Abstract:
A two-piece sensor assembly is disclosed comprising a sensor body insert having a thermoplastic sensor body molding that can be snap-fit into a thermoplastic sensor housing a spherical-type snap-fit eliminating leak paths or openings that may damage the sensor body.

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a sensor assembly, and more specifically, a snap-fit sensor assembly. 
     In a number of industries, including the automotive industry, sensors are used to monitor a variety of parameters, including, for example, temperature. These sensors typically have a sensor housing encasing a sensor body (e.g., a thermistor assembly for measuring temperature) to protect the sensor body from damage or corrosion caused by the environment in which the sensor must operate, including, for example, chemicals and inclement weather. In addition to offering protection, the sensor housing is typically configured to be mounted on and mate with a part having an opening to receive the sensor housing. For example, the sensor housing may have threads to mate with threads in an opening on the part onto which the sensor is mounted. 
     In order to provide the required protection of the sensor body and configuration to mate with the receiving parts, sensor housings are typically made using injection molded thermoplastic that covers the sensor body and is shaped to mate with the receiving parts. Sensor housings are preferably formed by injecting the thermoplastic material into a mold. It is desirable that the thermoplastic material sufficiently encase the sensor body without any areas of the sensor body touching the outer surface of the thermoplastic material (i.e., touching out) since these areas with thin or no cover of the sensor body by the thermoplastic material provide unwanted leak paths or other openings to the environment which can, over time, lead to damage and corrosion of the sensor body by, e.g., chemicals, inclement weather, etc. (causing an electrical short, high resistance, or an open circuit). 
     In many cases, however, it is difficult to avoid the formation of these areas of touching out. For example, in a typical manufacturing process, the sensor body is placed into the center of the injection mold for the sensor housing prior to the injection of the thermoplastic material. During injection of the thermoplastic material, the force of the plastic can push or move the sensor body from its original centered position to one side of the injection mold such that the sensor body comes in contact with the side of the injection mold, limiting the amount of thermoplastic material that can flow through that touching out point to cover the sensor body. In addition to the risk of touching out, this typical manufacturing process can also be labor intensive since it requires the careful placement of the sensor body into the injection mold prior to injection of the thermoplastic material. 
     It would be advantageous to eliminate the risk of touching out and minimize the labor required in manufacturing these sensor assemblies. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A two-piece sensor assembly is disclosed comprising a sensor body insert having a thermoplastic sensor body molding that can be snap-fit into a thermoplastic sensor housing a spherical-type snap-fit eliminating leak paths or openings that may damage the sensor body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of invention. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which: 
         FIG. 1  is a sensor body in one exemplary embodiment of the invention. 
         FIG. 2  is a sensor body insert in one exemplary embodiment of the invention. 
         FIG. 3  is a cross-section of a sensor housing in one exemplary embodiment of the invention. 
         FIG. 4  is partial cross-section of a sensor assembly in one exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the invention is described using the exemplary sensor assembly of an outdoor air temperature (OAT) sensor, it will be understood that the invention can be used for a variety of different types of sensor assemblies suitable for use with the inventive two-piece design. 
       FIG. 1  illustrates an exemplary sensor body  10  (e.g., a thermistor assembly) for an OAT sensor in one exemplary embodiment of the invention. In this example, the sensing device  18  (e.g., a ceramic NTC thermistor) used for sensing temperature by varying resistance can be connected to a pair of sensor terminals  12  via a pair of wires  16  that can be crimped to the sensor terminals  12  at crimp locations  14 . In order to protect the sensor body  10 , and in particular the sensing device  18 , from the environment, thermoplastic material can be used to cover the sensor body  10 . 
       FIG. 2  illustrates an exemplary sensor body insert  20  (male) in one exemplary embodiment of the invention. The sensor body insert  20  can include a thermoplastic sensor body molding  21  covering at least a portion of the sensor body  10 , including the sensing device  18 , wires  16 , crimp locations  14 , and a portion of the sensor terminals  12 . In one embodiment, the thermoplastic sensor body molding  21  can be molded over the sensor body  10 . The sensor body molding  21  can perform both functions of covering the sensor body  10  and interfacing with the sensor housing  30 . 
     As for the first function, covering the sensor body  10 , the sensor body molding  21  can include a sensor body cover  22  at its core contacting and covering the sensor body  10 . The sensor body cover  22  can include a tip  23  that covers the sensing device  18  of the sensor body  10 , but allows for “touching out.” As for the second function, interfacing with the sensor housing  30 , the sensor body molding  21  can include an arcuate ring  24  on its periphery, at least a portion of which is of greater diameter than the sensor body cover  22  that can interface with the sensor housing  30  using a spherical-type snap-fit, which will be discussed below. The arcuate ring  24  can extend around a portion of the sensor body cover  22  forming an open space between the arcuate ring  24  and the sensor body cover  22 . This arcuate ring  24  can include one or more size-adjustable slots  28  (i.e., openings) that form separate arms  26  in the arcuate ring  24  that can increase the flexibility of the arcuate ring  24  allowing the arms  26  to bend toward the sensor body cover  22  through the open space between the arcuate ring  24  and the sensor body cover  22  under force during assembly. 
       FIG. 3  illustrates a cross-section of an exemplary sensor housing  30  (female) in one exemplary embodiment of the invention. The sensor housing  30  can include a sensor housing cavity  31  designed and shaped to mate with and receive sensor body insert  20  shown in  FIG. 2 . For example, the sensor housing cavity  31  can include a tip  33  to receive the tip  23  of the sensor body cover  22 . Similarly, the sensor housing cavity  31  can include an arcuate inner surface  34  circumscribing the sensor housing cavity  31  and shaped to receive the arcuate ring  24  of the sensor body molding  21  after the arcuate ring  24  deforms during assembly and passes the ridge  35  circumscribing the sensor housing cavity  31 . A step  36  can be located after the arcuate inner surface  34  to control the insert distance of the sensor body insert  20  into the sensor housing  30 . In one embodiment, threads  38  can be provided on the exterior of the sensor housing  30  for mating with threads located on a part having an opening to receive the sensor housing  30 . 
     In one embodiment, the thermoplastic sensor housing  30  can be injection molded. In order to avoid knit lines or other areas where the flow front of multiple streams of thermoplastic come together and do not melt together creating small openings in the sensor housing  30 , in one embodiment, the thermoplastic material can be injected into the die in a fountain flow gated at the end of sensor housing tip  33  of the sensor body insert housing  30 . 
       FIG. 4  illustrates an exemplary partial cross-section of a sensor assembly  40  in one exemplary embodiment of the invention. To better illustrate the invention, the exemplary sensor body insert  20  of  FIG. 2  (non-cross-sectioned) has been shown inserted into the exemplary cross-section of a sensor housing  30  of  FIG. 3 . As illustrated in  FIG. 3 , the sensor body insert  20  is protected from the environment by the sensor body housing  30  such that, even if the sensing device  18  in the sensor body insert tip  23  were at or close to the surface of the sensor body cover  22  (e.g., if the sensing device  18  touched out during molding of the sensor body insert  20 ), the sensing device  18  is still fully enclosed by the sensor housing  30 . 
     In order to assemble the sensor body insert  20  to the sensor housing  30 , the sensor body insert  20  can be pushed axially into the sensor housing  30  causing the arms  26  of the arcuate ring  24  formed by the slots  28  to contact the ridge  35  in the sensor housing cavity  31 . As the sensor body insert  20  is pushed axially into the sensor housing cavity  31 , the radial force applied by ridge  35  bends the arcuate ring  24  (e.g., the arms  26 ) toward the sensor body cover  22  through the open space between the arcuate ring  24  and the sensor body cover  22 . When sufficient axial force is applied to the sensor body insert  20  during assembly to push the arcuate ring  24  past the ridge  35  and be seated into the arcuate inner surface  34  circumscribing the sensor housing cavity  31 , the sensor body insert  20  and the sensor housing  30  form a spherical-type snap-fit, preventing removal of the sensor body insert  20  from the sensor housing. Once assembled, removal of the sensor body insert  20  from the sensor housing  30  can require significant axial removal force that would most likely damage the sensor body insert  20 . The fact that damage of the sensor body insert  20  would result from any attempted removal from the sensor housing  30  can be useful when determining if a customer has tampered with a sensor assembly  40  prior to seeking replacement of a defective part. 
     A number of different thermoplastic materials can be used for the sensor body insert  20  and the sensor body housing. The particular thermoplastic materials chosen for the sensor body insert  20  and the sensor housing  30 , as well as the design of the shape and configuration of the arcuate ring  24 , ridge  35 , and the arcuate inner surface  34  (e.g., radii, number of slots, etc.), can determine the amount of assembly force and removal force required by the particular spherical-type snap-fit. In some embodiments, the sensor body insert  20  can be more flexible than the rigid sensor housing  30 , while in other embodiments, the opposite configuration may be used (i.e., more rigid sensor body insert  20  and more flexible sensor housing  30 ). In one embodiment, the sensor body insert  20  can be made from PA 66 (i.e., Polyamide 6/6 or Nylon 6/6) while the sensor housing  30  can be made using PBT GF30 (i.e., polybutylene terephthalate with glass fiber reinforcement 30%). The selection of PBT GF30 can provide non-hydroscopic properties, when molded without knit lines, so moisture cannot penetrate to the sensing device  18 . In other embodiments, other thermoplastics with similar flexural modulus and elongation properties can be used for the sensor body insert  20  and the sensor housing  30 . 
     This particular combination of thermoplastic materials used with the exemplary design of the sensor assembly  40  shown in  FIG. 4  can require approximately 50 lbs. of axial assembly force to assemble the sensor body insert  20  into the sensor housing  30 . The choice of thermoplastic materials and design of the spherical-type snap-fit can be made to provide a particular range of acceptable assembly and removal forces (e.g., provide a certain assembly force to allow automation of the assembly process). 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.