EP0168488A1

EP0168488A1 - Piezoelectric sensor

Info

Publication number: EP0168488A1
Application number: EP19850900895
Authority: EP
Inventors: Michael A. Virello; Christopher D. White
Original assignee: Stanadyne LLC
Current assignee: Stanadyne LLC
Priority date: 1984-01-16
Filing date: 1985-01-16
Publication date: 1986-01-22
Also published as: WO1985003127A1

Abstract

Système d'injection de carburant diesel (10) possèdant un détecteur de pression piézo-électrique (12) pour produire un signal de synchronisation d'injection de carburant de référence. Le détecteur comporte deux transducteurs de pression piézo-électriques (50) placés dans des positions diamétralement opposées, les deux transducteurs (50) étant connectés électriquement pour combiner leurs sorties afin de produire un signal répondant à un accroissement de pression et d'atténuer leurs trains de signaux sonores répondant aux vibrations.A diesel fuel injection system (10) having a piezoelectric pressure sensor (12) for producing a reference fuel injection timing signal. The detector comprises two piezoelectric pressure transducers (50) placed in diametrically opposite positions, the two transducers (50) being electrically connected to combine their outputs in order to produce a signal responding to an increase in pressure and to attenuate their trains sound signals responding to vibrations.

Description

PIEZOELECTRIC SENSOR

Description

Technical Field And Summary Of Invention

The present invention relates generally to piezoelectric sensors of the type used for sensing a transient or momentary mechanical displacement, deformation or strain and more particularly to a new and improved piezoelectric sensor of the type described having notable utility in internal combustion engine fuel injection systems for generating a reference fuel injection timing signal.

It is a primary aim of the present invention to provide a new and improved piezoelectric pressure sensor for use in internal combustion engine fuel injection systems for generating a reference fuel injection timing signal which is substantially noise free and which has a high signal to noise ratio. In the fuel injection system application of the present invention, the piezoelectric sensor can be provided as part of a separate unit in a high pressure fuel line leading to a fuel injection nozzle, as part of a fuel injection nozzle or as part of a unit fuel injector, in each case for generating a reference timing signal of the fuel injection event and useful for example (a) for operating a timing light for use in setting the fuel injection timing; (b) for timing an ignition spark in desired synchronized relationship with the fuel injection event; and (c) for continually maintaining and adjusting the timing of the fuel injection event in desired synchronized relationship with the associated internal combustion engine. Also, the piezoelectric sensor can be employed at a fuel injection pump for generating a reference fuel injection timing signal useful for example in controlling the timing of the delivery of discrete charges of fuel by the pump to each fuel injection nozzle.

It is another aim of the present invention to provide a new and improved piezoelectric sensor for a diesel type fuel injection system useful in a feedback loop of a microprocessor based control system for continually maintaining and adjusting the fuel injection timing in accordance with the changing operating conditions of the associated engine.

It is a another aim of the present invention to provide a new and improved piezoelectric sensor operable for generating a primary signal in response to a momentary hydraulic pressure pulse of up to 10,000 p.s.i. or more without being operated to generate significant spurious signals or noise when the sensor is mechanically vibrated by either the hydraulic pressure pulse or by another source. In accordance with the present invention, the piezoelectric sensor provides for combining two separately produced piezoelectric noise trains in substantially 180 degrees out-of-phase relationship so as to produce a combined practically noise-free output.

It is a further aim of the present invention to provide a new and improved method for generating a piezoelectric signal in response to a momentary or transient fluid pressure change, without generating noise in response to mechanical vibration of the sensor.

It is a further aim of the present invention to provide a new and improved piezoelectric sensor for sensing a momentary or transient hydraulic pressure increase or decrease by sensing the accompanying expansion and/or contraction of a hydraulic fluid conduit or other fluid enclosure. In accordance with the present invention, the sensor is operable by a momentary or transient hydraulic pressure increase or decrease to generate a strong primary signal having a high signal to noise ratio by automatically attenuating spurious signals resulting from mechanical vibration.

