JP2002188705A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct smooth continuous speed variation by eliminating relative sliding between balls in a ball screw for driving a movable pulley of a CVT. SOLUTION: This ball screw is formed by housing many balls so as to be capable of rolling between facing ball screw grooves formed in a screw shaft 6 and a nut 7 fit to the screw shaft 6. The balls are composed of load balls 9a for supporting a load and spacer balls 9b having the diameter smaller than that of the load ball 9a, and by arranging the balls 9a, 9b so that one spacer ball 9b is interposed between two load balls 9b, the spacer ball 9b and the load balls 9a adjoining the spacer ball 9b are sequentially rotated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ball screw, and more particularly to a ball screw for driving a movable pulley of a belt-type continuously variable transmission (CVT) for an automobile or the like.

[0002]

2. Description of the Related Art FIG. 2 schematically shows a CVT. The power input side pulley 1 and the output side pulley 2 are fixed pulleys 1 respectively.
a, 2a and movable pulleys 1b, 2b opposed to each other. A steel belt 3 connects the input pulley 1 and the output pulley 2 to each other. Each fixed pulley 1
The facing surfaces of the movable pulleys 1a and 2a and the movable pulleys 1b and 2b are formed in a tapered shape.
Are moved in the axial direction, so that the fixed pulleys 1a, 2a,
The speed is changed by changing the distance between the movable pulleys 1b and 2b and changing the ratio of the winding radius of the belt 3.

A ball screw 5 is used to move the movable pulleys 1b and 2b in the axial direction.
The ball screw 5 is formed by fitting a nut 7 to a screw shaft 6, and as shown in FIG.
Are stored so as to circulate infinitely. The screw shaft 6 is driven by a motor 8.

As shown in FIG. 3 (b), the balls 9 housed in the ball screw 5 have no difference in ball diameter and all can receive a load, that is, a total load ball. It is a specification.

[0005]

When a vehicle equipped with the above-mentioned CVT is mounted on a so-called town, the vehicle repeats between the LO gear side and an intermediate position between the LO gear and the Hi gear while continuously changing the speed. There are many uses. The moving distance of the variable pulley in the CVT is usually as short as about 30 mm even at a full stroke of Lo to Hi.
Since the number of rotations of the ball screw 5 is reduced to about 1 to 2 times, and sometimes to 1 or less, when the lead is about 4 mm, the moving distance of the movable pulleys 1b and 2b becomes very short.

[0006] In the ball screw in the above use condition, the same tendency as in the case where the ball screw has been subjected to a rocking motion repeating a reciprocating motion occurs. That is, when the ball screw 5 reciprocates, as shown by an arrow in FIG. 3B, the adjacent balls 9 rotate in the reverse direction, so that relative lubrication between the balls 9 causes local lubrication failure, Slip friction occurs. As a result, the efficiency of the ball screw 5 for moving the movable pulleys 1b, 2b is degraded, and further, smooth shifting is hindered.

[0007] The relative slip as described above may also be caused by vibration of an engine of an automobile or the like.

Accordingly, the present invention provides a CVT capable of performing a smooth continuously variable transmission by eliminating relative slip between balls.
It is an object to provide a ball screw for driving a movable pulley.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method of rolling a large number of balls between ball screw grooves formed on a screw shaft and nuts fitted thereto. In a ball screw housed movably,
The balls are formed by a load ball supporting a load and a spacer ball having a smaller diameter than the load ball, and the balls are arranged such that one spacer ball is interposed between the two load balls. That is, the belt-type continuously variable transmission is used for driving a movable pulley.

[0010] According to the above configuration, since the adjacent balls rotate in the forward rotation direction, relative slip between the balls in the forward rotation portion can be eliminated, and the efficiency of the ball screw can be increased.

The ratio of the number of the spacer balls to the number of the load balls is set to any one of 1: 1, 1: 2, 1: 3, and 1: 4, and the diameter of the spacer balls is set to the diameter of the load balls. On the other hand, a configuration formed smaller by 10 μm to 100 μm can be adopted.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The ball screw 5 of the embodiment shown in FIG. 1 is a movable pulley 1 of the CVT shown in FIG.
b, 2b, which is used as a driving ball screw, in which a nut 7 is fitted to a screw shaft 6 in the same manner as described above. Many load balls 9a and spacer balls 9b are interposed between 11 'at a ratio of 1: 1 (FIG. 1 (b)).
reference).

The spacer ball 9b is formed to have a ball diameter smaller than the load ball 9a by 10 to 100 μm, preferably smaller by 20 μm to 50 μm.
It is incorporated so as to be adjacent to a. Adjacent balls 9
a and 9b rotate forward as shown by the arrow, and the ball 9
The relative slip between a and 9b is suppressed.

The load balls 9 of the spacer balls 9b
When the ball diameter difference with respect to a is less than 10 μm, the diameter difference from the load ball 9a, that is, (diameter of the load ball 9a) −
Since the (diameter of the spacer ball 9b) is too small, it is difficult to improve the efficiency and obtain the effect on the relative slip between the adjacent balls. In the case of 100 μm or more, the thread groove 1
Because the gap between 1, 11 'and the ball 9b becomes excessive,
The ball 9b does not roll smoothly, and a smooth operation of the ball screw cannot be obtained. The diameter difference is preferably 20 μm
５０50 μm.

The above-mentioned spacer ball 9b and load ball 9
As the ratio of the number of a, in addition to the above 1: 1, 1: 2,
1: 3 or 1: 4.

In the case of 1: 1, as shown in FIG. 1 (b), all the adjacent balls of the load ball 9a and the spacer ball 9b rotate forward, and the relative slip is eliminated. In the case of 1: 2, as shown in FIG. 1 (c), reverse rotation occurs on the surface where the load balls 9a are in contact with each other, and the lubrication state is locally severer, but it is in contact with the spacer ball 9b On the side, forward rotation occurs and relative slip is eliminated. The reverse rotation surface is located on one side of each load ball 9a.
The efficiency is higher than (b). Even in the case of 1: 3 (see FIG. 1D) or 1: 4, the surface in contact with the spacer ball 9b rotates forward, so that the efficiency is higher than that of the full load ball specification. However, in order to obtain stable high efficiency, 1: 1 or 1: 2 is preferable.

In general, the efficiency of a ball screw is determined by measuring the dynamic torque of a nut when an axial load is applied to the ball screw as a measurement torque, and calculating the dynamic torque theoretically calculated when the ball screw has no friction. Assuming the theoretical torque, it means (measured torque) / (theoretical torque) × 100 [%]. In other words, poor efficiency means that the friction is large and the nut cannot be moved smoothly.

[Embodiment] For a ball screw having the specifications shown in Table 1, the ratio (ball ratio) of the number of the spacer balls 9b to the number of the loaded balls 9a is 1: 1.
For the cases of 1: 2, 1: 3, and 1: 4, the efficiency on the forward rotation side (forward efficiency) and the efficiency on the reverse rotation side (reverse efficiency) were measured. Table 2 shows the results.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

As described above, the ball screw for driving the movable pulley of the CVT according to the present invention eliminates the relative slippage between the adjacent balls and the spacer balls. It is possible to reduce friction between balls caused by vibrations of an engine of a car, etc., to prevent local lubrication failure, to prevent an increase in ball screw torque (decrease in efficiency), and to smooth a CVT shift. it can.
In addition, as a result of reducing the friction between the balls, the life of the ball screw can be extended, and the life of the CVT can also be extended.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view showing a part of an embodiment. FIGS. 1B to 1D are schematic partial enlarged cross-sectional views of the embodiment.

FIG. 2 is a schematic diagram of a CVT.

FIG. 3A is a cross-sectional view showing a part of a conventional example. FIG.

[Explanation of symbols]

 1 Input Pulley 1a Fixed Pulley 1b Movable Pulley 2 Output Pulley 2a Fixed Pulley 2b Movable Pulley 3 Belt 5 Ball Screw 6 Screw Shaft 7 Nut 8 Motor 9 Ball 9a Load Ball 9b Spacer Ball 11, 11 'Ball Screw Groove

Claims (3)

[Claims] 1. A ball screw comprising a plurality of balls rotatably accommodated between opposing ball screw grooves formed in a screw shaft and a nut fitted to the screw shaft. And a spacer ball having a smaller diameter than the load ball, and each of the balls is arranged so that one spacer ball is interposed between the two load balls. A ball screw used for driving a movable pulley of a transmission. 2. The ball screw according to claim 1, wherein the ratio between the number of the spacer balls and the number of the load balls is one of 1: 1, 1: 2, 1: 3, and 1: 4. 3. The ball screw according to claim 1, wherein a diameter of the spacer ball is smaller than a diameter of the load ball by 10 μm to 100 μm.