both ends of the connection shaft are coupled and supported; and, a pinion shaft extending through the motor shaft, and having one end thereof on an outer peripheral surface of which a pinion gear is mounted to be engaged with a rack gear formed on a rack bar, and the other end thereof which is connected to the input shaft by means of the torsion bar, the pinion shaft being connected to the second ring gear.

According to the embodiment of the present invention, an electric power steering apparatus for a vehicle has a structure in that a motor shaft, an input shaft, a pinion shaft, and the like are coaxially disposed to improve a structure of a conventional art in which an electric motor is essentially exposed, so as to prevent interference with other structures, thereby forming a layout structure of the steering apparatus to be compact.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will be described with reference to the exemplary drawings. In the description of the elements of the present invention, terms “first”, “second”, “A”, “B”, “(a)”, “(b)” and the like may be used. These terms are merely used to distinguish one structural element from other structural elements, and a property, an order, a sequence and the like of a corresponding structural element are not limited by the term. In the case that it is described that a certain structural element “is connected to”, “is coupled to”, or “is in contact with” another structural element, it should be interpreted that another structural element may “be connected to”, “be coupled to”, or “be in contact with” the structural elements as well as that the certain structural element is directly connected to or is in direct contact with another structural element.

FIG. 2is a view illustrating a structure of an electric power steering apparatus for a vehicle according to an embodiment of the present invention.FIG. 3is a sectional view partially illustrating the electric power steering apparatus ofFIG. 2.FIG. 4is an exploded perspective view partially illustrating the electric power steering apparatus ofFIG. 3.FIG. 5is a perspective view illustrating a planetary gear assembly ofFIG. 3.FIG. 6is an exploded perspective view illustrating the planetary gear assembly ofFIG. 5.FIG. 7is an exploded perspective view illustrating a connection shaft and first and second planetary gears ofFIG. 4.

As shown in the drawings, the electric power steering apparatus200for the vehicle according to the embodiment of the present invention includes: an electric motor210supported on an inner peripheral surface of a housing310and having a hollow motor shaft311on an outer peripheral surface of one end which a sun gear351is mounted; a planetary gear assembly which has a plurality of first planetary gears355which is externally engaged with the sun gear351and internally engaged with a first ring gear353fitted in the housing310, a plurality of second planetary gears352connected to the first planetary gears355by connection shafts357respectively and internally engaged with a second ring gear359, and a carrier354for supporting both ends of the connection shaft357; and, a pinion shaft250which extends through the motor shaft311, has one end thereof on which a pinion gear251is mounted and engaged with a rack gear112formed on a rack bar109and the other end thereof, which is connected to the input shaft290by means of a torsion bar330, and is connected to the second ring gear359.

The input shaft290is connected to a steering shaft102by means of a universal joint103, and the steering shaft102is connected to a steering wheel101. Thus, the steering shaft102and the input shaft290are associated with each other and rotate together as the steering wheel101rotates.

The electric motor210is supported on an inner peripheral surface of the housing310, which has the motor shaft311with a hollow shape, and the sun gear351integrally mounted on the inner peripheral surface of one end of the motor shaft311.

On the other hand, the electric motor210generates an auxiliary power based on a control signal transferred from an electric control unit (ECU)123, which rotates the sun gear351through the motor shaft311by using the auxiliary power.

Further, the motor210is provided with the input shaft290and the pinion shaft250described later which are mounted on an upper portion thereof, and a torque sensor270for measuring a value of torque applied to the input shaft290, and the torque value of the input shaft290measured by the torque sensor270is converted into an electric signal and transferred to the ECU123, so as to control the electric motor210.

The planetary gear assembly230includes a plurality of first planetary gears355, a plurality of second planetary gears352, a first ring gear353, a second ring gear359, and a carrier354.

The first planetary gears355are disposed between the sun gear351and the first ring gear353, and externally engaged with the sun gear351while internally engaged with the first ring gear353. The first ring gear353is fitted in the housing310.

Accordingly, when the sun gear351mounted on the motor shaft311is rotated by the auxiliary power provided from the electric motor210, the first planetary gears355externally engaged with the sun gear351rotates and revolve around the sun gear351between the sun gear351and the first ring gear353.

The second planetary gears352are connected to the first planetary gears355by the connection shaft357respectively. The connection shaft357and the first and second planetary gears352are coupled to one another in such a manner that a first serration portion711is axially formed on an outer peripheral surface of the connection shaft357, a second serration portion713is formed on an inner peripheral surface of each of the plurality of first planetary gears355, and a third serration portion715is formed on an inner peripheral surface of each of the plurality of second planetary gears352, so that the first planetary gears355and the second planetary gears352may be coupled to the connection shaft357by the serration.

On the other hand, the second planetary gear352is internally engaged with the second ring gear359. Since the first planetary gears355rotate and revolve as described above, the second planetary gears352also rotate and revolve. Accordingly, as the second ring gear359rotates, the pinion shaft250connected to the second ring gear359by means of a connection body370and described later is rotated by the auxiliary power provided by the electric motor210.

Here, the second ring gear359is integrally fitted in the connection body370having a hollow cylindrical shape, so that a rotation force of the second ring gear359is transferred to the pinion shaft250through the connection body370.

Both ends of the connection shaft357are coupled to and supported by the carrier354. The structure of the carrier354will be described in detail. The carrier354includes: a first supporting portion411having an annular shape and a first hole413in which one end of the connection shaft357is inserted; a second supporting portion415having an annular shape and a second hole417which is opposite to the first hole413and in which the other end of the connection shaft357is inserted; and, a connection portion419which connects the first supporting portion411with the second supporting portion415and supports the first supporting portion411and the second supporting portion415.

The first supporting portion411may be made of an annular plate. Since the first hole413is formed in the first supporting portion411, one end of the connection shaft357is inserted in and coupled to the first hole413.

The second supporting portion415may be also made of an annular plate. Since the second hole417is formed in the second supporting portion415, the other end of the connection shaft357is inserted in and coupled to the second hole417.

The connection portion419connects the first supporting portion411with the second supporting portion415, which may be integrally formed on the supporting portion411or the second supporting portion415.

That is, as the connection portion419is integrally formed on the first supporting portion411, the connection portion419and the first supporting portion411may be formed to be one structure. In the drawings, the one structure is shown.

Of course, alternatively, the connection portion419may be integrally formed on the second supporting portion415so that the second supporting portion415and the connection portion419construct one structure.

As described above, since the connection portion419is integrally formed on the first supporting portion411or the second supporting portion415, a management of parts is convenient, and the planetary gears352and355and the carrier354may be easily assembled and separated.

On the other hand, a first bearing431is mounted on an outer peripheral surface of one end of the connection shaft357and may be press-fitted in the first hole413, while a second bearing731is mounted on an outer peripheral surface of the other one of the connection shaft357and may be press-fitted in the second hole417.

The pinion shaft250extends through the motor shaft311, and has one end thereof on which a pinion gear251is formed to be engaged with the rack gear112formed on the rack bar109, and the other end thereof connected to the input shaft290by the torsion bar330.

Further, the pinion shaft311is connected to the second ring gear359through the connection body370, and thus rotates along with the second ring gear359.

Hereinafter, an operation of the electric power steering apparatus for the vehicle according to the embodiment of the present invention will be described with reference to the drawings.

When the driver rotates the steering wheel101, the steering shaft102and the input shaft290connected to the steering shaft102by means of the universal joint103rotate. In turn, the pinion shaft250connected to the input shaft290by means of the torsion bar330rotates, so that the rotation force of the steering wheel101is transferred as a driving force to enable the rack bar109to straightly move left and right.

The torque value of the input shaft290is measured by the torque sensor270, and the measured torque value is converted into an electric signal and transmitted to the ECU123.

On the other hand, the ECU123controls the electric motor210to generate the auxiliary power, based on an electric signal transmitted from the torque sensor270and electric signals transmitted from various sensors, and the generated auxiliary power rotates the motor shaft311, resulting in the rotation of the sun gear351.

Then, when the sun gear351rotates, the first planetary gears355interposed between the sun gear351and the first ring gear353rotate and revolve while the second planetary gears352connected to the first planetary gears355by the connection shaft357also rotate and revolve. Accordingly, the second ring gear359, engaged with the second planetary gears352, rotates to enable the pinion shaft250connected to the second ring gear359by means of the connection body370to rotate. As a result, the auxiliary power of the electric motor210is transferred to the pinion shaft250so as to assist the steering force of the driver.

As described above, according to the embodiment of the present invention, an electric power steering apparatus for a vehicle has a structure in that a motor shaft, an input shaft, a pinion shaft, and the like are coaxially disposed to improve a structure of a conventional art in which an electric motor is essentially exposed, so as to prevent interference with other structures, thereby forming a layout structure of the steering apparatus to be compact.

Even if it was described above that all of the components of an embodiment of the present invention are coupled as a single unit or coupled to be operated as a single unit, the present invention is not necessarily limited to such an embodiment. At least two elements of all structural elements may be selectively joined and operate without departing from the scope of the present invention. Although the embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention. The scope of the present invention shall be construed on the basis of the accompanying claims in such a manner that all of the technical ideas included within the scope equivalent to the claims belong to the present invention.

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