It is another aim of the present invention to provide a new and improved method, using a pair of piezoelectric transducers, of generating a primary piezoelectric signal without generating significant noise in response to mechanical vibration of the piezoelectric transducers.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

A better understanding of the invention will be obtained from. the following detailed description and the accompanying drawings of an illustrative application of the invention.

Brief Description Of The Drawings

Fig. 1 is a partial schematic view, partly broken away and partly in section, of a fuel injection system having a fuel line connector incorporating a preferred embodiment of a piezoelectric sensor of the present invention;

Fig. 2 is an enlarged generally axial section view, partly broken away and partly in section, of the fuel line connector;

Fig. 3 is an enlarged transverse section view, partly broken away and partly in section, of the fuel line connector taken generally along line 3-3 of Fig. 2?

Fig. 4 is an enlarged transverse section view, partly broken away and partly in section, showing a piezoelectric transducer of the piezoelectric sensor;

Fig. 5 is a voltage/time graph showing two representative signal trains independently generated by two piezoelectric transducers of the piezoelectric sensor during operation of the fuel injection system;

Fig. 6 is a voltage/time graph showing the output signal train of the sensor produced by combining the two independent signal trains represented in Fig. 5;

Fig. 7 is a voltage/time graph showing two representative signal noise trains independently generated by the two piezoelectric transducers when a vibrator pencil is applied to the fuel line connector and the fuel injection system is inoperative; and

Fig. 8 is a voltage/time graph showing the output signal train of the sensor produced by combining the two independent signal noise trains represented in Fig. 7.

Description Of Preferred Embodiment

Referring now to the drawings in detail wherein like numerals represent the same or like parts throughout the drawings, a fuel injection system 10 incorporating a preferred embodiment 12 of a piezoelectric sensor of the present invention is schematically shown in Fig. 1. The fuel injection system 10, in a conventional manner, comprises a diesel type high pressure fuel injection pump 14 driven by an associated internal combustion engine (not shown) and a high pressure fuel injection nozzle 16 for each engine cylinder. The fuel injection pump 14 may be of conventional design excepting as described herein and therefore will not be described in detail. For example, the fuel injection pump 14 may be of the type disclosed in U.S. Patent No. 4,224,916 of Charles . Davis, dated September 30, 1980 and entitled "Timing Control For Fuel Injection Pump", and accordingly the disclosure of said U.S. Patent No. 4,224,916 is incorporated herein by reference. In a well-known manner, the fuel injection pump is driven by the associated internal combustion engine (not shown) to periodically supply high pressure pulses of fuel to each fuel injection nozzle 16 of the engine for injection of discrete charges of fuel into the respective engine cylinder in synchronism with the engine. For that purpose, the fuel pump 14 is connected to each nozzle 16 by a separate high pressure fuel line 18. In a conventional manner, each nozzle 16 is operated to inject a discrete charge of fuel into the respective engine cylinder by the high pressure fuel pulse delivered to the nozzle 16. Each such fuel injection pulse has a short duration and a maximum pressure of up to 10,000 p.s.i. or more, the duration and pressure being primarily dependent on the design of the fuel injection system 10 and the engine speed and load.

Excepting as described herein, the fuel injection pump 14 may be regulated as disclosed in the co-pending U.S. patent application No. 447,535 of Daniel E. Salzgeber, filed December 7, 1982 and entitled "Method And System For Fuel Injection Timing" and assigned to the same assignee as the present application, and accordingly the disclosure of said U.S. patent application No. 447,535 is incorporated herein by reference. Briefly however, and referring to Fig. 1, a suitable microprocessor based electrical control unit 20 is connected to the pump 14 for controlling the fuel injection timing and to suitable engine operation sensors for receiving certain engine operation data for computing both the actual and the desired fuel injection timing. The electrical control unit 20 uses those computations to compute the desired timing adjustment and then adjusts the pump timing accordingly. The timing adjustment may be effected by a suitable bidirectional rotary stepping motor 22 as disclosed in said application No. 447,535 or as disclosed in U.S. Patent No. 4,329,961 of Laird E. Johnston, dated May 18, 1982 and entitled "Diesel Injection Pump Timing Control With Electronic Adjustment" and incorporated herein by reference.

Referring to Fig. 1, the engine sensors preferably include (a) an engine load or throttle position sensor 24; (b) an engine inlet manifold pressure sensor 25; (c) an engine coolant temperature sensor 26 and (d) a crankshaft position sensor 27 operable for generating a crankshaft reference position signal during each revolution of the engine crankshaft. The engine speed may be separately sensed and transmitted to the control unit or may be calculated by the control unit from the pulse rate of the crankshaft reference position signals. The piezoelectric sensor 12 generates reference fuel injection timing signals which are used in combination with the crankshaft reference position signals and a predetermined substantially constant short time delay (stored in the microprocessor of the electrical control unit 20) between the initial rise or edge of each reference fuel injection timing signal and the beginning of the respective fuel injection event (i.e. when the fuel injection valve (not shown) of the fuel nozzle 16 lifts off its seat) to calculate the actual fuel injection timing. For example, the actual fuel injection timing is calculated with reference to the top dead center (TDC⁾ position of the engine crankshaft for the engine cylinder with which the single piezoelectric sensor 12 is associated. Thus, the piezoelectric sensor forms part of a feedback loop to the control unit 20 for calculating the actual fuel injection timing. The control unit 20 is programmed to calculate the desired fuel injection timing from the input data received from the engine operation sensors 24-27 and then operate the bidirectional stepping motor 22 to adjust the timing accordingly.

In the shown embodiment, the piezoelectric sensor 12 is provided as part of a separate connector 30 mounted adjacent the nozzle 16 in the high pressure fuel line 18 connecting the fuel pump 14 to the nozzle 16. The connector 30 is shown connected directly to the nozzle inlet, for example with a suitable compression fitting 32 like that shown in U.S. Patent No. 4,163,521 of Vernon D. Roosa, dated August 7, 1979 and entitled "Fuel Injector". Also, the nozzle 16 may be of the type disclosed in said U.S. Patent No. 4,163,521 and therefore will not be described in detail and the disclosure of U.S. Patent No. 4,163,521 is incorporated herein by reference. A conventional high pressure fuel conduit 34 of the high pressure fuel line 18 is connected to the inlet of the connector 30, for example also by means of a suitable compression fitting 36.

The connector 30 has an elongated metal body 38, made for example of high grade steel, with a central, axial fuel passageway or bore 40 (having a diameter of approximately 0.070 inches (0.178 cm)) for conducting each high pressure fuel injection pulse to the nozzle 16. The connector body 38 has an axial sensor section with a pair of aligned diametrically opposed radial bores 42 with inner parallel flat end faces 44. A pair of substantially identical integral wall or web sections 46 are thereby formed intermediate the central axial fuel passageway 40 and the inner flat end faces 44 of the two opposed radial bores 42. The wall or web sections 46 have for example a minimum thickness of approximately 0.070 inches (0.178 cm). Those wall or web sections 46 have curved internal surfaces defining in part an intermediate section of the central axial fuel passageway 40 and are adapted to be momentarily deformed or flexed slightly outwardly substantially simultaneously by each momentary high pressure fuel injection pulse delivered to the nozzle 16.

A circular, flat, disc-like piezoelectric transducer 50 is mounted in each of the diametrically opposed bores 42 in direct engagement with the bottom or inner end face 44 of the bore 42 and is securely held in place by a suitable encapsulating epoxy or other material 52. The two .. piezoelectric transducers 50 are preferably identical and have aligned coaxial polar axes which are normal to their parallel end faces and thus normal to the axis of the intermediate axial fuel passageway 40. As hereinafter more fully described, the two transducers 50 may be mounted either with the same or opposite poles facing the axial fuel passageway 40.

Referring to Fig. 4, each transducer 50 comprises a very thin piezoceramic crystal layer or wafer element 54 of known material and of conventional design and having for example a thickness of about 0.010 inches (0.025 cm). Electrode layers or coatings 56 may be provided on both.of the two opposed parallel faces of the piezoelectric wafer 54 or on just the outer face. If an electrode layer 56 is provided on the inner face, a suitable insulating disc 58, of Mylar plastic for example, is provided between the bottom 44 of the transducer mounting bore 42 and the inner electrode layer 56. In the alternative, the metal connector body 38 may serve as the electrode for the inner faces of both piezoelectric wafers 54, in which case the inner electrode layers 56 and insulating discs 58 are not provided.

The electrode layers 56 may be provided in a conventional manner by suitable silver coatings. An electrical lead 60 is connected to each electrode layer 56 (and therefore only to each outer electrode layer where the connector body 38 serves as the inner electrode for both transducers) and so that each transducer 50 may have one or two leads depending on the transducer configuration used.

In accordance with a first embodiment of the present invention, the two transducers 50 are mounted with their inner opposed parallel pole faces having the same polarity (e.g. positive) . The two transducers 50 are connected by a parallel electrical connection — i.e. with the leads 60 from their positive pole electrodes connected together to provide one sensor output lead 62 (Fig. 1) and the leads 60 from their negative pole electrodes connected together to provide a second sensor output lead 64 (Fig. 1) . The resulting two leads (one connected to the connector body 38 if it serves as the inner electrodes as described) are then connected directly to the microprocessor based control unit 20 to transmit the reference fuel injection timing signals to the control unit 20. In the alternative, the two piezoelectric transducers 50 are connected by a series electrical connection as shown in broken lines in Fig. 3, i.e. with the positive pole electrode lead 60 of one transducer 50 connected to the negative pole electrode lead 60 of the other transducer 50 and with the other two electrode leads 60 providing the output leads for supplying a signal to the electrical control unit 20. Also, in both the series and parallel connection modes described, the two transducers 50 may be mounted with their inwardly facing parallel poles having either the same or the opposite polarity. In either mode, poles of the same polarity are joined together for a parallel connection and poles of opposite polarity are joined together for a series connection.

It has been found, by independently measuring the outputs of the two transducers 50, that they generate corresponding substantially simultaneous and identical primary voltage signals in response to the passage of a hydraulic high pressure pulse through the connector 30 followed by corresponding generally simultaneous and identical voltage noise signal trains (apparently resulting from mechanical vibration of the connector body 38 caused by the momentary high pressure hydraulic pulse) excepting that the two noise signal trains are in substantially 180 degree out-of-phase. Thus, in either the parallel or series connection mode, the two in-phase primary voltage signals generated by the two transducers 50 are combined to provide an enhanced signal. With regard to the 180 degree out-of-phase noise signal trains independently generated by the two transducers 50, in both the parallel and series modes of operation, the two noise trains combine to attenuate and substantially cancel each other by virtue of their voltages being substantially equal and opposite.

Fig. 5 illustrates a voltage/time graph of representative signal trains produced by the two transducers 50 when the transducers 50 are mounted with opposed inwardly facing positive poles and their outputs independently measured. Fig. 6 is a voltage/time graph of the corresponding combined output signal when the two transducers 50 are connected in parallel as described. With reference to Fig. 5, it can be seen that the two primary voltage signals 64 (each having a full cycle of two successive negative and plus voltage phases corresponding to compression and expansion of the respective piezoelectric crystal) are in-phase whereas the succeeding noise signal trains are substantially identical except for being in substantially 180 degrees out-of-phase. Accordingly, by electrically connecting the two transducers 50 as described, the out-of-phase noise signal trains 66 substantially completely attenuate or cancel each other. As shown in the graph of Fig. 6, the resultant sensor output or reference fuel injection timing signal 70 transmitted to the t electrical control unit 20 is substantially free of noise.

Accordingly, by properly connecting the two transducers 50 either in parallel or in series as described, the primary signals 64 generated by the two transducers 50 will combine to provide an enhanced primary or timing signal 70 and the noise signal trains generated by the two transducers will be combined to substantially completely attenuate or cancel each other to provide a practically noise-free output. It has been found that in the fuel injection system application, that result is achieved at various engine speeds and loads, including at an engine cranking speed of 150 RPM, idle speed of 750 RPM and engine operating speeds up to 3200 RPM.

The above operation of the sensor 12 is explained as follows. As a fuel injection pulse is conducted through the sensor section (at a velocity equal to the sonic velocity in fuel) , the two opposed wall sections 46 are momentarily and substantially simultaneously deformed outwardly slightly to substantially simultaneously and equally stress the two piezoelectric crystals 54 (i.e first compress and then decompress the crystals 54) . The crystal strain produced by the compression and decompression of each crystal 54 produces a momentary, single cycle, two-phase voltage signal or spike 64 as shown in Fig. 5. Those two signals 64, being substantially simultaneous and equal, combine to produce an enhanced reference fuel injection timing signal 70 as shown in Fig. 6.

However, as further shown in Fig. 5, vibration produced noise signal trains 66 generated by the two transducers 50 are in approximately 180 degrees out-of-phase in relationship to the primary signals 64 because the wall sections 46 vibrate in synchronism in the same direction, rather than in opposite directions as when they are deformed by a momentary or transient hydraulic pressure increase or decrease. In that regard, it is believed that the thin piezoelectric crystal wafers 54 are responsive primarily if not solely to the normal (or radial) vector component of any vibration caused deformation of the metal connector body 38, in which event that vector component will affect the two opposed transducers 50 substantially equally and oppositely at substantially the same time, i.e. one of the transducers

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50 will be compressed when the other transducer 50 is decompressed and vice versa as the connector body 38 vibrates. The foregoing occurs irrespective of whether the connector body vibration is produced by the momentary high pressure fuel injection pulse or by another source. For example, vibrating the connector 30 with a vibrator pencil (not shown) has been used to verify the above explanation. A graph showing representative independent signal trains 74 produced by the two transducers 50 (when the fuel injection system is inoperative and the transducers 50 are mounted to have inner opposed positive poles) is shown in the graph of Fig. 7 and the combined output signal 76 produced by the sensor 12 when the two transducers 50 are connected in parallel is shown in Fig. 8. In Fig. 7, the two independent noise signal trains 74 are substantially equal but in substantially direct out-of-phase relationship and such that, as shown in Fig. 8, their combined signal is practically noise-free.

Although mounting the two transducers 50 in diametrically opposed parallel relationship as described is deemed to provide a preferred orientation of the two transducers 50 and their actuators 46, it seems that a different orientation might be employed to generate equal and opposite noise signal trains which, when combined, provide a substantially noise-free output as described. For example, it seems that the two transducers 50 might be mounted in some predetermined spaced, parallel relationship so that only one transducer 50 is affected by the hydraulic pressure change and yet so that both are affected substantially equally by mechanical vibration as described. The two transducer outputs can then be suitably connected so that the two noise trains cancel out each other as described.

Although in the described embodiment the sensor is employed for sensing a momentary or transient pressure change in a high pressure hydraulic system, it could also be similarly employed with a pneumatic system or a relatively low pressure fluid system — such as with a low pressure chamber of a fuel injection system. For example, the sensor could be suitably connected to the advance piston chamber of the fuel injection pump and used to generate a reference fuel injection timing signal in response to a reaction hydraulic pulse to the actuation of the fuel charge pump (generally as disclosed in said U.S. Patent No. 4,329,961 or said U.S. application Serial No. 447,535) .

Thus, as can be seen from the enclosed drawings and the above description, the present invention provides a method and apparatus using two piezoelectric transducers for generating a piezoelectric signal in response to a momentary or transient fluid pressure charge, which is practically noise free and which has a high signal to noise ratio. The use of two transducers 50 in the described manner provides a combined, practically noise-free output signal without the need for an electronic filter circuit. Thus, the two transducers 50 are preferably directly connected in series or parallel as described; however in the alternative the two outputs of the two piezoelectric transducers 50 can be combined by a suitable electronic circuit to achieve a similar substantially noise-free output signal. Also, it seems that the sensor might be configured so that only one of the two transducers 50 produces a primary signal and yet so that the outputs of the two transducers can be suitably combined to provide a noise-free output.

As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

Claims

1. A piezoelectric sensor for sensing a fluid pressure pulse, comprising a fluid pressure conduit with an internal fluid passageway for conducting a fluid pressure pulse therethrough and a wall section with an internal surface defining a section of said internal passageway and deformable by a said fluid pressure pulse conducted through the passageway, first and second piezoelectric transducers, each having a piezoelectric transducer element with a pair of opposed substantially parallel faces and each operable to generate a piezoelectric voltage signal between its opposed faces by varying the stress applied thereto, means mounting the first and second piezoelectric transducers in predetermined fixed relationship and orientation to the fluid pressure conduit for the said operation thereof by said deformable wall section to generate corresponding in-phase primary piezoelectric voltage signals by deformation of the wall section by a said fluid pressure pulse conducted through said passageway, the said fixed relationship and orientation of the first and second piezoelectric transducers providing for the said operation thereof to generate corresponding out-of-phase secondary piezoelectric voltage signals from mechanical vibration produced stress applied to the transducers and circuit means connected to the opposed faces of the first and second piezoelectric transducer elements to combine the said signals generated thereby to produce an enhanced combination primary signal of said in-phase primary signals and to attenuate the out-of-phase secondary signals.

2. A piezoelectric sensor according to claim 1 wherein each of said transducer elements has piezoelectric poles of opposite polarity at said opposed parallel faces thereof and wherein the circuit means comprises lead means connecting like poles of the transducer elements in parallel to provide the said combination of the signals generated thereby.

3. A piezoelectric sensor according to claim 1 wherein each of said transducer elements has piezoelectric poles of opposite polarity at said opposed parallel faces thereof and wherein the circuit means comprises lead means connecting unlike poles of the transducer elements in series to provide the said combination of signals generated thereby.

4. A piezoelectric sensor according to claim 1 wherein the first and second transducers are mounted with their said faces in parallel relationship and wherein each of said transducer elements has piezoelectric poles of opposite polarity at said opposed parallel faces thereof and the first and second transducer elements have respective polar axes which are generally normal to the opposed parallel faces of the transducer elements respectively.

5. A piezoelectric sensor according to claim 4 wherein the polar axes of the first and second transducer elements are coaxial.

6. A piezoelectric sensor according to claim 1 wherein each of the transducer elements is a thin wafer-like element.

7. A piezoelectric sensor according to claim 1 wherein the mounting means comprises a pair of opposed parallel mounting faces in the high pressure conduit on opposite sides of the hydraulic passageway and means securing the first and second transducers to the said pair of mounting faces respectively to provide the said fixed relationship and orientation of the transducers and wherein the said deformable wall section is provided between the said opposed mounting faces and the hydraulic passageway.

8. A piezoelectric sensor according to claim 1 wherein the fluid pressure pulse is a high pressure hydraulic fuel injection pulse.

9. A piezoelectric sensor according to claim 1 wherein the mounting means comprises a pair of opposed parallel mounting faces in the high pressure conduit and means securing the first and second transducers to the said pair of mounting faces respectively to provide the said fixed relationship and orientation of the transducers and wherein the said deformable wall section is provided between the said opposed mounting faces.

10. A piezoelectric sensor for sensing a high pressure fuel injection pulse in a high pressure fuel injection system, comprising a fuel enclosure having a cavity for receiving the said high pressure fuel injection pulse and a deformable wall section with an internal surface defining a section of said fuel cavity, first and second piezoelectric transducer elements, each having a pair of opposed parallel faces and each operable to generate a piezoelectric voltage output signal between the opposed faces by varying the stress applied thereto, means mounting the first and second piezoelectric transducer elements in association with said cavity wall section for said operation of the transducer elements to generate corresponding in-phase primary piezoelectric voltage signals by slight outward deformation of said deformable wall section by a high pressure fuel injection pulse and with the first and second elements being in spaced generally parallel relationship to generate corresponding out-of-phase secondary piezoelectric voltage signals from mechanical vibration produced stress applied to the transducers, and circuit means electrically connected to the opposed faces of the first and second piezoelectric transducer elements to combine the output signals thereof to produce an enhanced combination primary signal of said in-phase primary signals and to attenuate the out-of-phase secondary signals.

