FR2841651A1 - Piezoelectric vibration sensor fixing for car knock sensor is tensioned by tightening bolt against spacer sleeve flange - Google Patents

Abstract

A piezoelectric vibration sensor (1) fixing has a hexagonal head (4) bolt (20) in a threaded hole (22) and stressed by the spacer (26) sleeve flange (24) which can include a recess for the bolt head and a toothed sleeve end.

Description

The invention relates to an assembly for applying to an organ, with a view to

  its maintenance vis-à-vis a receiving part intended to receive it, a limited stress exerted, in the direction of this member, by means of pressure and

  fixation, by means of a force control.

  In particular, it involves attaching to a vibrating structure (i.e.,

  likely to emit vibrations) a vibration sensor.

  Typically, it may be a sensor intended to be installed in a motor vehicle in contact with the engine block, in particular to constitute an accelerometric sensor and more particularly, a sensor sensitive to knocking which

  regularly affect the operation of internal combustion engines.

  To fix a member, and in particular such a sensor, to its receiving part, in particular an engine block, it is known to use a bolt, which is commonly

screwed using a screwdriver.

  In any case, the organ is designed to withstand the forces exerted during

fixation.

  In the case of knock sensors, a base is typically used which takes up the screwing effort and which also often serves as a support for the sensor, since the base then has a part in the form of a crown interposed between the sensor and the engine block, while a clamping nut engaged on the tubular base of the base

  against which the bolt head rests, tighten the sensor against the crown.

  The object of the invention is to propose: - a solution which avoids the use of such a base, - which does not require the presence of two tightening steps (tightening of the bolt and tightening of the nut), - which makes it possible to control effectively the clamping force of the member to be fixed, which therefore ensures appropriate stressing of the member, while ensuring that it is fixed securely,

  -which limits the cost and intervention time for the operator.

  An important characteristic of the solution of the invention consists, under these conditions, and in order to satisfy at least part of these aims, in that the assembly is such that: - the member to be stressed and maintained is a vibration sensor comprising, along an axis, a stack of elements including an element made of piezoelectric material and electrodes in electrical connection with this element, the electrodes having connection pins so that the sensor can transmit data relating to the vibrations received, - the receiving part intended to receive this sensor is capable of transmitting vibrations to the sensor, - the pressure and fixing means comprises a support head and a first traction part engaged on a second part of additional traction of the first part, to ensure traction on the support head when the latter is arranged facing a first surface of the collector r opposite a second surface disposed opposite the receiving part, and the force control means comprises a ft axially defining a spacer between the sensor and the receiving piece, the ft extending for this axially to -from the first surface of the sensor o it cooperates with a crown arranged coaxially with the sensor and having a wall inclined relative to its axis, the crown being interposed between the head of the pressure and fixing means and said first surface of the sensor for ensure the stressing of this sensor, under the effect of a pressure exerted on it by the crown and an axial force of the head on the

1 5 ft.

  In particular if it is a vibration sensor to be fixed on an engine block, it is also advised that: - the stacked elements of the sensor have an annular shape, with a central orifice extending along the axis , - the ft of the force control means is tubular and extends inside the orifice of the stack of sensor elements, - and the pressure and fixing means comprises a rod extending axially inside the tubular ft, this rod being provided with the first part of

  traction which is engaged inside a passage formed in the reception room.

  In order to be exempt from the presence of the base mentioned above, and in particular of its crown on which the prior art typically provided for tightening the sensor by means of a nut, another characteristic of the invention advises that: - the second surface of the sensor is applied (directly) against a surface of the receiving part, - and the ft of the force control means is also in abutment against this

surface of the reception room.

  To favor the distribution of the clamping force between the axial force exerted by the pressure and fixing means and the favorable stress to be exerted directly on the sensor by means of the force control means (thus promoting close contact between the stacked elements of the sensor which in this case have an annular shape as indicated above), it is advisable that the tubular ft is connected to the crown, towards its first end, and the head of the pressure means and fixing comes into contact with the force control means substantially at the point of the connection between the

ft and the crown.

  To possibly gain in bulk or ensure even more direct control of the force exerted on an annular sensor, another characteristic of the invention provides that the tubular barrel of the force control means can be connected to the crown, towards its first end and, that nearby, this ft has a radial shoulder increasing its section towards this first end and defining a cavity inside which is received the head of the pressure means and

1 0 fixing.

  In particular when the sensor consists of a vibration sensor (knock sensor on engine block), it is known, once the sensor fixed on the part intended to receive it, to coat this sensor by overmolding of a plastic material, in particular to make the sensor waterproof and to freeze and protect the stacked elements which

constitute it.

  Within the framework of the invention, to promote the cohesion and the protection of these stacked elements, including with regard to their electrical connection, while promoting reliable tightening over time with an appropriate tightening stress, another characteristic of the invention recommends that the stacked elements of the sensor be arranged inside a plastic casing comprising at least two parts joined together along the axis of the sensor and therefore along the axis of the force exerted on it

  by means of pressure and fixing.

  The radial positioning of the elements of the sensor vis-à-vis the force control means being important for an effective functioning of the sensor as well as for the good progress of the tightening operations of this sensor on its receiving part, another characteristic. of the invention recommends that: - the stacked elements of the sensor have an annular shape, with a central orifice extending along the axis, and - the ft of the force control means is tubular and has an outer surface provided lugs towards the free end of the ft located opposite the crown,

  the ft being forcibly engaged inside the stack of sensor elements.

  An even more detailed description of the invention will now be provided

  with reference to the accompanying drawings in which: in FIG. 1, there is shown in two half-views (left / right) attached to the principle of fixing the member to be maintained which contributes to limiting the forces exerted on the stacked elements of the 'member while ensuring reliable maintenance of the latter, in Figures 2 and 3, there is shown respectively in exploded view and in assembled view a vibration sensor which may correspond to the member to be fixed shown schematically in Figure 1, on Figure 4, there is shown in vertical section an assembly corresponding functionally to the solution of Figure 1, but with a particular embodiment for the force control means, which is again shown in section in Figure 5 , with an associated clamping screw (enlarged view compared to that of FIG. 4), in FIGS. 6 and 7, the previous embodiment of the force control member is again shown, followed by vant a perspective view (Figure 6) and in a bottom view (Figure 7), in the direction of arrow VII of Figure 6, and in Figure 8, there is shown schematically, again in section

  vertical, an alternative embodiment of this effort control means.

  In FIG. 1, a diagram 2 therefore shows an assembly 2 comprising a bolt 4 for tightening a member 1 against a part 3, with interposition

  an intermediate force control means 8.

  The pressure and fixing means is therefore a bolt screwed along the axis 19 inside a threaded orifice 12 of the part 3. Alternatively, one could have envisaged another fixing means, such as for example that a rivet engaged with a surface of the part 3. The force control means comprises a ft 14 defining, along the axis 19, a spacer between the member 1 and the part 3, as well as a crown 16 having a wall inclined relative to the axis 19. The crown 16 is frustoconical and interposed between the enlarged head of the pressure and fixing means 4 and a first surface 9a of the member 1 opposite to the surface 1 by which the member 1 comes to bear against the surface 3a of

room 3.

  On the left in FIG. 1, the spacer 14 which therefore extends between the base (defining a shoulder) of the enlarged head 4a and the surface 3a, directly receives the axial pressure following the screwing of the bolt, the frustoconical crown 16

  transmitting part of this effort to organ 1.

  On the right, the shoulder at the base of the head 4a rests on an annular part 16'a of the crown 16 'which is perpendicular to the axis 19, this part 16'a being itself in contact with the spacer 14' whose nominal length L 'is less than the

  length L of a distance corresponding to the thickness of the annular part 16'a.

  Like the spacer 14 on the left, the spacer 14 'on the right also comes

  resting against the surface 3a of the part 3.

  Thus, a pressure exerted along the axis 19 by the pressure and fixing means 4 causes an axial pressure on the spacer 14 'with, as a corollary, a reduction in the axial length L', a part of the force therefore passing through organ 1, via

the large base of the crown 16 '.

  In FIG. 1, the member 1 has been shown diagrammatically as comprising, in the direction of the axis 19, a stack of elements including an element 13 made of piezoelectric material and electrodes 15a, 15b, in electrical connection with this element, the electrodes being adapted so that the sensor can transmit the data relating to the vibrations received by the member 1 which may in particular be metallic, in particular if it

  this is the engine block of a vehicle as is a priori expected.

  In FIGS. 2 and 3, the member 1 shown is a vibration sensor and in particular a knock sensor responsible for detecting the vibrations transmitted by

  the engine block 3 of a motor vehicle.

  The sensor 1 thus comprises a series of stacked elements 5 whose role is to capture the acoustic vibrations and transform them into an electrical signal, which is transmitted to a computer 6 designed to process this information and to provide, if

  necessary, a correction to the operation of the engine (see Figure 3).

  The stacked elements 5 are housed inside a housing 7 comprising two complementary parts 9, 11, in the sense that once the parts are assembled, the housing constitutes a globally closed assembly protecting and bringing together the

  stacked elements 5 hereinafter called "sensitive elements".

  These sensitive elements include in particular the piezoelectric element

  13 interposed between the two electrodes 15a, 15b.

  The electrodes 15a, 15b are each attached to one of the two opposite faces of the element 13 and are therefore separated from each other. Each electrode has a pin 17a, 17b through which the electrical data supplied by the element

  made of piezoelectric material 13 will be transmitted to the computer.

  As can be seen in Figure 2, starting from the bottom of the stack, we find first in the illustrated embodiment and along the stacking axis 19, the first electrode 15a, the element 13 of piezo material electric, the second electrode 15b, then

  a block 21 constituting a seismic mass. Typically, it is a metal block.

  Such a stack can be directly housed, thus stacked axially, inside the housing 7, when its two parts 9, 11 are axially close together,

as shown in figure 3.

  For effective protection and maintenance of the elements 5, each part of

  housing includes a bottom 9a, 1a from which stands an outer side wall 9b, 11b.

  In the assembled state, the outer side walls 9b, 11b extend

  substantially parallel to the stacking axis 19.

  For effective retention of the sensitive elements 1 inside the housing, the internal surface of the external lateral wall of each housing part has projecting protrusions marked 23, and the section of the stacked elements is adapted so that these elements are engaged in force inside the housing parts, in

  close contact with the growths 23.

  The side walls 9b, 11b extend along angular sectors and do not

  are therefore not continuous along the perimeter.

  In the illustrated embodiment, these side walls somehow each define a toothing oriented parallel to the axis 19, with its pillars such

  that 29a, 29b; 31 a, 31 b, and its openings, such as 39a, 39b; 41a, 41 b.

  Such a crenellated shape allows (by relative displacement along the axis 19) to

  pillars of one of the parts to engage in the openings of the other part of the housing 7.

  Advantageously, the angular sector along which the pillars of one of the parts develop advantageously corresponds, in a relative angular position determined with respect to the axis 19 of one part with respect to the other, to the sector of the openings of the 'other part, so that in the engaged or nested state of Figure 3,

  we obtain an angular blocking of a housing part relative to the other.

  In this position, it can be seen that the pins 17a, 17b pass in turn through two openings 33a, 33b, of identical cord It barely greater than the width 12 of each pin 17a, 17b. These openings are separated by a narrow

wall 35.

  Since, preferably, the two parts 7, 11 of the housing are identical, the other part 7 is here provided with the same two cutouts of rope II close to one another. It is the large opening 39a which we see, in FIG. 3, receiving the zone

  o are arranged pins 17a, 17b.

  It will also be noted that, taking into account the attachment of the sensor 1 by a clamping means which engages along the axis 19, for attachment "from the center", the sensor 1 is generally presented, in this embodiment, as a annular assembly, with a series of elements 5 themselves individually annular, stacked along the axis of revolution 19, the two housing parts 9, 11 also being annular, with each

a central opening 9c, 11c.

  In FIG. 2, it can be seen that each part 9, 11 of the housing is such that its central orifice 9c, 11c is bordered by a continuous inner side wall 59, 63 extending parallel to the axis 19 and of height, according to this axis, less than the height

  pillars such as 29a, 29b, if the two housing parts are identical.

  Preferably the outside diameter of the (each) inner wall, respectively 59, 63, of the corresponding housing part will be substantially equal (barely smaller) than the inside diameter of each ring constituting one of the elements

  sensitive 5, so that the clearance of the rings in the housing is, at this location, limited.

  Note that the transfer of the protuberances 23 on the inner face of the outer lateral walls of the housing allows better centering and a more efficient tight retention of these elements than if these protuberances protruding from the wall had been produced.

lateral interior 59.

  In Figure 3, we can also see the appearance of the sensor 1 once the housing 7 closed around its sensitive elements, and after a plastic material

  coating was injected around the thus closed housing, in a mold suitable for this purpose.

  It should be noted in this regard that radial grooves 67 will advantageously be provided in the bottom of each housing part to promote the distribution of the coating material, these grooves being able to be connected radially to circular channels respectively inside 69 and outside 71 limited by ledges provided at the right of the

  inner side wall and outer side wall, respectively.

  In FIG. 4, the member 1 to be held and fixed is represented as a single, annular block, linked to the part 3 by the screw 4, the rod of which is engaged in the orifice 12,

  with its threads 20 engaged with the thread 22 of the hole 12.

  In this figure, it can be seen that the intermediate means for controlling the force exerted on the member 1 is constituted by a single piece 24 which is seen more in

  detail, according to this embodiment, in FIGS. 5, 6 and 7.

  The part 24 comprises a tubular ft 26 which extends inside the orifice

  1 ic of sensor 1, along the clamping axis 19.

  Opposite its free end 26a by which it bears against the surface 3a, the ft 26 is connected to the crown 28 so as to constitute the part

monobloc desired.

  In FIGS. 4 and 5, it will be seen that the base of the enlarged head 3 of the pressure and fixing means exerts its axial force in the bent or curved zone

  30 o connects the ft and the crown.

  The crown 28 defines an elastic pressure means and the stiffness / flexibility balance of this crown 28 is adapted by the choice of the material of the part 24 and thanks to

  to the openings 32 made in this ring as seen in FIGS. 6 and 7.

  Typically, the intermediate piece 24 will be metallic.

  For information, for a knock sensor such as that of FIGS. 2 and 3 mounted on a motor unit and fixed to the latter by a bolt, the order of magnitude of the tightening of the bolt will advantageously be of the order of a few tonnes, while the stress necessary for maintaining and performing the sensor 1 effectively does not

  will then be only from a few tens to a few hundred kilograms.

  This will in particular allow plastic housing 7 to be produced,

  without risk of significant creep of the housing, due to tightening.

  In FIG. 4, it will be noted that the sensor 1 and the intermediate piece

  24 are mounted radially tightened (almost without play) around the rod of the bolt 4.

  To precisely ensure a tight hold of the part 24 with respect to the sensor, and in particular of its housing 7, the tubular ft 26 of the part 24 is, in particular in FIGS. 6 and 7, provided towards its end 26a lugs 30 projecting laterally from its outer wall, so as to tighten the contact with the outer surface of the wall

inside 59 of the housing.

  In other words, the outside diameter of the ft 26, in particular at the location of the lugs 34 and the inside diameter of the housing 7, at the location of the interior annular wall 59, will be adapted so that the ft 26 is engaged by force inside the sensor

  and more particularly, from the central orifice of its housing.

  In FIG. 8, we find the same clamping means 4 as well as the member to be clamped 1, and the force control means (here referenced 40) is always a single piece, one piece, with a tubular ft defining a spacer, coaxial to the axis

tightening 19.

  In addition, this ft 42 which extends between the base and the sensor 1 (resting on the wall 3a of the part 3) and the base of the bulged head 4a always extends substantially

  radially, on this side, by an elastically deformable ring 44.

  But, near the connection of the crown, the tubular ft 42 now has a radial shoulder 46 defining a cavity 48 in which is housed

  (part of) the head 4a of the pressure and fixing means 4.

  In other words, the elastically deformable crown (or collar) 44 begins where the cavity 48 ends, so that the crown 44 receives the force by

  through the annular wall 50 which radially delimits the cavity 48.

Claims (7)

  Il.- Assembly for applying to a member (1), with a view to its maintenance vis-à-vis a receiving part intended to receive it, a limited stress exerted, in the direction of this member, by means (4 ) pressure and fixing, by means of a force control means (8,24), in which assembly: - the member (1) to be stressed and maintained is a vibration sensor comprising, along an axis, a stack of elements including an element (13) made of piezoelectric material and electrodes (15a, 15b) in electrical connection with this element, the electrodes having connection pins so that the sensor can transmit data relating to the vibrations received, - the receiving part (3) intended to receive this sensor is capable of transmitting vibrations to the sensor, - the pressure and fixing means (4) comprises a support head (4a) and a first traction part (20) engaged on a second traction part (22) complementary to the first part, to ensure traction on the support head when the latter is disposed facing a first surface (la) of the sensor opposite to a second surface disposed opposite of the receiving part, and the force control means (8,24) comprises a ft axially defining a spacer (14,26) between the sensor and the receiving piece, the ft extending axially for this beyond the first surface of the sensor o it cooperates with a crown (16,28) arranged coaxially with the sensor and having a wall inclined relative to its axis, the crown being interposed between the head of the pressure and fixing means and said first surface of the sensor to ensure the stressing of this sensor, under the effect of a pressure exerted on it by the crown and   of an axial force of the head on the ft.   2. An assembly according to claim 1, characterized in that: - the stacked elements (5) of the sensor have an annular shape, with a central orifice extending along the axis (19), - the ft (26) of the the force control means is tubular and extends inside the orifice of the stack of sensor elements, - and the pressure and fixing means comprises a rod extending axially inside tubular ft, this rod being provided with the first traction part (20) which is engaged inside a passage (12) made in the receiving part. 3.- An assembly according to claim 1 or claim 2, characterized in that: - the second surface (11 b) of the sensor is applied against a surface (3a) of the receiving part, - and the ft (26) of the force control means is also supported against   this surface of the receiving room.   4. An assembly according to claim 2, characterized in that the tubular ft (26) is connected to the crown (28), towards its first end, and the head of the means (4) for pressure and fixing comes into contact with the effort control means substantially at   the location of the connection between the ft and the crown.   5. An assembly according to claim 2, characterized in that the tubular ft (42) is connected to the crown (44), towards its first end, and nearby, the tubular ft has a radial shoulder (46) increasing its section towards this first end and defining a cavity (48) inside which the head of the means is received pressure and fixing.   6.- assembly according to any one of the preceding claims,   characterized in that the stacked elements (5) of the sensor are arranged inside a plastic housing (7) comprising at least two parts (9,11) joined together   together along the axis (19) of the sensor and therefore along the axis of the force exerted on it.   7. An assembly according to claim 1, characterized in that: - the stacked elements (5) of the sensor have an annular shape, with a central orifice (11 c) extending along the axis (19), and - the ft of the force control means is tubular and has an external surface provided with lugs (34) towards the free end of the ft situated opposite the   crown, the ft being forcibly engaged inside the stack of sensor elements.