GB1564901A

GB1564901A - Device for determining the pressure in a hydraulic or pneumatic system

Info

Publication number: GB1564901A
Application number: GB3557875A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1975-08-28
Filing date: 1975-08-28
Publication date: 1980-04-16
Also published as: DE2638785A1

Description

(54) A DEVICE FOR DETERMINING THE PRESSURE IN A HYDRAULIC OR PNEUMATIC SYSTEM (71) I, NILS AAGE JUUL EILERSEN, a Danish subject of 22W232 Gongehusvej, DK-29S6 Vedbaek, Denmark, do hereby declare the invention, for which I pray that a patent may be granted to me, to be particutardy described in and by the following statement: This invention relates to a device for determining the pressure in a hydraulic or pneumatic system.

It is known to measure such pressure by disconnecting a pipe or the like from the hydraulic or pneumatic system at some screw connection and instead to mount a pressure gauge, which may consist of a tubular clement surrounded by a capacitor electrode, the tubular element and the electrode forming a capar, the value of which depends on the degree of expansion of the element resulting from the pressure prevailing in the hydraulic system, the pressure gauge further comprising electronic means for producing a signal representative of the capacity value of said capacitor, which signal may be supplied to an electric measuring instrument calibrated 1n terms of pressure.

This procedure has the disadvantage that when the hydraulic system is opened as described impurities may penetrate into the system, and that the system must be put out of operation for as Iong as the measurement Xkes. The whole procedure is rather time consuming. Sometimes a pressure gauge of the type described is therefore permanently mounted in the system. However, the price of such a pressure gauge is prohibitive for many uses where inspection is only required from time to time.

m order to remove this drawback, an arrmgement has been proposed in U.K.

patent specification No. 1,402,756, in which an element of the system, which constitutes a flow passage in the normal operation of the system, is constructed with a wall of a length aRt thickness suitable for making it operable aa a pressure sensing member. As disclosed in the said U.K. patent specification the wall of trhe element is utilized as a pressure sensitive electrode and is permanently surrounded by a tubular element forming a counter iectrode of a pressure sensing capacitor, which may, when it is desired to determine the pressure within the element, be connected to a portable calibrated capacity measuring device. Thus, in the arrangement of U.K. patent specification No. 1,402,756, by a slight and inexpensive modification of an element, which in that case is an outlet valve of a fuel injection pump, the advantage has been obtained as compared with the normal pressure determining procedure for such systems that the determination takes place without any dismounting and mounting operations on the hydraulic system, and without having to put the system out of operation, and with the aid of a measuring device that does not form part of the system and therefore does not add to its price.

It is the object of the present invention to obtain a still further simplification and reduction of the price of the arrangement.

According to the present invention, there is provided a device for use in determining the pressure in a hydraulic or pneumatic system by sensing movement of the wall of a tubular element forming a flow passage of said system, which movement is in consequence of pressure variations in said flow passage, said device comprising a portable measuring tool in the form of a 'lamp being detachably engageable with said element and carrying at least one capacitor electrode which upon engagement of the clamp with said element is cooperable with said wall to form a capacitance whose value is variable in dependence upon the spacing between said electrode and said wall.

In this manner the advantages of the arrangement according to U.K. patent specification No. 1,402,756 are fully maintained and a simplification and reduction of costs is obtained by the fact that the electrode cooperating with the wall of the tubular element to form a measuring capacitor does no lower form part of the tubular element, but is carried independently thereof by the clamp.

The expenses incurred by keeping the system permanently ready for measuring therefore no longer fall on the hydraulic or pneumatic system, but n the measuring device which, as a workshop equipment, may be used for the testing of any system provided with a tubular element as above defined.

The capacitor electrode or electrodes may carry dielectric material which, upon engagement of the clamp with the element, is sandwiched between the capacitor electrode and the wall, whereby the capacitance value is increased and can be adjusted as desired by selection of the dimensions and the material.

Advantageously, two capacitor electrodes may be so arranged in the measuring clamp that upon engagement of the clamp with the wall of the tubular element said electrodes will be located symmetrically with respect to the axis of the element, whereby inaccuracies of measurement resulting from acceleration forces may be reduced.

Ordinarily it is recommendable to construct the measuring clamp in such a manner that it can be rigidly clamped on the tubular element. However, it is also possible, particularly where two capacitor electrodes carrying a dielectric material are symmetrically arranged, to construct the clamp in such a manner that it is resiliently yieldable and upon engagement with the tubular element is supported thereon via said dielectric material.

