JP3229429B2 - Micro volume flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a micro-volume flow meter, and more particularly to a micro-volume flow meter having a bearing structure in which a micro-diameter rotor shaft is fixed in a measuring chamber via a shaft holder.

[0002]

2. Description of the Related Art As is well known, in a positive displacement flowmeter, a pair of rotors are driven to rotate by a fluid differential pressure of a measurement fluid in a measuring chamber.
This is a flow meter of the actual measurement type that measures the flow rate by using the fact that the fluid in the measuring chamber is proportional to the rotation speed of the rotor. Since the rotor of the flowmeter rotates in proportion to the flow rate in this way, the main part of the volumetric flowmeter is composed of a measuring chamber, a rotor, a rotor shaft, and a bearing for bearing the rotor shaft. ing. In many medium and small volume flow meters, a so-called fixed shaft type in which one end of a rotor shaft is fixed in a measuring chamber and a bearing is fitted in the rotor. As described above, the fixed-shaft type volume flow meter has a simple structure, and therefore, particularly in a minute volume flow meter, the fixed-shaft structure is the mainstream.

[0003] As described above, the volume flow meter is a volume flow meter that measures the flow rate from the number of revolutions of the rotor with the volume of the fluid in the measuring chamber removed by the rotor as a reference volume. An ideal volumetric flow meter is one in which the flow is removed from the metering chamber in the zero to flow range without fluid leakage. That is, the rotor is rotated by a rotational moment acting on the rotor due to a pressure difference between the front and rear of the rotor, but an ideal volume flow meter is a flow meter with zero differential pressure. However, since the differential pressure changes due to various factors and the reference volume also changes due to the leak based on the differential pressure, it is impossible to actually realize an ideal volumetric flowmeter with zero differential pressure. is there.

As described above, in an actual volumetric flowmeter, the reference volume of the fluid removed from the metering chamber by the rotor is not constant from a small flow rate to a large flow rate range, and various error factors are added. One of them is friction torque due to bearing friction. Naturally, the rotational moment due to the measurement fluid acting on the rotor is large at a large flow rate and small at a small flow rate.
If only bearing friction torque is taken into account, the friction torque can be neglected in the large flow rate region compared to the rotational moment of the rotor if the lubrication of the bearing is sufficient, but cannot be ignored in the small flow rate region and the rotational moment and the bearing friction torque The rotor stops when a collision occurs. As a result, the rotation speed and the flow rate of the rotor are proportional to the flow rate in the large flow rate range, but in the small flow rate range, fluid leaks from the minute gap between the rotor and the measuring chamber wall until the rotor stops, and The proportional relationship with the rotation of the rotor is lost, and the rotation of the rotor gradually decreases toward the flow rate that comes to a stop.

[0005] Among the factors of the above-mentioned reduction in accuracy, in order to reduce bearing friction, it is necessary to combine materials which reduce the mutual surface roughness and friction coefficient in order to reduce the sliding resistance between the shaft and the bearing. Alternatively, the condition is that the surface area of the shaft is reduced and the shaft diameter is reduced. However, in the case of a fixed shaft fixed in a measuring chamber with a reduced shaft diameter, the shaft easily falls down, and it is difficult to properly secure the rotation center of the rotor.

FIG. 3 shows an inner chamber 2 of a conventional minute volume flow meter.
FIG. 1 shows a state in which the rotor shaft is press-fitted into 1, in order to clarify the state, a state in which the rotor shafts 23 and 24 are press-fitted into the inner chamber portion 21 at an extremely inclined angle.
The rotor shafts 23 and 24 are minute linear members of the same outer diameter, for example, stainless steel having an outer diameter of 0.3 mm. Weighing room 2
2 is provided on the bottom surface 22a of the inner chamber 21 having the rotor shaft 2
A pair of parallel shaft holes 21 slightly smaller in diameter than 3, 24
The rotor shafts 23, 24 having a small diameter are placed in a measuring chamber 22 having a small volume and a complicated shape in which a and 21b are perforated vertically.
It is difficult to press-fit into the shaft stand holes 21a and 21b in parallel, and a failure such as inclination or bending occurs as shown in the figure, resulting in poor yield.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a cylindrical shaft holder having a shaft hole as a center axis.
One end of a small-diameter rotor shaft is inserted in advance, and the outer peripheral surface of the shaft holder into which the rotor shaft is inserted is press-fitted or adhered to a precisely drilled holder hole on the bottom surface of the measuring chamber 22. Rotor shafts with high accuracy
An object of the present invention is to provide a high-precision micro volume flow meter at a low cost, which enables the fixing with good yield.

[0008]

To achieve the above object, the present invention provides (1)
A main body having a measuring chamber communicating with an inflow and an outflow of a measurement fluid, a pair of rotors rotating in proportion to the flow rate of the measurement fluid in the measurement chamber, and a rotor shaft rotatably supporting the rotors And a cylindrical body, having a shaft holder that fits one end of the rotor shaft to a shaft center and fixes the rotor shaft to the end face of the measuring chamber via the cylindrical body. In 1), the end face of the shaft holder on the measuring chamber side is higher than the measuring chamber end face by the same plane as the measuring chamber end face or by a distance equal to the thrust float dimension defined between the measuring chamber end face and the rotor. It is characterized by the following. Hereinafter, a description will be given based on examples of the present invention.

