WO2000036382A2

WO2000036382A2 - An apparatus for measuring internal pressure and method therefor

Info

Publication number: WO2000036382A2
Application number: PCT/IL1999/000661
Authority: WO
Inventors: Victor Spivak; Michael Gandelsman; Mark Novikov; Eugeny Kofman
Original assignee: Sonvert Ltd.
Priority date: 1998-12-11
Filing date: 1999-12-05
Publication date: 2000-06-22
Also published as: AU1511800A; WO2000036382A3; IL143581A0

Abstract

The internal pressure of a resilient-walled vessel such as a car tire is measured in accordance with a relationship between the internal pressure and representative parameter associated with vibrations submitted to the tire and response vibrations induced in the tire. The vibrations can be submitted to a wall of the vessel either by mechanical means or by piezo-electric means. The response vibrations are sensed and converted into electrical signals. The representative parameter is converted into pressure with the aim of previously established reference curve for the same vessel expressing dependence of the internal pressure on the representative parameter.

Description

An apparatus for measuring internal pressure and method therefor

Field of the invention

The present invention relates to measuring of internal pressure within a resilient-walled vessel. More particularly the invention refers to measuring of internal pressure of a pneumatically inflated tire of a vehicle.

Background of the invention

There are known various methods and devices which have been devised for measuring of internal pressure within a pneumatically inflated tire of a vehicle. Those means can be divided into various groups according to the principle of their operation:

The first group includes monitoring systems mounted on a vehicle wheel and capable to detect and indicate the pressure within a tire when the vehicle moves and the wheel spins. Those systems usually comprise non-contact sensors attached to the wheel and capable to activate an alarm to alert a driver that the pressure in one of his tires is abnormally low. An example of such a system is a tire pressure sensing system disclosed in US4330774.

The other group refers to gauges mounted on a wheel so as to be in air connection with the interior of a tire. Those devices operate when the wheel is not moving. An example of such a system is an electronic tire gauge disclosed in US5394343. This system comprises valve stem fitting means for receiving the valve stem of a tire and pressure transducer means coupled to the valve stem fitting means and capable to generate a pressure signal representing the pressure sensed.

The third group refers to pressure gauges operating without air connection with the tire and suitable for measuring of internal pressure of a non-moving wheel.

In US4615211 is disclosed a pressure gauge for tires and other elastic vessels which measures the pressure by sensing deformation of a wall of the vessel without establishing a connection to the interior of the vessel. The deformation within the wall of the vessel is induced by engagement of the wall by a deformable element. The engagement may be achieved by moving either the gauge or the vessel: the gauge could be swung to strike a tire or the tire could be driven onto the gauge. The pressure gauge comprises a deformable element, a rigid guard element surrounding the deformable element and means for sensing the deformation of the deformable elemenrt.

The sensing means measures the instant strain on the surface of the deformable element which is determined by its geometry and the pressure in the vessel.

Objects of the invention

The main object of the present invention is to provide a new and improved device for measuring internal pressure of a tire and a method therefor.

In particular the main object of the invention is to provide for a new and functionally versatile device which is capable to measure the internal pressure by inducing vibrations in the wall of a tire and by deriving the value of the internal pressure from the relationship between the internal pressure and a representative parameter defining said vibrations.

The other object of the present invention is to provide a new and improved device, which is inexpensive, simple and can be manufactured from available materials.

Still further object of the invention is to provide a device, which is convenient in use and is suitable to measure internal pressure of a tire reliably irrespective of its size.

The above and other objects and advantages of the present invention can be achieved in accordance with the following combination of its essential features, referring to the different embodiments thereof.

The first preferred embodiment of the present invention refers to an apparatus for measuring internal pressure within a resilient-walled vessel, said apparatus comprising

- an actuating means capable to submit vibrations to the vessel's wall so as to induce response vibrations emanated by the vessel's wall,

- a receiving means capable to sense said emanated vibrations so as upon transforming them into electrical signals to establish a relationship between the internal pressure and at least one representative parameter associated with said signals, said parameter correlating with the value of internal pressure to be measured - a processing means capable to process said relationship and to derive therefrom the value of internal pressure.

