GB2038946A

GB2038946A - Rotary Flowmeter

Info

Publication number: GB2038946A
Application number: GB7943554A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-12-21
Filing date: 1979-12-18
Publication date: 1980-07-30
Also published as: GB2038946B; DE2855292C2; FR2444930B1; IT1126188B; FR2444930A1; IT7983638A0; DE2855292B1

Abstract

A flowmeter of the orbiting-piston type has an annular measuring chamber 11 and a slotted ring-shaped piston 15 embracing a fixed partition 16, and a sensor (not shown) which extends through a bore 13 into the measuring chamber and detects orbital movement of the piston about a fixed hollow cylinder 18. The piston is kept in contact with the cylinder by magnetic means e.g. a permanent magnet 12. <IMAGE>

Description

SPECIFICATION Oscillating-piston Flowmeter The present invention relates to a flowmeter working on the oscillating-piston principle.

Oscillating-piston flowmeters consist basically of a cylindrical measuring or displacer chamber which is formed by an outside cylinder and an inside cylinder. The two cylinders are interconnected by a partition, so that the displacer chamber is divided. The dispiacer chamber contains a slotted oscillating piston or displacer whose slot clasps the partition. The diameter of the oscillating piston is chosen so that, when the piston rests against the inside wall of the outside cylinder, it simultaneously rests against the opposite outside wall of the inside cylinder, always along one generating line, so that three compartments are obtained which are sealed from each other.

Since the oscillating piston is freely movable, it is set into a rotary oscillatory motion (nutation) by the medium flowing into an outer compartment.

The oscillating piston is provided with mechanical means which permit its motion to be transmitted to a movement.

Such flowmeters have been known for a long time (German Patent 713,163) and are used as high-accuracy water meters. As stated in the foregoing, purely mechanical guidance of the oscillating piston takes place, namely the translatory guidance of the oscillating-piston slot by the partition in the measuring chamber and the circular guidance of the oscillating piston, whose center must be located at the axis of symmetry of the oscillating-piston flowmeter, because only there does the motion of the oscillating piston project itself as a circular motion (cf e.g., German Offenlegungschrift 27 03 549). The rigid connection between the oscillating piston and the movement presents additional sealing difficulties and, besides being of complicated design and thus substantially increasing the weight of the oscillating piston, imposes considerable requirements on manufacturing, accuracy.In addition, the rotary motion derived from the oscillating piston to mechanically drive the movement is not exactly proportional to the volume of fluid passing through the meter but varies periodically about a mean value (cf.

German Patent 713,163).

These properties of the known flowmeters have particularly unfavourable consequences or make the use of the meters impossible if measurements are to be performed at very small rates of flow, e.g. 1 I/h, and low pressure (e.g.

< 0.05 bars), as is necessary when measuring the fuel consumption of motor vehicles.

Accordingly, the object of the invention is to provide an oscillating-piston flowmeter which is simple in construction as well as reliable and accurate even on small flow rates.

The subject matter of the invention is an oscillating-piston flowmeter comprising a measuring chamber (displacer chamber) formed by two concentric cylinders and sealed by a bottom and a cover, and a ring-shaped piston (displacer) embracing the inside cylinder, the displacer being slotted to permit the two cylinders to be interconnected by a partition dividing the displacer chamber.

The invention is characterized in that the displacer is designed as a freely movable ring, that the ring-shaped displacer is magnetically guided so as to always rest against the inside wall of the outside cylinder along one generating line and against the outside wall of the inside cylinder along a generating line displaced by 1 800, and that there is provided at least one sensor which extends into the displacer chamber and converts the passage of the displacer into a count pulse by means of a suitable transducer.

The principle of the solution according to the invention thus consists in the fact that the purely mechanical guidance is replaced by a magnetic guidance.

According to an advantageous aspect of the invention, the magnetic guidance may be effected by making the displacer of soft magnetic material and placing an annular permanent magnet into the inside cylinder. The permanent magnet may be replaced by an electromagnet.

The annular magnet may also be magnetized only over a segment including an angle of 900, and pivoted about its central axis.

According to another aspect of the invention, however, it is also possible to effect the magnetic guidance by designing the displacer as a permanent magnet of hard magnetic material and making the inside cylinder and/or outside cylinder of the displacer chamber of soft magnetic material.

If the displacer is designed as a permanent magnet, it may also be advantageous to provide in the inside cylinder a yoke of soft magnetic material which has the shape of a ring segment and is pivoted about its central axis.

The invention has the advantage of being simple in construction; since there is no connection of moving parts between the displacer and the circular eccentric guide, practically no sealing problems are encountered. In addition, because of the easily movable displacer, the meter is so sensitive that accurate measurements are possible even at small flow rates and small pressure drops.

If the resolution of the indication is to be improved, according to a further aspect of the invention, several sensors may be spaced at equal intervals along the circumference of the outside cylinder.

As can be seen, the displacer, due to the magnetic attraction, touches both the cylindrical inside wall and the cylindrical outside wall of the displacer chamber along one generating line. The magnetic field strength may be chosen so that the force exerted by the moving incompressible fluid on the displacer will overcome the magnetic force only at the maximum desired flow rate. In this condition, the displacer moves away from the cylindrical walls of the displacer chamber and comes to rest. This protects the flow meter from overloading.

The invention will now be expiained in more detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a cross section of the novel flowmeter; Fig. 2 is a section taken along line A-B of Fig.

