Method for determining bolt tightening torque

Abstract

Disclosed is a method for determining a bolt fixing torque, comprising: a preparation step of preparing a sample of an object to be bolted and a sample of a bolt; a sample breaking torque acquisition step of measuring and acquiring the sample breaking torque when at least one of the sample of the object and the sample of the bolt breaks when the sample of the object and the sample of the bolt are bolted; an effective tightening torque region determination step of determining an effective tightening torque region for tightening without breaking based on the sample breaking torque; an experimental torque selection step of selecting a plurality of experimental torques within the effective tightening torque region; a bolt tightening angle measurement step of test-tightening the sample according to each of the selected plurality of experimental torques and measuring the bolt tightening angle; and a bolt fixing torque determination step of determining a bolt fixing torque to be used for bolting the object to the bolt from a plurality of experimental torques based on the plurality of measured bolt tightening angles.

Description

Technical Field

[0001] The present invention relates to a method for determining a bolt fixing torque, and more particularly, to a method for determining a bolt fixing torque capable of accurately determining the bolt fixing torque to improve the quality of the bolt. Background Art

[0002] Secondary batteries (hereinafter referred to as "batteries") are used as energy sources in a variety of fields, including large devices such as electric vehicles and energy storage systems, as well as portable electronic devices such as smartphones, laptop computers, and tablet computers. Among these fields, many require large capacities, particularly in electric vehicles and smart grid systems, where batteries are being used extensively.

[0003] To increase the capacity of a battery, one method involves increasing the capacity of a single battery cell. However, this method does not significantly increase the capacity, physically limits the expansion of battery size, and makes management difficult. Therefore, medium-sized or large-sized battery packs, in which multiple battery cells are electrically connected, have been used.

[0004] Such a battery pack may include an outer case that is separated from a pack case and capable of protecting a plurality of battery cells from external impact, and the pack case may be fixed to an inner side of the outer case.

[0005] In the prior art, the battery pack case is secured to the outer casing by bolt tightening (hereinafter referred to as "bolting") using a torque wrench, nut runner, or other similar method. When bolting is arbitrarily selected within a certain torque range (hereinafter referred to as the "tightening torque range"), the bolt tightening torque applied to the bolt is generally less than the breaking torque. The selection of the bolt tightening torque depends on the operator's experience.

[0006] However, in this method, as the breaking torque increases, the torque deviation within the tightening torque range also increases. In other words, as the breaking torque increases, the operator's options become greater, making it difficult for the operator to empirically determine the bolt tightening torque.

[0007] Furthermore, the tightening force required for bolting can vary depending on bolting conditions such as the dimensional accuracy, surface roughness, and lubrication conditions of the bolts, outer casing, and battery pack case. However, it is difficult for operators to accurately consider these conditions each time they perform bolting. Therefore, even when tightening bolts using an empirically determined bolt tightening torque, operators cannot achieve the required breaking torque. This means that during bolting, tightening may be insufficient or excessive, resulting in inconsistent bolting quality.

[0008] Background art of the present invention is disclosed in the following patent documents.

[0009] (Patent Document 1) KR 10-2020-0092783 A

[0010] (Patent Document 2) JP 2009-274152 A Summary of the Invention

[0011] Technical issues

[0012] The present invention provides a method for determining the bolt fixing torque, which can accurately determine the bolt fixing torque to improve the bolt fixing quality.

[0013] Technical Solution

[0014] A method for determining a bolt fixing torque according to an exemplary embodiment of the present invention includes: a preparation process of preparing a sample of an object to be bolted and a sample of a bolt; a sample breaking torque acquisition process of measuring and acquiring a sample breaking torque at which at least one of the sample of the object and the sample of the bolt breaks when the sample of the object and the sample of the bolt are bolted; an effective tightening torque region determination process of determining an effective tightening torque region for performing tightening without breaking based on the sample breaking torque; an experimental torque selection process of selecting a plurality of experimental torques within the effective tightening torque region; a bolt tightening angle measurement process of test tightening the sample according to each of the plurality of selected experimental torques and measuring the bolt tightening angle; and a bolt fixing torque determination process of determining a bolt fixing torque for bolt fixing the object to the bolt from the plurality of experimental torques based on the plurality of measured bolt tightening angles, wherein, in the bolt tightening angle measurement process, the rotation angle of each sample bolt is measured from a predetermined reference time point to a time point at which the test tightening ends.

