Electric power steering apparatus

In the electric power steering apparatus, a supporting mechanism for supporting a steering assist motor on a stationary member comprises: a projection provided at one end of a motor housing; a recess provided at the stationary member, into which said projection is inserted; a movement permitting portion for permitting relative movement of the projection in the recess; and a slip-off portion from where the projection slips off said movement permitting portion. When impact energy of a primary crash and/or a secondary crash is applied to the motor housing, support of the motor on the stationary member is automatically released by rotating said motor housing.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to an electric power steering apparatus using a motor as a generation source of steering assistance force.

2. Description of Related Art

FIG. 1is a front view showing a constitution of a conventional electric power steering apparatus.

As shown inFIG. 1, for example, an electric power steering apparatus for a vehicle comprises: a steering shaft101joined to a steering wheel100for steering; a shaft housing102for accommodating said steering shaft101; a steering assist motor104for assisting operation of a steering mechanism joined via a joint to the steering shaft101, the steering assist motor104having a rotor arranged so that a rotational center thereof intersects an axis of the steering shaft101and a cylindrical motor housing103for supporting said rotor; fastening members105for supporting one end portion of the motor housing103on a lower end portion of the shaft housing102; a lower mounting member106for mounting a lower end portion of the shaft housing102to a car body (see FIG.2); and an upper mounting member108for mounting an axially middle portion of the shaft housing102to the car body109, the upper mounting member108having an impact energy absorber107for absorbing impact energy of a secondary crash.

The steering shaft101is divided into an upper shaft101ajoined to the steering wheel100and a lower shaft101bjoined to the joint, the divided end portions being connected to each other by an impact energy absorber for absorbing impact energy of a secondary crash. The shaft housing102is divided into an upper shaft housing102ato which the upper mounting member108is mounted and a lower shaft housing102bto which the motor104and the lower mounting member106are mounted, the divided end portions being engaged with each other so as to be movable relatively.

FIG. 2is a schematic representation showing a state of a conventional electric power steering apparatus mounted to a car body.

The electric power steering apparatus constituted as above is disposed in a passenger's room. As shown inFIG. 2, the lower mounting member106and the upper mounting member108are mounted to the car body109. The joint110, which connects the steering shaft101and the steering mechanism of the electric power steering apparatus mounted to the car body109, is disposed through an instrument panel111of the car body109.

When a vehicle having an electric power steering apparatus mounted thereto as above makes a crash, such as a frontal crash, the instrument panel111of the car body109is occasionally transformed toward the interior of the passenger's room by the crash (a primary crash). When a driver crashes (a secondary crash) into the steering wheel100by the action of a shock of a primary crash, impact energy is applied to the upper steering shaft101a, and further to the upper shaft housing102avia said upper steering shaft101a. Since the upper steering shaft101aand the upper shaft housing102aare pressured in an axial direction in this case, the impact energy absorber of the steering shaft101and the impact energy absorber107of the upper mounting member108are destroyed, and the upper steering shaft101aand the upper shaft housing102amove relatively with the lower steering shaft101band the lower shaft housing102b. The impact energy of the secondary crash can thus be absorbed.

However, the steering assist motor104of the electric power steering apparatus which is constituted as the above projects outward in a radial direction of the shaft housing102on a relatively large scale. Moreover, said motor104is fixed to the lower shaft housing102bwith fastening members105. At the time of the secondary crash, a driver's leg occasionally strikes against the motor104since the upper shaft housing102amoves relatively with the upper shaft housing102bto which the motor104is mounted. Consequently, there arises a problem in that driver's damage becomes serious. Moreover, when the instrument panel111or the like of the car body109strikes against the motor104at the time of the primary crash, transformation of the instrument panel111or the like is hindered by the motor104, thereby preventing absorption of impact energy.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made with the aim of solving the above problems, and one object of the invention is to provide an electric power steering apparatus in which a supporting mechanism for supporting a steering assist motor on a stationary member has a releasing mechanism for releasing support of the motor on the stationary member by impact energy applied to the motor, with which support of the motor is automatically released when impact energy is applied to the motor.

