Abstract:
The invention relates to a clamp ( 10 ) which is used mainly in a vibroacoustic diagnosis tool during an automobile maintenance or after-sales assistance opération, including two hinged arms ( 11, 12 ), each comprising a jaw ( 13, 14 ) at one end and a handle ( 15, 16 ) at the other end. A pad ( 20 ) is mounted on each jaw ( 13, 14 ) via a ball-and-socket joint ( 21 ), such that the pad ( 20 ) ensures effective contact between the clamp ( 10 ) and the part being tested, and séparâtes the body of the clamp from the listening part. The invention is useful in the field of motor vehicles. The invention is also useful in the vibroacoustic diagnosis of motor vehicles or motor vehicle subunits.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage under 36 U.S.C. §371 of International App. No. PCT/FR2010/052830 filed Dec. 20, 2010, and which claims priority to French App. Nos. 1050016 filed on Jan. 4, 2010 and 1050291 filed on Jan. 18, 2010, the contents of which (text, drawings and claims) are incorporated her by reference. 
     BACKGROUND 
     The present invention relates to a listening clamp for an acoustical vibration analysis tool, and an acoustical vibration analysis tool using such a listening clamp. These objects are used in particular during maintenance operations or after-sales service of automotive vehicles. 
     An acoustical vibration analysis tool comprises, in a known manner, a headset suitable for noisy environments, a microphone, four clamps for the detection of noise of a structural nature and a selector for immediate identification of the clamp nearest to the acoustical vibration phenomenon to be detected. 
     A known type of listening clamp comprises two pivotally connected arms, each comprising a jaw and a handle arranged on both sides of the pivot point. This kind of clamp comprises a return spring defining a closed rest position of the jaws. The jaws are rigid metallic bodies that directly grip on the element to be measured, such as the usual jaws of battery charge clamps. The sensor comprises a single axis accelerometer glued on one jaw at a distance from the contact zone. With such a clamp, only the vibrations produced in a direction perpendicular to the positioning of the accelerometer in the clamp are transformed into electric signals and can be heard by the operator. In addition, significant loudness and level variations are induced by the positioning of the clamp on the structure to be analyzed. The sensing quality is mediocre and makes diagnosis relatively difficult. In addition, with this type of clamp there is a risk of short circuits, which can be particularly inconvenient, in particular when the clamps are used with hybrid vehicles. Furthermore, the different types of applications of such a clamp in a vehicle, specifically on a powertrain group or on ground connections, require the use of several sets of listening clamps of different dimensions (in general the listening clamps of the same tool are of three different sizes), and on the same element of the structure, listening is chosen according to the selected clamp, which consequently creates difficulties and/or interpretation errors. 
     BRIEF SUMMARY 
     The goal is to provide a listening clamp for an acoustical vibration analysis tool, specifically a listening clamp which facilitates and improves, on the one hand, the acoustical vibration analysis performed during automotive maintenance or after-sales service operations, and on the other hand, the work of experts who can benefit jointly from a quick tool for investigating, analyzing and reporting, through the intermediary of registered sounds and videos. 
     Another goal is to supply a listening clamp with good frequency response, specifically between 0 and 4000 Hz, which has a good clamping opening and reduced overall dimensions, which avoids all risk of electrical short circuits, and which is inexpensive. 
     Finally, another goal is to provide an acoustical vibration analysis tool which allows for simultaneous monitoring of several instrumented clamps. 
     To achieve these goals, a listening clamp is provided for an acoustical vibration analysis tool. The listening claim is comprised of a body formed of two arms articulated around an axis of articulation, each arm comprising, in one extremity a jaw, and in the other extremity a handle. In this new clamp, a pad is mounted on each jaw through the intermediary of a swivel joint so that the pad ensures effective contact between the clamp and the structure being tested, while decoupling the body of the clamp from the sensing part. 
     According to one particular embodiment, the listening clamp comprises a spring, coaxial with the articulation axis of the two arms, which presses or urges the two jaws against each other in the absence of a clamp opening effort on the arms, whereby the spring has relatively high stiffness to limit non-linear effects. 
