FR2660431A1 - Temperature sensor with thermistor - Google Patents

Abstract

The present invention relates to a temperature sensor using at least one thermistor whose output terminals are formed by filamentary linkages, characterised in that it comprises a support body (230) moulded in one piece from thermoplastic material and including a base (240) moulded over electrically conducting contact tongues (241, 242, 243, 244), which tongues emerge on either side of the base (230) and a core (260) capable of supporting the thermistor (210, 220) and provided with at least one small wall (264, 266) provided with two cutouts (267, 268) designed to hold the wires (212, 214) of the thermistor by clip fastening.

Description

 The present invention relates to the field of thermistor temperature sensors.

 The present invention finds particular, but not exclusively, application to the monitoring of the temperature of motor vehicle engines.

 Numerous thermistor temperature sensors have already been proposed.

 Generally, the thermistor temperature sensors hitherto proposed comprise a casing made of a material which is thermally and electrically conductive, against the bottom of which the thermistor is stressed by an electrically conductive spring. In this case, the thermistors are formed of pellets, the two opposite main faces of which are metallized to form the output terminals of the thermistor. The information representative of the detected temperature is thus taken between the body of the casing housing the thermistor and the spring associated with it.

 Thermistor sensors of the aforementioned type have already done great service. However, they have various drawbacks.

 In particular, the known thermistor temperature sensors have a high manufacturing cost. This high manufacturing cost is justified in particular by the difficulty of assembling the sensor.

 The object of the present invention is to propose a new device eliminating the drawbacks of the prior art.

 This object is achieved according to the present invention by means of a temperature sensor using at least one thermistor, the output terminals of which are formed of wire connections, characterized in that it comprises a support body molded from a plastic part and comprising d on the one hand, a base overmolded on electrically conductive contact tabs, which emerge on either side of the base, and on the other hand, a core capable of housing the thermistor and having a wall provided with two adapted cutouts to maintain the wire connections of the thermistor by snap-fastening.

 Thanks to the structure proposed according to the present invention, the thermistor output wires being held by snap-fastening on the support body, the latter forms with the thermistor an autonomous subassembly which can be easily handled without risk of losing the thermistor, even before all connections between its output terminals and the contact tabs carried by the base of the support body.

 This arrangement greatly facilitates the assembly process of the sensor.

 According to another advantageous characteristic of the present invention, the core has symmetry with respect to the axis of the support body and is adapted to thus receive two separate thermistors.

 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 schematic view in exploded perspective view of a temperature sensor according to the present invention, - Figures 2 and 3 show two views respectively orthogonal to each other, in axial longitudinal section of the same sensor, - Figures 4 and 5 show two views respectively orthogonal to each other in axial longitudinal section of another variant of sensor according to the present invention, and - Figure 6 shows a schematic perspective view of a support body according to this other variant.

 The temperature sensor according to the present invention shown in FIGS. 1 to 3 appended essentially comprises a casing 100 which receives an autonomous sub-assembly 200 comprising two thermistors 210, 220 carried by a support body 230.

 The structure of the housing 100 is classic in itself.

 The housing 100 is made of a material which is good conductor on the thermal and electrical plan. I1 can be for example brass.

 The casing 100 is substantially symmetrical of revolution about an axis 102. The casing 100 defines an internal chamber 104 centered on this axis 102. The chamber 104 is generally cylindrical of revolution around the axis 102. The chamber 104 is blind. The bottom of the casing 100 which delimits one of the ends of the chamber 104 is referenced 106 in the figures.

 Preferably, a part 108 of the external surface of the casing 100 is threaded while another part 110 of the casing 100 is of hexagonal cross section or equivalent to allow the sensor to be easily fixed in a threaded bore formed in a wall delimiting the medium. whose temperature is to be detected.

 The support body 230 essentially comprises a base 240 and a core 260.

 The base 240 is overmolded on electrically conductive contact tabs.

 According to the particular embodiment shown in Figures 1 to 3, there are thus provided four electrically conductive tabs 241, 242, 243 and 244. These tabs 241 to 244 extend parallel to the axis 202 of the support body. They are associated in pairs with each of the thermistors 210, 220.

 More specifically, according to the particular embodiment shown in the appended figures, the base 240 of the support body comprises a cylindrical block 246 of revolution around the axis 202, which is molded onto the aforementioned tabs 241 to 244, so that these emerge on each side of block 246 respectively.

 The block 246 is extended on one side by the core 260 which will be described in more detail below. On the other side, the block 246 is extended by a skirt 248 which surrounds the tongues 241 to 244 and forms a connector body capable of receiving a homologous connector element comprising electrical contacts capable of cooperating respectively with the tongues 241 to 244.

 Such a connector body can be the subject of numerous variant embodiments and will therefore not be described in detail below.

 Preferably, the block 246 is provided with a peripheral rib 249 adjacent to its transverse face 250 opposite the skirt 248.

 Thus, the support body 230 can be fixed on the casing 100 by simple crimping on the rib 249 as shown at 120 in the figures.

 Preferably an O-ring seal 300 is interposed between the aforementioned transverse face 250 of the support body and a homologous bearing surface 112 provided on the casing 100 at the mouth of the latter.

 It will be noted that at their end emerging from the core side 260 the tabs 241 to 244 are provided with axial cutouts capable of receiving the end of the leads of the thermistors 210, 220 in order to facilitate the connection by welding between said tabs 241 to 244 and the thermistor output wires, such as the wires referenced 212, 214 in FIG. 1.

 The core 260 is circumscribed in a cylindrical envelope of dimension slightly smaller than that of the chamber 104.

 More specifically, the core 260 essentially comprises a central fabric 262, two walls 264, 266 and retaining structures of the thermistors referenced 270, 274.

 The central fabric 262 is planar, parallel to the axis 202 is centered thereon.

 The structures 270 and 274 for retaining the thermistors are provided on the free end of the fabric 262, that is to say opposite the base 230.

 As indicated above, the thermistors 210, 220 used according to the invention comprise wired outlet connections 212, 214. In use, these wires are mutually parallel and parallel to the axis 102.

 The retaining structures 270, 274 comprise more precisely, according to the particular embodiment shown in FIGS. 1 to 3, a disc 272 normal to the axis 202 secured to the free end of the core 262 and two fingers 273, 275 integral with the disc 272. The fingers 273, 275 are directed towards the base 230. They extend parallel to the fabric 262.

 The fingers 273, 275 are connected to the disc 272 in the vicinity of the periphery thereof. The fingers 273, 275 are delimited by external surfaces 276 of cylindrical envelope of revolution and internal surfaces 277 planes parallel to the fabric 262.

 The distance between the internal surfaces 277 of the fingers 273, 275 and the central fabric 262 must be slightly greater than the thickness of the thermistors 210, 220 so that the latter can be placed in the housings defined by the central fabric 262 and the fingers 273, 275.

 The walls 264, 266 extend transversely to the axis 202.

They are provided respectively on each of the faces of the central fabric 262, between the aforementioned retaining structures 270, 274 and the base 230.

Each of the walls 264, 266 is provided, respectively in the vicinity of its ends with two cutouts 267, 268. These cutouts are designed to receive and immobilize by snap-fastening the output wires 212, 214 of the thermistors 210. To further reinforce the immobilization of the thermistors 210, 220 on the support body 230, provision can be made on each of the faces of the central fabric 262 between the walls 264, 266 and the retaining structures 273, 274, three projecting fingers 280, 282, 284. The fingers 280 are provided projecting from the center of the fabric 262. In use, they are thus placed between the output wires 212, 214 of a given thermistor.

 The fingers 282, 284 are provided on the longitudinal edges of the fabric 262. They extend the cylindrical envelope of the latter. Thus the fingers 282, 284 are placed on the inside of the output wires 212, 214 of the thermistors.

 The support body can be molded in one piece on the tongues 241, 244.

 The support body 230 must of course be made of an electrically insulating material.

 It can advantageously be a polyamide, such as a polyamide 6.6, loaded, if necessary, with glass fibers.

 We can also consider using to make the support body 230 a thermoplastic material sold under the name VECTRA.

 To assemble the temperature sensor according to the present invention described above, the procedure is as follows.

 Initially, the thermistors 210, 220 are placed on the support 230 between the central fabric 262 and one of the fingers 273, 275. During this operation the output wires 212, 214 of the thermistors are placed between the finger central 280 and respectively one of the lateral fingers 282, 284, engaged in the cutouts 267, 268 of the walls 264, 266 and their free end is introduced into the axial cutouts provided at the end of the tongues 241 to 244. In this position thanks to the holding the output wires 212, 214 by snap-fastening in the cutout 267, 268, the thermistors 210, 220 cannot fall from the support body 230. This gives an autonomous assembly that is easy to handle.

 The output wires 212, 214 of the thermistors are then welded to the tabs 241 to 244. Then, the support body 230 thus equipped is engaged on the casing 100 and the latter is crimped on the support body.

 The device is then ready for use.

 The welds of the output wires 212, 214 of the thermistors on the tabs 241 to 244 have been schematically referenced under the reference 290.

 Preferably, a thermal grease is also placed on the thermistor and / or in the chamber 104 of the casing before introducing the support body 230 therein, in order to establish a good heat exchange between the casing 100 in direct contact with the medium whose temperature is to be measured and the thermistors 210, 220.

 The variant embodiment of the temperature sensor according to the present invention shown in FIGS. 4 to 6 comprises a support body 2300 provided with two thermistors 210, 220 and on which a casing 1000 is overmolded.

 The support body 2300 comprises a core 260 similar to that described with reference to FIGS. 1 to 3 and a base 2400. The base 2400 shown in FIGS. 4 to 6 is overmolded on the tongues 241 to 244. The base 2400 is distinguished of the base 240 shown in Figures 1 to 3 in that it comprises only a generally cylindrical block 2460. The base 2400 therefore does not include a skirt forming a connector body.

Claims (20)

 The support body 2300 comprising the core 260 and the base 2400 will therefore not be described in more detail below.  The housing 1000 is molded in one piece on the support body 2300. The housing 1000 corresponds to the production in the form of a single plastic part of a housing and of a skirt forming connector body similar to the elements referenced 100 and 248 in Figures 1 to 3.  The elements of the casing 1000 represented in FIGS. 4 and 5 equivalent to the elements represented in FIGS. 2 and 3 are matched with similar reference numbers with a multiplying coefficient of 10.  We find in particular in FIGS. 4 and 5, a skirt 2480 forming a connector body, a part of a hexagonal cross-section casing 100 and a part of a threaded casing 1080.  Note that according to the embodiment of Figures 4 to 6, it is no longer necessary to use an O-ring.  The thermoplastic material used to produce the casing 1000 by overmolding must be both a good conductor thermally and have good mechanical strength to allow a satisfactory tightening torque. Société Général Electric under the brand ULTEM 2400.  By way of nonlimiting example, the thermoplastic material forming the support body 2300 may correspond to polybutylene terephthalate loaded with glass fibers at 30% such as the product sold by the General Electric Company under the brand VALOX 420, while the material component casing 1000 may correspond to polyetherimide loaded with 40% glass fibers such as the product marketed by the  In the context of the present application, the term "thermistor" means all the elements having an electrical resistance which varies according to the temperature, the coefficient of variation of resistance being able to be negative (CTN) or positive (CTP).  In the case of thermistors presenting a variation of non-linear resistance as a function of temperature, it is advantageous to linearize the response curve of the sensor, in a manner known per se, using a resistor placed in parallel with the thermistor .  The linearization resistance is advantageously welded on the links 212, 214. If necessary, it can be provided to pre-hold it on the support body 230 or 2300 using clamping structures similar to those previously described for the thermistors.  Of course the present invention is not limited to the particular embodiment which has just been described, but extends to all variants in accordance with its spirit.  In particular, the temperature sensor can be used with a single thermistor.  1. Temperature sensor using at least one thermistor, the output terminals of which are formed by wire connections, characterized in that it comprises a support body (230) molded in one piece from thermoplastic material and comprising a molded base (240). on electrically conductive contact tongues (241, 242, 243, 244) which tongues emerge on either side of the base (230) and, a core (260) capable of supporting the thermistor (210, 220) and provided with at least one low wall (264, 266) provided with two cutouts (267, 268) designed to hold the wires (212, 214) of the thermistor by snap-fastening.  2. Sensor according to claim 1, characterized in that the support body is made in one piece of polyamide.  3. Sensor according to one of claims 1 or 2, characterized in that the support body is made of polyamide 6.6.  4. Sensor according to one of claims 1 to 3, characterized in that the support body is made of polyamide loaded with glass fibers.  5. Sensor according to claim 1, characterized in that the support body (230) is made of VECTRA.  6. Sensor according to claim 1, characterized in that the support body (2300) is made of polybutylene terephthalate.  7. Sensor according to one of claims 1 to 6, characterized in that the core of the support body is designed to support two thermistors (210, 220) and that it is provided with two walls (264, 266) capable maintaining the snap-in wires of the thermistors (210, 220) respectively.  8. Sensor according to one of claims 1 to 7, characterized in that the core (260) of the support body (230) is formed of a central fabric (262) provided with the wall (264, 266) and provided in addition to retaining structures (270, 274) of the thermistors.  9. Sensor according to claim 8, characterized in that the retaining structures are formed by a disc (272) integral with the end of the central fabric (262) and fingers (273, 275) projecting from the disc (272).  10. Sensor according to one of claims I to 9, characterized in that the wires (212, 214) of the thermistors (210, 220) are welded to the tabs (241, 242, 243, 244) carried by the base.  11. Sensor according to one of claims 1 to 10, characterized in that the walls (264, 266) extend transversely to the axis (202) of the support body (200).  12. Sensor according to one of claims 1 to 11 taken in combination with claim 7, characterized in that the central fabric is further provided with projecting fingers (280, 282, 284) between the walls (264, 266 ) and the structures (270, 274) for retaining the thermistors.  13. Sensor according to one of claims 1 to 12, characterized in that the base (230) is shaped as a connector body.  14. Sensor according to one of claims 1 to 13, characterized in that the support body (230) equipped with at least one thermistor (210, 220) is designed to be fixed, for example by crimping on a casing ( 100) of electrically and thermally conductive material.  15. Sensor according to claim 14, characterized in that the casing (100) is made of brass.  16. Sensor according to one of claims 1 to 12, characterized in that the housing (1000) of thermoplastic material is molded onto the support body (2300).  17. Sensor according to claim 16, characterized in that the molded casing (1000) is formed of polyetherimide.  18. Sensor according to one of claims 16 and 17, characterized in that the molded housing (1000) defines a connector body (2480).  19. Sensor according to one of claims 1 to 8, characterized in that the thermistors (210, 220) are coated with thermal grease.  20. Sensor according to one of claims 1 to 19, characterized in that a linearization resistor is welded in parallel with the thermistor (210, 220).