Method for evaluating and predicting insulated electric wire with terminal

Abstract

The present application provides a method for easily predicting the result of a free fall test of an insulated electric wire with a terminal. The evaluation prediction method for solving the above problem is an evaluation prediction method for an insulated electric wire with a terminal (20) that has been subjected to a free fall test, the insulated electric wire with a terminal (20) having an insulated electric wire (1) and a terminal (10) connected to at least one end of the insulated electric wire (1), the insulated electric wire (1) having a conductor (2) in which a plurality of bare wires are stranded and a covering layer (3) covering the conductor, the evaluation prediction method for the insulated electric wire with a terminal having a process of confirming whether the tensile strength of the conductor and the 3% tenacity of the covering layer satisfy the following formula.

Description

TECHNICAL FIELD

[0001] The present application relates to an evaluation prediction method of an insulated electric wire with a terminal. BACKGROUND

[0002] As a power line or a signal line for a vehicle or an industrial machine, an insulated electric wire having a conductor and a covering layer covering the conductor has been used. Recently, along with complicated control and automation of a vehicle and an industrial machine, thinning and high strength of the electric wire are required. As an insulated electric wire for a vehicle, an insulated electric wire in which the sectional area of the conductor is set to be substantially 0.22 mm 2 , an insulated electric wire in which the amount of oil attached to the conductor is adjusted in order to suppress buckling, and the like have been proposed.

[0003] Here, in general, the insulated electric wire is less used alone, and terminals are connected to both ends of the insulated electric wire, and various devices are connected via the terminals. Also, at the time of assembling a vehicle or an industrial machine, or at the time of using a vehicle or an industrial machine, sometimes the devices are dropped in a state in which the devices are connected to the electric wire. Due to this, stress toward a free falling direction is instantaneously applied to the insulated electric wire, and the electric wire is sometimes broken. If such a breakage occurs, the devices are damaged or sufficient conduction between the devices cannot be achieved.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent No. 6134103

[0007] Patent Literature 2: Japanese Patent No. 6864856 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] The resistance of the insulated electric wire to the free fall of the above-described device is generally evaluated by a free fall test. Also, at the time of selecting a material of the conductor or the covering layer of the above-described insulated electric wire, or at the time of evaluating the performance of the insulated electric wire with a terminal, the free fall test needs to be performed every time, and it is very troublesome. Therefore, it is desirable to provide a method capable of more easily evaluating the result of the free fall test.

[0010] The main object of the present application is to provide a method capable of easily predicting the evaluation of the free fall test of the insulated electric wire with a terminal.

[0011] SOLUTION TO PROBLEM

[0012] According to an aspect of the present application, there is provided an evaluation prediction method for a terminal-equipped insulated wire, which is an evaluation prediction method when a terminal-equipped insulated wire is subjected to a free fall test, the terminal-equipped insulated wire having an insulated wire and a terminal connected to at least one end of the insulated wire, the insulated wire having a conductor in which a plurality of bare wires are stranded and a covering layer covering the conductor,

[0013] The evaluation prediction method for the terminal-equipped insulated wire includes a step of confirming whether the tensile strength of the conductor and the 3% tenacity of the covering layer satisfy the following equation.

[0014] 100 [N] ≤ (tensile strength of the conductor [N] × 0.7) + (3% tenacity of the covering layer [N])

[0015] According to another aspect of the present application, there is provided an evaluation prediction method for a terminal-equipped insulated wire, which is an evaluation prediction method when a terminal-equipped insulated wire is subjected to a free fall test, the terminal-equipped insulated wire having an insulated wire and a terminal connected to an end of the insulated wire, the insulated wire having a conductor in which a plurality of bare wires are stranded and a covering layer covering the conductor,

[0016] The evaluation prediction method for the terminal-equipped insulated wire includes:

[0017] a step of determining a minimum value of a terminal fixing force required for the free fall test to have a 100% pass rate; and

[0018] a step of confirming whether the minimum value, the tensile strength of the conductor, and the 3% tenacity of the covering layer satisfy the following equation.

[0019] Minimum value [N] ≤ (tensile strength of the conductor [N] × 0.7) + (3% tenacity of the covering layer [N])

[0020] Effects of the Invention

[0021] According to the evaluation prediction method for the terminal-equipped insulated wire of the present application, it is possible to easily predict the result of the free fall test of the terminal-equipped insulated wire. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a side view showing an example of a terminal-equipped insulated wire.

[0023] Figure 2A is a schematic cross-sectional view showing an example of an insulated wire.

[0024] Figure 2B is a schematic cross-sectional view showing another example of an insulated wire.

[0025] Figure 3is a flowchart showing steps of an evaluation prediction method of a terminal-equipped insulated electric wire according to an embodiment.

[0026] Figure 4 is a flowchart showing steps of an evaluation prediction method of a terminal-equipped insulated electric wire according to another embodiment.

[0027] Figure 5 is a graph showing the correlation between the terminal fixing force of a terminal-equipped insulated electric wire and the pass rate of a free fall test.

[0028] Figure 6 is a graph showing the relationship between the tensile strength of a conductor and the cross-sectional area of the conductor, and the fixing force when the conductor is fixed to a terminal. DETAILED DESCRIPTION

[0029] First, the terminal-equipped insulated electric wire, which is the object of the evaluation prediction method of the present application, will be described, and then the evaluation prediction method will be described.

[0030] 1. Terminal-equipped insulated electric wire

[0031] The shape of one end of the terminal-equipped insulated electric wire 20 according to an embodiment of the present application is shown in Figure 1 In the terminal-equipped insulated electric wire 20 according to the present embodiment, the terminal 10 can be connected to only one end portion of the insulated electric wire 1, or can be connected to both end portions. Hereinafter, specific examples of the insulated electric wire 1 and the terminal 10 will be shown, but the insulated electric wire 1 and the terminal 10 of the terminal-equipped insulated electric wire 20 are not limited to these, and the evaluation prediction method described later can be applied to terminal-equipped electric wires other than the terminal-equipped electric wire shown below.

[0032] (1) Insulated electric wire

[0033] The cross-sectional view of the insulated electric wire 1 according to the present embodiment is shown in Figure 2A The cross-sectional view of the insulated electric wire 1 according to another embodiment is shown in Figure 2B The insulated electric wire 1 has a conductor 2 in which a plurality of bare wires 2a, 2b are stranded, and a covering layer 3 for covering the conductor 2.

[0034] In the insulated electric wire 1 shown in Figure 2A and Figure 2B , the conductor 2 is composed of one central bare wire 2a and six concentric bare wires 2b that concentrically surround the one central bare wire 2a. The number of bare wires 2a, 2b is appropriately selected depending on the purpose of the insulated electric wire 1 (terminal-equipped insulated electric wire 20) and the like. In addition, the conductor 2 can be a non-compression conductor in which only a plurality of bare wires 2a, 2b are stranded as shown in Figure 2A , or can be a compression conductor in which a plurality of bare wires 2a, 2b are stranded and then compressed as shown in Figure 2BThe diagram shows a compressed conductor formed by twisting multiple bare wires 2a and 2b together and compressing them into a desired shape. It should be noted that when conductor 2 is a compressed conductor, the compression ratio is preferably 3% to 4%. The compression ratio of conductor 2 is derived from the following formula.

[0035] Compression ratio = (Cross-sectional area of ​​conductor before compression - Cross-sectional area of ​​conductor after compression) / Cross-sectional area of ​​conductor before compression × 100%

[0036] The cross-sectional area and diameter of each bare wire 2a and 2b constituting conductor 2 are not particularly limited, but the total cross-sectional area of ​​each bare wire 2a and 2b, i.e., the cross-sectional area of ​​conductor 2, is preferably 0.16 mm. 2 The cross-sectional area of ​​conductor 2 is more preferably 0.120 mm². 2 Above and 0.16mm 2 Hereinafter, 0.125mm is further preferred. 2 Above and 0.16mm 2 The evaluation and prediction methods described below can also be applied to components with a ratio of 0.16 mm. 2 Insulated wire 20 with terminals and a large cross-sectional area conductor. However, in recent years, there has been a demand to reduce the cross-sectional area of ​​conductor 2, leading to the development of conductor 2 with a cross-sectional area of ​​0.16 mm². 2 The following insulated wire 1 is particularly suitable for use. It should be noted that the cross-sectional shape of conductor 2 can be approximately circular, elliptical, or polygonal, etc. The thickness of each bare wire 2a, 2b constituting conductor 2 can be the same or different, but is usually the same.

[0037] Furthermore, the conductor 2 preferably consists of a center bare wire 2a and concentric bare wires 2b arranged around it, twisted in a certain direction with the center bare wire 2a as the axis. The twist pitch is not particularly limited and can be appropriately selected according to the desired performance of the insulated wire 1. It is generally preferred to be 5 mm or more and 10 mm or less, more preferably 6 mm or more and 8 mm or less. "Twisting pitch" refers to the length of the conductor 2 required to rotate 360° about the center bare wire 2a as the axis.

[0038] In addition, the bare wires 2a and 2b of conductor 2 are untreated bare wires. Furthermore, the amount of oil attached to the bare wires 2a and 2b of conductor 2 can be adjusted.