The actuating means may comprise a spring-loaded hammer releasable secured within a housing, said hammer is capable upon release thereof to protrude from the housing and to strike the vessel's wall so as to induce mechanical vibrations emanated thereby. As per an alternative embodiment said transforming means comprises an accelerometer. The accelerometer can be provided with a contact surface capable to perceive mechanical vibrations.

In yet another embodiment the contact surface is in physical contact with the vessel's wall so as to receive mechanical vibrations emanated therefrom and the accelerometer can reside within a carrier means coupled with the housing.

According to another alternative embodiment the carrier comprises a bracket made of resilient material, said bracket is capable to absorb mechanical vibrations induced by the actuating means In a further preferred embodiment the apparatus comprises a display means capable to visualize the value of internal pressure established by the computing means.

The apparatus may comprise also an amplifier capable to amplify the electrical signals generated by the transforming means.

In still further embodiment the actuating means and receiving means comprise respectively transmitting and receiving membrane, said membranes reside within a housing, said membranes are provided with respective tips protruding from the housing towards the vessel's wall so as to be in physical contact therewith and respectively to transmit mechanical vibrations to the vessel's wall or to receive response vibrations emanated thereby, said membranes are made of piezo-ceramic material and are mounted within the housing so as to be acoustically insulated therefrom.

The apparatus according to this embodimentt comprises a transformer for energizing the transmitting membrane and an electronic module, said module is capable to generate a reference signal with a phase ψ_A for initiating the transmitting membrane and to receive a response signal with a phase φ_B associated with the response vibrations emanated by the vessel^'s wall, said electronic module is coupled with the processing means. The electronic module can be electrically coupled with a normally open micro-switch for putting the transmitting membrane into operation upon establishing physical contact between its tip and the vessel's wall.

The processing means of the apparatus is provided with - a phase detector capable to establish phases associated respectively with the reference signal and the response signal, - a memory means for storing a pre-established calibration curve expressing dependence of internal pressure within the vessel on the phase shift Δ_φ=φA-φB, associated with the reference signal and response signal, - a micro-controller capable to establish the instant phase shift value and to translate this value into instant internal pressure according to the calibration curve stored in the memory means.

The present invention refers also to a method for measuring internal pressure within a resilient- walled vessel. In accordance with the first preferred embodiment of the method it comprises the following main sequence of steps:

- submitting vibrations to the vessel's wall and inducing response vibrations emanated by the vessel's wall,

- sensing said response vibrations and establishing a function defining a relationship between the internal pressure and at least one representative parameter associated with said vibrations, said representative parameter correlating with the value of internal pressure to be measured.,

- deriving the value of internal pressure within the vessel from a calibration curve empirically pre-established for the same kind of vessel having known internal pressure, said calibration curve expressing dependence of the internal pressure on the representative parameter.

In accordance with the second embodiment of the method the step of inducing of said vibrations is effected by mechanical means.

In the further alternative embodiment of the method the representative parameter is associated with the amplitudes of said vibrations and their frequencies and it can be set as at least one frequency set within the frequencies 2 and 400 Hz. According to an alternative embodiment of the method the step of submitting of said vibrations to the vessel^'s wall and the step of sensing of response vibrations is effected by piezo-electrical means.

In accordance with this alternative embodiment said representative parameter is set as phase shift associated with submitted vibrations and response vibrations.

For a better understanding of the present invention as well of its benefits and advantages, reference will now be made to the following description of its embodiments taken in combination with the accompanying drawings.

Brief description of the drawings

FigsJJ are examples of reference curves empirically pre-established for various tires

FigsJa-e depict the apparatus of the present invention when it is used in practice for

measuring internal pressure of a tire.

Fig.4 shows a cross-section of an actuator with a spring-loaded hammer residing therein.

Figs.5,6 are correspondingly signal-time relationship and amplitude-frequency relationship associated with the vibrations induced in a tire.

Fig.7 shows a computer generated flow-chart of an acquisition system of the present invention.

Fig.8 is an algorithm for processing of vibrations induced in a tire in accordance with the present invention.

Fig.9 is a display of the pressure measured by the apparatus of the present invention.

Figs. 10,1 1 are examples of reference curves empirically pre-established for various tires showing dependence of pressure on the delay of propagation of induced vibrations. Figs. 12,13,14 depict the apparatus in accordance with alternative embodiment of the present invention when it is used in practice for measuring internal pressure of a tire.

Fig. 15 shows a cross-section of a transceiver referring to alternative embodiment shown in Fig.14. Fig.16 shows a schematic presentation of a block scheme referring to various electric components of the transceiver and of a processing means.

Figs. 17,18 are signal-time relationships associated correspondingly with submitted vibrations and response vibrations.

Fig. 19 is an algorithm for processing of vibrations induced in a tire in accordance with the alternative embodiment of the present invention.

Detailed description of specific embodiments

The working principle of the apparatus for measuring internal pressure according to the first embodiment of the present invention is based on the acoustical analysis of vibrations generated by a mechanical impact upon the external surface of a resilient vessel, primarily an inflated tire.

According to the theory known from the engineering mechanics there exists a relationship between the spectrum of vibrations induced within a resilient membrane and the degree of the membrane's tension . This relationship is represented by the following formula; P= aMf² where P is pressure within the membrane, f is resonance frequency, M is mass of the membrane and a is a coefficient.

Based on the above theory it was empirically revealed that there exists a relationship between the internal pressure of an inflated tire and the acoustical spectrum of vibrations induced within the tire and emanated by its surface. This relationship can be approximated and represented as a polynomial of the second order.

An example of such relationship presented by a curve established for a particular tire G351 lr22.5 is shown in fig.L Thus, if such a relationship is pre-established for a certain tire it can be used as a reference curve for measuring inner pressure within this tire. With reference to figJ one can see graphical representation of plurality of reference curves pre-established for various tires. These curves correspond to polynomials representing particular relationships between the inner pressure within the tires and acoustical frequency characteristics associated with vibrations induced in those tires. It can be readily appreciated that for measuring of unknown pressure within a tire for which such a reference curve is available one should induce vibrations within the tire so as to obtain acoustical characteristics associated therewith. By inserting these characteristics within the curve the value of inner pressure can be derived.

The above principle of operation is implemented in the apparatus of the present invention, which is shown in figsJa-e.

This apparatus in fact constitutes an acoustical transceiver 10 suitable for inducing mechanically vibrations within a tire 12 and then receiving and processing of signals associated with those vibrations within a suitable acquisition and processing means 14, linked with the ransceiver. The processing means may output the derived value of pressure via an outlet link 16 to an external display (not shown) or within the processing means itself. The outlet link can be also used for communication.

The transceiver comprises two main parts, i.e. a mechanical actuator 18 capable to induce vibrations in the tire and connected therewith an accelerometer 20 capable to sense the emanated vibrations, to transform them into electrical signals and to present the instant value of those signals as a function of time.

The actuator is provided with a hammer 22 mounted within a housing 24 with possibility to protrude therefrom toward the tire and to strike thereof so as to induce the vibrations.

Secured within the upper part of the housing a spring 26 is provided urging the hammer to protrude.

In figJa it is shown how the present device is put onto the tire, the spring is pressed and the hammer is secured within the upper part of the housing being ready for striking the tire. In figJb is shown the situation when the hammer is released and the spring urges the hammer to strike the tire. The induced vibrations schematically designated by numeral 28 are emanated by the tire's surface, sensed by the lower contact surface 20' of the accelerometer and upon amplifying and transformation thereof into digital signals are processed within the processing means. It should be realized however that the accelerometer can sense the emanated vibrations also without being in the physical contact with the tire.

The situation corresponding to figJa is depicted also in figs 3c,d. As best seen in figJe the actuator is held manually and the striking is effected by pressing the upper part of the actuator accompanied by release the hammer.