[0015] The reference time point is a time point when the force applied to the sample bolt during test tightening increases and exceeds a torque corresponding to a certain percentage (%) of the lower limit of the experimental torque.

[0016] The reference time point is a time point when the force applied to the sample bolt during the test tightening increases and exceeds 40% of the lower limit of the experimental torque.

[0017] The reference time point is the time point when the force applied to the sample bolt during the test tightening changes from the rotational force to the tightening force.

[0018] The reference time point is a time point when the current value and the revolutions per minute of the bolt fastening device drastically change during the test tightening, wherein the bolt fastening device rotates the sample bolt to bolt-fasten the sample bolt to the sample object.

[0019] The reference time point is the time point when the head of the sample bolt comes into contact with the sample object during the test tightening.

[0020] In the effective tightening torque region determination process, when a first torque smaller than the sample breaking torque is set as a lower limit and a second torque between the first torque and the sample breaking torque is set as an upper limit, a range from the first torque to the second torque is determined as the effective tightening torque region.

[0021] In the effective tightening torque region determination process, the range of 60% to 80% of the breaking torque of the sample is determined as the effective tightening torque region.

[0022] In the test torque selection process, the difference between two consecutive test torques is set to a certain value, and a plurality of test torques are sequentially selected within the effective tightening torque region.

[0023] The plurality of experimental torques includes at least one of a lower limit or an upper limit of the effective tightening torque region.

[0024] The bolt tightening angle measurement process includes: an experimental torque distribution process in which a plurality of experimental torques are respectively distributed to a plurality of bolt fixing devices that perform test tightening on a sample; and a sample bolt fixing process in which sample bolts are respectively bolted to a sample object by the plurality of bolt fixing devices to which the experimental torques are distributed, wherein the rotation angle of each sample bolt is measured in the sample bolt fixing process.

[0025] The bolt tightening angle measurement process includes: an experimental torque distribution process in which a lowest value to a highest value or a highest value to a lowest value among a plurality of experimental torques are distributed in sequence to a bolt fixing device that performs test tightening on a sample; and a sample bolt fixing process in which a plurality of sample bolts are respectively bolted to a plurality of sample objects by the bolt fixing device in the order in which the experimental torques are distributed, wherein the rotation angle of each sample bolt is measured in the sample bolt fixing process.

[0026] The bolt tightening torque determination process includes: a bolt tightening angle screening process, in which a measured bolt tightening angle is compared with a predetermined reference bolt angle to screen out a bolt tightening angle smaller than the reference bolt angle; and an experimental torque screening process, in which when there is one screened bolt tightening angle, the experimental torque in a test tightening in which the corresponding bolt tightening angle is measured is screened out, or when there are a plurality of screened bolt tightening angles, their average value is calculated, a minimum bolt tightening angle having a standard deviation of less than 3 with respect to the average value is checked, and the experimental torque in the test tightening in which the corresponding bolt tightening angle is measured is screened out, wherein the experimental torque screened in the experimental torque screening process is determined as the bolt tightening torque.

[0027] The base bolt angle is 30 degrees.

[0028] Beneficial effects

[0029] According to an exemplary embodiment of the present invention, test tightening is performed according to a plurality of experimental torques selected within the tightening torque region, and the results thereof are used to finally determine the bolt fixing torque, and thus, an accurate bolt fixing torque reflecting the deviation of the materials between the object to be bolted and the bolt can be determined.

[0030] Therefore, since the operator can freely and directly determine the bolt tightening torque within the tightening torque range, the bolt tightening torque can be accurately determined compared to the existing technology that only reflects the breaking torque in the bolt tightening torque. Therefore, when bolting the object and the bolt, sufficient tightening force can be provided to tighten the bolt. This prevents the bolt from being tightened too loosely or too tightly, and ensures a uniform quality level of bolt tightening. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flowchart schematically illustrating a method for determining a bolt fastening torque according to an embodiment of the present invention.