[0039] The metal of each bare wire 2a, 2b constituting the conductor 2 is not particularly limited and is the same as the metal contained in the conductor of a publicly known insulated electric wire. The metal can be a metal single body or an alloy. In particular, from the viewpoint of conductivity and workability, a copper alloy is preferably used. Examples of the copper alloy include an alloy containing one or more kinds of additive elements selected from the group consisting of Fe, Ti, Mg, Sn, Ag, Ni, In, Zn, Cr, Al, P, Be, Co, and Si, with the remainder being composed of Cu and inevitable elements. The additive elements are preferably Mg and / or Sn. The above additive elements can be one or a combination of two or more. Usually, they are three or less.

[0040] The amount of the additive elements in the copper alloy can also be appropriately selected depending on the properties of the desired insulated electric wire. For example, it is preferably 0.2 mass% or more and 0.4 mass% or less, more preferably 0.25 mass% or more and 0.35 mass% or less, and further preferably 0.28 mass% or more and 0.32 mass% or less. If the amount of the additive elements in the copper alloy is 0.2 mass% or more, there is a tendency that the strength of the conductor 2 increases and the tensile strength becomes strong. On the other hand, if the amount of the additive elements in the copper alloy is 0.4 mass% or less, there is a tendency that the electrical conductivity of the conductor 2 easily increases.

[0041] In addition, the electrical conductivity of the conductor 2 is not particularly limited, but if it is 75% IACS or more, the insulated electric wire 1 can be used for various purposes, and thus it is preferable, and more preferably 80% IACS or more. The electrical conductivity of the conductor 2 is a value calculated from the electrical resistance value according to Japanese Industrial Standard JIS H 0505. The electrical resistance value is measured by a double bridge method using a conductor having a length of 500 mm. The electrical conductivity of the conductor 2 can be adjusted, for example, by the kind or amount of the above additive elements.

[0042] On the other hand, the covering layer 3 is a layer that insulates the conductor 2 and is usually composed of a resin alone or a combination of a resin and other components. The kind of the resin is not particularly limited and, for example, as shown in the examples described later, can be polyvinyl chloride or polyphenylene ether resin, or the like. In addition, an olefin-based resin such as polyethylene or polypropylene can also be contained. Furthermore, the covering layer 3 can contain any component other than the resin, such as a plasticizer, a filler, a stabilizer, a processing aid, or the like.

[0043] The thickness of the covering layer 3 is not particularly limited, but is preferably 0.15 mm or more and 0.25 mm or less, more preferably 0.15 mm or more and 0.20 mm or less. If the thickness of the covering layer 3 is 0.15 mm or more, sufficient insulating properties are easily obtained. On the other hand, if the thickness of the covering layer 3 is 0.25 mm or less, the insulated electric wire 1 can be made thinner. However, the evaluation prediction method described later can also be applied to the terminal-equipped insulated electric wire 20 having a covering layer 3 with a thickness of less than 0.15 mm or a thickness exceeding 0.25 mm.

[0044] The method of manufacturing the insulated electric wire 1 having the conductor 2 and the covering layer 3 described above is not particularly limited, and the evaluation prediction method described later can be applied regardless of the method of manufacturing the insulated electric wire 1. Generally, a plurality of bare wires 2a, 2b are prepared, and are stranded to a desired cross-sectional area to form the conductor 2. Thereafter, an insulating material is extruded and coated around the conductor 2 to form the covering layer 3, and the insulated electric wire 1 is obtained.

[0045] (2) Terminal

[0046] The shape and type of the terminal 10 are not particularly limited, and can be appropriately selected in accordance with the use of the terminal-equipped electric wire 20.

[0047] In Figure 1 The terminal 10 shown in FIG. 1 is provided with, in order, a female or male fitting portion 11 for connection to various devices, a wire barrel portion 12 for fixing the conductor 2 of the insulated electric wire 1, and an insulating barrel portion 13 for supporting the covering layer 3 of the insulated electric wire 1.

[0048] The shape of the fitting portion 11 is a structure that can be connected to various devices, and can be appropriately selected in accordance with the type of the device.

[0049] The wire barrel portion 12 is a portion for reliably electrically or mechanically connecting the conductor 2 to the terminal 10, and has a structure for compressing and fixing the conductor 2.

[0050] The insulating barrel portion 13 has a structure for compressing and fixing the covering layer 3. These are the same as the structure of a general terminal.

[0051] The method of connecting the terminal 20 to the insulated electric wire 1 is not particularly limited, and can be connected, for example, by the following method.

[0052] First, the covering layer 3 is peeled from the end portion of the insulated electric wire 1 to expose the conductor 2. The method of exposing the conductor 2 can use a general method, or the conductor 2 can be exposed by a special tool such as a stripper.

[0053] Next, the terminal 10 is connected to the exposed conductor 2. Specifically, the following method can be used: the covering layer 3 of the insulated wire 1 is fixed to the insulating cylinder portion 13 of the terminal 10, while the wire cylinder portion 12 is pressed, so that the exposed conductor 2 is press-bonded to the wire cylinder portion 12.

[0054] 2. Evaluation prediction method for insulated wire with terminal

[0055] An evaluation prediction method for the insulated wire with terminal described above (hereinafter, also simply referred to as "evaluation prediction method") will be described.

[0056] The evaluation prediction method of one embodiment of the present application can predict the evaluation result of the following test (free fall test): a test in which a weight is attached to one end of an insulated wire with terminal including an insulated wire having a length of 300 mm, and the weight is allowed to freely fall from the other end side in a state where the other end of the insulated wire with terminal is fixed to a prescribed height (for example, a height of 1000 mm). Specifically, the result of whether or not a break occurs in the insulated wire when the weight is allowed to freely fall can be predicted. Note that the prediction result described above is the result when the weight is attached in a manner in which a load is applied to the wire cylinder portion and the insulating cylinder portion of the terminal. Hereinafter, the method will be described.

[0057] In the flowchart of Figure 3 the steps of the evaluation prediction method of one embodiment of the present application are shown.

[0058] First, the tensile strength A [N] of the conductor of the insulated wire of the insulated wire with terminal to be evaluated, and the 3% tenacity B [N] of the covering layer of the insulated wire are determined (SI).

[0059] The "tensile strength A of the conductor" in this specification refers to the tensile strength of a conductor in the same state as in the insulated wire, i.e., the tensile strength of a conductor in a state where a plurality of bare wires are twisted in a certain direction. Note that the tensile strength of the conductor can vary depending on whether or not the bare wires are compressed, the compression rate, the cross-sectional area of the conductor, the twist pitch of the conductor, and the amount of oil attached to the bare wires. Thus, the "tensile strength A of the conductor" is preferably a value obtained by actually producing an insulated wire, extracting the conductor therefrom, and measuring the tensile strength, or a value obtained by producing only a conductor in the same steps as when an insulated wire is produced, and measuring the tensile strength of the conductor. The tensile strength of the conductor can be determined by an Autograph manufactured by Shimadzu Corporation or the like.

[0060] On the other hand, "3% elongation of the covering layer B" means 3% elongation of the covering layer in the same state as in the insulated wire, that is, 3% elongation of the covering layer of a prescribed thickness and in a tubular shape. The "3% elongation of the covering layer B" is preferably a value obtained by peeling the covering layer from the insulated wire and measuring the 3% elongation thereof, or a value obtained by producing only the covering layer in the same procedure as when the insulated wire is produced and measuring the 3% elongation thereof. The 3% elongation of the covering layer is measured in accordance with the JASO D618 standard.

[0061] Next, it is investigated whether or not the "tensile stress of the conductor A" and the "3% elongation of the covering layer B" determined in the above satisfy the following equation (S2).

[0062] 100 [N] ≤ (tensile strength of the conductor A [N] x 0.7) + (3% elongation of the covering layer B [N])

[0063] The right side of the above equation corresponds to the terminal fixing force of the insulated wire with a terminal, as verified in the examples described later. In addition, the value (100 N) of the left side of the above equation is the minimum value of the terminal fixing force at which the pass rate is necessarily 100% when the above free fall test is performed, as demonstrated in the examples described later. This value is a value derived from the examples described later.

[0064] Then, it is determined to be a pass (S3) in the case where the above equation is satisfied, and to be a fail (S4) in the case where the above equation is not satisfied.

[0065] Note that, as needed, the thickness, composition of the covering layer, or various conditions such as the composition, diameter, compression ratio, and lay pitch of the conductor can be changed, and the above evaluation prediction method can be repeatedly performed to determine the optimum kind and structure of the conductor and the covering layer. That is, according to this evaluation prediction method, even if the insulated wire is not actually produced and the free fall test is not actually performed, the evaluation result of the free fall test can be easily predicted. Thus, this is very useful when a new insulated wire is developed or the specifications are changed. In addition, not only in the case of a newly developed insulated wire, but also in quality management, the above evaluation prediction method can be utilized.

[0066] Furthermore, if it is a field in which the above free fall test is performed, the above evaluation prediction method is useful in any field. For example, it is useful in the development, quality management, and the like of insulated wires used in various electrical equipment of control equipment of devices such as automobiles or aircraft, industrial robots, and the like. In particular, it is useful in the evaluation of insulated wires with a terminal for a wire harness for automobiles.

[0067] (Other Embodiments)

[0068] The evaluation prediction method described above can be applied to the free fall test in which the weight of the heavy object is 400 g and the length of the insulated wire is 300 mm. However, in a case where the conditions of the free fall test are changed, or the like, it is preferable to perform the evaluation prediction method in the following manner. In Figure 4 The steps of the evaluation prediction method are shown in the flowchart of FIG. 1.

[0069] First, the minimum value C of the terminal fixing force of the terminal-equipped insulated wire required for the pass rate to be 100% in the desired free fall test is determined (Sll). Specifically, a plurality of terminal-equipped insulated wires including insulated wires having arbitrary conductors and arbitrary covering layers are prepared. Further, the terminal fixing force of each of the terminal-equipped insulated wires is measured. Further, the desired free fall test is performed on each of the terminal-equipped insulated wires, and the pass rate of each kind is calculated. Then, the terminal fixing force and the pass rate of the free fall test are compared, and the minimum value C of the terminal fixing force at which the pass rate is necessarily 100% is determined. For example, in a case where, for the same terminal fixing force, there are both an example in which the pass rate is 100% and an example in which the pass rate is less than 100%, it is not appropriate to take the terminal fixing force as the above minimum value C. The smallest value among the terminal fixing forces at which the pass rate is necessarily 100% is selected as the above minimum value C.

[0070] Next, as with the above embodiment, the tensile strength A [N] of the conductor and the 3% proof stress B [N] of the covering layer of the terminal-equipped insulated wire for which the evaluation result is to be predicted are determined by the desired free fall test (S 12).

[0071] After that, it is investigated whether the above determined "tensile stress A of the conductor", "3% proof stress B of the covering layer", and "minimum value C" satisfy the following equation (S 13).

[0072] Minimum value C [N] ≤ (tensile strength A [N] of the conductor x 0.7) + (3% proof stress B [N] of the covering layer)

[0073] Then, in a case where the above equation is satisfied, it is determined to be a pass (S 14), and in a case where the above equation is not satisfied, it is determined to be a fail (S 15).

[0074] According to the evaluation prediction method, it is possible to easily predict the evaluation result of the desired free fall test without actually producing the insulated wire and actually performing the free fall test, only by initially setting the minimum value C. Thus, it is very useful at the time of development of a new insulated wire or change of specifications. In addition, not only in the case of development of a new insulated wire, but also in quality management, it is possible to utilize the above evaluation prediction method.

[0075] [EMBODIMENT]

[0076] The above evaluation prediction method is based on the following verification derivation. In addition, verification is also performed on whether the evaluation results derived by the above evaluation prediction method are consistent with the actual results (Verification 3).

[0077] Verification 1 (Confirmation of Correlation between Terminal Fixing Force and Free Drop Test Evaluation)

[0078] (1) Preparation of Samples

[0079] Ten samples 1 to 11 were each prepared by the following method.

[0080] (1.1) Preparation of Sample 1

[0081] A copper alloy containing 0.3 mass% of Sn and the remainder composed of Cu and inevitable elements was continuously cast by a horizontal continuous casting machine having a graphite mold provided with a water cooling jacket on the outer periphery, to prepare a cast rod having a diameter of 12 mm. Cold working was applied to the cast rod to obtain a plurality of bare wires each having a diameter of about 0.16 mm.

[0082] Subsequently, seven bare wires were prepared, one of which was used as a center bare wire, and the remaining six were used as concentric bare wires arranged in a concentric manner around the center bare wire. These were twisted in such a manner that the cross-sectional area of the conductor was 0.155 mm 2 .

[0083] A polyvinyl chloride resin (PVC1) manufactured by Mitsubishi Chemical Corporation was extruded from a die of an extruder in such a manner as to cover the periphery of the conductor, to form a covering layer around the conductor, to prepare an insulated wire. The thickness of the covering layer was 0.2 mm.

[0084] Subsequently, a terminal was attached to one end portion of the above insulated wire Figure 1 , to prepare a terminal-equipped insulated wire.

[0085] (1.2) Preparation of Sample 2

[0086] A covering layer was formed using a resin composition 1 composed of a mixture of a polyvinyl chloride resin, a plasticizer, a heavy calcium carbonate filler, a Ca / Zn-based stabilizer, and an acrylic processing aid (see Table 2 for the proportions). Other than this, a terminal-equipped insulated wire was prepared in the same manner as Sample 1.

[0087] (1.3) Preparation of Sample 3

[0088] A covering layer was formed using a polyvinyl chloride resin (PVC2) manufactured by RIKEN TECHNOS Corporation. Other than this, a terminal-equipped insulated wire was prepared in the same manner as Sample 1.

[0089] (1.4) Preparation of Sample 4

[0090] Seven bare wires were prepared in the same manner as in Sample 1 so that the cross-sectional area of the conductor was 0.160 mm 2 in the same manner as in Sample 1. Thereafter, an insulation wire with a terminal was produced by forming a covering layer using a modified polyphenylene ether resin (m-PPE) manufactured by SABIC Co., Ltd. and mounting a terminal in the same manner as in Sample 1.

[0091] (1.5) Production of Sample 5

[0092] A covering layer was formed using the same resin composition 1 as in Sample 2. Other than that, an insulation wire with a terminal was produced in the same manner as in Sample 4.

[0093] (1.6) Production of Sample 6

[0094] Seven bare wires were prepared in the same manner as in Sample 1 so that the cross-sectional area of the conductor was 0.137 mm 2 in the same manner as in Sample 1. Thereafter, an insulation wire with a terminal was produced by forming a covering layer using a modified polyphenylene ether resin (m-PPE) manufactured by SABIC Co., Ltd. and mounting a terminal in the same manner as in Sample 1.

[0095] (1.7) Production of Samples 7 to 11

[0096] The material of the covering layer was changed as shown in Table 1 below. Other than that, an insulation wire with a terminal was produced in the same manner as in Sample 6.

[0097] Note that the resin composition 2 and the resin composition 3 in Table 1 were produced by changing the ratio of the resin composition 1, and the ratio is shown in Table 2.

[0098] [Table 1]

[0099]

[0100] [Table 2]

[0101] Resin composition Resin composition 1 Resin composition 2 Resin composition 3 Polyvinyl chloride resin 100 parts by mass 100 parts by mass 100 parts by mass Plasticizer 25 parts by mass 28 parts by mass 30 parts by mass Heavy calcium carbonate-based filler 6 parts by mass 6 parts by mass 6 parts by mass Ca / Zn-based stabilizer 4 parts by mass 4 parts by mass 6 parts by mass Acrylic-based processing aid - - 8 parts by mass

[0102] (2) Free fall test

[0103] A weight of 400 g was added to the front end of the terminal to apply a load to the bobbin portion and the insulation cylinder portion of the terminal of each of the above-described insulation wires with a terminal (the length of the insulation wire was 300 mm). Then, the end portion on the side on which the terminal was not mounted was fixed at a position of a height of 1000 mm. Then, the weight was allowed to freely fall from the position of a height of 1000 mm, and it was visually confirmed whether or not the insulation wire was broken. The evaluation was performed based on the following criteria. Moreover, the qualification rate of the free fall test was calculated for each sample.

[0104] Qualification: the insulation wire was not broken

[0105] Failure: The insulated wire was broken.

[0106] (3) Terminal fastening force

[0107] The terminal bonding force (N) of the insulated wires with terminals for each of the above samples was determined as follows. The sheathing was peeled off at one end of the insulated wire to expose the conductor, and a terminal was installed at one end of the conductor. Commercially available crimp terminals were used as terminals and crimped onto the conductor. An appropriate installation height was adjusted according to the combination of the conductor and sheathing. Then, the maximum load (N) at which the terminal did not detach when stretched at a speed of 100 mm / min was determined using a general-purpose tensile testing machine. This maximum load was taken as the terminal bonding force.

[0108] (4) Correlation between terminal fastening force and free drop test evaluation

[0109] A graph was created using the terminal bonding force as the horizontal axis and the pass rate of the free-fall test as the vertical axis. Figure 5 The chart is shown in [the image / image]. From [the image / image] Figure 5 It can be seen that the pass rate of the free-fall test increases with the increase of the terminal fastening force, indicating a correlation between the two. Furthermore, based on the test results, the minimum terminal fastening force required to achieve 100% pass rate in the aforementioned free-fall test is 100N.

[0110] Verification 2 (Regarding the relationship between terminal bonding force, conductor bonding force, and sheath bonding force)

[0111] As mentioned above, there is a correlation between the terminal bonding force of insulated wires with terminals and the evaluation results of free-fall tests. It is known that if the terminal bonding force exceeds 100N, the free-fall test results will definitely be good. However, when selecting materials for insulated wires with terminals, manufacturing insulated wires with terminals and measuring their terminal bonding forces individually is cumbersome. Here, the connection of the terminal to the insulated wire is achieved by pressing the conductor's spool portion and the insulating spool portion of the sheathing layer together. That is, the terminal bonding force can be expressed by the following formula, which combines the bonding force between the conductor and the terminal, and the bonding force between the sheathing layer and the terminal. Based on this prediction, the following verification was performed.