Another object of the present invention is to provide an electric power steering apparatus in which the supporting mechanism comprises a projection and a recess into which said projection is inserted and the releasing mechanism comprises a movement permitting portion for permitting relative movement of the projection in the recess and a slip-off portion from where the projection slips off said movement permitting portion, with which the projection can move from the recess to the movement permitting portion, and further outward from the slip-off portion when impact energy is applied to the motor, thereby releasing support of the motor on the stationary member preferably.

Another object of the present invention is to provide an electric power steering apparatus in which the releasing mechanism has an elastic body for pushing the projection or the recess portion outward at the position of the slip-off portion, with which the projection or the recess portion is pushed outward by the elastic body.

A further object of the present invention is to provide an electric power steering apparatus in which the projection is configured as a screw member and the recess is configured as a through bore, with which the motor can be supported in a manner that the support can be released, utilizing an existing motor supporting structure having fastening members.

Another object of the present invention is to provide an electric power steering apparatus in which an impact energy receiver for applying rotational force to the motor housing by the impact energy is provided at a peripheral face of the cylindrical motor housing which is arranged to intersect an axis of a steering shaft, with which impact energy can be suitably applied to the impact energy receiver and the motor housing can be rotated preferably.

A further object of the present invention is to provide an electric power steering apparatus in which a supporting mechanism for supporting a cylindrical motor housing on a shaft housing comprises at least one projection provided at a peripheral position of the motor housing, at least one arc-shaped groove provided at the shaft housing, into which groove the projection is inserted so as to be movable in a longitudinal direction, and at least one slip-off portion from where the projection slips off the arc-shaped groove when the projection moves, with which the projection can move from the recess to the movement permitting portion, and further outward from the slip-off portion when impact energy is applied to the motor, thereby automatically releasing support of the motor on the stationary member.

The electric power steering apparatus according to an embodiment of the present invention comprises a steering assist motor for assisting operation of a steering mechanism by turning a steering member and a supporting mechanism for supporting said motor on a stationary member, the supporting mechanism having a releasing mechanism for releasing support of the motor on the stationary member by impact energy applied to the motor. Consequently, when impact energy of a primary crash and/or a secondary crash is applied to the motor, support of the motor on the stationary member can be automatically released, impact energy of a primary crash can be absorbed preferably, and driver's damage caused by a secondary crash can be reduced.

In the electric power steering apparatus, the supporting mechanism comprises a projection provided at one of the motor and the stationary member and a recess provided at the other of the motor and the stationary member, the projection being inserted into the recess. Moreover, the releasing mechanism comprises a movement permitting portion for permitting relative movement of the projection in the recess and a slip-off portion from where the projection slips off the movement permitting portion. The motor can be supported on the stationary member by inserting the projection into the recess. In this supporting state, the projection provided at the motor or at the stationary member moves in the recess to the movement permitting portion, and further outward from the slip-off portion when impact energy of a primary crash and/or a secondary crash is applied to the motor. Support of the motor on the stationary member can thus be released preferably.

In the electric power steering apparatus, the releasing mechanism further has an elastic body for pushing the projection or the recess portion, which is provided at the motor, outward at the position of the slip-off portion. Consequently, when the projection provided at the motor or at the stationary member moves along the movement permitting portion to the position of the slip-off portion in the recess, the elastic body pushes the projection or the recess portion outward, thus releasing support of the motor on the stationary member nimbly.

In the electric power steering apparatus, the projection is configured as a screw member and the recess is configured as a through bore. Since the motor is supported in a manner that the support can be released utilizing an existing motor supporting structure having fastening members, costs can be relatively reduced.