[0032] Figure 2 1 is a conceptual diagram for explaining a bolt tightening angle, a test torque, and a reference time point according to an embodiment of the present invention.

[0033] Figure 3 Schematic diagram for explaining a measurement process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention can be implemented in different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, embodiments of the present invention are provided to make this disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art. In order to describe embodiments of the present invention, the drawings may be shown exaggeratedly, parts not related to the description will be omitted in the drawings, and the same reference numerals in the drawings refer to the same elements.

[0035] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0036] 1. Method for determining bolt tightening torque according to an embodiment of the present invention

[0037] Figure 1 is a flowchart schematically illustrating a method for determining a bolt fastening torque according to an embodiment of the present invention. Figure 2 1 is a conceptual diagram for explaining a bolt tightening angle, a test torque, and a reference time point according to an embodiment of the present invention. Figure 3 (a) to (c) are schematic diagrams for explaining a measurement process according to an embodiment of the present invention.

[0038] Will refer to Figures 1 to 3 A method for determining a bolt fastening torque according to an embodiment of the present invention is described in detail.

[0039] Reference Figure 1 , a method for determining a bolt fastening torque according to an embodiment of the present invention may include the following processes.

[0040] 1.1. Preparation process (S100)

[0041] The preparation step ( S100 ) is a step for preparing samples of objects to be bolted and samples of bolts. The samples may include a plurality of sample objects 10 and a plurality of sample bolts 20. The number of sample objects 10 and sample bolts 20 prepared may be based on the number of test fastenings (described later). Specifically, if three test fastenings are performed, three sample objects 10 and three sample bolts 20 may be prepared.

[0042] Of course, the number of each of the sample objects 10 and sample bolts 20 may be greater than the number of test tightenings. For example, even if three test tightenings are performed, three or more sample objects 10 and three or more sample bolts 20 may be prepared for the acquisition process described later.

[0043] Reference Figure 3 The sample objects 10 may be specific plate members having the same material and the same thickness as the object to be bolted (not shown). For example, each sample object 10 may include a lower plate 11 and an upper plate 12. The lower plate 11 and the upper plate 12 are stacked vertically, and fastening holes are formed through these plates in the vertical direction.

[0044] The object to be bolted may be a battery pack. Lower plate 11 may be made of the same material as the battery pack housing and have the same thickness. Furthermore, upper plate 12 may be made of the same material as the outer shell and have the same thickness. Of course, the type of object to be bolted may vary, in addition to the battery pack housing. Therefore, the materials and thicknesses of lower plate 11 and upper plate 12 may also vary.

[0045] The sample bolt 20 can be a bolt of the same type as the bolt used to assemble the battery pack case and the outer shell when manufacturing the battery pack. Each sample bolt 20 may include a head 21 and a screw portion 22. The head 21 may extend in the up and down directions and may have an upper portion formed in a nut shape or may have a drive groove formed in the top surface to connect to a bolt fixing device (not shown), which will actually perform the test tightening of the sample and the bolt fixing operation of the object and the bolt. The screw portion 22 may be formed in the shape of a round rod and extend downward from the head 21, and may have a thread formed on its outer circumferential surface. Of course, the sample bolt 20 may have various structures.

[0046] The bolt fixing device may use, for example, an electric tool such as a nut runner or a torque wrench. When a bolt fixing torque is input, the bolt fixing device can rotate the sample bolt 20 and the bolt axially at the bolt fixing torque, thereby tightening the sample bolt 20 and the bolt to the sample object 10 and the object. In addition, the bolt fixing device may be provided with an electronic goniometer. When the sample bolt 20 and the bolt are axially rotated and tightened, the bolt fixing device may use the electronic goniometer to measure the rotation angle of the sample bolt 20 and the actual bolt from the desired time point until the bolt fixing is completed (hereinafter referred to as the "bolt tightening angle"), and then provide the rotation angle to the operator via a screen. Of course, the bolt fixing device may have various structures and methods.