     According to another embodiment, the plastic material of the clamp&#39;s body has a Shore D hardness of about 80 and the pad has a Shore D hardness of about 40. 
     According to another embodiment, the length of the clamp is between 8.5 cm and 9 cm, while the distance between the two pads is about 3.5 cm when the clamp is open. 
     Also disclosed is an acoustical vibration analysis tool which comprises a headset suitable for noisy environments, a microphone for measuring airborne noise, a plurality of the listening clamps for measuring noise transmitted through structures, and a selection box used by an operator to immediately identify the listening clamp closest to the acoustical vibration phenomenon being investigated. 
     According to a particular embodiment, the acoustical vibration analysis tool comprises four of the listening clamps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other goals, advantages and characteristics of the invention will appear in the following description of three preferred, non-limiting, embodiments, accompanied by drawings in which: 
         FIG. 1  shows the components of an acoustical vibration analysis tool; 
         FIG. 2  shows in a schematic manner, a first illustrative embodiment of a listening clamp for an acoustical vibration analysis tool; 
         FIG. 3  is a schematic perspective view of a pad of the listening clamp of  FIG. 2 ; 
         FIG. 4  is a representative graph of the elasticity characteristic of the spring of the listening clamp of  FIG. 2 ; 
         FIG. 5  is a perspective view of the listening clamp of  FIG. 2  showing the connection of the pads; 
         FIG. 6  shows four tested listening clamps of different type and form; 
         FIG. 7  is a representative graph of the vibratory response as a function of the frequency, in the case where the vibration sensor is placed in the jaws of the listening clamp; 
         FIG. 8  is also a representative graph of the vibratory response as a function of the frequency, in the case where the vibration sensor is placed in the swiveling pad of the listening clamp; 
         FIG. 9  is similar to  FIG. 2  and represents a second illustrative embodiment of the listening clamp; 
         FIG. 10  is a cross-sectional view of a pad of the listening clamp of  FIG. 9 ; 
         FIG. 11  is a schematic perspective view of the structure of a pad of a listening clamp according to a third embodiment; and 
         FIG. 12  is a transverse cross-sectional view of the pad of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an acoustical vibration analysis tool suitable for diagnostics performed on automotive vehicles during maintenance and after-sales service operations by mobile teams called “after-sales service mobile teams.” This type of tool is used to carry out vibration analysis of different sources of noise in order to identify dysfunctions in a vehicle (a certain number of breakdowns or dysfunctions induce acoustic and vibration symptoms). 
     The analysis tool comprises a headset  1  suitable for noisy environments, a microphone  2  suitable for measuring airborne noise (noise produced by a source that has no contact with the analyzed structure), a plurality of listening clamps  10  (here, four listening clamps  10 ) suitable for measuring structural noise (noise emitted by direct vibration of the analyzed structure), and a selection box  4  used by an operator to immediately identify the listening clamp closest to the acoustical vibration phenomenon to be studied. Headset  1 , microphone  2  and the listening clamps  10  are equipped with plugs for connection to the selection box  4 . On the basis of the electrical signals supplied by the microphone  2  and the listening clamps  10 , the selection box  4  performs signal processing in order to generate an audible signal for each of the measured noises. The selection box  4  comprises a switch with which the operator can select a listening clamp  10  in order to hear the audible signal in the headset  1 . By preference, all listening clamps  10  are of the same size. 
     With the listening clamp  10 , acoustical vibration analysis is possible by simultaneously listening to several clamps. With reference to  FIGS. 2 and 9 , the listening clamp  10  comprises a body  10   a  formed from two arms  11 ,  12  which are articulated around an articulation axis A, which is here in the median part of the arms  11 ,  12 . In addition to the body  10   a , the listening clamp  10  comprises two pads  20 ,  30  (here, identical). Each arm  11 ,  12  comprises, in one extremity, a jaw  13 ,  14  and in the other extremity a handle  15 ,  16 . The distal extremities  18 ,  19  of jaws  13 ,  14  face each other and each comprises a pad  20 . 
     The body  10   a  of the listening clamp is made of rigid plastic material so that no electrical short circuit can occur during the use of the listening clamp  10 . The selected plastic material can be, for instance, an ABS type rigid elastomer (Acrylonitrile-Butadiene-Styrene Terpolymer) with a Shore D hardness of about 80. 
     Advantageously, the pads  20  are made of hard plastic material, for instance with a Shore D hardness of about 40. 
     The listening clamp  10  is lighter than the known state of the art clamps, due to the fact that the two arms  11 ,  12  are formed of perforated ribs  11 A,  11 B;  12 A,  12 B in order to make them lighter, except in their median part at the articulation A where, on the contrary, the arms are reinforced. 
     With reference to  FIGS. 2 and 3 , the listening clamp  10  can have the following dimensions: 
     Distance (a) between the arms  11 ,  12  at the location of the free extremity of the handles  15 ,  16 : 4.5 cm; 
     Distance (b) between the arms  11 ,  12  at the base of the upper parts: 2.5 cm; 
     Length (c) of the handles  15 ,  16 : 4 cm; 
     Length (e) of the median reinforced part of the arms  11 ,  12 : 1.5 cm; 
     length (f) of the jaws  13 ,  14 : 3.5 cm; 
     Length (g) of the pads  20 : 1 cm; 
     Thickness (h) of the pads  20 : 0.4 cm; 
     Length (k) of the pads  20 : 1.5 cm; 
     Advantageously, the length of the listening clamp  10  is between 80 mm and 100 mm; by preference, its total length (l) is between 8.5 cm and 9 cm, and the distance between the two pads  20  of the listening clamp  10 , when open, is about 3.5 cm. The listening clamp  10  therefore has a large clamping opening in a small footprint. 
     In spite of its small size, the listening clamp  10  has a center distance greater than the large clamp used in current state of the art diagnostic tools. It should be noted that the size of the clamp  10  is much smaller than the size of the average clamp used in currently known diagnostic tools. Because of the size and center distance of the clamp  10 , the automotive listening device can be equipped with four clamps of the same size, which allows for simultaneous listening at different points without risking a degradation of the sensing quality by a structural response of a differently sized clamp. 
     Each pad  20  is mounted on the corresponding jaw  13 ,  14  through the intermediary of a swivel joint so that the pads  20  ensure effective contact between body  10   a  of the listening clamp and the structure to be analyzed and proper collection of vibrations. The pads are pivotally mounted to the jaws  13 ,  14  through the intermediary of pins  21 , their pivoting angle can be, for example, about 30° to ensure optimal fixation and sensing. The swiveling articulation ensures that the pads  20  are decoupled from body  10   a  and provides a variable point of contact with the structure to be tested. Although in the illustrated examples the pads are pivotally mounted about an axis relative to jaws  13  and  14 , it is also possible to mount the pads with two degrees of pivoting freedom relative to the jaws. 
     The listening clamp  10  comprises a spring  17  (advantageously, a torsion spring coaxial with the axis of articulation A) which presses the two jaws  13  and  14  together in the absence of an opening force on handles  15  and  16 . This spring  17  has relatively high stiffness to limit non-linear effects. The graph of  FIG. 4  shows the forces “E” on spring  17  (expressed in Newtons) as a function of the displacements “d”, (expressed in millimeters) which characterize spring  17 . Clamp  10  offers a greater clamping force than prior art clamps. 
       FIG. 5  illustrates more precisely the geometry of the distal extremities  18 ,  19  of the jaws  13 ,  14  at the location of pins  21 . As illustrated in  FIG. 3 , pad  20  of the first embodiment of the present invention comprises a cylindrical cavity  24  suitable for receiving pin  21  to form the articulation of pad  20  in body  10   a  of the listening clamp  10 . Pin  21  is inserted in pad  20  by means of guides  23 , and snaps in place in body  10   a , and is retained in position due to tab  22  protruding above the cylindrical cavity  24 . 
     Vibration tests have been performed with the four types of listening clamps P 1 , P 2 , P 3  and P 4  shown in the drawing of  FIG. 6 . These four clamps, all made of plastic material in order not to cause electrical short circuits and risk for the users, have pads of hard plastic material mounted through the intermediary of swivel joints according to the above described example. The swivel joints of the pads provide, on the one hand, effective contact between the clamp and the part or assembly to be tested, and on the other hand, decoupling of the body of the clamp from the listening sensor part. These four types of clamps have different dimensions. These vibration tests have led to the conclusion that the most suitable clamp for the application of acoustical vibration analysis in maintenance or after-sales service is the clamp designated as P 2 . 
       FIGS. 7 and 8  are representative graphs of the vibration response (power spectral density or PSD), expressed conventionally in g 2 /Hz, as a function of the frequency in Hertz (Hz). The tests of  FIG. 7  were carried out with a sensor (accelerometer) placed in the jaws, and the tests of  FIG. 8  with the sensor (accelerometer) in the swiveling pads. In these figures, the curves EX correspond with the excitation and are relatively “flat”, the curves F(P 2 ) represent the response of the clamp P 2 , and the curves F(P) represent the response of the average clamp (clamp P 1  of  FIG. 6 ). 
     It is important to note that when the accelerometer is located in the pad ( FIG. 8 ), the over-voltages are highly dampened and the response is rather “flat” up to a frequency of about 3800 Hz. The listening clamp  10  according to the invention meets the requirement of a rather “flat” vibration response in the frequency range 0 to 4000 Hz. 
       FIG. 9  illustrates a listening clamp  10  according to a second embodiment in which one of the pads  30  includes an accelerometer (not illustrated in this figure) which is connected by means of an electrical cable  28  to a plug  27  suitable for being plugged into selection box  4 . The electrical cable  28  can have a separation at the extremity of a handle  16  in the form of a freely moving connector. In this way, listening clamp  10  can be easily mounted on the structure to be tested without being bothered by the cable  28 . Cable  28  can pass through the body  10   a  and be attached to it by means of a glued joint. 
     The clamp can also have an accelerometer mounted in one jaw, and the corresponding pad has a ball which protrudes relative to one pad, whereby the ball serves as collector of vibrations from an element clamped between the jaws of the clamp. 
     As more precisely illustrated in  FIG. 10 , the pads  30  comprise a flat plate  32  oriented towards the clamping space and a mounting part  33  in which the cylindrical cavity  24  for pin  21  is formed. The illustrated pad  30  comprises an accelerometer  36  placed in the bottom of the cavity  35 . Depending on the desired accuracy of listening, an accelerometer  36  with one or more axes is used. 
     Plate  32  of pad  30  comprises a hole in the form of a partial sphere in which a ball  34  is housed. The ball  34  forms a collection element for structural noise. The ball  34  has, in practice, a part protruding, relative to plate  32 , into free air, in order to come into contact with an element to be tested. Due to its spherical form, the ball  34  when contacting the structure to be tested collects vibration information independently of the orientation of pad  30  relative to this element. The flat part  32  of the mounting part  33  serves for transmission of vibration information collected by ball  34  to the accelerometer  36 . In practice, the sensing quality obtained with this type of pad  30  is significantly improved: on the one hand the functions of vibration collection and transmission of the vibrations to the accelerometer are dissociated, and on the other hand the vibrations are transmitted from the element to the ball  23  which constitutes a collector with perfectly identified and controlled properties. Indeed, even when a three-axis accelerometer is used, in a listening clamp without a collecting ball, the amplitude of the measured signal remains heavily dependent on the orientation of the clamp. 
     Advantageously, the accelerometer  36  is disposed in vertical alignment with the ball  34 . In this way, the collected vibrations undergo relatively limited distortions when they are transmitted to accelerometer  36 . In the illustrated example, ball  34  is placed plumb with the cavity  24 , in the bottom of which the accelerometer  36  is housed. In order not to undergo vibratory perturbations, the accelerometer  36  is, in practice, spaced from pin  21 . Advantageously, for a multi-axis accelerometer, the summing circuit will be placed at a distance from accelerometer  36 , inside the arm of the listening clamp  10 . To avoid distortion phenomena, the phase shift between the different axes of the accelerometer  36  will be advantageously zero. Accelerometers such as the ones integrated in mobile phones can be used. 
     Ball  34  is advantageously made of stainless steel to optimize its life and the quality of vibration transmission. Ball  34  can have a diameter smaller than or equal to half the width of the flat part  32 . The flat part  32  can have the following dimensions: length 25 mm, width 5 mm, and thickness slightly larger than the diameter of ball  34 . The bore in the flat part  32  receiving the ball  34  can have a depth slightly smaller than the radius of ball  34 . The ball  34  can be mounted in the flat part  32  by means of a rigid glue, thereby optimizing the transmission of vibrations. The glue used is advantageously resistant to high surface temperatures generally encountered with components of an internal combustion engine. 
     The flat part  32  and the mounting part  33  are advantageously formed from a monoblock elastomer pad. The hardness of this elastomer can be greater than or equal to 40 Shore (D) to optimize the transmission of vibrations towards the accelerometer. Advantageously, the hardness of ball  34  is at least 5 times greater than the hardness of the pad. 
       FIG. 11  is a perspective view of a variant of pad  40  for a listening clamp  10  according to a third embodiment. With the exception of pads  40 , a listening clamp according to the third embodiment has a structure similar to the second embodiment. 
     Pad  40  comprises a flat part  42  solidly connected with a not shown mounting part. The mounting part is suitable for mounting to a jaw of the listening clamp  10  in order to mount pad  40  pivotally about an axis parallel to the pivoting axis between the jaws. A ball  44  is placed in contact with the flat part  42  on the opposite side of the mounting part. Another flat part  45  has a face in contact with ball  44  and another face intended to come into contact with the structure to be tested. The flat parts  42  and  45  are parallel at rest and the distance between them is therefore determined by the diameter of the ball  44 . The volume delimited in dotted line between the flat parts  42  and  45  comprises an insert of elastomer material  47 . Ball  44  is surrounded by the elastomer insert  47 . The thickness of the elastomer insert  47  is equal to the diameter of the ball  44 . 
     The flat part  45  has an important surface which facilitates the grip on the structure to be tested. Due to its spherical form, the ball  44  makes point contact with the flat part  45  and serves as collector for gathering vibration information independently of the orientation of pad  40  relative to this element. The flat part  42  and the mounting part serve to transmit the vibration information collected by ball  44  to a not shown accelerometer. The elastomer insert  47  holds the ball  44  in position between the flat parts  42  and  45 . The insert  47  also connects the flat parts  42  and  45  together, while allowing a certain amount of pivoting between them. The insert also reduces the vibrations between the flat plates  42  and  45  so that the vibrations transmitted by ball  44  remain paramount. The insert  47  can be glued to the flat parts  42  and  45 . 
     As in the preceding embodiment, the accelerometer is advantageously arranged plumb to the ball  44 . For instance, the accelerometer can be arranged in a cylindrical cavity made in the mounting part and placed plumb to ball  44 . 
     The ball  44  is advantageously made of stainless steel and its hardness is advantageously much greater than the hardness of flat parts  42  and  45 . The flat parts  42  and  45  are advantageously made of an elastomeric material. The hardness of this elastomer material is greater than or equal to 40 Shore (D). The elastomer material used for insert  47  has a distinctly lower hardness than plates  42  and  45 . By preference, the hardness of the insert is less than 40 Shore (A). 
     The illustrated dimensions are intended to facilitate the understanding of the structure of pad  40 , the size of the ball  44  and the thickness of insert  47  relative to the flat plates  42  and  45  are in reality distinctly smaller. 
     The listening clamp improves the sensing quality by using a collecting instrument that recovers vibrations from the element to be tested through the intermediary of a point contact. Furthermore, the listening clamp facilitates the vibration analysis performed during maintenance operations or after-sales service of automobiles, or facilitates the work of experts who can benefit from a quick investigation and analysis tool. Such a listening clamp additionally provides good frequency response, specifically between 0 and 4000 Hertz, while limiting the risk of an electrical short.