In the electric power steering apparatus, the motor has a rotor arranged so that a rotational center thereof intersects an axis of the steering shaft joined to the steering member and a cylindrical motor housing for supporting said rotor, and a peripheral face of the motor housing is provided with an impact energy receiver for applying rotational force to the motor housing by the impact energy. Consequently, impact energy of a primary crash and/or a secondary crash can be suitably applied to the impact energy receiver. Since the motor housing can be rotated preferably, support of the motor on the stationary member can released more preferably.

The electric power steering apparatus according to another embodiment of the present invention comprises: a steering shaft joined to a steering member; a shaft housing for accommodating said steering shaft; a steering assist motor for assisting operation of a steering mechanism joined to the steering shaft, the steering assist motor having a rotor arranged so that a rotational center thereof intersects an axis of the steering shaft and a cylindrical motor housing for supporting said rotor; and a supporting mechanism for supporting one end portion of the motor housing on the shaft housing, the supporting mechanism further comprising: at least one projection provided at a peripheral position of the motor housing; at least one arc-shaped groove provided at the shaft housing, into which groove the projection is inserted so as to be movable in a longitudinal direction; and at least one slip-off portion from where the projection slips off the arc-shaped groove when the projection moves. The motor can be supported on the shaft housing by inserting the projection into the arc-shaped groove of the shaft housing. In this supporting state, a projection provided at the motor housing can move in an arc-shaped groove, and further outward from a slip-off portion when impact energy of a primary crash and/or a secondary crash is applied to the motor housing. Support of the motor housing on the shaft housing can thus be automatically released.

DETAILED DESCRIPTION OF THE INVENTION

The following description will explain the present invention in detail with reference to the drawings illustrating some embodiments thereof.

FIG. 3is a front view showing a constitution of an electric power steering apparatus according to the present invention, andFIG. 4is a sectional view showing a constitution of the electric power steering apparatus.

As shown in FIG.3andFIG. 4, the electric power steering apparatus comprises: a steering shaft2joined to a steering wheel1for steering; a shaft housing3for supporting and accommodating said steering shaft2; a torque sensor4for detecting steering torque applied to the steering wheel1; a steering assist motor5driven based on a result of the detection of the torque sensor4, the steering assist motor5having a rotor54(see FIG.7andFIG. 9) arranged so that a rotational center thereof intersects an axis of the steering shaft2and a cylindrical motor housing51for supporting said rotor54; a supporting mechanism6for supporting one end portion of the motor housing51on a lower end portion of the shaft housing3; a lower mounting member7for mounting a lower end portion of the shaft housing3to a car body; and an upper mounting member8for mounting an axially middle portion of the shaft housing3to the car body, the upper mounting member8having an impact energy absorber81for absorbing impact energy of a secondary crash. The apparatus is constituted so that operation of a steering mechanism joined via a joint9to a lower end of the steering shaft2is assisted by rotation of the motor5, thereby reducing driver's load for steering.

The steering shaft2comprises a first shaft21joined to the steering wheel1, a second shaft22connected to a lower end portion of the first shaft21via an impact energy absorber24made of synthetic resin for absorbing impact energy applied to the steering wheel1by a driver, and a third shaft23connected to a lower end portion of said second shaft22via a torsion bar25. Said third shaft23is joined via a reduction gear mechanism10to the rotor54of the motor5. A lower end of the third shaft23is joined via a joint9to a steering mechanism. The torque sensor4is adapted to detect steering torque by relative rotational displacement of the second shaft22and the third shaft23.

The shaft housing3comprises a cylindrical first shaft housing31for supporting and accommodating the first shaft21; a cylindrical second shaft housing32for accommodating the second shaft22, the second shaft housing32being engaged into a lower end portion of the first shaft housing31so as to be movable relatively; and a third shaft housing33having a first receiver33afor accommodating the torque sensor4and a driven gear10aof the reduction gear mechanism10, the third shaft housing33being fitted to a lower end portion of the second shaft housing32. The lower mounting member7is mounted at a lower end of said third shaft housing33.

FIG. 5is a partly sectional front view of a motor portion.

The third shaft housing33is provided with a substantially cylinder-shaped second receiver33bfor accommodating a driving gear10bof the reduction gear mechanism10and a ring-shaped motor supporting portion34for supporting the motor housing51. The second receiver33bis coupled to one side of the first receiver33a, and the motor supporting portion34is provided at one end side of said second receiver33b.

At the motor supporting portion34the motor housing51is supported by the supporting mechanism6so as to be angularly rotatable. The motor5is arranged to intersect an axis of the steering shaft2, supported by the motor housing51. In this arrangement of the motor5, said motor5projects outward in a radial direction of the shaft housing3on a relatively large scale. Consequently, the motor5suitably strikes against an instrument panel or the like of a car body at the time of a primary crash.

FIG. 6is a sectional view taken along the line VI—VI of FIG.5.

A peripheral face of the motor housing51of the motor5is provided with upper and lower impact energy receivers52and53for applying rotational force to said motor housing51when impact energy of a primary crash and/or a secondary crash is applied to the motor5, particularly to the motor housing51.

Said impact energy receivers52and53are formed by arranging a plurality of ribs at diagonal positions with regard to a rotational center of the rotor54on faces, which are supposed to be upper and lower faces of the motor5when the electric power steering apparatus is mounted to the car body. Though the impact energy receivers52and53are formed to cover the total length of the motor housing51in this embodiment, the impact energy receivers52and53may be formed only at a part in an axial direction of the motor housing51, and moreover, may be configured so that a plurality of rib portions are provided throughout the motor housing51.

The supporting mechanism6comprises two tongues11aconfigured as projections11provided at peripheral positions of the motor housing51, two arc-shaped grooves12aconfigured as recesses12which are provided in an arc shape within the motor supporting portion34and into which the tongues11aare inserted so as to be movable in a longitudinal direction thereof, and two slip-off portions13from where said tongues11aslip off the arc-shaped grooves12awhen the tongues11amove with angular rotation of the motor housing51.

Though two tongues11aare provided at a peripheral face of one end portion of the motor housing51with equal phase difference in this embodiment, one tongue11aor more than two tongues11amay be provided.

An arc-shaped groove12ais formed to cover an angle of approximately 45° eccentrically to the motor supporting portion34. One longitudinally end portion of the arc-shaped groove12aconstitutes a supporting mechanism6for supporting the motor5in engagement with a tongue11a. The other end side excepting the supporting mechanism6constitutes a movement permitting portion12bfor permitting relative movement of the tongue11a. The movement permitting portion12band the slip-off portion13provided at the other longitudinally end portion of the arc-shaped groove12aconstitute a releasing mechanism for releasing support of the motor5by impact energy applied to the motor5.

Within the arc-shaped groove12a, a thin arc-shaped contact plate14made of a material with relatively low frictional resistance, such as synthetic resin, and an elastic body15consisting of a coiled spring for pushing said contact plate14against one face of the tongue11aare provided. Said elastic body15prevents the tongue11afrom trembling in the arc-shaped groove12a. The contact plate4can reduce frictional resistance caused when the tongue11amoves. The tongue11acan thus move preferably.

The slip-off portion13is formed by cutting one side wall of one end of the arc-shaped groove12aoff in accordance with a form of the tongue11a. With angular rotation of the motor housing51, the tongue11aslips outward from the slip-off portion13when the tongue11amoves to one end of the arc-shaped groove12a.

The lower mounting member7has a first mounting portion71mounted to a lower end portion of the third shaft housing33and a second mounting portion72mounted to the car body.

The upper mounting member8comprises a first mounting portion82mounted to the first shaft housing31, a second mounting portion83mounted to the car body, and an impact energy absorber81made of synthetic resin for connecting the first mounting portion82and the second mounting portion83.