[0047] 1.2. Sample Fracture Torque Acquisition Step (S200)

[0048] Reference Figure 1 The sample breaking torque acquisition step ( S200 ) is a step of measuring and acquiring the sample breaking torque at which at least one of the sample object 10 and the sample bolt 20 breaks when the sample object 10 and the sample bolt 20 are bolted together. Specifically, the sample breaking torque may be a specific torque at which at least one of the sample object 10 and the sample bolt 20 may break when the sample object 10 and the sample bolt 20 are bolted together by applying torque to the sample bolt 20. For example, the sample breaking torque may be the torque applied to the sample bolt 20 when the stress developed in the sample bolt 20 during bolting is equal to the yield stress of the sample bolt 20, or the torque applied to the sample bolt 20 when the stress developed in the sample object 10 during bolting is equal to the yield stress of the sample bolt 20.

[0049] The sample breaking torque can be experimentally obtained from the torque applied to the sample bolt 20 when at least one of the components breaks by bolting the sample bolt 20 and the sample object 10 until one of the components breaks, or can be theoretically calculated based on the material properties and shape of the sample bolt 20 and the material properties and shape of the sample object 10.

[0050] 1.3. Effective Tightening Torque Range Determination Step (S300)

[0051] The effective tightening torque range determination step (S300) is a step of determining an effective tightening torque range in which the sample can be tightened without breaking, based on the sample breaking torque. In this step, when a first torque less than the sample breaking torque is set as a lower limit and a second torque between the first torque and the sample breaking torque is set as an upper limit, the range from the first torque to the second torque is determined as the effective tightening torque range.

[0052] The effective tightening torque may refer to the torque applied to the bolt to obtain the tightening force required to secure the object and the bolt to each other, and the effective tightening torque range may refer to the range of torque applied to the bolt to obtain the tightening force required to secure the object and the bolt to each other. Here, even when multiple identical objects are bolted together using multiple identical bolts, the tightening conditions of the respective bolts and the respective objects (such as surface roughness, dimensional accuracy, and lubrication status) may differ slightly from each other.

[0053] Therefore, even when bolting the same object and the same bolt using the same tool and the same torque, the resulting tightening force may vary. Therefore, in an embodiment of the present invention, an effective tightening torque range is determined, a test tightening is performed based on this range, and the bolt tightening torque is determined by utilizing the performance results of the test tightening. Thus, a bolt tightening torque can be determined that minimizes the variation in tightening force, for example, achieving optimal reproducibility when bolting multiple times. In other words, a bolt tightening torque can be obtained that reflects the deviations in tightening conditions that may occur between multiple bolt tightening operations using the same type of bolt and object. Furthermore, the bolt tightening torque can represent the tightening torque ultimately used to perform a bolt tightening between an actual object and an actual bolt.

[0054] The description will continue with the effective tightening torque region determining process ( S300 ).

[0055] The first torque may be 60% of the sample's breaking torque, and the second torque may be 80% of the sample's breaking torque. The effective tightening torque range is defined as the range between 60% and 80% of the sample's breaking torque. That is, when the sample's breaking torque is 100 kgf·cm, the effective tightening torque range may be between 60 and 80 kgf·cm. Furthermore, when the sample's breaking torque is 200 kgf·cm, the effective tightening torque range may be between 120 and 160 kgf·cm.

[0056] The effective tightening torque range shows the relationship between the test torque and the breaking torque to determine the bolt tightening torque. Bolting is performed at a torque less than the breaking torque, thereby ensuring stable bolting. When bolting is performed at a torque significantly less than the breaking torque, the bolt may become loosely tightened. Furthermore, when bolting is performed at a torque very close to the breaking torque, excessive tension is applied to the bolt, and the structure of the bolted portion may become unstable due to external impact. The effective tightening torque range can be determined empirically by the operator.

[0057] For example, a worker may repeatedly perform bolting using various objects and bolts at a torque selected within the range of X% to Y% of the breaking torque. Upon confirming that the bolting quality is superior to other conditions, the worker may determine that selecting and performing bolting at a torque within the range of X% to Y% of the breaking torque ensures the desired bolting quality. Therefore, the effective tightening torque range can be determined to be within the range of X% to Y% of the sample's breaking torque. In an embodiment of the present invention, this effective tightening torque range is determined to be within the range of 60% to 80% of the sample's breaking torque.

[0058] For example, when the lower limit of the effective tightening torque region is less than 60% of the sample breaking torque, a test tightening may be performed at a torque less than 60% of the sample breaking torque during the test tightening. Therefore, in this test tightening, the tightening between the sample object 10 and the sample bolt 20 may be loose.

[0059] Furthermore, when the upper limit of the effective tightening torque region is greater than 80% of the sample breaking torque, a test tightening may be performed at a torque greater than 80% of the sample breaking torque during the test tightening. Therefore, during the test tightening, the sample bolt 20 may be excessively deformed, for example, elongated, and the tightened portion may be weak.

[0060] Of course, the effective tightening torque area can be obtained from a specific model that models the bolt and the bolted structure of the object.

[0061] 1.4. Experimental Torque Selection Process (S400)

[0062] The test torque selection process (400) is a process for selecting multiple test torques within the effective tightening torque range. This process can be performed by setting the difference between two consecutive test torques to a certain value and sequentially selecting multiple test torques within the effective tightening torque range. In other words, multiple test torques can be selected within the effective tightening torque range so that the test torques are evenly distributed within the effective tightening torque range. Here, the multiple test torques can include at least one of the lower limit and the upper limit of the effective tightening torque range.

[0063] For example, if the effective tightening torque range is 60kgf·cm to 80kgf·cm, you can select 60kgf·cm, 70kgf·cm, and 80kgf·cm as the test torque. Of course, within the same range, you can select 60kgf·cm, 65kgf·cm, 70kgf·cm, 75kgf·cm, and 80kgf·cm as multiple test torques.

[0064] 1.5. Bolt Tightening Angle Measurement Process (S500)

[0065] The bolt tightening angle measuring step (S500) is a step of performing a test tightening on a sample according to each of a plurality of test torques and measuring the bolt tightening angle. Figure 2 The measurement of the bolt tightening angle is performed for each test tightening, and torques from 0 to the test torque are sequentially applied to the sample bolt 20 at the start of tightening. When a predetermined reference time point is reached after a certain time has passed, the rotation angle of the sample bolt (20) (referred to as "bolt tightening angle") can be measured from the predetermined reference time point to the time point when the test tightening ends after the torque applied to the sample bolt 20 reaches the test torque.

[0066] 1.6. Definition and meaning of benchmark time point

[0067] Here, the reference time point can be defined as follows.

[0068] Reference Figure 2 The reference time point may be defined as the time point at which the force applied to the sample bolt during the test tightening increases and exceeds a torque corresponding to a specific percentage (%) of the lower limit of the test torque. Specifically, the reference time point may be the time point at which the force applied to the sample bolt during the test tightening increases and exceeds 40% of the lower limit of the test torque.

[0069] The meaning of the reference time point is as follows. Figure 3 (a), the reference time point may be the time when the force applied to the sample bolt 20 during the test tightening changes from the rotational force F A Converted into tightening force F B The time point of time.

[0070] For example, when the test tightening starts, torque is applied to the sample bolt 20 while the torque increases from 0 to the test torque. Figure 3 As shown in (a) and (b), the sample bolt 20 is rotated by a certain angle θ A and then inserted into the hole of the sample object 10. After a certain period of time, the head 21 comes into contact with the sample object 10.

[0071] Here, the torque may be slowly changed until the head 21 of the sample bolt 20 comes into contact with the sample object 10. That is, the sample bolt 20 may be inserted into the hole with only a small force, and the sample bolt 20 may be smoothly rotated by a certain angle θ of approximately 360° or more. A While being lightly tightened to the sample object 10. Here, the force applied to the sample bolt 20 may be referred to as a rotational force FA.

[0072] Subsequently, after the point in time when the head 21 of the sample bolt 20 contacts the sample object 10, the sample bolt 20 is forcibly rotated, and the sample bolt 20 undergoes elastic deformation or plastic deformation. Therefore, when the bolt fixing is completed by firmly tightening the sample bolt 20 until the torque reaches the test torque, the desired tightening force between the sample bolt 20 and the sample object 10 can be obtained. That is, as Figure 3 As shown in (b) and (c), when the sample bolt 20 is rotated with a large force, the sample bolt 20 gradually rotates to a certain angle θ B The bolt fixation can be completed by being firmly fastened to the sample object 10 at the same time. Here, the force applied to the sample bolt 20 can be referred to as the fastening force F B Here, in the figure, L represents the length of the sample bolt 20 before deformation, and L' represents the length of the sample bolt 20 after elastic deformation or plastic deformation.

[0073] That is, referring to the above description, the reference time point may be the time point when the head 21 of the sample bolt 20 comes into contact with the sample object 10 during test tightening. Furthermore, in other words, the reference time point may be the time point when the current value and the number of revolutions per minute of the bolt fastening device (not shown) that rotates the sample bolt 20 during test tightening suddenly change. In particular, during test tightening, the reference time point may be the time point when the current of the bolt fastening device begins to increase sharply and the number of revolutions per minute begins to decrease sharply.

[0074] Meanwhile, when the sample bolt 20 is rotated more than 30° while the tightening force is applied to it, the screw portion of the sample bolt and the sample object may be excessively plasticized, and the tightening force may not increase even if the sample bolt 20 continues to rotate. A Converted into tightening force F B It is desirable that the rotation angle of the sample bolt 20 during the test tightening may be 30° or less after the time point at which the bolt is tightened until the bolt is tightened.

[0075] 1.7. Detailed Configuration of the Bolt Tightening Angle Measurement Process (S500)

[0076] Hereinafter, the bolt tightening angle measuring process (S500) will be described in detail. The bolt tightening angle measuring process (S500) may include the following detailed processes.

[0077] A. Experimental Torque Distribution Process

[0078] First, multiple test torques can be respectively assigned to multiple bolt fastening devices for test fastening of samples. That is, when multiple test fastening experiments are simultaneously performed using multiple bolt fastening devices, multiple test torques can be respectively input to the multiple bolt fastening devices.

[0079] Of course, multiple test torque values ​​can also be assigned sequentially from the lowest to the highest, or vice versa, to the bolt-tightening device used to perform test tightening on the sample. In this case, multiple test tightening experiments can be performed sequentially using a single bolt-tightening device. The bolt-tightening process described later is performed separately between the assigned processes, allowing the test tightening experiments to be performed sequentially.

[0080] B. Sample Bolt Fixing Process

[0081] Subsequently, while simultaneously performing a test tightening experiment, the sample bolts 20 can be bolted to the sample object 10 using a plurality of bolt fixing devices to which the test torque is assigned. During this process, the rotation angle of each sample bolt 20 can be measured. The rotation angle of the sample bolt 20 can be measured using an inclinometer provided in the bolt fixing device. Of course, various other tools can be used to measure the rotation angle.

[0082] Furthermore, when performing a test tightening experiment sequentially, a plurality of sample bolts are bolted to a plurality of sample objects by a bolt fastening device in the order in which the test torque is distributed. In this process, the rotation angle of each sample bolt can be measured.

[0083] For example, when the test torque is 60kgf·cm, 70kgf·cm, and 80kgf·cm, the sample bolt 20 and the sample 10 are first tested with a torque of 60kgf·cm, and the bolt tightening angle can be measured from the time point when the torque of 24kgf·cm is reached until the time point when the test tightening is completed. Next, a new sample bolt 20 and a new sample object 10 are tested with a torque of 70kgf·cm, and the bolt tightening angle can be measured from the time point when the torque of 28kgf·cm is reached until the time point when the corresponding test tightening is completed. Subsequently, another sample bolt 20 and another sample object 10 are tested with a torque of 80kgf·cm, and the bolt tightening angle can be measured from the time point when the torque of 32kgf·cm is reached.

[0084] 1.8. Bolt Fastening Torque Determination Step (S600)

[0085] The bolt tightening torque determination step (S600) is a step for determining the bolt tightening torque for bolting an object and a bolt from a plurality of experimental torques based on a plurality of measured bolt tightening angles. This step can determine a bolt tightening torque with good reproducibility in the tightening force of the bolt tightening within an effective tightening torque range.

[0086] The above-mentioned bolt tightening torque determination process (S600) may include: a bolt tightening angle screening process, in which the measured bolt tightening angle is compared with a predetermined reference bolt angle to screen out a bolt tightening angle smaller than the reference bolt angle; and an experimental torque screening process, when there is one screened bolt tightening angle, screening out the experimental torque in the test tightening for measuring the corresponding bolt tightening angle, or when there are multiple screened bolt tightening angles, calculating their average value, checking the lowest bolt tightening angle with a standard deviation of less than 3 relative to the average value, and screening out the experimental torque in the test tightening for measuring the corresponding bolt tightening angle.

[0087] In the bolt tightening torque screening process, the predetermined reference bolt angle may be 30 degrees. Therefore, through this process, the test tightening at the end of the rotation of the sample bolt 20 can be screened out before the screw portion of the sample bolt 20 and the sample object 10 may be excessively plasticized.

[0088] In the experimental torque screening process, the bolt fixing torque can be obtained by using the experimental torque corresponding to the screened test tightening. Here, when there is an experiment of the screened test tightening, the experimental torque that has been used for the corresponding test tightening is screened out and determined as the bolt fixing torque. When there are multiple screened experiments, the bolt fixing torque should be determined from the multiple experimental torques used in the multiple experiments of the screened test tightening. To this end, the average value of the screened bolt tightening angles is calculated, and its standard deviation relative to the average value is calculated. In addition, the bolt tightening angles with a standard deviation of less than 3 are selected, and the bolt tightening angle with the lowest value is checked among them. Accordingly, the experimental torque in the test tightening measured for the checked bolt tightening angle is screened out, and it is determined as the bolt fixing torque. Through this process, the accurate bolt fixing torque to be used in bolt fixing can be determined.

[0089] When determining the bolt fastening torque, an operation of bolting an actual object and an actual bolt at the bolt fastening torque may be performed a plurality of times, and thereby a battery pack having excellent quality may be manufactured.

[0090] According to exemplary embodiments of the present invention, an effective tightening torque range can be determined based on the breaking torques obtained from samples of the object to be bolted and samples of the bolt. Multiple test torques can be selected within the effective tightening torque range to perform test tightening, thereby measuring the bolt tightening angle after a reference time point. These multiple measured bolt tightening angles can be used to ultimately determine the bolt tightening torque within the effective tightening torque range. In other words, in embodiments of the present invention, through these procedures, an accurate bolt tightening torque can be determined that accounts for variations in bolting conditions caused by material deviations between the object to be bolted and the bolt.

[0091] The above-described embodiments of the present invention are used to describe the present invention and are not intended to limit the present invention. It should be noted that the configurations and methods disclosed in the embodiments of the present invention can be combined and modified into various forms by combining or crossing, and these modified embodiments can also be considered to be within the scope of the present invention. That is, the present invention can be implemented in various forms within the scope of the claims and their equivalent technical concepts, and those skilled in the art will understand that various embodiments can be made within the scope of the technical concept of the present invention.

[0092] [Explanation of Reference Numerals]

[0093] 10: Sample object

[0094] 11: Lower the board

[0095] 12: On the board

[0096] 20: Sample bolt

[0097] 21: Head

[0098] 22: Screw

[0099] FA: rotational force

[0100] FB: Fastening force

[0101] L: sample bolt length

Claims

1. A method for determining a bolt tightening torque, comprising: A preparation process of preparing a sample of the object to be bolted and a sample of the bolt; a sample breaking torque obtaining step of measuring and obtaining a sample breaking torque when at least one of the sample of the object and the sample of the bolt breaks when the sample of the object and the sample of the bolt are fixed by the bolt; an effective tightening torque region determining step of determining an effective tightening torque region for tightening without breaking based on the sample breaking torque; An experimental torque selection step of selecting a plurality of experimental torques within the effective tightening torque region; a bolt tightening angle measuring step of performing test tightening on the sample according to each of the selected plurality of experimental torques and measuring a bolt tightening angle; and a bolt fastening torque determining step of determining a bolt fastening torque to be used for bolt fastening of the object and the bolt from among the plurality of experimental torques based on the plurality of bolt fastening angles measured, wherein, in the bolt tightening angle measurement process, the rotation angle of each of the bolt samples is measured from a predetermined reference time point to a time point when the test tightening is completed, and The reference time point is a time point when the force of the sample applied to the bolt during the test tightening is converted from a rotational force to a tightening force.

2. The method for determining the bolt tightening torque according to claim 1, wherein: The reference time point is a time point when the force applied to the sample of the bolt during the test tightening increases and exceeds a torque corresponding to a specific percentage of the lower limit of the experimental torque.

3. The method for determining the bolt tightening torque according to claim 2, wherein: The reference time point is a time point when the force applied to the sample of the bolt during the test tightening increases and exceeds 40% of the lower limit of the experimental torque.

4. The method for determining the bolt tightening torque according to claim 1, wherein: The reference time point is a time point when a current value and a revolution per minute of a bolt fastening device, which rotates the sample of the bolt so as to be bolted to the sample of the object, suddenly change during the test fastening.

5. The method for determining the bolt tightening torque according to claim 1, wherein: The reference time point is a time point when the head of the sample of the bolt comes into contact with the sample of the object during the test tightening.

6. The method for determining the bolt tightening torque according to claim 1, wherein: In the effective tightening torque range determining step, when a first torque smaller than the sample breaking torque is set as a lower limit and a second torque between the first torque and the sample breaking torque is set as an upper limit, a range from the first torque to the second torque is determined as the effective tightening torque range.

7. The method for determining the bolt tightening torque according to claim 6, wherein: In the effective tightening torque region determining step, a range from 60% to 80% of the breaking torque of the sample is determined as the effective tightening torque region.

8. The method for determining the bolt tightening torque according to claim 1, wherein: In the test torque selection step, a difference between two consecutive test torques is set to a certain value, and the plurality of test torques are sequentially selected within the effective tightening torque range.

9. The method for determining the bolt tightening torque according to claim 6, wherein: The plurality of experimental torques include at least one of the lower limit or the upper limit of the effective tightening torque region.

10. The method for determining the bolt tightening torque according to claim 1, wherein: The bolt tightening angle measurement process includes: an experimental torque distribution step of respectively distributing the plurality of experimental torques to a plurality of bolt fixing devices that perform the test tightening on the sample of the bolt; and a sample bolting process in which the samples of the bolts are respectively bolted to the samples of the object by the plurality of bolting devices to which the test torque is distributed, In the sample bolt fixing step, a rotation angle of each of the samples of the bolt is measured.

11. The method for determining the bolt tightening torque according to claim 1, wherein: The bolt tightening angle measurement process includes: an experimental torque distribution process in which the plurality of experimental torques are sequentially distributed from the lowest value to the highest value or from the highest value to the lowest value to a bolt fixing device that performs the test tightening on the sample of the bolt; and a sample bolting process in which the samples of the bolts are respectively bolted to the samples of the object by the bolting device in the order in which the test torque is distributed, In the sample bolt fixing step, a rotation angle of each of the samples of the bolt is measured.

12. The method for determining the bolt tightening torque according to any one of claims 2 to 5, wherein: The bolt tightening torque determination process includes: a bolt tightening angle screening step of comparing the measured bolt tightening angle with a predetermined reference bolt angle to screen out bolt tightening angles smaller than the reference bolt angle; and an experimental torque screening step, in which, when there is one selected bolt tightening angle, the experimental torque in the test tightening at which the corresponding bolt tightening angle is measured is screened, or, when there are a plurality of selected bolt tightening angles, an average value of the plurality of selected bolt tightening angles is calculated, a minimum bolt tightening angle having a standard deviation of less than 3 relative to the average value is checked, and the experimental torque in the test tightening at which the corresponding bolt tightening angle is measured is screened, The experimental torque screened out in the experimental torque screening step is determined as the bolt fixing torque.

13. The method for determining the bolt tightening torque according to claim 12, wherein: The reference bolt angle is 30 degrees.

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