[0112] Terminal bonding force = bonding force between conductor and terminal + bonding force between sheathing layer and terminal

[0113] • Terminal-based bonding force of conductors

[0114] For the three types of conductors used in each sample (the conductor cross-sectional area is 0.155 mm²), 2 0.160mm 2 and 0.137mm 2The tensile strength of each of the conductors was determined by a universal testing machine (Autograph) manufactured by Shimadzu Corporation, etc.

[0115] Next, only the conductors were connected to the terminals, and the fixing force was determined by the same method as described above. The cross-sectional area of the conductor was plotted as the horizontal axis, and the strength was plotted as the vertical axis in Figure 6 The tensile strength of the conductor is indicated by black dots, and the fixing force to the terminal is indicated by white dots in Figure 6 Furthermore, the degree to which the strength is reduced by fixing the conductor to the terminal is indicated by gray dots in Figure 6 As shown in Figure 6 , in any of the conductors having the cross-sectional area, a reduction in the strength of about 25 to 30% was observed by fixing the conductor to the terminal. That is, it was found that the fixing force of the conductor to the terminal was "the tensile strength of the conductor x 0.7" or more. The tensile strength, the fixing force to the terminal, and the reduction ratio of the strength are shown as average values in Figure 6

[0116] • Terminal-based fixing force of the covering layer

[0117] The covering layer of each of the 11 types of terminal-equipped insulated electric wires used in the samples was measured by the following methods: the "fixing strength between the conductor and the covering layer" that can predict the correlation with the terminal fixing force, the tensile properties of the covering layer, i.e., the "yield point strength", and the tensile properties of the covering layer, i.e., the "3% tenacity".

[0118] (Measurement of the fixing strength of the covering layer)

[0119] The fixing strength of the covering layer was measured based on JASO D618. Specifically, an insulated electric wire having a length of 100 mm was prepared in the same manner as the sample described above, the covering layer was removed from one end portion to expose the conductor by 25 mm, and the other end portion was cut off and discarded by 25 mm. The entire length of 75 mm of the insulated electric wire was used as the measurement object, and the exposed conductor was inserted through the through hole (a hole having a diameter larger than the outer diameter of the conductor and smaller than the outer diameter of the insulated electric wire) of the holder. The holder was fixed, and the one end portion of the conductor protruding from the holder was stretched. Furthermore, the minimum load at which the covering layer was peeled from the conductor and the conductor was pulled out was measured as the fixing strength. A universal testing machine (Autograph) manufactured by Shimadzu Corporation was used as the measurement device.

[0120] (Measurement of the yield point strength and the 3% tenacity of the covering layer)

[0121] ​The yield point strength and the 3% resistance of the covering layer were measured based on JASO D618. Specifically, from the above-described samples, a tubular test piece having a length of about 150 mm was used, and a yield point strength and a 3% resistance were measured for the tubular test piece using an Autograph manufactured by Shimadzu Corporation.

[0122] (analysis)

[0123] Only the covering layer of each of the above-described samples was fixed to the terminal, and the fixing force was measured by the same method as described above. Furthermore, the fixing force of the covering layer was taken as the horizontal axis, and the adhesion strength, the yield point strength, and the 3% resistance obtained in the above-described test were taken as the vertical axes, respectively, and graphed (not shown), and the relationship between each of the characteristics (adhesion strength, yield point strength, 3% resistance) and the fixing force of the insulated electric wire with a terminal was shown as a linear function (approximation formula). The calculated linear functions are shown in Table 3. In addition, for each of the approximation formulas, a determination coefficient R 2 The results are shown in Table 3. From the values of the determination coefficients, it is known that the correlation between the 3% resistance and the fixing force of the covering layer is very high, and it is known that the value of the 3% resistance is approximately equal to the fixing force of the covering layer to the terminal.

[0124] [Table 3]

[0125] Contact force Yield point strength 3% resistance Approximate formula y = 1.4271x - 6.3342 y＝0.9293+0.2069 y＝1.0106-2.8301 Determination coefficient R 2 ]] 0.6906 0.4454 0.7568

[0126] • Results

[0127] From the above results, it is known that the minimum value of the terminal fixing force of the insulated electric wire with a terminal, which is predicted, can be expressed by the following formula.

[0128] Terminal fixing force (predicted minimum value) = tensile strength of the conductor x 0.7 + 3% resistance of the covering layer

[0129] Verification 3 (verification of the correlation between the terminal fixing force (predicted value) and the free drop test)

[0130] From Verification 1, it is known that, in the case where the above-described free drop test is performed, there is a correlation between the evaluation result thereof and the terminal fixing force of the insulated electric wire with a terminal, and the terminal fixing force with which the evaluation result of the free drop test is necessarily achieved to be 100% qualified is 100 N.

[0131] On the other hand, from Verification 2, it is known that the minimum value of the terminal fixing force of each of the insulated electric wires with a terminal, which is predicted, is "tensile strength of the conductor x 0.7 + 3% resistance of the covering layer".

[0132] In view of the above, it can be said that, in the production of an insulated electric wire with a terminal, if the tensile strength of the conductor and the 3% proof stress of the covering layer satisfy the following equation, the result of the free drop test is necessarily a pass.

[0133] 100 [N] ≤ (tensile strength of the conductor [N] x 0.7) + (3% proof stress of the covering layer [N])

[0134] Therefore, the value calculated from the equation was compared with the test result of the free drop test performed in Verification 1 described above, and the effectiveness of the above equation was confirmed. The results are shown in Table 4.

[0135]

Table 4

[0136]

[0137] ※ (The upper column of the data is the calculated terminal fixing force, and the lower column is the actual pass rate of the drop impact test)

[0138] As shown in Table 4 above, in the case where the above equation (100 [N] ≤ (tensile strength of the conductor [N] x 0.7) + (3% proof stress of the covering layer [N])) is satisfied, the pass rate of any free drop test is 100%, and it was confirmed that the above evaluation prediction method is useful.

[0139] Note that, in the case where the above equation is not satisfied, the pass rate is not always 100%. Therefore, it can be said that, in order to achieve a 100% pass, the above equation needs to be satisfied.

[0140] Industrial applicability

[0141] The evaluation prediction method according to the present application can predict the result of the free drop test of an insulated electric wire with a terminal, which has a conductor in which a plurality of bare wires are stranded and a covering layer that covers the conductor, even without actually producing the insulated electric wire with a terminal. Therefore, it is very useful in the development and quality management of insulated electric wires.

[0142] Explanation of reference signs

[0143] 1 Insulated electric wire

[0144] 2 Conductor

[0145] 2a Center bare wire

[0146] 2b Concentric bare wire

[0147] 3 Covering layer

[0148] 10 Terminal

[0149] 11 Embedding portion

[0150] 12 Bobbin portion

[0151] 13 insulating cylindrical portion

[0152] 20 insulated electric wire with terminal

Claims

1. An evaluation prediction method for a terminal-equipped insulated electric wire, which is an evaluation prediction method when a terminal-equipped insulated electric wire is subjected to a free fall test, the terminal-equipped insulated electric wire having an insulated electric wire and a terminal connected to at least one end of the insulated electric wire, the insulated electric wire having a conductor in which a plurality of bare wires are stranded and a covering layer covering the conductor, the evaluation prediction method for the terminal-equipped insulated electric wire comprising: a step of confirming whether or not a tensile strength of the conductor and a 3% tenacity of the covering layer satisfy the following equation, 100 ≦ (tensile strength of the conductor x 0.7) + (3% tenacity of the covering layer), in which, in the equation, 100, the tensile strength of the conductor, and the 3% tenacity of the covering layer are in N, and the 3% tenacity of the covering layer is measured in accordance with JASO D618.

2. The evaluation prediction method for the terminal-equipped insulated electric wire according to claim 1, wherein the free fall test is a test in which a 400 g weight is added to one end of the terminal-equipped insulated electric wire having the insulated electric wire with a length of 300 mm, the other end of the terminal-equipped insulated electric wire is fixed, and the weight is freely dropped from the other end side together with the one end of the terminal-equipped insulated electric wire.

3. The evaluation prediction method for the terminal-equipped insulated electric wire according to claim 1, wherein a thickness of the covering layer is 0.15 mm or more and 0.25 mm or less.

4. An evaluation prediction method for a terminal-equipped insulated electric wire, which is an evaluation prediction method when a terminal-equipped insulated electric wire is subjected to a free fall test, the terminal-equipped insulated electric wire having an insulated electric wire and a terminal connected to an end portion of the insulated electric wire, the insulated electric wire having a conductor in which a plurality of bare wires are stranded and a covering layer covering the conductor, the evaluation prediction method for the terminal-equipped insulated electric wire comprising: a step of determining a minimum value of a terminal fixing force required for the free fall test to have a 100% pass rate; and a step of confirming whether or not the minimum value, a tensile strength of the conductor, and a 3% tenacity of the covering layer satisfy the following equation, minimum value ≦ (tensile strength of the conductor x 0.7) + (3% tenacity of the covering layer), in which, in the equation, the minimum value, the tensile strength of the conductor, and the 3% tenacity of the covering layer are in N, and the 3% tenacity of the covering layer is measured in accordance with JASO D618. wherein ​ ​ ​ ​ ​ The cross-sectional area of the conductor is 0.16 mm 2 The following, moreover ​ ​ ​ ​ ​ wherein, ​ ​

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