JP2011122642A - Ball screw with ball spline - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw with ball splines, capable of solving dropping of a spline ball into a thread groove without differing the diameter of a shaft. <P>SOLUTION: A screw shaft 2 has a circular sectional shape. A reinforcement portion 20 is formed in each pocket 17 of a retainer 15 so as to be located radially inside the cylindrical surface of the screw shaft 2, and an interference preventing groove 21 is formed in the screw shaft 2 to prevent the interference with the reinforcement portion 20. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a ball screw with a ball spline.

  As a ball screw with a ball spline, a screw shaft provided so that the screw groove and the spline groove intersect each other, a ball screw nut screwed to the screw groove of the screw shaft via a ball, and a ball on the spline groove of the screw shaft Are known (see Patent Document 1), and such ball screws with ball splines are often used for electric actuators and shock absorbers. Yes.

JP-A-6-300106

  In the ball spline in the ball screw with the ball spline as shown in Patent Document 1 above, when forming the spline groove on the outer periphery of the screw shaft, the outer diameter of the shoulder portion sandwiched between the pair of spline grooves is increased. In other words, in addition to the cylindrical surface of the reference shaft, a different-diameter screw shaft having a large cylindrical surface connecting the outer diameters of the shoulders is considered. However, in order to obtain a screw shaft with such a different diameter, it is necessary to cut by machining so that the diameter other than the shoulder is small. There is a problem that the cost increases.

  On the other hand, when the screw shaft has a round cross-sectional shape, the inner diameter of the cage also becomes round, and a portion where the spline groove and the screw groove intersect exists in the screw shaft. Since the screw groove is formed deeper than the spline groove, if the cage pocket lacks rigidity, the spline ball moving along the spline groove falls into the screw groove at the intersection. there is a possibility. When the spline ball falls into the screw groove, there is a problem that the ball spline is locked and does not operate, and it is desired to eliminate the possibility that the spline ball falls into the screw groove.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a ball screw with a ball spline in which the shaft does not have a different diameter and the drop of the spline ball into the screw groove is eliminated.

  A ball screw with a ball spline according to the present invention includes a screw shaft provided so that the screw groove and the spline groove intersect each other, a ball screw nut screwed to the screw groove of the screw shaft via the ball, and a spline of the screw shaft. A ball spline outer cylinder fitted to the groove via a ball. The ball spline outer cylinder has an outer cylinder main body formed with a spline groove corresponding to the spline groove of the screw shaft and a spline ball at a predetermined position. In a ball screw with a ball spline, which has a pocket to hold in and a cage fitted into the spline outer cylinder body, the screw shaft has a round cross-sectional shape, and in each pocket of the cage, A reinforcement portion is formed that is located radially inward of the cylindrical surface of the screw shaft, and interference with the reinforcement portion is provided on the screw shaft. It is characterized in that the interference prevention groove for sealing is formed.

  The screw shaft has a round cross-sectional shape. The screw shaft has two cylindrical surfaces (a cylindrical surface serving as a reference on which a screw groove is formed and a shoulder on which a spline groove is formed are protruded from the reference cylindrical surface. This means that there is only a cylindrical surface that serves as a reference for the thread groove to be formed, and a spline groove is formed on this reference cylindrical surface. In addition, an interference prevention groove for preventing interference with the reinforcing portion is also formed on the reference surface.

  Each pocket of the cage of the spline outer cylinder is tapered such that the opening on the radially outer side is larger than the opening on the radially inner side, and its radially intermediate portion is made equal to the diameter of the spline ball. This prevents the spline ball from being held in a predetermined position and moving further inward in the radial direction. The cage is made of resin and is slightly deformable. When a large radial inward force acts on the spline ball, the spline ball resists the frictional force received from the cage pocket surface. Movement inward in the radial direction is possible. Normally, the spline ball is held by the spline groove of the screw shaft and the spline groove of the spline outer cylinder body, so that the spline ball is prevented from moving inward in the radial direction. Since they are formed deeper than the grooves, the spline balls may fall into the screw grooves due to the radially inward force at these intersecting portions. When the spline ball falls into the screw groove, the movement of the spline ball along the spline groove stops, and the ball spline locks and does not operate. In the ball screw with a ball spline according to the present invention, a reinforcing portion positioned radially inward from the cylindrical surface of the screw shaft is formed in each pocket of the cage, so that rigidity in the radially inner opening of the pocket is formed. The possibility that the spline ball falls into the screw groove is eliminated.

  The reinforcing portion may be provided on either one of the pocket surfaces on both sides of the ball, or may be provided on both. A plurality of pairs of spline grooves for receiving clockwise rotation of the screw shaft and spline grooves for receiving counterclockwise rotation of the screw shaft are formed on the outer periphery of the screw shaft. A spline groove for receiving clockwise rotation and a spline groove for receiving counterclockwise rotation are formed so as to face each of these spline grooves. Accordingly, one of the pocket surfaces on both sides of the ball is a side that receives torque, and the other is a side that does not receive torque, but the reinforcing portion is more preferably provided only on the pocket surface on the side receiving torque. .

  The number of screw grooves may be one, two, or more.

  The screw shaft, ball screw nut, and ball spline outer cylinder main body are made of carbon steel such as S45C and S55C or SAE4150 steel, and the ball is made of bearing steel (SUJ2), for example.

  A ball screw with a ball spline according to the present invention may be used as an actuator (a configuration in which a ball screw nut is rotated by a motor, whereby the screw shaft moves linearly), and a shock absorber (the screw shaft is externally connected). In some cases, the ball screw nut is rotated by the force, whereby the ball screw nut rotates and the electromagnetic force generated by the motor becomes a damping force.

  When used in an actuator or shock absorber, for example, a ball screw with a ball spline, a hollow shaft integrated with a ball screw nut, a hollow shaft rotatably supported via a bearing and a ball spline outer cylinder And a motor composed of a motor rotor fixed to the hollow shaft and a motor stator fixed to the inner diameter of the housing.

  According to the ball screw with the ball spline of the present invention, since the screw shaft has a round cross-sectional shape, it is easy to process the screw shaft, and each pocket of the cage has a cylindrical surface of the screw shaft. In addition, a reinforcing portion positioned radially inward is formed, and an interference prevention groove for preventing interference with the reinforcing portion is formed on the screw shaft. By being reinforced, the spline ball is prevented from moving radially inward beyond the opening, and the spline ball is prevented from dropping into the screw groove at the intersection. It is easy to process the interference prevention groove to prevent interference with the reinforcing part, and this maintains the feature that the screw shaft is easily processed, and a large radial inward force acts on the spline ball. In this case, the ball spline can be prevented from being locked.

FIG. 1 is a longitudinal sectional view showing a ball screw with a ball spline according to the present invention. FIG. 2 is a front view of a ball spline portion of a ball screw with a ball spline according to the present invention. FIG. 3 is an enlarged view of FIG. FIG. 4 is a view corresponding to FIG. 2 showing a ball spline portion of a conventional ball screw with a ball spline.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the top and bottom refer to the top and bottom of FIG. Further, the clockwise direction and the counterclockwise direction refer to FIG.

  1 to 3 show an embodiment of a ball screw with a ball spline according to the present invention.

  Ball screw with ball spline (1) consists of two screw grooves (2a) and a steel screw shaft (2) extending vertically, and a plurality of spline grooves (2b) (2c) extending vertically. A rotatable steel ball screw nut (3) screwed to the screw groove (2a) of the shaft (2) via a ball, and a spline groove (2b) (2c) on the lower end side of the screw shaft (2). A ball spline outer tube (4) that is fitted via a ball to guide the vertical (axial) linear movement of the screw shaft (2), and a hollow shaft that is integrated with the ball screw nut (3) and extends upward ( 5), a housing (6) that rotatably supports the hollow shaft (5) through the bearing (7) and supports the ball spline outer cylinder (4), and a cylindrical shape fixed to the hollow shaft (5). A motor rotor (9) and a motor (8) comprising a cylindrical motor stator (10) fixed to the inner diameter of the housing (6).

  The motor (8) is a permanent magnet type three-phase synchronous motor, the motor rotor (9) is a permanent magnet, and a U-phase, V-phase and W-phase three-phase coil (10a) is provided on the motor stator (10). ) Is wound.

  The screw shaft (2) and the hollow shaft (5) are arranged concentrically, and the ball screw with ball spline (1) includes the ball screw nut (3), the hollow shaft (5) and the motor rotor (9). The screw shaft (2) is used in such a form that it is rotated and moved linearly.

  The hollow shaft (5) has a small-diameter portion (11) for guiding the screw shaft (2), and a large diameter whose inner peripheral surface is fixed to the outer peripheral surface of the ball screw nut (3) and that holds the bearing (7) on the outer peripheral surface. It consists of a diameter part (12).

  The ball spline outer cylinder (4) is prevented from rotating with respect to the housing (6) by a detent (for example, a key) (13) to prevent the screw shaft (2) from rotating and guide its vertical movement. The

  As shown in FIG. 2, the ball spline outer cylinder (4) has a substantially cylindrical metal outer surface formed with a plurality of linear spline grooves corresponding to the spline grooves (2b) (2c) of the screw shaft (2). A cylinder main body (14) and a substantially cylindrical cage (15) fixed to the inner periphery of the outer cylinder main body (14) are provided. The screw shaft (2) is a hollow shaft having a round cross section.

  The cage (15) holds a spline ball (16) that rolls between the spline groove (2b) (2c) of the screw shaft (2) and the spline groove of the ball spline outer cylinder body (14). A pocket (17) is formed for this purpose. The space between the spline groove (2b) (2c) of the screw shaft (2) and the spline groove of the ball spline outer cylinder body (14) facing each other through the pocket (17) is rotated by the spline ball (16). It is a moving main passageway (18). The retainer (15) is further formed with a return passage (19) communicating with both left and right ends of the main passage (18).

  Each pocket (17) of the retainer (15) has a tapered shape in which the opening on the radially outer side is larger than the opening on the radially inner side, and the intermediate portion in the radial direction is a spline ball (16 ), The spline ball (16) is held at a position where the main passage (18) can roll, and further movement inward in the radial direction is prevented.

  In each pocket (17) of the cage (15), a reinforcing portion (20) positioned radially inward from the cylindrical surface (2d) of the screw shaft (2) is formed, and at the screw shaft (2) An interference prevention groove (21) for preventing interference with the reinforcing portion (20) is formed.

  The spline ball (16) is disposed in the main passage (18) and the return passage (19), and the spline ball (16) rolling on the main passage (18) is connected to the screw shaft (2) and the ball spline. It guides the relative linear motion of the tube (4). The main passage (18) and the return passage (19) constitute a spline ball circulation path. A total of six spline ball circulation paths are provided, and a pair of main passages (18) are provided close to each other, and one pair of main passages (18) is on the counterclockwise side. Is provided with a return passage (19) on the counterclockwise side, and a return passage (19) is provided on the clockwise side for the one on the clockwise side, so that a pair of spline ball circulation paths is formed. A total of three pairs are arranged at equal intervals in the circumferential direction.

  By rotating the ball screw nut (3) in the above state, the screw shaft (2) moves linearly in the axial direction without rotating with the ball spline outer cylinder (4) as a guide. At this time, in the portion of the ball screw nut (3), the screw ball is circulated through the screw ball circulation path. In the ball spline outer cylinder (4), the spline ball (16) is circulated through the spline ball circulation path.

  This ball screw with ball spline (1) fixes the ball spline outer cylinder (4) so that it does not rotate or move to a fixed position in the axial direction, and the ball screw nut (3) rotates at a fixed position in the axial direction. However, it is used in a supported state so as not to move. Here, although the spline ball (16) and the screw ball are the same size, the main passage (18) in which the spline ball (16) rolls in the ball spline that prevents the screw shaft (2) from rotating. ) Has a smaller clearance between the ball (16) and the main passage (18) than the main passage where the screw ball rolls.Therefore, in the screw shaft (2), the spline groove ( The screw groove (2a) is formed deeper than 2b) and (2c). For this reason, at the intersection of the screw groove (2a) and the spline groove (2b) (2c), the spline ball (16) resists the frictional force received from the pocket surface of the cage (15) and By moving in the direction, the spline ball (16) moving along the spline groove (2b) (2c) may fall into the screw groove (2a). When the spline ball (16) falls into the screw groove (2a), the movement of the spline ball (16) along the spline groove (2b) (2c) stops, and the ball spline locks and does not operate.

  In the prior art, as shown in FIG. 4, with respect to the same screw shaft (2), the inner peripheral surface (35a) of the cage (35) is more than the cylindrical surface (2d) of the screw shaft (2). There is no portion located radially inward. Even in this case, the spline ball (16) is prevented from dropping into the screw groove (2a) by the retainer (15) of the ball spline outer cylinder (4), but the spline ball (16) is radially inward. When a large force is applied, the spline ball (16) is easily moved radially inward.

  In contrast, in the ball screw with ball spline (1) according to the present invention, even when a large radial inward force acts on the spline ball (16), as shown in an enlarged view in FIG. Reinforcement (20) is provided in each pocket (17) of the cage (15), so that the opening of the pocket (17) is reinforced and the spline ball (16) moves radially inward. It is difficult to move.

  The spline groove (2b) shown in FIG. 3 is for receiving the clockwise rotation of the screw shaft (2), and the reinforcing portion (20) has the screw shaft (2) in the clockwise direction. It is formed on the pocket surface (clockwise pocket surface) (17a) that receives this torque when it is about to rotate. And although the enlarged view is omitted, in the spline groove (2c) that receives the counterclockwise rotation of the screw shaft (2), the reinforcing portion (20) tries to rotate the screw shaft (2) counterclockwise. At this time, it is formed on the pocket surface (counterclockwise pocket surface) on the side receiving this torque.

(1) Ball screw with ball spline
(2) Screw shaft
(2a) Screw slot
(2b) (2c) Spline groove
(3) Ball screw nut
(4) Ball spline outer cylinder
(14) Outer cylinder body
(15) Cage
(16) Spline ball
(17) Pocket
(20) Reinforcement part
(21) Interference prevention groove

Claims (1)

A screw shaft provided so that the screw groove and the spline groove cross each other, a ball screw nut screwed to the screw groove of the screw shaft via the ball, and a ball fitted to the spline groove of the screw shaft via the ball A spline outer cylinder, and the ball spline outer cylinder has an outer cylinder main body formed with a spline groove corresponding to the spline groove of the screw shaft, and a pocket for holding the spline ball at a predetermined position. In a ball screw with a ball spline consisting of a cage fitted in the body,
The screw shaft has a round cross-sectional shape, and each pocket of the cage is formed with a reinforcing portion located radially inward from the cylindrical surface of the screw shaft, and the reinforcing portion is formed on the screw shaft. A ball screw with a ball spline, wherein an interference preventing groove for preventing interference with the ball spline is formed.

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