FR2692351A1 - Automobile wheel integrated rotation sensor operational to indicate vehicle speed and distance travelled - uses flexible printed circuit with two folded, perforated tabs to make connection to coaxial cable. - Google Patents

Abstract

The sensor includes a transducer(300) mounted in an enclosure (100) and connection device (500,600) consisting of coaxial-type cable (600) and flexible printed circuit (500) in isolating material. The connection circuit includes two conducting strips to which the sensor leads are soldered. The circuit substrate is formed with two folded tabs each carrying a perforation (520,522) surrounded by a conducting ring (514,518). The core (602) and sheath (606) of a coaxial cable (600) are passed through the perforations and are soldered to the conducting rings. USE/ADVANTAGE - As displacement, anti-skid or anti-lock system sensor. Improved rotation sensor exhibits simple structure, low cost and improved reliability.

Description

 The present invention relates to the field of sensors of physical or electrical quantities, for example displacement sensors.

 The present invention finds particular, but not exclusively, application in the production of a rotation sensor integrated in a wheel hub or axle bearing of a motor vehicle.

 Such a rotation sensor integrated in a motor vehicle axle bearing delivers a signal representative of the speed of rotation of the axle. It can be used to control various pieces of equipment in the vehicle, for example a speedometer, a trip distance recorder, an on-board computer or even a traction control system or an anti-lock system.

 Numerous displacement sensors have already been proposed, including rotation sensors. It has also already been proposed to integrate rotation sensors into wheel hub or axle bearings of a motor vehicle.

 Known sensors generally include a box which houses an electrical transducer and means for connecting the transducer to external operating means.

 The present invention however aims to improve the known displacement sensors by proposing a new sensor of simple structure, at low cost and particularly reliable.

 The present invention also aims to provide a sensor resistant to physicochemical attack and temperature, and having a reduced size.

These objects are achieved according to the present invention by means of a sensor of the type comprising - a housing which houses - an electrical transducer and - means for connecting the transducer to external operating means, characterized in that the connection means comprise - a coaxial type cable ensuring the connection with the external operating means and - a flexible printed circuit made of electrically insulating material having at least
a curved leg and comprising
at least two tracks of electrically conductive material on which the connection pins of the transducer are respectively welded, and
two rings of conductive material respectively connected to said tracks, one of these rings being placed at the level of said curved tab so that the two rings are coaxial and can be engaged respectively on the two conductors of the coaxial cable and welded on them .

 Other characteristics, objects and advantages of the present invention will appear on reading the detailed description which follows and with reference to the appended drawings given by way of nonlimiting example and in which - FIG. 1 represents a view in axial section longitudinal of a sensor according to a preferred embodiment of the present invention, and - Figure 2 shows a perspective view of the connection means according to the preferred embodiment of the present invention.

 The sensor according to the preferred embodiment of the present invention, shown in Figures 1 and 2 attached, is intended to be assembled on the fixed cage, internal or external, of a wheel hub bearing or vehicle axle automobile.

 More precisely, this sensor is intended to be placed radially with respect to the axis of the hub or of the axle, facing the edge of the movable cage, external or internal, of the bearing, so that the sensor detects the relative rotation of the two bearing cages.

 To this end, the movable bearing cage preferably includes a specific element adapted to be detected by the sensor. More precisely still, preferably the transducer of the sensor according to the present invention is formed of a Hall effect probe.

In this case, said specific element carried by the movable cage of the bearing is formed by a magnetic target, for example a multipolar plastoferrite magnet.

 The sensor according to the present invention shown in FIGS. 1 and 2 appended comprises - a box 100, - a cover 200, - a Hall effect probe 300, - a pad 400 made of elastic material, - a flexible printed circuit 500 coated with tracks of electrically conductive material 510, - a coaxial cable 600 and - a rod 700.

 The box 100 can be the subject of numerous variant embodiments depending on the space available at its location.

 Preferably, this case 100 comprises a jacket 102 centered around an axis 104 and closed in leaktight manner at one end 106 by a wall 108 transverse to the axis 104.

 Where appropriate, the external surface of the jacket 102 may include structures adapted to ensure the attachment of the sensor to an associated support.

 The housing 100 is advantageously provided at its second end 110 with a bloom 112 oriented radially outwards.

 The radial recess 113, formed between this opening 112 and the external surface 103 of the jacket 102 serves as a stop for the housing 100 against the casing on which the sensor is fixed.

 The cover 200 is adapted to be fixed on the second end 110 of the housing 100.

 More precisely, the cover 200 is molded onto the coaxial cable 600. The external surface of the cover 200 preferably has two portions 210, 212 axially juxtaposed, respectively external and internal.

 The two portions 210, 212 are preferably centered on the axis 104.

 The external portion 210 advantageously has a section identical to the second end 110 of the housing 100.

 On the other hand, the internal portion 212 has a section identical to the internal housing 114 defined at the level of the opening 112 so that this internal portion 212 can be engaged in said housing 114. In the engagement position of the cover 200 on the housing 100, the radial recess 214, defined between the two portions 210 and 212, rests against the transverse end face 116 of the housing 100.

 The cover 200 and the housing 100 are preferably made by molding of thermoplastic material.

 Preferably the cover 200 is fixed to the housing 100 by ultrasonic welding, in order to seal the sensor housing.

To this end, the cover 200 and the housing 100 are formed from the same material, very advantageously from the material sold by the Société General.
Electric Plastics under the name Ultem. This material
Ultem is composed of polyetherimide. It is preferably loaded with glass fibers, for example at 30%.

 The electrical transducer 300 is placed inside the housing 100 near the transverse bottom 108. More precisely, the electrical transducer 300 is placed opposite the internal face of the jacket 102, ie parallel to the axis 104. Preferably, the wall of the jacket 102 of the housing 100 has a reduced thickness opposite the electrical transducer 300.

 The electrical transducer 300 is immobilized in position in the housing 100 by any suitable means.

The electrical transducer 300 is advantageously immobilized in the case by means of the pad 400. This is formed from electrically insulating elastic material, for example from elastomeric material. Its section at rest is at least complementary to the section of the box left free by the electric transducer 300. Thus the electric transducer 300 is elastically blocked in the box 100 and pressed against the internal surface of the latter when the pad 400 is engaged in the housing 100. If necessary, the pad 400 can itself be locked in position in the housing 100 by any suitable means, for example by gluing. The pad 400 also serves as a block for immobilizing and positioning the transducer 300 during the sensor assembly phase.

 According to an alternative embodiment not shown in the appended figures, this pad 400 can be extended in the direction of the cover 200 so that this pad 400 surrounds the coaxial cable 600 and forms a tight annular seal between the external surface of the cable 600 and the surface internal of the box 100, to reinforce the protection of the transducer 300.

 As indicated above, the transducer 300 is preferably formed of a Hall effect probe. It is advantageously a probe with two output pins.

 By way of nonlimiting example, the electrical transducer 300 can be formed by the device sold by the company Honeywell under the reference S 41.

 Such a transducer is formed of an integrated circuit which brings together a Hall effect probe and an associated processing circuit. This transducer comprises, in a manner known per se, two connection pins 302, one which receives a bias voltage and the other which delivers an output signal.

 The flexible printed circuit 500 provided with electrically conductive tracks 510 can be formed of any flexible printed circuits known to those skilled in the art.

 It may for example be a printed circuit based on the product sold under the name Kapton by the company Dupont de Nemours. Kapton is formed from polyimide. Of course the printed circuit 500 could be formed from all equivalent products.

 The tracks 510 are deposited on the flexible printed circuit 500 by all techniques known to those skilled in the art. It can for example be a deposit by screen printing or a conformation by photoengraving.

 The flexible printed circuit 500 extends essentially parallel to the axis 104 in the housing 100.

 As shown in FIG. 2, the flexible printed circuit 500 preferably comprises two tracks 512 and 516 which run along the printed circuit 500 and end at one end by respective rings 514 and 518. The two rings 514 and 518 are spaced axially on the flexible printed circuit 500.

 Holes 520, 522 are drilled in the center of the rings 514, 518.

 The connection pins 302 of the transducer 300 are welded to the end of the tracks 512, 516 opposite the rings 514 and 518.

 the flexible printed circuit 500 has a tab 530 cut in its outline and folded substantially at 900 around a fold line 532 substantially transverse to the axis 104.

 This tab 530 is formed at the level of the intermediate ring 514. The extension of the tab 530 is such that the orifice 520 and the associated ring 514 are centered on the axis 104, although as indicated above the printed circuit support 500 extends essentially parallel to the axis 104.

 The end of the printed circuit 500 on which the second ring 518 is placed is also folded substantially at 900, around a fold line 534 substantially transverse to the axis 104, so that the orifice 522 and the ring 518 are also centered on the axis 104 while being axially spaced from the aforementioned ring 514.

 When the cover 200 is engaged on the housing 100, the cable 600 extends coaxially to the axis 104.

 We see in Figures 1 and 2 attached the core 602, the first electrically insulating internal coating 604, the coaxial shield 606 and the 'electrically insulating external coating 608 of the coaxial cable 600.

This coaxial cable 600 is stripped to make the core 602 and the shielding 606 accessible.

 Thus the core 602 can be engaged in the ring 514 and welded thereon, while the shield 606 can be engaged in the second ring 518 and welded thereon.

 It is thus understood that the two pins 302 for connection of the electrical transducer 300 are respectively connected to the core 602 and to the shield 606. Preferably, the core 602 receives the output signal, advantageously a logic output signal, from the transducer 300 , while shield 606 receives the bias signal.

 The outer sheath 608 of the cable 600 is preferably formed of a crosslinked polymer to guarantee good immunity to the external environment.

 Preferably the coaxial cable 300 is of the shielded type 606 called "wrapped", that is to say that the coaxial cable 300 comprises a shield 606 formed by simple winding on the insulating coating 604 and not by a braid.

 The coaxial cable 300 has good flexibility in itself and thus allows any required travel, controlled by the suspension, between the hub or axle and the chassis of the vehicle.

 The coaxial cable 300 is also chosen for its good mechanical strength, the fact that it can be easily stripped and that it allows good relative positioning of the associated parts.

 As indicated above, the cover 200 is overmolded on the coaxial cable 600. To guarantee perfect immobilization of the overmolded cover 200 on the coaxial cable 600, it is preferably fixed, by crimping, the rod 700 on the cable 600 before overmolding the cover 200, so that the rod 700 projects at least slightly from the external surface of the cable 600. The rod 700 is advantageously formed of metal. It is preferably split radially. The cover 200 is preferably centered on the axis of the coaxial cable 600.

 Those skilled in the art will appreciate that the sensor according to the present invention comprises a relatively limited number of parts, can be assembled quickly and by its design presents an extremely reduced risk of defect. These parameters ensure low cost and reliability, as indicated in the preamble.

In addition, the sensor is very resistant to physical and chemical attack due to its tightness. It is also temperature resistant and has a particularly small footprint.

 Of course the present invention is not limited to the embodiment which has just been described, but extends to all variants in accordance with its spirit.

Claims (9)

 1.Physical or electrical magnitude sensor, in particular of displacement, of the type comprising - a housing (100) which houses - an electrical transducer (300) and - means (500, 600) for connecting the transducer (300) to means operating devices, characterized in that the connection means comprise - a cable (600) of coaxial type ensuring the connection with the external operating means and - a flexible printed circuit (500) made of electrically insulating material having at least  a curved tab (530) and comprising  at least two tracks (510) of electrically conductive material on which the connection pins (302) of the transducer (300) are respectively welded, and  two rings (514, 518) of conductive material respectively connected to said tracks (510), one of these rings (514) being placed at the level of said curved tab (530) so that the two rings (514, 518) are coaxial and can be engaged respectively on the two conductors (602, 606) of the coaxial cable (600) and soldered thereon.  2.Sensor according to claim 1, characterized in that the flexible printed circuit (300) is formed of polyimide.  3.Sensor according to one of claims 1 or 2, characterized in that the coaxial cable (600) is of the wrapped type, comprising a shield (606) wound.  4.Sensor according to one of claims 1 to 3, characterized in that it comprises a cover (200) welded to the housing (100), preferably by ultrasonic welding.  5. Sensor according to claim 4, characterized in that the cover (200) and the housing (100) are made of thermoplastic material, preferably polyetherimide.  6.Sensor according to one of claims 1 to 5, characterized in that the electric transducer (300) is immobilized in the housing (100) thanks to a pad (400) made of elastic material.  7.Sensor according to one of claims 1 to 6, characterized in that the cover (200) is molded onto the coaxial cable (600), and that the coaxial cable (600) extends parallel to the axis of the case (100).  8.Sensor according to claim 7, characterized in that a rod (700) is crimped on the cable (600) before molding of the cover (200).  9.Sensor according to one of claims 1 to 8, characterized in that it comprises - a housing (100), - a cover (200) fixed to the housing (100), - an electrical transducer formed of a effect probe Hall (300) placed in the housing (100), - a cushion (400) of elastic material which immobilizes the Hall effect probe (300) in the housing (100), - a flexible printed circuit (500) coated with tracks electrically conductive material (510) welded to the connection pins of the electrical transducer (300), - a coaxial cable (600), the two conductors of which are welded to the tracks (510) of the flexible printed circuit (500) and - a ring ( 700) crimped on the coaxial cable (600) before crimping the cover (200) on this cable (600).  11. Sensor according to one of Claims 1 to 10, characterized in that it is installed on a bearing cage, preferably on a bearing cage of the wheel hub or axle of a motor vehicle.  1O.Sensor according to one of claims 1 to 9, characterized in that it further comprises an elastic pad which surrounds the coaxial cable (600) to form an annular seal between this cable (600) and the case (100)