Power slider

A power slider includes a lower rail and an upper rail which are engaged with each other so as to be mutually slidable along each other, a screw rod which is rotatably supported on one of the lower rail and the upper rail, a feed nut which is supported on the other of the lower rail and the upper rail and is screw-engaged with the screw rod, and a gearbox which is supported on the one of the lower rail and the upper rail via a holder and which rotatably drives the screw rod. The gearbox is provided with a mounting bolt through-hole and is supported by the holder via a mounting bolt that is inserted through the mounting bolt through-hole. A resilient member is positioned in a space defined between the mounting bolt through-hole of the gearbox and the mounting bolt.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power slider for use, e.g., in a vehicle for slidably moving a vehicle seat.

2. Description of Related Art

Generally, a power slider comprises a lower rail, an upper rail that is engaged with the lower rail so as to be mutually slidably along each other, a screw rod (spindle) and a feed nut which are supported on one and the other of the lower rail and the upper rail, the feed nut being screw-engaged with the screw rod. The power slider is further provided with a gearbox, which rotatably drives the screw rod via a holding bracket (holder), on the rail which supports the screw rod (screw-rod supporting rail).

The gearbox is provided with a mounting-bolt through-hole, and the gearbox is supported by the holding bracket (holder) via amounting bolt that is inserted through the mounting-bolt through-hole. Furthermore, the gearbox supports a rotational mechanism (including a worm that is rotatably driven by a motor, and a worm wheel which is screw-engaged with the worm) which rotates the screw rod.

The applicant of the present invention has proposed a gearbox provided with a vibration-absorption rubber sheet (Japanese Unexamined Patent Publication No. 2010-6098) for cutting out/reducing the transmission of vibrations generated by (the rotational mechanism of) the gearbox to the holding bracket (holder) and the screw-rod supporting rail.

However, according to the inventors of the present invention, since a slight amount of space (clearance) is provided between the mounting-bolt through-holes and the mounting bolts, the gearbox cannot sufficiently conform to the undulations that occur in the rotation of the screw rod (i.e., eccentrical rotation with respect to the ideal rotational axis of the screw rod), so that the transmission of vibrations between the gearbox and the screw-rod support rail cannot be sufficiently suppressed. Furthermore, there is the possibility of abnormal noise occurring when the mounting bolts contact the wall surface of the mounting-bolt through-holes of the gearbox.

SUMMARY OF THE INVENTION

The present invention has been devised with consideration of the above-described problems and achieves a power slider in which a gearbox favorably conforms to (follows) the undulations that occur in the rotation of the screw rod, wherein transmission of vibration between the gearbox and the screw-rod support rail can be adequately suppressed, and does not generate abnormal noise.

The present invention has been devised with a focus on providing a resilient member and placing this resilient member into a space between the mounting-bolt through-hole of the gearbox and the mounting bolt, therefore, since this resilient member absorbs undulations that occur during the rotation of the screw rod while allowing for movement of the mounting bolt within the mounting-bolt through-hole, the gearbox can conform to the undulations that occur during the rotation of the screw rod and can suppress the transmission of vibration between the gearbox and the screw-rod support rail; and furthermore, since the mounting bolt does not come in contact with the wall surface of the gearbox in which the mounting-bolt through-hole is formed, abnormal noise can be prevented from occurring.

Namely, according to an aspect of the present invention, a power slider is provided, including a lower rail and an upper rail which are engaged with each other so as to be mutually slidable along each other; a screw rod which is rotatably supported on one of the lower rail and the upper rail; a feed nut which is supported on the other of the lower rail and the upper rail and is screw-engaged with the screw rod; and a gearbox which is supported on the one of the lower rail and the upper rail via a holder and which rotatably drives the screw rod. The gearbox is provided with a mounting bolt through-hole and is supported by the holder via a mounting bolt that is inserted through the mounting bolt through-hole. A resilient member is positioned in a space defined between the mounting bolt through-hole of the gearbox and the mounting bolt.

It is desirable for the resilient member to be provided with a facing wall which is positioned in between mutually facing surfaces of the holder and the gearbox.

It is desirable for the mounting bolt through-hole of the gearbox to extend in a direction parallel to the axis of the screw rod, and for a pair of the facing walls of the resilient member to be separated in a direction parallel to the axis of the screw rod and to be each positioned between the mutually facing surfaces of the holder and the gearbox so that the gearbox is sandwiched between the pair of mutually facing walls.

It is desirable for the holder to include a U-shaped section defined by a pair of mutually facing walls and a connecting portion which connects the pair of mutually facing walls, wherein the connecting portion is provided with an insertion groove. The resilient member is provided with a neck portion which is fitted into the insertion groove, and a fall-out prevention portion which is connected to the connecting portion via the neck portion.

In an embodiment, a power slider is provided, including a screw rod supporting rail which supports a screw rod; a feed nut supporting rail which supports a feed nut that is screw-engaged with the screw rod, the screw rod supporting rail and the feed nut supporting rail being engaged with each other so as to be relatively slidable in length-wise directions thereof; and a gearbox which is supported on the screw rod supporting rail to drive the screw rod. The gearbox is provided with a mounting bolt through-hole, through which a mounting bolt is inserted to mount the gearbox onto the screw rod supporting rail. A resilient member is positioned in an annular space defined between the mounting bolt through-hole of the gearbox and the mounting bolt.

According to the present invention, a power slider can be achieved in which a gearbox favorably conforms to undulations that occur in the rotation of the screw rod, transmission of vibration between the gearbox and the screw-rod support rail can be adequately suppressed, and abnormal noise is not generated.

The present disclosure relates to subject matter contained in Japanese Patent Application No. 2010-118416 (filed on May 24, 2010) which is expressly incorporated herein in its entirety.

DESCRIPTION OF THE EMBODIMENT

An embodiment of a power slider to which the present invention is applied will be hereinafter described with reference toFIGS. 1 through 4. The front/rear directions and left/right directions referred to in the following descriptions signify the directions as indicated by arrows in the drawings.

A front bracket11and a rear bracket12, which constitute a pair of brackets, are fixed onto a floor inside a vehicle (not shown) so that one (left) pair of front and rear brackets11and12are arranged on the left side on the floor and another (right) pair of front and rear brackets11and12are arranged on the right side on the floor. The upper surfaces of the left and right pairs of front and rear brackets11and12are fixed to underside surfaces of left and right lower rails (feed-nut support rails)20, at the front and rear ends thereof by rivets R1and R2, respectively. The lower rails20are each formed as a metal channel member that linearly extends in the front/rear directions, and includes left and right horizontal upper-portions21that project inwardly from upper edges of respective left and right side-walls of the metal channel member. Downward-extending portions22project downwardly from inwardly facing edges of the left and right upper-portions21, respectively. Left and right upper rails (screw-rod support rails)30(constituting a pair of upper rails), each of which is formed from a metal channel member that extends in the front/rear direction and is provided on a (vehicle) seat, are slidably engaged with the left and right lower rails20, respectively. Each upper rail30includes a body section31constituting an upside down U-shaped section, and upward-facing engaging portions32which extend outwardly from both left and right sides, respectively, of the body section31and thereafter extend upwardly. Each upper rail30is positioned in each corresponding lower rail20with the left and right upward-facing engaging portions32positioned in each space defined by the left and right side walls of the lower rail20and the left and right downward-extending portions22, respectively, and the body section31is positioned in between the left and right downward-extending portions22of the lower rail20so that the upper rails30are slidably engaged with the lower rails20, respectively. A left seat bracket13and a right seat bracket14are respectively fixed to the upper surfaces of the left and right upper rails30by a plurality of nuts N1and bolts B1. Left and right sides of the underside of a vehicle seat (not shown) are fixed to the left seat bracket13and the right seat bracket14, respectively. A cut-and-raised portion33which projects upwardly from the body section31is formed on a front end of each of the left and right upper rails30. A through-hole33ais formed through each cut-and-raised portion33.

A nut unit40is supported on the base surface of each of the left and right lower rails20by a pair of front and rear bolts B2. The nut unit40is configured of a metal case (carrier bracket)41, a resin nut (carrier nut/feed nut)44and a pair of resilient members45and46; the resin nut44and the pair of resilient members45and46are accommodated inside the metal case41. The metal case41is provided with a pair of axially separated walls42and a pair of axially parallel plates43. A pair of female screw-holes43aare formed in the lower of the axially parallel plates43. Hence, each nut unit40is supported by each lower rail20by the pair of bolts B2(which are also screwed through the base section of the corresponding lower rail20) being respectively screw-engaged with the pair of female screw-holes43a.

As shown inFIGS. 3 and 4, the resin nut44includes a central base portion44b, and (two) insertion portions44cwhich extend forwardly and rearwardly from each end of the central base portion44b, respectively. The cap-shaped resilient members45and46are fitted onto the insertion portions44c, respectively. Upwardly protruding inclined surface-portions45band46bare formed on the top surfaces (the surfaces which directly face the inner side of the upper plate of the axially parallel plates43) of the resilient members45and46, respectively. The inclined surface-portions45band46bprotrude upwardly in a state where the resilient members45and46are fitted onto the insertion portions44c, respectively, of the resin nut44. The underside surfaces (the surfaces which directly face the lower of the axially parallel plates43) of the resilient members45and46are flat surfaces. As shown inFIG. 4, upon a combined member47, consisting of the resin nut44and the resilient members45and46, being accommodated (press-fitted) into the metal case41, the front end of the resilient member45and the rear end of the resilient member are forcefully driven up against the front axially separated wall42and the rear axially separated wall42, respectively, and hence, these members constitute an assembled nut unit40with the axial position (i.e., the position with respect to the front/rear direction) of the combined member47the resin nut44and the resilient members45and46) in a restricted state. With the nut unit40in the assembled state, the combined member47is accommodated inside the metal case41in a “floated state” so as to be movable in a direction orthogonal to the axial direction thereof (i.e., in a vertical direction). Specifically, the inclined surface-portions45band46bof the resilient members45and46resiliently abut against the inner surfaces of the upper plate of the axially parallel plates43of the metal case41so that a gap is formed (defined) between the top surface of the central base portion44band the inner surface of the upper plate of the axially parallel plates43, and a gap is formed (defined) between the top surfaces of the resilient members45and46(except for the inclined surface-portions45band46b) and the inner surface of the upper plate of the axially parallel plates43. Whereas, the underside surfaces of the resilient members45and46resiliently abut against the inner surface of the lower of the axially parallel plates43of the metal case41so that a gap is formed (defined) between the underside surface of the central base portion44band the inner surface of the lower part of the axially parallel plates43. Accordingly, the resin nut44can be moved within the metal case41in a direction orthogonal to the axial direction thereof by elastically deforming the inclined surface-portions45band46bof the top surfaces of the resilient members45and46and the underside surfaces of the resilient members45and46.

A through-hole42ais formed in each of the axially separated walls42of the metal case41, and through-holes45aand46aare respectively formed through the resilient members45and46. A female screw-hole44ais formed completely through the resin nut44(the central base portion44band the insertion portions44c) so as to align with the positions of the through-holes42a,45aand46a.

A load transfer bracket50is supported at the front end of each body section31of the left and right upper rails30. As shown inFIGS. 1 and 2, the load transfer bracket50is U-shaped and includes a pair of load transfer walls51, which are separated from each other in the axial direction, and a mounting plate52which connects the pair of load transfer walls51and extends along the corresponding upper rail30. A through-hole51ais formed through each of the pair of load transfer walls51. As shown inFIG. 2, the load transfer bracket50is mounted to the (corresponding) upper rail30by a mounting bolt53that is inserted through the upper rail30from the mounting plate52, and a mounting nut54that is screw-engaged onto the mounting bolt53. Low-friction synthetic resin sleeves55and56are respectively fitted into the through-holes51aof the pair of load transfer walls51. A nut member (load-receiving member)57is positioned in between the pair of load transfer walls51so as to be sandwiched between the sleeves55and56.

A screw rod (spindle)60is rotatably supported in each of the left and right upper rails30and is screw-engaged with the female screw-hole44ain the resin nut44of the corresponding nut unit40that is mounted on each of the left and right lower rails20. Namely, a gearbox70and a bearing member15rotatably support the front and rear ends of the screw rod60, respectively, at the front and rear ends of each upper rail (screw-rod support rail)30. The gearbox70is provided with a housing71which supports a worm wheel72and a worm73which engages with the worm wheel72. The axis of the worm wheel72extends in the front/rear direction, and the axis of the worm73extends in the left/right direction. The screw rod60has a splined section61formed at the front end portion thereof, and the splined section61is engaged with a splined hole72a, which is formed through the center (central axis) of the worm wheel72, so as not to be relatively rotatable therewith (i.e., so that the worm wheel72rotates integrally with the screw rod60). The screw rod60is provided with a non-threaded stepped section62, which does not have a male thread, and a male threaded section63, in that order rearwardly from the splined section61. The male threaded section63is screw-engaged with a female threaded section57aformed through the nut member57which is positioned between the pair of load transfer walls51, and the male threaded section63is also screw-engaged with the female screw-hole44aof the resin nut44of the nut unit40. A rear-end bearing section64is formed at a rear end portion of the screw rod60, and the rear-end bearing section64is supported by the bearing member15so as to be rotatable relative thereto and to be relatively slidable therein.

The left and right upper rails30are connected to each other by a metal holding bracket (holder)80. Each of the left and right side ends of the holding bracket80is provided with a U-shaped section defined by a pair of mutually facing walls81which are separated from each other in a direction parallel to the axis of the screw rod60(i.e., in the front/rear direction) and a connecting plate (connecting portion)82, which connects the pair of mutually facing walls81. The pair of mutually facing walls81is provided with mounting bolt through-holes81a, respectively, which mutually face (align with) each other in the front/rear direction. The left and right connecting plates82are each provided with a resilient-member insertion groove83, which extends in the left/right direction, so that the left and right ends of the left and right connecting plates82are respectively open.

The left and right resilient-member insertion grooves83of the holding bracket80support the pair of left and right gearboxes70, respectively. Each gearbox70is provided with a mount74which is positioned inside the corresponding U-shaped section (defined by the pair of mutually facing walls81and the connecting plate82) at the left and right ends of the holding bracket80. The mount74is provided with a mounting bolt through-hole74awhich extends in a direction parallel to the axis of the screw rod60(i.e., extends in a front/rear direction).

A resilient member90is provided between the left gearbox70and the left end of the holding bracket80and another resilient member90is provided between the right gearbox70and the right end of the holding bracket80. Each resilient member90is provided with a U-shaped section defined by a pair of mutually facing walls91, which are separated in a direction parallel to the axis of the screw rod60(front/rear direction), and a connecting portion92which connects the pair of mutually facing walls91; this U-shaped section of the resilient member90is inserted inside the corresponding U-shaped section of the holding bracket80so as to be placed between the U-shaped section of the holding bracket80and the mount74of the of the gearbox70. In other words, the connecting portion92of the resilient member90is positioned along the connecting plate82of the holding bracket80and is positioned (sandwiched) between the connecting plate82and the mount74of the gearbox70, and the pair of mutually facing walls91of the resilient member90are separated in a direction parallel to the axis of the screw rod60(front/rear direction) so that the mount74of the gearbox70is sandwiched in between the pair of mutually facing walls91via the mutually facing surfaces81of the holding bracket80and the gearbox70.

Cylindrical portions91bare integrally formed on the pair of mutually facing walls91, respectively, of the resilient member90and mutually approach (extend toward) each other on a common axis (that is parallel to the axis of the screw rod60). The outer diameter of the inwardly extending cylindrical portions91bare formed (set)) at a diameter so as to fit into the mounting bolt through-hole74aformed in the mount74of the gearbox70. Upon fitting the cylindrical portions91binto the mounting bolt through-hole74a, the gearbox70is engaged with the resilient member90with the axes of the through-holes91aand the axis of the mounting bolt through-hole74aaligned with each other (in a coaxial manner) in the front/rear direction (i.e., aligned on a common axis).