1; Fig. 3 is a section taken along line C-D of Fig.

1,and Fig. 4 shows four selected positions of the displacer during its movement.

The flowmeter in the embodiment shown in Figs. 1, 2 and 3 is a fuel (e.g. gasoline) flowmeter.

It has a three-part housing, consisting of the lower part 1, the middle part 2, and the upper part 3. These parts are forced together by means of screws 7, 8 and 9, with sealing rings 4, 5, and 6 placed between them to make the housing pressure-tight.

The lower part 1 has inlet bores 10 and outlet bores 10', into which unions for hose pipes (not shown) can be screwed. The inlet and outlet connections are interchangeable. The inside cylinder 18 and outside cylinder 19 of the middle part 2 form the displacer chamber 11 with a partition 1 6. The central bore 1 7 contains a permanent annular magnet 12, e.g. of ferrite. A lateral bore 1 3 in the outside wall serves to receive a suitable sensor 14 (e.g. proximity detector or sliding contact). The displacer 1 5 is a slotted cylindrical ring of soft magnetic steel.Its inside and outside diameters are chosen so that, when the displacer touches the inside wall of the displacer chamber 11, it also touches the diametrically opposed generating line of the outside wall of this chamber.

The upper part 3 forms the upper end face of the displacer chamber 11 and contains only the grooves for the sealing rings 4 and 5 as well as the through holes for the screws 7 and 8.

The operation is as follows: When the meter is at rest, the displacer 1 5 is in any position of its possible cycle of motions, since it is always attracted to the inside wall of the displacer chamber 11 by the permanent magnet 12. The displacer 1 5 thus blocks the passage from the inlet to the outlet and divides the chamber into four compartments A, A' and B, B', which, depending on the position of the displacer, are open toward the entrance side or the discharge side, as shown in Fig. 4.1. The medium flowing into the compartments A and B' urges the displacer 1 5 into the position shown in Fig. 4.2 and, hence, the contents of compartment B into the outlet. The compartment A has now reached its largest volume and is closed against entry of further fluid.The fluid pressure now acts exclusively in compartment B' and urges the displacer into the position shown in Fig. 4.3.

Compartment A thus opens towards the outlet 10', and the medium contained therein is forced out.

In the further course of events, compartment B' reaches its maximum volume, is blocked against entry of further fluid, and begins to open toward the outlet as shown in Fig. 4.4. This cycle repeats itself. Thanks to the symmetrical design, the direction of flow is reversible. The annular magnet 12 and the displacer 1 5 are shown schematically above Figs. 4.1 to 4.4. The dotted magnetic field lines indicate the magnetic flux conditions by their density.

The motion of the displacer 1 5 is converted into electrical pulses by suitable sensors 14, which respond at a given position of the displacer, and these pulses operate an electronic or electromechanical counter, which will not be described here. The present embodiment uses an electrical sliding contact which is insulated from the outside wall of, and extends slightly into, the displacer chamber 11. The circuit between the electrically conductive middle part and the sensor 14, designed as a sliding contact, is closed when the displacer passes by the sensor. By distributing several sensors evenly along the circumference of the housing, the cycle of operation of the displacer can be divided into individual steps, whereby the resolution of the indication is considerably improved. The individual contacts may be connected in parallel in the manner of a logic AND gate. In this manner, a continuous pulse sequence is obtained which can be registered with an inexpensive single-channel counting unit.

While the invention has been described with reference to an embodiment in which an annular magnet is provided and the displacer is made of soft magnetic material, it is also possible and sometimes appropriate or advantageous within the scope of the principle of the invention, i.e., magnetic guidance of the displacer, to design the displacer as a permanent magnet and make the cylindrical walls of soft magnetic material.

Claims

1. Oscillating-piston flowmeter comprising a measuring chamber (displacer chamber) formed by two concentric cylinders and sealed by a bottom and a cover, and a ring-shaped piston (displacer) embracing the inside cylinder, the displacer being slotted to permit the two cylinders to be interconnected by a partition dividing the displacer chamber, characterized in that the displacer is designed as a freely movable ring, that the ring-shaped displacer is magneticaliy guided so as to always rest against the inside wall of the outside cylinder along one generating line and against the outside wall of the inside cylinder along a generating line displaced by 1 800, and that there is provided at least one sensor which extends into the displacer chamber and converts the passage of the displacer into a count pulse by means of a suitable transducer.

2. A flowmeter as claimed in claim 1, characterized in that the displacer is made of soft magnetic material, and that the inside cylinder contains an annular permanent magnet.

3. A flowmeter as claimed in claims 1 and 2, characterized in that the magnetic force of the annular magnet can be produced by an electromagnet.

4. A flowmeter as claimed in claims 1 and 2, characterized in that the annular magnet is pivoted about its central axis and magnetized only in a segment including an angle of about 900.

5. A flowmeter as claimed in claim 1, characterized in that the displacer is a permanent magnet made of hard magnetic material, and that the inside cylinder and/or the outside cylinder are/is made of soft magnetic material.

6. A flowmeter as claimed in claims 1 and 5, characterized in that the displacer is a permanent magnet, and that the inside cylinder contains a yoke of soft magnetic material which is designed as a ring segment and pivoted about its central axis.

7. A flowmeter as claimed in any one or more of the preceding claims, characterized in that two or more sensors are spaced equidistantly along the circumference of the displacer chamber.

8. A flowmeter substantially as described herein with reference to the accompanying drawings.