The electric power steering apparatus constituted as above is disposed in a passenger's room and the second mounting portion72of the lower mounting member7is mounted to the car body with bolts in the same way as the conventional power steering apparatus shown in FIG.2. The third shaft housing33is supported on the car body. The second mounting portion82of the upper mounting member8is fixed to the car body with bolts. Moreover, the first shaft housing31is mounted to the car body via the upper mounting member8. In the electric power steering apparatus mounted to the car body, a joint9connecting the steering shaft2and the steering mechanism is disposed through an instrument panel of the car body.

When the instrument panel or the like of the car body is transformed toward the interior of a passenger's room by a frontal crash or the like (a primary crash) of a vehicle, the transformed portion of the instrument panel or the like occasionally strikes against the motor5. In such a case, since a peripheral face of the motor housing51is provided with the upper and lower impact energy receivers52and53, the transformed portion of the instrument panel or the like strikes against a lower impact energy receiver53for example, thereby allowing impact energy to be applied to said lower impact energy receiver53.

FIG. 7is a representation illustrating a state of a motor when support of the motor is released.

Since the upper and lower impact energy receivers52and53are provided at diagonal positions with regard to a rotational center of the rotor54, rotational force in a counterclockwise direction ofFIG. 6is applied to the motor housing51by impact energy applied to the lower impact energy receiver53. With rotation of the motor housing51caused by this rotational force, the tongue11aof the motor housing51moves in the arc-shaped groove12aof the shaft housing3to the movement permitting portion12b, and further to the slip-off portion13(see FIG.7), and slips outward from said slip-off portion13. Thus, support of the motor5on the third shaft housing33is automatically released. Consequently, a transformed portion of an instrument panel or the like which has struck against the motor5by a primary crash can be further transformed, thereby allowing impact energy of a primary crash to be absorbed preferably.

Moreover, when a driver crashes (a secondary crash) into the steering wheel1by the action of a shock of the primary crash and impact energy thereof is applied to the first shaft housing31via the first shaft21and a ball bearing26, the first shaft21and the first shaft housing31are pressured in an axial direction, the impact energy absorber24of the steering shaft2and the impact energy absorber81of the upper mounting member8are destroyed, and the first shaft21and the first shaft housing31move relatively with the second shaft22and the second shaft housing32. Impact energy of the secondary crash can thus be absorbed.

When a driver crashes into the steering wheel1by the action of a shock of a primary crash as mentioned above, a driver's leg occasionally strikes against the motor5. In such a case, since a peripheral face of the motor housing51is provided with the upper impact energy receiver52, a driver's leg strikes against the upper impact energy receiver52for example, thereby allowing impact energy to be applied to the upper impact energy receiver52.

Since the upper and lower impact energy receivers52and53are provided at diagonal positions with regard to a rotational center of the rotor54, rotational force in a counterclockwise direction ofFIG. 6is applied to the motor housing51by impact energy applied to the upper impact energy receiver52. With rotation of said motor housing51caused by this rotational force, the tongue11aof the motor housing51moves in the arc-shaped groove12aof the shaft housing3to the movement permitting portion12b, and further to the slip-off portion13(see FIG.7), and slips outward from said slip-off portion13. Support of the motor5on the third shaft housing33is thus automatically released. Consequently, driver's damage caused by a second crash can be reduced.

Within arc-shaped groove12aa contact plate14is provided to reduce frictional resistance caused when the tongue11amoves along the movement permitting portion12b. Consequently, the motor housing51provided with the tongue11acan be angularly rotated preferably. Further, since the contact plate14in the arc-shaped groove12ais pushed against one face of the tongue11aby the elastic body15, the tongue11ais prevented from trembling in the arc-shaped groove12a.

Though a coiled spring is used as an elastic body15in a releasing mechanism in the above embodiment, synthetic rubber or a leaf spring may be employed instead of a coiled spring. When a leaf spring is used, an apparatus without the contact plate14may be constituted by disposing the leaf spring at a slant with regard to one side of the arc-shaped groove12aso that the leaf spring contacts with one face of the tongue11a.

