JP2000346689A - Improvement of noncircular gear and noncircular gear- type flowmeter using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a metering error in a small flow-rate region by reducing the leak amount of a tooth tip gap. SOLUTION: A noncircular gear in an oval gear-type flowmeter is formed of a continuous curve wherein its major axis parts are formed of arcs of r=a/(1-b), its minor axis parts are formed of arcs of r=a/(1+b) and parts between them are connected by oval curves of r=a/[1-b cos (πθ/θ0)] (0<=θ<=θ0) [where (a) represents a similarity factor and (b) represents a flatness degree]. Thereby, the number of teeth of a gear coming into contact with the inner wall surface of a metering chamber is increased, the leakage amount of a tooth tip gap is reduced, and a metering error can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved non-circular gear in a non-circular gear flow meter and a non-circular gear flow meter using the same.

[0002]

2. Description of the Related Art FIG. 3 is a schematic diagram of a conventional oval gear type flow meter using an oval gear. A rotation chamber O _{1 is provided} in a measuring chamber 3 in which an inlet 1 and an outlet 2 are integrally formed. , O ₂
Is a fixed point, and the rolling contact is made at a distance of r ₁ , r ₂ given as a function of the rotation angles θ ₁ , θ ₂ from each fixed point. R ₁ + r ₂ = constant (1) r ₁ · dθ ₁ = pitch curve satisfying _{r 2 · dθ 2 ... (2} ) r i = a / (1 ± bcos2θ i) (i = 1,2) ... (3) ( where, a is similar factor, b is flatness The rotors 4 and 5 of the oval gear are rotatably supported and contained.

[0003] The oval gear flow meter, as is well known, the torque difference based on the difference P inflow pressure P ₁ and the outlet pressure P ₂ of the fluid to be measured, both oval gear is rotated in the arrow direction, 1 A volume of fluid that is four times the three-month volume V formed by the measuring chamber and the oval gear per rotation is delivered. This oval gear type flow meter is excellent in sensitivity to a small flow rate because the influence of physical properties (density, viscosity) and flow velocity distribution of the fluid is small. Here, assuming that Q is the fluid passing amount within a predetermined time, n is the number of rotations, and q is the amount of leakage from the gap between the gear and the measuring chamber wall, Q = 4Vn + q (4) The quantity q becomes the weighing error.

[0004]

However, the leakage amount q is determined by the leakage qδ of the tooth gap and the leakage qS of the side clearance.
In particular, in the minute flow rate range, the proportional relationship between the rotation of the non-circular gear, which is the rotor, and the flow rate is lost, and the leak qδ due to the tooth gap which can be ignored normally becomes a problem as an error. q = qδ + qS (5)

[0005] Figure 4 is a enlarged view of a gap tooth tips and the metering chamber of the gear, in FIG. 4, the pressure difference between the inlet pressure P ₁ and the outlet pressure P ₂ of the fluid to be measured P, the viscosity of the non-measured fluid , The gap between the tooth tip and the wall surface of the measuring chamber is δ, the peripheral speed of the tooth tip is U, the number of teeth whose tooth tip is in contact with the wall surface of the measuring chamber is z ₀ , the tooth thickness is t, When the width is w, the leakage amount Qderuta addendum gap is represented by ^{qδ = (P · δ 3/} 6 · z 0 · t · μ-U · δ) w ... (6).

An object of the present invention is to reduce a measurement error in a small flow rate region by reducing a leak amount qδ of a tooth gap in a non-circular gear type flow meter as described above.

[0007]

According to the equation (6), in order to reduce the amount of leakage qδ in the tooth gap, the number z ₀ of the teeth whose teeth are in contact with the wall surface of the measuring chamber is reduced. It turns out that more should be done. According to a first aspect of the present invention, there is provided a non-circular gear type flowmeter characterized in that the major axis and the minor axis of the pitch curve are arcs concentric with the measuring chamber and are connected by an oval curve. It relates to a gear.

According to a second aspect of the present invention, in the oval gear type flow meter having a pair of oval gears that mesh and rotate according to the flow rate, each oval gear uses the non-circular gear according to the first aspect. Accordingly, the present invention relates to a flowmeter in which the number of teeth whose teeth are in contact with the inner wall surface of the measuring chamber is increased and the amount of leakage from the tooth gap is reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a pitch curve of a non-circular gear according to the present invention and a pitch curve of a conventional oval gear. The pitch curve of the non-circular gear according to the present invention is a condition where the rolling contact is made at a distance r provided from the fixed point as a function of the rotation angle θ with the rotation center O of the non-circular gear as a fixed point. A pitch curve that satisfies (2), where r = a / (1-b) (arc) between A and B r = a / (1-bcos (πθ / θ ₀ )) between B and C (oval curve ) Between C and D r = a / (1 + b) (circular arc) (where a is a similarity coefficient and b is a flatness) (7)

Here, when θ ₀ is obtained, since the length of the curve between A and B and the length between C and D are equal from the rolling contact condition, a · θ _A / (1-b) = a Θ _B / (1 + b) (where θ _A is the central angle of arc AB, θ _B is the central angle of arc CD) θ ₀ = π / 2− (θ _A + θ _B ) = π / 2−2 · θ _A / (1-b) (8) FIG. 2 shows an example in which the flatness b is set to 0.1, 0.2, 0.3.
FIG. 5 is a diagram showing a pitch curve of a non-circular gear according to the present invention and a pitch curve of a conventional oval gear in the first quadrant portion in detail when the above is set.

[0011] In the non-circular gear formed by the pitch curve profile defined by the above equation (7) of the present invention, the tip of the gear provided on the arc portion extending over the central angle 2 × θ _{A of the} long diameter portion has all the teeth. It comes into contact with the inner wall of the measuring chamber. On the other hand, in the conventional oval gear formed by the oval curve represented by the above equation (3), only the tip of one to three gears is theoretically in contact with the wall surface of the measuring chamber. As described above, conventionally, at most about 1 to 3 tooth tips of gears are in contact with the wall surface of the measuring chamber, whereas in the present invention, the inner diameter of the measuring chamber is equal to the tooth tip of the non-circular gear, and the center of the non-circular gear is equal. can be increased freely by selection of the size of the angle theta _a, preferably by 5 to 7 carbon atoms, it can greatly reduce the leakage from the tooth tip to the fraction of comparison with the conventional .

Further, since the two arc portions of the long diameter portion and the short diameter portion of the gear are connected by a single continuous oval curve, the tangent angles at the connection points B and C of the arc and the oval curve are continuous. In addition, since a non-circular gear having a pitch curve that changes smoothly with a small change in relative angular acceleration is realized, the inertial force interacting with the non-circular gear becomes smooth. As a result, local wear of the tooth profile as in the conventional example is reduced, and not only the durability is increased, but also the change in friction torque caused by the increase in the tooth profile contact pressure is reduced, so that the flow meter device With improved accuracy and stability,
Further, it is possible to realize a volume flow meter having extremely excellent characteristics such as reduced noise during operation. If the major axis of the non-circular gear according to the present invention matches the internal diameter of the measuring chamber, it goes without saying that the rotor of the conventional oval gear can be replaced structurally.

[0013]

As described above, according to the present invention, the number of teeth of the gear in contact with the inner wall surface of the measuring chamber is obtained by forming the major axis of the pitch curve of the non-circular gear into an arc concentric with the measuring chamber. Can be increased, and the amount of leakage of the tooth gap can be reduced. In addition, by connecting a single oval curve between the long diameter part and the short diameter part which are concentric arcs with the measuring chamber, the fluctuation of tangential acceleration becomes smooth, and the tooth peculiar to the oval gear flow meter. Can be prevented from being locally worn, and the adverse effects associated with the pulsation of the measurement fluid can be reduced. Then, by simply using the measuring chamber of the conventional oval gear type flow meter and replacing the used oval gear with the gear of the present invention, it can be changed to a highly accurate flow meter.

[Brief description of the drawings]

FIG. 1 is a diagram showing a profile of a non-circular gear of the present invention.

FIG. 2 is a detailed view of quadrant I of the profile of the non-circular gear of the present invention.

FIG. 3 is a view showing a conventional oval gear flow meter.

FIG. 4 is an enlarged view of a clearance between a tooth tip of a gear and a measuring chamber.

[Explanation of symbols]

1 ... inlet, 2 ... outlet, 3 ... measuring chamber, 4,5 ... rotor
(Non-circular gear), 10: profile of non-circular gear according to the present invention, 20: profile of conventional oval gear.

Claims (2)

[Claims] 1. A non-circular gear type flow meter characterized in that a long diameter portion and a short diameter portion of a pitch curve of a non-circular gear are arcs concentric with a measuring chamber and are connected by an oval curve therebetween. Non-circular gear used. 2. A non-circular gear type flow meter having a pair of non-circular gears which mesh and rotate according to a flow rate, wherein the non-circular gear according to claim 1 is used as each non-circular gear. Flow meter.