JPS601503B2 - ball screw device - Google Patents

Description

[Detailed Description of the Invention] The present invention comprises a ball nut having a ball screw groove on the inner peripheral surface, a worm shaft having a pole screw groove on the outer peripheral surface, and a worm shaft that is iron-coupled with the two ball screw grooves and rolls. The present invention relates to a ball screw device including a large number of balls, and particularly relates to a ball screw device in which the shape of the pawl screw groove is a Gothic arch.

Conventionally, this type of device has been used in many machine tools, steering devices of automobiles, and various mechanical devices because of its good transmission efficiency and positioning accuracy. Its function is to convert the rotational motion of the worm shaft 1 into the linear motion of the pole nut 3 in the ball direction in a ball screw device shown in FIG. There are various functions such as converting, conversely, converting the linear motion of the ball nut 3 into a rotational motion of the worm 1, and others, and their functions are used depending on the purpose of the various devices that use the ball screw device. In addition, in many ball screw devices, the cross-sectional shape of the groove is a so-called Gothic arch shape as shown in Figure 2.
Contact angle between pole 2 and pole screw groove IA of worm shaft 1 8
W is the contact angle O of the ball nut 3 with the ball screw groove 3A
It was designed to be equal to N. However, when using a ball screw for equipment in various industrial fields, depending on the purpose of use, the rotational movement of the worm shaft 1 is transferred to the ball nut 3.
The transmission efficiency when converting the linear motion of the ball nut 3 into the rotational motion of the worm shaft 1 (hereinafter referred to as reverse efficiency) is as high as possible. There is also a desire to keep the energy consumption low, or a desire to increase reverse efficiency, regardless of production efficiency. In response to these demands, conventional pole screw devices
Even if the design is performed by changing the absolute value of the contact angle, the above request may not be satisfied in some cases. The present invention
The present invention provides a ball screw device that satisfies the above requirements by providing an angular difference between the contact angle ON on the nut side and the contact angle 8W on the worm shaft side, which were conventionally equal.

To explain this with reference to the embodiment shown in the figure, Fig. 3 shows a manual steering device in which the steering torque applied to the worm shaft 1 is transmitted to the sector via the ball 2, the ball nut 3, and the rack 3a of the ball nut. Sector axis 5 with gear 5a
It is transmitted from the sector axis to the wheel side.

Since the steering force needs to be transmitted to the wheels with less loss, it is desirable that the positive efficiency is high. On the other hand, since the reaction force from the wheels needs to be suppressed to an appropriate level, it is desirable that the reverse efficiency be low to some extent. Therefore, as shown in FIG. 4, the ball screw groove 3 of the ball 2 and ball nut 3 is
The contact angle 8N between the ball 2 and the pole screw groove IA of the worm shaft 1 is set to be smaller than the contact angle 8W between the ball 2 and the pole screw groove IA of the worm shaft 1. The size of the contact angle can be changed as appropriate by shifting the center position of the arc of the ball screw groove to the left or right in FIG. 4, or by changing the size of the radius of the arc. To explain the operation of the bow-like screw in this steering device, the ball is generally twisted with a constant lead angle at the center line of the ball's transfer, but the groove between the ball and the worm shaft and the groove of the ball nut are twisted. Since the lead angle at the contact point is different from the lead angle of the center line of the pole's displacement, the ball experiences a sliding friction force at the contact point.

The direction of this frictional force is perpendicular to the direction in which the ball is transferred. Therefore, this frictional force is caused by the rotation of the worm shaft,
Alternatively, the direct movement of the ball nut causes the ball to move in a direction perpendicular to the transfer direction, causing the ball to bite into the mating thread groove. On the other hand, a force is generated to counter the steepness caused by the wedge action of the groove, so the two move until they balance out, reach a steady state, transfer, and transmit the operation. That is, in FIG. 2, when the worm shaft 1 side is rotated and the ball nut 3 side is moved linearly, the ball 2 is moved into the groove 3 of the pole nut.
It moves in the direction of A and tries to bite in the direction of making two-point contact on the threaded groove 3A side of the ball nut 3.

On the other hand, when the pole nut 3 is moved directly to rotate the worm shaft 1, the ball 2 moves in the direction of the groove IA of the worm shaft 1 and bites in the direction where it contacts the threaded groove IA of the worm shaft 1 at two points. It causes congestion, reaches a steady state, transfers, and transmits the operation. As shown in the example, when the groove cross section is a Gothic arch shape, before the pole 2 moves and reaches a steady state, it makes a third contact with the mating thread groove, and the ball 2 makes three-point contact (warm). When the shaft 1 rotates, it makes two points of contact with the ball nut groove 13A, and one point makes contact with the worm shaft groove IA, and when the ball nut 3 moves linearly, it makes contact with the worm shaft groove IJ.
2-point contact with the ball nut groove 3A, and 1-point contact with the ball nut groove 3A), and transfer, resulting in an increase in bran loss and a decrease in transmission efficiency.

Therefore, as shown in FIG. 4 of the specification, in a ball screw in which the contact angle 8N between the threaded groove 3A of the ball nut 3 and the ball 2 is smaller than the contact angle 8W between the threaded groove IA of the worm koji 1 and the ball 2, When rotating the worm shaft 1 to move the ball nut 3 in a direct motion (direct action), the ball 2 bites into the ball nut 3 side (moves in a direction that causes two-point contact on the ball nut 3 side), or remains unchanged. It will operate either by maintaining two-point contact. In this case, the load on the third contact point becomes smaller, and even if there is a three-point contact, the positive efficiency is improved compared to the conventional one with the same contact angle. When converting the direct motion of the pole nut 3 to the rotation of the worm shaft 1 (reverse action), the ball 2 moves toward the worm shaft 1, but before reaching a steady state, it makes contact at three points (the worm shaft groove and the three points). (one point contact with the ball nut groove), and the load on the third point is also large.

Therefore, although the bioefficiency improves, the reverse efficiency tends to decrease. In the embodiment shown in FIG. 5 of the specification, ON>8W
Therefore, the positive efficiency and reverse efficiency of the pole screw with this configuration show the opposite direction to that shown in FIG. 4.

By configuring as described above, the forward efficiency is improved and the reverse efficiency is decreased compared to the conventional manual steering system, which has the effect of reducing the steering force. Compared to a steering wheel with a larger steering wheel, there are advantages in that the angle of steering wheel operation and the shaking of the steering wheel during high-speed driving can be reduced, and increases in weight and cost due to an increase in the size of the steering device can be prevented.

Additionally, since the reaction force from the road surface is reduced, the large and small vibrations transmitted to the steering wheel are reduced, further ensuring safe steering.
In other words, by reducing the steering force and keeping the gear ratio to 4.0, it is possible to create a steering device that has sharp cutting ability, is small, lightweight, and inexpensive, and has less kickback and less shimmy. . Further, although not shown in the drawings, in a power steering device, when steering, the steering wheel can be operated with a light steering force using auxiliary power such as a hydraulic device, so a higher positive efficiency is desirable, but this does not pose a particular problem. However, the steering wheel return characteristic when returning to straight running after completing a curve is generally worse than that of a manual type because the internal resistance of the auxiliary power device adds to the frictional resistance of the steering device body. Because of this, there is a danger in steering, so it is necessary to improve the return characteristics, and it is desirable to reduce the frictional resistance and improve the reverse efficiency. As shown in FIG. 5, a ball screw device that meets the above requirements has a contact angle of 8N between the ball 2 and the ball screw groove 3A of the ball nut 3.
The angle is larger than the contact angle aW between the worm shaft 1 and the pole screw groove IA. 6 and 7 are graphs showing experimental data of one example, respectively.
The figure shows the forward efficiency, and FIG. 7 shows the reverse efficiency.

The solid line 1 is data of a conventional ball screw device in which the contact angle 8N on the ball nut side and the contact angle 8W on the worm shaft side are both 42.50, and the dotted line 0' is data for a conventional ball screw device in which the contact angle 8N on the ball nut side is 37.5o and the worm shaft side contact angle 8N is 37.5o. The contact angle on the shaft side is 47. The data of ON<8W when set to y, the chain line m indicates the contact angle of 8N on the ball nut side is 47.5o, and the contact angle of 8W on the worm shaft side is 37
．． 50 is shown for 8N>OW, and the dotted line 0 is the 4th
The embodiment shown in FIG. 5 corresponds to the experimental data of the embodiment shown in dashed line m' in FIG. That is, at 8N x 8W, the forward efficiency is improved compared to the slave ball screw, but on the other hand, the reverse efficiency is decreased.
On the other hand, it has been shown that when N>8W, the forward efficiency decreases and the reverse efficiency increases. As described above, the ball screw device of the present invention provides an angular difference between the contact angle aN between the pole and the ball screw groove of the ball nut and the contact angle aW between the pole and the ball screw groove of the worm shaft. This has the effect of easily ensuring various transmission efficiencies required depending on the purpose of use and without any increase in cost.

In addition, compared to other devices to obtain similar transmission efficiency, it is only necessary to change the position of the arc center of the screw groove and the radius of the arc in the design. It also has effects such as being extremely advantageous in terms of manufacturing costs.

[Brief explanation of drawings]

Fig. 1 is a vertical sectional view of a conventional ball screw device, Fig. 2 is an enlarged sectional view showing the groove shape of the follower, Figs. 3 to 7 are examples of the present invention, and Fig. 3 is a manual type. A vertical cross-sectional view of the worm ball of the steering device, FIG. 4 is an enlarged cross-sectional view showing its groove shape, FIG. 5 is an enlarged cross-sectional view showing the groove shape of another embodiment, and FIG. 6 is an experiment of positive efficiency. Graph showing data, 7th
The figure is a graph showing experimental data on reverse efficiency. Explanation of symbols, 1... Worm axis, 2... Ball, 3
...Ball nut, 5...Sector axis, O, No Box O, Z Figure 3 O, 4 Figure Gata O, K Illustration? taste

Claims (1)

[Claims] 1. A ball nut having a ball screw groove on its inner peripheral surface;
a worm shaft having a ball screw groove on its outer circumferential surface;
In a ball screw device, the ball screw device includes a large number of balls that fit into one ball screw groove and roll, and the two ball screw grooves have a gossic arch shape. , the contact angle θW between the ball and the ball screw groove of the worm shaft
A ball screw device characterized by having a difference in angle between the two. 2. The ball screw device according to claim 1, wherein the ball screw device is effective for a power-driven steering device as the contact angle θW between the ball and the ball screw groove of the ball nut is larger than the contact angle θW. 3 Contact angle θ of ball and ball nut with ball screw groove
The ball screw device according to claim 1, wherein N is a smaller angle than the contact angle θW between the ball and the worm shaft, making the ball screw device effective for a manual steering device.