FIG. 8is a partly sectional front view of a motor portion showing a constitution of Embodiment 2 of an electric power steering apparatus according to the present invention;FIG. 9is a sectional view taken along the line IX—IX ofFIG. 8;FIG. 10is a sectional view taken along the line X—X ofFIG. 8, in which an interior portion of the motor is omitted; andFIG. 11is a presentation illustrating a state of a motor when support of the motor is released.

In the electric power steering apparatus of this embodiment, the projection11for supporting the motor5on the shaft housing3is configured as a screw member11band the recess12is configured as a through bore12cinto which the screw member11bis inserted.

In this embodiment, two threaded holes61are provided at the ring-shaped motor supporting portion34, which is provided at one end side of the second receiver33bof the third shaft housing33, with equal phase difference in a peripheral direction. A screw member11bis screwed into said threaded hole61.

The screw member11bis configured as a bolt which has a non-thread portion11ewith larger diameter than a thread portion11cand a slip-off preventing portion11fwith larger diameter than said non-thread portion11eand the through bore12cbetween a thread portion11cat one end side and a rotation operating portion1dat the other end side. In a state where the thread portion11cis screwed into the threaded hole61, the non-thread portion11e, the slip-off preventing portion11fand the rotation operating portion11dare exposed to the exterior of the motor supporting portion34.

Two mounting tongues55are provided at one end portion of the motor housing51having the impact energy receivers52and53, more particularly at positions facing the screw members11b, in a radial direction. At said mounting tongues55the through bores12care provided. The non-thread portion11eof the screw member11bis inserted into the through bore12cso as to be movable relatively.

One side of the through bore12cis left open in an arc shape, a center of which is the rotor54. In said open portion a releasing mechanism is constituted which has a movement permitting portion12dfor permitting relative movement of the screw member11bin the through bore12cand a slip-off portion13afrom where the screw member11bslips off said movement permitting portion12d. Though two pairs of screw members11band through bores12care arranged at regular intervals in this embodiment, one pair of screw member11band through bore12cor more than two pairs of screw members11band through bores12cmay be arranged.

In Embodiment 2, when impact energy is applied to the lower impact energy receiver53of the motor5by a primary crash as mentioned in Embodiment 1, rotational force in a counterclockwise direction ofFIG. 9is applied to the motor housing51by said impact energy. With rotation of said motor housing51caused by this rotational force, the mounting tongue55(the through bore12cportion) of the motor housing51moves away from the screw member11bof the motor supporting portion34, and the through bore12cmoves along the movement permitting portion12dand slips off the screw member11bat the position of the slip-off portion13. Support of the motor5on the third shaft housing33is thus automatically released. Consequently, a transformed portion of an instrument panel or the like which has struck against the motor by a primary crash can be further transformed, thereby allowing impact energy of the primary crash to be absorbed preferably.

Moreover, when impact energy is applied to the upper impact energy receiver52of the motor5by a secondary crash as mentioned in Embodiment 1, rotational force in a counterclockwise direction ofFIG. 9is applied to the motor housing51by said impact energy. With rotation of said motor housing51caused by this rotational force, the mounting tongue55(the through bore12cportion) of the motor housing51moves away from the screw member11bof the motor supporting portion34, and the through bore12cmoves along the movement permitting portion12dand slips off the screw member11bat the position of the slip-off portion13. Support of the motor5on the third shaft housing33is thus automatically released. Consequently, driver's damage caused by a secondary crash can be reduced.

In Embodiment 2, since other structures and functions are the same as those of Embodiment 1, like codes are used to refer to like parts and detailed explanation thereof are omitted.

In the above embodiment, the impact energy receivers52and53are provided at diagonal positions with regard to a rotational center of the rotor54on faces which are supposed to be upper and lower faces of the motor housing51of the motor5when the electric power steering apparatus is mounted to the car body. However, one impact energy receiver52or53may be provided at one of the upper and lower faces of the motor housing51of the motor5at said position. Moreover, impact energy receivers52and53may be provided at both sides with regard to the rotational center of the rotor54on an upper face and/or a lower face of the motor51of the motor at said position.