JP5233426B2 - Ball spline - Google Patents

Description

  The present invention relates to a ball spline, and more particularly, to a ball spline used under conditions that are susceptible to excessive torque.

Ball splines are often used for electric actuators and shock absorbers in combination with ball screws. For example, in Patent Document 1, a ball screw nut rotates by connecting a motor to the ball screw nut. It is disclosed that a ball screw having a configuration in which a screw shaft extending vertically moves linearly in an axial direction is applied to a shock absorber.
JP 2005-264992 A

  Some actuators and shock absorbers using ball screws with ball splines are configured to be stopped suddenly by a stopper from the state where the screw shaft moves at high speed and the ball screw nut rotates at high speed. An excessive impact load is applied to the ball screw, and an excessive torque is generated, which may cause indentation on the spline track.

  An object of the present invention is to provide a ball spline that prevents indentation from occurring on a spline track even when excessive torque is applied.

The ball spline according to the present invention is a ball spline having a shaft provided with a spline track and a ball spline outer cylinder fitted to the shaft via a ball, in order to reduce torsional rigidity. In addition, since at least one of the thin portions is provided in the spline outer cylinder , the spline outer cylinder is characterized in that its rigidity is set so as to follow the torsion of the shaft.

  The ball spline is preferably combined with a ball screw, a screw shaft provided with a ball screw raceway and an axially extending spline raceway, and a rotatable ball screwed to the ball screw raceway of the screw shaft via a ball. A screw nut and a ball spline outer tube that is fitted to the spline track via a ball and guides the axial linear motion of the screw shaft are included.

  In such a ball screw with a ball spline, the ball spline is configured such that the ball spline outer cylinder is prevented from rotating with respect to the housing by a rotation-preventing part such as a key, and a plurality of balls are arranged in the axial direction inside the spline outer cylinder. Prevents the rotation of the screw shaft and receives the reaction force of the torque generated by the ball screw nut. In conventional ball screws with ball splines, the torsional rigidity of the spline outer cylinder is several times that of the screw shaft. Therefore, if excessive torque acts on the screw shaft, the screw shaft is twisted against the spline outer cylinder. The load sharing of a plurality of balls arranged in the axial direction in the spline outer cylinder becomes non-uniform, and the value of the maximum load increases accordingly, and the indentation is likely to occur on the spline track. In order to prevent twisting, the rigidity of the screw shaft may be increased. However, if the shaft diameter is increased, the entire ball screw becomes undesirably large. According to the ball spline of the present invention, since the torsional rigidity of the spline outer cylinder and the torsional rigidity of the shaft are close to each other, when the shaft is twisted, the spline outer cylinder is easily twisted accordingly. By increasing the load sharing of each ball, the increase in the maximum load can be suppressed.

  It is optimal when the torsional rigidity of the spline outer cylinder matches the torsional rigidity of the shaft. However, when the torsional rigidity of the spline outer cylinder is set to follow the torsion of the shaft, the impact load increases. However, the load applied to the ball becomes almost uniform, and a partial increase in surface pressure is prevented. The torsional rigidity of the spline outer cylinder is 0.5 to 1.5 times (± 50%), more preferably 0.9 to 1.1 times (± 10%) of the torsional rigidity of the shaft. Is done.

  In adjusting the torsional rigidity of the spline outer cylinder, in order to reduce the torsional rigidity, it is sufficient that at least one of the notch, the hole and the thin part is provided in the spline outer cylinder. By appropriately adjusting the size, number, etc., the torsional rigidity target value of the spline outer cylinder based on the torsional rigidity of the shaft can be easily obtained.

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

  The ball spline according to the present invention may be used in combination with a ball screw 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 (screw shaft). Is moved linearly by an external force, whereby the ball screw nut is rotated and the electromagnetic force generated by the motor is used as 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.

  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).

  According to the ball spline of the present invention, since the torsional rigidity of the spline outer cylinder is set so as to follow the torsion of the shaft, when the shaft is twisted due to excessive torque, the spline outer cylinder is also accompanied by this. As a result, the load applied to each ball arranged in the axial direction in the spline outer cylinder becomes uniform, and the maximum load does not increase. Therefore, even when excessive torque is applied, indentation is prevented and the life of the ball spline is improved.

  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. 1 shows a ball screw device with a motor using a ball spline according to the present invention.

  The motorized ball screw device (1) consists of a ball screw raceway (2a) and a vertically extending steel screw shaft (2) provided with a spline raceway (2b), and a ball screw of the screw shaft (2). A rotatable steel ball screw nut (3) screwed to the raceway (2a) via a ball, and a screw shaft fitted onto the spline raceway (2b) via the ball on the lower end side of the screw shaft (2). The ball spline outer cylinder (4) that guides the vertical movement (axial direction) of (2), the hollow shaft (5) that is integrated with the ball screw nut (3), and the bearing (7) Through which the hollow shaft (5) is rotatably supported and the ball spline outer cylinder (4) is supported, a cylindrical motor rotor (9) fixed to the hollow shaft (5), and the housing (6 And a motor (8) comprising a cylindrical motor stator (10) fixed to the inner diameter.