A particularly important example of the said tubular element is an outlet valve of a fuel injection pump. In the conventional construction of such a valve it is not suitable for sensing the injection pressure in the man- ner described above. However, in order to make it suitable for the purposes of the invention it suffices to make the wall of the housing of such a valve longer and thinner than in the conventional construction.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a longitudinal section through an outlet valve of conventional type as mounted on a fuel injection pump, Fig. 2 is a similar section through a modified outlet valve with one embodiment of a device according to the present invention applied thereto, Fig. 3 is a top view of the parts shown in Fig. 2, Fig. 4 is a longitudinal section through a valve with a device according to a second embodiment of the invention applied thereto, Fig. 5 is a longitudinal section through a valve with a device according to a third embodiment of the invention applied thereto, and Fig. 6 is a top view of the parts shown in Fig. 5.

A conventional screw fitting can be constructed as shown in the longitudinal section in Fig. 1 with a thread r for mounting the fitting on a machine part, such as the housing 2 of a fuel pump. A pipe can be connected to the fitting or valve housing by means of a cap engaging a thread 3 at the top of the fitting so as to engage a flange of the pipe with a conical seat 4 of the fitting. 5 is a ball which together with a spring symbolized by an arrow 6 forms a non-return valve which is necessary for the function of the fuel pump.

It will be realized that this non-return valve is just an example of the element referred to above and that where a valve is referred to in the following this could within the scope of the invention be replaced by any element of any hydraulic or pneumatic system, which constitutes a flow passage in the normal operation of the system.

In the embodiment of the invention illustrated in Fig. 2, the valve housing of the valve as illustrated in Fig. 1 has been made longer and its wall thickness has been reduced so that a tubular portion is formed which is suitable to be used as an electrode of a measuring capacitor because the outer shape of the cylindrical surface 7 of the said tubular portion is measurably changed when the pressure in the valve housing changes.

When it is desired to measure the pressure prevailing in the valve, a clamp 8 consisting of two pivotably connected jaws, see Fig. 3, is applied to the valve housing from the side and is rigidly clamped around the valve housing, e.g. by means of a wing-nut 8a.

The clamp 8 contains two capacitor electrodes 11 and 12. These may take the form of two halves of a cylindrical shell mounted insulated in the clamp in a position to become coaxial with the outer cylindrical surface 7 of the element. In that way a measuring capacitor is formed where the capacity depends on the distance between the surface 7 and the capacitor electrodes 11 and 12 and thus on the pressure in the valve. In connection with suitable electrical measuring circuits, that may be housed in the clamp, a signal is obtained corresponding to the pressure in the valve. Owing to the symmetrical arrangement of the capacitor electrodes 11 and 12, the influence of acceleration forces resulting from vibration of the equipment on which the valve is mounted is substantially eliminated.

The clamp 8 may preferably be mounted on stiff zones of the valve housing which zones then act as a reference surface, the measuring capacitor sensing the relative movement between the wall around the cavity and this reference surface.

The measuring device in Figs. 2 and 3 may be modified as shown in Fig. 4, by lining the inner surface of the capacitor electrodes 11 and 12 with a compressible or elastic dielectric material 13. This brings the advantage that the sensitivity of the measurement is increased, and that a short circuit between the capacitor electrodes and the surface 7 is less likely to occur. By replacing the mainly dielectric material with a mainly conducting material measurement is permitted both of a capacitive component and of a resistive component, which may be an advantage under humid conditions. This constitutes a further embodiment of the invention.

In applications of the measuring principle where the vibrations of the element are less pronounced, it is possible to dispense with the provision of a rigid reference surface by a clamp engaged with rigid portions of the element.

Thus, in the embodiment of Figs. 5 and 6, the measuring clamp is constructed in the form of a resiliently yieldable frame 14 con taining two capacitor electrodes 11 and 12 which are lined on their inner surface with compressible or elastic dielectric material 13 via which the frame 14 is directly supported on the surface 7. This dielectric material in creases the sensitivity and aligns the whole measuring device with the outer surface 7 of - the element A change of shape of the surface 7 resulting from pressure variations in the valve will change the distance between the capacitor electrodes 11 and 12 and the surface 7 and thereby change the capacity between these parts. By connecting the two capacitor electrodes together and to a suitable electrical circuit, that may be contained in the frame, a signal corresponding to the pressure varia tions is obtained. Small vibrations of the element with respect to the electrodes 11 and 12 will increase the distance between one electrode and the element and decrease the distance between the other electrode and the element. Thus, the sum of the distances and thereby the sum of the capacities is constant to a high degree, and the vibrations will give only a small error.

The frame 14 consists of two halves 14a, 14b which are pivotably connected at 14c and are urged towards one another by means of a helical spring 14d. Thereby it becomes possible to open the clamp sufficiently to apply it to the element from the side.