FIGS. 1A, 1B and 1C are views for explaining the structure of a micro volume flow meter according to the present invention.
The figure is a cross-sectional view taken along the line AA of the figure (b), and the figure (b) is
(A) is a cross-sectional view taken along line BB in the figure, and (c) is a view showing the rotor shaft inserted into the shaft holder.
2 is the inner chamber, 3 is the measuring chamber, 4 is the inlet, 5 is the outlet,
Reference numerals 6, 7 are rotor shafts, 8, 9 are shaft holders, 10, 11 are rotors, 12 is a lid, and 13 is a thrust ring.

1A is an integral member having a measuring chamber 3, an inlet 4 and an outlet 5 communicating with the measuring chamber 3, and the measuring chamber 3 is closed by a lid 12. Inner room 2 and lid 1
2 form the main body 1. The measuring chamber 3 includes the rotor 1
This is a room for rotating reference numerals 0 and 11 with a small clearance by a thrust ring 13 and the like, with a small friction torque, and for discharging a reference fluid having a reference volume introduced by rotation of the rotors 10 and 11. . The illustrated rotors 10 and 11
Is a pair of non-circular gears, which mesh with each other,
It rotates on the basis of the pressure difference between the fluid and the outlet 5. The rotor shafts 6 and 7 are linear cylindrical linear bodies made of stainless steel or ceramics having a small diameter and the same dimensions, and their surfaces are polished.

One end of the rotor shaft 6 (same for the rotor shaft 7) is fitted in a rotor shaft hole 8a of the shaft holder 8 as shown in FIG. The shaft holder 8 is a cylindrical body having a central axis passing through the rotor shaft hole 8a, and has an outer diameter of the rotor shaft hole 8a.
Much larger than the inside diameter of Therefore, the shaft holder 8 can be easily machined into a cylinder with high concentric accuracy.

On the other hand, holder holes 2b, 2b penetrate through the bottom surface of the measuring chamber 3 formed in the inner chamber part 2 at a distance between the axes of the rotating elements 10, 11. The holder hole 2b is slightly smaller or substantially the same diameter as the outer diameter of the shaft holder 8, and the outer periphery of the shaft holder 8 in which the rotor shaft 6 shown in FIG. The surface 8b is fixed by press-fitting or bonding with an adhesive. Shaft holders 8, 9 machined separately
In addition, since the large-diameter holder hole 2b can be machined with high dimensional accuracy, remarkable shaft-standing accuracy can be ensured as compared with the conventional case where a small-diameter rotor shaft is directly press-fitted into the bottom of the measuring chamber.

FIG. 2 is a view for explaining another embodiment of the micro-volume flowmeter according to the present invention, in which parts having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG. are doing.

In FIG. 2, upper end surfaces 8 of shaft holders 8, 9 are shown.
c and 9c are used in place of the thrust ring 13, and the shaft holders 8 and 9 are attached to the rotors 10, 1 with respect to the bottom surface 2a of the measuring chamber.
In order to maintain a clearance from the first member, the member is press-fitted or bonded with a distance of d. Therefore, a special thrust ring 13 is not required.

[0015]

As is apparent from the above description, according to the present invention, one end of the rotor shaft is set in the measuring chamber on the outer peripheral surface of the shaft holder portion which is previously inserted into a separately provided shaft holder. I have. Since the shape of the shaft holder is large and easy to machine, machining of the shaft stand alone with the shaft holder can be performed with high precision, and the shaft can be easily formed by press-fitting or bonding the shaft. In addition, the shaft holder hole drilled in the bottom of the weighing chamber in the inner chamber has a large diameter that is easy to machine, so high-precision machining can be easily performed, and the shaft holder with a rotor shaft can also be easily press-fitted. . As a result, the rotor shaft having an extremely small diameter can be easily and accurately assembled in the inner chamber, so that a shaft friction torque having a small value can be obtained, and instrumental performance is improved. Further, since the clearance in the thrust direction can be obtained by press-fitting the shaft holder using a jig, a stable instrument difference characteristic can be obtained without requiring a thrust ring.

[Brief description of the drawings]

FIG. 1 is a view for explaining the structure of a micro volume flow meter according to the present invention.

FIG. 2 is a view for explaining another embodiment of the shaft stand of the micro volume flow meter according to the present invention.

FIG. 3 is a diagram showing a state in which a rotor shaft is press-fitted into an inner chamber portion of a conventional minute volume flow meter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Main body, 2 ... Inner chamber part, 3 ... Measuring chamber, 4 ... Inlet, 5 ...
Outlet, 6, 7 ... rotor shaft, 8, 9 ... shaft holder, 10,
11 ... rotor, 12 ... lid, 13 ... thrust ring.

Continuation of the front page (56) References JP-A-4-343027 (JP, A) JP-A-63-199027 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01F 1 / 00-9/02

Claims (2)

(57) [Claims] 1. A main body having a measuring chamber communicating with an inflow and an outflow of a measurement fluid, a pair of rotors rotating in proportion to the flow rate of the measurement fluid in the measurement chamber, and a rotatable shaft. A rotor shaft to be supported, and a cylindrical body, wherein one end of the rotor shaft is inserted into a shaft center and the shaft holder is fixed to the end face of the measuring chamber through the cylindrical body. Micro volume flow meter. 2. An end face of the shaft holder on the measuring chamber side which is higher than the measuring chamber end face by a distance equal to the thrust floating dimension defined between the measuring chamber end face and the rotor. 2. The micro volume flow meter according to claim 1, wherein: