Electric power steering apparatus

An electric power steering apparatus for assisting steering of a steered wheel. The electric power steering apparatus includes an electric motor with a built-in controller for controlling rotation, a transmission mechanism for transmitting the rotation of the electric motor to the steering shaft, a connector used to pull out wiring from the controller to the outside, a first casing in which the connector and the electric motor are to be mounted and which includes an work hole used for a wire connection operation of the controller and the connector, a lid member for closing the work hole, and a second casing to be fixed to the first casing while housing the transmission mechanism. The second casing including a cover part for covering the lid member in a state fixed to the first casing.

RELATED APPLICATIONS

The present application is based on, and claims priority from, Japanese Application Number 2011-62714, filed Mar. 22, 2011, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to an electric power steering apparatus for vehicle.

BACKGROUND OF THE INVENTION

An electric power steering apparatus for assisting a steering wheel operation utilizing a rotational force of an electric motor is known as a power steering apparatus for assisting a steering wheel operation performed by a driver.

JP2001-31755A discloses an electric power steering apparatus with a motor unit in which a control board and a power device board are integrally provided to an electric motor.

SUMMARY OF THE INVENTION

In the case of using a control board integrated electric motor in which a control board is integrally provided, a connector used to take wiring out to the outside and the control board need to be connected by wire in mounting the electric motor in a casing. Thus, a work hole used to connect the control board and the connector by wire is formed in the casing in some cases. In the case of forming the work hole in the casing, a lid member needs to be mounted in the work hole to close the work hole.

The present invention aims to reliably mount a lid member for closing a work hole used for wire connection of a connector in the case of using a controller integrated electric motor.

To achieve the object described above, this invention provides an electric power steering apparatus for assisting steering of a steered wheel. The electric power steering apparatus includes an electric motor with a built-in controller for controlling rotation, a transmission mechanism for transmitting the rotation of the electric motor to the steering shaft, a connector used to pull out wiring from the controller to the outside, a first casing in which the connector and the electric motor are to be mounted and which includes an work hole used for a wire connection operation of the controller and the connector, a lid member for closing the work hole, and a second casing to be fixed to the first casing while housing the transmission mechanism. The second casing including a cover part for covering the lid member in a state fixed to the first casing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The entire construction of an electric power steering apparatus100according to an embodiment of the present invention is described with reference toFIGS. 1 and 2.

The electric power steering apparatus100is installed in a vehicle to assist a steering wheel operation performed by a driver.

The electric power steering apparatus100includes a steering input shaft1to which a torque resulting from a steering wheel operation by the driver is input, an unillustrated steering output shaft coaxially coupled to the steering input shaft1via an unillustrated torsion bar and linked with wheels, a torque sensor2for detecting a torque acting on the torsion bar, and an assist unit10for giving an assist force corresponding to an output of the torque sensor2to the steering output shaft.

The steering input shaft1is a tubular shaft, one end of which is coupled to an unillustrated steering wheel at a driver's seat. The torsion bar for detecting a torque is inserted into the inner periphery of the other end of the steering input shaft1.

The torsion bar has one end fixed to the steering input shaft1and synchronously rotates with the steering input shaft1. The other end of the torsion bar is press-fitted into one end of the steering output shaft. In this way, the steering output shaft is coupled to the steering input shaft1via the torsion bar and the steering input shaft1and the steering output shaft are relatively rotated by a twisted amount of the torsion bar.

When being input to the steering input shaft1, the torque resulting from the steering wheel operation by the driver is transmitted to the steering output shaft via the torsion bar. At this time, the torque sensor2detects the torque acting on the torsion bar based on the twisted amount of the torsion bar.

An unillustrated steering pinion to be engaged with an unillustrated rack shaft mounted movably in an axial direction in a rack casing3fixed to the vehicle is provided on the outer periphery of the steering output shaft. This causes the rack shaft to move in the axial direction and the steered wheel coupled to the rack shaft via an unillustrated tie rod to be steered when the steering output shaft rotates.

A worm wheel32of a worm speed reducer30to be described later is fixed to the outer periphery on the other end of the steering output shaft. This causes the steering output shaft to rotate integrally with the worm wheel32.

The torque sensor2is a noncontact sensor for detecting the twisted amount of the torsion bar based on a change in magnetic field. Besides, the torque sensor2may be a contact sensor such as a sensor using a potentiometer. The torque sensor2includes a connector2afor outputting a signal corresponding to the detected torque.

Next, the assist unit10is described with reference toFIGS. 3 to 6.

The assist unit10includes an electric motor20operating in correspondence with the output from the torque sensor2, the worm speed reducer30as a transmission mechanism for transmitting a rotational force of the electric motor20to the steering output shaft while decelerating and amplifying it, and a connector25for taking out wiring from an ECU21built in the electric motor20to the outside. The assist unit10assists steering of the steered wheel by the rotational force of the electric motor20transmitted via the worm speed reducer30.

Further, the assist unit10includes a first casing40with a work hole41used for a wire connection operation of the ECU21and the connector25in mounting the connector25and the electric motor20, a lid member45for closing the work hole41, and a second casing50in which the worm speed reducer30is housed and which is fixed to the first casing40.

The electric motor20is driven by electricity supplied from an unillustrated power supply device of the vehicle and generates a rotational force for assisting the steering wheel operation by the driver. The rotational force of the electric motor20is transmitted from an output shaft of the electric motor20to the worm speed reducer30.

The ECU (Electronic Control Unit)21as a controller for controlling the rotation is built in the electric motor20.

The ECU21is composed of a microcomputer including a CPU (Central Processing Unit), a ROM (Read-Only Memory), a RAM (Random Access Memory) and an I/O interface (Input/Output interface). The RAM stores data in the processing of the CPU, the ROM stores a control program of the CPU and the like in advance, and the I/O interface is used to input and output information to and from connected devices. By operating the CPU and the RAM in accordance with the program stored in the ROM, a control of the electric power steering apparatus100is realized. The ECU21is electrically connected to the torque sensor2. The ECU21controls an output of the electric motor20according to the torque detected by the torque sensor2.

The connector25is a terminal for taking out the wiring from the ECU21to the outside. An unillustrated power line electrically connected to the power supply device and an unillustrated signal line electrically connected to the connector2aof the torque sensor2are connected to the connector25. By this, power is supplied to the ECU21and a signal from the torque sensor2is input thereto.

The worm speed reducer30transmits the rotation of the electric motor20to a steering shaft via the steering output shaft. The worm speed reducer30includes a worm31which rotates integrally with the output shaft of the electric motor20, and the worm wheel32which is engaged with the worm31and outputs the rotation of the electric motor20while converting a rotational direction.

The worm31is a screw gear arranged coaxially with the output shaft of the electric motor20. The base end of the worm31is fixed to the output shaft of the electric motor20. The free end of the worm31is supported on the second casing50via an unillustrated bearing.

The worm wheel32is a helical gear whose central axis crosses that of the worm31and so arranged as to have a predetermined center distance. A drive force transmitted to the worm31is output while the rotational direction thereof is changed by the worm wheel32. The worm wheel32has the steering output shaft press-fitted into the inner periphery thereof and integrally rotates. This enables the rotational force of the electric motor20to be transmitted to the steering output shaft via the worm speed reducer30and the steering wheel operation by the driver to be assisted.

The first casing40is formed to have a substantially cylindrical shape with open opposite ends in the axial direction. The first casing40includes a motor mounting part42which is open so that the electric motor20can be mounted, a connector mounting part43which is open in the same direction as the motor mounting part42and into which the connector25is to be mounted, a heat sink part44for radiating heat generated from the ECU21housed therein, and the work hole41formed on a side opposite to the motor mounting part42and the connector mounting part43.

The motor mounting part42is in the form of a recess recessed in an axial direction of the first casing40. The motor mounting part42is shaped in conformity with the electric motor20. The electric motor20is mounted in the motor mounting part42and fixed by fastening screws20ashown inFIG. 4.

The motor mounting part42is formed with a through hole through which the output shaft of the electric motor20is inserted and which penetrates in the axial direction of the first casing40.

The connector mounting part43is in the form of a recess formed on the outer periphery of the same surface as the one where the motor mounting part42is formed. The connector25is mounted in the connector mounting part43and fixed by fastening a screw25ashown inFIG. 4.

The connector mounting part43communicates with the motor mounting part42in the first casing40. This enables the ECU21of the electric motor20and the connector25to be connected by wire.

