Patent Description:
A ball screw device is one of the machine element parts for converting linear motion to rotational motion or rotational motion to linear motion. Since balls roll between a screw shaft and a nut, a higher efficiency can be obtained compared to a sliding screw device in which a screw shaft is in direct contact with a nut. Therefore, in order to convert rotational motion of a driving source such as an electric motor to linear motion, the ball screw device is assembled in various mechanical devices such as an electric braking device and an automatic manual transmission (AMT) of an automobile and a positioning device of a machine tool.

The ball screw device has a screw shaft having a shaft-side ball thread groove having a spiral shape on the outer-circumferential surface, a nut having a nut-side ball thread groove having a spiral shape on the inner-circumferential surface, and balls arranged between the shaft-side ball thread groove and the nut-side ball thread groove. In the ball screw device, either one of the screw shaft or the nut is used as a rotational motion element and the other of the screw shaft and the nut is used as a linear motion element, depending on the application.

In the ball screw device, the stroke end of the linear motion element is regulated in order to prevent the linear motion element from linearly moving beyond a predetermined range. <FIG> illustrates a ball screw device <NUM> having a conventional structure for regulating the stroke end of the linear motion element described in <CIT>.

The ball screw device <NUM> includes a screw shaft <NUM>, a nut <NUM>, balls (not illustrated), and a stopper <NUM>.

The screw shaft <NUM> has a screw portion <NUM>, and a fitting shaft portion <NUM> arranged adjacent to one side in the axial direction of the screw portion <NUM>. A shaft-side ball thread groove having a spiral shape <NUM> is formed on the outer-circumferential surface of the screw portion <NUM>. The fitting shaft portion <NUM> has an outer diameter smaller than that of the screw portion <NUM>, and has male spline teeth on the outer-circumferential surface. The screw shaft <NUM> is arranged coaxially with the nut <NUM> in a state where the screw portion <NUM> is inserted inside the nut <NUM>.

The nut <NUM> has a cylindrical shape, and has a nut-side ball thread groove having a spiral shape and a circulation groove having a substantially S-shape on the inner-circumferential surface (not illustrated). The nut <NUM> has an engaging portion <NUM> at an end portion on the one side in the axial direction.

The shaft-side ball thread groove <NUM> and the nut-side ball thread groove are arranged so as to face each other in the radial direction to form a load path having a spiral shape. The start point and the end point of the load path are connected by the circulation groove formed on the inner-circumferential surface of the nut <NUM>. Therefore, the balls that have reached the end point of the load path are returned to the start point of the load path through the circulation groove. Here, the start point and the end point of the load path are interchanged depending on the direction of relative displacement in the axial direction between the screw shaft <NUM> and the nut <NUM>.

The stopper <NUM> has a boss portion <NUM> having an annular shape and a claw portion <NUM> having a projection shape. The boss portion <NUM> is externally fitted to the fitting shaft portion <NUM> of the screw shaft <NUM> so as not to be able to rotate relative to the fitting shaft portion <NUM>. Specifically, the boss portion <NUM> is externally fitted to the fitting shaft portion <NUM> so as not to be able to rotate relative to the fitting shaft portion <NUM> by spline-engaging female spline teeth formed on the inner-circumferential surface with the male spline teeth formed on the outer-circumferential surface of the fitting shaft portion <NUM>. The claw portion <NUM> protrudes in the radial direction from a part in the circumferential direction of the outer-circumferential surface of the boss portion <NUM>.

In the ball screw device <NUM> having a conventional structure, when the linear motion element of either the screw shaft <NUM> or the nut <NUM> linearly moves and reaches the stroke end, the engaging portion <NUM> provided in the nut <NUM> and the claw portion <NUM> provided in the stopper <NUM> engage in the circumferential direction. As a result, rotation of the rotational motion element of either the screw shaft <NUM> or the nut <NUM> is prevented, and it becomes possible to regulate the stroke end of the linear motion element.

<CIT> describes a threaded spindle with a drive part, which has a longitudinal axis and is mounted by a first journal, and having a threaded part, which likewise has a longitudinal axis, and having a threaded nut, which is mounted to a second journal and in which the threaded part is guided.

In the ball screw device <NUM> having a conventional structure described in <CIT>, the stopper <NUM>, which is a dedicated component, is used for regulating the stroke end of the linear motion element. Therefore, for example, when the screw shaft <NUM> is used as a rotational motion element and the nut <NUM> is used as a linear motion element, a driving member for rotationally driving the screw shaft <NUM> is required to be provided separately from the stopper <NUM>. As a result, the number of parts increases, and the ball screw device <NUM> tends to be large.

Further, in the ball screw device <NUM> having a conventional structure described in <CIT>, the stopper <NUM> may be elastically deformed when the engaging portion <NUM> provided in the nut <NUM> and the claw portion <NUM> provided in the stopper <NUM> are engaged in the circumferential direction, and the screw shaft <NUM> may be twisted between the stopper <NUM> and the driving member, and the driving member may stop after the screw shaft <NUM> rotates by that amount accordingly. Thus, the rotation stop position of the driving member may deviate from the initial position. As a result, it becomes difficult to strictly manage the axial position (stroke amount) of the nut <NUM>, and the controllability of the ball screw device <NUM> may deteriorate.

The present invention has been made to solve the above problems, and the objective of the present invention is to provide a ball screw device capable of regulating the stroke end of the nut, which is a linear motion element, with a small number of parts so as to make the ball screw device more compact and improve the controllability. Preferred examples are defined in the dependent claims.

With the ball screw device of the present invention, regulation of the stroke end of the nut, which is a linear motion element, can be achieved with a small number of parts, and the ball screw device can be more compact, and the controllability can be improved.

A first example of an embodiment of the present invention will be described with reference to <FIG>.

The ball screw device <NUM> of this example is incorporated in, for example, an electric booster device and is used for applications such as converting rotational motion of an electric motor, which is a driving source, into linear motion to operate a piston of a hydraulic cylinder.

The ball screw device <NUM> includes a screw shaft <NUM>, a nut <NUM>, balls <NUM>, and a driving member <NUM>.

The screw shaft <NUM> is a rotational motion element that is rotationally driven by a driving source (not illustrated) through the driving member <NUM> and rotationally moves during use. The screw shaft <NUM> is inserted inside the nut <NUM> and arranged coaxially with the nut <NUM>. The nut <NUM> is a linear motion element that is prevented from co-rotating with respect to the screw shaft <NUM> by an anti-rotation mechanism (not illustrated) and linearly moves during use. Therefore, the ball screw device <NUM> of this example is used in an aspect wherein the screw shaft <NUM> is rotationally driven and the nut <NUM> is linearly moved.

A load path <NUM> having a spiral shape is provided between the outer-circumferential surface of the screw shaft <NUM> and the inner-circumferential surface of the nut <NUM>. Balls <NUM> are arranged in the load path <NUM> so as to be able to roll. When the screw shaft <NUM> and the nut <NUM> are relatively rotated, the balls <NUM> that have reached the end point of the load path <NUM> are returned to the start point of the load path <NUM> through a circulation groove <NUM> formed on the inner-circumferential surface of the nut <NUM>. The structures of the components of the ball screw device <NUM> will be described below.

In the description of an embodiment of the present invention including this example, the axial direction, the radial direction, and the circumferential direction mean, unless specified otherwise, the axial direction, the radial direction, and the circumferential direction in relation to the screw shaft <NUM>. One side in the axial direction is referred to as the right side in <FIG>, and the other side in the axial direction is referred to as the left side in <FIG>. The embodiment of the present invention is characterized by regulation of the stroke end of the nut <NUM>, which is a linear motion element, on the one side in the axial direction. It is noted that one side in the circumferential direction means the direction of rotation of the screw shaft <NUM> that allows the nut <NUM> to linearly move to the one side in the axial direction.

The screw shaft <NUM> is made of metal, and has a screw portion <NUM> and a fitting shaft portion <NUM> arranged adjacent to the one side in the axial direction of the screw portion <NUM>. The screw portion <NUM> and the fitting shaft portion <NUM> are coaxially arranged and integrally configured with each other. The fitting shaft portion <NUM> has an outer diameter smaller than that of the screw portion <NUM>.

The screw portion <NUM> has a shaft-side ball thread groove <NUM> having a spiral shape on the outer-circumferential surface. The shaft-side ball thread groove <NUM> is formed by performing a griding process, cutting process, or a rolling process to the outer-circumferential surface of the screw portion <NUM>. In this example, the number of threads of the shaft-side ball thread groove <NUM> is one. The groove shape (groove bottom shape) of the shaft-side ball thread groove <NUM> is a Gothic arch shape or a circular arc shape. In this example, the direction of formation (winding direction) of the shaft-side ball thread groove <NUM> is regulated to the direction in which the nut <NUM> is linearly moved to the one side in the axial direction when the screw shaft <NUM> is rotated to the one side in the circumferential direction.

The fitting shaft portion <NUM> has male spline teeth <NUM> on the outer-circumferential surface over the entire circumference. Due to this, the fitting shaft portion <NUM> is a spline shaft portion. In the illustrated example, the male spline teeth <NUM> are configured by involute spline teeth, but they can also be configured by angular spline teeth.

The screw shaft <NUM> is arranged coaxially with the nut <NUM> in a state where the screw portion <NUM> is inserted inside the nut <NUM>. In this example, the screw shaft <NUM> is configured by the screw portion <NUM> and the fitting shaft portion <NUM>, however, in a case of implementing the present invention, it is possible to further provide the screw shaft with a supporting shaft portion (second fitting shaft portion) for fixing a rolling bearing or the like to be rotatably supported with respect to the housing or the like, and a spline or a serration that function as torque transmission parts, and so on.

The nut <NUM> is made of metal and is configured to be cylindrical as a whole. The nut <NUM> has a nut-side ball thread groove <NUM> having a spiral shape and a circulation groove <NUM> on the inner-circumferential surface.

The nut-side ball thread groove <NUM> has a spiral shape, and is formed by performing, for example. a griding process, cutting process, a rolling tapping process, or cutting tapping process to the inner-circumferential surface of the nut <NUM>. The nut-side ball thread groove <NUM> has the same lead as the shaft-side ball thread groove <NUM>. Therefore, in a state where the screw portion <NUM> of the screw shaft <NUM> is inserted inside the nut <NUM>, the shaft-side ball thread groove <NUM> and the nut-side ball thread groove <NUM> are arranged so as to face each other in the radial direction to form the load path <NUM> having a spiral shape. The number of threads of the nut-side ball thread groove <NUM> is one, as the same as that of the shaft-side ball thread groove <NUM>. The groove shape of the nut-side ball thread groove <NUM> is a Gothic arch shape or a circular arc shape as the same as the shaft-side ball thread groove <NUM>.

The circulation groove <NUM> has a substantially S-shape, and is formed on the inner-circumferential surface of the nut <NUM> by, for example, a forging process or cold forging process. The circulation groove <NUM> smoothly connects axially adjacent portions of the nut-side ball thread groove <NUM> and connects the start point and the end point of the load path <NUM>. Therefore, the balls <NUM> that have reached the end point of the load path <NUM> are returned to the start point of the load path <NUM> through the circulation groove <NUM>. Here, the start point and the end point of the load path <NUM> are interchanged depending on the direction of relative rotation that is a direction of relative displacement between the screw shaft <NUM> and the nut <NUM> with respect to the axial direction.

The circulation groove <NUM> has a semi-circular cross-sectional shape. The circulation groove <NUM> has a groove width slightly larger than the diameter of the balls <NUM> and a groove depth that allows the balls <NUM> moving in the circulation groove <NUM> to climb over the threads of the shaft-side ball thread groove <NUM>.

The nut <NUM> has a non-rotating side engaging portion <NUM> having a protruding shape at an end portion on the one side in the axial direction. The non-rotating side engaging portion <NUM> is provided on a portion in the circumferential direction of a side surface 3a on the one side in the axial direction of the nut <NUM>, and protrudes toward the one side in the axial direction. The non-rotating side engaging portion <NUM> has a fan column shape.

The non-rotating side engaging portion <NUM> has a flat non-rotating side stopper surface <NUM> on a side surface on the other side in the circumferential direction (the side surface on the front side in <FIG> and <FIG>, and the left side surface in <FIG>). The non-rotating side stopper surface <NUM> is arranged so as to be substantially parallel to the center axis of the nut <NUM>. Further, the tip-end surface of the non-rotating side engaging portion <NUM> (end surface on the one side in the axial direction) exists on a virtual plane perpendicular to the center axis of the nut <NUM>.

The dimension in the axial direction of the non-rotating side engaging portion <NUM> (non-rotating side stopper surface <NUM>) can be set to a dimension equal to or larger than the lead of the shaft-side ball thread groove <NUM>. The formation range of the non-rotating side engaging portion <NUM> in the circumferential direction is appropriately determined in a range in which interference with a side surface 15a on the other side in the axial direction of the base plate portion <NUM>, which will be described later, can be prevented, and a force applied from the rotating-side stopper surface <NUM> to the non-rotating side stopper surface <NUM> can be supported. That is, the formation range (center angle α) in the circumferential direction of the non-rotating side engaging portion <NUM> can be made smaller than the formation range (center angle θ) in the circumferential direction of the rotating-side engaging groove portion <NUM>, which will be described later. Therefore, the relationship α<θ is satisfied. In this example, the non-rotating side engaging portion <NUM> is formed in a range of about <NUM>/<NUM> of the entire side surface 3a on the one side in the axial direction.

In this example, although the nut <NUM> is integrally configured as a whole including the non-rotating side engaging portion <NUM>, in a case of implementing the present invention, the nut can also be configured by connecting and fixing a cylindrical member having a nut-side ball thread groove and a circulation groove on the inner-circumferential surface and a non-rotating side engaging portion.

The ball screw device <NUM> of this example uses the nut <NUM> as a linear motion element. Therefore, in this example, an anti-rotation mechanism (not illustrated) is used to prevent the nut <NUM> from rotating. As the anti-rotation mechanism, conventionally known various structures can be adopted. For example, a structure in which a protrusion or a key provided on the inner-circumferential surface of a fixed member such as a housing are engaged with a concave groove that is formed in the axial direction on the outer-circumferential surface of the nut <NUM> may be adopted.

The balls <NUM> are steel balls having a predetermined diameter, and are arranged in the load path <NUM> and the circulation groove <NUM> so as to be able to roll. The balls <NUM> arranged in the load path <NUM> roll while receiving a compressive load, whereas the balls <NUM> arranged in the circulation groove <NUM> are pushed by the succeeding balls <NUM> and roll without receiving a compressive load.

The driving member <NUM> rotationally drives the screw shaft <NUM> by transmitting torque input from a driving source such as an electric motor to the screw shaft <NUM>. The driving member <NUM> of this example has not only a function of rotationally driving the screw shaft <NUM> but also a function of regulating the stroke end of the nut <NUM>, which is a linear motion element.

In the ball screw device <NUM> of this example, when the driving member <NUM> is rotationally driven toward the one side in the circumferential direction, the nut <NUM> moves toward the one side in the axial direction relative to the screw shaft <NUM>. On the other hand, when the driving member <NUM> is rotationally driven toward the other side in the circumferential direction, the nut <NUM> moves toward the other side in the axial direction relative to the screw shaft <NUM>.

The driving member <NUM> has a base plate portion <NUM>, a cylindrical portion <NUM>, a torque input portion <NUM>, and a rotating-side engaging groove portion <NUM>. The driving member <NUM> is made of metal such as carbon steel or stainless steel, or made of synthetic resin. As the driving member <NUM>, for example, a gear, a pulley, a sprocket, or the like can be applied.

The base plate portion <NUM> has a circular plate shape. The base plate portion <NUM> has a mounting hole <NUM> that penetrates in the axial direction in the central portion in the radial direction. Female spline teeth <NUM> are formed on the inner-circumferential surface of the mounting hole <NUM>. The base plate portion <NUM> is externally fitted and fixed to the fitting shaft portion <NUM> so as not to be able to rotate relative to the fitting shaft portion <NUM> by spline-engaging the female spline teeth <NUM> formed on the inner-circumferential surface of the mounting hole <NUM> with the male spline teeth <NUM> formed on the outer-circumferential surface of the fitting shaft portion <NUM>. The inner-side portion in the radial direction of the side surface 15a on the other side in the axial direction of the base plate portion <NUM> abuts or closely faces the end surface the end surface on the one side in the axial direction of the screw portion <NUM> of the screw shaft <NUM>.

The cylindrical portion <NUM> has a cylindrical shape and is provided at an end portion on the outside in the radial direction of the driving member <NUM>. The end portion on the one side in the axial direction of the cylindrical portion <NUM> is connected to the end portion on the outside in the radial direction of the base plate portion <NUM>. The cylindrical portion <NUM> has an inner diameter larger than that of the outer diameter of the nut <NUM>. The cylindrical portion <NUM> covers around the end portion on the one side in the axial direction of the screw portion <NUM>.

The torque input portion <NUM> is provided on the outer-circumferential surface of the driving member <NUM>. In this example, the torque input portion <NUM> is provided on the outer-circumferential surface of the cylindrical portion <NUM>. Therefore, the torque input portion <NUM> is arranged at a position overlapping the screw portion <NUM> in the radial direction. In the illustrated example, the outer diameter of the portion of the cylindrical portion <NUM> where the torque input portion <NUM> is provided is larger than the outer diameter of the portions shifted in the axial direction from the torque input portion <NUM>. That is, the torque input portion <NUM> is provided at a large diameter portion of the cylindrical portion <NUM>.

The torque input portion <NUM> serves as a gear portion when a gear is applied as the driving member <NUM>, and as a belt receiving surface (tooth portion) on which a belt is stretched when a pulley is applied as the driving member <NUM>, and as a tooth portion on which a chain is stretched when a sprocket is applied as the driving member <NUM>. In either case, the torque from the driving source is input to the torque input portion <NUM>.

The rotating-side engaging groove portion <NUM> allows the non-rotating side engaging portion <NUM> having the protruding shape to be inserted in the axial direction, and can be engaged with the non-rotating side engaging portion <NUM> in the circumferential direction on the other side in the circumferential direction. The rotating-side engaging groove portion <NUM> has an arch shape (C-shape) when viewed in the axial direction, and is provided at an intermediate portion in the radial direction of the side surface 15a on the other side in the axial direction of the base plate portion <NUM>. The rotating-side engaging groove portion <NUM> is formed by, for example, performing a cutting process or a forging process to the side surface 15a on the other side in the axial direction of the base plate portion <NUM>.

The rotating-side engaging groove portion <NUM> is a through groove that penetrates the base plate portion <NUM> in the axial direction.

The rotating-side engaging groove portion <NUM> has a width dimension in the radial direction that allows the non-rotating side engaging portion <NUM> to be inserted in the axial direction. Therefore, the inner-side surface 21a on the outer-side in the radial direction of the rotating-side engaging groove portion <NUM> has a partially concave cylindrical surface shape centered on the center axis of the driving member <NUM>, and has an inner diameter slightly larger than the diameter of a circumscribed circle passing through the outer-circumferential surface of the non-rotating side engaging portion <NUM>. Further, the inner-side surface 21b on the inner-side in the radial direction of the rotating-side engaging groove portion <NUM> has a partially convex cylindrical surface shape centered on the center axis of the driving member <NUM>, and has an outer diameter slightly smaller than the diameter of an inscribed circle passing through the inner-circumferential surface of the non-rotating side engaging portion <NUM>. The inner-side surface 21a on the outer-side in the radial direction and the inner-side surface 21b on the inner-side in the radial direction of the rotating-side engaging groove portion <NUM> are concentrically arranged.

The rotating-side engaging groove portion <NUM> has a flat rotating-side stopper surface <NUM> facing in the circumferential direction at the end portion on the other side in the circumferential direction. The rotating-side stopper surface <NUM> comes into surface contact with the non-rotating side stopper surface <NUM> when the nut <NUM> has moved to the one side in the axial direction relative to the screw shaft <NUM> and reached the stroke end. For this reason, the rotating-side stopper surface <NUM> exists on a virtual plane including the center axis of the driving member <NUM>. In order to be able to identify the position in the circumferential direction (phase) of the rotating-side stopper surface <NUM> when externally fitting and fixing the driving member <NUM> to the fitting shaft portion <NUM> of the screw shaft <NUM>, the outer surface of the driving member <NUM> may be provided with an externally recognizable identification mark (symbol), or may be formed with an externally recognizable identification shape such as a recess, hole, groove, or a width across flat shape.

The dimension in the axial direction of the rotating-side stopper surface <NUM> is the same as the thickness dimension in the axial direction of the base plate portion <NUM>. The dimension in the axial direction of the rotating-side stopper surface <NUM> is set to a size that ensures sufficient engagement allowance δ (width in the axial direction of the contact portion with the non-rotating side stopper surface <NUM>) to prevent the rotation of the screw shaft <NUM> between the non-rotating side stopper surface <NUM> of the non-rotating side engaging portion <NUM>. In this example, the dimension in the axial direction of the rotating-side stopper surface <NUM> is larger than the dimension in the axial direction of the non-rotating side engaging portion <NUM> (non-rotating side stopper surface <NUM>).

The rotating-side engaging groove portion <NUM> has a flat stepped surface <NUM> facing in the circumferential direction at an end portion on the one side in the circumferential direction.

In this example, as illustrated in <FIG> and <FIG>, the size of the center angle θ of the rotating-side engaging groove portion <NUM> is approximately <NUM> degrees. For this reason, the rotating-side engaging groove portion <NUM> is formed in a half area of the entire base plate portion <NUM>.

The formation range (center angle θ) of the rotating-side engaging groove portion <NUM> in the circumferential direction has a correlation with the size of the engagement allowance δ between the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM>. For example, when the center angle θ of the rotating-side engaging groove portion <NUM> is increased, the engagement allowance δ tends to increase, and when the center angle θ of the rotating-side engaging groove portion <NUM> is decreased, the engagement allowance δ tends to decrease. However, when the center angle θ of the rotating-side engaging groove portion <NUM> becomes too large, the nut <NUM> reaches the stroke end on the one side in the axial direction, the clearance in the axial direction between the side surface 3a on the one side in the axial direction of the nut <NUM> and the side surface 15a on the other side in the axial direction of the driving member <NUM> becomes small in a state where the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> are engaged, and therefore the nut <NUM> and the driving member <NUM> are likely to interference with each other. Therefore, the center angle θ of the rotating-side engaging groove portion <NUM> is required to be set to a size where the minimum necessary engagement allowance δ can be secured to prevent the rotation of the screw shaft <NUM>, and interference between the nut <NUM> and the driving member <NUM> can be prevented.

Specifically, in order to prevent the screw shaft <NUM> from rotating, it is desirable to ensure that the size of the engagement allowance δ is <NUM>/<NUM> (<NUM>%) or more of the lead of the shaft-side ball thread groove <NUM>. As a result, the lower limit of the center angle θ of the rotating-side engaging groove portion <NUM> can be set to <NUM> degrees.

On the other hand, in order to prevent interference between the nut <NUM> and the driving member <NUM>, the size of the clearance in the axial direction between the side surface 3a on the one side in the axial direction of the nut <NUM> and the side surface 15a on the other side in the axial direction of the base plate portion <NUM> in a state where the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> are engaged is desired to be <NUM>/<NUM> (<NUM>%) or more of the lead of the shaft-side ball thread groove <NUM>. Therefore, the upper limit of the center angle θ of the rotating-side engaging groove portion <NUM> can be set to <NUM> degrees. When the center angle θ of the rotating-side engaging groove portion <NUM> is set to <NUM> degrees, the size of the engagement allowance δ can be secured up to <NUM>/<NUM> (<NUM>%) of the lead of the shaft-side ball thread groove <NUM> at maximum.

As described above, the center angle θ of the rotating-side engaging groove portion <NUM> can be set within the rage of <NUM> degrees or more and <NUM> degrees or less.

Further, in order to secure the strength of the driving member <NUM>, the size of the center angle (<NUM>-θ) of the portion of the base plate portion <NUM> that is deviated in the circumferential direction from the rotating-side engaging groove portion <NUM> is secured to some extent. In this example, the center angle (<NUM>-θ) of the portion deviated in the circumferential direction from the rotating-side engaging groove portion <NUM> is set larger than the center angle (α) of the non-rotating side engaging portion <NUM>. That is, the relationship <NUM>-θ > α is satisfied. Therefore, in this example, the center angle α of the non-rotating side engaging portion <NUM> and the center angle θ of the rotating-side engaging groove portion <NUM> satisfy the relationship α < θ < <NUM>-α.

In the ball screw device <NUM> of this example, the nut <NUM> is linearly moved by rotationally driving the screw shaft <NUM> through the driving member <NUM> by a driving source (not illustrated). In particular, in the ball screw device <NUM> of this example, when the driving member <NUM> (screw shaft <NUM>) is rotationally driven toward the one side in the circumferential direction through the torque input portion <NUM> provided in the driving member <NUM>, the nut <NUM> moves to the one side in the axial direction relative to the screw shaft <NUM>. On the other hand, when the driving member <NUM> (screw shaft <NUM>) is rotationally driven toward the other side in the circumferential direction through the torque input portion <NUM>, the nut <NUM> moves to the other side in the axial direction relative to the screw shaft <NUM>.

When the nut <NUM> moves to the one side in the axial direction relative to the screw shaft <NUM> and approaches the stroke end, as illustrated as (A) in <FIG>, the end portion on the one side in the axial direction (tip end portion) of the non-rotating side engaging portion <NUM> enters inside the rotating-side engaging groove portion <NUM> provided in the driving member <NUM>. Specifically, the end portion on the one side in the axial direction of the non-rotating side engaging portion <NUM> enters the portion on the one side in the circumferential direction of the rotating-side engaging groove portion <NUM>.

When the driving member <NUM> is further rotated toward the one side in the circumferential direction, the nut <NUM> moves to the one side in the axial direction by the amount corresponding to the lead of the shaft-side ball thread groove <NUM>. Therefore, while the non-rotating side engaging portion <NUM> increases the amount of entry in the axial direction into the rotating-side engaging groove portion <NUM> by moving toward the one side in the axial direction as indicated by the black arrows, the non-rotating side engaging portion <NUM> relatively moves inside the rotating-side engaging groove portion <NUM> toward the other side in the circumferential direction from the one side in the circumferential direction as indicated by the white arrows. As a result, the non-rotating side engaging portion <NUM> relatively moves inside the rotating-side engaging groove portion <NUM> to the other side in the circumferential direction in the order of A-B-C as in <FIG>.

When the nut <NUM> reaches the stroke end on the one side in the axial direction, the non-rotating side engaging portion <NUM> engages with the rotating-side engaging groove portion <NUM> in the circumferential direction at the end portion on the other side in the circumferential direction of the rotating-side engaging groove portion <NUM>. Specifically, as in the state illustrated as (C) in <FIG>, the non-rotating side stopper surface <NUM> provided on the side surface on the other side in the circumferential direction of the non-rotating side engaging portion <NUM> and the rotating-side stopper surface <NUM> provided at end portion on the other side in the circumferential direction of the rotating-side engaging groove portion <NUM> engage in the circumferential direction. In this example, the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> come into surface contact. As a result, the screw shaft <NUM> is prevented from rotating.

Further, when the driving member <NUM> is rotationally driven toward the other side in the circumferential direction from the state where the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> are engaged in the circumferential direction, the non-rotating side engaging portion <NUM> relatively moves inside the rotating-side engaging groove portion <NUM> toward the one side in the circumferential direction and the other side in the axial direction in the order of C-B-A as in <FIG>. Then, the non-rotating side engaging portion <NUM> moves from the end portion on the one side in the circumferential direction of the rotating-side engaging groove portion <NUM> to the outside of the rotating-side engaging groove portion <NUM> without contacting the stepped surface <NUM> of the rotating-side engaging groove portion <NUM>.

As described above, with the ball screw device <NUM> of this example, the driving member <NUM> can be used to regulate the stroke end associated with the relative movement of the nut <NUM> to the screw shaft <NUM> toward the one side in the axial direction. The stroke end associated with the relative movement of the nut <NUM> to the other side in the axial direction with respect to the screw shaft <NUM> can be regulated using various conventionally known stroke limiting mechanisms.

With the ball screw device <NUM> of this example, regulation of the stroke end of the nut <NUM>, which is a linear motion element, can be achieved with a small number of parts, and the ball screw device <NUM> can be more compact, and the controllability can be improved.

That is, in this example, the driving member <NUM> can not only rotationally drives the screw shaft <NUM>, but also regulate the stroke end associated with the relative movement of the nut <NUM> to the one side in the axial direction with respect to the screw shaft <NUM>. Therefore, unlike the conventional structure described in <CIT>, a dedicated component (stopper) for regulating the stroke end of the nut is not required to be used. Accordingly, with the ball screw device <NUM> of this example, the number of parts can be reduced. Further, since the dimension in the axial direction of the screw shaft <NUM> can be shortened by omitting a dedicated component for regulating the stroke end, the dimension in the axial direction of the ball screw device <NUM> can be shortened. As a result, it is possible to make the ball screw device <NUM> more compact.

In this example, in a state where the non-rotating side engaging portion <NUM> provided on the nut <NUM> is inserted inside the rotating-side engaging groove portion <NUM> provided in the driving member <NUM> in the axial direction, the non-rotating side stopper surface <NUM> of the non-rotating side engaging portion <NUM> and the rotating-side stopper surface <NUM> of the rotating-side engaging groove portion <NUM> can be engaged in the circumferential direction. As a result, it is possible to achieve both securing of the stroke amount of the nut <NUM> and miniaturization of the ball screw device <NUM>.

In this example, in order to regulate the stroke end of the nut <NUM>, the non-rotating side engaging portion <NUM> provided on the nut <NUM> and the rotating-side stopper surface <NUM> of the rotating-side engaging groove portion <NUM> provided in the driving member <NUM> are engaged in the circumferential direction. As a result, when the non-rotating side engaging portion <NUM> of the nut <NUM> and the rotating-side stopper surface <NUM> of the driving member <NUM> are engaged in the circumferential direction, the rotation of the driving member <NUM> can be immediately stopped. Therefore, it is possible to prevent the rotation stop position of the driving member <NUM> from deviating from the initial position. As a result, the axial position (stroke amount) of the nut <NUM> can be strictly controlled, and the controllability of the ball screw device <NUM> can be improved.

Further, since the rotating-side engaging groove portion <NUM> is a through groove that penetrates the base plate portion <NUM> in the axial direction, the weight of the driving member <NUM> can be reduced compared to the case where the rotating-side engaging groove portion is a bottomed groove.

Furthermore, since the torque input portion <NUM> provided on the outer-circumferential surface of the cylindrical portion <NUM> of the driving member <NUM> is arranged at a position overlapping the screw portion <NUM> in the radial direction, it is advantageous in terms of shortening the dimension in the axial direction of the ball screw device <NUM>.

In this example, the torque input portion <NUM> is arranged at a position radially overlapping the portion of the rotating-side stopper surface <NUM> on the other side in the axial direction that contacts the non-rotating side stopper surface <NUM>. In other words, as illustrated in <FIG>, the portion of the rotating-side stopper surface <NUM> on the other side in the axial direction that contacts the non-rotating side stopper surface <NUM> exists in the range R where the torque input portion <NUM> exists in the axial direction. Therefore, also from this aspect, the dimension in the axial direction of the ball screw device <NUM> can be shortened. Further, it is possible to prevent a moment load based on an impact load caused by collision between the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> from being applied from the torque input portion <NUM> to the driving source side.

A second example of an embodiment of the present invention will be described with reference to <FIG>.

In the case of this example, the center angle θ of the rotating-side engaging groove portion 18a of the driving member 5a is made smaller than in the construction of the first example. Specifically, the center angle θ of the rotating-side engaging groove portion 18a is set to the lower limit of <NUM> degrees.

Further, in order to secure the size of the engagement allowance δ between the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> to be <NUM>/<NUM> (<NUM>%) of the lead of the shaft-side ball thread groove <NUM> even when the center angle θ of the rotating-side engaging groove portion 18a is set to <NUM> degrees, the shape of the tip-end surface (end surface on the one side in the axial direction) of the non-rotating side engaging portion 13a is devised.

That is, a flat inclined surface (chamfer) <NUM> inclined with respect to a virtual plane perpendicular to the center axis of the nut <NUM> is formed on the tip-end surface of the non-rotating side engaging portion 13a. Specifically, the inclined surface <NUM> is formed on the entire tip-end surface of the non-rotating side engaging portion 13a so as to be inclined in a direction that retreats toward the other side in the axial direction toward the one side in the circumferential direction. The inclination angle of the inclined surface <NUM> can be set to be equal to or larger than the lead angle β of the shaft-side ball thread groove <NUM>, and in the illustrated example, the angle is slightly larger than the lead angle β of the shaft-side ball thread groove <NUM>.

In the case of this example as well, when the nut <NUM> moves to the one side in the axial direction relative to the screw shaft <NUM> and approaches the stroke end, as indicated by the chain line in <FIG>, the end portion on the one side in the axial direction (tip end portion) of the non-rotating side engaging portion 13a enters the inside of the rotating-side engaging groove portion 18a. Specifically, the end portion on the one side in the axial direction of the non-rotating side engaging portion 13a enters the portion on the one side in the circumferential direction of the rotating-side engaging groove portion 18a. In this example, since the inclined surface <NUM> is formed on the tip-end surface of the non-rotating side engaging portion 13a, the end portion on the other side in the circumferential direction of the end portion on the one side in the axial direction of the non-rotating side engaging portion 13a enters the portion on the one side in the circumferential direction of the rotating-side engaging groove portion 18a without the tip-end surface of the non-rotating side engaging portion 13a and the side surface 15a on the other side in the axial direction of the base plate portion <NUM> interference with each other.

When the driving member 5a is further rotated toward the one side in the circumferential direction, the non-rotating side engaging portion 13a relatively moves inside of the rotating-side engaging groove portion 18a from the one side in the circumferential direction to the other side in the circumferential direction while increasing the amount of entry in the axial direction into the rotating-side engaging groove portion 18a.

When the nut <NUM> reaches the stroke end on the one side in the axial direction, the non-rotating side engaging portion 13a engages with the rotating-side engaging groove portion 18a in the circumferential direction at the end portion on the other side in the circumferential direction of the rotating-side engaging groove portion 18a. Specifically, as indicated by the solid line in <FIG>, the non-rotating side stopper surface <NUM> provided on the side surface on the other side in the circumferential direction of the non-rotating side engaging portion 13a and the rotating-side stopper surface <NUM> provided at the end portion on the other side in the circumferential direction of the rotating-side engaging groove portion 18a engage in the circumferential direction. Due to this, the screw shaft <NUM> is prevented from rotating.

In this example, when the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> are engaged in the circumferential direction, the size of the engagement allowance δ is <NUM>/<NUM> of the lead of the shaft-side ball thread groove <NUM>.

Further, in the case of this example, since the center angle θ of the rotating-side engaging groove portion 18a is smaller than that of the construction of the first example, the amount of rotation of the driving member 5a, from which the end portion on the one side in the axial direction of the non-rotating side engaging portion 13a enters inside the rotating-side engaging groove portion 18a to the point where the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> are engaged in the circumferential direction, is smaller than that of the construction of the first example.

In this example, by forming the inclined surface <NUM> on the tip-end surface of the non-rotating side engaging portion 13a, it is possible to prevent the tip-end surface of the non-rotating side engaging portion 13a from interfering with the side surface 15a on the other side in the axial direction of the base plate portion <NUM>. Therefore, even when the center angle θ of the rotating-side engaging groove portion 18a is set to <NUM> degrees, the size of the engagement allowance δ can be secured by <NUM>/<NUM> of the lead of the shaft-side ball thread groove <NUM>. Accordingly, the reduction in strength of the driving member 5a caused by forming the rotating-side engaging groove portion 18a can be suppressed, and the rotation of the screw shaft <NUM> can be prevented. Here, in a case of implementing the present invention, the inclined surface formed on the tip-end surface of the non-rotating side engaging portion is not limited to a flat surface, and may be configured to be a convex curved surface or a concave curved surface.

Other Configurations and operational effects of the second example are the same as in the first example.

A third example of an embodiment of the present invention will be described with reference to <FIG>.

In the case of this example, the center angle θ of the rotating-side engaging groove portion 18b of the driving member 5b is made larger than that of the construction of the first example. Specifically, the center angle θ of the rotating-side engaging groove portion 18b is set to the upper limit of <NUM> degrees.

Therefore, of the base plate portion <NUM>, the portion that exists on radially inward of the rotating-side engaging groove portion 18b and the portion that exists on radially outward of the rotating-side engaging groove portion 18b are connected through a connecting portion <NUM> with a center angle of <NUM> degrees located at a discontinuous portion of the rotating-side engaging groove portion 18b.

In this example, in order to ensure the size of the engagement allowance δ to be <NUM>/<NUM> (<NUM>%) of the lead of the shaft-side ball thread groove <NUM> and to ensure the size of the clearance C in the axial direction between the side surface 3a on the one side in the axial direction of the nut <NUM> and the side surface 15a on the other side in the axial direction of the base plate portion <NUM> to be <NUM>/<NUM> (<NUM>%) or more of the lead of the shaft-side ball thread groove <NUM>, the center angle θ of the rotating-side engaging groove portion 18b is set to <NUM> degrees, the dimension in the axial direction of the non-rotating side engaging portion 13b is set to be the same as the lead of the shaft-side ball thread groove <NUM>, and a flat inclined surface <NUM> inclined with respect to a virtual plane perpendicular to the center axis of the nut <NUM> is formed on the tip-end surface of the non-rotating side engaging portion 13b. Specifically, similar to the construction of the second example, the inclined surface <NUM> is formed on the entire tip-end surface of the non-rotating side engaging portion 13b so as to be inclined in a direction that retreats toward the other side in the axial direction toward the one side in the circumferential direction. The inclination angle of the inclined surface <NUM> can be set to be equal to or larger than the lead angle β of the shaft-side ball thread groove <NUM>, and in the illustrated example, the angle is slightly larger than the lead angle β of the shaft-side ball thread groove <NUM>.

In the case of this example as well, when the nut <NUM> moves to the one side in the axial direction relative to the screw shaft <NUM> and approaches the stroke end, as indicated by the chain line in <FIG>, the end portion on the one side in the axial direction (tip end portion) of the non-rotating side engaging portion 13b enters the inside of the rotating-side engaging groove portion 18b. Specifically, the end portion on the one side in the axial direction of the non-rotating side engaging portion 13b enters the portion on the one side in the circumferential direction of the rotating-side engaging groove portion 18b. In this example, since the inclined surface <NUM> is formed on the tip-end surface of the non-rotating side engaging portion 13b, the end portion on the other side in the circumferential direction of the end portion on the one side in the axial direction of the non-rotating side engaging portion 13b enters the portion on the one side in the circumferential direction of the rotating-side engaging groove portion 18b without the tip-end surface of the non-rotating side engaging portion 13b and the side surface 15a on the other side in the axial direction of the base plate portion <NUM> interference with each other.

When the driving member 5b is further rotated toward the one side in the circumferential direction, the non-rotating side engaging portion 13b relatively moves inside of the rotating-side engaging groove portion 18b from the one side in the circumferential direction to the other side in the circumferential direction while increasing the amount of entry in the axial direction into the rotating-side engaging groove portion 18b.

When the nut <NUM> reaches the stroke end on the one side in the axial direction, the non-rotating side engaging portion 13b engages with the rotating-side engaging groove portion 18b in the circumferential direction at the end portion on the other side in the circumferential direction of the rotating-side engaging groove portion 18b. Specifically, as indicated by the solid line in <FIG>, the non-rotating side stopper surface <NUM> provided on the side surface on the other side in the circumferential direction of the non-rotating side engaging portion 13b and the rotating-side stopper surface <NUM> provided at the end portion on the other side in the circumferential direction of the rotating-side engaging groove portion 18b engage in the circumferential direction. Due to this, the screw shaft <NUM> is prevented from rotating.

In this example, when the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> are engaged in the circumferential direction, the size of the engagement allowance δ is <NUM>/<NUM> of the lead of the shaft-side ball thread groove <NUM>. Further, in the case of this example, since the center angle θ of the rotating-side engaging groove portion 18b is larger than that of the construction of the first example, the amount of rotation of the driving member 5a, from which the end portion on the one side in the axial direction of the non-rotating side engaging portion 13b enters inside the rotating-side engaging groove portion 18b to the point where the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> are engaged in the circumferential direction, is larger than that of the construction of the first example.

In the case of this example, since the size of the engagement allowance δ can be ensured to be <NUM>/<NUM> of the lead of the shaft-side ball thread groove <NUM>, the rotation of the screw shaft <NUM> can be effectively prevented. Further, since the size of the clearance C in the axial direction between the nut <NUM> and the driving member 5b can be ensured to be <NUM>/<NUM> of the lead of the shaft-side ball thread groove <NUM>, interference between the nut <NUM> and the driving member 5b can be prevented. Furthermore, the stroke amount of the nut <NUM> can also be ensured.

Other Configurations and operational effects of the third example are the same as in the first example.

A fourth example of an embodiment of the present invention will be described with reference to <FIG>.

In this example, an inclined surface 24a is formed in a range extending from the intermediate portion in the circumferential direction to the end portion on the one side in the circumferential direction, excluding the end portion on the other side in the circumferential direction, of the tip-end surface of the non-rotating side engaging portion 13c. Therefore, of the tip-end surface of the non-rotating side engaging portion 13c, the end portion on the other side in the circumferential direction exists on a virtual plane perpendicular to the center axis of the nut <NUM>. The inclination angle of the inclined surface 24a can be set to be equal to or greater than the lead angle β of the shaft-side ball thread groove <NUM>.

In the case of this example, compared to the construction of the first example in which the tip-end surface of the rotating-side engaging portion is a flat surface existing on a virtual plane perpendicular to the center axis of the nut, it is advantageous in securing the size of the engagement allowance δ while preventing interference with the driving member <NUM> (see <FIG>, etc.).

Other Configurations and operational effects of the fourth example are the same as in the first example.

A fifth example of an embodiment of the present invention will be described with reference to <FIG>.

This example is a modification of the third example. The driving member 5c of this example has one reinforcing portion <NUM> in the intermediate portion in the circumferential direction (center portion in the illustrated example) of the rotating-side engaging groove portion 18b, provided for connecting the inner-side surface 21a on the outer-side in the radial direction and the inner-side surface 21b on the inner-side in the radial direction. The reinforcing portion <NUM> connects the end portion on the one side in the axial direction of the inner-side surface 21a on the outer-side in the radial direction and the end portion on the one side in the axial direction of the inner-side surface 21b on the inner-side in the radial direction. The reinforcing portion <NUM> has a sector shape when viewed in the axial direction.

The position in the circumferential direction and the thickness dimension of the reinforcing portion <NUM> are regulated to a position and thickness that can prevent interference with the non-rotating side engaging portion <NUM> entering the inside of the rotating-side engaging groove portion 18b. In the illustrated example, the thickness dimension of the reinforcing portion <NUM> is about <NUM>/<NUM> of the thickness dimension of the base plate portion <NUM>. In a case of implementing the present invention, it is also possible to provide reinforcing portions at a plurality of locations in the circumferential direction of the rotating-side engaging groove portion.

In this example, the reinforcing portion <NUM> is configured integrally with the base plate portion <NUM>. However, in a case of implementing the present invention, the reinforcing portion can also be configured separately from the base plate portion and fixed to the base plate portion. For example, the end portion on the outer-side in the radial direction and the end portion on the inner-side in the radial direction of the reinforcing portion can be fixed to the inner-side surface on the outer-side in the radial direction and the inner-side surface on the inner-side in the radial direction of the of the rotating-side engaging groove portion by adhesion or welding.

In this example, of the base plate portion <NUM>, the portion existing on the inner-side in the radial direction of the rotating-side engaging groove portion 18b and the portion existing on the outer-side in the radial direction of the rotating-side engaging groove portion 18b are connected not only by the connecting portion <NUM>, but also by the reinforcing portion <NUM>. Therefore, it is possible to improve the rigidity of the portion of the base plate portion <NUM> surrounding the mounting hole <NUM>, which is located on the inner-side in the radial direction of the rotating-side engaging groove portion 18b. Accordingly, the (torsional rigidity) of the female spline teeth <NUM> formed on the inner-circumferential surface of the mounting hole <NUM> can be secured even when the center angle θ of the rotating-side engaging groove portion 18b formed on the base plate portion <NUM> is large. As a result, a larger torque can be transmitted to the screw shaft <NUM> by the driving member 5c.

Other Configurations and operational effects of the fifth example are the same as in the first example and the third example.

A sixth example of an embodiment of the present invention will be described with reference to <FIG>.

Unlike the constructions of the first example to the fifth example, the driving member 5d of this example has two rotating-side engaging groove portions 18c formed on the base plate portion <NUM>. In this example, the size of the center angle θ of the two rotating-side engaging groove portions 18c is set to <NUM> degrees respectively. Further, the two rotating-side engaging groove portions 18c are arranged so as to be evenly spaced in the circumferential direction of the driving member 5d. Therefore, the center angles of the portions existing between the two rotating-side engaging groove portions 18c are the same with each other (<NUM> degrees). Further, the inner-side surfaces 21a on the outer-side in the radial direction and the inner-side surfaces 21b of the two rotating-side engaging groove portions 18c have the same diameter. However, in a case of implementing the present invention, the center angles of the plurality of rotating-side engaging groove portions can be made different from each other, and the diameters of the inner-side surfaces on the outer-side in the radial direction and the inner-side surfaces on the inner-side in the radial direction can also be made different from each other.

Each of the two rotating-side engaging groove portions 18c has a rotating-side stopper surface <NUM> at the end portion on the other side in the circumferential direction. In the illustrated example, the two rotating-side stopper surface <NUM> exist on the same virtual plane including the center axis of the driving member 5d.

In the case of this example, the driving member 5d as described above is used in combination with the nut <NUM> having only one non-rotating side engaging portion <NUM> (13a to 13c) as in the constructions of the first example to the fifth example (see <FIG>, etc.).

In this example, since the driving member 5d is provided with two rotating-side engaging groove portions 18c, phase matching between any one of rotating-side engaging groove portions 18c and the non-rotating side engaging portion <NUM> is achieved during assembly of the ball screw device <NUM>. Therefore, compared to a structure with only one rotating-side engaging groove portion, it is possible to facilitate the assembly work. Further, since the two rotating-side engaging groove portions 18c are arranged so as to be evenly spaced in the circumferential direction of the driving member 5d, the rotation balance of the driving member 5d can be improved.

As a modification of this example, the driving member 5d provided with two rotating-side engaging groove portions 18c can be used in combination with a nut provided with the same number of non-rotating side engaging portions as the rotating-side engaging groove portions 18c. In this case, the stroke end of the nut is regulated by simultaneously engaging the two rotating-side engaging groove portions 18c and the two non-rotating side engaging portions in the circumferential direction. Therefore, it is possible to reduce the force acting on each of the rotating-side engaging groove portions 18c, and effectively prevent damage to the driving member 5d.

Other Configurations and operational effects of the sixth example are the same as in the first example.

A seventh example of an embodiment of the present invention will be described with reference to <FIG>.

In the driving member 5e of this example, the base plate portion <NUM> is formed with three rotating-side engaging groove portions 18d. In this example, the size of the center angle θ of each of the three rotating-side engaging groove portions 18d is <NUM> degrees. Further, the three rotating-side engaging groove portions 18d are arranged so as to be evenly spaced in the circumferential direction of the driving member 5e. Due to this, the size of the center angle of the each of the portions existing between two rotating-side engaging groove portions 18d adjacent in the circumferential direction is the same (<NUM> degrees). Further, the diameters of the inner-side surfaces 21a on the outer-side in the radial direction and the inner-side surfaces 21b on the inner-side in the radial direction of the three rotating-side engaging groove portions 18d are the same.

Each of the three rotating-side engaging groove portions 18d has a rotating-side stopper surface <NUM> at the end portion on the other side in the circumferential direction.

In the case of this example as well, compared to a structure with only one rotating-side engaging groove portion, it is possible to facilitate the assembly work. Further, since the three rotating-side engaging groove portions 18d are arranged so as to be evenly spaced in the circumferential direction of the driving member 5e, the rotation balance of the driving member 5e can be improved.

As in the sixth example, the driving member 5e of this example can be used in combination with a nut <NUM> having only one non-rotating side engaging portion <NUM> (13a to 13c), or can also be used in combination with a nut provided with the same number of non-rotating side engaging portions as the rotating-side engaging groove portions <NUM>.

Other Configurations and operational effects of the seventh example are the same as in the first example and the sixth example.

An eighth example of an embodiment of the present invention will be described with reference to <FIG>.

In this example, unlike the first example to the seventh example, the rotating-side engaging groove portion 18e of the driving member 5f is a bottomed groove (concave groove) that is open to the side surface 15a on the other side in the axial direction of the base plate portion <NUM> and has a depth (groove depth) in the axial direction that is constant along the circumferential direction. Therefore, the groove bottom surface <NUM> of the rotating-side engaging groove portion 18e exists on a virtual plane perpendicular to the center axis of the driving member 5f.

The dimension in the axial direction of the rotating-side stopper surface <NUM>, which corresponds to the depth in the axial direction of the rotating-side engaging groove portion 18e, is set to a size that can ensure a sufficient engagement allowance δ to prevent the rotation of the screw shaft <NUM> between the non-rotating side stopper surface <NUM> of the non-rotating side engaging portion <NUM>. In this example, the dimension in the axial direction of the rotating-side stopper surface <NUM> is larger than the dimension in the axial direction of the non-rotating side engaging portion <NUM> (non-rotating side stopper surface <NUM>).

In this example, since the rotating-side engaging groove portion 18e is a bottomed groove, compared to the case where the rotating-side engaging groove portion is a through groove, it is possible to suppress the reduction in strength of the driving member <NUM> due to the formation of the rotating-side engaging groove portion.

In this example, the rotating-side engaging groove portion 18e is formed in the intermediate portion in the radial direction of the side surface 15a on the other side in the axial direction of the base plate portion <NUM>. Therefore, an outer diameter-side cylindrical portion <NUM> having a partially cylindrical shape, which protrudes more to the other side in the axial direction than the groove bottom surface <NUM> of the rotating-side engaging groove portion 18e, is formed in a portion on the outer-side in the radial direction of the rotating-side engaging groove portion 18e of the base plate portion <NUM>. Further, an inner diameter-side cylindrical portion <NUM> having a partially cylindrical shape, which protrudes more to the other side in the axial direction than the groove bottom surface <NUM> of the rotating-side engaging groove portion 18e, is formed in a portion on the inner-side portion in the radial direction of the rotating-side engaging groove portion 18e of the base plate portion <NUM>. Furthermore, in this example, the rotating-side stopper surface <NUM> is connected to each of the outer diameter-side cylindrical portion <NUM> and the inner diameter-side cylindrical portion <NUM>. Therefore, the rigidity of the rotating-side stopper surface <NUM> can be improved. Here, in a case of implementing the present invention, the rigidity of the rotating-side stopper surface can be improved by connecting the rotating-side stopper surface to at least one of the outer diameter-side cylindrical portion and the inner diameter-side cylindrical portion.

Other Configurations and operational effects of the eighth example are the same as in the first example.

A ninth example of an embodiment of the present invention will be described with reference to <FIG>.

In this example, unlike the first example to the eighth example, the rotating-side engaging groove portion 18f of the driving member <NUM> is a bottomed groove (concave groove) that is open to the side surface 15a on the other side in the axial direction of the base plate portion <NUM> and has a depth (groove depth) in the axial direction that changes along the circumferential direction.

Specifically, the depth in the axial direction of the rotating-side engaging groove portion 18f becomes larger (deeper) from the one side in the circumferential direction toward the other side in the circumferential direction. Due to this, the groove bottom surface 27a of the rotating-side engaging groove portion 18f is inclined with respect to a virtual plane perpendicular to the center axis of the driving member <NUM>. In this example, the groove bottom surface 27a is inclined by the same angle α1 as the lead angle β1 of the shaft-side ball thread groove <NUM> (and the nut-side ball thread groove <NUM>) in a direction toward the one side in the axial direction toward the other side in the circumferential direction with respect to a virtual plane perpendicular to the center axis of the driving member <NUM> (α1 = β1).

The rotating-side engaging groove portion 18f has a width dimension in the radial direction that allows the non-rotating side engaging portion <NUM> provided on the nut <NUM> to be inserted in the axial direction. Therefore, the inner-side surface 21a on the outer-side in the radial direction of the rotating-side engaging groove portion 18f has an inner diameter slightly larger than the diameter of a circumscribed circle passing through the outer-circumferential surface of the non-rotating side engaging portion <NUM>. Further, the inner-side surface 21b on the inner-side in the radial direction of the rotating-side engaging groove portion 18f has an outer diameter slightly smaller than the diameter of an inscribed circle passing through the inner-circumferential surface of the non-rotating side engaging portion <NUM>. The inner-side surface 21a on the outer-side in the radial direction and the inner-side surface 21b on the inner-side in the radial direction of the rotating-side engaging groove portion 18f are arranged on a concentric circle.

The rotating-side engaging groove portion 18f has a flat rotating-side stopper surface <NUM> facing in the circumferential direction at the end portion on the other side in the circumferential direction where the depth in the axial direction is the largest. Therefore, the end portion on the other side in the circumferential direction of the groove bottom surface 27a of the rotating-side engaging groove portion 18f is connected to the side surface 15a on the other side in the axial direction of the base plate portion <NUM> through the rotating-side stopper surface <NUM>. The rotating-side stopper surface <NUM> comes into surface contact with the non-rotating side stopper surface <NUM> when the nut <NUM> has moved to the one side in the axial direction relative to the screw shaft <NUM> and reached the stroke end. For this reason, the rotating-side stopper surface <NUM> is arranged substantially parallel to the center axis of the driving member <NUM>. The dimension in the axial direction of the rotating-side stopper surface <NUM> is set to a size that ensures sufficient engagement allowance δ (width in the axial direction of the contact portion with the non-rotating side stopper surface <NUM>) to prevent the rotation of the screw shaft <NUM> between the non-rotating side stopper surface <NUM> of the non-rotating side engaging portion <NUM>. In this example, the dimension in the axial direction of the rotating-side stopper surface <NUM> is substantially the same as the dimension in the axial direction of the non-rotating side engaging portion <NUM> (non-rotating side stopper surface <NUM>), and is approximately <NUM>/<NUM> of the axial direction thickness dimension of the base plate portion <NUM> (for example, it is about <NUM> in the case of a ball screw device incorporated in an electric booster device).

The rotating-side engaging groove portion 18f has a flat stepped surface <NUM> facing in the circumferential direction at the end portion on the one side in the circumferential direction where the depth in the axial direction is the smallest. Therefore, the end portion on the one side in the circumferential direction of the groove bottom surface 27a of the rotating-side engaging groove portion 18f is connected to the side surface 15a on the other side in the axial direction of the base plate portion <NUM> through the stepped surface <NUM>. In the illustrated example, the dimension in the axial direction of the stepped surface <NUM> is approximately <NUM>/<NUM> of the rotating-side stopper surface <NUM> (for example, it is about <NUM> in the case of a ball screw device incorporated in an electric booster device). In a case of implementing the present invention, the stepped surface can be omitted. In this case, the end portion on the one side in the circumferential direction of the groove bottom surface of the rotating-side engaging groove portion and the side surface on the other side in the axial direction of the driving member can be smoothly connected without a stepped surface.

In this example, as illustrated in <FIG>, the center angle θ of the rotating-side engaging groove portion 18f is approximately <NUM> degrees. Therefore, the rotating-side engaging groove portion 18f is formed in a range of <NUM>/<NUM> of the entire side surface 15a on the other side in the axial direction of the base plate portion <NUM>. The formation range (center angle θ) in the circumferential direction of the rotating-side engaging groove portion 18f is determined based on such as the size of the lead angle β1 of the shaft-side ball thread groove <NUM> and the size of the engagement allowance δ between the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM>.

Also in this example, when the nut <NUM> moves to the one side in the axial direction relative to the screw shaft <NUM> and approaches the stroke end, the end portion (tip end portion) on the one side in the axial direction of the non-rotating side engaging portion <NUM> enters inside the rotating-side engaging groove portion 18f provided in the driving member <NUM>. Further, as the nut <NUM> moves toward the one side in the axial direction, while increasing the amount of entry in the axial direction into the rotating-side engaging groove portion 18f, the nut <NUM> relatively moves inside the rotating-side engaging groove portion 18f from the one side in the circumferential direction toward the other side in the circumferential direction. In this example, since the inclination angle α1 of the groove bottom surface 27a of the rotating-side engaging groove portion 18f is set to the same size as the lead angle β1 of the shaft-side ball thread groove <NUM>, the non-rotating side engaging portion <NUM> relatively moves inside the rotating-side engaging groove portion 18f toward the other side in the circumferential direction in the order of A-B-C as in <FIG> with a gap <NUM> of a certain size interposed between the end surface on the one side in the axial direction of the non-rotating side engaging portion <NUM> and the groove bottom surface 27a. When the nut <NUM> reaches the stroke end on the one side in the axial direction, the non-rotating side engaging portion <NUM> engages with the rotating-side engaging groove portion 18f in the circumferential direction at the end portion on the other side in the circumferential direction of the rotating-side engaging groove portion 18f. Also in this example, even in a state where the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> are in surface contact, the gap <NUM> exists between the end surface on the one side in the axial direction of the non-rotating side engaging portion <NUM> and the groove bottom surface 27a.

Also in this example, when the driving member <NUM> is rotationally driven toward the other side in the circumferential direction, the non-rotating side engaging portion <NUM> moves inside the rotating-side engaging groove portion 18f toward the one side in the circumferential direction and to the other side in the axial direction in the order of C-B-A as in <FIG> with the gap <NUM> interposed between the end surface on the one side in the axial direction and the groove bottom surface 27a. Further, the non-rotating side engaging portion <NUM> moves from end portion on the one side in the circumferential direction of the rotating-side engaging groove portion 18f to the outside of the rotating-side engaging groove portion 18f without contacting the stepped surface <NUM>.

Also in this example, since the rotating-side engaging groove portion 18f is a bottomed groove, compared to the case where the rotating-side engaging groove portion is a through groove, it is possible to suppress the reduction in strength of the driving member <NUM> due to the formation of the rotating-side engaging groove portion.

In this example, the depth in the axial direction of the rotating-side engaging groove portion 18f becomes larger from the one side in the circumferential direction toward the other side in the circumferential direction. Therefore, compared to the case where the depth in the axial direction of the rotating-side engaging groove portion 18f is constant over the circumferential direction as in the eighth example, the amount of processing of the rotating-side engaging groove portion 18f can be reduced. As a result, the number of man-hours for processing the driving member <NUM> can be reduced, and the manufacturing cost can be reduced. Further, compared to the case where the depth in the axial direction of the rotating-side engaging groove portion 18f is constant in the circumferential direction, the thickness dimension in the axial direction of the base plate portion <NUM> of the driving member <NUM> can be secured in the portion excluding the end portion on the other side in the circumferential direction of the portion where the rotating-side engaging groove portion 18f is formed. Accordingly, the rigidity and strength of the driving member <NUM> can be secured.

Further, since the inclination angle α1 of the groove bottom surface 27a of the rotating-side engaging groove portion 18f is set to the same size as the lead angle β1 of the shaft-side ball thread groove <NUM>, the non-rotating side engaging portion <NUM> can be moved in the circumferential direction relative to the rotating-side engaging groove portion 18f with a gap <NUM> having a certain size interposed between the end surface on the one side in the axial direction of the non-rotating side engaging portion <NUM> and the groove bottom surface 27a. Due to this, it is possible to prevent interference between the end surface on the one side in the axial direction of the non-rotating side engaging portion <NUM> and the groove bottom surface 27a. Therefore, since the end surface on the one side in the axial direction of the non-rotating side engaging portion <NUM> and the groove bottom surface 27a interfere with each other before the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> engage in the circumferential direction, the position of the stroke end of the nut <NUM> can be prevented from being deviated.

Also in this example, the rotating-side engaging groove portion 18f is formed in the intermediate portion in the radial direction of the side surface 15a on the other side in the axial direction of the base plate portion <NUM>. That is, in this example as well, the rotating-side stopper surface <NUM> is connected to the outer diameter-side cylindrical portion <NUM> having a partially cylindrical shape, which is formed in a portion on the outer-side in the radial direction of the rotating-side engaging groove portion 18f of the base plate portion <NUM> and protrudes more to the other side in the axial direction than the groove bottom surface 27a, and to the inner diameter-side cylindrical portion <NUM> having a partially cylindrical shape, which is formed in a portion on the inner-side portion in the radial direction of the rotating-side engaging groove portion 18f of the base plate portion <NUM> and protrudes more to the other side in the axial direction than the groove bottom surface 27a. Therefore, the rigidity of the rotating-side stopper surface <NUM> can be improved. Here, in a case of implementing the present invention, the rigidity of the rotating-side stopper surface can be improved by connecting the rotating-side stopper surface to at least one of the outer diameter-side cylindrical portion and the inner diameter-side cylindrical portion.

Other Configurations and operational effects of the ninth example are the same as in the first example.

A tenth example of an embodiment of the present invention will be described with reference to <FIG>.

In the case of this example as well, as in the ninth example, the inclination angle α2 of the groove bottom surface 27b of the rotating-side engaging groove portion <NUM> with respect to the virtual plane perpendicular to the center axis of the driving member <NUM> is the same as the lead angle β2 of the shaft-side ball thread groove <NUM> (α2 = β2). However, in this example, the lead angle β2 of the shaft-side ball thread groove <NUM> and the inclination angle α2 of the groove bottom surface 27b of the rotating-side engaging groove portion <NUM> are set to larger values than in the construction of the ninth example (β2 > β1, α2 > α1).

In this example, the center angle θ of the rotating-side engaging groove portion <NUM> is approximately <NUM> degrees. For this reason, the rotating-side engaging groove portion <NUM> is formed in a half area of the entire base plate portion <NUM>.

In this example, compared to the construction of the ninth example, the processing range of the rotating-side engaging groove portion <NUM> can be made smaller. As a result, it is advantageous in increasing the rigidity and strength of the driving member <NUM>.

Other Configurations and operational effects of the tenth example are the same as in the first example and the ninth example.

An eleventh example of an embodiment of the present invention will be described with reference to <FIG>.

In this example, unlike the ninth example and the tenth example, the inclination angle α3 of the groove bottom surface 27c of the rotating-side engaging groove portion <NUM> with respect to the virtual plane perpendicular to the center axis of the driving member 5i is smaller than the lead angle β1 of the shaft-side ball thread groove <NUM> (α3 < β1).

Therefore, the gap 28a formed between the end surface on the one side in the axial direction of the non-rotating side engaging portion <NUM> entering the rotating-side engaging groove portion <NUM> and the groove bottom surface 27c becomes smaller as the non-rotating side engaging portion <NUM> relatively moves inside the rotating-side engaging groove portion <NUM> to the other side in the circumferential direction. However, also in this example, even in a state where the non-rotating side stopper surface <NUM> and the rotating-side stopper surface <NUM> are in surface contact with each other, the inclination angle α3 of the groove bottom surface 27c and the dimension in the axial direction of the rotating-side stopper surface <NUM> and the like are regulated so that the gap 28a between the end surface on the one side in the axial direction of the non-rotating side engaging portion <NUM> and the groove bottom surface 27c does not become zero.

In this example, compared to the construction of the ninth example, it is possible to reduce the amount of processing of the rotating-side engaging groove portion <NUM>. As a result, the number of man-hours for processing the driving member 5i can be reduced, and the manufacturing cost can be reduced. Further, it is advantageous in ensuring the rigidity and strength of the driving member 5i.

Other Configurations and operational effects of the eleventh example are the same as in the first example and the ninth example.

A twelfth example of an embodiment of the present invention will be described with reference to <FIG>.

In the ball screw device 1a of this example, a motor shaft is used as the driving member 5j. A rotor (not illustrated) is supported on a portion on the one side in the axial direction of the driving member 5j, and a stator (not illustrated) is arranged around the rotor. The driving member 5j has a mounting hole 19a that is open in the central portion in the radial direction of the side surface (end surface) on the other side in the axial direction. Female spline teeth <NUM> are formed on the inner-circumferential surface of the mounting hole 19a. By spline-engaging the female spline teeth <NUM> formed on the inner-circumferential surface of the mounting hole 19a and the male spline teeth <NUM> formed on the outer-circumferential surface of the fitting shaft portion <NUM>, the driving member 5j is externally fitted to the fitting shaft portion <NUM> so as not to be able to rotate relative to the fitting shaft portion <NUM>.

The driving member 5j includes a rotating-side engaging groove portion 18f on a side surface on the other side in the axial direction. The rotating-side engaging groove portion 18f has a depth in the axial direction that increases from the one side in the circumferential direction toward the other side in the circumferential direction, and regulates the stroke end of the nut <NUM> by engaging with the non-rotating side engaging portion <NUM> provided on the nut <NUM> at the end portion on the other side in the circumferential direction.

Also in this example, regulation of the stroke end of the nut <NUM>, which is a linear motion element, can be achieved with a small number of parts, and the ball screw device 1a can be more compact.

Other Configurations and operational effects of the twentieth example are the same as in the first example and the ninth example.

A thirteenth example of an embodiment of the present invention will be described with reference to <FIG>.

In this example, an annular protruding portion <NUM> having an annular shape protruding toward the other side in the axial direction is provided on the inner-side in the radial direction of the rotating-side engaging groove portion <NUM> of the side surface 15a on the other side in the axial direction of the base plate portion <NUM> of the driving member <NUM>. The end surface on the other side in the axial direction of the annular protruding portion <NUM> abuts against the end surface on the one side in the axial direction of the screw portion <NUM> of the screw shaft <NUM>.

The outer diameter of the annular protruding portion <NUM> is slightly smaller than the inner diameter of the nut <NUM> and larger than the root diameter of the shaft-side ball thread groove <NUM> formed on the outer-circumferential surface of the screw shaft <NUM>. Preferably, the outer diameter of the annular protruding portion <NUM> can be made the same as the outer diameter of the screw thread of the shaft-side ball thread groove <NUM>. More preferably, the outer diameter of the annular protruding portion <NUM> can be made larger than the outer diameter of the screw thread of the shaft-side ball thread groove <NUM>.

In the case of this example, in a state where the non-rotating side stopper surface <NUM> provided on the nut <NUM> and the rotating-side stopper surface <NUM> provided on the driving member <NUM> are engaged in the circumferential direction, the annular protruding portion <NUM> is inserted in the axial direction into the inner diameter side of the end portion on the one side in the axial direction of the nut <NUM>. Furthermore, the outer-circumferential surface of the annular protruding portion <NUM> and the end portion on the one side in the axial direction of the inner-circumferential surface of the nut <NUM> are closely faced over the entire circumference.

In this example, when the nut <NUM> moves to the one side in the axial direction relative to the screw shaft <NUM>, by inserting the annular protruding portion <NUM> into the inner diameter side of the end portion on the one side in the axial direction of the nut <NUM>, the grease filled inside the nut <NUM> can be pushed back to the other side in the axial direction by the annular protruding portion <NUM>. As a result, it is possible to effectively prevent grease from accumulating at the end portion on the one side in the axial direction of the inner-circumferential surface of the nut <NUM> and leaking out from the opening on the one side in the axial direction of the nut <NUM>.

Other Configurations and operational effects of the thirteenth example are the same as in the first example and the ninth example.

A fourteenth example of an embodiment of the present invention will be described with reference to <FIG>.

This example is a modification of the thirteenth example. In this example, in a state where the non-rotating side stopper surface <NUM> provided on the nut <NUM> and the rotating-side stopper surface <NUM> provided on the driving member <NUM> are engaged in the circumferential direction, the outer-circumferential surface of the annular protruding portion <NUM> and the end portion on the one side in the axial direction of the inner-circumferential surface of the nut <NUM> are closely faced over the entire circumference, and the side surface 15a on the other side in the axial direction of the base plate portion <NUM> of the driving member <NUM> and the side surface 3a on the one side in the axial direction of the nut <NUM> are closely faced over the entire circumference.

In this example, when the annular protruding portion <NUM> is inserted in the axial direction into the inner diameter side of the end portion on the one side in the axial direction of the nut <NUM>, it is possible to suppress leakage of grease to the outside from the gap between the side surface 15a on the other side in the axial direction of the base plate portion <NUM> of the driving member <NUM> and the side surface 3a on the one side in the axial direction of the nut <NUM>.

Other Configurations and operational effects of the fourteenth example are the same as in the first example, the ninth example, and the thirteenth example.

The construction of each example of an embodiment of the present invention may be appropriately combined and implemented as long as there is no contradiction.

In each example of an embodiment of the present invention, the non-rotating side engaging portion having a fan column shape was described as an example of the protruding non-rotating side engaging portion, however, in a case of implementing the present invention, the shape of the non-rotating side engaging portion is not limited to the fan column shape, and other shapes such as a columnar shape and a rectangular columnar shape can be adopted.

In a case of implementing the present invention, when the rotating-side engaging groove portion provided in the driving member is configured by two or more rotating-side engaging groove portions, the number of the rotating-side engaging groove portions is not limited to two or three, and it can be four or more. Further, the size of the center angle of the two or more rotating-side engaging groove portions can be made different from each other, and the two or more rotating-side engaging groove portions can be arranged so as to be unevenly spaced in the circumferential direction of the driving member.

In each example of an embodiment of the present invention, the fitting shaft portion of the screw shaft has male spline teeth on the outer-circumferential surface, and the driving member has a mounting hole having female spline teeth on the inner-circumferential surface, and a structure in which the driving member is spline-fitted to the fitting shaft portion has been described. However, in a case of implementing the present invention, the structure for fixing the driving member to the fitting shaft portion is not particularly limited. For example, the fitting shaft portion may have an elliptical cross section (racetrack oval shape) and has a width across flat shape having a pair of flat outer surfaces parallel to each other on the outer-circumferential surface, and the mounting hole of the driving member may be an oblong hole (stadium shaped hole) and may have a width across flat shape having a pair of flat inner surfaces parallel to each other on the inner-circumferential surface, and a structure in which the driving member is non-circularly fitted to the fitting shaft portion may be adopted.

Claim 1:
A ball screw device (<NUM>, 1a) comprising:
a screw shaft (<NUM>) having a shaft-side ball thread groove (<NUM>) having a spiral shape on an outer-circumferential surface thereof, the screw shaft (<NUM>) rotationally moving during use,
a nut (<NUM>) having a nut-side ball thread groove (<NUM>) having a spiral shape on an inner-circumferential surface thereof and a non-rotating side engaging portion (<NUM>, 13a-13c) having a protruding shape at an end portion on one side in an axial direction, the nut (<NUM>) linearly moving during use,
balls (<NUM>) arranged between the shaft-side ball thread groove (<NUM>) and the nut-side ball thread groove, and
a driving member fixed to the screw shaft (<NUM>) so as not to be able to rotate relative to the screw shaft (<NUM>), and rotationally driving the screw shaft (<NUM>),
characterized in that the driving member has an arc-shaped rotating-side engaging groove portion (<NUM>, 18a-<NUM>) into which the non-rotating side engaging portion (<NUM>, 13a-13c) can be inserted in the axial direction, and which can be engaged with the non-rotating side engaging portion (<NUM>, 13a-13c) in a circumferential direction at an end portion in the circumferential direction,
and in that
the rotating-side engaging groove portion (<NUM>, 18a-<NUM>) is a through groove that penetrates the driving member in the axial direction or a bottomed groove that is open to a side surface (3a, 15a) on the other side in the axial direction of the driving member.