JPH0139052B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a positive displacement flowmeter using a novel non-circular gear that exhibits less variation in meshing pressure angle, less wear, and is durable.

In general, the tooth profile of a non-circular gear (elliptical gear known as the trade name OVAL) used as a rotor in a positive displacement flow meter is formed as an involute tooth profile, and the reference rack tooth profile that makes rolling contact with the pitch curve has a pressure angle. It is a straight line that is constant. That is, to explain the structural analysis diagrams of conventional elliptical gears shown in FIGS. 1 to 4, the standard rack tooth profile curve g that makes rolling contact with the pitch curve l has a constant pressure angle α. It is a straight line.

For this, the instantaneous center o of the non-circular pitch curve l
A tooth profile is carved against (the center of curvature of the pitch curve),
The meshing pressure angle α _c at this instantaneous center o has approximately the same configuration as a normal internal gear.

However, the meshing pressure angle α′ _c with respect to the rotation center o′ of the elliptical gear is the tangent angle of the pitch curve l to σ
Then, α' _c = β'± (π/2-σ) + α ... (), and especially at pitch point P, α' = α± (π/2-σ) ... () . Therefore, if the value of α is constant, depending on the tangent angle σ of each pitch point P when teeth are placed on the pitch curve l, one tooth profile will have a larger meshing pressure angle, and the other tooth profile will have a larger meshing pressure angle. It can also be small and negative.

This phenomenon in which the meshing pressure angle α' _c with respect to the center of rotation o' becomes negative is unique to elliptical gears. When α _c > 0, the axial force Pd ( Pd > 0) works, but if α _c < 0 then Pd
<0, a force acts in the direction of reducing the center distance (wedge effect), which not only impedes smooth rotation and causes noise and vibration, but also has a serious effect on the instrumental error performance (especially low flow characteristics) of the flowmeter. affect.

This invention has been made by focusing on the above points, and is designed to assume different reference rack tooth profiles corresponding to the toothed positions of each tooth profile, and to maintain an ideal meshing relationship. The purpose of this invention is to obtain a positive displacement flowmeter using non-circular gears in which the meshing pressure angle α _c is not negative. Another object of the present invention is to construct a non-circular gear with a small flatness, that is, one close to a circular gear, so that the meshing pressure angle of the center of rotation at the pitch point is constant. An object of the present invention is to provide a positive displacement flowmeter using a non-circular gear.

An embodiment of the present invention will be described below regarding an elliptical gear called OVAL, whose pitch curve l is expressed by ρ=a/1−b cos 2θ.

First, the embodiment shown in FIG. 5 is an embodiment having a pitch curve l with a large degree of flatness, and the tooth profile curve g according to the present invention is formed in the left half of the diagram, and the conventional tooth profile curve g is formed in the right half. It has been extracted for the purpose.
At this time, b=0.3 and z=26 (z is the number of teeth).
Reference numerals 1 to 13 and 1' to 13' indicate the positions of the respective tooth profiles.

The rotation center meshing pressure angle α′ _c of a conventional elliptical gear is α
If = 20 degrees, the result will be as shown in Fig. 6, and the meshing pressure angle of even-numbered teeth may be negative, and in particular, the meshing pressure angle of the tooth profile portion 6 is all negative in terms of the tooth profile.

By the way, in this invention, the substantial part of the tooth profile curve carved on the pitch curve of the non-circular gear is always toothed in the direction of the rotation center, so that the tooth profile parts 1 to 1.
13 is directed as far as possible toward the center of rotation o', thereby minimizing changes in the meshing pressure angle _α'c and ensuring that it never becomes negative. That is, the odd number of tooth profile parts 1', 3', 5', 7', 9', 1
1' and 13' prevent the increase in the meshing pressure angle _α'c by using a cycloid curve (the meshing pressure angle at the pitch point is π/2-σ), and the tooth profile parts 2' and 4 are even numbers. ', 6', 8', 10', and 12' are involute tooth profiles (large instantaneous center pressure angle α) that increase the meshing pressure angle α′ _c to prevent it from becoming negative. In addition, when a pair of teeth are meshed, meshing tooth sections 1' and 13', 2' and 12', 3' and 11', 4' and 10', 5' and 9', 6' and 8', 7 Since ' and 7' are in phase contact with each other, in the case of an involute tooth profile, they share the instantaneous central direction pressure angle α, and in the case of a cycloid tooth profile, it is necessary to keep their rolling circles in a shared relationship.

The rotation center engagement pressure angle α' _c calculated in this way is shown in FIG. 7, which was obtained under the condition that the minimum engagement pressure angle α' _c min=0.

According to this embodiment, unlike the conventional example shown in FIG. 6 described above, the meshing pressure angle α' _c of all the tooth profile portions 1' to 13' is positive, and smooth meshing rotation can be achieved.

Next, another embodiment based on a pitch curve with a small degree of flatness will be described with reference to FIG. In this embodiment, similarly to FIG. 5, the tooth profile according to the present invention is formed on the left half of the figure, and the conventional tooth profile is extracted on the right half for comparison. That is, an example is shown in which the number of teeth is the same as in the previous embodiment, but the value of b is relatively small, for example, b=0.15.

In this case, the rotation center meshing pressure angle at the pitch point can be kept constant (=20°), and α=20°〓(π/2−σ) for each toothed position, and even number teeth By using an involute tooth profile and an odd number of teeth having a composite tooth profile of an involute and a cycloid, it is possible to obtain an elliptical gear with little change in the meshing pressure angle at the center of rotation. Furthermore, Fig. 9 shows the change in the meshing pressure angle α′ _c of a conventional gear.
Although negative meshing occurs, in this embodiment, as shown in FIG. 10, all meshing pressure angles α' _c become positive meshing, and the same effects as in the previous embodiments can be obtained.

In addition, in the two embodiments described above, the desired elliptical gear can be obtained by combining the configurations of the left half shown in the drawings with line symmetry in the horizontal and vertical directions and point symmetry in the diagonal direction.

The elliptical gears shown in the two embodiments described above have a large wall thickness in the axial direction and are rotatably housed in pairs within the flow meter body occupying the desired measurement space, thereby achieving the desired volumetric flow rate. You can get the meter.

Further, in the above embodiments, only the case where the non-circular gear according to the present invention is an elliptical gear has been described, but it is also possible to obtain a non-circular gear such as a three-lobed or four-lobed gear in exactly the same manner.

According to this invention, since the tooth profile carved on the pitch curve is toothed in the direction of the rotation center, there is no unreasonable meshing, and meshing and rotation can be performed in the same manner as circular gears. Therefore, meshing noise can be reduced. It can be made small and rotate smoothly, and its durability can be significantly improved, so when used as a rotor in a positive displacement flowmeter, it has the effect of reducing rotational resistance and maintaining measurement accuracy for an even longer period of time. There is.

[Brief explanation of drawings]

1 to 4 are diagrams showing structural analysis of a conventional elliptical gear, and FIG. 6 and 7 are respective graphs of meshing pressure angles as above, FIG. 8 is a comparative explanatory diagram combining other embodiments of the non-circular gear according to the present invention and a conventional gear, and FIG. 9 and FIG. 10 is a graph of the meshing pressure angles of the same as above. 1 to 13...Tooth profile of conventional oval gear, 1'
~13′...Tooth profile portion of the elliptical gear according to the present invention,
l...Pitch curve, o...Momentary center, o'...Rotation center, _αc , _α'c ...Meshing pressure angle.

Claims (1)

[Scope of Claims] 1. Two non-circular gears are incorporated as a rotor so that the substantial part of the tooth profile curve carved on the pitch curve of the non-circular gear always meshes with each other in the direction of the center of rotation. A positive displacement flowmeter using a characteristic non-circular gear. 2. A positive displacement flowmeter using a non-circular gear according to claim 1, wherein the tooth profile curve is an involute curve. 3. A positive displacement flowmeter using a non-circular gear according to claim 1, wherein the tooth profile curve is a cycloid curve. 4. A positive displacement flowmeter using a non-circular gear according to claim 1, wherein the tooth profile curve is a composite curve of an involute curve and a cycloid curve.