RU2674641C2 - Gear and belt drive and method of making the smallest of its pulleys - Google Patents

Abstract

FIELD: machine building.SUBSTANCE: group of inventions relates to the field of engineering, namely to the transfer of machine tools and mechanisms. Toothed belt drive contains gear pulleys. For the smaller of the pulleys that work together, the number of teeth is a function of the angle at the top of the tooth of the belt used. At the same time, the sides of the tooth profile are flat and parallel to each other. Teeth are cut using the copy method using two disk cutters spaced at a distance equal to the cross-section of the tooth. Thickness of each of the mills is less than the width of the depression, but more than half of it.EFFECT: increase in gear ratio is achieved.2 cl, 6 dwg

Description

The invention relates to the field of mechanical engineering, namely to the transmission of machine tools and mechanisms. It can be used in other areas of technology.

It is known that the gear ratio of the gear belt transmission depends on the ratio of the diameters of its pulleys. When designing machines, it is often necessary to increase this ratio. To increase the gear ratio of the stage, it is necessary either to increase the diameter of the larger pulley or to reduce the diameter of the smaller one. When transferring large powers, and long transmission operation modes, it is more profitable to increase the diameter of a larger pulley, and also use various methods of balancing the load between the belt surfaces and the pulley teeth (RF patents for inventions No. 20166290, 2051301, 2207460, 1668781, 1770644), while increases belt life. When transmitting relatively small torques and powers, as well as a short-term transmission operation mode, it is more advantageous to reduce the number of teeth and the diameter of a smaller joint pulley.

Toothed belts produced by industry have a profile at which the angle between the lateral planes of the tooth profile ϕ (Fig. 1.) is 40 ° (less often 50 °). Toothed pulleys are made with the same tooth profile. In the manufacture of pulleys, the fact is not taken into account that when the belt is bent, especially on the smaller of the transmission pulleys, the actual angle between the belt planes ϕ in contact with the pulley tooth is reduced (Fig. 2). Some pulley manufacturers reduce this angle, but by no more than 2 °. With large gear ratios, this is not enough.

On pulleys of small diameter, with a small number of teeth, it would be desirable to reduce the angle ϕ by a significantly larger value (Fig. 3). In the extreme case, this angle can be taken equal to zero. That is, the lateral planes of the pulley tooth are parallel to each other. Such a measure will make it possible to equalize the load along the contact plane, and ultimately reduce the number of teeth, the smaller of the jointly working pulleys. So, while maintaining the dimensions of the transmission, increase its gear ratio.

The stiffness of the toothed belt in bending, in any of its cross sections, is determined by the characteristics of the material and such geometric characteristics as the moment of inertia of section I.

Where

b is the width of the considered section;

h is the height in the considered section.

Applied to the belt:

b - belt width;

h is the height (or thickness) of the belt in the considered section.

For standard timing belts, the total profile height is at least 2.4 times greater than in the area between the teeth.

This means that the moment of inertia of the cross section, and hence the stiffness of the belt to bending, between the teeth, is 13.8 times less than in the teeth.

We can assume that when the belt is bent, its teeth practically do not change their geometric shape.

In this case, the same plane of the adjacent teeth of the pulley should be rotated by the angle at the top of the tooth.

The larger the angle at the apex of the tooth, the smaller the number of teeth can have a smaller number of pulleys working together.

For most standard timing belts, the apex angle is 40 °. In this case, the number of pulley teeth at which the side faces of the tooth are parallel to each other should be:

Z = 360: 30 = 12.

For belts with a tooth tip angle of 50 ° - 9 teeth.

The question immediately arises of a method for manufacturing the pulleys described above. The prior art methods of cutting the teeth of the pulleys by the method of rolling using worm cutters (RF patents for inventions No. 2169060, 2412027, 2396152, 2442678, 2414335). The break-in method is the most progressive, as it provides high labor productivity, good accuracy and surface cleanliness, at a low manufacturing cost. However, this manufacturing method, as the final type of processing, cannot be used in the manufacture of gear pulleys in which the sides of the tooth profile are parallel to each other. This is due to the fact that when cutting the teeth, the milling cutter and the workpiece, being meshed, run in each other with a change in the angle of relative position. In this case, when turning, the tooth will be jammed by the cutter, which contradicts the requirement of parallelism of the tooth lateral planes.

The prior art method of copying, when cutting gears, using dividing heads is widely known. It is less productive, but provides the specified geometry of the pulley. In this case, disk modular (less often finger) mills are used, made for a specific module and the number of pulley teeth. That is, the geometry of the cutting part of the cutter must exactly match the geometry of the cavity between the teeth. And it depends not only on the module, but also on the number of pulley teeth. In this case, the smaller the number of pulley teeth, the greater the angle of the cavity solution. While ensuring the parallelism of the lateral planes of the tooth profile, the angle of the depression can always be determined by the formula:

Where Z is the selected number of teeth of the manufactured pulley.

For each tooth module, and for each number of pulley teeth 2, an individual modular cutter 3 is required (Fig. 4). In this regard, this method of cutting teeth is quite acceptable for large-scale production, but is not acceptable for small-scale production.

The aim of the proposed method of cutting teeth is to significantly reduce the required range of cutters used when cutting the teeth of the pulleys. This is achieved by the fact that in the manufacture of the pulley 2 (Fig. 5), it is not the shape of the cavity that is formed, but the shape of the tooth, by means of two disk milling cutters 4, spaced apart by the washer 5 by a distance equal to the width of the tooth. The width of the cutter 4 should be less than the width of the cavity, but more than half.

The cavity between the teeth of the manufactured pulley 2 (Fig. 6) will consist of four pairwise intersecting planes. At the same time, the two middle ones intersect at an angle

ψ = 180-ϕ;

The presence of this kink in the plane of the cavity does not affect the transmission performance at all, since the belt 1 does not lie on this surface.

The technical task of the claimed group of inventions is:

1. Reducing the size and metal consumption of the gear-belt transmission, while maintaining the same gear ratio, or increasing the gear ratio, while maintaining the previous dimensions.

2. Reducing the cost of manufacturing pulleys.

The technical result of the claimed group of inventions is expressed in the use of a gear-belt transmission, characterized in that the sides of the tooth profile, the smaller of the jointly working pulleys, are made flat and parallel to each other, and the number of its teeth is a function of the angle at the top of the tooth used by the belt.

3. A method of manufacturing small pulleys of a toothed belt drive, characterized in that the cutting of the teeth is carried out by copying using two disk cutters, spaced apart from each other by a distance equal to the cross section of the tooth, and the thickness of each of the cutters is less than the width of the cavity, but more than half of it.

The essential distinguishing features of the claimed group of inventions are given in the distinctive parts of the claims.

The technical nature of the claimed group of inventions is illustrated by drawings.

In FIG. 1 shows the geometry of a belt-belt transmission.

In FIG. 2 shows a change in the geometry of the belt-belt transmission when it is bent.

In FIG. Figure 3 shows the geometry of the belt when it is bent close to the limit, on the smaller of the pulleys, the gear-belt transmission.

In FIG. 4 shows a method of cutting teeth by copying using a modular cutter.

In FIG. 5 shows the proposed method of cutting teeth using two disk cutters, spaced from each other by a distance equal to the width of the tooth.

In FIG. 6 shows that the belt does not lie on the flat intersecting surfaces of the cavity between the teeth.

Toothed pulley 2 (Fig. 5, and Fig. 6) with 12 teeth, is the smallest possible pulley with a toothed belt with ϕ = 40 °. This is due to the fact that on each subsequent tooth there is a rotation of the lateral contact surface by 40 °. At ϕ = 50 °, the minimum possible number of teeth would be 9.

In the process of transmission, on a straight section of the belt, the angle ϕ between adjacent planes of the depression remains the original (40 ° or 50 °). When switching to a circular motion, it decreases to zero. Then, when switching from a circular motion to a rectilinear one, it again increases to the initial one. Thus, with the minimum allowable number of teeth, it is advisable that the angle between the working planes of the pulley tooth is zero. That is, these planes were parallel to each other.

The method of cutting teeth of the smaller of the jointly operating pulleys shown in FIG. 5, does not require a large variety of modular cutters. It provides cutting teeth with simple disk cutters, removed from each other's goth at a distance equal to the width of the tooth. What is economically beneficial for small-scale production and a large range of manufactured pulleys.

The process of cutting teeth occurs as follows. The workpiece, the diameter of which is designed for a given number of teeth, is fixed in the dividing head, configured for a given number of teeth. Two disk cutters are selected, the thickness of which is less than the width of the cavity, but more than half of it. The cutters are mounted on the spindle of the milling machine, at a distance equal to the width of the tooth. This distance is determined by the washer sandwiched between the disk cutters. Then the teeth are cut using the copy method.

Claims (2)

1. Toothed belt transmission, characterized in that the sides of the tooth profile of the smaller of the working pulleys are made flat and parallel to each other, and the number of teeth is a function of the angle at the top of the tooth used belt. 2. A method of manufacturing a pulley according to claim 1, characterized in that the cutting of the teeth is made by copying using two disk cutters, spaced apart from each other by a distance equal to the cross section of the tooth, and the thickness of each of the cutters is less than the width of the cavity, but more than half .

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