POSITIVE TEMPERATURE COEFFICIENT THERMISTOR DEVICE

Abstract: A positive temperature coefficient thermistor device comprises a case (1), a positive temperature coefficient thermistor element (2) which is located in the case (1), a pair of first terminals (3, 4) arranged in the case (1) to be in contact with corresponding electrodes of the thermistor element (2), a pair of second terminals (5, 6) arranged on the case (1) and associated with the pair of the first terminals (3, 4), and pin members (14, 15) for electrically and mechanically connecting the first terminals (3, 4) with the second terminals (5 6) through an outer wall of the case (1). Such a thermistor device may be used for starting a single phase asynchronous electrical motor.

Description: The present invention relates to a device including a thermistor element having a characteristic of a positive temperature coefficient of electrical resistivity (hereinafter referred to as a PTC), where the PTC thermistor element is enclosed in a case. In particular, the present invention relates to a PTC thermistor device for use in starting a single phase, asynchronous electrical motor, for example in a refrigerator compressor. In one known form, the thermistor element of the PTC thermistor device for use in starting an electrical motor is connected to an electrical power source in series with an auxiliary start winding for starting the motor. In motor starting, the temperature of the thermistor element itself of the PTC thermistor device is low so that it remains in a low resistance condition. Consequently, in motor starting, the thermistor element permits a high initial current to be supplied to the auxiliary start winding for starting the motor, so that the motor can start. Subsequently, the thermistor element is heated up and stabilized in a high resistance condition due to the self-heating thereof, which is generated by the current supplied during the running of the motor so that the supply of current to the auxiliary start winding is automatically stopped. Conventionally, this type of PTC thermistor device is removably coupled with the projected hermetic terminals which are provided for the motor. One example of such conventional device is disclosed in the Specification of US Patent No. 4,241,370. Figs. 4 and 5 of the accompanying drawings show respectively, the above-described example, in which Fig. 4 is a side elevation view and Fig. 5 an underneath plan view of the conventional type PTC thermistor device as disclosed in US Patent Specification No. 4,241,370. As will be evident from Figs. 4 and 5 of the accompanying drawings, this type of device includes a case 1₀ having a pair of openings 2₀, 3₀ in which "plug-in" type terminals 4₀, 5₀ are, respectively, provided. The corresponding hermetic terminals A and B are, respectively, inserted in the "plug-in" terminals 4₀, 5₀. The "plug-in" type terminals 4₀, 5₀ are, respectively, connected to the corresponding contact terminals 7₀, 8₀ which are accommodated in the case 1₀ to be in contact with the respective electrodes of a PTC thermistor element 6₀. It should be noted that the reference symbol C in Fig. 4 indicates a common terminal to be connected with a power source. This common terminal C connects a terminal of a main winding (not shown) with the terminal A or B of the auxiliary start winding for starting the motor. As described above, the conventional PTC thermistor device has the openings which are through an outer wall of the case 1₀, therein two hermetic terminals A and B are, respectively, connected with the corresponding "plug-in" terminals 4₀, 5₀. Accordingly, humid air and/or oxidizing gas are able to easily penetrate into the inside of the case 1₀ through the openings. This causes the thermistor element 6₀ to be degraded. Furthermore, the respective contact terminals 7₀, 8₀ are oxidized by humid air which penetrates into the inside of the case 1₀, thus causing an electrically imperfect contact between the contact terminals 7₀, 8₀ and the electrodes of the thermistor element 6₀. The above disadvantages are common to all conventional PTC thermistor devices which are used for starting single phase motors. In addition to the above, in the case where the hermetic terminals A and B are inserted from the wrong direction to the respective "plug-in" terminals 4₀, 5₀, the above-mentioned two members are not properly connected with each other. In this case, sparking at a connecting portion of two members may occur. However, it is difficult to find out whether or not a connected condition of both terminals 4₀, A; 5₀, B is correct since the connecting portion of the two is covered by the outer wall of the case 1₀. As a result an incorrect connection can be made in the apparatus to which the PTC thermistor device is associated, so that a defective product can be delivered from the factory. Accordingly, the possibility of the above-mentioned situation, i.e., the incorrect contact, is possible as well in