Now with reference to fig. 4 the construction of the actuator will be explained in more details. The actuator comprises an external casing 30 with secured therein cylindrical housing 32 having an upper covering portion 34. Inserted within the cylindrical housing is an elongated guiding block 36 formed with a through going opening 38 extending along the block for receiving therein the hammer 22.

The outside diameter of the hammer corresponds to the inner diameter of the opening so as to allow free linear reciprocating movement of the hammer within the through going opening.

Residing between the covering portion of the housing and the upper end of the hammer the spring 26 is provided which is strong enough to urge the hammer downward and to strike the tire.

The inner diameter of the lower part of the block exceeds the outside diameter of the hammer to allow easy protrusion of the hammer from the block. The central part of the hammer is provided with an annular recess 40 having V-shaped cross-section. The upper portion of the block, which is proximate to the recessed part of the hammer, is formed with at least two discrete openings 42.

The lower portion of the housing is formed with an annular V-shaped recess 44 similar to the recess made within the hammer.

Plurality of locking balls 46 are placed between the opposite recesses 40,44 with possibility to pass through the openings 42 either toward the outwardly facing recess 40 or towards the inwardly facing recess 44.

It can be appreciated that when the balls are within the inwardly facing recess 44 the spring-loaded hammer is free to move along the through going bore of the guiding block. On the other hand when the balls are within the recess 40 the hammer is locked and can not be urged by the spring to hit the tire. In order to allow the balls to be displaced one should bring the recess 44 opposite to the recess 40 either by pressing on the covering part of the housing or by inserting the hammer within the housing against the spring 26. The vibrations, which are induced by the actuator within the tire, are sensed by the accelerometer 20. It is advantageous if the accelerometer is mechanically coupled with the actuator as shown in FigsJa,b by a bracket made of resilient material.

It can be realized that such a bracket serves as an acoustic damper filtering the unnecessary vibrations.

The accelerometer suitable for the above purpose should be capable to measure acceleration associated with vibrations in the range between 1Hz and 1000Hz.

It should be realized that instead of accelerometer one can use other instruments capable to measure velocity or displacements associated with vibrations in the same frequency range. In practice one can use analogous or digital accelerometers, for example manufactured by company Wilcoxon, Model 731A,731 -207,736T, or by company Analog Devices, Model ADXL05, ADXL50, ADXL150.

The accelerometer senses the vibrations and produces a time domain analogous signal, amplifies it and then transforms into digital time domain signal if required. It should be appreciated that transformation of the signal can be carried out also outside of the instrument sensing the vibrations, for example within the processing-acquisition means itself.

The output signal produced by the accelerometer is a time domain signal as shown in FigJ. This signal is used as an input to the processing-acquisition means which converts it into a frequency domain signal as shown in Fig 6.

The acquisition can be implemented on a portable computer as an application of an commercially available "DASYlab 32 net" laboratory software.

An example of a computer generated flow-chart of an acquisition system is shown in figJ. As a processing means one can use also dedicated miniature electronic device provided with appropriate electronic scheme.

The acquisition process is executed according to the algorithm shown in Fig.8.

In accordance with this algorithm the time domain signal is transformed to a frequency domain signal by virtue of a discrete Fourier transform FFT.

The windowing process applied during the FFT is used to cutoff the frequencies below 2 Hz and above 400 Hz. The transformed signal is now smoothed by an averaging process .The acquisition algorithm looks after the first and second order maxima and arranges them according to their relative power .The resulting first and second order maxima represent the coefficients of the polynomial related to the inspected tire. The resulting polynomial can now be compared with a data base containing previously established reference curve referring to the particular tire. This data base can be stored either in the processing means itself or retrieved from an external data base which can be contacted for example through the Internet.

For easy communication with the external data base the processing means can be provided with appropriate communication means, e.g. modem. The result of this comparison is a frequency-pressure relationship which is used for calculation the inner pressure of the tire.

Both the frequency and the calculated equivalent pressure are displayed on the computer display as shown in Fig 9.

Now with reference to FigsJO-19 it will be explained the alternative embodiment of the apparatus.

The working principle of the apparatus according to this embodiment is based on the empirically established dependence between the internal pressure within the vessel and a phase shift associated with the vibrations submitted to the vessel's wall and response vibrations induced in the vessel's wall and emanated thereby. Suppose we submit sinusoidal vibrations to the vessel's wall at a certain point A thereof. The response vibrations will be induced and emanated by the vessel's wall. These response vibrations can be detected at a certain point B of the vessel's wall that is remote from the point A by a distance 1. If the phase of submitted vibrations at the point A is q>_A , then the phase of the emanated vibrations at the point B is φβ. It has been empirically revealed that the phase shift

-(p_A is inversely proportional to the internal pressure within the vessel. In fact this phase shift reflects the delay of propagation of vibrations induced within the vessel's wall. Based on the above assumptions it was empirically revealed that there exists a relationship between the internal pressure of an inflated tire and the phase shift of vibrations submitted to the tire and emanated by its surface.

This relationship was approximated and it is represented as shown in FigJO. Thus, if such a relationship is pre-established for a certain tire, it can be used as a reference curve for measuring instant inner pressure within this tire.

With reference to Fig.H, one can see a graphical representation of plurality of reference curves empirically pre-established for various tires. These graphs correspond to particular relationships between the inner pressure existing within the tires and the delay in propagation of vibrations associated with submitted and response vibrations.

It can be readily appreciated that for measuring of unknown pressure within a tire for which such a reference curve is available, one should submit vibrations to the tire so as to obtain response vibrations and to measure the phase shift associated with those vibrations.

By substituting this phase shift within the reference graph, the value of inner pressure can be derived.

The above principle of operation is implemented in the apparatus of the present invention, which is schematically shown in Figs. 12,13. This apparatus, in fact, constitutes an acoustical transceiver 100 suitable for submitting vibrations within a tire 120, receiving induced response vibrations and then processing of signals associated with those vibrations within a suitable acquisition and processing means 140, linked with the transceiver.

The processing means may output the derived value of pressure via an outlet link 160 to an external display (not shown) or dedicated display within the processing means itself. The outlet link can be also used for communication.

In FigJ 4 is seen how the transceiver 100 is manually brought in contact with the outer surface of a tire and the measured value of pressure is read from the dedicated display of the processing means 140. Referring now to FigJ 5 is shown transceiver 100 comprising a housing H in which are mounted a transmitting membrane 180 and a receiving membrane 200.

The transmitting membrane submits vibrations to the tire's surface and the receiving membrane senses the induced response vibrations emanated by the tire's surface. The induced response vibrations are schematically designated by numeral 120'.

Associated with the membranes respective substantially cylindrical tips 220,240 are also seen. The tips protrude from the housing towards the tire's surface and can be brought in mechanical contact therewith in two remote locations A and B in which the vibrations are respectively submitted and sensed. The membranes are formed as relatively thin plates made of a piezo-ceramic material capable either to undergo periodical distortion once an alternating voltage is applied thereto or to convert vibrations sensed thereby into alternating electrical signal.

In practice the membranes are manufactured of ceramic materials based on Ba-TiO₃ or PbTiO₃-PbZrO₃, for example ceramic 7B produced by Murata, Japan. Rigidly connected to each of the membranes 180,200 mechanical loads 260,280 are provided. The loads and the membranes are carried by a bracket 300 connected to a central post 320.

The loads 260,280 are connected to the upper part of the post by respective flat springs 340,360. By virtue of this provision it is insured that membranes are acoustically insulated from the housing since the loads function as dampers diminishing any vibrations which could propagate from the membranes towards the housing.

It can be appreciated that vibrations submitted to the tire's surface by membrane 180 at location A induce response vibrations which propagate substantially through the tire and do not return back to the transceiver. The induced vibrations propagating through the tire are sensed in the point B by the receiving membrane. The flat springs also ensure that constant force can be applied manually on the transceiver housing when it is brought to the tire's surface

Supported by legs 380,400 and residing within the housing an electronic module 420 is provided. The module is coupled with a transformer 440 and with an amplifier (not shown) that are electrically wired respectively to the transmitting membrane 180 by a wiring 460 and to the receiving membrane 200 by a wiring 480.

Secured on the load 260 and wired to the transformer by wiring 520 a normally open micro-switch 500 is shown. This micro-switch ensures that energizing of the transceiver takes place only when the housing is put on the tire and is pressed to its surface by a force sufficient to bring its tip T in physical contact with the inner wall of the housing. It can be appreciated that by virtue of this provision the transceiver is put into operation at the same conditions each time when a new tire is tested.

Now with reference to FigJ 6 the structure of the electronic module and of the processing unit will be explained in more details. The electronic module includes a resistor-divider 540 that is connected to the transformer's winding. The operating voltage is supplied to resistor-divider, which converts it into electrical signal having phase φ_A. This signal proceeds simultaneously to the transmitting membrane and to a reference channel 560. The reference signal proceeds further through the reference channel to the processing unit and is filtered in a dedicated band pass filter (BPF-,). The voltage supplied to the transmitting membrane induces vibrations that are submitted through tip 220 to the tire's surface. Tip 240 of the receiving membrane senses the response vibrations emanated by the tire's surface. The receiving membrane converts these vibrations into sinusoidal electrical response defined by its phase φ-j. The response signal is amplified by an amplifier 580 and proceeds through the receiving channel 600 further to the dedicated band pass filter BPF₂ of the processing unit. Here both signals are separately cleaned from the possible disturbances and then proceed to a phase detector 600' where the phases of each signal are established.

The phases are inputted into a micro-controller 620 in which the phase shift Δ_φ is calculated and the value of the phase shift is translated into pressure according to the calibration curve stored in a flash EROM 640. The value of pressure can be displayed in a display means 660.

The processing unit is provided also with a control block 680 that has appropriate knobs and switches for operation the micro-controller.

The processing unit is provided with a D/A converter 700 for producing low voltage initiation signal for energizing the transceiver. This signal is amplified in an amplifier 720 and proceeds to the processing unit output designated as EXE.

From this output the initiation low voltage signal proceeds to the transceiver's input to energize the transformer, which increases the voltage and supplies it to the resistor-divider.

With reference to FigJ 7 it is shown sinusoidal initiation signal for inducing vibrations submitted to the tire by transmitting membrane 180.

This signal is defined by its phase Φ_A-

In Fig.18 is shown response sinusoidal signal corresponding to vibrations induced in the tire and sensed by the receiving membrane (dotted line). This signal is defined by its phase 9^*3. The response signal is superimposed with the initiating signal and one can see the phase shift Δ_φ=φ_A-φB-

The process of measuring of internal pressure in accordance with the present embodiment is executed according to an algorithm shown in Fig. 19.

This algorithm is executed upon pushing down a dedicated knob "measuring" of the control block (not shown). Then the micro-controller reads from the memory value of the sinusoidal initiation-submitting signal and transmits it to the D/A converter. The sinusoidal voltage generated in the converter is passed over to the input of the transceiver. This voltage is increased by the transformer and after passing the resistor-divider is supplied to the transmitting membrane for submitting vibrations and to the reference channel as reference signal. The receiving membrane of the transceiver generates response sinusoidal signal corresponding to the induced vibrations.

The response and reference signals are transmitted by the transceiver simultaneously to the processing unit. Here both signals upon filtering and establishing their phases in the phase detector are processed by micro-controller that calculates the phase shift.

The value of phase shift is compared with a data base containing previously established reference curve referring to the particular tire. This data base can be stored either in the processing means itself or retrieved from an external database which can be contacted for example through the Internet. For easy communication with the external data base the processing means can be provided with appropriate communication means, e.g., modem.

The result of this comparison is a phase shift-internal pressure relationship which is used for calculation of the inner pressure in a tire.

It will be appreciated that the disclosure set forth above will enable those skilled in the art

It should be appreciated that the present invention is not limited to the above-described embodiments and that changes and one skilled in the art can make modifications ordinarily without deviation from the scope of the invention, as will be defined in the appended claims.

It should also be appreciated that the features disclosed in the foregoing description, and/or in the following claims, and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realizing the present invention in diverse forms thereof.

Claims

Claims:

1. An apparatus for measuring internal pressure within a resilient-walled vessel, said apparatus comprising

- a receiving means capable to sense said emanated vibrations so as upon transforming them into electrical signals to establish a relationship between the internal pressure and at least one representative parameter associated with said signals, said parameter correlating with the value of internal pressure to be measured

- a processing means capable to process said relationship and to derive therefrom the value of internal pressure.

2. The apparatus as defined in claim 1, in which said actuating means comprises a spring- loaded hammer releasable locked within a housing, said hammer is capable upon release thereof to protrude from the housing and to strike the vessel's wall so as to induce mechanical vibrations emanated thereby.

3. The apparatus as defined in claim 2, in which said receiving means comprises an accelerometer.

4. The apparatus as defined in claim 3, in which said accelerometer is provided with a contact surface capable to perceive mechanical vibrations.

5. The apparatus as defined in claim 4, in which said contact surface is in physical contact with the vessel's wall so as to receive mechanical vibrations emanated therefrom.

6. The apparatus as defined in claim 5, in which said accelerometer resides within a carrier means coupled with the housing.

7. The apparatus as defined in claim 5, in which said carrier comprises a bracket made of resilient material, said bracket is capable to absorb mechanical vibrations induced by the actuating means.

8. The apparatus as defined in claim 1, which comprises a display means capable to indicate the value of internal pressure established by the computing means.

9. The apparatus as defined in claim 8, which said actuating means and said receiving means comprise respectively transmitting and receiving membrane, said membranes reside within a housing, said membranes are provided with respective tips protruding from the housing towards the vessel^'s wall so as to be in physical contact therewith and respectively to transmit mechanical vibrations to the vessel's wall or to receive response vibrations emanated thereby, said membranes are made of piezo-ceramic material and are mounted within the housing so as to be acoustically insulated therefrom.

10. The apparatus as defined in claim 9, said apparatus comprises a transformer for energizing the transmitting membrane and an electronic module, said module is capable to generate a reference signal with a phase φ_A for initiating the transmitting membrane and to receive a response signal with a phase c _B associated with the response vibrations emanated by the vessel's wall, said electronic module is coupled with the processing means.

1 1. The apparatus as defined in claim 10, in which said electronic module is electrically coupled with a micro-switch for putting the transmitting membrane into operation, said micro-switch is provided with a tip and is capable to put the transmitting membrane into operation upon establishing physical contact between said tip and the vessel's wall.

12. The apparatus as defined in claim 10. in which said processing means is provided with

- a phase detector capable to establish phases associated respectively with the reference signal and the response signal, - a memory means for storing a pre-established calibration curve expressing dependence of internal pressure within the vessel on the phase shift Δ_φ=φ_A-φB, associated with the reference signal and response signal,

- a micro-controller capable to establish the phase shift value and to translate this value into internal pressure according to the calibration curve stored in the memory means.

13. A method for measuring internal pressure within a resilient- walled vessel said method comprises the following main sequence of steps:

- submitting vibrations to the vessel's wall so as to induce response vibrations emanated by the vessel's wall,

- sensing said response vibrations and establishing a function defining a relationship between the internal pressure and at least one representative parameter associated with said vibrations, said representative parameter correlating with the value of internal pressure to be measured,

14. The method as defined in claim 13, in which the step of submitting said vibrations is effected by striking the vessel's wall by mechanical means.

15. The method as defined in claim 14, in which said representative parameter is associated with amplitudes of said vibrations and their frequencies.

16. The method as defined in claim 15, in which said representative parameter is set as at least one frequency corresponding to the vibration having maximal amplitude.

17. The method as defined in claim 13, in which the step of submitting of said vibrations to the vessel's wall and the step of sensing of response vibrations is effected by piezo-electrical means.

18. The method as defined in claim 18, in which said representative parameter is associated with delay in propagation of response vibrations

19. The method as defined in claim 14, in which said representative parameter is set as phase shift associated with submitted vibrations and response vibrations.