WHAT I CLAIM IS 1. A device for use in determining the pressure in a hydraulic or pneumatic system by sensing movement of the wall of a tubular element forming a flow passage of said system, which movement is in consequence of pressure variations in said flow passage, said device comprising a portable measuring tool in the form of a clamp being detachably engageable with said element and carrying at least one capacitor electrode which upon engagement of the clamp with said element is cooperable with said wall to form a capacit ance whose value is variable in dependence upon the spacing between said electrode and said wall.

2. A device as claimed in claim 1, in which the or each electrode carries a dielectric material which, upon engagement of the clamp with said element, is sandwiched between the electrode and said wall.

3. A device as claimed in claim 1 in which the or each electrode carries an electrically conducting material which, upon engagement of the clamp with said element, is sandwiched between the electrode and said wall.

4. A device as claimed in claim 2 or 3, in which the clamp is resiliently yieldable and upon engagement with said element is supported thereon via said material.

5. A device as claimed in any of claims 1 to 4, in which two said electrodes are so arranged in the clamp that upon engagement of the clamp with said element the electrodes are located symmetrically with respect to the wall axis.

6. A device as claimed in any of the preceding claims, in which the clamp is arranged to be clamped rigidly on the tubular element.

7. A device as claimed in any of the preceding claims, in which said tubular element is an outlet valve of a fuel injection pump.

8. A device for determining the pressure in a hydraulic or pneumatic system, said arrangement being substantially as hereinbefore described with reference to Figs. 2 and 3, or Fig. 4, or Figs. 5 and 6 of the accompany ing drawings.

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Claims

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capacitor electrodes and the surface 7 is less likely to occur. By replacing the mainly dielectric material with a mainly conducting material measurement is permitted both of a capacitive component and of a resistive component, which may be an advantage under humid conditions. This constitutes a further embodiment of the invention.

In applications of the measuring principle where the vibrations of the element are less pronounced, it is possible to dispense with the provision of a rigid reference surface by a clamp engaged with rigid portions of the element.

Thus, in the embodiment of Figs. 5 and 6, the measuring clamp is constructed in the form of a resiliently yieldable frame 14 con taining two capacitor electrodes 11 and 12 which are lined on their inner surface with compressible or elastic dielectric material 13 via which the frame 14 is directly supported on the surface 7. This dielectric material in creases the sensitivity and aligns the whole measuring device with the outer surface 7 of - the element A change of shape of the surface 7 resulting from pressure variations in the valve will change the distance between the capacitor electrodes 11 and 12 and the surface 7 and thereby change the capacity between these parts. By connecting the two capacitor electrodes together and to a suitable electrical circuit, that may be contained in the frame, a signal corresponding to the pressure varia tions is obtained. Small vibrations of the element with respect to the electrodes 11 and

12 will increase the distance between one electrode and the element and decrease the distance between the other electrode and the element. Thus, the sum of the distances and thereby the sum of the capacities is constant to a high degree, and the vibrations will give only a small error.

The frame 14 consists of two halves 14a, 14b which are pivotably connected at 14c and are urged towards one another by means of a helical spring 14d. Thereby it becomes possible to open the clamp sufficiently to apply it to the element from the side.

WHAT I CLAIM IS 1. A device for use in determining the pressure in a hydraulic or pneumatic system by sensing movement of the wall of a tubular element forming a flow passage of said system, which movement is in consequence of pressure variations in said flow passage, said device comprising a portable measuring tool in the form of a clamp being detachably engageable with said element and carrying at least one capacitor electrode which upon engagement of the clamp with said element is cooperable with said wall to form a capacit ance whose value is variable in dependence upon the spacing between said electrode and said wall.
2. A device as claimed in claim 1, in which the or each electrode carries a dielectric material which, upon engagement of the clamp with said element, is sandwiched between the electrode and said wall.
3. A device as claimed in claim 1 in which the or each electrode carries an electrically conducting material which, upon engagement of the clamp with said element, is sandwiched between the electrode and said wall.
4. A device as claimed in claim 2 or 3, in which the clamp is resiliently yieldable and upon engagement with said element is supported thereon via said material.
5. A device as claimed in any of claims

1 to 4, in which two said electrodes are so arranged in the clamp that upon engagement of the clamp with said element the electrodes are located symmetrically with respect to the wall axis.
6. A device as claimed in any of the preceding claims, in which the clamp is arranged to be clamped rigidly on the tubular element.
7. A device as claimed in any of the preceding claims, in which said tubular element is an outlet valve of a fuel injection pump.
8. A device for determining the pressure in a hydraulic or pneumatic system, said arrangement being substantially as hereinbefore described with reference to Figs. 2 and 3, or Fig. 4, or Figs. 5 and 6 of the accompany ing drawings.