The heat sink part44is formed on an end part of the first casing40where the work hole41is formed. The heat sink part44is made of a material with high heat radiation. Together with the through hole through which the output shaft of the electric motor20is inserted, the work hole41is formed in an end surface of the heat sink part44facing the second casing50. The first casing40may be integrally formed to include the heat sink part44instead of separately forming the heat sink part44.

The work hole41is an arcuate hole formed along the outer periphery of the through hole through which the output shaft of the electric motor20is inserted. The work hole41penetrates the first casing40in the axial direction and communicates with the connector mounting part43. The work hole41is used to insert a tool by an operator for the wire connection operation of the ECU21of the electric motor20and the connector25. The work hole41is open toward the second casing50. Note that the wire connection of the ECU21and the connector25may be automatically performed using a facility instead of being manually performed by the operator.

The work hole41is provided only for connecting wires of the ECU21and the connector25. Thus, the work hole41is closed by mounting the lid member45after the wire connection of the ECU21and the connector25is completed.

The lid member45is an arcuate plate having the same curvature as the work hole41. The lid member45has opposite circumferential ends fastened by a pair of screws46and is fixed to the first casing40. The lid member45is formed to be larger than the opening area of the work hole41and completely closes the work hole41in a state mounted on the first casing40.

The second casing50includes a transmission mechanism housing part51for housing the worm speed reducer30, a plurality of fastening parts52to be fastened to the first casing40by bolts50a, and a cover part55for covering the lid member45in a state fixed to the first casing40.

The transmission mechanism housing part51is shaped in conformity with the worm speed reducer30and houses the worm speed reducer30. An opening is formed in an end surface of the transmission mechanism housing part51facing the first casing40so that the outer shaft of the electric motor20is insertable.

The fastening parts52are formed on an end part of the second casing50facing the first casing40. The fastening parts52are formed to bulge out from the outer periphery of the transmission mechanism housing part51. The fastening parts are substantially cylindrical bosses each formed with a through hole through which a bolt50afor fastening the second casing50and the first casing40is inserted. The fastening parts52are formed at three positions on the outer periphery of the transmission mechanism housing part51.

End surfaces of the fastening parts52are held in contact with the heat sink part44with the second casing50attached to the first casing40. Thus, generated heat from the ECU21is transmitted to the fastening parts52via the heat sink part44.

The fastening parts52can fix the first casing40and the second casing50by the fastened bolts50aif being formed at two or more positions. Thus, the fastening parts52may be at as many positions as needed, not limited to three positions, as long as the positions are plural.

The cover part55is an arm formed at one of the three fastening parts52to straddle the lid member45. The cover part55may be provided not only at one fastening part52, but also at two or more fastening parts52. That is, the cover part55only has to be provided between at least one of the fastening parts52and the transmission mechanism housing part51.

The cover part55is held in contact with the lid member45and presses the lid member45against the first casing40with the second casing50fixed to the first casing40. This enables the lid member45to be reliably mounted on the first casing40. Further, by covering the lid member45by the cover part55, collision of a flying stone or the like from the outside with the lid member45while the vehicle is moving can be prevented.

Generated heat from the ECU21is transmitted to the cover part55from the heat sink part44via the fastening parts52and the lid member45. The generated heat from the ECU21can be radiated, since the entire surface of the cover part55is in contact with the air. Thus, a heat radiation area increased by providing the cover part55improves heat radiation of the ECU21can be improved.

Note that the cover part55may be so formed as to be separated from the lid member45instead of being held in contact with the lid member45. In this case as well, the cover part55covers the lid member45, wherefore the lid member45can be reliably mounted on the first casing40and collision of a flying stone or the like from the outside with the lid member45while the vehicle is moving can be prevented.

Further, an elastic member may be interposed in a clearance between the cover part55and the lid member45. If the cover part55and the lid member45are directly in contact, the cover part55and the lid member45are required to have high dimensional accuracy. By interposing the elastic member, dimensional accuracy required for the cover part55and the lid member45is moderated.

According to the above embodiment, the following effect is achieved.

The lid member45for closing the work hole41used for wire connection of the ECU21of the electric motor20and the connector25is pressed against the first casing40by the cover part55of the second casing50with the second casing50fixed to the first casing40. Therefore, the lid member45can be reliably mounted on the first casing40.

Although the invention has been described above with reference to certain embodiments, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, within the scope of the claims.

The contents of Tokugan 2011-62714, with a filing date of Mar. 22, 2011 in Japan, are hereby incorporated by reference.

The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: