JP2009299697A - Ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw by which a quantity of applied grease does not change in shipping and packing work, while applying a proper quantity of grease to a proper position. <P>SOLUTION: This ball screw 1 has a cylindrical cover 21 put on a screw shaft 2 and holding the grease G between an outer peripheral surface of the screw shaft 2 and itself, and a cap 22 fitted to and put on the upper end part inner periphery of the cover 21 in addition to a ball screw nut 3 screw-fitted to the screw shaft 2 and its ball screw track groove 2a via a ball. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a ball screw.

A ball screw including a screw shaft and a ball screw nut screwed to the screw shaft is often used for an electric actuator or a shock absorber. For example, Patent Document 1 discloses that a motor is mounted on a ball screw nut. It is disclosed that a ball screw having a configuration in which a ball screw nut rotates by rotating and a screw shaft extending vertically moves linearly in the axial direction is applied to a shock absorber.
JP 2005-264992 A

  The ball screw is usually lubricated with grease (non-greased). However, the grease is easily consumed when the screw shaft is frequently put in and out of the ball screw nut. Further, when the screw shaft extending vertically is used in such a form that it moves straight, there is a possibility that the applied grease hangs down as it is used, resulting in insufficient lubrication. In order to eliminate insufficient lubrication, the amount of grease applied should be increased. However, if too much grease is added, heat is easily generated due to stirring resistance, and resistance to movement of the screw shaft also increases. It was difficult to apply an appropriate amount of grease in advance. In addition, even if an appropriate amount of grease is applied at the time of manufacture, there is a problem that the amount of grease changes during packaging and shipping.

  An object of the present invention is to provide a ball screw in which an appropriate amount of grease can be applied at an appropriate position, and the amount of applied grease does not change during shipping and packaging operations.

  The ball screw according to the present invention is a ball screw comprising a screw shaft and a ball screw nut screwed to the screw shaft via a ball, and grease is applied between the screw shaft and the outer peripheral surface of the screw shaft. A cylindrical cover to be held and a cap fitted on the inner periphery of the end of the cover are further provided.

  The ball screw of the present invention is usually used in a form integrated with a motor. In this case, the ball screw with a motor is, for example, a screw shaft extending in a housing and extending vertically, and a screw shaft with a ball interposed therebetween. And a rotatable ball screw nut that is screwed together, a hollow shaft that is arranged concentrically with the screw shaft and rotates integrally with the ball screw nut, a motor rotor fixed to the hollow shaft, and a motor stator fixed to the inner diameter of the housing A motor, and the ball screw nut rotates, and the screw shaft linearly moves in the vertical direction (axial direction).

  The ball screw is composed of a screw shaft, a ball screw nut, a cover, and a cap at the time of manufacture. After the grease is filled between the screw shaft and the cover, the cap is fitted over the inner periphery of the cover. Then, the cover is pulled out from the screw shaft before being packed and shipped in the form as manufactured, and assembled to the actuator or the shock absorber. By holding the cap at the time of pulling, the movement of the grease is blocked by the cap, and an appropriate amount of grease is applied to the entire surface of the screw shaft.

  The material of the cover and cap is not particularly limited, but is preferably made of a synthetic resin excellent in grease resistance.

  The inner diameter of the cover may be just equal to the outer diameter of the screw shaft (in this case, the total volume of the raceway grooves on the screw shaft is the amount of gours). May be larger than the outer diameter of the screw shaft (for example, about 1 mm at the maximum).

  It is preferable that a convex portion that is fitted into the ball screw raceway groove of the screw shaft is provided on the inner periphery of the cap. In this case, grease may be filled between the screw shaft and the cover after the cap is attached to the screw shaft. This prevents the cap from moving when the cover is pulled out due to the engagement between the ball screw raceway groove and the convex portion, so that it is not necessary to hold the cap by hand and the workability is good. Become. For example, the convex portion of the cap may have a spiral shape that is continuously screwed into the raceway groove of the screw shaft, or may be, for example, one hemispherical protrusion.

  Further, the cap may have a double structure, and in addition to the cap, for example, a frustum-shaped plug that can seal the cover opening may be put on the cover opening. In this case, since air does not enter the cover, the cover does not come off at atmospheric pressure, and the ball screw nut can be prevented from falling off.

  The ball screw according to the present invention may be used as an actuator (a configuration in which a hollow shaft and a ball screw nut are rotated by a motor, whereby the screw shaft moves linearly), and a shock absorber (the screw shaft is externally connected). It is sometimes used as a form in which the hollow shaft and the ball screw nut are rotated by the force, whereby the electromagnetic force generated by the motor becomes a damping force.

  The screw shaft reciprocates linearly and is usually provided with a stopper for preventing movement beyond a predetermined amount. The stopper can be formed, for example, by providing the screw shaft with a flange portion that contacts the housing when the screw shaft moves by a predetermined amount or more, and the stopper is formed on a member that moves linearly integrally with the screw shaft. Alternatively, it may be provided on a member that does not move linearly (a housing or a hollow shaft).

  Immediately before the screw shaft is stopped by the stopper, the screw shaft moves at a high speed and the ball screw nut rotates at a high speed, so that a large rotational inertia force is generated in the ball screw nut due to a sudden stop of the screw shaft, Since this rotatory inertia force may cause indentation in the raceway part of the ball screw, an increase in the rotatory inertia force is not preferable, but with the above cover and cap, an appropriate amount of grease can be applied to an appropriate position, Insufficient lubrication can be resolved by avoiding an increase in the moment of inertia of the rotating part.

  A spline for guiding the linear movement of the screw shaft may be provided integrally with the screw shaft. The spline in this case may be a ball spline, for example, a fitting spline such as an involute spline.

  According to the ball screw of the present invention, it includes a cylindrical cover that covers the screw shaft and holds the grease between the outer periphery of the screw shaft and a cap that is fitted on the inner periphery of the end of the cover. By setting the inner diameter of the cover to a predetermined value, an appropriate amount of grease can be applied at an appropriate position, and the applied grease is protected by the cover, and the amount of grease is shipped and packed. Therefore, it is easy to handle, and an optimum amount of grease can be obtained in a state where it is assembled to an actuator or a shock absorber.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, “upper and lower” means the upper and lower sides of the figure.

  FIG. 4 shows a ball screw device with a motor as an example in which the ball screw according to the present invention is used.

  The ball screw device with a motor includes a steel screw shaft (2) extending in a vertical direction in a housing (8) and a ball screw raceway groove (2a) of the screw shaft (2) via a ball (not shown). A rotatable steel ball screw nut (3) screwed together, a hollow shaft (4) rotating integrally with the ball screw nut (3), and a cylindrical motor rotor (6) fixed to the hollow shaft (4) And a motor (5) comprising a cylindrical motor stator (7) fixed to the inner diameter of the housing (8).

  The motor (5) is a permanent magnet type three-phase synchronous motor, the motor rotor (6) is a permanent magnet, and a U-phase, V-phase, and W-phase coil (7a) is provided on the motor stator (7). ) Is wound.

  The screw shaft (2) and the hollow shaft (4) are arranged concentrically, and the ball screw (1) rotates the ball screw nut (3), the hollow shaft (4) and the motor rotor (6). The screw shaft (2) is used in the form of linear movement.

  The hollow shaft (4) has a small-diameter portion (11) for guiding the screw shaft (2), and a large shaft whose inner peripheral surface is fixed to the outer peripheral surface of the ball screw nut (3) and holds the bearing (9) on the outer peripheral surface. It consists of a diameter part (12), and is rotatably supported by the housing (8) via the bearing (9).

  This ball screw device with a motor is suitable for use as, for example, an electromagnetic shock absorber of an automobile. In the electromagnetic shock absorber, the screw shaft (2) linearly moves in the axial direction due to the external force transmitted from the tire, and the ball screw nut (3) and the hollow shaft (4) rotate accordingly. 5), the electromagnetic force generated by the motor (5) is used as a damping force.

  Such an electromagnetic shock absorber has a motor (5) that has been rotating at a high speed due to a bump stopper that moves up and down integrally with the screw shaft (2) colliding with the housing (8), etc. May stop suddenly and an excessive axial force may be applied to the ball screw raceway groove (2a) due to the inertia torque of the motor (5). In this case, protection of the ball screw raceway groove (2a) is an issue. .

  Grease as a lubricant is applied (greased) in advance to the screw shaft (2). If the coating amount is small, lubrication is insufficient. However, if the coating amount is too large, problems such as heat generation due to stirring resistance occur.

  The ball screw (1) according to the present invention solves the above-mentioned problems. As shown in FIGS. 1 (a) and 1 (b), a ball is inserted into the screw shaft (2) and its ball screw raceway groove (2a) via a ball. In addition to the ball screw nut (3) screwed together, a cylindrical cover (21) that covers the screw shaft (2) and holds grease (G) between the outer periphery of the screw shaft (2), and a cover And a cap (22) fitted on the inner periphery of the upper end of (21).

  The cap (22) has a cylindrical shape having a top wall, and a helical convex portion (23) is formed on the inner peripheral surface thereof as shown in an enlarged manner in FIG. This helical projection (23) can be moved along the ball screw raceway groove (2a) of the screw shaft (2) by screwing the cap (22) onto the upper end of the screw shaft (2). Thus, the cap (22) cannot be removed from the upper end of the screw shaft (2) only by pulling in the axial direction.

  When the ball screw (1) is manufactured, the grease (G) is filled between the screw shaft (2) and the cover (21) as shown in FIG. Packed and shipped in the form of time. Then, immediately before being assembled to the actuator or the shock absorber, as shown in FIG. 1B, the cover (21) is pulled out from the screw shaft (2). The movement of the grease (G) is blocked by the cap (22), and thus, an appropriate amount of grease (G) is applied to the entire surface of the screw shaft (2) in the initial state of use.

  According to this ball screw (1), variation in the amount of grease (G) applied in the initial state of use can be extremely reduced, and lack of lubrication between the screw shaft (2) and the ball screw nut (3) can be eliminated. Moreover, an increase in stirring resistance due to the grease (G) can be suppressed. In addition, since the rotating portion is not enlarged, the ball screw raceway groove (2a) is protected without increasing the rotational inertia force, and problems such as generation of indentations are prevented.

  The inner diameter of the cover (21) is set to a predetermined value corresponding to the appropriate amount of grease (G). Here, since there is a ball screw raceway groove (2a), the inner diameter of the cover (21) may be equal to the outer diameter of the screw shaft (2). For example, the outer diameter of the screw shaft ≦ the inner diameter of the cover ≦ (screw The outer diameter of the shaft + 1 mm) can be set as appropriate. Also, by setting the outer diameter of the cover (21) to be equal to or less than the inner diameter of the part where the screw shaft (2) and the ball screw nut (3) are installed (for example, a housing or a hollow shaft), the screw shaft (2) and the ball It is also possible to remove the cover (21) after attaching the screw nut (3).

  The cap (22) is not limited to that shown in FIG. 2 and is changed, for example, from a spiral convex portion (23) to one hemispherical convex portion (projection), for example. can do. Further, the convex portion (23) is not necessarily required, and the cap may be a short column shape instead of a cylindrical shape, and only fit into the upper end portion of the cover (21).

  As shown in FIG. 3, the cap has a double structure, and in addition to the cap (22), a truncated cone-shaped plug (24) that can seal the opening of the cover (21) has a top end of the cover (21). You may make it cover an opening. In this way, since air does not enter the cover (21), the cover (21) does not come off at atmospheric pressure, and the ball screw nut (3) can be prevented from falling off.

  In addition, said ball screw (1) can also be used as an electric actuator with the form shown in FIG. In this case, the rotational driving force of the motor (5) is converted into the axial thrust of the screw shaft (2) via the ball screw nut (3), and the axial reaction force of the thrust is supported by the bearing (9) and screwed. The shaft (2) is linearly moved so that the axial load acting on the screw shaft (2) is applied by the ball screw nut (3), and the torque is supported by the ball spline outer cylinder.

FIG. 1 is a longitudinal sectional view showing a ball screw according to an embodiment of the present invention. FIG. 1 (a) is a view showing a state at the time of shipment and packing, and FIG. It is a figure to do. FIG. 2 is a perspective view showing a preferred example of the cap. FIG. 3 is a longitudinal sectional view showing another preferred example of the cap. FIG. 4 is a view showing an example of a ball screw device with a motor as an example in which the ball screw of the present invention is used.

Explanation of symbols

(1) Ball screw
(2) Screw shaft
(3) Ball screw nut
(21) Cover
(22) Cap
(23) Convex

Claims (2)

In a ball screw comprising a screw shaft and a ball screw nut screwed onto the screw shaft via a ball,
A ball screw characterized by further comprising: a cylindrical cover that covers the screw shaft and holds grease between the outer peripheral surface of the screw shaft; and a cap that is fitted on the inner periphery of the end of the cover.   2. The ball screw according to claim 1, wherein a convex portion that is fitted into a ball screw raceway groove of the screw shaft is provided on an inner periphery of the cap.

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