conventional PTC thermistor devices because of their structure. It is an object of the present invention to provide an improved PTC thermistor device which is capable of preventing humid air and/or oxidizing gas from penetrating into the inside of the device so that degradation of the thermistor element as well as oxidation of the contact terminals can be prevented, due to the intrusion of the above-mentioned air or gas into the inside of the device. It is a second object of the present invention to provide a desirable PTC thermistor device having improved reliability and durability. According to the present invention there is provided a positive temperature coefficient thermistor device including: a case (1), a positive temperature coefficient thermistor element (2) located in said case (1); a pair of first terminais (3, 4) located in said case (1) to be in contact with corresponding electrodes of said thermistor element (1); a pair of second terminals (5, 6) to be connected with said first terminals (3, 4); and connecting means (14, 15) for electrically connecting said first terminals (3, 4) with said second terminals (5, 6) respectively; characterized in that said second terminals (5, 6) are mounted on an outer surface of said case (1) and that said connecting means comprises pin members (14, 15) which penetrate said case (1) to mechanically connect the respective first terminals (3, 4) with the respective second terminals (5, 6). In the PTC thermistor device having the above-mentioned structure, the second terminals are electrically connected with the respective electrodes of the thermistor element through the corresponding pin members and first terminals. Accordingly, the case is a totally enclosed structure, so that there is no penetration of humid air and/or oxidizing gas into the case from the outside. Furthermore, electrical connection between this device and a motor can be fulfilled through the second terminals of this device. That is, a condition of the connection between the second terminals and terminals of the motor side can be easily confirmed visually since the second terminals are located on the case outside. As described above, the totally enclosed casing is applicable to the case of this device, so that accommodated members in the case such as the thermistor element and the first terminals are protected against humid air and/or oxidizing gas. Therefore, degradation of the thermistor element and oxidation of the first terminals the influence of atmosphere surrounding the device is prevented. As a result the life of the device is greatly increased. Further, since the connecting condition of both terminals can be easily confirmed, incorrect contact between the second terminals of the device and the terminals of the motor can be effectively avoided. As a result, the occurrence of an accident which could be caused by the above-mentioned incorrect contact is prevented, thus resulting in improved reliability. The present invention will be now described in greater detail by way of example with reference to the accompanying drawings, in which: Fig. 1 is a side elevation view of a positive temperature coefficient thermistor device according to one preferred embodiment of the present invention; Fig. 2 is a transverse cross-section view taken along line II-II of Fig. 1; and Fig. 3 is an exploded perspective illustration of the PTC thermistor device; Before commencing detailed description of the present invention proceeds, it should be noted that like parts are designated by like reference numerals and symbols throughout the accompanying drawings. Referring first to drawings of Figs. 1 and 2, particularly to Fig. 2 thereof, a positive temperature coefficient thermistor device, for use in starting a motor, according to the example of the present invention includes a case 1 inside of which is positioned a thermistor element 2 of a material with a positive temperature coefficient (PTC) of a type well known to those skilled in the art. This device is of a type where the thermistor element 2 is totally enclosed by the case 1. As shown in Figs. 1 and 2, the device comprises: the case 1; the disk-formed PTC thermistor element 2; a pair of contact terminals 3, 4, constituting a first terminal of the device, these terminals consisting of plane metal plates which are circularly formed and which are brought into contact with the respective electrodes of the thermistor element 2: and a pair of "plug-in" type terminals 5, 6, constituting a second terminal of the device, which terminals are connected with hermetic terminals A and B provided on the side of a motor (not shown). The above-mentioned case 1 is so constructed that the width of the case is slightly shorter than the length between the above-mentioned two hermetic terminals A and B which are removably jointed to this device. The case 1 comprises a casing 11 having an opening on one side and a lid 12 by which the opening of the casing 11 is covered tightly. In the casing 11, a projecting member 7 is fitted therearound. The purpose of this member 7 is for pressing down another hermetic terminal C which is one of three hermetic terminals A, B and C and is not connected to the device. Furthermore, projections 11b, 12b are arranged around central portions of a bottom surface of the casing 11 and a rear surface of the lid 12, respectively. The respective projections 11b, 12b have the function of positioning the pair of contact terminals 3, 4, which function will be described later on. The above-mentioned thermistor element 2 and the pair of contact terminals 3, 4 are located in the case 1 which is tightly sealed. In addition, an angularly formed insulating holder 8 made of an inorganic material is provided around the thermistor element 2 so as to position the thermistor element 2 in the case 1. Both the contact terminals 3, 4 described above are, respectively, made of a round metal plate so as to correspond to a shape of the thermistor element 2. The contact terminal 3 has a plurality of tongue-shaped contact portions 3a, which have the characteristic function of a spring. Each of the tongue-shaped contact portions 3a protrudes towards the thermistor element 2 and comes in contact with one of the electrodes of the thermistor element 2. The other contact terminal 4 has a plurality of contacting projections 4a, which make contact with the other of the electrodes on its surface facing the thermistor element 2. Furthermore, around a central portion of each contact terminal 3, 4, there is provided a respective mating hole 3c; 4c to enable each contact terminal 3, 4 to be easily located in the case 1 when fitting the respective contact terminals 3, 4 onto the respective case members, i.e., the casing 11 and the lid 12. These mating holes 3c, 4c are designed so as to be engaged by the respective projections 11b, 12b correspondingly arranged on the respective case members 11, 12. Both of the "plug-in" type terminals 5, 6 have a female type connecting portion 5a; 6a by which the hermetic terminals A and B are held elastically therein, respectively. The terminal 5 has a male type connecting terminal 5c, formed as one body thereof, being capable of connecting with a connector (not shown) on the power source side. The above-mentioned two "plug-in" type terminals 5, 6 are arranged at a certain position on the outer surface of the case, where these terminals 5, 6 confront the contact terminals 3, 4 located in the case 1 through the case wall. When each terminal 5; 6 is fitted at its position on the outer surface, it is so designed that an interval of two terminals 5, 6 accords with that of two hermetic terminals A and B to be connected with this device. In this embodiment, the terminal 5 is arranged on the front surface of the lid 12, and the other terminal 6 is arranged on the rear surface of the casing 11. On the outer surface of the case 1 (i.e., the front surface of the lid 12 and the rear surface of the casing 11) where the respective "plug-in" type terminals 5, 6 are arranged, there is formed a protruding portion 9 for positioning each central part of each terminal 5; 6 and a protruding portion 10 for positioning the above-mentioned connecting portion 5a; 6a of each terminal 5; 6, respectively. It should be noted that each shape of the respective protruding portions arranged on the rear face of the casing 11 is the same as that of the respective protruding portions 9, 10 arranged on the lid 12. Further more, a spare protruding portion 13 is provided for fitting one more terminal. The respective "plug-in" type terminals 5, 6 and contact terminals 3, 4 which correspond to these terminals 5, 6 are, respectively, connected with each other by pin members 14, 15, such as rivets or machine screws, which are either made of a material having electrical conductivity, or are covered with electrically conductive material. These pin members 14, 15 are members for penetrating the outer wall of the case 1. The pin member 14, penetrates the lid 12, the contact terminals 3, and the "plug-in" terminal 5 so that they are mechanically and electrically connected with each other through the lid wall. At the same time, the "plug-in" terminal 5 is held in position on the front surface of the lid 12. The other pin member 15 penetrates the bottom wall of the casing 11, the other contact terminal 4 and the "plug-in" terminal 6 so that they are similarly mechanically and electrically connected with each other through the bottom wall. At the same time, the "plug-in" terminal 6 is held in position on the rear surface of the casing 11. Fig. 3 shows an arrangement of the PTC thermistor device of this embodiment. Reference numerals 3b, 4b, respectively, designate through-holes formed at the respective contact terminals 3, 4 so as to insert the pin members 14, 15 therein, and reference numerals 11a, 12a, respectively, designate through-holes formed at the casing 11 and the lid 12, in which the respective pin members 14, 15 penetrate, and reference numerals 5b, 6b, respectively, designate through-holes formed at the respective "plug-in" type terminals 5, 6 so as to insert the respective pin members 14, 15 therein. The PTC thermistor device is arranged in such a way that the respective "plug-in" type terminals 5, 6 are coupled to the corresponding hermetic terminals A, B provided for the motor, in the case where these "plug-in" terminals 5, 6 are inserted into the corresponding hermetic terminals A and B after positional adjustments to the hermetic terminals A and B, so as to couple these "plug-in" terminals 5, 6 to the hermetic terminals A, B. Thus, the respective hermetic terminals A, B are electrically connected with the thermistor element 2 since the respective "plug-in" terminals 5, 6 are electrically connected with the electrodes of the thermistor element through the corresponding contact terminals 3, 4 and pin members 14, 15. As will be apparent from the above-mentioned description, the PTC thermistor element 2 and the contact terminals 3, 4 are not influenced by the outer atmosphere surrounding the device since the case 1 accommodating these members 2, 3, 4 is tightly sealed. Moreover, the "plug-in" terminals 5, 6 are arranged outside the case, so that the correct connection of these terminals 5, 6 to the respective hermetic terminals A and B can be visually ascertained. Accordingly, the members accommodated in the case 1, i.e., the thermistor element 2 and two contact terminals 3, 4, are kept in desirably good condition, in other words, prevented from degradation. In addition, it is possible to prevent accidents caused by the electrical incorrect connection of the connecting terminals between the motor and the device since it is easily possible to verify the correct electrically connection therebetween. Although the present invention has been fully described by way of example with reference to the accompanying drawings, it should be noted that various changes and modifications will be apparent to those skilled in the art. For example, the PTC thermistor element 2, the pair of the contact terminals 3, 4 and the insulating holder 8 are circular or annular in this embodiment. However, these members could be rectangular or in the form of any other shape, as the occasion demands. Furthermore, regarding the shape of the contact terminals 3, 4, it is permitted that both contact terminals have a plurality of the tongue-shaped contact portions the same as the above description, respectively or have a plurality of projections as the contact portions to the electrodes, respectively.

Claims: A positive temperature coefficient thermistor device including: a case (1), a positive temperature coefficient thermistor element (2) located in said case (1); a pair of first terminals (3, 4) located in said case (1) to be in contact with corresponding electrodes of said thermistor element (1); a pair of second terminals (5, 6) to be connected with said first terminals (3, 4); and connecting means (14, 15) for electrically connecting said first terminals (3, 4) with said second terminals (5 6) respectively; characterized in that said second terminals (5, 6) are mounted on an outer surface of said case (1) and that said connecting means comprises pin members (14, 15) which penetrate said case (1) to mechanically connect the respective first terminals (3, 4) with the respective second terminals (5, 6). A positive temperature coefficient thermistor device according to claim 1, further including a positioning member (8) provided in said case (1) so as to surround said thermistor element (2) which is flat board-shaped, to hold said thermistor element (2) at a predetermined position in said case (1). A positive temperature coefficient thermistor device according to claim 2, characterized in that said case (1) has respective support portions for supporting said first terminals (3, 4), each support portion having a plane surface for supporting said first terminals (3, 4), while each one of said first terminals (3, 4) is thin disk-shaped and has through-holes (3c; 4c) engaged by respective projections (11b; 12b) which are formed on the plane surface of said supporting portion. A positive temperature coefficient thermistor device according to claim 3, characterized in that at least one of said first terminals (3, 4) has contact means comprising a plurality of springy tongue members (3a) which respectively protrude toward said thermistor element (2) to contact with said electrode. A positive temperature coefficient thermistor device according to any one of the preceding claims, characterized in that said case (1) has positioning means (9, 10) arranged on said outer surface thereof to locate said second terminals (5, 6) at predetermined positions.

Inventors: MIHARA, MASAHITO, SHIKAMA, TAKASHI, TAKAOKA, YUICHI, YAMADA, YOSHIHIRO
Applicants: MURATA MANUFACTURING CO., LTD.
Application year: 1988
Main classification: H01C7
IPC codes: H01C1, H01C7