11. A piezoelectric sensor according to claim 10 wherein each of said transducer elements has piezoelectric poles of opposite polarity at said opposed parallel faces thereof and wherein the circuit means comprises lead means connecting like poles of the transducer elements in parallel to provide the said combination of the signals generated thereby.

12. A piezoelectric sensor according to claim 10 wherein each of said transducer elements has piezoelectric poles of opposite polarity at said opposed parallel faces thereof and wherein the circuit means comprises lead means connecting unlike poles of the transducer elements in series to provide the said combination of signals generated thereby.

13. A piezoelectric sensor according to claim 10 wherein each of the transducer elements is a thin wafer-like element.

14. A piezoelectric sensor according to claim 10 wherein the mounting means comprises a pair of opposed parallel mounting faces in the enclosure on opposite sides of the cavity and means securing the first and second transducers to the said pair of mounting faces respectively to provide the said fixed relationship and orientation of the transducers and wherein the said deformable wall section is provided between the said opposed mounting faces and the fuel cavity.

15. A method of piezoelectric generation of a primary electrical signal in response to the application of a predetermined external force to a piezoelectric transducer actuator, comprising the steps of providing first and second piezoelectric transducer elements, each having a pair of opposed parallel faces and each operable to generate a piezoelectric voltage signal between its opposed faces by varying the stress applied thereto, mounting the first and second piezoelectric transducer elements in predetermined fixed relationship and orientation to said transducer actuator for the said operation of the transducer elements by the actuator to generate corresponding in-phase primary piezoelectric voltage signals upon the said application of said predetermined external force to the actuator, the said predetermined fixed relationship and orientation of the first and second piezoelectric transducer elements providing for the said operation thereof to generate corresponding out-of-phase secondary piezoelectric voltage signals from mechanical vibration produced stress applied to the transducers, and combining the primary and secondary signals generated by the said first and second piezoelectric transducer elements so as to provide a combination primary signal of said in-phase primary signals and to attenuate the out-of-phase secondary signals.

16. A method of piezoelectric generation of a primary electrical signal according to claim 15 wherein each of said transducer elements has piezoelectric poles of opposite polarity at the said opposed parallel faces thereof and wherein the combining step comprises electrically connecting the said first and second piezoelectric transducer elements in parallel so as to provide the said combination of the signals generated thereby.

17. A method of piezoelectric generation of a primary electrical signal according to claim 15 wherein each of said transducer elements has piezoelectric poles of opposite polarity at the said opposed parallel faces thereof and wherein the combining step comprises electrically connecting the said first and second piezoelectric transducer elements in series so as to provide the said combination of the signals generated thereby.

18. A method of piezoelectric generation of a primary electrical signal in response to the application of a predetermined external force to a piezoelectric transducer actuator, comprising the steps of providing first and second piezoelectric transducer elements, each having a pair of opposed parallel faces and each operable to generate a piezoelectric voltage signal between its opposed faces by varying the stress applied thereto, mounting the first and second piezoelectric transducer elements in predetermined fixed relationship and orientation to said transducer actuator for the said operation thereof by the actuator to generate, with at least one of the piezoelectric transducer elements, a primary electrical signal upon the said application of said predetermined external force to the actuator, the said predetermined fixed relationship and orientation of the said first and second piezoelectric transducer elements providing for the said operation of both of the piezoelectric elements by the actuator to generate corresponding secondary voltage signals by mechanical vibration produced stress applied to the transducers, and combining the primary and secondary signals generated by the said first and second piezoelectric transducer elements so as to provide respectively a primary output signal thereof and an out-of-phase combination of corresponding secondary signals for attenuation thereof.