  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 device (1) rotates the ball screw nut (3), the hollow shaft (5), and the motor rotor (9). Thus, the screw shaft (2) is used in the form of linear movement.

  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

  In addition to the keyway, the ball spline outer cylinder (4) is provided with a plurality of holes (14) as means for reducing torsional rigidity.

  The motor-equipped ball screw device (1) is suitable for use as, for example, an automobile electromagnetic shock absorber. 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 (5) rotate accordingly. 8), the electromagnetic force generated by the motor (8) is used as the damping force.

  Such an electromagnetic shock absorber has a motor (8) that has been rotating at a high speed when the bump stopper that moves up and down integrally with the screw shaft (2) collides with the housing (6) etc. during an overstroke such as over the protrusion. May stop suddenly and an excessive torque may be applied to the spline raceway (2b) of the ball spline due to the inertia torque of the motor (8), and its protection is a problem.

  Therefore, in the ball spline according to the present invention, focusing on the ball spline outer cylinder (4), the conventional ball spline outer cylinder has a high torsional rigidity, and the screw spline (2) itself is not twisted, so that While the load applied to the ball increases as the torsion of the shaft (2) increases, the means (14 in the example shown in FIG. 1) (14) for reducing the torsional rigidity is provided with a spline outer cylinder (4 ), The torsional rigidity of the spline outer cylinder (4) is close to the torsional rigidity of the screw shaft (2).

  The means for reducing torsional rigidity may be a notch (15) as shown in FIG. 2 (b) instead of the hole (14) (see FIG. 2 (a)). It may be a thin portion having the same position and the same size as (14) or the notch (15). The ball spline outer cylinder (4) is provided with a spline track (4a), and the hole (14), the notch (15) and the like are provided at a position where the spline track (4a) is removed.

  According to the ball spline having the spline outer cylinder (4) provided with a hole (14) as a means for reducing torsional rigidity, the screw shaft (2) is moved upward in the normal state shown in FIG. When a force causing twisting acts on the screw shaft (2), the screw shaft (2) is twisted, and the amount of twist becomes large on the upper side of the figure. At this time, since the ball spline outer cylinder (4) easily follows the twist of the screw shaft (2), the spline corresponds to the twist of the screw shaft (2) as shown in FIG. Twist also occurs in the outer cylinder (4).

  Therefore, when an excessive torque is applied to the conventional ball spline, as shown in FIG. 4A, the screw shaft (2) is twisted and the spline raceway groove (2b) is indicated by a two-dot chain line in the figure. At this time, the spline outer cylinder (24) has high torsional rigidity and does not substantially deform, so that a force corresponding to the torsional amount of the screw shaft (2) acts on the ball (16) as it is. Will do. Therefore, the increase in the load sharing of the ball (16) becomes larger at the upper part of the spline track (24a), and the ball (16) in this part is larger on the upper side where the twist is large, as shown by the arrow in FIG. Due to the force, there is a high possibility that indentation will occur in the spline track (2b) (24a) in this part.

  On the other hand, in the ball spline according to the present invention, as described above, since the ball spline outer cylinder (4) follows the twist of the screw shaft (2), the spline raceway groove (2b) of the screw shaft (2) is illustrated in FIG. When the ball spline outer cylinder (4) is deformed to the position indicated by the two-dot chain line, the spline track (4a) of the ball spline outer cylinder (4) is also deformed to the position indicated by the two-dot chain line in the figure, and the load sharing of the ball (16) The amount of increase is only an amount corresponding to the difference between the twist amount of the screw shaft (2) and the twist amount of the spline outer cylinder (4), and the load on the ball (16) is made uniform. This prevents indentation from occurring in the spline tracks (2b) (4a).

  Although the above ball screw with ball spline (1) has been described for an electromagnetic shock absorber, the present invention is not limited to this and can also be used as an electric actuator. In this case, the rotational driving force of the motor (8) is converted to 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 (7) and screwed. The shaft (2) is moved linearly, 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 (4). .

FIG. 1 is a longitudinal sectional view showing a ball screw device using a ball spline according to the present invention. FIG. 2 is a perspective view showing some examples of the ball spline outer cylinder of the ball spline of the present invention. FIG. 3 is a perspective view showing a state when torque acts on the shaft of the ball spline of the present invention. FIG. 4 is a diagram schematically showing a characteristic part of the ball spline of the present invention.

Explanation of symbols

(2) Screw shaft (shaft)
(2b) Spline track
(4) Ball spline outer cylinder
(6) Housing
(14) Hole
(15) Notch
(16) Ball

Claims (2)

In a ball spline comprising a shaft provided with a spline track and a ball spline outer cylinder fitted to the shaft via a ball,
In order to reduce the torsional rigidity, at least one of the notch, the hole and the thin wall portion is provided in the spline outer cylinder, so that the rigidity of the spline outer cylinder is set so as to follow the torsion of the shaft. A ball spline characterized by 2. The ball spline according to claim 1, wherein the torsional rigidity of the spline outer cylinder is 0.5 to 1.5 times the torsional rigidity of the shaft .

Images