A fall-out prevention plate (fall-out prevention portion)94, having a rectangular shape in a plan view, is continuously formed with, and provided on top of, the connecting portion92of the resilient member90via a neck portion93. The neck portion93is directly inserted into the resilient-member insertion groove83of the holding bracket80. Hence, the resilient member90is engaged with the holding bracket80with the positions of the through-holes91aand the mounting bolt through-holes81aaligned in the front/rear direction (axial direction) upon fitting the neck portion93of the resilient member90into the resilient-member insertion groove83of the holding bracket80with the fall-out prevention plate94positioned on the outer (upper) side of the connecting plate82.

As shown inFIG. 2andFIG. 5, the left and right gearboxes70are supported on the left and right upper rails (screw-rod support rail)30, respectively, via the holding bracket80(at the left and right ends of the holding bracket80) by a mounting bolt100that is tightly fastened by a mounting nut110in a state where the gearbox70, the holding bracket80and the resilient member90are engaged with each other with the mounting bolt through-hole74a, the mounting bolt through-holes81a, the through-holes91aand the through-hole33aof the cut-and-raised portion33aligned and the mounting bolt100extending therethrough in the front/rear direction (axial direction).

A motor130, the axis of which extends in the left/right direction, is mounted onto the holding bracket80via an L-shaped mounting member120. Namely, the L-shaped mounting member120is provided with a pair of female screw-holes121that extend in the vertical direction, and a pair of mounting bolts124are passed through the pair of female screw-holes121and the holding bracket80via a pair of washers122and a spacer123and are fastened to thereby mount the L-shaped mounting member120to the holding bracket80. Furthermore, the motor130is mounted onto the L-shaped mounting member120.

A right end of a flexible shaft FS1, which is made of a soft metal material, is connected with (and supported by) the left end of an in-built output shaft (not shown) of the motor130and rotates about an axis extending in the left/right direction (horizontal direction), and a left end of a flexible shaft FS2which is longer than the flexible shaft FS1and is made of the same metal material as that of the flexible shaft FS1is connected with (and supported by) the right end of the in-built output shaft of the motor130. The left end of the flexible shaft FS1is connected with the worm73that is supported in the left gearbox70so as not to be rotatable relative thereto (i.e., so as to integrally rotate with the worm73). The right end of the flexible shaft FS2is connected with the worm73that is supported in the right gearbox70so as not to be rotatable relative thereto (i.e., so as to integrally rotate with the worm73). The flexible shaft FS2is surrounded by a pipe-shaped cover member131, which is formed from a flexible material. A left end portion of the pipe-shaped cover member131is fixed onto a right end portion of the motor130and a right end portion of the pipe-shaped cover member131is fixed onto a left end portion of the right gearbox70.

The power slider, having the above-described configuration, is assembled in the following manner. Firstly, the process for assembling a floor-mounting unit that is mounted onto the floor of a vehicle will be discussed hereinafter. The nut units40are respectively mounted on the lower rails (feed-nut support rails)20, and the load transfer brackets50and the bearing members15are respectively mounted on the upper rails (screw-rod support rails)30. Thereafter, the screw rods60are supported by the upper rails30by respectively inserting each rear-end bearing section64of the screw rods60into each corresponding bearing member15, and screw-engaging each male threaded section63into the female screw-hole44aof the corresponding resin nut44of the corresponding nut unit40and the female threaded section57aof the corresponding nut member57that is positioned in between the pair of load transfer walls51of the load transfer bracket50. Accordingly, the left and right pairs of lower rails20and upper rails30are supported on the floor of the vehicle so that the lower rails20and the upper rails30are mutually slidable along each other.

On the other hand, the assembly process of a connecting unit which connects to the floor-mounting unit will discussed hereinafter. First the motor130is mounted onto the holding bracket80via the L-shaped mounting member120. Thereafter, the flexible shafts FS1and FS2, which are supported by the in-built output rotational shaft (not shown) of the motor130, are connected with the worms73that are supported by the left and right gearboxes70, respectively, so as to not to be rotatable relative to the worms73. Thereafter, the left and right gearboxes70are engaged into the corresponding left and right resilient members90with the mounting bolt through-hole74aof each gearbox70and the through-holes91aof the corresponding resilient member90being aligned in the front/rear direction by fitting the cylindrical portions91bof each resilient member90into the mounting bolt through-hole74aof the corresponding gearbox70. Thereafter, the left and right resilient members90(into which the left and right gearboxes70are respectively engaged) are engaged with the left and right ends of the holding bracket80with the mounting bolt through-holes81aof the left and right pairs of mutually facing walls81(of the holding bracket80) and the through-holes91aof the corresponding resilient members90(each mounting bolt through-hole74aof the corresponding gearbox70) aligned in the front/rear direction (axial direction) upon fit-inserting each neck portion93of the left and right resilient members90into the corresponding resilient-member insertion groove83of the holding bracket80so that each respective fall-out prevention plate94is positioned on the outer side of the corresponding connecting plate82. Thereafter, each gearbox70is supported on the corresponding upper rail30via the holding bracket80by a mounting bolt100that is tightly fastened by a mounting nut110in a state where each gearbox70, the holding bracket80and the corresponding resilient member90are engaged with each other with the mounting bolt through-hole74a, the mounting bolt through-holes81a, the through-holes91aand the through-hole33aof the corresponding cut-and-raised portion33aligned in the front/rear direction (axial direction). At the same time, the splined section61of each screw rod60is engaged into the splined hole72aof the corresponding worm wheel so as not to be rotatable relative to each other. Thereafter, the floor-mounting unit is connected to the connecting unit, and hence, the assembly of the power slider is thus completed.

The operation of the power slider, according to the present invention, having the above-described configuration will be discussed hereinafter. A slide switch (not shown) is provided inside a vehicle (e.g., a side surface of a seat to be slided) and is slidable between an OFF position (neutral position), a first ON position (forward slide position) and a second ON position (rearward slide position). For example, if the slide switch is moved from the OFF position to the first ON position, electrical current is supplied from a battery (not shown) to the motor130to rotate (drive) the motor130forward. Subsequently, the flexible shafts FS1and FS2which are (rotatably) integral with the output rotational shaft of the motor130, rotate in the clockwise direction with respect toFIG. 2. Subsequently, the worms73in the left and right gearboxes70also rotate in the clockwise direction, and furthermore, each worm wheel72that is engaged with the corresponding worm73and each corresponding screw rod60rotate in the anticlockwise direction, as viewed from the front. Accordingly, upon the screw rods60rotating, since each screw rod60moves forward while rotating with respect to each corresponding nut unit40(resin nut44), the left and right upper rails30and the seat (not shown) mounted thereto move forward relative to the left and right lower rails20(and the vehicle floor), respectively. If the slide switch is reverted back to the OFF position from the first ON position, the sliding movement of the upper rails30and the seat mounted thereto stops since the supply of electrical current from the battery to the motor130is shut off.

Whereas, if the position of the slide switch is moved to the second ON position, electrical current is supplied from the battery to the motor130to rotate the motor130in reverse, thereby rotating each worm wheel72and each screw rod60in the clockwise direction, as viewed from the front. Subsequently, since the screw rods60move rearwards while rotating relative to each corresponding nut unit40(resin nut44), the left and right upper rails30and the seat that is mounted thereto move rearward with respect to the left and right lower rails20. When the slide switch is reverted back to the OFF position from the second ON position, since the supply of electrical current from the battery to the motor130is shut off, the movement of the upper rails30and the seat that is mounted thereto stops.

Accordingly, upon the forward and reverse rotations of the screw rods60by the rotational driving force of the motor130, undulations that occur in the rotation of the screw rods60(eccentrical rotation with respect to the ideal rotational axis of the screw rods60) are transmitted to each gearbox70, and if the undulations are transmitted from the gearboxes70to the holding bracket80and the upper rails30, this would be have an undesirable effect on the operation of the power slider, and this also generates abnormal noise.

The present invention solves this problem by positioning the cylindrical portions91bprovided in each resilient member90into a cylindrical space that is defined between the mounting bolt through-hole74aof the corresponding gearbox70and (the outer peripheral surface of) the mounting bolt100, as shown inFIG. 2andFIG. 5. According to this configuration, since each resilient member90absorbs the undulations that occur during the rotation of the corresponding screw rod60while allowing for movement of the mounting bolt100inside the mounting bolt through-hole74a, each gearbox70can favorably conform to (follow) the undulations that occur during the rotation of the corresponding screw rod60, and transmission of vibrations from the gearboxes70to the holding bracket80and the upper rails30can be sufficiently suppressed. Furthermore, since the mounting bolts100do not contact the surfaces of the corresponding mounting bolt through-holes74aof the gearboxes70, abnormal noise can be prevented from being generated.

In addition, the operational effectiveness of the nut unit40of the illustrated embodiment is described hereinafter. Roller balls (not shown) are inserted between the lower rails20and the upper rails30in order to provide a smoother sliding action therebetween, however, it is possible for the relative position in a (vertical) direction orthogonal to the axes of the screw rods60and the nut unit40to shift relative to each other due to slight variations in the diameters of the roller balls. In the present invention, however (as shown in the illustrated embodiment), due to the structure of the combined member47, which includes the resin nut44and the resilient members45and46accommodated (press-fitted) into the metal case41, the axial position (front/rear position) of the combined member47is restricted due to the front end of the resilient member45and the rear end of the resilient member46forcefully abutting against the front axially separated wall42and the rear axially separated wall42, respectively, while the combined member47is accommodated inside the metal case41in a “floated state” so as to be movable in a direction orthogonal to the axial direction (i.e., in a vertical direction). In other words, the inclined surface-portions45band46bof the resilient members45and46resiliently abut against the inner surface of the upper axially parallel plate43of the metal case41, so as to define a space (gap) between the upper surface of the central base portion44band the inner surface of the upper axially parallel plate43, and define a space (gap) between the upper surfaces of the resilient members45and46(except for the inclined surface-portions45band46b) and the inner surface of the upper axially parallel plate43. Whereas, the undersurfaces of the resilient members45and46resiliently abut against the inner surface of the lower portion of the pair of axially parallel plates43of the metal case41, so as to define a space (gap) between the undersurface of the central base portion44band the inner surface of the lower portion of the pair of axially parallel plates43. Accordingly, the resin nut44can move in a direction orthogonal to the axial direction thereof (i.e., a vertical direction) within the metal case41by elastically deforming the inclined surface-portions45band46bof the resilient members45and46, and elastically deforming the undersurfaces of the resilient members45and46, so as to absorb variations in the relative position in a (vertical) direction orthogonal to the axes of the screw rods60and the nut unit40.

In the above-described embodiment, the cut-and-raised portions33are formed in the left and right upper rails30, respectively, and the gearboxes70are supported on the upper rails30, respectively, via the holding bracket80by inserting each mounting bolt100through the corresponding through-hole33aof each cut-and-raised portion33and fastening each mounting nut110onto each mounting bolt100; however, the present invention is not limit to such a configuration. For example, it is possible to provide a gearbox support bracket as a separate member and mount this gearbox support bracket to each of the left and right upper rails30or to each load transfer bracket50, and support each gearbox70on the upper rails30via the holding bracket80by inserting each mounting bolt100through through-holes of the corresponding gearbox support bracket and fastening each mounting nut110onto each mounting bolt100.

In the above-described embodiment, a gap (space) is defined (formed) between the cylindrical portions91bof the pair of mutually facing walls91of each resilient member90, however, the cylindrical portions91bcan be longer (in the axial direction) so that the ends thereof contact each other. Furthermore, the axial lengths of the cylindrical portions91bdo not have to be equal.

In the above-described embodiment, U-shaped sections provided at each of the left and right ends of the holding bracket80support the resilient members90, to which the gearboxes70are engaged, respectively; however, the cut-and-raised portions33of the upper rails30can be further extended forward to each form a holding portion, and the resilient members90, into which the gearbox70are respectively engaged, can be held by these holding portions, respectively.